basri

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Author name code: basri
ADS astronomy entries on 2022-09-14
author:"Basri, Gibor"

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Title: A New Method for Estimating Starspot Lifetimes Based on
Autocorrelation Functions
Authors: Basri, Gibor; Streichenberger, Tristan; McWard, Connor;
Edmond, Lawrence, IV; Tan, Joanne; Lee, Minjoo; Melton, Trey
2022ApJ...924...31B Altcode: 2021arXiv211013284B
We present a method that utilizes autocorrelation functions from
long-term precision broadband differential light curves to estimate the
average lifetimes of starspot groups for two large samples of Kepler
stars: stars with and without previously known rotation periods. Our
method is calibrated by comparing the strengths of the first few
normalized autocorrelation peaks using ensembles of models that have
various starspot lifetimes. We find that we must mix models of short and
long lifetimes together (in heuristically determined ratios) to align
the models with the Kepler data. Our fundamental result is that short
starspot-group lifetimes (one to four rotations) are implied when the
first normalized peak is weaker than about 0.4, long lifetimes (15 or
greater) are implied when it is greater than about 0.7, and in between
are the intermediate cases. Rotational lifetimes can be converted to
physical lifetimes if the rotation period is known. Stars with shorter
rotation periods tend to have longer rotational (but not physical) spot
lifetimes, and cooler stars tend to have longer physical spot lifetimes
than warmer stars with the same rotation period. The distributions of
the physical lifetimes are log-normal for both samples and generally
longer in the first sample. The shorter lifetimes in the stars without
known periods probably explain why their periods are difficult to
measure. Some stars exhibit longer than average physical starspot
lifetimes; their percentage drops with increasing temperature from
nearly half at 3000 K to nearly zero for hotter than 6000 K.

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Title: An Introduction to Stellar Magnetic Activity
Authors: Basri, Gibor
2021isma.book.....B Altcode:
This book provides an introduction to our current knowledge of
stellar magnetic activity. It is intended for graduate or advanced
undergraduate students or researchers new to the field. Starting with
the Sun, it extends to stars of all masses and ages. Topics include
the production and measurement of the fields themselves, their effects
on the stellar atmospheres, the diagnostics we use to understand them,
and the effects of the magnetic activity on the star and its surrounds
over time. This field is rapidly advancing, and the book will serve as
an initial resource for those new to the area, or as an overview for
those already involved who want a wider or historical perspective, along
with suggestions as to which directions that new research might take.

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Title: The Information Content in Analytic Spot Models of Broadband
Precision Light Curves. II. Spot Distributions and Lifetimes and
Global and Differential Rotation
Authors: Basri, Gibor; Shah, Riya
2020ApJ...901...14B Altcode: 2020arXiv200804969B
With the advent of space-based precision photometry missions,
the quantity and quality of starspot light curves has greatly
increased. This paper presents a large number of starspot models and
their resulting light curves to (1) better determine light-curve
metrics and methods that convey useful physical information and
(2) understand how the underlying degeneracies of the translation
from physical starspot distributions to the resulting light curves
obscure that information. We explore models of relatively active
stars at several inclinations while varying the number of (dark)
spots, random spot distributions in position and time, timescales of
growth and decay, and differential rotation. We examine the behavior of
absolute and differential variations of individual intensity dips and
overall light curves and demonstrate how complex spot distributions
and behaviors result in light curves that typically exhibit only one
or two dips per rotation. Unfortunately, simplistic "one- or two-spot"
or "active longitude" descriptions or modeling of light curves can
often be highly misleading. We also show that short "activity cycles"
can easily be simply due to random processes. It turns out to be quite
difficult to disentangle the competing effects of spot lifetime and
differential rotation, but under most circumstances, spot lifetime
is the more influential of the two. Many of the techniques tried
to date only work when spots live for many rotations. These include
autocorrelation degradation for spot lifetimes and periodograms for
both global and differential rotation. Differential rotation may be
nearly impossible to accurately infer from light curves alone unless
spots live for many rotations. The Sun and solar-type stars its age
or older are unfortunately the most difficult type of case. Further
work is needed to have increased confidence in light-curve inferences.

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Title: Double-dipping to refine stellar rotation periods
Authors: Tan, Joanne; Basri, Gibor
2020AN....341..513T Altcode:
We present a refined analysis of 15,038 Kepler main sequence light
curves to determine the stellar rotation periods. The initial period
estimates come from an autocorrelation function, as has been done
before. We then measure the duration of every intensity dip in the
light curve, expressed as fractions of the initial rotation period
estimate. These dip duration distributions are subdivided into several
regions whose relation to each other helps determine which harmonic of
the initial rotation period is most physically plausible. We compare
our final rotation periods to those from McQuillan et al. (2014) and
find that the great majority agree, but about 10% of their periods
are doubtful (usually twice as long as is most plausible). We are
still refining our method, and will later extend it to more stars to
substantially increase the sample of reliable stellar rotation periods.

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Title: Barriers to Equity, Inclusion, and Diversity in Astronomy
Authors: Rudolph, A.; Basri, G.; Norman, D.; Wimberly, M. K. R.
2019ASPC..524...11R Altcode:
Astronomy, like many other sciences, has struggled to engage and
include traditionally underrepresented groups such as underrepresented
minorities (URMs), women, members of the LGBTQ+ community, disabled
persons, and others. The reasons for this struggle are many and various,
but three important, well-known, well-studied issues are: Stereotype
Threat, Imposter Syndrome, and Implicit Bias. These issues can arise
in a variety of settings: in the classroom, in research settings,
in mentor/adviser relations, and in community outreach. This highly
interactive session will help participants learn about these three
topics and how they manifest themselves in their work engaging various
constituencies in appreciating, studying, and practicing astronomy.

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Title: Promoting Diversity and Inclusion in Astronomy Graduate
Education
Authors: Rudolph, Alexander; Basri, Gibor; Agüeros, Marcel;
Bertschinger, Ed; Coble, Kim; Donahue, Megan; Ivie, Rachel L.;
Monkiewicz, Jackie; Pfund, Christine; Posselt, Julie; Speck, Angela
2019BAAS...51g..29R Altcode: 2019astro2020U..29R; 2019arXiv190706769R
The purpose of this white paper is to provide guidance to funding
agencies about strategies for (1) improving access to advanced education
for people from populations that have long been underrepresented and
(2) improving the climates of departments where students enroll. This
white paper has been endorsed by the Board of Trustees of the AAS.

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Title: Chapter 11 - The Solar-Stellar Connection
Authors: Basri, Gibor
2019sgsp.book..363B Altcode:
This chapter discusses the Sun compared with other stars that have
the common property of an outer convective envelope. We have vastly
more detailed information on the Sun than for any other star; it
is the only one with the advantages of spatial imaging (at a wide
variety of wavelengths) and extensive time coverage. Information on
the unresolved properties of other stars is slowly beginning to catch
up, and the Sun often provides a point of reference in interpreting
these observations. The chapter discusses photometry, spectroscopy,
magnetic activity, heated regions of the atmospheres, and mass and
angular momentum loss. Observing other stars provides a window into
the behavior of solar-type stars with a wide range of masses, ages,
rotation rates, and other stellar properties. This allows us to build
a full picture of solar-type stellar atmospheres and put the Sun into
a larger context.

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Title: Final Report of the 2018 AAS Task Force on Diversity and
Inclusion in Astronomy Graduate Education
Authors: Rudolph, Alexander; Basri, Gibor; Agüeros, Marcel;
Bertschinger, Ed; Coble, Kim; Donahue, Megan; Ivie, Rachel L.;
Monkiewicz, Jackie; Pfund, Christine; Posselt, Julie; Speck, Angela;
Stassun, Keivan
2019BAAS...51a0101R Altcode: 2019BAAS...51.0101R
The AAS Task Force on Diversity and Inclusion in Astronomy Graduate
Education has completed its final report, and the AAS Board of Trustees
has voted to endorse it. The Task Force presented its findings at a
plenary held at the AAS 233rd meeting in Seattle. The main report begins
with an Executive Summary which highlights the recommendations of the
Task Force both to departments and to the AAS. The remainder of the
main report has sections on each of the categories of recommendations
with details about each recommendation, including both practical steps
a department can take to implement the recommendation, as well as
providing the research basis for each recommendation. The Appendices
(pages 32-74) provide substantially more details and resources that
departments can dive into to help them implement the recommendations,
as well as additional useful information. The Task Force believes this
structure will allow departments to quickly grasp the main points of
the report while also providing enough specific detail and resources to
make this a useful handbook for change. There are additional features
that make the report very user-friendly: - The Table of Contents
has live hyperlinks to move to any section of the report. There is a
"Back to Table of Contents" link on the bottom of every page, making it
easy to return to the top to explore a new section - The report also
included many live hyperlinks to outside resources that departments
(and the AAS) might find useful.

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Title: Calibration of Differential Light Curves for Physical Analysis
of Starspots
Authors: Basri, Gibor
2018ApJ...865..142B Altcode: 2018arXiv180900071B
This paper presents detailed consideration of methodologies to calibrate
differential light curves for accurate physical starspot modeling. We
use the Sun and starspot models as a testbed to highlight some factors
in this calibration that that have not yet been treated with care. One
unambiguously successful procedure for converting a differential light
curve into a light deficit curve appears difficult to implement, but
methodologies are presented that work in many cases. The years-long
time coverage of Kepler provides a strong advantage, but unresolved
issues concerning the competing and sometimes similar effects of
surface differential rotation versus spot number and size evolution can
prevent the confident recovery of correct spot covering fractions in
certain cases. We also consider whether faculae are detected by Kepler
and/or must be accounted for. We conclude their effects are such that
absolute photometry is not required for spot deficit calibrations. To
elucidate their signature, we re-examine correlations between absolute
brightness, differential variability, and apparent spot coverage for
hundreds of Kepler stars with absolute calibrations from Montet et
al. The results are similar to theirs, but we draw somewhat different
conclusions. Most of the stars in this active solar-type sample are
spot-dominated as expected. Partly because of a dearth of longer period
stars, the evidence for facular dominance in this sample is both sparse
and relatively weak. The facular population exhibits a puzzling lack
of dependence on rotation period, which raises questions about the
apparent detection of a “facular” signal at short periods.

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Title: Double Dipping: A New Relation between Stellar Rotation and
Starspot Activity
Authors: Basri, Gibor; Nguyen, Hieu T.
2018ApJ...863..190B Altcode: 2018arXiv180504587B
We report the discovery of a new relationship between a simple
morphological characteristic of light curves produced by starspots
and stellar rotation periods. The characteristic we examine is whether
the light curve exhibits one dip or two during a single rotation. We
analyze thousands of Kepler light curves of main-sequence stars with
temperatures from 3200 to 6200 K. Almost all the stars exhibit segments
of their light curve that contain either single- or double-dip segments
(very few have more than two significant dips per rotation). We define
a variable, the “single/double ratio” (SDR) that expresses the
ratio of the time spent in single mode to the time spent in double
mode. Unexpectedly, there is a strong relationship between the SDR and
the stellar rotation period, in the sense that longer periods come
with a larger fraction of double segments. Even more unexpectedly,
the slopes of the SDR-period relations are a clear function of stellar
temperature. We also show that the relationships of spot variability
amplitude (R var) to rotation period have similar levels
of scatter, slopes, and dependence on temperature as the SDR-period
relations. Finally, the median R var of single segments tends
to be about twice that of double segments in a given light curve. We
offer some tentative interpretations of these new results in terms of
starspot coverage and lifetimes. It will be fruitful to look further
into this novel “rotation-activity” relation, and better understand
what information these aspects of the morphology of light curves bring
to our knowledge of stellar magnetic activity.

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Title: What is Kepler Really Telling Us about Starspots?
Authors: Basri, Gibor
2018csss.confE..73B Altcode:
The signature of starspots in Kepler data is obvious and
pervasive. There have been many papers discussing aspects of these light
curves, including rotation period detection, dependence of amplitude on
rotation, differential rotation signatures, and activity cycles. There
are some subtleties of interpretation, however, that have received
much less attention (but are relevant to these analyses). 1) as the
light curves change, how much of that is due to differential rotation
(spots changing phase with respect to each other) and how much is due
to spot evolution (spots growing and decaying in various locations)? 2)
given that Kepler only provides differential photometry, how can we
properly convert light deficits to actual spot areas (what does the
unspotted star look like)? 3) how much information is actually in the
light curves, given that there are generally only one or two dips in
intensity per rotation? I discuss progress on these questions, utilizing
a large search of parameter space with spot models. I also present a
new rotation-activity relation: there is a strong correlation between
a) the ratio of of the time spent by a light curve in single dip mode
to that spent in double dip mode, and b) the rotation period of that
star. I give a tentative interpretation of this new result. Most of
the contents of this presentation have been published in 2018 in ApJ:
v. 863, p. 190 and v. 865, p. 142.

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Title: Planets in Binary Star Systems: Keck/HIRES Search for Planets
Around Sun-like Stars Within 25 pc
Authors: Basri, Gibor
2017koa..prop..221B Altcode:
No abstract at ADS

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Title: Discovery of a Group of Receding, Variable Halo Stars toward
Norma
Authors: Chakrabarti, Sukanya; Angeloni, Rodolfo; Freeman, Kenneth;
Sargent, Benjamin; Simon, Joshua D.; Konorski, Piotr; Gieren, Wolfgang;
Sesar, Branimir; Lipnicky, Andrew; Blitz, Leo; Basri, Gibor; Vacca,
William; Marengo, Massimo; Guhathakurta, Puragra; Quillen, Alice;
Chang, Philip
2017ApJ...844..159C Altcode:
We present results from spectroscopic observations of a trio of
Cepheid candidates identified from K s -band light curves
toward Norma. The spectra show that these stars are moving with a
large and similar radial velocity—the heliocentric velocities are
171 ± 32 km s-1, 164 ± 37 km s-1, and 173
± 20 km s-1. The average radial velocity is ∼169 km
s-1, which is large and distinct from typical stars in the
Galaxy’s stellar disk. Given the radial velocities and associated 1σ
error, we find that the combined probability that these three stars are
foreground Milky Way disk stars is ∼7 × 10-4%, and the
probability that these are large-amplitude spotted stars in a binary
is ∼10-5%. These objects at l ∼ 333° and b ∼ -1°
are therefore associated with the stellar halo. The identification of
these sources as Type I Cepheids is not certain, and thus the distances
of these sources are not yet well established. Assuming the 3.6 μm
period-luminosity relation of Type I Cepheids gives a distance of
∼78 kpc for these sources.

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Title: Investigation into the Morphology and Temporal Variability
of Auroral Hα Emission from LSR J1835+3259
Authors: Pineda, J. Sebastian; Hallinan, Gregg; Littlefair, Stuart;
Watson, Chris; Basri, Gibor S.
2017AAS...22943301P Altcode:
The emergence of auroral phenomena at the end of the main sequence
has been heralded by the detections of strong radio pulses in the
atmospheres of ultracool dwarfs. These findings have been led by the
detailed study of benchmark targets, like LSR J1835+3259, displaying
the key observations indicative of auroral radio emission and the
corresponding auroral surface features (Hallinan et al. 2015). Building
on these findings, I present a preliminary investigation into the
morphology and variability of the Hα emission of LSR J1835+3259 using
high-resolution optical spectroscopy with Keck HIRES. We monitored the
target for a full night to determine the shape of the Hα line profile
and how the profile changes with rotational period. We examined these
profiles to determine the nature of the emission and reconstruct the
stellar emission surface through doppler imaging techniques. We find
that the emission is consistent with a high-latitude auroral surface
feature being responsible for the rotationally varying Hα emission.

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Title: Differential rotation as a model for starspots in magnetically
active stars
Authors: Agostino, Christopher James; Basri, Gibor S.
2017AAS...22924023A Altcode:
The Kepler mission has provided an opportunity to significantly expand
our understanding of starspots. We have implemented a MCMC method to
determine spot parameters of input light curves using a differential
rotation spot model. We generated model light curves and explored
parameter space in order to test the reliability of our method
in retrieving input parameters and to investigate what constraints
on spot parameters can be determined from photometric data. We also
applied our method to light curves of magnetically active Kepler stars,
using only a few spots. One interesting initial conclusion is that
it is often possible to replicate complicated light curves over many
rotation periods without the need for any spot evolution on stars with
rotation periods less than 20 days. We have also begun investigating
to what extent spot evolution is preferred as the alternative model
for stellar variability. Of course, it is very likely that real stars
exhibit both phenomena.

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Title: Rotation-Activity-Age Relations For Solar-Type And Cooler Stars
Authors: Basri, Gibor
2016csss.confE..17B Altcode:
The fact that stellar rotation and chromospheric emission are correlated
with age was explicitly noted by Wilson (1963) and reinforced by
Kraft (1967). Wilson knew that Ca II emission was correlated with
surface magnetic field in the Sun. Skumanich (1972) suggested a simple
functional for the age-activity relation, and suggested that magnetic
braking was the likely reason for the decline in activity. A theory for
the rotation-activity connection was elucidated by Noyes et al. (1984),
who invoked the Rossby number as important to the stellar dynamo. This
calibrated the relation by convection zone depth and turnover time,
although it was noted early and recently confirmed that it is not
clear whether Rossby number is empirically superior to the rotation
period itself in producing a clear rotation-activity relation. In fact,
turnover times are hard to properly define, and the Rossby number is
itself calibrated to tighten the relations. The number of stars in
samples used to study this has increased dramatically, as have the
diagnostics available to assess magnetic activity. It remains clear
is that there is a strong relationship between magnetic activity and
stellar rotation, and that magnetic braking forces both activity and
rotation to decrease with age. These relations are also subject to
modification as a function of stellar mass. There has recently been
a great increase in the number of measured stellar rotation periods,
and in the calibration of these relations using star clusters (whose
ages can be independently assessed). I will summarize some of the
ongoing progress on this topic.

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Title: The Structure and Dynamics of Multi-planet Systems
Authors: Basri, Gibor
2016koa..prop..431B Altcode:
No abstract at ADS

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Title: VizieR Online Data Catalog: Stellar surface gravity measures
of KIC stars (Bastien+, 2016)
Authors: Bastien, F. A.; Stassun, K. G.; Basri, G.; Pepper, J.
2016yCat..18180043B Altcode:
In our analysis we use all quarters from the Kepler mission except for
Q0, and we only use the long-cadence light curves. Additionally, we only
use the Pre-search Data Conditioning, Maximum A Posteriori (PDC-MAP)
light curves, as further discussed in Section 3.4.1. (1 data file).

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Title: A Granulation "Flicker"-based Measure of Stellar Surface
Gravity
Authors: Bastien, Fabienne A.; Stassun, Keivan G.; Basri, Gibor;
Pepper, Joshua
2016ApJ...818...43B Altcode: 2015arXiv151203454B
In our previous work we found that high-quality light curves, such as
those obtained by Kepler, may be used to measure stellar surface gravity
via granulation-driven light curve “flicker” (F8). Here,
we update and extend the relation originally presented by Bastien et
al. in 2013 after calibrating F8 against a more robust set of
asteroseismically derived surface gravities. We describe in detail how
we extract the F8 signal from the light curves, including
how we treat phenomena, such as exoplanet transits and shot noise,
that adversely affect the measurement of F8. We examine
the limitations of the technique, and, as a result, we now provide an
updated treatment of the F8-based {log} g error. We briefly
highlight further applications of the technique, such as astrodensity
profiling or its use in other types of stars with convective outer
layers. We discuss potential uses in current and upcoming space-based
photometric missions. Finally, we supply F8-based {log} g
values, and their uncertainties, for 27,628 Kepler stars not identified
as hosts of transiting planets, with 4500 K &lt; Teff &lt;
7150 K, 2.5 &lt; {log}\g &lt; 4.6, Kp ≤ 13.5, and overall
photometric amplitudes &lt;10 parts per thousand.

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Title: A Light Curve Probe of Stellar Surface Convection and Measure
of Stellar Surface Gravity
Authors: Bastien, Fabienne A.; Stassun, Keivan; Basri, Gibor S.;
Pepper, Joshua
2016AAS...22710502B Altcode:
We recently found that high quality light curves, such as those obtained
by NASA's Kepler, K2, and the soon-to-be-launched TESS missions, may
be used to measure stellar surface gravity via granulation-driven
light curve "flicker." Here, we describe our updated and extended
the relation, which is now calibrated against a more robust set
of asteroseismically derived surface gravities and which we apply
to over 28,000 Kepler stars. We discuss how we treat phenomena,
such as exoplanet transits and shot noise, that adversely affect
the measurement of flicker, and we explore the limitations of the
technique. We suggest that flicker may be used to probe convection
in stars with surface gravities as low as 1.5, and we show that, in
concert with asteroseismically measured surface gravities, it might be
used to examine differences in the convective properties of red giant,
red clump, and secondary clump stars. Finally, we highlight further
applications of flicker, such as astrodensity profiling or its use in
studying other types of stars with convective outer layers.

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Title: Galactoseismology: Discovery of a cluster of receding,
variable halo stars
Authors: Chakrabarti, Sukanya; Angeloni, Rodolfo; Freeman, Kenneth;
Sargent, Benjamin; Simon, Joshua D.; Konorski, Piotr; Gieren, Wolfgang;
Sesar, Branimir; Lipnicky, Andrew; Blitz, Leo; Basri, Gibor; Marengo,
Massimo; Vacca, William; Guhathakurta, Puragra; Quillen, Alice;
Chang, Philip
2016arXiv160103381C Altcode:
A dynamical characterization of dark matter dominated dwarf galaxies
from their observed effects on galactic disks (i.e. Galactoseismology)
has remained an elusive goal. Here, we present preliminary results
from spectroscopic observations of three clustered Cepheid candidates
identified from $K$-band light curves towards Norma. The average
heliocentric radial velocity of these stars is $\sim$ 156 km/s, which is
large and distinct from that of the Galaxy's stellar disk. These objects
at $l \sim 333 ^\circ$ and $b \sim -1 ^\circ$ are therefore halo stars;
using the $3.6~\micron$ period-luminosity relation of Type I Cepheids,
they are at $\sim$ 73 kpc. Our ongoing $I$-band photometry indicates
variability on the same time scale as the period determined from
the $K_{s}$-band light curve. Distances determined from the $K$-band
period-luminosity relation and the 3.6 $\micron$ period-luminosity
relation are comparable. The observed radial velocity of these stars
agrees roughly with predictions from dynamical models. If these stars
are indeed members of the predicted dwarf galaxy that perturbed the
outer HI disk of the Milky Way, this would mark the first application
of Galactoseismology.

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Title: Increasing Diversity in Earth and Space Sciences
Authors: Meinke, B. K.; Ali, N. A.; Shackelford, R.; Mendez, B.;
Acevedo, S.; Basri, G.; Kenney, K.; Lee, A. S.
2015ASPC..500....7M Altcode:
In this interactive discussion, panelists shared their perspectives
from working with diverse audiences, including Native Americans,
African Americans, Hispanic/Latinos, and girls and women. Among the
objectives of the panel discussion was to identify and discuss the
challenges to engagement of specific audiences, learn strategies for
connecting to various audiences, and understand how to adapt engagement
for different educational settings with various audiences.

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Title: Brown Dwarf
Authors: Basri, Gibor
2015enas.book..337B Altcode:
No abstract at ADS

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Title: The Sun Among Stars: A Photometric Comparison from Kepler
Authors: Basri, Gibor
2015IAUGA..2255663B Altcode:
I review what we have learned about the levels of variability and
characteristics of precisely measured long-term light curves of
solar-type stars compared with the Sun. Both in a general way,
and along a number of specific metrics, the Sun is very much an
“average” solar-type star. The general levels of variability on
different timescales of the large sample of Kepler stars fit in the
expected way with the set of behaviors that the Sun displays over
a solar cycle. Although some have argued that the Sun is unusually
photometrically quiet, the evidence does not support that. On the other
hand, there are relatively few stars in the Kepler sample whose light
curves over four years could be presented to solar experts as real solar
data and actually fool them. I therefore also discuss the ways in which
the Sun is not the same most of the Kepler stars, and which metrics
highlight those differences. Finally I spend a little time talking about
what we might further learn from the Kepler data on solar-type stars,
and what tools will be needed to succeed in those projects.

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Title: Magnetospherically driven optical and radio aurorae at the
end of the stellar main sequence
Authors: Hallinan, G.; Littlefair, S. P.; Cotter, G.; Bourke, S.;
Harding, L. K.; Pineda, J. S.; Butler, R. P.; Golden, A.; Basri, G.;
Doyle, J. G.; Kao, M. M.; Berdyugina, S. V.; Kuznetsov, A.; Rupen,
M. P.; Antonova, A.
2015Natur.523..568H Altcode: 2015arXiv150708739H
Aurorae are detected from all the magnetized planets in our Solar
System, including Earth. They are powered by magnetospheric current
systems that lead to the precipitation of energetic electrons into
the high-latitude regions of the upper atmosphere. In the case of the
gas-giant planets, these aurorae include highly polarized radio emission
at kilohertz and megahertz frequencies produced by the precipitating
electrons, as well as continuum and line emission in the infrared,
optical, ultraviolet and X-ray parts of the spectrum, associated
with the collisional excitation and heating of the hydrogen-dominated
atmosphere. Here we report simultaneous radio and optical spectroscopic
observations of an object at the end of the stellar main sequence,
located right at the boundary between stars and brown dwarfs, from which
we have detected radio and optical auroral emissions both powered by
magnetospheric currents. Whereas the magnetic activity of stars like
our Sun is powered by processes that occur in their lower atmospheres,
these aurorae are powered by processes originating much further out in
the magnetosphere of the dwarf star that couple energy into the lower
atmosphere. The dissipated power is at least four orders of magnitude
larger than what is produced in the Jovian magnetosphere, revealing
aurorae to be a potentially ubiquitous signature of large-scale
magnetospheres that can scale to luminosities far greater than those
observed in our Solar System. These magnetospheric current systems may
also play a part in powering some of the weather phenomena reported
on brown dwarfs.

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Title: VizieR Online Data Catalog: Properties of KOI host stars
(Walkowicz+, 2013)
Authors: Walkowicz, L. M.; Basri, G. S.
2014yCat..74361883W Altcode:
We chose to work with the light curves from Kepler Quarter 9, as this
was the first quarter reduced using the PDC-MAP detrending pipeline
(previous quarters have since been reprocessed, such that all Kepler
data have now been detrended using PDC-MAP). (1 data file).

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Title: Rotation &amp; differential rotation of the active Kepler stars
Authors: Reinhold, Timo; Reiners, Ansgar; Basri, Gibor
2014IAUS..302..216R Altcode:
Stellar rotation is a well-known quantity for tens of thousands
of stars. In contrast, differential rotation (DR) is only known
for a handful of stars because DR cannot be measured directly. We
present rotation periods for more than 24,000 active stars in the
Kepler field. Thereof, more than 18,000 stars show a second period,
which we attribute to surface differential rotation. Our rotation
periods are consistent with previous measurements and the theory of
magnetic braking. Our results on DR paint a rather different picture:
The temperature dependence of the absolute shear δΩ is split into
two groups separated around 6000 K. For the cooler stars δΩ only
slightly increases with temperature, whereas stars hotter than 6000 K
show large scatter. This is the first time that DR has been measured
for such a large number of stars.

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Title: VizieR Online Data Catalog: Small Kepler planets radial
velocities (Marcy+, 2014)
Authors: Marcy, G. W.; Isaacson, H.; Howard, A. W.; Rowe, J. F.;
Jenkins, J. M.; Bryson, S. T.; Latham, D. W.; Howell, S. B.;
Gautier, T. N., III; Batalha, N. M.; Rogers, L.; Ciardi, D.; Fischer,
D. A.; Gilliland, R. L.; Kjeldsen, H.; Christensen-Dalsgaard, J.;
Huber, D.; Chaplin, W. J.; Basu, S.; Buchhave, L. A.; Quinn, S. N.;
Borucki, W. J.; Koch, D. G.; Hunter, R.; Caldwell, D. A.; van Cleve,
J.; Kolbl, R.; Weiss, L. M.; Petigura, E.; Seager, S.; Morton, T.;
Johnson, J. A.; Ballard, S.; Burke, C.; Cochran, W. D.; Endl, M.;
MacQueen, P.; Everett, M. E.; Lissauer, J. J.; Ford, E. B.; Torres,
G.; Fressin, F.; Brown, T. M.; Steffen, J. H.; Charbonneau, D.; Basri,
G. S.; Sasselov, D. D.; Winn, J.; Sanchis-Ojeda, R.; Christiansen,
J.; Adams, E.; Henze, C.; Dupree, A.; Fabrycky, D. C.; Fortney, J. J.;
Tarter, J.; Holman, M. J.; Tenenbaum, P.; Shporer, A.; Lucas, P. W.;
Welsh, W. F.; Orosz, J. A.; Bedding, T. R.; Campante, T. L.; Davies,
G. R.; Elsworth, Y.; Handberg, R.; Hekker, S.; Karoff, C.; Kawaler,
S. D.; Lund, M. N.; Lundkvist, M.; Metcalfe, T. S.; Miglio, A.; Silva
Aguirre, V.; Stello, D.; White, T. R.; Boss, A.; Devore, E.; Gould,
A.; Prsa, A.; Agol, E.; Barclay, T.; Coughlin, J.; Brugamyer, E.;
Mullally, F.; Quintana, E. V.; Still, M.; Thompson, S. E.; Morrison,
D.; Twicken, J. D.; Desert, J. -M.; Carter, J.; Crepp, J. R.; Hebrard,
G.; Santerne, A.; Moutou, C.; Sobeck, C.; Hudgins, D.; Haas, M. R.;
Robertson, P.; Lillo-Box, J.; Barrado, D.
2014yCat..22100020M Altcode:
Here we report measured masses, radii, and densities (or upper limits
on those values) for 42 transiting planet candidates contained within
22 bright Kepler Objects of Interest (KOIs) from Batalha et al. (2013,
Cat. J/ApJS/204/24). We carried out multiple Doppler-shift measurements
of the host stars using the Keck 1 telescope. From the spectroscopy
and Doppler measurements, we compute self-consistent measurements of
stellar and planet radii, employing either stellar structure models
or asteroseismology measurements from the Kepler photometry. We also
search for (and report) 7 additional non-transiting planets revealed
by the precise radial velocities (RVs), for a total of 49 planets. We carried out "reconnaissance" high-resolution spectroscopy on ~1000
KOIs with spectral resolution, R~50000, and S/N=20-100 per pixel. The
dual goals were searching for false positives and refining the stellar
parameters. We obtained one or two such reconnaissance spectra using
one of four facilities: the McDonald Observatory 2.7m, the Tillinghast
1.5m on Mt. Hopkins, the Lick Observatory 3m, and the 2.6m Nordic
Optical Telescope. Speckle imaging of each of the selected 22
KOIs was obtained using the two-color DSSI speckle camera at the WIYN
3.5m telescope on Kitt Peak. All 22 KOIs were observed with the
Keck NIRC2-AO system. (3 data files).

---------------------------------------------------------
Title: Radial Velocity Variations of Photometrically Quiet,
Chromospherically Inactive Kepler Stars: A Link between RV Jitter
and Photometric Flicker
Authors: Bastien, Fabienne A.; Stassun, Keivan G.; Pepper, Joshua;
Wright, Jason T.; Aigrain, Suzanne; Basri, Gibor; Johnson, John A.;
Howard, Andrew W.; Walkowicz, Lucianne M.
2014AJ....147...29B Altcode: 2013arXiv1310.7152B
We compare stellar photometric variability, as measured from Kepler
light curves by Basri et al., with measurements of radial velocity (RV)
rms variations of all California Planet Search overlap stars. We newly
derive rotation periods from the Kepler light curves for all of the
stars in our study sample. The RV variations reported herein range from
less than 4 to 135 m s-1, yet the stars all have amplitudes
of photometric variability less than 3 mmag, reflecting the preference
of the RV program for chromospherically "quiet" stars. Despite the
small size of our sample, we find with high statistical significance
that the RV rms manifests strongly in the Fourier power spectrum of
the light curve: stars that are noisier in RV have a greater number of
frequency components in the light curve. We also find that spot models
of the observed light curves systematically underpredict the observed
RV variations by factors of ~2-1000, likely because the low-level
photometric variations in our sample are driven by processes not
included in simple spot models. The stars best fit by these models
tend to have simpler light curves, dominated by a single relatively
high-amplitude component of variability. Finally, we demonstrate that
the RV rms behavior of our sample can be explained in the context
of the photometric variability evolutionary diagram introduced by
Bastien et al. We use this diagram to derive the surface gravities
of the stars in our sample, revealing many of them to have moved off
the main sequence. More generally, we find that the stars with the
largest RV rms are those that have evolved onto the "flicker floor"
sequence in that diagram, characterized by relatively low amplitude
but highly complex photometric variations which grow as the stars
evolve to become subgiants.

---------------------------------------------------------
Title: Masses, Radii, and Orbits of Small Kepler Planets: The
Transition from Gaseous to Rocky Planets
Authors: Marcy, Geoffrey W.; Isaacson, Howard; Howard, Andrew W.;
Rowe, Jason F.; Jenkins, Jon M.; Bryson, Stephen T.; Latham, David
W.; Howell, Steve B.; Gautier, Thomas N., III; Batalha, Natalie M.;
Rogers, Leslie; Ciardi, David; Fischer, Debra A.; Gilliland, Ronald
L.; Kjeldsen, Hans; Christensen-Dalsgaard, Jørgen; Huber, Daniel;
Chaplin, William J.; Basu, Sarbani; Buchhave, Lars A.; Quinn, Samuel
N.; Borucki, William J.; Koch, David G.; Hunter, Roger; Caldwell,
Douglas A.; Van Cleve, Jeffrey; Kolbl, Rea; Weiss, Lauren M.;
Petigura, Erik; Seager, Sara; Morton, Timothy; Johnson, John Asher;
Ballard, Sarah; Burke, Chris; Cochran, William D.; Endl, Michael;
MacQueen, Phillip; Everett, Mark E.; Lissauer, Jack J.; Ford, Eric
B.; Torres, Guillermo; Fressin, Francois; Brown, Timothy M.; Steffen,
Jason H.; Charbonneau, David; Basri, Gibor S.; Sasselov, Dimitar D.;
Winn, Joshua; Sanchis-Ojeda, Roberto; Christiansen, Jessie; Adams,
Elisabeth; Henze, Christopher; Dupree, Andrea; Fabrycky, Daniel C.;
Fortney, Jonathan J.; Tarter, Jill; Holman, Matthew J.; Tenenbaum,
Peter; Shporer, Avi; Lucas, Philip W.; Welsh, William F.; Orosz,
Jerome A.; Bedding, T. R.; Campante, T. L.; Davies, G. R.; Elsworth,
Y.; Handberg, R.; Hekker, S.; Karoff, C.; Kawaler, S. D.; Lund,
M. N.; Lundkvist, M.; Metcalfe, T. S.; Miglio, A.; Silva Aguirre, V.;
Stello, D.; White, T. R.; Boss, Alan; Devore, Edna; Gould, Alan; Prsa,
Andrej; Agol, Eric; Barclay, Thomas; Coughlin, Jeff; Brugamyer, Erik;
Mullally, Fergal; Quintana, Elisa V.; Still, Martin; Thompson, Susan
E.; Morrison, David; Twicken, Joseph D.; Désert, Jean-Michel; Carter,
Josh; Crepp, Justin R.; Hébrard, Guillaume; Santerne, Alexandre;
Moutou, Claire; Sobeck, Charlie; Hudgins, Douglas; Haas, Michael R.;
Robertson, Paul; Lillo-Box, Jorge; Barrado, David
2014ApJS..210...20M Altcode: 2014arXiv1401.4195M
We report on the masses, sizes, and orbits of the planets orbiting
22 Kepler stars. There are 49 planet candidates around these stars,
including 42 detected through transits and 7 revealed by precise
Doppler measurements of the host stars. Based on an analysis of the
Kepler brightness measurements, along with high-resolution imaging and
spectroscopy, Doppler spectroscopy, and (for 11 stars) asteroseismology,
we establish low false-positive probabilities (FPPs) for all of the
transiting planets (41 of 42 have an FPP under 1%), and we constrain
their sizes and masses. Most of the transiting planets are smaller
than three times the size of Earth. For 16 planets, the Doppler
signal was securely detected, providing a direct measurement of the
planet's mass. For the other 26 planets we provide either marginal mass
measurements or upper limits to their masses and densities; in many
cases we can rule out a rocky composition. We identify six planets
with densities above 5 g cm-3, suggesting a mostly rocky
interior for them. Indeed, the only planets that are compatible with a
purely rocky composition are smaller than ~2 R ⊕. Larger
planets evidently contain a larger fraction of low-density material (H,
He, and H2O). Based in part on observations obtained
at the W. M. Keck Observatory, which is operated by the University of
California and the California Institute of Technology.

---------------------------------------------------------
Title: Flicker, Jitter, Crackle: Lifting the Veil on Stellar
Variability and Understanding its Impact on Planet Detection with
Kepler
Authors: Bastien, Fabienne A.; Stassun, K.; Basri, G. S.; Pepper, J.
2014AAS...22310302B Altcode:
The high-precision light curves obtained by NASA's Kepler mission
unveiled a rich variety of photometric behavior in Sun-like stars. Using
only long-cadence light curves and different ways of characterizing the
stellar photometric variability, we examine how magnetic activity and
radial velocity (RV) “jitter” both manifest photometrically. First,
we present a unified picture of how the photometric behavior of
Sun-like stars on time scales of hours to days evolves with time
through an “evolutionary diagram” that involves only three simple
measures of photometric variability. In this diagram, we observe
clear evolutionary sequences: the light curves of the stars become
"quieter" as the stellar spot coverage decreases with time, but they
become suddenly and significantly more complex (they “crackle”) as
the stars approach their evolution off the main-sequence and spots no
longer dominate the brightness variations. Using an asteroseismically
analyzed sample of stars, we demonstrate that the sequences in our
diagram are a strong function of stellar surface gravity, yielding a
simple tool - “flicker” - to accurately measure surface gravity to
better than 0.1 dex with just the long-cadence light curve. We next use
this diagram to gain insight into the RV jitter of magnetically inactive
stars, stars that exhibit RV jitter ranging from less than 3 m/s to
over 130 m/s despite their low levels of magnetic activity and low
levels of photometric variability. We find that photometric complexity
(“crackle”), linked to higher frequency photometric variations,
drives the RV jitter of these stars. Finally, we close the loop on
our study with Ca II H&amp;K magnetic activity measurements of over
700 Kepler stars, and we relate magnetic activity to our photometric
variability evolutionary sequences.

---------------------------------------------------------
Title: The Discovery of the First Lithium Brown Dwarf: PPl 15
Authors: Basri, Gibor
2014ASSL..401...51B Altcode:
The search for brown dwarfs (BDs) covered decades between the
time they were first proposed theoretically and the time that a
public announcement of the discovery of a BD was made which did not
have to be recanted later (as was the case for a number of previous
announcements). In a convergence of scientific progress, 1995 saw 3 real
discoveries of BDs, as well as the first exoplanets. The substellar
realm had suddenly opened up. This chapter describes the process that
led to the first of these announcements: the identification of PPl 15 as
a BD. It lay just below the substellar limit in the Pleiades cluster. To
distinguish it from very similar-looking stars, the first successful
application of the "lithium test" was applied by my group at UC Berkeley
using the new Keck 10 m telescope and HIRES spectrograph. As part of
the analysis, the new technique of "lithium dating" was developed. I
place this discovery in the context of the broader search for BDs,
and of the subsequent discoveries and progress in the field.

---------------------------------------------------------
Title: Rotation and differential rotation of active Kepler stars
Authors: Reinhold, Timo; Reiners, Ansgar; Basri, Gibor
2013A&A...560A...4R Altcode: 2013arXiv1308.1508R
Context. The Kepler space telescope monitors more than 160 000 stars
with an unprecedented precision providing the opportunity to study
the rotation of thousands of stars. Aims: We present rotation
periods for thousands of active stars in the Kepler field derived from
Q3 data. In most cases a second period close to the rotation period
was detected that we interpreted as surface differential rotation
(DR). We show how the absolute and relative shear (ΔΩ and α =
ΔΩ/Ω, respectively) correlate with rotation period and effective
temperature. Methods: Active stars were selected from the whole
sample using the range of the variability amplitude. To detect different
periods in the light curves we used the Lomb-Scargle periodogram
in a pre-whitening approach to achieve parameters for a global sine
fit. The most dominant periods from the fit were associated to different
surface rotation periods. Our purely mathematical approach is capable of
detecting different periods but cannot distinguish between the physical
origins of periodicity. We ascribe the existence of different periods
to DR, but spot evolution could also play a role. Because of the large
number of stars the period errors are estimated statistically. We
thus cannot exclude the existence of false positives among our
periods. Results: In our sample of 40 661 active stars we
found 24 124 rotation periods P1 between 0.5 and 45 days,
with a mean of ⟨P1⟩ = 16.3 days. The distribution
of stars with 0.5 &lt; B - V &lt; 1.0 and ages derived from angular
momentum evolution that are younger than 300 Myr is consistent with
a constant star-formation rate; the detection among older stars is
incomplete probably because of our active sample selection. A second
period P2 within ±30% of the rotation period P1
was found in 18 616 stars (77.2%). Attributing these two periods to DR
we found that for active stars other than the Sun the relative shear α
increases with rotation period, and slightly decreases with effective
temperature. The absolute shear ΔΩ slightly increases from ΔΩ =
0.079 rad d-1 at Teff = 3500 K to ΔΩ = 0.096
rad d-1 at Teff = 6000 K. Above 6000 K, ΔΩ
shows much larger scatter. The dependence of ΔΩ on rotation period
is weak over a large period range. Conclusions: Latitudinal
differential rotation measured for the first time in more than 18 000
stars provides a comprehensive picture of stellar surface shear. This
picture is consistent with major predictions from mean-field theory,
and seems to support these models. To what extent our observations are
prone to false positives and selection bias has not been fully explored,
and needs to be addressed using other data, including the full Kepler
time coverage. Appendix A is available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>A table with
rotation periods is only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/560/A4">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/560/A4</A>

---------------------------------------------------------
Title: Rotation periods, variability properties and ages for Kepler
exoplanet candidate host stars
Authors: Walkowicz, Lucianne M.; Basri, Gibor S.
2013MNRAS.436.1883W Altcode: 2013arXiv1309.2159W; 2013MNRAS.tmp.2426W
We report rotation periods, variability characteristics,
gyrochronological ages for ∼950 of the Kepler Object of Interest host
stars. We find a wide dispersion in the amplitude of the photometric
variability as a function of rotation, likely indicating differences
in the spot distribution among stars. We use these rotation periods
in combination with published spectroscopic measurements of v sin
i and stellar parameters to derive the stellar inclination in the
line of sight, and find a number of systems with possible spin-orbit
misalignment. We additionally find several systems with close-in planet
candidates whose stellar rotation periods are equal to or twice the
planetary orbital period, indicative of possible tidal interactions
between these planets and their parent stars. If these systems survive
validation to become confirmed planets, they will provide important
clues to the evolutionary history of these systems.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Rotation periods of active Kepler
stars (Reinhold+, 2013)
Authors: Reinhold, T.; Reiners, A.; Basri, G.
2013yCat..35600004R Altcode: 2013yCat..35609004R
Active stars were selected from the whole sample using the range of the
variability amplitude. To detect different periods in the light curves
we used the Lomb-Scargle periodogram in a pre-whitening approach to
achieve parameters for a global sine fit. The most dominant periods
from the fit were ascribed to different surface rotation periods,
but spot evolution could also play a role. Due to the large number of
stars the period errors were estimated in a statistical way. We thus
cannot exclude the existence of false positives among our periods. (1 data file).

---------------------------------------------------------
Title: An observational correlation between stellar brightness
variations and surface gravity
Authors: Bastien, Fabienne A.; Stassun, Keivan G.; Basri, Gibor;
Pepper, Joshua
2013Natur.500..427B Altcode: 2013arXiv1308.4728B
Surface gravity is a basic stellar property, but it is difficult
to measure accurately, with typical uncertainties of 25 to 50
per cent if measured spectroscopically and 90 to 150 per cent if
measured photometrically. Asteroseismology measures gravity with an
uncertainty of about 2 per cent but is restricted to relatively small
samples of bright stars, most of which are giants. The availability
of high-precision measurements of brightness variations for more than
150,000 stars provides an opportunity to investigate whether the
variations can be used to determine surface gravities. The Fourier
power of granulation on a star's surface correlates physically with
surface gravity: if brightness variations on timescales of hours arise
from granulation, then such variations should correlate with surface
gravity. Here we report an analysis of archival data that reveals
an observational correlation between surface gravity and root mean
squared brightness variations on timescales of less than eight hours
for stars with temperatures of 4,500 to 6,750 kelvin, log surface
gravities of 2.5 to 4.5 (cgs units) and overall brightness variations
of less than three parts per thousand. A straightforward observation
of optical brightness variations therefore allows a determination of
the surface gravity with a precision of better than 25 per cent for
inactive Sun-like stars at main-sequence to giant stages of evolution.

---------------------------------------------------------
Title: A Fundamental Photometric Variability Sequence Tracing the
Evolution of Sun-like Stars
Authors: Bastien, Fabienne A.; Stassun, K.; Basri, G. S.; Pepper, J.
2013AAS...22230404B Altcode:
The brightness variability of Sun-like stars -- from long-timescale
variations attributed to the rotational modulation of spots to
high-frequency acoustic oscillations -- change as they spin down on
the main-sequence and then as they evolve to become subgiants and
red giants. Here, we use Kepler long-cadence light curves to present
a unified picture of how the photometric behavior of Sun-like stars
at intermediate timescales (hours to days) evolves with time. We
show that stars exhibit clear evolutionary sequences in diagrams
of three simple photometric variability measures; these measures
thus provide a "fundamental plane" of stellar evolution akin to
the Hertzsprung-Russell diagram, but involve only simple measures of
photometric variability. We observe that the light curves of these stars
become "quieter" as they age and spin down, but that the light curves
become suddenly and significantly more complex as they approach their
evolution off the main-sequence. Using an asteroseismically analyzed
sample of stars, we show that the sequences in our fundamental plane
correlate strongly with stellar surface gravity, thereby providing a
simple tool to accurately measure this quantity to better than 0.1
dex with just the long-cadence light curve. We find that the Sun
itself obeys these new-found relationships; its surface gravity is
correctly predicted to within 0.1 dex using only simple measures of its
photometric variability. We suggest that the brightness variations we
observe trace a mixture of both granulation and global oscillations,
akin to that traced in astroseismic analyses, but manifested in a
remarkably simpler fashion than previously appreciated.

---------------------------------------------------------
Title: Comparison of Kepler Photometric Variability with the Sun on
Different Timescales
Authors: Basri, Gibor; Walkowicz, Lucianne M.; Reiners, Ansgar
2013ApJ...769...37B Altcode: 2013arXiv1304.0136B
We utilize Kepler data to study the precision differential photometric
variability of solar-type and cooler stars at different timescales,
ranging from half an hour to three months. We define a diagnostic that
characterizes the median differential intensity change between data
bins of a given timescale. We apply the same diagnostics to Solar
and Heliospheric Observatory data that has been rendered comparable
to Kepler. The Sun exhibits similar photometric variability on all
timescales as comparable solar-type stars in the Kepler field. The
previously defined photometric "range" serves as our activity proxy
(driven by starspot coverage). We revisit the fraction of comparable
stars in the Kepler field that are more active than the Sun. The exact
active fraction depends on what is meant by "more active than the Sun"
and on the magnitude limit of the sample of stars considered. This
active fraction is between a quarter and a third (depending on the
timescale). We argue that a reliable result requires timescales of
half a day or longer and stars brighter than M Kep of 14,
otherwise non-stellar noise distorts it. We also analyze main sequence
stars grouped by temperature from 6500 to 3500 K. As one moves to
cooler stars, the active fraction of stars becomes steadily larger
(greater than 90% for early M dwarfs). The Sun is a good photometric
model at all timescales for those cooler stars that have long-term
variability within the span of solar variability.

---------------------------------------------------------
Title: The Information Content in Analytic Spot Models of Broadband
Precision Light Curves
Authors: Walkowicz, Lucianne M.; Basri, Gibor; Valenti, Jeff A.
2013ApJS..205...17W Altcode: 2012arXiv1212.1672W
We present the results of numerical experiments to assess degeneracies
in light curve models of starspots. Using synthetic light curves
generated with the Cheetah starspot modeling code, we explore
the extent to which photometric light curves constrain spot model
parameters, including spot latitudes and stellar inclination. We
also investigate the effects of spot parameters and differential
rotation on one's ability to correctly recover rotation periods and
differential rotation in the Kepler light curves. We confirm that in
the absence of additional constraints on the stellar inclination, such
as spectroscopic measurements of vsin i or occultations of starspots
by planetary transits, the spot latitude and stellar inclination are
difficult to determine uniquely from the photometry alone. We find that
for models with no differential rotation, spots that appear on opposite
hemispheres of the star may cause one to interpret the rotation period
to be half of the true period. When differential rotation is included,
the changing longitude separation between spots breaks the symmetry
of the hemispheres and the correct rotation period is more likely
to be found. The dominant period found via periodogram analysis is
typically that of the largest spot. Even when multiple spots with
periods representative of the star's differential rotation exist, if
one spot dominates the light curve the signal of differential rotation
may not be detectable from the periodogram alone. Starspot modeling is
applicable to stars with a wider range of rotation rates than other
surface imaging techniques (such as Doppler imaging), allows subtle
signatures of differential rotation to be measured, and may provide
valuable information on the distribution of stellar spots. However,
given the inherent degeneracies and uncertainty present in starspot
models, caution should be exercised in their interpretation.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Kepler planetary
candidates. III. (Batalha+, 2013)
Authors: Batalha, N. M.; Rowe, J. F.; Bryson, S. T.; Barclay, T.;
Burke, C. J.; Caldwell, D. A.; Christiansen, J. L.; Mullally, F.;
Thompson, S. E.; Brown, T. M.; Dupree, A. K.; Fabrycky, D. C.; Ford,
E. B.; Fortney, J. J.; Gilliland, R. L.; Isaacson, H.; Latham,
D. W.; Marcy, G. W.; Quinn, S. N.; Ragozzine, D.; Shporer, A.;
Borucki, W. J.; Ciardi, D. R.; Gautier, T. N., III; Haas, M. R.;
Jenkins, J. M.; Koch, D. G.; Lissauer, J. J.; Rapin, W.; Basri,
G. S.; Boss, A. P.; Buchhave, L. A.; Carter, J. A.; Charbonneau, D.;
Christensen-Dalsgaard, J.; Clarke, B. D.; Cochran, W. D.; Demory,
B. -O.; Desert, J. -M.; DeVore, E.; Doyle, L. R.; Esquerdo, G. A.;
Everett, M.; Fressin, F.; Geary, J. C.; Girouard, F. R.; Gould, A.;
Hall, J. R.; Holman, M. J.; Howard, A. W.; Howell, S. B.; Ibrahim,
K. A.; Kinemuchi, K.; Kjeldsen, H.; Klaus, T. C.; Li, J.; Lucas,
P. W.; Meibom, S.; Morris, R. L.; Prsa, A.; Quintana, E.; Sanderfer,
D. T.; Sasselov, D.; Seader, S. E.; Smith, J. C.; Steffen, J. H.;
Still, M.; Stumpe, M. C.; Tarter, J. C.; Tenenbaum, P.; Torres, G.;
Twicken, J. D.; Uddin, K.; van Cleve, J.; Walkowicz, L.; Welsh, W. F.
2013yCat..22040024B Altcode:
The data employed for transit identification were acquired between 2009
May 13 00:15 UTC and 2010 Sep 22 19:03 UTC (Q1-Q6). Over 190000 stars
were observed at some time during this period. (6 data files).

---------------------------------------------------------
Title: Planetary Candidates Observed by Kepler. III. Analysis of
the First 16 Months of Data
Authors: Batalha, Natalie M.; Rowe, Jason F.; Bryson, Stephen
T.; Barclay, Thomas; Burke, Christopher J.; Caldwell, Douglas A.;
Christiansen, Jessie L.; Mullally, Fergal; Thompson, Susan E.; Brown,
Timothy M.; Dupree, Andrea K.; Fabrycky, Daniel C.; Ford, Eric B.;
Fortney, Jonathan J.; Gilliland, Ronald L.; Isaacson, Howard; Latham,
David W.; Marcy, Geoffrey W.; Quinn, Samuel N.; Ragozzine, Darin;
Shporer, Avi; Borucki, William J.; Ciardi, David R.; Gautier, Thomas
N., III; Haas, Michael R.; Jenkins, Jon M.; Koch, David G.; Lissauer,
Jack J.; Rapin, William; Basri, Gibor S.; Boss, Alan P.; Buchhave,
Lars A.; Carter, Joshua A.; Charbonneau, David; Christensen-Dalsgaard,
Joergen; Clarke, Bruce D.; Cochran, William D.; Demory, Brice-Olivier;
Desert, Jean-Michel; Devore, Edna; Doyle, Laurance R.; Esquerdo,
Gilbert A.; Everett, Mark; Fressin, Francois; Geary, John C.; Girouard,
Forrest R.; Gould, Alan; Hall, Jennifer R.; Holman, Matthew J.; Howard,
Andrew W.; Howell, Steve B.; Ibrahim, Khadeejah A.; Kinemuchi, Karen;
Kjeldsen, Hans; Klaus, Todd C.; Li, Jie; Lucas, Philip W.; Meibom,
Søren; Morris, Robert L.; Prša, Andrej; Quintana, Elisa; Sanderfer,
Dwight T.; Sasselov, Dimitar; Seader, Shawn E.; Smith, Jeffrey C.;
Steffen, Jason H.; Still, Martin; Stumpe, Martin C.; Tarter, Jill C.;
Tenenbaum, Peter; Torres, Guillermo; Twicken, Joseph D.; Uddin, Kamal;
Van Cleve, Jeffrey; Walkowicz, Lucianne; Welsh, William F.
2013ApJS..204...24B Altcode: 2012arXiv1202.5852B
New transiting planet candidates are identified in 16 months (2009
May-2010 September) of data from the Kepler spacecraft. Nearly 5000
periodic transit-like signals are vetted against astrophysical and
instrumental false positives yielding 1108 viable new planet candidates,
bringing the total count up to over 2300. Improved vetting metrics
are employed, contributing to higher catalog reliability. Most notable
is the noise-weighted robust averaging of multi-quarter photo-center
offsets derived from difference image analysis that identifies likely
background eclipsing binaries. Twenty-two months of photometry are used
for the purpose of characterizing each of the candidates. Ephemerides
(transit epoch, T 0, and orbital period, P) are tabulated
as well as the products of light curve modeling: reduced radius
(R P/R sstarf), reduced semimajor axis (d/R
sstarf), and impact parameter (b). The largest fractional
increases are seen for the smallest planet candidates (201% for
candidates smaller than 2 R ⊕ compared to 53% for
candidates larger than 2 R ⊕) and those at longer orbital
periods (124% for candidates outside of 50 day orbits versus 86% for
candidates inside of 50 day orbits). The gains are larger than expected
from increasing the observing window from 13 months (Quarters 1-5)
to 16 months (Quarters 1-6) even in regions of parameter space where
one would have expected the previous catalogs to be complete. Analyses
of planet frequencies based on previous catalogs will be affected by
such incompleteness. The fraction of all planet candidate host stars
with multiple candidates has grown from 17% to 20%, and the paucity of
short-period giant planets in multiple systems is still evident. The
progression toward smaller planets at longer orbital periods with each
new catalog release suggests that Earth-size planets in the habitable
zone are forthcoming if, indeed, such planets are abundant.

---------------------------------------------------------
Title: A Large Sample of Magnetically-Active Stars Observed With
Kepler
Authors: Wells, Mark; Neff, J. E.; Brown, A.; Ayres, T. R.; Basri,
G. S.; Berdyugina, S.; Harper, G.; Hawley, S. L.; Korhonen, H.;
Kowalski, A.; Micela, G.; Piskunov, N. E.; Ramsey, L. W.; Saar, S. H.;
Walkowicz, L. M.
2013AAS...22135415W Altcode:
We have observed about 325 stars in our Kepler Guest Observer
programs (Cycles 1 through 4). For most of these targets, we are
analyzing extremely high-precision light curves that have been
continuously sampled every 30 minutes for up to 3 years. Our sample
of candidate magnetically-active stars was selected primarily using
GALEX colors. Starspots, pulsations, and variations due to eclipsing
and contact binaries combine to produce a rich variety of light
curves. We have developed semi-automated procedures to characterize
this variability and thus to classify the targets and identify the
physical mechanisms that dominate their Kepler light curves. We will
describe these procedures and discuss the range of physical properties
covered by our final classification scheme. We are using this Kepler
database of variability over timescales of minutes to years to provide
diagnostics of flares, starspot formation, evolution, migration, and
ultimately of stellar cycles in general. This work contains results
obtained using the NASA Kepler satellite and from the Apache Point
Observatory, the MMT (using NOAO community access time), and the
Hobby-Eberly Telescope. Funding is provided by NASA Kepler grants
NNX10AC51G, NNX11AC79G, and NNX12AC85G to the University of Colorado,
by NSF grant AST-1109695 to the College of Charleston, and by a grant
from the South Carolina Space Grant consortium.

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Title: Young Star Populations in the Kepler Field
Authors: Brown, Alexander; Neff, J. E.; Wells, M.; Saar, S.; Furesz,
G.; Walkowicz, L. M.; Ayres, T. R.; Basri, G. S.; Berdyugina, S.;
Harper, G.; Hawley, S. L.; Korhonen, H.; Kowalski, A.; Micela, G.;
Piskunov, N. E.; Ramsey, L. W.
2013AAS...22135414B Altcode:
The Kepler satellite is providing spectacular optical photometric
light-curves of unprecedented precision and duration that routinely
allow detailed studies of stellar magnetic activity on late-type stars
that were difficult previously. Kepler provides multi-year duration
light-curves that allow investigation of how activity phenomena --
such as the growth, migration, and decay of star-spots, differential
rotation, activity cycles, and flaring -- operate on a wide variety of
single and binary stars. The 105 square degree Kepler Field contains
tens of thousands of late-type stars showing rotational modulation due
to star-spots with periods ranging from one day to a “solar-like”
month. Short rotation periods and high levels of magnetic activity are
strongly correlated. However, there are only two basic reasons why stars
with rotation periods of a few days possess such high angular momentum
--- either they are close binaries or they are young stars. During
Kepler GO Cycles 1 through 4 we have been studying the Long-cadence
(30 minute sampling) photometry of hundreds of active late-type stars
and as an absolutely essential complement we have been obtaining high
resolution optical spectra to understand the physical properties of
these stars. We present results from a spectroscopic survey using the
MMT Hectochelle multi-object echelle of 4 square degrees of the Kepler
Field. We have discovered a significant population of young stars with
Li I absorption indicating ages of ~100 Myr or less at a spatial density
of at least 20 stars per square degree. Our detected young star sample
comprises at least 80 stars and represents a dramatic advance compared
to the previously known sample over the full Kepler Field of three
stars in this age range. Roughly one sixth of the stars observed are
young and a similar number short-period binaries based on 2-4 radial
velocities. We show how the rotational properties of the stars and their
physical properties are related. This work is based on data obtained
with the NASA Kepler satellite and the MMT Hectochelle spectrograph
using NOAO community access time. Support by NASA Kepler grants to the
University of Colorado and by NSF grant to the College of Charleston.

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Title: Planet Occurrence within 0.25 AU of Solar-type Stars from
Kepler
Authors: Howard, Andrew W.; Marcy, Geoffrey W.; Bryson, Stephen T.;
Jenkins, Jon M.; Rowe, Jason F.; Batalha, Natalie M.; Borucki, William
J.; Koch, David G.; Dunham, Edward W.; Gautier, Thomas N., III; Van
Cleve, Jeffrey; Cochran, William D.; Latham, David W.; Lissauer,
Jack J.; Torres, Guillermo; Brown, Timothy M.; Gilliland, Ronald
L.; Buchhave, Lars A.; Caldwell, Douglas A.; Christensen-Dalsgaard,
Jørgen; Ciardi, David; Fressin, Francois; Haas, Michael R.; Howell,
Steve B.; Kjeldsen, Hans; Seager, Sara; Rogers, Leslie; Sasselov,
Dimitar D.; Steffen, Jason H.; Basri, Gibor S.; Charbonneau, David;
Christiansen, Jessie; Clarke, Bruce; Dupree, Andrea; Fabrycky,
Daniel C.; Fischer, Debra A.; Ford, Eric B.; Fortney, Jonathan J.;
Tarter, Jill; Girouard, Forrest R.; Holman, Matthew J.; Johnson,
John Asher; Klaus, Todd C.; Machalek, Pavel; Moorhead, Althea V.;
Morehead, Robert C.; Ragozzine, Darin; Tenenbaum, Peter; Twicken,
Joseph D.; Quinn, Samuel N.; Isaacson, Howard; Shporer, Avi; Lucas,
Philip W.; Walkowicz, Lucianne M.; Welsh, William F.; Boss, Alan;
Devore, Edna; Gould, Alan; Smith, Jeffrey C.; Morris, Robert L.;
Prsa, Andrej; Morton, Timothy D.; Still, Martin; Thompson, Susan E.;
Mullally, Fergal; Endl, Michael; MacQueen, Phillip J.
2012ApJS..201...15H Altcode: 2011arXiv1103.2541H
We report the distribution of planets as a function of planet radius,
orbital period, and stellar effective temperature for orbital periods
less than 50 days around solar-type (GK) stars. These results are based
on the 1235 planets (formally "planet candidates") from the Kepler
mission that include a nearly complete set of detected planets as
small as 2 R ⊕. For each of the 156,000 target stars,
we assess the detectability of planets as a function of planet
radius, R p, and orbital period, P, using a measure of the
detection efficiency for each star. We also correct for the geometric
probability of transit, R sstarf/a. We consider first
Kepler target stars within the "solar subset" having T eff
= 4100-6100 K, log g = 4.0-4.9, and Kepler magnitude Kp &lt; 15 mag,
i.e., bright, main-sequence GK stars. We include only those stars
having photometric noise low enough to permit detection of planets
down to 2 R ⊕. We count planets in small domains of R
p and P and divide by the included target stars to calculate
planet occurrence in each domain. The resulting occurrence of planets
varies by more than three orders of magnitude in the radius-orbital
period plane and increases substantially down to the smallest radius
(2 R ⊕) and out to the longest orbital period (50 days,
~0.25 AU) in our study. For P &lt; 50 days, the distribution of planet
radii is given by a power law, df/dlog R = kRR α
with kR = 2.9+0.5 - 0.4, α = -1.92 ±
0.11, and R ≡ R p/R ⊕. This rapid increase
in planet occurrence with decreasing planet size agrees with the
prediction of core-accretion formation but disagrees with population
synthesis models that predict a desert at super-Earth and Neptune
sizes for close-in orbits. Planets with orbital periods shorter than
2 days are extremely rare; for R p &gt; 2 R ⊕
we measure an occurrence of less than 0.001 planets per star. For all
planets with orbital periods less than 50 days, we measure occurrence
of 0.130 ± 0.008, 0.023 ± 0.003, and 0.013 ± 0.002 planets per
star for planets with radii 2-4, 4-8, and 8-32 R ⊕,
in agreement with Doppler surveys. We fit occurrence as a function
of P to a power-law model with an exponential cutoff below a critical
period P 0. For smaller planets, P 0 has larger
values, suggesting that the "parking distance" for migrating planets
moves outward with decreasing planet size. We also measured planet
occurrence over a broader stellar T eff range of 3600-7100
K, spanning M0 to F2 dwarfs. Over this range, the occurrence of 2-4 R
⊕ planets in the Kepler field increases with decreasing
T eff, with these small planets being seven times more
abundant around cool stars (3600-4100 K) than the hottest stars in
our sample (6600-7100 K). Based in part on observations obtained
at the W. M. Keck Observatory, which is operated by the University of
California and the California Institute of Technology.

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Title: Harnessing the Power of NASA's Kepler Mission for Understanding
Stellar Activity and Enhancing Planet Discovery
Authors: Bastien, Fabienne A.; Stassun, K. G.; Pepper, J.; Walkowicz,
L.; Basri, G.; Carpenter, K. G.
2012AAS...21934504B Altcode:
The magnetic activity of stars, which often manifests itself in the
form of starspots, can induce short-timescale photometric variability,
thereby adding to the difficulty of detecting planets, particularly
those in the Earth mass range. Indeed, photometric "noise” caused
by stellar magnetic activity can preclude the detection of the tiny
transit signature that a planet like ours would produce. Hence, in order
to successfully detect Earth-like planets via the transit method, the
exoplanet community needs a way characterize the photometric stability
of a star in advance. The goal of our project is to empirically relate
chromospheric activity and photometric variability for a large sample
of stars, spanning a range of stellar masses and evolutionary states,
in order to develop an index that is predictive of stellar photometric
variability. The inclusion of stars with a range of known rotation
periods, as well as subgiants, giants, and Kepler asteroseismology
targets, will allow us to more finely examine the relationship
between a star's age and its magnetic activity. This work will aid
in a fundamental understanding of the physics of magnetic activity
in solar-type stars. We acknowledge support through NSF PAARE grant
AST-0849736.

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Title: Kepler Light Curves and Stellar Rotational Periods
Authors: Reinhold, T.; Reiners, A.; Basri, G.; Walkowicz, L. M.
2011ASPC..448.1033R Altcode: 2010arXiv1012.2217R; 2011csss...16.1033R
The Kepler space telescope monitors over 156,000 stars with an
unprecedented photometric precision. We are interested in stellar
rotational periods which we find using Lomb-Scargle periodograms. This
work focuses on the 306 exoplanet candidate host stars released on
June 15, 2010. We present statistics on how many of them show periodic
photometric variability, providing preliminary periods and estimates of
stellar activity. In the future, our work will focus on spot evolution
and differential rotation.

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Title: Starspots and Stellar Rotation: Stellar Activity with Kepler
Authors: Walkowicz, L. M.; Basri, G. S.
2011ASPC..448..177W Altcode: 2011csss...16..177W
While the telescopic study of starspots dates back to Galileos
observations of our own Sun, recent space-borne photometric
missions (such as MOST, CoRoT, and Kepler) are opening a new window
into understanding these ubiquitous manifestations of stellar
activity. Because of the intimate link between stellar rotation and
the generation of the magnetic field, starspots cause a modulation in
the lightcurve at the rate of stellar rotation. To complicate matters,
stars rotate differentially, so the stellar rotation rate is not really
best characterized by a single value but rather by a range of rotation
rates. Through high-precision, long-term photometric monitoring of stars
of different spectral types and activity strengths, it is possible to
determine stellar rotation rates and differential rotation measures. In
addition, modeling these lightcurves can tell us about the properties
of stellar spots, such as location, areal coverage, and lifetime. New
observations provide precision photometry for a large cohort of
stars, ranging from Sun-like to rather different stellar properties,
at a spread of ages, making these lightcurves a powerful tool for
understanding magnetic activity for stars of all activity levels. Here,
I will discuss how Kepler can provide new insight into the continuum
of stellar activity and our own Suns place amongst the stars.

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Title: VizieR Online Data Catalog: Kepler planetary
candidates. I. (Borucki+, 2011)
Authors: Borucki, W. J.; Koch, D. G.; Basri, G.; Batalha, N.; Boss,
A.; Brown, T. M.; Caldwell, D.; Christensen-Dalsgaard, J.; Cochran,
W. D.; DeVore, E.; Dunham, E. W.; Dupree, A. K.; Gautier, T. N.,
III; Geary, J. C.; Gilliland, R.; Gould, A.; Howell, S. B.; Jenkins,
J. M.; Kjeldsen, H.; Latham, D. W.; Lissauer, J. J.; Marcy, G. W.;
Monet, D. G.; Sasselov, D.; Tarter, J.; Charbonneau, D.; Doyle, L.;
Ford, E. B.; Fortney, J.; Holman, M. J.; Seager, S.; Steffen, J. H.;
Welsh, W. F.; Allen, C.; Bryson, S. T.; Buchhave, L.; Chandrasekaran,
H.; Christiansen, J. L.; Ciardi, D.; Clarke, B. D.; Dotson, J. L.;
Endl, M.; Fischer, D.; Fressin, F.; Haas, M.; Horch, E.; Howard,
A.; Isaacson, H.; Kolodziejczak, J.; Li, J.; MacQueen, P.; Meibom,
S.; Prsa, A.; Quintana, E. V.; Rowe, J.; Sherry, W.; Tenenbaum, P.;
Torres, G.; Twicken, J. D.; van Cleve, J.; Walkowicz, L.; Wu, H.
2011yCat..17280117B Altcode:
In the spring of 2009, the Kepler Mission commenced high-precision
photometry on nearly 156000 stars to determine the frequency and
characteristics of small exoplanets, conduct a guest observer program,
and obtain asteroseismic data on a wide variety of stars. On 2010
June 15, the Kepler Mission released most of the data from the first
quarter of observations. At the time of this data release, 705 stars
from this first data set have exoplanet candidates with sizes from as
small as that of Earth to larger than that of Jupiter. Here we give
the identity and characteristics of 305 released stars with planetary
candidates. Data for the remaining 400 stars with planetary candidates
will be released in 2011 February. More than half the candidates on
the released list have radii less than half that of Jupiter. Five
candidates are present in and near the habitable zone; two near
super-Earth size, and three bracketing the size of Jupiter. The
released stars also include five possible multi-planet systems. One
of these has two Neptune-size (2.3 and 2.5 Earth radius) candidates
with near-resonant periods. (1 data file).

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Title: VizieR Online Data Catalog: Kepler planetary
candidates. II. (Borucki+, 2011)
Authors: Borucki, W. J.; Koch, D. G.; Basri, G.; Batalha, N.; Brown,
T. M.; Bryson, S. T.; Caldwell, D.; Christensen-Dalsgaard, J.;
Cochran, W. D.; DeVore, E.; Dunham, E. W.; Gautier, T. N.; Geary,
J. C.; Gilliland, R.; Gould, A.; Howell, S. B.; Jenkins, J. M.;
Latham, D. W.; Lissauer, J. J.; Marcy, G. W.; Rowe, J.; Sasselov,
D.; Boss, A.; Charbonneau, D.; Ciardi, D.; Doyle, L.; Dupree, A. K.;
Ford, E. B.; Fortney, J.; Holman, M. J.; Seager, S.; Steffen, J. H.;
Tarter, J.; Welsh, W. F.; Allen, C.; Buchhave, L. A.; Christiansen,
J. L.; Clarke, B. D.; Das, S.; Desert, J. -M.; Endl, M.; Fabrycky,
D.; Fressin, F.; Haas, M.; Horch, E.; Howard, A.; Isaacson, H.;
Kjeldsen, H.; Kolodziejczak, J.; Kulesa, C.; Li, J.; Lucas, P. W.;
Machalek, P.; McCarthy, D.; MacQueen, P.; Meibom, S.; Miquel, T.;
Prsa, A.; Quinn, S. N.; Quintana, E. V.; Ragozzine, D.; Sherry, W.;
Shporer, A.; Tenenbaum, P.; Torres, G.; Twicken, J. D.; van Cleve,
J.; Walkowicz, L.; Witteborn, F. C.; Still, M.
2011yCat..17360019B Altcode:
The results discussed in this paper are based on three data segments:
the first segment (labeled Q0) started on JD 2454953.53 and ended on
2454963.25 and was taken during commissioning operations, the second
data segment (labeled Q1) taken at the beginning of science operations
that started on JD 2454964.50 and finished on JD 2454997.99, and a
third segment (labeled Q2) starting on JD 2455002.51 and finishing on
JD 2455091.48. The durations of the segments are 9.7, 33.5, and 89.0
days, respectively. The observations span a total period of 137.95
days including the gaps. A total of 156097 long cadence (LC) targets
in Q1, and 166247 LC and 1492 short cadence (SC) targets in Q2 were
observed. The results reported here are for the LC observations of
153196 stars observed during Q2. The selected stars are primarily
main-sequence dwarfs chosen from the Kepler Input Catalog (KIC,
Cat. V/133). (4 data files).

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Title: Kepler Mission Stellar and Instrument Noise Properties
Authors: Gilliland, Ronald L.; Chaplin, William J.; Dunham, Edward
W.; Argabright, Vic S.; Borucki, William J.; Basri, Gibor; Bryson,
Stephen T.; Buzasi, Derek L.; Caldwell, Douglas A.; Elsworth, Yvonne
P.; Jenkins, Jon M.; Koch, David G.; Kolodziejczak, Jeffrey; Miglio,
Andrea; van Cleve, Jeffrey; Walkowicz, Lucianne M.; Welsh, William F.
2011ApJS..197....6G Altcode: 2011arXiv1107.5207G
Kepler mission results are rapidly contributing to fundamentally new
discoveries in both the exoplanet and asteroseismology fields. The
data returned from Kepler are unique in terms of the number of stars
observed, precision of photometry for time series observations, and
the temporal extent of high duty cycle observations. As the first
mission to provide extensive time series measurements on thousands
of stars over months to years at a level hitherto possible only for
the Sun, the results from Kepler will vastly increase our knowledge
of stellar variability for quiet solar-type stars. Here, we report
on the stellar noise inferred on the timescale of a few hours of
most interest for detection of exoplanets via transits. By design the
data from moderately bright Kepler stars are expected to have roughly
comparable levels of noise intrinsic to the stars and arising from a
combination of fundamental limitations such as Poisson statistics and
any instrument noise. The noise levels attained by Kepler on-orbit
exceed by some 50% the target levels for solar-type, quiet stars. We
provide a decomposition of observed noise for an ensemble of 12th
magnitude stars arising from fundamental terms (Poisson and readout
noise), added noise due to the instrument and that intrinsic to the
stars. The largest factor in the modestly higher than anticipated
noise follows from intrinsic stellar noise. We show that using stellar
parameters from galactic stellar synthesis models, and projections
to stellar rotation, activity, and hence noise levels reproduce the
primary intrinsic stellar noise features.

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Title: Assessing the Nature and Impact of Observed Stellar Variability
on Kepler’s Ability to Detect Earth-Size Planets
Authors: Jenkins, Jon Michael; Dunham, E. W.; Argabright, V. S.;
Borucki, W. J.; Caldwell, D. A.; Chaplin, W. J.; Christiansen, J. L.;
Gautier, T. N.; Gilliland, R. L.; Kolodziejczak, J.; Machalek, P.;
Van Cleve, J.; Basri, G.; Buzasi, D. L.; Haas, M. R.; Howell, S. B.;
Tenenbaum, P.; Walkowicz, L. M.; Welsh, W. F.
2011ESS.....2.1914J Altcode:
The Kepler spacecraft was launched on March 6 2009 on a 3.5-year mission
to determine the frequency of Earth-size and larger planets in or near
the habitable zones of their stars. Kepler has been observing 160,000
stars to detect transiting planets for over two years and has discovered
more than 16 confirmed or validated planets and has identified over
1200 candidate planets. There is sufficient data and experience with the
photometer to characterize Kepler’s ability to detect weak signatures
of small, terrestrial planets. The photometer’s sensitivity depends
on the total combined differential photometric precision (CDPP) and on
the mission lifetime. These driving requirements for Kepler called for
a total CDPP of 20 ppm for 12th magnitude G2 dwarf stars in 6.5 hours,
and a mission lifetime of 3.5 years. The noise budget includes 14 ppm
for shot noise, 10 ppm for instrument noise and 10 ppm adopted for
intrinsic stellar variability. The CDPP requirement was necessarily set
without knowledge of actual typical levels of stellar variability. We
find that Kepler’s noise metrics for 12th magnitude dwarf stars
are dominated by stellar variability and the overall combined noise
is ∼50% higher than the required value. While this does reduce
Kepler’s ability to achieve its scientific objectives, Kepler’s
originally envisioned capability to detect terrestrial planets can be
recovered by extending the duration of the flight mission to 8 years.

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Title: Characteristics of Planetary Candidates Observed by
Kepler. II. Analysis of the First Four Months of Data
Authors: Borucki, William J.; Koch, David G.; Basri, Gibor; Batalha,
Natalie; Brown, Timothy M.; Bryson, Stephen T.; Caldwell, Douglas;
Christensen-Dalsgaard, Jørgen; Cochran, William D.; DeVore, Edna;
Dunham, Edward W.; Gautier, Thomas N., III; Geary, John C.; Gilliland,
Ronald; Gould, Alan; Howell, Steve B.; Jenkins, Jon M.; Latham, David
W.; Lissauer, Jack J.; Marcy, Geoffrey W.; Rowe, Jason; Sasselov,
Dimitar; Boss, Alan; Charbonneau, David; Ciardi, David; Doyle,
Laurance; Dupree, Andrea K.; Ford, Eric B.; Fortney, Jonathan; Holman,
Matthew J.; Seager, Sara; Steffen, Jason H.; Tarter, Jill; Welsh,
William F.; Allen, Christopher; Buchhave, Lars A.; Christiansen,
Jessie L.; Clarke, Bruce D.; Das, Santanu; Désert, Jean-Michel;
Endl, Michael; Fabrycky, Daniel; Fressin, Francois; Haas, Michael;
Horch, Elliott; Howard, Andrew; Isaacson, Howard; Kjeldsen, Hans;
Kolodziejczak, Jeffery; Kulesa, Craig; Li, Jie; Lucas, Philip W.;
Machalek, Pavel; McCarthy, Donald; MacQueen, Phillip; Meibom, Søren;
Miquel, Thibaut; Prsa, Andrej; Quinn, Samuel N.; Quintana, Elisa V.;
Ragozzine, Darin; Sherry, William; Shporer, Avi; Tenenbaum, Peter;
Torres, Guillermo; Twicken, Joseph D.; Van Cleve, Jeffrey; Walkowicz,
Lucianne; Witteborn, Fred C.; Still, Martin
2011ApJ...736...19B Altcode: 2011arXiv1102.0541B
On 2011 February 1 the Kepler mission released data for 156,453
stars observed from the beginning of the science observations on
2009 May 2 through September 16. There are 1235 planetary candidates
with transit-like signatures detected in this period. These are
associated with 997 host stars. Distributions of the characteristics
of the planetary candidates are separated into five class sizes:
68 candidates of approximately Earth-size (R p &lt;
1.25 R ⊕), 288 super-Earth-size (1.25 R ⊕
&lt;= R p &lt; 2 R ⊕), 662 Neptune-size
(2 R ⊕ &lt;= R p &lt; 6 R ⊕),
165 Jupiter-size (6 R ⊕ &lt;= R p &lt;
15 R ⊕), and 19 up to twice the size of Jupiter (15 R
⊕ &lt;= R p &lt; 22 R ⊕). In the
temperature range appropriate for the habitable zone, 54 candidates
are found with sizes ranging from Earth-size to larger than that
of Jupiter. Six are less than twice the size of the Earth. Over 74%
of the planetary candidates are smaller than Neptune. The observed
number versus size distribution of planetary candidates increases to a
peak at two to three times the Earth-size and then declines inversely
proportional to the area of the candidate. Our current best estimates
of the intrinsic frequencies of planetary candidates, after correcting
for geometric and sensitivity biases, are 5% for Earth-size candidates,
8% for super-Earth-size candidates, 18% for Neptune-size candidates,
2% for Jupiter-size candidates, and 0.1% for very large candidates; a
total of 0.34 candidates per star. Multi-candidate, transiting systems
are frequent; 17% of the host stars have multi-candidate systems,
and 34% of all the candidates are part of multi-candidate systems.

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Title: The Science in Science Fiction: Using Popular Entertainment
as a Gateway
Authors: Basri, Gibor S.
2011AAS...21811606B Altcode: 2011BAAS..43G11606B
Science fiction on television and in movies reaches a wide audience
of young people. Some of them are avid fans of particular stories,
and more are enthralled by some of the special effects and other
science fiction themes that have become ever more compelling as media
technology improves. It actually doesn't matter whether the physics
behind the science fiction is solid, the latest in speculative theory,
or absolute nonsense - all provide a backdrop against which to present
solid science. I'll talk about the opportunities provided by a few
recent series and movies and how they can be woven into discussions
of physics, astrophysics, or how science really works.

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Title: Understanding Stellar Variability in Kepler Lightcurves
Authors: Basri, Gibor S.
2011AAS...21831102B Altcode: 2011BAAS..43G31102B
The Kepler mission is generating an unprecedented set of lightcurves
for stars, with the best precision and coverage ever achieved. Not
surprisingly, there have been many new phenomena seen. Some of these
we think we understand, and some remain mysterious. We present a
short sampler of some of these, both as individual cases, and also
certain classes of variables. In addition to variability in the stars,
there are substantial instrumental effects. We discuss our current
understanding and ability to correct for these (which are different
from quarter to quarter), and what sorts of stellar variability cannot
currently be confidently measured.

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Title: The Kepler Cluster Study: Stellar Rotation in NGC 6811
Authors: Meibom, Søren; Barnes, Sydney A.; Latham, David W.; Batalha,
Natalie; Borucki, William J.; Koch, David G.; Basri, Gibor; Walkowicz,
Lucianne M.; Janes, Kenneth A.; Jenkins, Jon; Van Cleve, Jeffrey;
Haas, Michael R.; Bryson, Stephen T.; Dupree, Andrea K.; Furesz,
Gabor; Szentgyorgyi, Andrew H.; Buchhave, Lars A.; Clarke, Bruce D.;
Twicken, Joseph D.; Quintana, Elisa V.
2011ApJ...733L...9M Altcode: 2011arXiv1104.2912M
We present rotation periods for 71 single dwarf members of the open
cluster NGC 6811 determined using photometry from NASA's Kepler
mission. The results are the first from The Kepler Cluster Study,
which combines Kepler's photometry with ground-based spectroscopy for
cluster membership and binarity. The rotation periods delineate a tight
sequence in the NGC 6811 color-period diagram from ~1 day at mid-F
to ~11 days at early-K spectral type. This result extends to 1 Gyr
similar prior results in the ~600 Myr Hyades and Praesepe clusters,
suggesting that rotation periods for cool dwarf stars delineate a
well-defined surface in the three-dimensional space of color (mass),
rotation, and age. It implies that reliable ages can be derived for
field dwarf stars with measured colors and rotation periods, and it
promises to enable further understanding of various aspects of stellar
rotation and activity for cool stars.

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Title: Kepler's First Rocky Planet: Kepler-10b
Authors: Batalha, Natalie M.; Borucki, William J.; Bryson, Stephen
T.; Buchhave, Lars A.; Caldwell, Douglas A.; Christensen-Dalsgaard,
Jørgen; Ciardi, David; Dunham, Edward W.; Fressin, Francois;
Gautier, Thomas N., III; Gilliland, Ronald L.; Haas, Michael R.;
Howell, Steve B.; Jenkins, Jon M.; Kjeldsen, Hans; Koch, David G.;
Latham, David W.; Lissauer, Jack J.; Marcy, Geoffrey W.; Rowe, Jason
F.; Sasselov, Dimitar D.; Seager, Sara; Steffen, Jason H.; Torres,
Guillermo; Basri, Gibor S.; Brown, Timothy M.; Charbonneau, David;
Christiansen, Jessie; Clarke, Bruce; Cochran, William D.; Dupree,
Andrea; Fabrycky, Daniel C.; Fischer, Debra; Ford, Eric B.; Fortney,
Jonathan; Girouard, Forrest R.; Holman, Matthew J.; Johnson, John;
Isaacson, Howard; Klaus, Todd C.; Machalek, Pavel; Moorehead, Althea
V.; Morehead, Robert C.; Ragozzine, Darin; Tenenbaum, Peter; Twicken,
Joseph; Quinn, Samuel; VanCleve, Jeffrey; Walkowicz, Lucianne M.;
Welsh, William F.; Devore, Edna; Gould, Alan
2011ApJ...729...27B Altcode: 2011arXiv1102.0605B
NASA's Kepler Mission uses transit photometry to determine
the frequency of Earth-size planets in or near the habitable
zone of Sun-like stars. The mission reached a milestone toward
meeting that goal: the discovery of its first rocky planet,
Kepler-10b. Two distinct sets of transit events were detected: (1)
a 152 ± 4 ppm dimming lasting 1.811 ± 0.024 hr with ephemeris
T [BJD] =2454964.57375+0.00060 -0.00082 +
N*0.837495+0.000004 -0.000005 days and (2)
a 376 ± 9 ppm dimming lasting 6.86 ± 0.07 hr with ephemeris
T [BJD] =2454971.6761+0.0020 -0.0023 +
N*45.29485+0.00065 -0.00076 days. Statistical
tests on the photometric and pixel flux time series established the
viability of the planet candidates triggering ground-based follow-up
observations. Forty precision Doppler measurements were used to confirm
that the short-period transit event is due to a planetary companion. The
parent star is bright enough for asteroseismic analysis. Photometry was
collected at 1 minute cadence for &gt;4 months from which we detected
19 distinct pulsation frequencies. Modeling the frequencies resulted in
precise knowledge of the fundamental stellar properties. Kepler-10 is
a relatively old (11.9 ± 4.5 Gyr) but otherwise Sun-like main-sequence
star with T eff = 5627 ± 44 K, M sstarf = 0.895
± 0.060 M sun, and R sstarf = 1.056 ± 0.021 R
sun. Physical models simultaneously fit to the transit light
curves and the precision Doppler measurements yielded tight constraints
on the properties of Kepler-10b that speak to its rocky composition: M
P = 4.56+1.17 -1.29 M ⊕,
R P = 1.416+0.033 -0.036 R
⊕, and ρP = 8.8+2.1 -2.9
g cm-3. Kepler-10b is the smallest transiting exoplanet
discovered to date. Based in part on observations obtained at
the W. M. Keck Observatory, which is operated by the University of
California and the California Institute of Technology.

---------------------------------------------------------
Title: White-light Flares on Cool Stars in the Kepler Quarter 1 Data
Authors: Walkowicz, Lucianne M.; Basri, Gibor; Batalha, Natalie;
Gilliland, Ronald L.; Jenkins, Jon; Borucki, William J.; Koch, David;
Caldwell, Doug; Dupree, Andrea K.; Latham, David W.; Meibom, Soeren;
Howell, Steve; Brown, Timothy M.; Bryson, Steve
2011AJ....141...50W Altcode: 2010arXiv1008.0853W
We present the results of a search for white-light flares on ~23,000
cool dwarfs in the Kepler Quarter 1 long cadence data. We have
identified 373 flaring stars, some of which flare multiple times during
the observation period. We calculate relative flare energies, flare
rates, and durations and compare these with the quiescent photometric
variability of our sample. We find that M dwarfs tend to flare more
frequently but for shorter durations than K dwarfs and that they emit
more energy relative to their quiescent luminosity in a given flare than
K dwarfs. Stars that are more photometrically variable in quiescence
tend to emit relatively more energy during flares, but variability is
only weakly correlated with flare frequency. We estimate distances for
our sample of flare stars and find that the flaring fraction agrees
well with other observations of flare statistics for stars within
300 pc above the Galactic plane. These observations provide a more
rounded view of stellar flares by sampling stars that have not been
pre-selected by their activity, and are informative for understanding
the influence of these flares on planetary habitability.

---------------------------------------------------------
Title: Characteristics of Kepler Planetary Candidates Based on the
First Data Set
Authors: Borucki, William J.; Koch, David G.; Basri, Gibor;
Batalha, Natalie; Boss, Alan; Brown, Timothy M.; Caldwell, Douglas;
Christensen-Dalsgaard, Jørgen; Cochran, William D.; DeVore, Edna;
Dunham, Edward W.; Dupree, Andrea K.; Gautier, Thomas N., III;
Geary, John C.; Gilliland, Ronald; Gould, Alan; Howell, Steve B.;
Jenkins, Jon M.; Kjeldsen, Hans; Latham, David W.; Lissauer, Jack
J.; Marcy, Geoffrey W.; Monet, David G.; Sasselov, Dimitar; Tarter,
Jill; Charbonneau, David; Doyle, Laurance; Ford, Eric B.; Fortney,
Jonathan; Holman, Matthew J.; Seager, Sara; Steffen, Jason H.; Welsh,
William F.; Allen, Christopher; Bryson, Stephen T.; Buchhave, Lars;
Chandrasekaran, Hema; Christiansen, Jessie L.; Ciardi, David; Clarke,
Bruce D.; Dotson, Jessie L.; Endl, Michael; Fischer, Debra; Fressin,
Francois; Haas, Michael; Horch, Elliott; Howard, Andrew; Isaacson,
Howard; Kolodziejczak, Jeffery; Li, Jie; MacQueen, Phillip; Meibom,
Søren; Prsa, Andrej; Quintana, Elisa V.; Rowe, Jason; Sherry, William;
Tenenbaum, Peter; Torres, Guillermo; Twicken, Joseph D.; Van Cleve,
Jeffrey; Walkowicz, Lucianne; Wu, Hayley
2011ApJ...728..117B Altcode: 2010arXiv1006.2799B
In the spring of 2009, the Kepler Mission commenced high-precision
photometry on nearly 156,000 stars to determine the frequency and
characteristics of small exoplanets, conduct a guest observer program,
and obtain asteroseismic data on a wide variety of stars. On 2010
June 15, the Kepler Mission released most of the data from the first
quarter of observations. At the time of this data release, 705 stars
from this first data set have exoplanet candidates with sizes from as
small as that of Earth to larger than that of Jupiter. Here we give
the identity and characteristics of 305 released stars with planetary
candidates. Data for the remaining 400 stars with planetary candidates
will be released in 2011 February. More than half the candidates on
the released list have radii less than half that of Jupiter. Five
candidates are present in and near the habitable zone; two near
super-Earth size, and three bracketing the size of Jupiter. The
released stars also include five possible multi-planet systems. One
of these has two Neptune-size (2.3 and 2.5 Earth radius) candidates
with near-resonant periods.

---------------------------------------------------------
Title: Photometric Variability in Kepler Target Stars. II. An Overview
of Amplitude, Periodicity, and Rotation in First Quarter Data
Authors: Basri, Gibor; Walkowicz, Lucianne M.; Batalha, Natalie;
Gilliland, Ronald L.; Jenkins, Jon; Borucki, William J.; Koch, David;
Caldwell, Doug; Dupree, Andrea K.; Latham, David W.; Marcy, Geoffrey
W.; Meibom, Soeren; Brown, Tim
2011AJ....141...20B Altcode: 2010arXiv1008.1092B
We provide an overview of stellar variability in the first quarter
data from the Kepler mission. The intent of this paper is to examine
the entire sample of over 150,000 target stars for periodic behavior
in their light curves and relate this to stellar characteristics. This
data set constitutes an unprecedented study of stellar variability
given its great precision and complete time coverage (with a half
hour cadence). Because the full Kepler pipeline is not currently
suitable for a study of stellar variability of this sort, we describe
our procedures for treating the "raw" pipeline data. About half of
the total sample exhibits convincing periodic variability up to two
weeks, with amplitudes ranging from differential intensity changes of
less than 10-4 up to more than 10%. K and M dwarfs have a
greater fraction of period behavior than G dwarfs. The giants in the
sample have distinctive quasi-periodic behavior, but are not periodic
in the way we define it. Not all periodicities are due to rotation,
and the most significant period is not necessarily the rotation
period. We discuss properties of the light curves, and in particular
look at a sample of very clearly periodic G dwarfs. It is clear that
a large number of them do vary because of rotation and starspots,
but it will take further analysis to fully exploit this.

---------------------------------------------------------
Title: Stellar Rotation and Activity with Kepler
Authors: Walkowicz, Lucianne M.; Basri, G.
2011AAS...21720105W Altcode: 2011BAAS...4320105W
Stellar magnetic activity leads to a plethora of observable effects,
from star spots that modulate the stellar brightness on the order of
weeks, to flares, which release highly energetic radiation over the
course of a few hours. Although Kepler's main goal is the discovery
of exoplanets, its unmatched precision photometry provides a wealth
of information regarding stellar astrophysics. Because of the intimate
link between stellar rotation and the generation of the magnetic field,
periodic brightness variations due to starspots may be used to gain
insight into the magnetic dynamo. In addition, an understanding of
the stellar radiation environment provides context for studies of
potential attendant planets. I will discuss our ongoing work with
Kepler to characterize stellar variability due to spots and flares,
and to determine rotation periods for the these stars. Kepler was
selected as the 10th mission of the Discovery Program. Funding for
this mission is provided by NASA, Science Mission Directorate.

---------------------------------------------------------
Title: Discovery and Rossiter-Mclaughlin Effect of Exoplanet Kepler-8b
Authors: Jenkins, Jon M.; Borucki, William J.; Koch, David G.;
Marcy, Geoffrey W.; Cochran, William D.; Welsh, William F.; Basri,
Gibor; Batalha, Natalie M.; Buchhave, Lars A.; Brown, Timothy M.;
Caldwell, Douglas A.; Dunham, Edward W.; Endl, Michael; Fischer,
Debra A.; Gautier, Thomas N., III; Geary, John C.; Gilliland,
Ronald L.; Howell, Steve B.; Isaacson, Howard; Johnson, John Asher;
Latham, David W.; Lissauer, Jack J.; Monet, David G.; Rowe, Jason F.;
Sasselov, Dimitar D.; Howard, Andrew W.; MacQueen, Phillip; Orosz,
Jerome A.; Chandrasekaran, Hema; Twicken, Joseph D.; Bryson, Stephen
T.; Quintana, Elisa V.; Clarke, Bruce D.; Li, Jie; Allen, Christopher;
Tenenbaum, Peter; Wu, Hayley; Meibom, Søren; Klaus, Todd C.; Middour,
Christopher K.; Cote, Miles T.; McCauliff, Sean; Girouard, Forrest R.;
Gunter, Jay P.; Wohler, Bill; Hall, Jennifer R.; Ibrahim, Khadeejah;
Kamal Uddin, AKM; Wu, Michael S.; Bhavsar, Paresh A.; Van Cleve,
Jeffrey; Pletcher, David L.; Dotson, Jessie L.; Haas, Michael R.
2010ApJ...724.1108J Altcode: 2010arXiv1001.0416J
We report on the discovery and the Rossiter-McLaughlin (R-M) effect
of Kepler-8b, a transiting planet identified by the NASA Kepler
Mission. Kepler photometry and Keck-HIRES radial velocities yield the
radius and mass of the planet around this F8IV subgiant host star. The
planet has a radius R P = 1.419 R J and a mass
M P = 0.60 M J, yielding a density of 0.26 g
cm-3, one of the lowest planetary densities known. The
orbital period is P = 3.523 days and the orbital semimajor axis is
0.0483+0.0006 -0.0012 AU. The star has a large
rotational vsin i of 10.5 ± 0.7 km s-1 and is relatively
faint (V ≈ 13.89 mag); both properties are deleterious to precise
Doppler measurements. The velocities are indeed noisy, with scatter of
30 m s-1, but exhibit a period and phase that are consistent
with those implied by transit photometry. We securely detect the R-M
effect, confirming the planet's existence and establishing its orbit
as prograde. We measure an inclination between the projected planetary
orbital axis and the projected stellar rotation axis of λ = -26fdg4 ±
10fdg1, indicating a significant inclination of the planetary orbit. R-M
measurements of a large sample of transiting planets from Kepler will
provide a statistically robust measure of the true distribution of
spin-orbit orientations for hot Jupiters around F and early G stars. Based in part on observations obtained at the W. M. Keck Observatory,
which is operated as a scientific partnership between the California
Institute of Technology, the University of California, and the National
Aeronautics and Space Administration. The Observatory was made possible
by the generous financial support of the W. M. Keck Foundation.

---------------------------------------------------------
Title: Kepler-9: A System of Multiple Planets Transiting a Sun-Like
Star, Confirmed by Timing Variations
Authors: Holman, Matthew J.; Fabrycky, Daniel C.; Ragozzine, Darin;
Ford, Eric B.; Steffen, Jason H.; Welsh, William F.; Lissauer,
Jack J.; Latham, David W.; Marcy, Geoffrey W.; Walkowicz, Lucianne
M.; Batalha, Natalie M.; Jenkins, Jon M.; Rowe, Jason F.; Cochran,
William D.; Fressin, Francois; Torres, Guillermo; Buchhave, Lars A.;
Sasselov, Dimitar D.; Borucki, William J.; Koch, David G.; Basri,
Gibor; Brown, Timothy M.; Caldwell, Douglas A.; Charbonneau, David;
Dunham, Edward W.; Gautier, Thomas N.; Geary, John C.; Gilliland,
Ronald L.; Haas, Michael R.; Howell, Steve B.; Ciardi, David R.;
Endl, Michael; Fischer, Debra; Fürész, Gábor; Hartman, Joel D.;
Isaacson, Howard; Johnson, John A.; MacQueen, Phillip J.; Moorhead,
Althea V.; Morehead, Robert C.; Orosz, Jerome A.
2010Sci...330...51H Altcode:
The Kepler spacecraft is monitoring more than 150,000 stars for
evidence of planets transiting those stars. We report the detection of
two Saturn-size planets that transit the same Sun-like star, based on
7 months of Kepler observations. Their 19.2- and 38.9-day periods are
presently increasing and decreasing at respective average rates of 4 and
39 minutes per orbit; in addition, the transit times of the inner body
display an alternating variation of smaller amplitude. These signatures
are characteristic of gravitational interaction of two planets near a
2:1 orbital resonance. Six radial-velocity observations show that these
two planets are the most massive objects orbiting close to the star and
substantially improve the estimates of their masses. After removing the
signal of the two confirmed giant planets, we identified an additional
transiting super-Earth-size planet candidate with a period of 1.6 days.

---------------------------------------------------------
Title: Photometric Variability in Kepler Target Stars: The Sun Among
Stars—a First Look
Authors: Basri, Gibor; Walkowicz, Lucianne M.; Batalha, Natalie;
Gilliland, Ronald L.; Jenkins, Jon; Borucki, William J.; Koch, David;
Caldwell, Doug; Dupree, Andrea K.; Latham, David W.; Meibom, Søren;
Howell, Steve; Brown, Tim
2010ApJ...713L.155B Altcode: 2010arXiv1001.0414B
The Kepler mission provides an exciting opportunity to study the
light curves of stars with unprecedented precision and continuity
of coverage. This is the first look at a large sample of stars with
photometric data of a quality that has heretofore been only available
for our Sun. It provides the first opportunity to compare the irradiance
variations of our Sun to a large cohort of stars ranging from very
similar to rather different stellar properties, at a wide variety of
ages. Although Kepler data are in an early phase of maturity, and we
only analyze the first month of coverage, it is sufficient to garner the
first meaningful measurements of our Sun's variability in the context
of a large cohort of main-sequence stars in the solar neighborhood. We
find that nearly half of the full sample is more active than the active
Sun, although most of them are not more than twice as active. The active
fraction is closer to a third for the stars most similar to the Sun, and
rises to well more than half for stars cooler than mid-K spectral types.

---------------------------------------------------------
Title: Kepler Observations of Transiting Hot Compact Objects
Authors: Rowe, Jason F.; Borucki, William J.; Koch, David; Howell,
Steve B.; Basri, Gibor; Batalha, Natalie; Brown, Timothy M.; Caldwell,
Douglas; Cochran, William D.; Dunham, Edward; Dupree, Andrea K.;
Fortney, Jonathan J.; Gautier, Thomas N., III; Gilliland, Ronald L.;
Jenkins, Jon; Latham, David W.; Lissauer, Jack J.; Marcy, Geoff;
Monet, David G.; Sasselov, Dimitar; Welsh, William F.
2010ApJ...713L.150R Altcode: 2010arXiv1001.3420R
Kepler photometry has revealed two unusual transiting companions: one
orbiting an early A-star and the other orbiting a late B-star. In both
cases, the occultation of the companion is deeper than the transit. The
occultation and transit with follow-up optical spectroscopy reveal a
9400 K early A-star, KOI-74 (KIC 6889235), with a companion in a 5.2
day orbit with a radius of 0.08 R sun and a 10,000 K late
B-star KOI-81 (KIC 8823868) that has a companion in a 24 day orbit with
a radius of 0.2 R sun. We infer a temperature of 12,250 K
for KOI-74b and 13,500 K for KOI-81b. We present 43 days of high duty
cycle, 30 minute cadence photometry, with models demonstrating the
intriguing properties of these objects, and speculate on their nature.

---------------------------------------------------------
Title: Kepler-7b: A Transiting Planet with Unusually Low Density
Authors: Latham, David W.; Borucki, William J.; Koch, David G.;
Brown, Timothy M.; Buchhave, Lars A.; Basri, Gibor; Batalha, Natalie
M.; Caldwell, Douglas A.; Cochran, William D.; Dunham, Edward W.;
Fűrész, Gabor; Gautier, Thomas N., III; Geary, John C.; Gilliland,
Ronald L.; Howell, Steve B.; Jenkins, Jon M.; Lissauer, Jack J.; Marcy,
Geoffrey W.; Monet, David G.; Rowe, Jason F.; Sasselov, Dimitar D.
2010ApJ...713L.140L Altcode: 2010arXiv1001.0190L
We report on the discovery and confirmation of Kepler-7b, a transiting
planet with unusually low density. The mass is less than half that of
Jupiter, M P = 0.43 M J, but the radius is 50%
larger, R P = 1.48 R J. The resulting density,
ρP = 0.17 g cm-3, is the second lowest reported
so far for an extrasolar planet. The orbital period is fairly long,
P = 4.886 days, and the host star is not much hotter than the Sun, T
eff = 6000 K. However, it is more massive and considerably
larger than the Sun, M sstarf = 1.35 M sun and
R sstarf = 1.84 R sun, and must be near the end
of its life on the main sequence. Based in part on observations
obtained at the W. M. Keck Observatory, which is operated by the
University of California and the California Institute of Technology.

---------------------------------------------------------
Title: Kepler-4b: A Hot Neptune-like Planet of a G0 Star Near
Main-sequence Turnoff
Authors: Borucki, William J.; Koch, David G.; Brown, Timothy M.;
Basri, Gibor; Batalha, Natalie M.; Caldwell, Douglas A.; Cochran,
William D.; Dunham, Edward W.; Gautier, Thomas N., III; Geary, John
C.; Gilliland, Ronald L.; Howell, Steve B.; Jenkins, Jon M.; Latham,
David W.; Lissauer, Jack J.; Marcy, Geoffrey W.; Monet, David; Rowe,
Jason F.; Sasselov, Dimitar
2010ApJ...713L.126B Altcode: 2010arXiv1001.0604B
Early time-series photometry from NASA's Kepler spacecraft
has revealed a planet transiting the star we term Kepler-4,
at R.A. = 19h02m27.s68, δ =
+50°08'08farcs7. The planet has an orbital period of 3.213 days
and shows transits with a relative depth of 0.87 × 10-3
and a duration of about 3.95 hr. Radial velocity (RV) measurements
from the Keck High Resolution Echelle Spectrometer show a reflex
Doppler signal of 9.3+1.1 -1.9 m s-1,
consistent with a low-eccentricity orbit with the phase expected from
the transits. Various tests show no evidence for any companion star
near enough to affect the light curve or the RVs for this system. From
a transit-based estimate of the host star's mean density, combined
with analysis of high-resolution spectra, we infer that the host
star is near turnoff from the main sequence, with estimated mass and
radius of 1.223+0.053 -0.091 M sun and
1.487+0.071 -0.084 R sun. We estimate
the planet mass and radius to be {M P, R P} =
{24.5 ± 3.8 M ⊕, 3.99 ± 0.21 R ⊕}. The
planet's density is near 1.9 g cm-3 it is thus slightly
denser and more massive than Neptune, but about the same size. Some of the data presented herein were obtained at the W. M. Keck
Observatory, which is operated as a scientific partnership among the
California Institute of Technology, the University of California,
and the National Aeronautics and Space Administration. The Observatory
was made possible by the generous financial support of the W. M. Keck
Foundation.

---------------------------------------------------------
Title: Kepler Mission Design, Realized Photometric Performance,
and Early Science
Authors: Koch, David G.; Borucki, William J.; Basri, Gibor;
Batalha, Natalie M.; Brown, Timothy M.; Caldwell, Douglas;
Christensen-Dalsgaard, Jørgen; Cochran, William D.; DeVore, Edna;
Dunham, Edward W.; Gautier, Thomas N., III; Geary, John C.; Gilliland,
Ronald L.; Gould, Alan; Jenkins, Jon; Kondo, Yoji; Latham, David W.;
Lissauer, Jack J.; Marcy, Geoffrey; Monet, David; Sasselov, Dimitar;
Boss, Alan; Brownlee, Donald; Caldwell, John; Dupree, Andrea K.;
Howell, Steve B.; Kjeldsen, Hans; Meibom, Søren; Morrison, David;
Owen, Tobias; Reitsema, Harold; Tarter, Jill; Bryson, Stephen T.;
Dotson, Jessie L.; Gazis, Paul; Haas, Michael R.; Kolodziejczak,
Jeffrey; Rowe, Jason F.; Van Cleve, Jeffrey E.; Allen, Christopher;
Chandrasekaran, Hema; Clarke, Bruce D.; Li, Jie; Quintana, Elisa V.;
Tenenbaum, Peter; Twicken, Joseph D.; Wu, Hayley
2010ApJ...713L..79K Altcode: 2010arXiv1001.0268K
The Kepler Mission, launched on 2009 March 6, was designed with the
explicit capability to detect Earth-size planets in the habitable zone
of solar-like stars using the transit photometry method. Results from
just 43 days of data along with ground-based follow-up observations
have identified five new transiting planets with measurements of their
masses, radii, and orbital periods. Many aspects of stellar astrophysics
also benefit from the unique, precise, extended, and nearly continuous
data set for a large number and variety of stars. Early results for
classical variables and eclipsing stars show great promise. To fully
understand the methodology, processes, and eventually the results from
the mission, we present the underlying rationale that ultimately led
to the flight and ground system designs used to achieve the exquisite
photometric performance. As an example of the initial photometric
results, we present variability measurements that can be used to
distinguish dwarf stars from red giants.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Velocities of 43 nearby L dwarfs
(Seifahrt+, 2010)
Authors: Seifahrt, A.; Reiners, A.; Almaghrbi, K. A. M.; Basri, G.
2010yCat..35120037S Altcode: 2010yCat..35129037S
We present radial velocity measurements of a sample of L0-L8 dwarfs
observed with VLT/UVES and Keck/HIRES. We combine these measurements
with distance and proper motion from the literature to determine space
motions for 43 of our targets. We identify nine candidate members of
young moving groups, which have ages of 50-600Myr according to their
space motion. (1 data file).

---------------------------------------------------------
Title: On the kinematic age of brown dwarfs: radial velocities and
space motions of 43 nearby L dwarfs
Authors: Seifahrt, A.; Reiners, A.; Almaghrbi, K. A. M.; Basri, G.
2010A&A...512A..37S Altcode: 2010arXiv1001.1780S
We present radial velocity measurements of a sample of L0-L8 dwarfs
observed with VLT/UVES and Keck/HIRES. We combine these measurements
with distance and proper motion from the literature to determine
space motions for 43 of our targets. We identify nine candidate
members of young moving groups, which have ages of 50-600 Myr
according to their space motion. From the total velocity dispersion
of the 43 L dwarfs, we calculate a kinematic age of ~5 Gyr for
our sample. This age is significantly higher than the ~3 Gyr age
known for late M dwarfs in the solar neighbourhood. We find that
the distributions of the U and V velocity components of our sample
are clearly non-Gaussian, placing the age estimate inferred from the
full space motion vector into question. The W-component exhibits a
distribution more consistent with a normal distribution, and from W
alone we derive an age of ~3 Gyr, which is the same age found for
late-M dwarf samples. Our brightness-limited sample is probably
contaminated by a number of outliers that predominantly bias the U
and V velocity components. The origin of the outliers remain unclear,
but we suggest that these brown dwarfs may have gained their high
velocities by means of ejection from multiple systems during their
formation. Table 2 is also available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A
href="http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/512/A37">http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/512/A37</A>

---------------------------------------------------------
Title: First thoughts on stellar variability from Kepler commissioning
data
Authors: Walkowicz, Lucianne M.; Basri, Gibor
2010IAUS..264..469W Altcode:
The Kepler mission will obtain high precision, continuous lightcurves
for more than ~150,000 stars over the next four years. Prior to primary
mission operations, ten days of commissioning data were obtained for
the ~52,000 brightest targets in the Kepler field. While Kepler's
main goal is the discovery of transiting low mass planets, it will
also provide a rich dataset for studies of variable stars. These
commissioning data give a first glimpse of the amazing diversity of
stellar variability Kepler will observe. Here, we discuss the tools we
are currently developing to quantify variability in the Kepler data,
and show initial results on the distribution of target stars in these
metrics. Ultimately these measures will be used both to characterize
the data and to select active rotationally modulated stars for rotation
period determination.

---------------------------------------------------------
Title: A Volume-Limited Sample of 63 M7-M9.5 Dwarfs. II. Activity,
Magnetism, and the Fade of the Rotation-Dominated Dynamo
Authors: Reiners, A.; Basri, G.
2010ApJ...710..924R Altcode: 2009arXiv0912.4259R
In a volume-limited sample of 63 ultracool dwarfs of spectral type
M7-M9.5, we have obtained high-resolution spectroscopy with UVES
at the Very Large Telescope and HIRES at Keck Observatory. In this
second paper, we present projected rotation velocities, average
magnetic field strengths, and chromospheric emission from the Hα
line. We confirm earlier results that the mean level of normalized
Hα luminosity decreases with lower temperature, and we find that
the scatter among Hα luminosities is larger at lower temperature. We
measure average magnetic fields between 0 and 4 kG with no indication
for a dependence on temperature between M7 and M9.5. For a given
temperature, Hα luminosity is related to magnetic field strength,
consistent with results in earlier stars. A few very slowly rotating
stars show very weak magnetic fields and Hα emission, and all stars
rotating faster than our detection limit show magnetic fields of
at least a few hundred Gauss. In contrast to earlier-type stars, we
observe magnetic fields weaker than 1 kG in stars rotating faster than
~3 km s-1, but we find no correlation between rotation and
magnetic flux generation among them. We interpret this as a fundamental
change in the dynamo mechanism; in ultracool dwarfs, magnetic field
generation is predominantly achieved by a turbulent dynamo, while
other mechanisms can operate more efficiently at earlier spectral types.

---------------------------------------------------------
Title: Rotation and Magnetic Activity in a Sample of M-Dwarfs
Authors: Browning, Matthew K.; Basri, Gibor; Marcy, Geoffrey W.;
West, Andrew A.; Zhang, Jiahao
2010AJ....139..504B Altcode:
We have analyzed the rotational broadening and chromospheric activity
in a sample of 123 M-dwarfs, using spectra taken at the W.M. Keck
Observatory as part of the California Planet Search program. We find
that only seven of these stars are rotating more rapidly than our
detection threshold of v sin i ≈ 2.5 km s-1. Rotation
appears to be more common in stars later than M3 than in the M0-M2.5
mass range: we estimate that less than 10% of early-M stars are
detectably rotating, whereas roughly a third of those later than
M4 show signs of rotation. These findings lend support to the view
that rotational braking becomes less effective in fully convective
stars. By measuring the equivalent widths of the Ca II H and K lines
for the stars in our sample, and converting these to approximate L
Ca/L bol measurements, we also provide constraints
on the connection between rotation and magnetic activity. Measurable
rotation is a sufficient, but not necessary condition for activity in
our sample: all the detectable rotators show strong Ca II emission,
but so too do a small number of non-rotating stars, which we presume may
lie at high inclination angles relative to our line of sight. Our data
are consistent with a "saturation-type" rotation-activity relationship,
with activity roughly independent of rotation above a threshold velocity
of less than 6 km s-1. We also find weak evidence for a
"gap" in L Ca/L bol between a highly active
population of stars, which typically are detected as rotators, and
another much less active group.

---------------------------------------------------------
Title: Kepler Planet-Detection Mission: Introduction and First Results
Authors: Borucki, William J.; Koch, David; Basri, Gibor; Batalha,
Natalie; Brown, Timothy; Caldwell, Douglas; Caldwell, John;
Christensen-Dalsgaard, Jørgen; Cochran, William D.; DeVore, Edna;
Dunham, Edward W.; Dupree, Andrea K.; Gautier, Thomas N.; Geary, John
C.; Gilliland, Ronald; Gould, Alan; Howell, Steve B.; Jenkins, Jon M.;
Kondo, Yoji; Latham, David W.; Marcy, Geoffrey W.; Meibom, Søren;
Kjeldsen, Hans; Lissauer, Jack J.; Monet, David G.; Morrison, David;
Sasselov, Dimitar; Tarter, Jill; Boss, Alan; Brownlee, Don; Owen,
Toby; Buzasi, Derek; Charbonneau, David; Doyle, Laurance; Fortney,
Jonathan; Ford, Eric B.; Holman, Matthew J.; Seager, Sara; Steffen,
Jason H.; Welsh, William F.; Rowe, Jason; Anderson, Howard; Buchhave,
Lars; Ciardi, David; Walkowicz, Lucianne; Sherry, William; Horch,
Elliott; Isaacson, Howard; Everett, Mark E.; Fischer, Debra; Torres,
Guillermo; Johnson, John Asher; Endl, Michael; MacQueen, Phillip;
Bryson, Stephen T.; Dotson, Jessie; Haas, Michael; Kolodziejczak,
Jeffrey; Van Cleve, Jeffrey; Chandrasekaran, Hema; Twicken, Joseph
D.; Quintana, Elisa V.; Clarke, Bruce D.; Allen, Christopher; Li,
Jie; Wu, Haley; Tenenbaum, Peter; Verner, Ekaterina; Bruhweiler,
Frederick; Barnes, Jason; Prsa, Andrej
2010Sci...327..977B Altcode:
The Kepler mission was designed to determine the frequency of
Earth-sized planets in and near the habitable zone of Sun-like
stars. The habitable zone is the region where planetary temperatures
are suitable for water to exist on a planet’s surface. During the
first 6 weeks of observations, Kepler monitored 156,000 stars, and
five new exoplanets with sizes between 0.37 and 1.6 Jupiter radii and
orbital periods from 3.2 to 4.9 days were discovered. The density of
the Neptune-sized Kepler-4b is similar to that of Neptune and GJ 436b,
even though the irradiation level is 800,000 times higher. Kepler-7b
is one of the lowest-density planets (~0.17 gram per cubic centimeter)
yet detected. Kepler-5b, -6b, and -8b confirm the existence of planets
with densities lower than those predicted for gas giant planets.

---------------------------------------------------------
Title: The Kepler Mission and Early Results
Authors: Koch, David; Borucki, William; Jenkins, Jon; Basri,
Gibor; Batalha, Natalie M.; Brown, Timothy M.; Caldwell, Douglas;
Christensen-Dalsgaard, Jørgen; Cochran, William D.; Devore, Edna;
Dunham, Edward W.; Gautier, Thomas N., III; Geary, John C.; Gilliland,
Ronald L.; Gould, Alan; Jenkins, Jon; Latham, David W.; Lissauer,
Jack J.; Marcy, Geoffrey; Monet, David; Sasselov, Dimitar; Boss, Alan;
Caldwell, John; Dupree, Andrea K.; Howell, Steve B.; Kjeldsen, Hans;
Meibom, Søren; Morrison, David; Tarter, Jill; Bryson, Stephen T.;
Dotson, Jessie L.; Haas, Michael R.; Kolodziejczak, Jeffrey; Rowe,
Jason F.; van Cleve, Jeffrey E.; Buzasi, Derek; Charbonneau, David;
Doyle, Lau-Rance; Ford, Eric; Fortney, Jonathan; Holman, Matthew;
Seager, Sara; Steffen, Jason; Welsh, William
2010cosp...38.2513K Altcode: 2010cosp.meet.2513K
Kepler is a Discovery-class mission designed to determine the frequency
of Earth-size planets in and near the habitable zone of solar-like
stars. The instrument consists of a 0.95 m aperture photometer designed
to obtain high-precision photometric measurement for more than 3.5
years of more than 100,000 stars to search for patterns of transits
of exoplanets. The focal plane of the Schmidt telescope contains 42
CCDs with a total of 95 megapixels that cover 115 square degrees of
sky. The single star field will be viewed for the entire duration
of the mission. The photometer was launched into an Earth-trailing
heliocentric orbit on March 6, 2009, finished its commissioning on May
12, and is now in the science operations mode. The bases for a number of
the design choices are described. Although the data have not yet been
fully corrected for the presence of systematic errors and artifacts,
the data show the presence of thousands of eclipsing binaries and
variable stars of amazing variety. The character of stellar variability
allows us to distinguish dwarf stars from giants. Astrometric stability
at the sub-millipixel level of the photocenters of stars allows us in
many cases to distinguish transit candidates from background eclipsing
binaries. Analysis of the early data shows transits, occultations and
even visible light emission from the hot exoplanet HAT-P-7b. The latest
results on exoplanet detections from Kepler will be presented. Funding
for this mission is provided by NASA's Science Mission Directorate.

---------------------------------------------------------
Title: Kepler Planet Detection Mission: Introduction and First Results
Authors: Borucki, William J.; Koch, D.; Basri, G.; Batalha, N. M.;
Brown, T.; Caldwell, D. A.; Caldwell, J.; Christensen-Dalsgaard, J.;
Cochran, W.; DeVore, E.; Dunham, E.; Dupree, A.; Gautier, T.; Geary,
J.; Gilliland, R.; Gould, A.; Howell, S.; Jenkins, J.; Kjeldsen, H.;
Kondo, Y.; Latham, D.; Lissauer, J.; Marcy, G.; Meibom, S.; Monet,
D.; Morrison, D.; Sasselov, D.; Tarter, J.
2010AAS...21510101B Altcode: 2010BAAS...42..215B
The Kepler Mission is designed to determine the frequency of Earth-size
and terrestrial size planets in and near the HZ of solar-like stars. It
was competitively selected as Discovery Mission #10 and launched on
March 6, 2009. Since completion of commissioning, it has continuously
observed over 145,000 main sequence stars. The photometric precision
reaches 20 ppm for 12th magnitude stars on the least
noisy detectors in 6.5 hours. During the first month of operation,
the photometer detected transit-like signatures from over 100
stars. Careful examination of these events shows many of them to
be false-positives such as background eclipsing binaries. However
ground-based follow up observations confirm the discovery of exoplanets
with sizes ranging from 0.6 Rj to1.5Rj and orbital periods ranging
from 3 to 9 days. Observations at Keck, Hobby-Eberly, Harlan-Smith,
WIYN, MMT, Tillighast, Shane, and Nordic Optic telescopes are vetting
many of the candidates and measuring their masses. Discovery of the
HAT-P7b occultation will be used to derive atmospheric properties
and demonstrates the precision necessary to detect Earth-size
planets. Asteroseismic analyses of several stars show the presence
of p-mode oscillations that can be used to determine stellar size
and age. This effort is being organized by the Kepler Asteroseismic
Science Consortium at Aarhus University in Denmark. Stellar parallaxes
are determined from the centroid motion of the stellar images and will
be combined with photometric measurements to get the sizes of stars
too dim for asteroseismic measurement. Four open clusters are being
observed to determine rotation rates with stellar age and spectral
type. Many types of stellar variability are observed with unprecedented
precision and over long continuous time periods. Examples of many of
these discoveries are presented. Funding by the Exoplanet Exploration
Program of the NASA Astrophysics Division is gratefully acknowledged.

---------------------------------------------------------
Title: The Design and On-Orbit Performance of the Kepler Mission
Authors: Koch, David G.; Borucki, W. J.; Batalha, N.; Brown, T.;
Caldwell, D. A.; Dunham, E.; Gautier, T. N.; Geary, J. J.; Gilliland,
R.; Jenkins, J.; Latham, D.; Basri, G.; Cochran, W.; DeVore, E.; Gould,
A.; Kondo, Y.; Lissauer, J.; Marcy, G.; Sasselov, D.; Kepler Team
2010AAS...21530501K Altcode: 2010BAAS...42..302K
The Kepler mission was designed and built to detect and determine the
frequency of Earth-size exoplanets orbiting in the habitable zone of
solar-like stars. Having very-narrow well-defined scientific objectives,
rather than being a general purpose facility, the design was optimized
solely to meet these objectives. The basis for many of the design
features are described, such as selection of a single star field
to view for the entire mission. The Discovery program and scientific
requirements that drove the design concept are described. Now operating
in solar orbit, the photometric performance of the Kepler mission is
presented, to demonstrate that the capability of the Kepler mission to
meet its scientific goals is right on the mark. Kepler was competitively
selected as the 10th mission of the Discovery Program. Funding for
this mission is provided by NASA's Science Mission Directorate.

---------------------------------------------------------
Title: Kepler Results for Previously Known Planets: the HAT-P-11
Planet System
Authors: Sasselov, Dimitar D.; Basri, G.; Marcy, G.; Latham, D.;
Bakos, G.; Kepler Team
2010AAS...21531707S Altcode: 2010BAAS...42..319S
The transiting Neptune-mass extrasolar planet HAT-P-11b in the Kepler
field was discovered by the ground-based HAT survey (Bakos et al. 2009),
with additional evidence for a possible massive second planet. The host
star shows activity, rotational modulation, and possibly an activity
cycle, but the ground-based photometry is inadequate to confirm and
characterize them. This hinders better understanding of the planetary
system. The Kepler photometric light curve obtained over a period of
45 days is used to measure the rotational modulation and the effect of
spots on the fit to the transits. Prospects for improving the planetary
parameters and measuring the secondary eclipse are discussed. Kepler
was selected as the 10th mission of the Discovery Program. Funding
for this mission is provided by NASA, Science Mission Directorate.

---------------------------------------------------------
Title: Doppler Follow-up of Kepler Planets
Authors: Marcy, Geoffrey W.; Borucki, W. J.; Basri, G.; Walkowicz,
L.; Latham, D. W.; Buchave, L.; Cochran, W.; Endl, M.; Gautier,
T. N.; Batalha, N.; Koch, D.; Johnson, J.; Fischer, D. A.; Howard,
A.; Isaacson, H.; Kepler Team
2010AAS...21531703M Altcode: 2010BAAS...42..318M
The Kepler Mission consists of a 1-meter Schmidt telescope in an
Earth-trailing orbit designed to detect transiting planets in a field of
100 square degrees in the Cygnus-Lyra region, with an input Catalog of
over 100,000 stars of V magnitude mostly 12 to 15. Doppler measurements
are useful for verifying the planets and measuring their masses and
orbits including eccentricity. The Kepler follow-up team is using the
Keck telescope and HIRES spectrometer to make Doppler measurements
with a precision of 3 m/s, a challenging goal for 13th mag stars. Novel
Doppler techniques are being developed. The Doppler observations have
helped confirm the discovery of exoplanets with sizes ranging from 0.6
Rj to1.5Rj with orbital periods of 3 to 9 days. Kepler was selected as
the 10th mission of the Discovery Program. Funding for this mission
is provided by NASA, Science Mission Directorate. Access to the Keck
telescope was provided by NASA and by the University of California.

---------------------------------------------------------
Title: Simultaneous Multi-Wavelength Observations of Magnetic Activity
in Ultracool Dwarfs. III. X-ray, Radio, and Hα Activity Trends in
M and L dwarfs
Authors: Berger, E.; Basri, G.; Fleming, T. A.; Giampapa, M. S.;
Gizis, J. E.; Liebert, J.; Martín, E.; Phan-Bao, N.; Rutledge, R. E.
2010ApJ...709..332B Altcode: 2009arXiv0909.4783B
As part of our on-going investigation into the magnetic field
properties of ultracool dwarfs, we present simultaneous radio, X-ray,
and Hα observations of three M9.5-L2.5 dwarfs (BRI 0021-0214, LSR
060230.4+391059, and 2MASS J052338.2-140302). We do not detect X-ray
or radio emission from any of the three sources, despite previous
detections of radio emission from BRI 0021 and 2M0523-14. Steady
and variable Hα emission are detected from 2M0523-14 and BRI
0021, respectively, while no Hα emission is detected from LSR
0602+39. Overall, our survey of nine M8-L5 dwarfs doubles the number
of ultracool dwarfs observed in X-rays, and triples the number of
L dwarfs, providing in addition the deepest limits to date, log(L
X/L bol) lsim -5. With this larger sample we find
the first clear evidence for a substantial reduction in X-ray activity,
by about two orders of magnitude, from mid-M to mid-L dwarfs. We
find that the decline in Hα roughly follows L Hα/L
bol vprop 10-0.4×(SP-6) for SP &gt;= 6, where SP
= 0 for spectral type M0. In the radio band, however, the luminosity
remains relatively unchanged from M0 to L4, leading to a substantial
increase in L rad/L bol. Our survey also
provides the first comprehensive set of simultaneous radio/X-ray/Hα
observations of ultracool dwarfs, and reveals a clear breakdown of the
radio/X-ray correlation beyond spectral type M7, evolving smoothly
from L ν,rad/L X ≈ 10-15.5 to
~10-11.5 Hz-1 over the narrow spectral-type range
M7-M9. This breakdown reflects the substantial reduction in X-ray
activity beyond M7, but its physical origin remains unclear since,
as evidenced by the uniform radio emission, there is no drop in the
field dissipation and particle acceleration efficiency. Based on the
results of our survey, we conclude that a further investigation of
magnetic activity in ultracool dwarfs will benefit from a two-pronged
approach: multi-rotation observations of nearby known active sources
and a snapshot survey of a large sample within ~50 pc to uncover rare
flaring objects.

---------------------------------------------------------
Title: A Volume-Limited Sample of 63 M7-M9.5 Dwarfs. I. Space Motion,
Kinematic Age, and Lithium
Authors: Reiners, A.; Basri, G.
2009ApJ...705.1416R Altcode: 2009arXiv0909.4647R
In a volume-limited sample of 63 ultracool dwarfs of spectral type
M7-M9.5, we have obtained high-resolution spectroscopy with UVES at the
Very Large Telescope and HIRES at Keck Observatory. In this first paper
we introduce our volume-complete sample from DENIS and 2MASS targets,
and we derive radial velocities and space motion. Kinematics of our
sample are consistent with the stars being predominantly members of
the young disk. The kinematic age of the sample is 3.1 Gyr. We find
that six of our targets show strong Li lines implying that they are
brown dwarfs younger than several hundred million years. Five of the
young brown dwarfs were unrecognized before. Comparing the fraction of
Li detections to later spectral types, we see a hint of an unexpected
local maximum of this fraction at spectral type M9. It is not yet
clear whether this maximum is due to insufficient statistics, or to
a combination of physical effects including spectral appearance of
young brown dwarfs, Li line formation, and the star formation rate at
low masses.

---------------------------------------------------------
Title: Magnetism and Rotation of Cool Dwarfs
Authors: Basri, Gibor
2009koa..prop...90B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Kepler’s Optical Phase Curve of the Exoplanet HAT-P-7b
Authors: Borucki, W. J.; Koch, D.; Jenkins, J.; Sasselov, D.;
Gilliland, R.; Batalha, N.; Latham, D. W.; Caldwell, D.; Basri, G.;
Brown, T.; Christensen-Dalsgaard, J.; Cochran, W. D.; DeVore, E.;
Dunham, E.; Dupree, A. K.; Gautier, T.; Geary, J.; Gould, A.; Howell,
S.; Kjeldsen, H.; Lissauer, J.; Marcy, G.; Meibom, S.; Morrison, D.;
Tarter, J.
2009Sci...325..709B Altcode:
Ten days of photometric data were obtained during the commissioning
phase of the Kepler mission, including data for the previously known
giant transiting exoplanet HAT-P-7b. The data for HAT-P-7b show a
smooth rise and fall of light from the planet as it orbits its star,
punctuated by a drop of 130 ± 11 parts per million in flux when the
planet passes behind its star. We interpret this as the phase variation
of the dayside thermal emission plus reflected light from the planet
as it orbits its star and is occulted. The depth of the occultation
is similar in importance to the detection of a transiting Earth-size
planet for which the mission was designed.

---------------------------------------------------------
Title: Surprisingly Weak Magnetism on Young Accreting Brown Dwarfs
Authors: Reiners, A.; Basri, G.; Christensen, U. R.
2009ApJ...697..373R Altcode: 2009arXiv0903.0857R
We have measured the surface magnetic flux on four accreting young
brown dwarfs and one nonaccreting young very low mass (VLM) star
utilizing high-resolution spectra of absorption lines of the FeH
molecule. A magnetic field of 1-2 kG had been proposed for one of
the brown dwarfs, Two Micron All Sky Survey (2MASS) J1207334-393254,
because of its similarities to higher mass T Tauri stars as manifested
in accretion and the presence of a jet. We do not find clear evidence
for a kilogauss field in any of our young brown dwarfs but do find a 2
kG field on the young VLM star. Our 3σ upper limit for the magnetic
flux in 2MASS J1207334-393254 just reaches 1 kG. We estimate the
magnetic field required for accretion in young brown dwarfs given the
observed rotations, and find that fields of only a few hundred gauss
are sufficient for magnetospheric accretion. This predicted value is
less than our observed upper limit. We conclude that magnetic fields
in young brown dwarfs are a factor of 5 or more lower than in young
stars of about one solar mass, and in older stars with spectral types
similar to our young brown dwarfs. It is interesting that, during the
first few million years, the fields scale down with mass in line with
what is needed for magnetospheric accretion, yet no such scaling is
observed at later ages within the same effective temperature range. This
scaling is opposite to the trend in rotation, with shorter rotation
periods for very young accreting brown dwarfs compared with accreting
solar-mass objects (and very low Rossby numbers in all cases). We
speculate that in young objects a deeper intrinsic connection may exist
between magnetospheric accretion and magnetic field strength, or that
magnetic field generation in brown dwarfs may be less efficient than
in stars. Neither of these currently has an easy physical explanation.

---------------------------------------------------------
Title: Periodic Radio and Hα Emission from the L Dwarf Binary 2MASSW
J0746425+200032: Exploring the Magnetic Field Topology and Radius
Of An L Dwarf
Authors: Berger, E.; Rutledge, R. E.; Phan-Bao, N.; Basri, G.;
Giampapa, M. S.; Gizis, J. E.; Liebert, J.; Martín, E.; Fleming, T. A.
2009ApJ...695..310B Altcode: 2008arXiv0809.0001B
We present an 8.5 hr simultaneous radio, X-ray, UV, and optical
observation of the L dwarf binary 2MASSW J0746425+200032. We detect
strong radio emission, dominated by short-duration periodic pulses
at 4.86 GHz with P = 124.32 ± 0.11 min. The stability of the pulse
profiles and arrival times demonstrates that they are due to the
rotational modulation of a B ≈ 1.7 kG magnetic field. A quiescent
nonvariable component is also detected, likely due to emission from
a uniform large-scale field. The Hα emission exhibits identical
periodicity, but unlike the radio pulses it varies sinusoidally
and is offset by exactly 1/4 of a phase. The sinusoidal variations
require chromospheric emission from a large-scale field structure,
with the radio pulses likely emanating from the magnetic poles. While
both light curves can be explained by a rotating misaligned magnetic
field, the 1/4 phase lag rules out a symmetric dipole topology since it
would result in a phase lag of 1/2 (poloidal field) or zero (toroidal
field). We therefore conclude that either (1) the field is dominated
by a quadrupole configuration, which can naturally explain the 1/4
phase lag; or (2) the Hα and/or radio emission regions are not
trivially aligned with the field. Regardless of the field topology,
we use the measured period along with the known rotation velocity (v
sin i ≈ 27 km s-1), and the binary orbital inclination
(i ≈ 142°), to derive a radius for the primary star of 0.078 ±
0.010 R sun. This is the first measurement of the radius of
an L dwarf, and along with a mass of 0.085 ± 0.010 M sun
it provides a constraint on the mass-radius relation below 0.1 M
sun. We find that the radius is about 30% smaller than
expected from theoretical models, even for an age of a few Gyr. The
origin of this discrepancy is either a breakdown of the models at the
bottom of the main sequence, or a significant misalignment between
the rotational and orbital axes.

---------------------------------------------------------
Title: A First Look at Rotation in Inactive Late-Type M Dwarfs
Authors: West, Andrew A.; Basri, Gibor
2009ApJ...693.1283W Altcode: 2008arXiv0812.1220W
We have examined the relationship between rotation and activity in
14 late-type (M6-M7) M dwarfs, using high-resolution spectra taken at
the W. M. Keck Observatory and flux-calibrated spectra from the Sloan
Digital Sky Survey. Most were selected to be inactive at a spectral type
where strong Hα emission is quite common. We used the cross-correlation
technique to quantify the rotational broadening; six of the stars in our
sample have v sin i &gt;= 3.5 km s-1. Our most significant
and perplexing result is that three of these stars do not exhibit
Hα emission, despite rotating at velocities where previous work has
observed strong levels of magnetic field and stellar activity. Our
results suggest that rotation and activity in late-type M dwarfs may not
always be linked, and open several additional possibilities, including
a rotationally dependent activity threshold, or a possible dependence
on stellar parameters of the Rossby number at which magnetic/activity
"saturation" takes place in fully convective stars.

---------------------------------------------------------
Title: On the magnetic topology of partially and fully convective
stars
Authors: Reiners, A.; Basri, G.
2009A&A...496..787R Altcode: 2009arXiv0901.1659R
We compare the amount of magnetic flux measured in Stokes V and
Stokes I in a sample of early- and mid-M stars around the boundary
to full convection (~M 3.5). Early-M stars possess a radiative core,
mid-M stars are fully convective. While Stokes V is sensitive to
the net polarity of magnetic flux arising mainly from large-scale
configurations, Stokes I measurements can see the total mean flux. We
find that in early-M dwarfs, only ~6% of the total magnetic flux is
detected in Stokes V. This ratio is more than twice as large, ~14%,
in fully convective mid-M dwarfs. The bulk of the magnetic flux on
M-dwarfs is not seen in Stokes V. This is presumably because magnetic
flux is mainly stored in small scale components. There is also more to
learn about the effect of the weak-field approximation on the accuracy
of strong field detections. In our limited sample, we see evidence for
a change in magnetic topology at the boundary to full convection. Fully
convective stars store a 2-3 times higher fraction of their flux in
fields visible to Stokes V. We estimate the total magnetic energy
detected in Stokes I and compare it to results from Stokes V. We find
that in early-M dwarfs only ~0.5% of the total magnetic energy is
detected in Stokes V while this fraction is ~2.5% in mid-M dwarfs.

---------------------------------------------------------
Title: Rotation and Activity in Late-type M Dwarfs
Authors: West, Andrew A.; Basri, Gibor
2009AIPC.1094..700W Altcode: 2009csss...15..700W; 2008arXiv0810.0061W
We have examined the relationship between rotation and activity in 14
late-type (M6-M7) M dwarfs, using high resolution spectra taken at the
Keck Observatory and flux-calibrated spectra from the Sloan Digital
Sky Survey. Most are inactive at a spectral type where Hα emission
has previously seen to be very common. We used the cross-correlation
technique to quantify the rotational broadening; six of the stars
in our sample have v sin i&gt;=3.5 kms-1. Three of these
stars do not exhibit Hα emission, despite rotating at velocities
where previous work has observed strong levels of magnetic field and
stellar activity. Our results suggest that rotation and activity in
late-type M dwarfs may not always be linked, and open several addtional
possibilities including a rotation dependant activity threshold,
or a Maunder-minimum phenomenon in fully convective stars.

---------------------------------------------------------
Title: Activity and rotation of low mass stars in young open clusters
Authors: Seifahrt, Andreas; Reiners, Ansgar; Scholz, Aleks; Basri,
Gibor
2009AIPC.1094..373S Altcode: 2009csss...15..373S; 2008arXiv0811.2485S
We present first results from a multi-object spectroscopy campaign
in IC2602, the Hyades, the Pleiades, and the Coma cluster using
VLT/FLAMES. We analysed the data for radial velocity, rotational
velocity (v sin i), and Hα-activity. Here, we highlight three
aspects of this study in the context of rotational braking and the
rotation-activity relationship among low mass stars. Finally we discuss
the cluster membership of sources in IC2602.

---------------------------------------------------------
Title: An Ultraviolet Spectroscopic Atlas of M Dwarfs
Authors: Basri, Gibor
2009koa..prop..188B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Magnetism and Rotation of Cool Dwarfs
Authors: Basri, Gibor
2009koa..prop...60B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Evidence for Magnetic Flux Saturation in Rapidly Rotating
M Stars
Authors: Reiners, A.; Basri, G.; Browning, M.
2009ApJ...692..538R Altcode: 2008arXiv0810.5139R
We present magnetic flux measurements in seven rapidly rotating
M dwarfs. Our sample stars have X-ray and Hα emission indicative
of saturated emission, i.e., emission at a high level, independent
of rotation rate. Our measurements are made using near-infrared FeH
molecular spectra observed with the High Resolution Echelle Spectrometer
at Keck. Because of their large convective overturn times, the rotation
velocity of M stars with small Rossby numbers is relatively slow and
does not hamper the measurement of Zeeman splitting. The Rossby numbers
of our sample stars are as small as 0.01. All our sample stars exhibit
magnetic flux of kG strength. We find that the magnetic flux saturates
in the same regime as saturation of coronal and chromospheric emission,
at a critical Rossby number of around 0.1. The filling factors of
both field and emission are near unity by then. We conclude that the
strength of surface magnetic fields remains independent of rotation
rate below that; making the Rossby number yet smaller by a factor
of 10 has little effect. These saturated M-star dynamos generate an
integrated magnetic flux of roughly 3 kG, with a scatter of about 1
kG. The relation between emission and flux also has substantial scatter.

---------------------------------------------------------
Title: Saturation of Magnetic Flux Generation at low Rossby Numbers:
The M Stars
Authors: Reiners, Ansgar; Basri, Gibor; Browning, Matthew
2009AIPC.1094..728R Altcode: 2009csss...15..728R
We present magnetic flux measurements in a sample of M dwarfs including
rapid rotators. In this work, we add seven stars with high X-ray
and H-alpha emission. Our measurements are made using near-infrared
FeH molecular spectra observed with HIRES at Keck. Because of their
large convective overturn times, the rotation velocity of M stars
with small Rossby numbers is relatively slow and does not hamper the
measurement of Zeeman splitting. The Rossby numbers of our sample
stars are as small as 0.01. We find that magnetic flux saturates in
the same regime as saturation of coronal and chromospheric emission,
at a critical Rossby number of around 0.1. The filling factors of
both field and emission are near unity by then. We conclude that the
strength of surface magnetic fields remains independent of rotation
rate below that; making the Rossby number yet smaller by a factor
often has little effect. These saturated M-star dynamos generate an
integrated magnetic flux of roughly 3 kG, with a scatter of about 1
kG. The relation between emission and flux also has substantial scatter.

---------------------------------------------------------
Title: Magnetic Activity in the Fully Convective Domain
Authors: Basri, Gibor
2009AIPC.1094..206B Altcode: 2009csss...15..206B
A key ingredient of solar-type dynamo action is the interface between
the convective and radiative zones, so there has been considerable
interest in the workings of dynamos in fully convective objects (lacking
radiative zones). These constitute by far the majority of objects with
dynamos. In the solar-type case, rotation period and convective overturn
time (whose ratio yields the Rossby number) have been implicated in the
production levels of “activity.” This is measured through coronal or
chromospheric emission, or by direct field determinations. Activity
can lead to magnetic braking, so the angular momentum history of the
object is also connected to it. With the advent of large telescopes,
most of the techniques applied to solar-type stars (or good substitutes)
have now been applied to low-mass stars and brown dwarfs. We measure
atmospheric heating produced by magnetic dissipation primarily through
Hα emission, and directly measure magnetic fields in M stars through
a molecular Zeeman diagnostic (L dwarfs provide fields through radio
flares). Rotation is measured through Doppler broadening, but further
progress will require photometric periods. I summarize this work, which
has led to a number of interesting conclusions: 1) magnetic fields
are produced down to very low masses, with magnetic fields remaining
strong and large-scale at least through M dwarfs (and likely L dwarfs)
2) rotation, convection, and activity are still connected in M dwarfs,
but not in L dwarfs (where heating and fields are disconnected due to
atmospheric neutrality) 3) saturation of both heating and total magnetic
flux occurs at similar a Rossby number whether fully convective or
not; 4) magnetic braking (implying coronae) is present in M stars,
but drops with effective temperature (mass), and dies out (braking
times become very long) in L dwarfs; 5) variable magnetic activity
extends well into L dwarfs, though at decreasing levels; and 6) there
are some oddities which still require explanation.

---------------------------------------------------------
Title: Understanding Activity in Low Mass Stars
Authors: Browning, Matthew K.; Walkowicz, Lucianne M.; West, Andrew
A.; Basri, Gibor; Browning, Matthew K.; Kowalski, Adam F.; Hilton,
Eric; Bouchanski, John J.
2009astro2010S..30B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Dynamos and magnetic fields of the Sun and other cool stars,
and their role in the formation and evolution of stars and in the
habitability of planets
Authors: Schrijver, Karel; Carpenter, Ken; Karovska, Margarita; Ayres,
Tom; Basri, Gibor; Brown, Benjamin; Christensen-Dalsgaard, Joergen;
Dupree, Andrea; Guinan, Ed; Jardine, Moira; Miesch, Mark; Pevtsov,
Alexei; Rempel, Matthias; Scherrer, Phil; Solanki, Sami; Strassmeier,
Klaus; Walter, Fred
2009astro2010S.262S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The moderate magnetic field of the flare star Proxima Centauri
Authors: Reiners, A.; Basri, G.
2008A&A...489L..45R Altcode:
We report moderate magnetic flux of 450 G &lt; Bf &lt; 750 G (3σ) on
the nearby M 5.5 flare star Proxima Centauri. A high resolution UVES
spectrum was used to measure magnetic flux from Zeeman broadening in
absorption lines of molecular FeH around 1 μm. The magnetic flux we
find is relatively weak compared with classical strong flare stars,
but so are Proxima's flaring rates and actual emission levels. We
compare what is known about the rotation rate, Rossby number, and
activity levels in this star to relations between these quantities that
are being developed more generally for M dwarfs. We conclude that the
magnetic flux is higher than the best estimates of the Rossby number
from period measurements. On the other hand, the activity levels of
Proxima Centauri are at the high end of what could be expected based
on the measured field, but not so high as to exceed the natural scatter
in these relations (other stars lie along this high envelope as well).

---------------------------------------------------------
Title: Chromospheric Activity, Rotation, and Rotational Braking in
M and L Dwarfs
Authors: Reiners, A.; Basri, G.
2008ApJ...684.1390R Altcode: 2008arXiv0805.1059R
We present results from a high-resolution spectroscopic survey of 45 L
dwarfs, which includes both very low mass stars and brown dwarfs. Our
spectra allow us to derive a significant number of new rotational
velocities, and discover a slowly rotating (in projected velocity) L
dwarf that allows more accurate measurement of spectroscopic rotations
for these objects. We measure chromospheric activity (and often its
variability) through the Hα emission line. Our primary new result is
good evidence that magnetic braking dominates the angular momentum
evolution of even brown dwarfs, although spindown times appear to
increase as mass decreases. We confirm that activity decreases as
effective temperature decreases, although a larger fraction of L dwarfs
are active than has previously been reported. Essentially all active
objects are also variable. We confirm the lack of a rotation-activity
connection for L dwarfs. We find a minimum limit for rotational
velocities that increases with later spectral types, rising from
near zero in older mid-M stars to more than 20 km s-1 for
mid-L objects. There is strong evidence that all L dwarfs are rapid
rotators. We derive a braking law that can depend on either temperature
or mass which can explain all the rotational results and provides an
age dependence for the angular momentum evolution. It is clear that
angular momentum loss mechanisms in smaller and cooler objects become
more inefficient, starting at the fully convective boundary.

---------------------------------------------------------
Title: The moderate magnetic field on the flare star Proxima Centauri
Authors: Reiners, Ansgar; Basri, Gibor
2008arXiv0808.2986R Altcode:
We report moderate magnetic flux of 450G &lt; Bf &lt; 750G (3sigma)
on the nearby M5.5 flare star Proxima Centauri. A high resolution UVES
spectrum was used to measure magnetic flux from Zeeman broadening in
absorption lines of molecular FeH around 1mu. The magnetic flux we find
is relatively weak compared with classical strong flare stars, but so
are Proxima's flaring rates and actual emission levels. We compare
what is known about the rotation rate, Rossby number, and activity
levels in this star to relations between these quantities that have
been recently being developed more generally for M dwarfs. We conclude
that the magnetic flux is higher than the best estimates of the Rossby
number from period measurements. On the other hand, the activity levels
on Proxima Centauri are at the high end of what could be expected based
on the measured field, but not so high as to exceed the natural scatter
in these relations (other stars lie along this high envelope as well).

---------------------------------------------------------
Title: Structural and compositional properties of brown dwarf disks:
the case of 2MASS J04442713+2512164
Authors: Bouy, H.; Huélamo, N.; Pinte, C.; Olofsson, J.; Barrado
Y Navascués, D.; Martín, E. L.; Pantin, E.; Monin, J. -L.; Basri,
G.; Augereau, J. -C.; Ménard, F.; Duvert, G.; Duchêne, G.; Marchis,
F.; Bayo, A.; Bottinelli, S.; Lefort, B.; Guieu, S.
2008A&A...486..877B Altcode: 2008arXiv0803.2051B
Aims: To improve our understanding of substellar formation, we
have performed a compositional and structural study of a brown
dwarf disk. Methods: We present the results of photometric,
spectroscopic, and imaging observations of 2MASS J04442713+2512164,
a young brown dwarf (M 7.25) member of the Taurus association. Our
dataset, combined with results from the literature, provides a complete
coverage of the spectral energy distribution from the optical range
to the millimeter, including the first photometric measurement of
a brown dwarf disk at 3.7 mm, and allows us to perform a detailed
analysis of the disk properties. Results: The target was known
to have a disk. High-resolution optical spectroscopy shows that it
is accreting intensely, and powers both a jet and an outflow. The
disk structure is similar to what is observed for more massive TTauri
stars. Spectral decomposition models of Spitzer/IRS spectra suggest
that the mid-infrared emission from the optically thin disk layers is
dominated by grains with intermediate sizes (1.5 μm). Crystalline
silicates are significantly more abundant in the outer part and/or
deeper layers of the disk, implying very efficient mixing and/or
additional annealing processes. Submillimeter and millimeter data
indicate that most of the disk mass is in large grains (&gt;1 mm).

---------------------------------------------------------
Title: Magnetism and Rotation of Cool Dwarfs
Authors: Basri, Gibor
2008koa..prop..110B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Kepler Mission: Design, expected science results,
opportunities to participate
Authors: Borucki, W. J.; Koch, D.; Basri, G.; Brown, T.; Caldwell,
D.; Devore, E.; Dunham, E.; Gautier, T.; Geary, J.; Gilliland, R.;
Gould, A.; Howell, S.; Jenkins, J.; Latham, D.
2008depn.conf...36B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Finding Earth-size planets in the habitable zone: the Kepler
Mission
Authors: Borucki, William; Koch, David; Basri, Gibor; Batalha, Natalie;
Brown, Timothy; Caldwell, Douglas; Christensen-Dalsgaard, Jørgen;
Cochran, William; Dunham, Edward; Gautier, Thomas N.; Geary, John;
Gilliland, Ronald; Jenkins, Jon; Kondo, Yoji; Latham, David; Lissauer,
Jack J.; Monet, David
2008IAUS..249...17B Altcode: 2007IAUS..249...17B
The Kepler Mission is a space-based mission whose primary goal is
to detect Earth-size and smaller planets in the habitable zone of
solar-like stars. The mission will monitor more than 100,000 stars
for transits with a differential photometric precision of 20 ppm
at V=12 for a 6.5 hour transit. It will also provide asteroseismic
results on several thousand dwarf stars. It is specifically designed
to continuously observe a single field of view of greater than 100
square degrees for 3.5 or more years. This overview describes the
mission design, its goals and capabilities, the measured performance
for those photometer components that have now been tested, the Kepler
Input Catalog, an overview of the analysis pipeline, the plans for the
Follow-up Observing Program to validate the detections and characterize
the parent stars, and finally, the plans for the Guest Observer and
Astrophysical Data Program.

---------------------------------------------------------
Title: Two-Micron All-Sky Survey J01542930+0053266: a new eclipsing
M dwarf binary system
Authors: Becker, A. C.; Agol, E.; Silvestri, N. M.; Bochanski, J. J.;
Laws, C.; West, A. A.; Basri, G.; Belokurov, V.; Bramich, D. M.;
Carpenter, J. M.; Challis, P.; Covey, K. R.; Cutri, R. M.; Evans,
N. W.; Fellhauer, M.; Garg, A.; Gilmore, G.; Hewett, P.; Plavchan,
P.; Schneider, D. P.; Slesnick, C. L.; Vidrih, S.; Walkowicz, L. M.;
Zucker, D. B.
2008MNRAS.386..416B Altcode: 2008MNRAS.tmp..453B; 2008arXiv0801.4474B
We report on Two-Micron All-Sky Survey (2MASS) J01542930+0053266,
a faint eclipsing system composed of two M dwarfs. The variability of
this system was originally discovered during a pilot study of the 2MASS
Calibration Point Source Working Data base. Additional photometry from
the Sloan Digital Sky Survey yields an eight-passband light curve
from which we derive an orbital period of 2.6390157 +/- 0.0000016
d. Spectroscopic followup confirms our photometric classification of the
system, which is likely composed of M0 and M1 dwarfs. Radial velocity
measurements allow us to derive the masses (M1 = 0.66 +/-
0.03Msolar M2 = 0.62 +/- 0.03Msolar)
and radii (R1 = 0.64 +/- 0.08Rsolar R2
= 0.61 +/- 0.09Rsolar) of the components, which are
consistent with empirical mass-radius relationships for low-mass stars
in binary systems. We perform Monte Carlo simulations of the light
curves which allow us to uncover complicated degeneracies between
the system parameters. Both stars show evidence of Hα emission,
something not common in early-type M dwarfs. This suggests that
binarity may influence the magnetic activity properties of low-mass
stars; activity in the binary may persist long after the dynamos in
their isolated counterparts have decayed, yielding a new potential
foreground of flaring activity for next generation variability surveys.

---------------------------------------------------------
Title: The Kepler Mission: Terrestrial Extrasolar Planets and
Stellar Activity
Authors: Basri, G.; Ramos-Stierle, F.; Soto, K.; Lewis, T.; Reiners,
A.; Borucki, W.; Koch, D.
2008ASPC..384..281B Altcode: 2008csss...14..281B
Kepler is a NASA mission designed to determine the frequency and
distribution of Earth-sized planets within 1 AU of F-M main sequence
stars. This is done by searching for planetary transits. The mission
will return up to 150,000 broad-band light curves with unprecedented
precision (20 micromag) and 30 minute resolution continuously for
several years. Along with a program to determine precise stellar
parameters, the size and orbital distance of the planets can be
estimated, as well as the relations between planets and the stars they
orbit. Hundreds of terrestrial planets should be discovered if they are
common. A null result would strongly imply that terrestrial planets are
rare. The Kepler dataset is also a treasure-trove of information
on stellar activity and rotation. We have begun a research program to
understand and simulate stellar microvariability. We first study the
Sun as a microvariable star (cf. Soto et al., this conference). Having
derived laws which connect continuum variability with magnetic
configurations, we explore photometry of simulated stars. This will
lead to improved methods of finding rotation periods, understanding
the change due to inclination (can we actually derive inclination?),
mapping of magnetic distributions, and sizes and time-scales for active
regions and starspots. Guest Investigators can propose targets that
are not part of the exoplanet search during the mission. Kepler can
greatly aid our understanding of the behavior of stellar activity as
a function of stellar mass and age.

---------------------------------------------------------
Title: Simultaneous Multiwavelength Observations of Magnetic Activity
in Ultracool Dwarfs. II. Mixed Trends in VB 10 and LSR 1835+32 and
the Possible Role of Rotation
Authors: Berger, E.; Basri, G.; Gizis, J. E.; Giampapa, M. S.;
Rutledge, R. E.; Liebert, J.; Martín, E.; Fleming, T. A.; Johns-Krull,
C. M.; Phan-Bao, N.; Sherry, W. H.
2008ApJ...676.1307B Altcode: 2007arXiv0710.3383B
As part of our ongoing investigation of magnetic activity in
ultracool dwarfs we present simultaneous radio, X-ray, UV, and
optical observations of LSR1835+32 (M8.5), and simultaneous X-ray
and UV observations of VB10 (M8), both with a duration of about 9
hr. LSR1835+32 exhibits persistent radio emission, and Hα variability
on timescales of 0.5-2 hr. The detected UV flux is consistent with
photospheric emission, and no X-ray emission is detected to a deep
limit of LX/Lbollesssim 10-5.7. The
Hα and radio emission are temporally uncorrelated, and the ratio of
radio to X-ray luminosity exceeds the correlation seen in F-M6 stars
by &gt;2 × 104. The lack of radio variability during
four rotations of LSR1835+32 requires a uniform stellar-scale field
of ~10 G, and indicates that the Hα variability is dominated by much
smaller scales, &lt;10% of the chromospheric volume. VB10, on the other
hand, shows correlated flaring and quiescent X-ray and UV emission,
similar to the behavior of early M dwarfs. Delayed and densely sampled
optical spectra exhibit a similar range of variability amplitudes and
timescales. Along with our previous observations of the M8.5 dwarf
TVLM513-46546 we conclude that late M dwarfs exhibit a mix of activity
patterns, which points to a transition in the structure and heating
of the outer atmosphere by large-scale magnetic fields. We find that
rotation may play a role in generating the fields as evidenced by a
tentative correlation between radio activity and rotation velocity. The
X-ray emission, however, shows evidence for supersaturation at vsin
i &gt; 25 km s-1, which could be the result of secondary
effects such as inefficient heating or centrifugal stripping of extended
coronal loops. These effects may underlie the severe violation of the
radio/X-ray correlation in ultracool dwarfs.

---------------------------------------------------------
Title: Follow-up observations of binary ultra-cool dwarfs
Authors: Bouy, H.; Martín, E. L.; Brandner, W.; Forveille, T.;
Delfosse, X.; Huélamo, N.; Basri, G.; Girard, J.; Zapatero Osorio,
M. -R.; Stumpf, M.; Ghez, A.; Valdivielso, L.; Marchis, F.; Burgasser,
A. J.; Cruz, K.
2008A&A...481..757B Altcode: 2008arXiv0801.4424B
Context: Astrometric observations of resolved binaries provide estimates
of orbital periods and will eventually lead to measurement of dynamical
masses. Only a few very low mass star and brown dwarf masses have
been measured to date, and the mass-luminosity relation still needs
to be calibrated. Aims: We have monitored 14 very low mass
multiple systems for several years to confirm their multiplicity and,
for those with a short period, derive accurate orbital parameters and
dynamical mass estimates. Methods: We have used high spatial
resolution images obtained at the Paranal, Lick and HST observatories
to obtain astrometric and photometric measurements of the multiple
systems at several epochs. The targets have periods ranging from 5 to
200 years, and spectral types in the range M7.5-T5.5. Results:
All of our 14 multiple systems are confirmed as common proper motion
pairs. One system (2MASSW J0920122+351742) is not resolved in our new
images, probably because the discovery images were taken near maximum
elongation. Six systems have periods short enough to allow dynamical
mass measurements within the next 15 to 20 years. We estimate that only
8% of the ultracool dwarfs in the solar neighborhood are binaries with
separations large enough to be resolved, and yet periods short enough
to derive astrometric orbital fits over a reasonable time frame with
current instrumentation. A survey that doubles the number of ultracool
dwarfs observed with high angular resolution is called for to discover
enough binaries for a first attempt to derive the mass-luminosity
relationship for very low-mass stars and brown dwarfs.

---------------------------------------------------------
Title: Simultaneous Multiwavelength Observations of Magnetic
Activity in Ultracool Dwarfs. I. The Complex Behavior of the M8.5
Dwarf TVLM 513-46546
Authors: Berger, E.; Gizis, J. E.; Giampapa, M. S.; Rutledge, R. E.;
Liebert, J.; Martín, E.; Basri, G.; Fleming, T. A.; Johns-Krull,
C. M.; Phan-Bao, N.; Sherry, W. H.
2008ApJ...673.1080B Altcode: 2007arXiv0708.1511B
We present the first simultaneous radio, X-ray, ultraviolet, and
optical spectroscopic observations of the M8.5 dwarf TVLM 513-46546,
with a duration of 9 hr. These observations are part of a program to
study the origin of magnetic activity in ultracool dwarfs, and its
impact on chromospheric and coronal emission. Here we detect steady
quiescent radio emission superposed with multiple short-duration, highly
polarized flares; there is no evidence for periodic bursts previously
reported for this object, indicating their transient nature. We also
detect soft X-ray emission, with LX/Lbol ≈
10-5.1, the faintest to date for any object later than M5,
and a possible X-ray flare. TVLM 513-46546 continues the trend of severe
violation of the radio/X-ray correlation in ultracool dwarfs, by nearly
4 orders of magnitude. From the optical spectroscopy we find that the
Balmer line luminosity exceeds the X-ray luminosity by a factor of a
few, ruling out chromospheric heating by coronal X-ray emission. More
importantly, we detect sinusoidal Hα and Hβ equivalent width light
curves with a period of 2 hr, matching the rotation period of TVLM
513-46546. This behavior points to a corotating chromospheric hot spot
or an extended magnetic structure, with a covering fraction of about
50%. This feature may be transitory based on the apparent decline in
light-curve peak during the four observed maxima. From the radio data
we infer a large-scale and steady magnetic field of ~102
G. A large-scale field is also required by the sinusoidal Balmer
line emission. The radio flares, on the other hand, are produced in a
component of the field with a strength of ~3 kG and a likely multipolar
configuration. The overall lack of correlation between the various
activity indicators suggests that the short-duration radio flares do
not have a strong influence on the chromosphere and corona, and that
the chromospheric emission is not the result of coronal heating.

---------------------------------------------------------
Title: Magnetism and Rotation of Cool Dwarfs
Authors: Basri, Gibor
2008koa..prop...53B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Dynamo Action in Fully Convective Low-Mass Stars
Authors: Browning, Matthew K.; Basri, Gibor
2007AIPC..948..157B Altcode: 2007arXiv0711.3474B
Recent observations indicate that fully convective stars can effectively
build magnetic fields without the aid of a tachocline of shear, that
those fields can possess large-scale components, and that they may
sense the effects of rotation. Motivated by these puzzles, we present
global three-dimensional simulations of convection and dynamo action
in the interiors of fully convective M-dwarfs of 0.3 solar masses. We
use the Anelastic Spherical Harmonic (ASH) code, adopting a spherical
computational domain that extends from 0.08-0.96 times the overall
stellar radius. We find that such fully convective stars can generate
magnetic fields of several kG strength, roughly in equipartition
with the convective flows. Differential rotation is established in
hydrodynamic progenitor calculations, but essentially eliminated in MHD
simulations because of strong Maxwell stresses exerted by the magnetic
fields. Despite the absence of interior angular velocity contrasts,
the magnetic fields possess strong mean (axisymmetric) components,
which we attribute partly to the very strong influence of rotation
upon the slowly overturning flows.

---------------------------------------------------------
Title: Magnetism and Rotation of Cool Dwarfs
Authors: Basri, Gibor
2007koa..prop...72B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Kepler Mission and Eclipsing Binaries
Authors: Koch, David; Borucki, William; Basri, Gibor; Brown, Timothy;
Caldwell, Douglas; Christensen-Dalsgaard, Jorgen; Cochran, William;
Devore, Edna; Dunham, Edward; Gautier, Thomas N.; Geary, John;
Gilliland, Ronald; Gould, Alan; Jenkins, Jon; Kondo, Yoji; Latham,
David; Lissauer, Jack; Monet, David
2007IAUS..240..236K Altcode: 2006IAUS..240E..21K
The Kepler Mission is a photometric mission with a precision of 14 ppm
( at R= 12) that is designed to continuously observe a single field of
view (FOV) of greater 100 sq deg in the Cygnus-Lyra region for four or
more years. The primary goal of the mission is to monitor &gt;100,000
stars for transits of Earth-size and smaller planets in the habitable
zone of solar-like stars. In the process, many eclipsing binaries
(EB) will also be detected and light curves produced. To enhance and
optimize the mission results, the stellar characteristics for all
the stars in the FOV with R&lt;16 will have been determined prior
to launch. As part of the verification process, stars with transit
candidates will have radial velocity follow-up observations performed to
determine the component masses and thereby separate eclipses caused by
stellar companions from transits caused by planets. The result will be
a rich database on EBs. The community will have access to the archive
for further analysis, such as, for EB modeling of the high-precision
light curves. A guest observer program is also planned to allow for
photometric observations of objects not on the target list but within
the FOV, since only the pixels of interest from those stars monitored
will be transmitted to the ground.

---------------------------------------------------------
Title: Periodic Accretion from a Circumbinary Disk in the Young
Binary UZ Tau E
Authors: Jensen, Eric L. N.; Dhital, Saurav; Stassun, Keivan G.;
Patience, Jenny; Herbst, William; Walter, Frederick M.; Simon, Michal;
Basri, Gibor
2007AJ....134..241J Altcode: 2007arXiv0704.0307J
Close pre-main-sequence binary stars are expected to clear central
holes in their protoplanetary disks, but the extent to which material
can flow from the circumbinary disk across the gap onto the individual
circumstellar disks has been unclear. In binaries with eccentric orbits,
periodic perturbation of the outer disk is predicted to induce mass
flow across the gap, resulting in accretion that varies with the binary
period. This accretion may manifest itself observationally as periodic
changes in luminosity. Here we present a search for such periodic
accretion in the pre-main-sequence spectroscopic binary UZ Tau E. We
present BVRI photometry spanning 3 years; we find that the brightness
of UZ Tau E is clearly periodic, with a best-fit period of 19.16+/-0.04
days. This is consistent with the spectroscopic binary period of 19.13
days, refined here from analysis of new and existing radial velocity
data. The brightness of UZ Tau E shows significant random variability,
but the overall periodic pattern is a broad peak in enhanced brightness,
spanning more than half the binary orbital period. The variability of
the Hα line is not as clearly periodic, but given the sparseness of
the data, some periodic component is not ruled out. The photometric
variations are in good agreement with predictions from simulations
of binaries with orbital parameters similar to those of UZ Tau E,
suggesting that periodic accretion does occur from circumbinary disks,
replenishing the inner circumstellar disks and possibly extending the
timescale over which they might form planets.

---------------------------------------------------------
Title: KEPLER Mission Status
Authors: Borucki, W. J.; Koch, D. G.; Lissauer, J.; Basri, G.;
Brown, T.; Caldwell, D. A.; Jenkins, J. M.; Caldwell, J. J.;
Christensen-Dalsgaard, J.; Cochran, W. D.; Dunham, E. W.; Gautier,
T. N.; Geary, J. C.; Latham, D.; Sasselov, D.; Gilliland, R. L.;
Howell, S.; Monet, D. G.; Batalha, N.
2007ASPC..366..309B Altcode:
Kepler is a Discovery-class mission designed to determine the frequency
of Earth-size and smaller planets in and near the habitable zone
(HZ) of dwarf stars. The instrument consists of a 0.95-m aperture
photometer capable of doing high precision photometry of more than
100,000 late-type main sequence stars to search for patterns of
transits. Multi-band ground-based observation of over 2 million stars
is currently underway to estimate the stellar parameters and to choose
appropriate targets. The association of planet size and occurrence
frequency with stellar mass and metallicity will be investigated. At
the end of the four year mission, several hundred terrestrial planets
(i.e., planets up to twice the diameter of the Earth) should be
discovered with periods between one day and 400 days if such planets
are common. As many as 100 Earth-size planets in the HZ could be
discovered. A null result would imply that terrestrial planets are
rare. The scientific community is invited to participate through the
"Participating Scientist", "Guest Observer' and Data Analysis programs.

---------------------------------------------------------
Title: T Tauri stars: from mystery to magnetospheric accretion
Authors: Basri, Gibor
2007IAUS..243...13B Altcode:
This is a selective historical overview of the progess in understanding
T Tauri spectra. Originally they were understood to be very young, but
the physical conditions (or even geometry) of the material on the star
and in its surroundings were mysterious. The origin and meaning of the
emission lines was largely unknown. Today we have a detailed consensus
of what is happening near and on these newly forming stars. They
are very magnetically active, and the stellar field is strong and
extensive enough to control both the final accretion onto the star and
the launching of outflows which solve the angular momentum problem
during formation. Much of this consensus has emerged from spectral
information, but much remains to be learned. I highlight some of the
seminal breakthroughs that have led to the current picture. There are
very complex and time-variable components to the entire physical system
that constitutes a T Tauri star, and spectral information at various
wavelengths and resolutions is crucial to making further progress.

---------------------------------------------------------
Title: A Reappraisal of The Habitability of Planets around M Dwarf
Stars
Authors: Tarter, Jill C.; Backus, Peter R.; Mancinelli, Rocco L.;
Aurnou, Jonathan M.; Backman, Dana E.; Basri, Gibor S.; Boss, Alan P.;
Clarke, Andrew; Deming, Drake; Doyle, Laurance R.; Feigelson, Eric D.;
Freund, Friedmann; Grinspoon, David H.; Haberle, Robert M.; Hauck,
Steven A., II; Heath, Martin J.; Henry, Todd J.; Hollingsworth, Jeffery
L.; Joshi, Manoj M.; Kilston, Steven; Liu, Michael C.; Meikle, Erik;
Reid, I. Neill; Rothschild, Lynn J.; Scalo, John; Segura, Antigona;
Tang, Carol M.; Tiedje, James M.; Turnbull, Margaret C.; Walkowicz,
Lucianne M.; Weber, Arthur L.; Young, Richard E.
2007AsBio...7...30T Altcode: 2006astro.ph..9799T
Stable, hydrogen-burning, M dwarf stars make up about 75% of all
stars in the Galaxy. They are extremely long-lived, and because
they are much smaller in mass than the Sun (between 0.5 and 0.08
MSun), their temperature and stellar luminosity are low
and peaked in the red. We have re-examined what is known at present
about the potential for a terrestrial planet forming within, or
migrating into, the classic liquid-surface-water habitable zone
close to an M dwarf star. Observations of protoplanetary disks
suggest that planet-building materials are common around M dwarfs,
but N-body simulations differ in their estimations of the likelihood of
potentially habitable, wet planets that reside within their habitable
zones, which are only about one-fifth to 1/50th of the width
of that for a G star. Particularly in light of the claimed detection
of the planets with masses as small as 5.5 and 7.5 MEarth
orbiting M stars, there seems no reason to exclude the possibility of
terrestrial planets. Tidally locked synchronous rotation within the
narrow habitable zone does not necessarily lead to atmospheric collapse,
and active stellar flaring may not be as much of an evolutionarily
disadvantageous factor as has previously been supposed. We conclude
that M dwarf stars may indeed be viable hosts for planets on which the
origin and evolution of life can occur. A number of planetary processes
such as cessation of geothermal activity or thermal and nonthermal
atmospheric loss processes may limit the duration of planetary
habitability to periods far shorter than the extreme lifetime of the
M dwarf star. Nevertheless, it makes sense to include M dwarf stars in
programs that seek to find habitable worlds and evidence of life. This
paper presents the summary conclusions of an interdisciplinary workshop
(http://mstars.seti.org) sponsored by the NASA Astrobiology Institute
and convened at the SETI Institute. Key Words: Planets-Habitability-M
dwarfs-Stars. Astrobiology 7, 30-65. M dwarf star. Observations of
protoplanetary disks suggest that planet-building materials are common
around M dwarfs, but N-body simulations differ in their estimations
of the likelihood of potentially habitable, wet planets that reside
within their habitable zones, which are only about one-fifth to
1/50th of the width of that for a G star. Particularly in
light of the claimed detection of the planets with masses as small
as 5.5 and 7.5 MEarth orbiting M stars, there seems no
reason to exclude the possibility of terrestrial planets. Tidally
locked synchronous rotation within the narrow habitable zone does not
necessarily lead to atmospheric collapse, and active stellar flaring
may not be as much of an evolutionarily disadvantageous factor as has
previously been supposed. We conclude that M dwarf stars may indeed be
viable hosts for planets on which the origin and evolution of life can
occur. A number of planetary processes such as cessation of geothermal
activity or thermal and nonthermal atmospheric loss processes may limit
the duration of planetary habitability to periods far shorter than the
extreme lifetime of the M dwarf star. Nevertheless, it makes sense to
include M dwarf stars in programs that seek to find habitable worlds
and evidence of life. This paper presents the summary conclusions of an
interdisciplinary workshop (http://mstars.seti.org) sponsored by the
NASA Astrobiology Institute and convened at the SETI Institute. Key
Words: Planets-Habitability-M dwarfs-Stars. Astrobiology 7, 30-65.

---------------------------------------------------------
Title: The Physical Properties of Cool Dwarfs
Authors: Basri, Gibor
2007koa..prop...68B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The First Direct Measurements of Surface Magnetic Fields on
Very Low Mass Stars
Authors: Reiners, A.; Basri, G.
2007ApJ...656.1121R Altcode: 2006astro.ph.10365R
We present the first direct magnetic field measurements on M dwarfs
cooler than spectral class M4.5. Utilizing a new method based on the
FeH band near 1 μm, we categorize the integrated surface magnetic flux
as low (well under 1 kG), intermediate (between 1 and about 2.5 kG),
or strong (greater than about 3 kG) for a set of more than 20 stars
ranging from M2 down to M9. Along with the field, we also measure the
rotational broadening (vsini) and Hα emission strength. Our goal is
to advance the understanding of how dynamo field production varies with
stellar parameters for very low mass stars, how the field and emission
activity are related, and whether there is a connection between the
rotation and magnetic flux. We find that fields are produced throughout
the M dwarfs. In the mid-M stars, there is a clear connection between
slow rotation and weak fields. In the late-M stars, rotation is always
measurable, and the strongest fields are associated with with the most
rapid rotators. Interestingly, these very cool rapid rotators appear
to have the largest magnetic flux in the whole sample (greater than in
the classical dMe stars). Hα emission is found to be a good proxy for
magnetic fields, although the relation between the fractional emission
and the magnetic flux varies with effective temperature. The drop-off
in this fractional emission near the bottom of the main sequence is
not accompanied by a drop-off in magnetic flux. It is clear that the
methodology we have developed can be further applied to discover more
about the behavior of magnetic dynamos and activity in cool and fully
convective objects.

---------------------------------------------------------
Title: Reconstruction of irradiance from 2D magnetograms and
modification of the 1/[mμ]-correction paradigm
Authors: Reiners, A.; Basri, G.; Soto, K.; Ramos Stierle, F.; Lewis, T.
2007msfa.conf..193R Altcode:
The key to understanding total Solar Irradiance (SI) variability is
understanding the mechanisms by which continuum contrast is affected
by the distribution of magnetic flux across the surface of the
Sun. The Michelson Doppler Imager (MDI) instrument on the Solar and
Heliospheric Observatory (SOHO) has measured full-disk magnetograms
along with contemporaneous continuum images. These pairs of images
can be used to study the correlation of continuum irradiance changes
with magnetogram signal over the entire disk. To study these effects,
however, we must first correct MDI magnetograms for geometrical effects
near the limb. We derive this correction using the assumption that
the distribution of true magnetic flux density (MFD) in the active
latitudes should exhibit the same average behavior irrespective from
the viewing angle. In a series of 106 magnetograms, we analyze annular
rings at various limb angles, ω, and follow individual active regions
over their full disk passage. We are able to find a simple function
which successfully corrects the magnetograms over the full disk, with
a minimal number of overcorrected points at the extreme limb. It is a
major improvement over the standard 1/[mμ] correction. We then examine
the relationship between continuum images (with limb darkening removed)
and contemporaneous corrected magnetograms over all limb angles. Using
a 2D function, we can predict the continuum contrast at any given disk
position as a function of measured magnetic flux. We demonstrate the
extent to which this procedure reproduces actual solar features.

---------------------------------------------------------
Title: Stellar and Molecular Radii of a Mira Star: First Observations
with the Keck Interferometer Grism
Authors: Eisner, J. A.; Graham, J. R.; Akeson, R. L.; Ligon, E. R.;
Colavita, M. M.; Basri, G.; Summers, K.; Ragland, S.; Booth, A.
2007ApJ...654L..77E Altcode: 2006astro.ph.11312E
Using a new grism at the Keck Interferometer, we obtained spectrally
dispersed (R~230) interferometric measurements of the Mira star R
Vir. These data show that the measured radius of the emission varies
substantially from 2.0 to 2.4 μm. Simple models can reproduce these
wavelength-dependent variations using extended molecular layers, which
absorb stellar radiation and reemit it at longer wavelengths. Because
we observe spectral regions with and without substantial molecular
opacity, we determine the stellar photospheric radius, uncontaminated
by molecular emission. We infer that most of the molecular opacity
arises at approximately twice the radius of the stellar photosphere.

---------------------------------------------------------
Title: The M Dwarf GJ 436 and its Neptune-Mass Planet
Authors: Maness, H. L.; Marcy, G. W.; Ford, E. B.; Hauschildt, P. H.;
Shreve, A. T.; Basri, G. B.; Butler, R. P.; Vogt, S. S.
2007PASP..119...90M Altcode: 2006astro.ph..8260M
We determine stellar parameters for the M dwarf GJ 436, which hosts a
Neptune-mass planet. We employ primarily spectral modeling at low and
high resolution, examining the agreement between model and observed
optical spectra of five comparison stars of type M0-M3. The modeling
of high-resolution optical spectra suffers from uncertainties in TiO
transitions, affecting the predicted strengths of both atomic and
molecular lines in M dwarfs. The determination of Teff,
gravity, and metallicity from optical spectra remains at ~10%. As
molecules provide opacity both in lines and as an effective continuum,
determining molecular transition parameters remains a challenge
facing models such as the PHOENIX series, best verified with high
resolution and spectrophotometric spectra. Our analysis of GJ 436
yields an effective temperature of Teff = 3350 +/- 300
K and a mass of 0.44 Msolar. New Doppler measurements of
GJ 436 with a precision of 3 m s-1 taken during 6 years
improve the Keplerian model of the planet, giving it a minimum mass
Msini=0.0713MJup = 22.6 M⊕, period P =
2.6439 days, and eccentricity e = 0.16 +/- 0.02. The noncircular
orbit contrasts with the tidally circularized orbits of all close-in
exoplanets, implying either ongoing pumping of eccentricity by a more
distant companion, or a higher Q value for this low-mass planet. The
velocities indeed reveal a long-term trend, indicating a possible
distant companion.

---------------------------------------------------------
Title: Continuum Contrast as a function of Magnetic Flux Density
and Disk Position: Results from a full Solar Cycle of SOHO/MDI data
Authors: Soto, K.; Basri, G.; Ramos-Stierle, F.; Lewis, T.; Reiners,
A.; Berger, T.
2006AGUFMSH11A0373S Altcode:
The key to understanding total solar irradiance variability is
to understand the mechanisms by continuum contrast is effected
by the distribution of magnetic flux across the surface of the
Sun. The Michelson Doppler Imager (MDI) instrument on the Solar and
Heliospheric Observatory (SOHO) satellite has measured full-disk
Stokes-V magnetograms along with cotemporal continuum images
throughout Solar Cycle 23. We present the results of an examination
of the relationship between corrected MDI continuum images with their
cotemporal corrected MDI magnetograms. By separating the series of
images into bins of Magnetic Flux Density (MFD) and limb angle,
we perform a non-linear least squares fit to the data to produce
a 3rd-order polynomial function of continuum contrast vs. MFD and
disk position. Using the obtained function we can accurately predict
continuum contrast at any given disk position as a function of MFD
measured in a given magnetogram. The resulting predictions can be used
to make simulated continuum images suitable for bolometric correction
and input into total irradiance models. This research was partially
supported by LWS TR&amp;T Grant NNG05GK46G

---------------------------------------------------------
Title: Sunspot Contrast Measurements from MDI Full-Disk Images:
Variations with Disk Position and Solar Cycle Phase
Authors: Lewis, T.; Soto, K.; Basri, G.; Ramos-Stierle, F.; Reiners,
A.; Berger, T.
2006AGUFMSH11A0374L Altcode:
We report measurements of sunspot umbral and penumbral contrast as
a function of Magnetic Flux Density (MFD), disk position, and time
over Solar Cycle 23 from full-disk magnetogram and continuum images
of the SOHO/MDI instrument. Using a technique of image segmentation
which utilizes region labeling of entire MDI intensity images in
order to segment prospective sunspots and then the application of
radial derivatives from the centers of the spots we successfully
identify the umbral-penumbral interface of large sunspots in the MDI
database. The extracted penumbral and umbral pixels of these images
are binned according to MFD and disk position to study the behavior
of sunspot contrast. We report measurements of sunspot umbral and
penumbral contrast as a function of Magnetic Flux Density (MFD), disk
position, and time over Solar Cycle 23 from full- disk magnetogram
and continuum images of the SOHO/MDI instrument. This research was
partially supported by LWS TR&amp;T Grant NNG05 GK48G.

---------------------------------------------------------
Title: Simulations of Convection and Magnetism in Fully Convective
Stars
Authors: Browning, Matthew K.; Basri, G.
2006AAS...209.8908B Altcode: 2006BAAS...38R1025B
We present three-dimensional simulations of convection and magnetism
within fully convective low-mass stars. Our spherical computational
domain encompasses the bulk of the convective interior of a 0.3 solar
mass M-dwarf, rotating at the solar angular velocity. We use the
Anelastic Spherical Harmonic (ASH) code to examine highly nonlinear
flows that extend over multiple scale heights and admit magnetic dynamo
action. We find that small seed magnetic fields are amplified by many
orders of magnitude and sustained against Ohmic decay. We assess the
strength and morphology of the resulting magnetism, the character
of the convective flows, and the nature of the differential rotation
established within the interior.

---------------------------------------------------------
Title: Correction of MDI Full-Disk Magnetograms for Limb Angle
Effects by the Assumption of Average Magnetic Uniformity
Authors: Ramos-Stierle, F.; Soto, K.; Basri, G.; Lewis, T.; Reiners,
A.; Berger, T.
2006AGUFMSH11A0375R Altcode:
Analysis of magnetic fields on the sun is crucial to understanding
the generation of solar active regions, plage, and the supergranular
network and their contributions to Total Solar Irradiance (TSI)
variation. The Michelson Doppler Imager (MDI) instrument on the Solar
and Heliospheric Observatory (SOHO) satellite has measured full-disk
Stokes-V magnetograms along with cotemporal continuum images throughout
Solar Cycle 23. These pairs of images can be used to study continuum
irradiance changes correlated to magnetogram signal over the entire
disk and over most of Cycle 23. However the MDI magnetogram signal
must be corrected for line-of-sight angle variations. Typically a 1/mu
correction factor (where mu is the cosine of the line-of-sight angle
to the surface normal) is applied across the entire disk. However
near-limb measurements where mu approaches zero are siginificantly
over-corrected by a simple 1/mu factor. We demonstrate a newly
developed geometric correction function for MDI magnetograms based on
the assumption that the distribution of Magnetic Flux Density (MFD)
in the active latitudes should exhibit the same behavior no matter
what angle it is viewed from. We examine a series of 106 magnetograms
in the time period from 01-January-2001 to 30-April-2001. This method
was successful in correcting MDI magnetograms to reasonable MFD in the
limbs, with a minimal number of overcorrected points in the extreme
limb, an improvement upon the typical approach of 1/mu. The resulting
distributions of MFD were more uniform over 50 bins of mu and can be
more successfully used to study continuum irradiance variations as a
function of MFD across the entire disk. This research was partially
supported by LWS TR&amp;T Grant NNG05GK46G.

---------------------------------------------------------
Title: Resolved Hubble space spectroscopy of ultracool binary systems
Authors: Martín, E. L.; Brandner, W.; Bouy, H.; Basri, G.; Davis,
J.; Deshpande, R.; Montgomery, M. M.
2006A&A...456..253M Altcode: 2006physics...5042M
Using the low-resolution mode of the Space Telescope Imaging
Spectrograph (STIS) aboard the Hubble Space Telescope (HST), we obtain
spectra from 20 spatially-resolved, ultracool dwarfs, eighteen of
which belong to nine very low-mass binary systems with known angular
separations in the range 0.37 arcsec-0.098 arcsec. For these dwarfs,
we derive their spectral types to be in the range dM7.5 to dL6 by
either obtaining their PC3 index value or by comparing our STIS spectra
with ground-based spectra of similar spectral resolution from Martín
et al. (1999b). We have searched for Hα emission in each object,
but the emission is clearly detected in only two of them. We find
that the distribution of Hα emission in our sample is statistically
different from that of single field dwarfs, suggesting an intriguing
anti-correlation between chromospheric activity and binarity for
M7-M9.5 dwarfs. We provide strength measuments of the main photospheric
features. We derive calibrations of spectral subclasses versus F814W
and K-band absolute magnitudes for a subset of 10 dwarfs in 5 binaries
that have known trigonometric parallaxes.

---------------------------------------------------------
Title: Kepler Mission: Mission Progress
Authors: Borucki, William J.; Koch, D. G.; Lissauer, J. J.; Basri,
G. S.; Caldwell, D. A.; DeVore, E.; Jenkins, J. M.; Caldwell, J. J.;
Christensen-Dalsgaard, J.; Cochran, W. D.; Dunham, E. W.; Gautier,
T. N.; Geary, J. C.; Latham, D. A.; Sasselov, D.; Gilliland, R. L.;
Gould, A.; Howell, S. B.; Brown, T. M.; Kondo, Y.; Monet, D. G.;
Batalha, N.
2006DPS....38.4501B Altcode: 2006BAAS...38..567B
Kepler is a Discovery-class mission designed to determine the
frequency of Earth-size planets in and near the habitable zone (HZ)
of solar-like stars. The instrument consists of a 0.95 m aperture
photometer designed to obtain high precision photometric measurements
of &gt;100,000 stars to search for patterns of transits. The focal
plane of the Schmidt-telescope contains 42 CCDs with a total of 96
megapixels that cover 100 square degrees of sky. Both the Schmidt
corrector and 1.4 m aperture primary mirror have been fabricated and
polished. All 50 CCD detectors have been delivered, tested and found to
perform better than required, and are now being mounted in modules to be
installed in the focal plane. Measurements of the ability of the first
module to detect transit amplitudes expected from Earth-size planets
are scheduled to start this month. A preliminary catalog classifying
11 million stars in the FOV has been produced. The science descope
that replaced the articulated antenna with a body-fixed antenna still
provides performance above the baseline design. A concise description of
the current mission design and expected science results are presented.

---------------------------------------------------------
Title: The Physical Properties of Cool Dwarfs
Authors: Basri, Gibor
2006koa..prop...49B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Kepler Mission: Astrophysics and Eclipsing Binaries
Authors: Koch, D.; Borucki, W.; Basri, G.; Brown, T.; Caldwell, D.;
Christensen-Dalsgaard, J.; Cochran, W.; Dunham, E.; Gautier, T. N.;
Geary, J.; Gilliland, R.; Jenkins, J.; Kondo, Y.; Latham, D.; Lissauer,
J.; Monet, D.
2006Ap&SS.304..391K Altcode: 2006Ap&SS.tmp..467K
The Kepler Mission is a photometric space mission that will continuously
observe a single 100 square degree field of view (FOV) of the sky of
more than 100,000 stars in the Cygnus-Lyra region for four or more
years with a precision of 14 parts per million (ppm) for a 6.5 hour
integration including shot noise for a twelfth magnitude star. The
primary goal of the mission is to detect Earth-size planets in the
habitable zone of solar-like stars. In the process, many eclipsing
binaries (EB) will also be detected. Prior to launch, the stellar
characteristics will have been determined for all the stars in the FOV
with K&lt;14.5. As part of the verification process, stars with transits
(about 5%) will need to have follow-up radial velocity observations
performed to determine the component masses and thereby separate
grazing eclipses caused by stellar companions from transits caused
by planets. The result will be a rich database on EBs. The community
will have access to the archive for uses such as for EB modeling of
the high-precision light curves. A guest observer program is also
planned for objects not already on the target list.

---------------------------------------------------------
Title: A Survey for Spectroscopic Binaries among Very Low Mass Stars
Authors: Basri, Gibor; Reiners, Ansgar
2006AJ....132..663B Altcode: 2006astro.ph..4259B
We report on the results of a survey for radial velocity variability
in a heterogeneous sample of very low mass stars and brown dwarfs. One
distinguishing characteristic of the survey is its time span, which
allows an overlap between spectroscopic binaries and those that can
be found by high angular resolution imaging. Despite our relatively
low velocity precision, we are able to place a new constraint on the
total binary fraction in these objects, which suggests that they are
more likely the result of extending the same processes at work at
higher masses into this mass range, rather than a distinct mode of
formation. Our basic result is that there are 6+/-2 out of 53, or
11%+0.07-0.04, spectroscopic binaries in the
separation range 0-6 AU, nearly as many as resolved binaries. This
leads to an estimate of an upper limit of 26%+/-10% for the binary
fraction of very low mass objects (it is an upper limit because of the
possible overlap between the spectroscopic and resolved populations). A
reasonable estimate for the very low mass binary fraction is 20%-25%. We
consider several possible separation and frequency distributions,
including the one found for GK stars, a compressed version of that,
a version of the compressed distribution truncated at 15 AU, and a
theoretical distribution that considers the evaporation of small-N
clusters. We conclude that the latter two bracket the observations,
which may mean that these systems form with intrinsically smaller
separations due to their smaller mass and then are truncated due to
their smaller binding energy. We do not find support for the “ejection
hypothesis” as their dominant mode of formation, particularly in view
of the similarity in the total binary fraction compared with slightly
more massive stars and the difficulty this mechanism has in producing
numerous binary systems. Our conclusions must be viewed as tentative
until studies with larger and better-posed samples and higher velocity
precision are conducted.

---------------------------------------------------------
Title: VizieR Online Data Catalog: RW Aur spectra (Alencar+, 2005)
Authors: Alencar, S. H. P.; Basri, G.; Hartmann, L.; Calvet, N.
2006yCat..34400595A Altcode:
The observations, obtained over a
decade, were carried out at Lick Observatory. **************************************************************************
* * * A major hard disk failure on the author's
workstation containing * * the FITS files of
the spectra made the files actually unavailable * * *
**************************************************************************
(1 data file).

---------------------------------------------------------
Title: Measuring Magnetic Fields in Ultracool Stars and Brown Dwarfs
Authors: Reiners, A.; Basri, G.
2006ApJ...644..497R Altcode: 2006astro.ph..2221R
We present a new method for direct measurement of magnetic
fields on ultracool stars and brown dwarfs. It takes advantage of
the Wing-Ford bands of FeH, which are seen throughout the M and
L spectral types. These molecular features are not as blended as
other optical molecular bands, are reasonably strong through most
of the spectral range, and exhibit a response to magnetic fields
that is easier to detect than other magnetic diagnostics, including
the usual optical and near-infrared atomic spectral lines that have
heretofore been employed. The FeH bands show a systematic growth
as the star gets cooler. We do not find any contamination by CrH in
the relevant spectral region. We are able to model cool and rapidly
rotating spectra from warmer, slowly rotating spectra utilizing an
interpolation scheme based on curve-of-growth analysis. We show that
the FeH features can distinguish between negligible, moderate, and
high magnetic fluxes on low-mass dwarfs, with a current accuracy of
about 1 kG. Two different approaches to extracting the information
from the spectra are developed and compared. Which one is superior
depends on a number of factors. We demonstrate the validity of our new
procedures by comparing the spectra of three M stars whose magnetic
fluxes are already known from atomic line analysis. The low- and
high-field stars are used to produce interpolated moderate-strength
spectra that closely resemble the moderate-field star. The assumption
of linear behavior for the magnetic effects appears to be reasonable,
but until the molecular constants are better understood, the method
is subject to that assumption and rather approximate. Nonetheless,
it opens a new regime of very low mass objects to direct confirmation
and testing of their magnetic dynamos.

---------------------------------------------------------
Title: Planetesimals to Brown Dwarfs: What is a Planet?
Authors: Basri, Gibor; Brown, Michael E.
2006AREPS..34..193B Altcode: 2006astro.ph..8417B
The past 15 years have brought about a revolution in our understanding
of our Solar System and other planetary systems. During this time,
discoveries include the first Kuiper belt objects (KBOs), the first
brown dwarfs, and the first extrasolar planets. Although discoveries
continue apace, they have called into question our previous perspectives
on planets, both here and elsewhere. The result has been a debate about
the meaning of the word "planet" itself. It is clear that scientists
do not have a widely accepted or clear definition of what a planet is,
and both scientists and the public are confused (and sometimes annoyed)
by its use in various contexts. Because "planet" is a very widely
used term, it seems worth the attempt to resolve this problem. In this
essay, we try to cover all the issues that have come to the fore and
bring clarity (if not resolution) to the debate.

---------------------------------------------------------
Title: The First High-Resolution Spectra of 1.3 L Subdwarfs
Authors: Reiners, A.; Basri, G.
2006AJ....131.1806R Altcode: 2005astro.ph.12130R
We present the first high-resolution (R~31,000) spectra of the cool
L subdwarf (sdL) 2MASS 0532+8246 and what was originally identified
as an early-type sdL, LSR 1610-0040. Our work, in combination with
contemporaneous work by Cushing and Vacca, makes it clear that the
latter object is more likely a mid-M dwarf with an unusual composition
that gives it some subdwarf spectral features. We use the data to
derive precise radial velocities for both objects and to estimate
space motion; both are consistent with halo kinematics. We measure the
projected rotational velocities, revealing a very slow rotation for the
old sd?M6 object LSR 1610-0040. The object 2MASS 0532+8246 exhibits a
rapid rotation of vsini=65+/-15 km s-1, consistent with the
behavior of L dwarfs. This means that the braking time for L dwarfs
is extremely long, or that perhaps they never slow down. A detailed
comparison of the atomic Rb and Cs lines with spectra of field L
dwarfs shows that the spectral type 2MASS 0532+8246 is consistent with
being mid- to late-L. The Rb I and K I lines of LSR 1610-0040 are like
those of an early-L dwarf, but the Cs I line is like that of a mid-M
dwarf. The appearance of the Ca II triplet in absorption in this object
is very hard to understand if it is not at least as warm as M6. We
explain these effects in a consistent way using a mildly metal-poor
mid-M model. M subdwarfs have weak metal oxides and enhanced metal
hydrides relative to normal M dwarfs. LSR 1610-0040 exhibits metal
hydrides like an M dwarf but metal oxides like a subdwarf. The same
explanation that resolves the atomic-line discrepancy explains this
as well. Our spectra cover the spectral region around a previously
unidentified absorption feature at 9600 Å and the region around
9400 Å in which detection of TiH has been claimed. We identify the
absorption around 9600 Å as being due to atomic lines of Ti and a
small contribution of FeH, but we cannot confirm a detection of TiH
in the spectra of cool sdLs. In 2MASS 0532+8246, both metal oxides and
metal hydrides are extremely strong relative to normal L dwarfs. It may
be possible to explain the strong oxide features in 2MASS 0532+8246
by invoking effects due to inhibited dust formation. High-resolution
spectroscopy has aided in beginning to understand the complex molecular
chemistry and spectral formation in metal-deficient and ultracool
atmospheres and the properties of early ultra-low-mass objects.

---------------------------------------------------------
Title: The Kepler Mission: A Transit-Photometry Mission to Discover
Terrestrial Planets
Authors: Borucki, William J.; Koch, David; Basri, Gibor; Brown,
Timothy; Caldwell, Douglas; Devore, Edna; Dunham, Edward; Gautier,
Thomas; Geary, John; Gilliland, Ronald; Gould, Alan; Howell, Steve;
Jenkins, Jon
2006ISSIR...6..207B Altcode:
The Kepler Mission is a NASA Discovery-class mission designed to
continuously monitor the brightness of 100,000 main sequence stars
to detect the transit of Earth-size and larger planets. It is a wide
field of view photometer with a Schmidt-type telescope and an array
of 42 CCDs covering the 100 sq. degree field-of-view (FOV). It has
a 0.95 m aperture and a 1.4 m primary and is designed to attain a
photometric precision of 20 parts per million (ppm) for 12th magnitude
solar-like stars for a 6.5-hour transit duration. It will continuously
observe 100,000 main sequence stars from 9th to 15th magnitude in the
Cygnus constellation for a period of four years with a cadence of
4 measurements per hour. Kepler is Discovery Mission #10 and is on
schedule for launch in 2007 into heliocentric orbit. A ground-based
program to classify all 450,000 stars brighter than 15th magnitude
in the FOV and to conduct a detailed examination of a subset of
the stars that show planetary companions is also planned. Hundreds
of Earth-size planets should be detected if they are common around
solarlike stars. Ground-based spectrometric observations of those stars
with planetary companions will be made to determine the dependences of
the frequency and size of terrestrial planets on stellar characteristics
such as type and metallicity. A null result would imply that terrestrial
planets are rare.

---------------------------------------------------------
Title: Measuring physical properties of very young brown dwarfs
Authors: Basri, G.
2006AN....327....3B Altcode:
I discuss the problem of finding the fundamental parameters (mass,
temperature, gravity, radius, and age) of ultra low-mass objects
when they are very young. This is the part of parameter space where
theoretical evolutionary models, which typically are used to extract the
difficult parameters of age, mass, and radius from more observationally
direct parameters like luminosity and spectral type, are expected to be
least reliable. Studying binaries is one way to get around this problem;
determining fundamental parameters from high resolution spectra is
another (which is applicable to single stars). All these methods have
their advantages and problems, and it is essential to make comparisons
between them to develop trust in any of their answers. Workshop
“Ultralow-mass star formation and evolution”, see AN 326, No. 10

---------------------------------------------------------
Title: Accretion in brown dwarfs down to nearly planetary masses
Authors: Mohanty, S.; Basri, G.; Jayawardhana, R.
2005AN....326..891M Altcode:
We show that in accreting ultra low-mass stars and brown dwarfs,
the CaII λ8662 emission line flux correlates remarkably well with
the mass accretion rate (\dot{M}), just as it does in higher mass
classical T Tauri stars (CTTs). A straightforward measurement of the
CaII flux thus provides an easier \dot{M} determination technique
than detailed modeling of the Hα emission line profile (except
at the very lowest accretion rates, where CaII does not appear
to be in emission for ultra low-mass objects, and Hα modeling is
required). Using optical high-resolution spectra, we infer \dot{M}
from CaII emission for young ultra low-mass objects down to nearly the
deuterium-burning (planetary-mass) limit. Our results, in combination
with previous determinations of \dot{M} in CTTs, illustrate that the
accretion rate declines steeply with mass, roughly as \dot{M}∝
{M*}2 (albeit with considerable scatter). A
similar relationship has been suggested by previous studies; we extend
it down to nearly the planetary regime. The physical reason for this
phenomenon is not yet clear; we discuss various possible mechanisms.

---------------------------------------------------------
Title: Kepler Mission Design
Authors: Koch, D. G.; Borucki, W. J.; Lissauer, J. J.; Basri, G. S.;
Gould, A. D.; Brown, T. M.; Caldwell, D. A.; DeVore, E. K.; Jenkins,
J. M.; Christensen-Dalsgaard, J.; Cochran, W. D.; Dunham, E. W.;
Gautier, T. N.; Geary, J. C.; Latham, D. W.; Gilliland, R. L.; Kondo,
Y.; Monet, D. G.
2005AAS...20711009K Altcode: 2005BAAS...37.1339K
The Kepler Mission is in the development phase with launch planned for
2008. The mission goal is to reliably detect a significant number of
Earth-size and smaller planets in the habitable zone of solar-like
stars. (see W. Borucki, et al, this meeting.) The mission design
allows for exploring the diversity of planetary sizes and orbital
periods for a wide variety of stellar spectral types, (see posters by
D. Latham, et al and T. Brown, et al, this meeting on stellar catalog
preparation). In this poster we describe the technical approach taken
for the mission design; describing the flight and ground system, the
detection methodology, the photometer design and capabilities, the way
the data are taken and processed, the Guest Observer opportunity and
the EPO aspects (see paper by E. DeVore, et al). Finally the detection
capability in terms of planet size is presented as a function of
planetary orbital period, mission duration, stellar type and combined
differential photometric precision.

---------------------------------------------------------
Title: Discovery of an M4 Spectroscopic Binary in Upper Scorpius:
A Calibration Point for Young Low-Mass Evolutionary Models
Authors: Reiners, Ansgar; Basri, Gibor; Mohanty, Subhanjoy
2005ApJ...634.1346R Altcode: 2005astro.ph..6501R
We report the discovery of a new low-mass spectroscopic (SB2) stellar
binary system in the star-forming region of Upper Scorpius. This
object, UScoCTIO 5, was discovered by Ardila and coworkers, who
assigned it a spectral class of M4. A Keck I HIRES spectrum revealed
it to be double-lined, and we then carried out a program at several
observatories to determine its orbit. The orbital period is 34 days, and
the eccentricity is nearly 0.3. The importance of such a discovery is
that it can be used to help calibrate evolutionary models at low masses
and young ages. This is one of the outstanding problems in the study
of formation mechanisms and initial mass functions at low masses. The
orbit allows us to place a lower limit of 0.64+/-0.02 Msolar
on the total system mass. The components appear to be of almost equal
mass. We are able to show that this mass is significantly higher than
predicted by evolutionary models for an object of this luminosity and
age, in agreement with other recent results. More precise determination
of the temperature and surface gravity of the components would be
helpful in further solidifying this conclusion.

---------------------------------------------------------
Title: Kepler Mission: Current Status
Authors: Borucki, W. J.; Koch, D. G.; Lissauer, J. J.; Basri,
G. S.; Caldwell, D. A.; DeVore, E.; Jenkins, J. M.; Caldwell, J. J.;
Christensen-Dalsgaard, J.; Cochran, W. D.; Dunham, E. W.; Gautier,
T. N.; Geary, J. C.; Latham, D. A.; Sasselov, D.; Gilliland, R. L.;
Gould, A.; Howell, S. B.; Kondo, Y.; Monet, D. G.
2005AAS...20715301B Altcode: 2005BAAS...37Q1412B
Kepler is a Discovery-class mission designed to determine the frequency
of Earth-size planets in and near the habitable zone (HZ) of solar-like
stars. The instrument consists of a 0.95 m aperture photometer designed
to obtain high precision photometric measurements of &gt;100,000 stars
to search for patterns of transits. The depth and repetition time of
transits provide the size of the planet relative to the star and its
orbital period. At the end of the four year mission, several hundred
terrestrial planets should be discovered if such planets are common. Multi-band ground-based observation of 5x106 stars in the
Kepler FOV is currently underway to estimate stellar parameters and
choose appropriate targets. The poster by Latham et al discusses the
filter set, magnitude range, and current status of the Kepler Input
Catalog. The poster by Brown et.al. describes the methods used to go
from these observations and stellar models to Teff and log(g). With
these parameters, dwarf stars can be selected and both the star and
planet diameters can be calculated. When transit patterns are detected,
the positions of discovered planets relative to the habitable zone
can be estimated. Both the Schmidt corrector and 1.4 m aperture
primary mirror have been fabricated and are being polished. Forty-six
CCD detectors have been delivered, tested, and are being prepared for
mounting in modules that will be installed in the focal plane. As of
Oct. 2005, the first CCD driver, data acquisition, and science data
accumulator boards have been functionally tested. And Build 0 of the
flight software has been completed and tested. These support reading
out of the 96 megapixel focal plane as often as every 3 sec. A more
complete discussion of the spacecraft and instrument development can
be found in the poster by Koch et al.

---------------------------------------------------------
Title: Lithium depletion in the brown dwarf binary GJ 569Bab
Authors: Zapatero Osorio, M. R.; Martín, E. L.; Lane, B. F.; Pavlenko,
Ya.; Bouy, H.; Baraffe, I.; Basri, G.
2005AN....326..948Z Altcode:
GJ 569Bab is the first brown dwarf binary for which the mass
of each component has been derived by solving the astrometric
and spectroscopic orbit of the pair, i.e., independently of any
theoretical assumption. This allows us to test the predictions of the
various evolutionary models available in the literature. Particularly
interesting are the predictions of lithium depletion for the mass
(0.08-0.05 M⊙) and likely age (300-800 Myr) of the
substellar components. High-resolution optical spectra of GJ 569B (the
pair is not resolved) obtained with HIRES at the Keck telescope show
that there has been significant lithium depletion in both components. We
will compare these results to state-of-the-art theoretical calculations.

---------------------------------------------------------
Title: The Kepler Mission: A wide-field transit search for terrestrial
planets [review article]
Authors: Basri, Gibor; Borucki, William J.; Koch, David
2005NewAR..49..478B Altcode:
The Kepler Mission is a NASA Discovery mission which will continuously
monitor the brightness of at least 100,000 main sequence stars, to
detect the transits of terrestrial and larger planets. It is scheduled
to be launched in 2007 into an Earth-trailing heliocentric orbit. It is
a wide-field photometer with a Schmidt-type telescope and array of 42
CCDs covering the 100 square degree field-of-view. It has a 1-m aperture
which enables a differential photometric precision of 2 parts in 100,000
for 12th magnitude solar-like stars over a 6.5-hour transit duration. It
will continuously observe dwarf stars from 8th to 15th magnitude in
the Cygnus constellation, for a period of four years, with a cadence
of 4 measurements per hour. Hundreds of terrestrial planets should
be detected if they are common around solar-type stars. Ground-based
spectrometry of stars with planetary candidates will help eliminate
false-positives, and determine stellar characteristics such as mass
and metallicity. A null result would imply that terrestrial planets
are rare.

---------------------------------------------------------
Title: The extreme T Tauri star RW Aur: accretion and outflow
variability
Authors: Alencar, S. H. P.; Basri, G.; Hartmann, L.; Calvet, N.
2005A&A...440..595A Altcode:
We present an analysis of the classical T Tauri star RW Aur A, based
on 77 echelle spectra obtained at Lick Observatory over a decade of
observations. RW Aur, which has a higher than average mass accretion
rate among T Tauri stars, exhibits permitted (Hα, Hβ, Ca II,
He I, NaD) and forbidden ([OI]6300 Å) emission lines with strong
variability. The permitted lines display multiple periodicities over
the years, often with variable accretion (redshifted) and outflow
(blueshifted) absorption components, implying that both processes
are active and changing in this system. The broad components of the
different emission lines exhibit correlated behavior, indicating
a common origin for all of them. We compute simple magnetospheric
accretion and disk-wind Hα, Hβ and NaD line profiles for RW Aur. The
observed Balmer emission lines do not have magnetospheric accretion line
profiles. Our modeling indicates that the wind contribution to these
line profiles is very important and must be taken into account. Our
results indicate that the Hα, Hβ and NaD observed line profiles of RW
Aur are better reproduced by collimated disk-winds starting from a small
region near the disk inner radius. Calculations were performed in a
region extending out to 100 R*. Within this volume, extended
winds originating over many stellar radii along the disk are not able
to reproduce the three lines simultaneously. Strongly open-angled winds
also generate profiles that do not look like the observed ones. We also
see evidence that the outflow process is highly dynamic - the low- and
high-velocity components of the [OI](6300 Å) line vary independently
on timescales of days. The apparent disappearance from December 1999
to December 2000 of the [OI](6300 Å) low velocity component, which is
thought to come from the disk-wind, shows that the the slow wind can
exhibit dramatic variability on timescales of months (placing limits
on how extended it can be). There is no comprehensive explanation yet
for the behavior of RW Aur, which may in part be due to complications
that would be introduced if it is actually a close binary.

---------------------------------------------------------
Title: The Magnetic Properties of an L Dwarf Derived from Simultaneous
Radio, X-Ray, and Hα Observations
Authors: Berger, E.; Rutledge, R. E.; Reid, I. N.; Bildsten, L.;
Gizis, J. E.; Liebert, J.; Martín, E.; Basri, G.; Jayawardhana, R.;
Brandeker, A.; Fleming, T. A.; Johns-Krull, C. M.; Giampapa, M. S.;
Hawley, S. L.; Schmitt, J. H. M. M.
2005ApJ...627..960B Altcode: 2005astro.ph..2384B
We present the first simultaneous, multiwavelength observations of
an L dwarf, the L3.5 candidate brown dwarf 2MASS J00361617+1821104,
conducted with the Very Large Array, the Chandra X-Ray Observatory,
and the Kitt Peak 4 m telescope. We detect strongly variable
and periodic radio emission (P=3 hr) with a fraction of about
60% circular polarization. No X-ray emission is detected to a
limit of LX/Lbol&lt;~2×10-5,
several hundred times below the saturation level observed in early
M dwarfs. Similarly, we do not detect Hα emission to a limit of
LHα/Lbol&lt;~2×10-7, the deepest for
any L dwarf observed to date. The ratio of radio to X-ray luminosity
is at least 4 orders of magnitude in excess of that observed in a
wide range of active stars (including M dwarfs), providing the first
direct confirmation that late-M and L dwarfs violate the radio/X-ray
correlation. The radio emission is due to gyrosynchrotron radiation
in a large-scale magnetic field of about 175 G, which is maintained
on timescales longer than 3 yr. The detected 3 hr period may be due
to (1) the orbital motion of a companion at a separation of about 5
stellar radii, similar to the configuration of RS CVn systems, (2)
an equatorial rotation velocity of about 37 km s-1 and an
anchored, long-lived magnetic field, or (3) periodic release of magnetic
stresses in the form of weak flares. In the case of orbital motion, the
magnetic activity may be induced by the companion, possibly explaining
the unusual pattern of activity and the long-lived signal. We conclude
that fully convective stars can maintain a large-scale and stable
magnetic field, but the lack of X-ray and Hα emission indicates that
the atmospheric conditions are markedly different than in early-type
stars and even M dwarfs. Similar observations are therefore invaluable
for probing both the internal and external structure of low-mass stars
and substellar objects, and for providing constraints on dynamo models.

---------------------------------------------------------
Title: The T Tauri Phase Down to Nearly Planetary Masses: Echelle
Spectra of 82 Very Low Mass Stars and Brown Dwarfs
Authors: Mohanty, Subhanjoy; Jayawardhana, Ray; Basri, Gibor
2005ApJ...626..498M Altcode: 2005astro.ph..2155M
Using the largest high-resolution spectroscopic sample to date of young,
very low mass stars and brown dwarfs, we investigate disk accretion
in objects ranging from just above the hydrogen-burning limit all
the way to nearly planetary masses. Our 82 targets span spectral
types from M5 to M9.5, or masses from 0.15 Msolar down to
about 15 jupiters. They are confirmed members of the ρ Ophiuchus,
Taurus, Chamaeleon I, IC 348, R Coronae Australis, Upper Scorpius,
and TW Hydrae star-forming regions and young clusters, with ages from
&lt;1 to ~10 Myr. The sample contains 41 brown dwarfs (spectral types
&gt;=M6.5). We have previously presented high-resolution optical
spectra for roughly half the sample; the rest are new. This is a
close to complete survey of all confirmed brown dwarfs known so far
in the regions examined, except in ρ Oph and IC 348 (where we are
limited by a combination of extinction and distance). We find that
(1) classical T Tauri-like disk accretion persists in the substellar
domain down to nearly the deuterium-burning limit; (2) while an Hα
10% width &gt;~200 km s-1 is our prime accretion diagnostic
(following our previous work), permitted emission lines of Ca II, O I,
and He I are also good accretion indicators, just as in classical T
Tauri stars (we caution against a blind use of Hα width alone, since
inclination and rotation effects on the line are especially important at
the low accretion rates in very low mass objects); (3) the Ca II λ8662
line flux is an excellent quantitative measure of the accretion rate
in very low mass stars and brown dwarfs (as in higher mass classical
T Tauri Stars), correlating remarkably well with the M˙ obtained
from veiling and Hα modeling; (4) the accretion rate diminishes
rapidly with mass-our measurements support previous suggestions that
M˙~M2* (albeit with considerable scatter) and
extend this correlation to the entire range of substellar masses;
(5) the fraction of very low mass stellar and substellar accretors
decreases substantially with age, as in higher mass stars; (6) at
any given age, the fraction of very low mass stellar and substellar
accretors is comparable to the accretor fraction in higher mass stars;
and (7) a number of our sources with infrared excesses arising from
dusty disks do not evince measurable accretion signatures, with the
incidence of such a mismatch increasing with age: this implies that
disks in the low-mass regime can persist beyond the main accretion
phase and parallels the transition from the classical to post-T Tauri
stage in more massive stars. These strong similarities at young ages,
between higher mass stars on the one hand and low-mass bodies close
to and below the hydrogen-burning limit on the other, are consistent
with a common formation mechanism in the two mass regimes.

---------------------------------------------------------
Title: A Decade of Brown Dwarfs
Authors: Basri, Gibor
2005S&T...109e..34B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A search for spectroscopic binaries among very low-mass stars
and brown dwarfs
Authors: Reiners, A.; Basri, G.
2005ESASP.560..907R Altcode: 2005csss...13..907R
No abstract at ADS

---------------------------------------------------------
Title: Accretion, jets and disk-locking in the brown dwarf domain
Authors: Mohanty, Subhanjoy; Jayawardhana, Ray; Basri, Gibor
2005MmSAI..76..303M Altcode:
We demonstrate that in accreting ultra-low mass stars and brown dwarfs,
the CaII lambda 8662 emission line flux yields a robust quantitative
estimate of the mass accretion rate (dot {M}), providing an easier
dot {M} determination technique than detailed Halpha line-profile
modeling. With optical high-resolution spectra, we derive dot {M}
from CaII fluxes for young ultra-low mass objects down to nearly
the deuterium-burning (planetary-mass) limit. Our results, combined
with prior studies of higher-mass classical T Tauri stars (CTTs),
show that dot {M} decreases steeply with (sub-)stellar mass, roughly
as dot {M} ∝ {M*}2 (albeit with considerable
scatter). A similar relationship has been suggested by previous studies;
we extend it to nearly the planetary regime. We also find forbidden [OI]
lambda 6300 emission in the ∼ 10 Myr-old, M8 accreting brown dwarf
2MASS 1207-3932, making this the oldest and one of the lowest-mass
brown dwarfs with a mass outflow. Finally, in CTTs, accretion and
jets are often linked to disk-locking. Using vsin i derived from
our high-resolution spectra, we show that the same phenomenon arises
in the ultra-low mass regime as well: accretors near and below the
sub-stellar boundary appear to be preferentially slow rotators compared
to non-accretors. These results suggests that ultra-low mass stellar
and sub-stellar objects pass, in their youth, through a T Tauri phase
completely analogous to that observed in higher-mass stars, bolstering
the idea of a common formation mechanism in the two mass regimes.

---------------------------------------------------------
Title: Surface Gravities and Masses in Substellar Objects
Authors: Mohanty, Subhanjoy; Basri, Gibor; Jayawardhana, Ray
2005HiA....13..813M Altcode:
We present an analysis of optical high-resolution spectra of very
young ultra-low mass stellar and substellar objects in Upper Scorpius
and Taurus. We show that a multi-feature spectral analysis combined
with the latest synthetic spectra can yield accurate surface gravities
(+/- 0.25 dex) and effective temperatures (+/- 50K). This represents
the most stringent observational constraint so far on gravity in young
ultra-low mass objects. Combining our gravity and temperature results
with observed and synthetic photometry and known cluster distance
we also derive masses and radii for our objects. These are the first
mass and radii measurements in young ultra-low mass objects that are
INDEPENDENT of theoretical evolutionary tracks. We find that two of our
faintest targets have planetary mass (~ 6 Jupiters). We also find that
significant discrepancies exist between our results and the theoretical
tracks for the coolest objects: our derived radii are substantially
larger than predicted. Recent studies of M dwarf eclipsing binaries
also show the theoretical radii to be underestimations. We conclude that
high-resolution spectroscopy is invaluable for guiding the evolutionary
modeling of young low-mass stars and brown dwarfs.

---------------------------------------------------------
Title: Accretion disks in the sub-stellar regime
Authors: Jayawardhana, Ray; Mohanty, Subhanjoy; Basri, Gibor
2005MmSAI..76..295J Altcode:
We discuss recent findings on accretion disks around young brown dwarfs
and very low mass stars, addressing both infrared and millimeter
measurements of dust emission and spectroscopic signatures of gas
accretion and outflow. It is now clear that a large fraction of
sub-stellar objects harbor near- and mid-infrared excesses consistent
with dusty disks, and that these disks exhibit a similar range of
geometries and dust properties as their T Tauri counterparts. Similarly,
many young brown dwarfs show evidence of on-going accretion and a
few also evince possible signatures of mass outflow. On average, the
accretion rate decreases steeply with mass, though there is considerable
scatter in this relation. Some objects, especially in the 5-10 Myr-old
associations, that harbor infrared excess do not show measurable signs
of accretion; this may imply that the disks persist beyond the main
accretion phase. These strong similarities between brown dwarfs and
low-mass stars in their infancy suggest a common formation mechanism.

---------------------------------------------------------
Title: Astrometric monitoring of the binary brown dwarf DENIS-P
J1228.2-1547
Authors: Brandner, W.; Martín, E. L.; Bouy, H.; Köhler, R.; Delfosse,
X.; Basri, G.; Andersen, M.
2004A&A...428..205B Altcode:
We present astrometric monitoring data of the binary brown dwarf
DENIS-P J1228.2-1547. The data have been obtained with the Hubble
Space Telescope over a time span of 5.5 yr, and confirm that DENIS-P
J1228.2-1547 is indeed a common proper motion, i.e., physical,
binary. The data cover about 1/8th of the binary orbit, indicating
an orbital period of ≈45 yr, and a semimajor axis of ≈6.4 AU. A
plausible fit of the orbital parameters indicates that both components
of the binary are substellar, which is in good agreement with previous
mass estimates based on the presence of lithium in the combined
spectra of both components. Since the next periastron passage of
DENIS-P J1228.2-1547 is expected for the years 2030 to 2035, long-term
astrometric monitoring is required to derive accurate mass estimates
for the system and the individual components. The photometry obtained
with HST/WFPC2 in the F814W band shows no indication for photometric
variability with an amplitude larger than 0.05 mag over a time span of
≈1000 days. Based on observations made with the NASA/ESA Hubble
Space Telescope, obtained at the Space Telescope Science Institute,
which is operated by the Association of Universities for Research in
Astronomy, Inc., under NASA contract NAS 5-26555. These observations
are associated with programmes GO 7952, 8720, 9157, 9345, 9968.

---------------------------------------------------------
Title: The Origin of X-rays in Pre-Main-Sequence Stars
Authors: Stassun, K. G.; Ardila, D. R.; Barsony, M.; Basri, G.;
Mathieu, R. D.
2004AAS...20510509S Altcode: 2004BAAS...36R1518S
We present an analysis of archival Chandra observations of the Orion
Nebula Cluster (ONC) to study the X-ray properties of a large sample
of pre-main-sequence (PMS) stars with optically determined rotation
periods. Our goal is to elucidate the origins of X-rays in PMS stars
by seeking out connections between the X-rays and the mechanisms most
likely driving their production---rotation and accretion. We find
that these stars have LX/Lbol near, but below,
the “saturation" value of 10-3, and that X-ray luminosity
is significantly correlated with stellar rotation, in the sense of
decreasing LX/Lbol with more rapid rotation. These
findings suggest that stars with optical rotation periods are in the
“super-saturated” regime of the rotation-activity relationship,
consistent with their Rossby numbers. However, we also find that
stars with optical rotation periods are significantly biased to high
LX. This is not the result of magnitude bias in the optical
rotation-period sample, but rather of the diminishingly small amplitude
of optical variations in stars with low LX. Evidently,
there exists in the ONC a population of stars whose rotation periods
are unknown and that possess lower average X-ray luminosities than those
of stars with known rotation periods. These stars may sample the linear
regime of the rotation-activity relationship. Accretion also manifests
itself in X-rays, though in a somewhat counterintuitive fashion:
while stars with spectroscopic signatures of accretion show harder
X-ray spectra than nonaccretors, they show lower X-ray luminosities
and no enhancement of X-ray variability. We interpret these findings
in terms of a common origin for the X-ray emission observed from both
accreting and nonaccreting stars, with the X-rays from accreting stars
simply being attenuated by magnetospheric accretion columns. We also
present preliminary results from a simultaneous optical/X-ray monitoring
study of variability in the ONC, where we find very little evidence for
correlated variability, indicating that X-ray events are not temporally
related to accretion events. These findings suggest that X-rays from
PMS stars have their origins primarily in chromospheres/coronae,
not accretion.

---------------------------------------------------------
Title: Opportunities for High Precision Photometric Measurements of
Variable Stars: Kepler Guest Investigator Program
Authors: Borucki, W. J.; Koch, D. G.; Basri, G. S.; Latham, D. W.;
Howell, S. B.
2004AAS...205.3305B Altcode: 2004BAAS...36R1400B
The Kepler Mission is designed to detect terrestrial planets by
monitoring the flux of more than 100,000 dwarf stars for a period of
four years at a cadence of 4/hour. During the early portion of the
mission when the telemetry rate is high, approximately 170,000 stars
will be monitored. The photometric precision for 6.5-hour integration
periods will be 20 ppm to 89 ppm for 12th to 15th magnitude stars,
respectively. Prior to the launch, multiband photometry of all target
stars will be made to estimate spectral type, brightness temperature,
and luminosity class. To the extent possible, the initial target list
will exclude evolved stars and those known to be variable. Sometime
after the first year, the target list will be trimmed by removing
those stars found to be too variable to detect planets unless requests
for continued observations are received from the stellar astrophysics
community. A Guest Observer program is being developed to accommodate
those wishing to observe targets in the 140 square degree Kepler
field of view centered at RA 19h 22m 40s, Dec +44° 30'. A webtool
is available to assess whether your favorite object is on the Kepler
detectors. This program represents an unprecedented opportunity to
obtain extremely high precision photometry over very long (typically
3 month) intervals with almost continuous coverage. At any given time
there will be 2000-3000 Guest Observer targets (a few of which can be
observed with a one-minute cadence).

---------------------------------------------------------
Title: First determination of the dynamical mass of a binary L dwarf
Authors: Bouy, H.; Duchêne, G.; Köhler, R.; Brandner, W.; Bouvier,
J.; Martín, E. L.; Ghez, A.; Delfosse, X.; Forveille, T.; Allard,
F.; Baraffe, I.; Basri, G.; Close, L.; McCabe, C. E.
2004A&A...423..341B Altcode: 2004astro.ph..5111B
We present here the results of astrometric, photometric
and spectroscopic observations leading to the determination
of the orbit and dynamical masses of the binary L dwarf 2MASSW
J0746425+2000321. High angular resolution observations spread over
almost 4 years and obtained with the Hubble Space Telescope (HST),
the ESO Very Large Telescope (VLT), and a the W. M. Keck Observatory
(Keck) allow us to cover ∼36% of the period, corresponding to 60%
of the orbit, and, for the first time, to derive a precise estimate of
the total and individual masses of such a late-type object. We find
an orbital period of 3850.9+904-767 days. The
corresponding total mass is 0.146+0.016-0.006
M⊙ with uncertainties depending on the distance. Spatially
resolved low resolution optical (550-1025 nm) spectra have been
obtained with HST/STIS, allowing us to measure the spectral
types of the two components (L0± 0.5 for the primary and L1.5
±0.5 for the secondary). We also present precise photometry of
the individual components measured on the high angular resolution
images obtained with HST/ACS and WFPC2 (visible), VLT/NACO (J, H and
KS bands) and Keck I (KS band). These spectral
and photometric measurements enable us to estimate their effective
temperatures and mass ratio, and to place the object accurately in a
H-R diagram. The binary system is most likely formed by a primary with
a mass of 0.085±0.010 M⊙ and a secondary with a mass of
0.066±0.006 M⊙, thus clearly substellar, for an age of
approximately 300±150 Myr. Hα variability indicates chromospheric
and/or magnetic activity. Based on observations obtained with
the the NASA/ESA Hubble Space Telescope, the ESO Very Large Telescope
(program 70.D-0773), and the W. M. Keck Observatory.

---------------------------------------------------------
Title: Extrasolar planets Too close for comfort
Authors: Basri, Gibor
2004Natur.430...24B Altcode:
Three gas-giant planets have now been found in puzzlingly close orbits
around their stars. These 'very hot Jupiters' raise questions about
planet-finding methods and our understanding of planetary systems.

---------------------------------------------------------
Title: Measuring Fundamental Parameters of Substellar
Objects. I. Surface Gravities
Authors: Mohanty, Subhanjoy; Basri, Gibor; Jayawardhana, Ray; Allard,
France; Hauschildt, Peter; Ardila, David
2004ApJ...609..854M Altcode: 2004astro.ph..3265M
We present an analysis of high-resolution optical spectra for a sample
of very young, mid- to late-M, low-mass stellar and substellar objects:
11 in the Upper Scorpius association, and two (GG Tau Ba and Bb) in the
Taurus star-forming region. Effective temperatures and surface gravities
are derived from a multiple-feature spectral analysis using TiO, Na
I, and K I, through comparison with the latest synthetic spectra. We
show that these spectral diagnostics complement each other, removing
degeneracies with temperature and gravity in the behavior of each. In
combination, they allow us to determine temperature to within 50
K and gravity to within 0.25 dex, in very cool young objects. Our
high-resolution spectral analysis does not require extinction
estimates. Moreover, it yields temperatures and gravities independent
of theoretical evolutionary models (although our estimates do depend on
the synthetic spectral modeling). We find that our gravities for most
of the sample agree remarkably well with the isochrone predictions
for the likely cluster ages. However, discrepancies appear in our
coolest targets: these appear to have significantly lower gravity (by
up to 0.75 dex) than our hotter objects, even though our entire sample
covers a relatively narrow range in effective temperature (~300 K). This
drop in gravity is also implied by intercomparisons of the data alone,
without recourse to synthetic spectra. We consider, and argue against,
dust opacity, cool stellar spots, or metallicity differences leading to
the observed spectral effects; a real decline in gravity is strongly
indicated. Such gravity variations are contrary to the predictions of
the evolutionary tracks, causing improbably low ages to be inferred
from the tracks for our coolest targets. Through a simple consideration
of contraction timescales, we quantify the age errors introduced into
the tracks through the particular choice of initial conditions and
demonstrate that they can be significant for low-mass objects that
are only a few megayears old. However, we also find that these errors
appear insufficient to explain the magnitude of the age offsets in
our lowest gravity targets. We venture that this apparent age offset
may arise from evolutionary model uncertainties related to accretion,
deuterium burning and/or convection effects. Finally, when combined with
photometry and distance information, our technique for deriving surface
gravities and effective temperatures provides a way of obtaining masses
and radii for substellar objects independent of evolutionary models;
radius and mass determinations are presented in Paper II.

---------------------------------------------------------
Title: Measuring Fundamental Parameters of Substellar
Objects. II. Masses and Radii
Authors: Mohanty, Subhanjoy; Jayawardhana, Ray; Basri, Gibor
2004ApJ...609..885M Altcode: 2004astro.ph..3269M
We present mass and radius derivations for a sample of very young, mid-
to late-M, low-mass stellar and substellar objects in Upper Scorpius
and Taurus. In a previous paper we determined effective temperatures
and surface gravities for these targets from an analysis of their
high-resolution optical spectra and comparisons to the latest synthetic
spectra. We now derive extinctions, radii, masses, and luminosities by
combining our previous results with observed photometry, surface fluxes
from the synthetic spectra, and the known cluster distances. These are
the first mass and radius estimates for young, very low mass bodies
that are independent of theoretical evolutionary models (although our
estimates do depend on spectral modeling). We find that for most of
our sample, our derived mass-radius and mass-luminosity relationships
are in very good agreement with the theoretical predictions. However,
our results diverge from the evolutionary model values for the
coolest, lowest mass targets: our inferred radii and luminosities are
significantly larger than predicted for these objects at the likely
cluster ages, causing them to appear much younger than expected. We
suggest that uncertainties in the evolutionary models-e.g., in the
choice of initial conditions and/or treatment of interior convection-may
be responsible for this discrepancy. Finally, two of our late-M objects
(USco 128 and 130) appear to have masses close to the deuterium-fusion
boundary (~9MJ-14MJ within a factor of 2). This
conclusion is primarily a consequence of their considerable faintness
compared to other targets with similar extinction, spectral type,
and temperature (difference of ~1 mag). Our result suggests that the
faintest young late-M or cooler objects may be significantly lower in
mass than current theoretical tracks indicate.

---------------------------------------------------------
Title: X-Ray Properties of Pre-Main-Sequence Stars in the Orion
Nebula Cluster with Known Rotation Periods
Authors: Stassun, Keivan G.; Ardila, David R.; Barsony, Mary; Basri,
Gibor; Mathieu, Robert D.
2004AJ....127.3537S Altcode: 2004astro.ph..3159S
We reanalyze all archival Chandra/ACIS observations of the Orion
Nebula Cluster (ONC) to study the X-ray properties of a large sample
of pre-main-sequence (PMS) stars with optically determined rotation
periods. Our goal is to elucidate the origins of X-rays in PMS stars
by seeking out connections between the X-rays and the mechanisms
most likely driving their production-rotation and accretion. Stars
in our sample have LX/Lbol near, but below,
the “saturation” value of 10-3. In addition, in this
sample X-ray luminosity is significantly correlated with stellar
rotation, in the sense of decreasing LX/Lbol
with more rapid rotation. These findings suggest that stars with
optical rotation periods are in the “super-saturated” regime of
the rotation-activity relationship, consistent with their Rossby
numbers. However, we also find that stars with optical rotation
periods are significantly biased to high LX. This is not
the result of magnitude bias in the optical rotation-period sample,
but rather of the diminishingly small amplitude of optical variations
in stars with low LX. Evidently, there exists in the ONC
a population of stars whose rotation periods are unknown and that
possess lower average X-ray luminosities than those of stars with
known rotation periods. These stars may sample the linear regime of
the rotation-activity relationship. Accretion also manifests itself in
X-rays, though in a somewhat counterintuitive fashion: while stars with
spectroscopic signatures of accretion show harder X-ray spectra than
nonaccretors, they show lower X-ray luminosities and no enhancement
of X-ray variability. We interpret these findings in terms of a
common origin for the X-ray emission observed from both accreting and
nonaccreting stars, with the X-rays from accreting stars simply being
attenuated by magnetospheric accretion columns. This suggests that
X-rays from PMS stars have their origins primarily in chromospheres,
not accretion.

---------------------------------------------------------
Title: Rotation and Magnetic Activity in Brown Dwarfs (Invited Review)
Authors: Basri, G.
2004IAUS..215..248B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Oxygen and magnesium abundance in the ultra-metal-poor giants
CS 22949-037 and CS 29498-043: Challenges in models of atmospheres
Authors: Israelian, G.; Shchukina, N.; Rebolo, R.; Basri, G.; González
Hernández, J. I.; Kajino, T.
2004A&A...419.1095I Altcode: 2004astro.ph..3033I
We report the results of a non-LTE Fe, O and Mg abundance analysis of
the carbon-nitrogen-rich ultra-metal-poor giants CS 29498-043 and CS
22949-037. The abundance of oxygen has been derived from measurements
of the oxygen triplet at 7771-5 Å in high resolution spectra obtained
with KeckI/HIRES and the forbidden line [O I] 6300 Å detected in
the TNG/SARG spectra of CS 29498-043. Detailed non-LTE analysis of
Fe lines has provided reliable stellar parameters which, however,
do not resolve the oxygen abundance conflict as derived from the O I
7771-5 Å triplet and the [O I] 6300 Å forbidden lines. We obtained
the following oxygen abundance: for CS 22949-037 [O/Fe] = 3.13, 1.95;
and for CS 29498-043; [O/Fe] = 3.02, 2.49, based on the O I 7771-5
Å triplet and the [O I] 6300 Å forbidden line, respectively. A
similar conflict appears to exist between the forbidden resonance
line Mg C I 4571 Å and several subordinate lines, such as Mg I
5172 and 5183 Å. Our analysis demonstrates the failure of standard
plane-parallel atmosphere models to describe the physical conditions
in the line-forming regions of these ultra-metal-poor giants.

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Title: The Kepler Mission
Authors: Basri, Gibor
2004wfis.confE..38B Altcode:
No abstract at ADS

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Title: Magnetic Activity at Very Low Masses
Authors: Basri, G.
2004IAUS..219..275B Altcode: 2003IAUS..219E.157B
The rotation-activity paradigm has proven very effective in solar-type
stars explaining both their activity and rotational histories. The
basic ingredients are rotationally-driven dynamos and conversion of
magnetic energy into heating. Things change near the bottom of the main
sequence. A saturation velocity persists cooler than M3 suggesting that
the remaining dynamo is not purely turbulent (even though the stars
are fully convective and cannot support a solar-type dynamo). At M9 the
levels of stellar activity plummet. This is probably due to a decoupling
of the field from atmospheric motions given extreme neutrality of the
atmospheres. It is no longer forced into dissipative configurations
and quiescent chromospheres and coronae disappear. The lack of
magnetic braking leaves these stellar and substellar objects very
rapid rotators. Thus the rotation-activity relation is REVERSED at the
low mass limit. Flaring persists in very cool objects suggesting some
field is still present. We don't know how these flares are generated
(they exhibit odd ratios of X-ray to radio flux). A further mystery
is the elevated activity of very young cool objects. Clearly we still
have much to learn in this area.

---------------------------------------------------------
Title: Oxygen Abundances in Ultra-metal-poor Giants CS29498-043
and CS22949-037
Authors: Israelian, G.; Shchukina, N.; Rebolo, R.; Basri, G.; González
Hernández, J. I.
2004oee..sympE..27I Altcode:
Abundances of oxygen in two ultra-metal-poor giants have been derived
from measurements of the oxygen triplet at 7771-5Å in the near-IR
performed in high-resolution and high S/N ratio spectra obtained with
KeckI/HIRES. A detailed non-LTE analysis of Fe lines has been carried
out for our targets providing more reliable stellar parameters and
metallicities.

---------------------------------------------------------
Title: VizieR Online Data Catalog: UBVRI light curves of AA Tau in
1999 (Bouvier+, 2003)
Authors: Bouvier, J.; Grankin, K. N.; Alencar, S. H. P.; Dougados,
C.; Fernandez, M.; Basri, G.; Batalha, C.; Guenther, E.; Ibrahimov,
M. A.; Magakian, T. Y.; Melnikov, S. Y.; Petrov, P. P.; Rud, M. V.;
Zapatero Osorio, M. R.
2004yCat..34090169B Altcode:
he photometric observations were carried out over a period extending
from Aug. 9, 1999, to Jan. 4, 2000. AA Tau's light curve is best sampled
in the BVRI filters over the period from Nov. 25 to Dec. 15, 1999, when
several sites observed simultaneously (see Table 1). (1 data file).

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Title: Brown Dwarfs: Up Close and Physical
Authors: Basri, G. B.
2003AAS...203.7402B Altcode: 2003BAAS...35.1321B
I review what has now been nearly a decade of progress in the study of
brown dwarfs as physical objects. The definition of brown dwarfs as
distinct from stars or planets has some subtlety, and is an amalgam
of considerations. I briefly discuss their internal structure,
and the evolution of luminosity sources within them. Deuterium and
lithium can be used as external probes of their internal state. I next
discuss the effective temperature scale for the new L and T spectral
classes. Formation of dust in the atmospheres of these objects is a
crucial determinant of their spectral appearance, as is the conversion
of typical molecules from oxides to hydrides. Not only is the chemical
formation of dust important, but proper treatment of cloud formation
and dust settling is clearly important (“meteorology” becomes a
consideration). This can strongly affect the colors of the objects,
and the visibility of spectral features. Finally, I summarize results
on other physical properties which can be studied using high spectral
and angular resolution, including angular momentum, magnetic activity,
surface gravity, and binarity.

---------------------------------------------------------
Title: What Is a "Planet"?
Authors: Basri, Gibor B.
2003Mercu..32f..27B Altcode:
Recent discoveries inside and outside the solar system have complicated
our perception of what constitutes a "planet."

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Title: Rotation &amp; Activity in Mid-M to L Dwarfs
Authors: Mohanty, S.; Basri, G.
2003csss...12..683M Altcode:
We analyze rotation velocities and chromospheric (Hα) activity,
derived from multi-year, high-resolution spectra, in 56 mid-M to L
dwarfs. Rotation velocities are found to increase from mid-M to L. This
is consistent with a lengthening of spin-down timescale with later type,
though in the L types the trend may also be a function of stellar
age. From M5 to M8.5, a saturation-type rotation-activity relation
is seen, similar to that in earlier types. However, the saturation
velocity in our case is much higher, at ∼ 12 km s-1. A
sharp drop in activity is observed at ∼ M9, with later types showing
little or no Hα emission, in spite of rapid rotation. This may be due
to the very high resistivities in the predominantly neutral atmospheres
of these cool objects.

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Title: Accretion Processes in T Tauri Stars: GHRS Observations
Authors: Ardila, D. R.; Basri, G.; Walter, F. M.; Valenti, J. A.;
Johns-Krull, C. M.
2003csss...12..723A Altcode:
We have performed observations of eight classical and one weak T
Tauri Star, using the GHRS instrument on board of HST. We observe the
ion{Si}{4} (1400 Å), ion{C}{4} (1550 Å), and ion{Mg}{2} (2800 Å)
resonance doublets, and numerous H2 lines. Here we discuss
the observational characteristics of these lines.

---------------------------------------------------------
Title: Kepler Mission: a mission to find Earth-size planets in the
habitable zone
Authors: Borucki, William J.; Koch, David; Basri, Gibor; Brown,
Timothy; Caldwell, Douglas; Devore, Edna; Dunham, Edward; Gautier,
Thomas; Geary, John; Gilliland, Ronald; Gould, Alan; Howell, Steve;
Jenkins, Jon
2003ESASP.539...69B Altcode: 2003toed.conf...69B
The Kepler Mission is a NASA Discovery-class mission designed to
continuously monitor the brightness of 100,000 main sequence stars
to detect the transit of Earth-size and larger planets. It is a wide
field of view photometer with a Schmidt-type telescope and an array
of 42 CCDs covering the 100 sq. degree field-of-view (FOV). It has
a 0.95 m aperture and a 1.4 m primary and is designed to attain a
photometric precision of 20 parts per million (ppm) for 12th magnitude
solar-like stars for a 6.5-hour transit duration. It will continuously
observe 100,000 main sequence stars from 9th to 15th magnitude in the
Cygnus constellation for a period of four years with a cadence of 4
measurements per hour. The photometer is scheduled to be launched in
2007 into heliocentric orbit. A ground-based program to classify all
450,000 stars brighter than 15th magnitude in the FOV and to conduct
a detailed examination of a subset of the stars that show planetary
companions is also planned. Hundreds of Earth-size planets should
be detected if they are common around solar-like stars. Ground-based
spectrometric observations of those stars with planetary companions
will be made to determine the dependences of the frequency and size
of terrestrial planets on stellar characteristics such as type and
metallicity. A null result would imply that terrestrial planets
are rare.

---------------------------------------------------------
Title: Eclipses by circumstellar material in the T Tauri star AA
Tau. II. Evidence for non-stationary magnetospheric accretion
Authors: Bouvier, J.; Grankin, K. N.; Alencar, S. H. P.; Dougados,
C.; Fernández, M.; Basri, G.; Batalha, C.; Guenther, E.; Ibrahimov,
M. A.; Magakian, T. Y.; Melnikov, S. Y.; Petrov, P. P.; Rud, M. V.;
Zapatero Osorio, M. R.
2003A&A...409..169B Altcode: 2003astro.ph..6551B
We report the results of a synoptic study of the photometric and
spectroscopic variability of the classical T Tauri star AA Tau on
timescales ranging from a few hours to several weeks. The AA Tau light
curve had been previously shown to vary with a 8.2 d period, exhibiting
a roughly constant brightness level, interrupted by quasi-cyclic
fading episodes, which we interpreted as recurrent eclipses of the
central star by the warped inner edge of its accretion disk (Bouvier
et al. \cite{Bouvier99}). Our observations show the system is dynamic
and presents non-stationary variability both in the photometry and
spectroscopy. The star exhibits strong emission lines that
show substantial variety and variability in their profile shapes and
fluxes. Emission lines such as Hα and Hβ show both infall and outflow
signatures and are well reproduced by magnetospheric accretion models
with moderate mass accretion rates (10-8-10-9
{M}_sun yr-1) and high inclinations (i &gt;=60degr ). The
veiling shows variations that indicate the presence of 2 rotationally
modulated hot spots corresponding to the two magnetosphere poles. It
correlates well with the He I line flux, with B-V and the V excess
flux. We have indications of a time delay between the main emission
lines (Hα, Hβ and He I) and veiling, the lines formed farther away
preceding the veiling changes. The time delay we measure is consistent
with accreted material propagating downwards the accretion columns at
free fall velocity from a distance of about 8 R_star . In addition,
we report periodic radial velocity variations of the photospheric
spectrum which might point to the existence of a 0.02 \msun object
orbiting the star at a distance of 0.08 AU. During a few days, the
eclipses disappeared, the variability of the system was strongly
reduced and the line fluxes and veiling severely depressed. We
argue that this episode of quiescence corresponds to the temporary
disruption of the magnetic configuration at the disk inner edge. The
smooth radial velocity variations of inflow and outflow diagnostics in
the Hα profile yield further evidence for large scale variations of
the magnetic configuration on a timescale of a month. These results
may provide the first clear evidence for large scale instabilities
developping in T Tauri magnetospheres as the magnetic field lines
are twisted by differential rotation between the star and the inner
disk. The interaction between the inner accretion disk and the
stellar magnetosphere thus appears to be a highly dynamical and time
dependent process. Based on observations obtained at Observatoire
de Haute Provence (CNRS, France), Mt Maidanak Obs. (Uzbekistan),
Calar Alto Obs. (Spain), Teide Obs. (Spain), Byurakan Obs. (Armenia),
Assy-Turgen Obs. (Kazakstan), ESO La Silla (Chile), Lick Obs. (NOAO,
USA), Tautenburg Obs. (Germany) and Roque de los Muchachos Obs. (Spain).

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Title: Multiplicity of Nearby Free-Floating Ultracool Dwarfs:
A Hubble Space Telescope WFPC2 Search for Companions
Authors: Bouy, Hervé; Brandner, Wolfgang; Martín, Eduardo L.;
Delfosse, Xavier; Allard, France; Basri, Gibor
2003AJ....126.1526B Altcode: 2003astro.ph..5484B
We present Hubble Space Telescope (HST) Wide Field Planetary Camera 2
(WFPC2) observations of a sample of 134 ultracool objects (spectral
types later than M7) coming from the Deep Near Infrared Survey
(DENIS), Two Micron All Sky Survey (2MASS), and Sloan Digital
Sky Survey (SDSS), with distances estimated to range from 7 to 105
pc. Fifteen new ultracool binary candidates are reported here. Eleven
known binaries are confirmed, and orbital motion is detected in some
of them. We estimate that the closest binary systems in this sample
have periods between 5 and 20 yr, and thus dynamical masses will be
derived in the near future. For the calculation of binary frequency,
we restrict ourselves to systems with distances less than 20 pc. After
correction of the binaries bias, we find a ratio of visual binaries
(at the HST limit of detection) of around 10%, and that ~15% of the
26 objects within 20 pc are binary systems with separations between 1
and 8 AU. The observed frequency of ultracool binaries is similar to
that of binaries with G-type primaries in the separation range from
2.1 to 140 AU. There is also a clear deficit of ultracool binaries
with separations greater than 15 AU, and a possible tendency for the
binaries to have mass ratios near unity. Most systems have indeed visual
and near-infrared brightness ratios between 1 and 0.3. We discuss our
results in the framework of current scenarios for the formation and
evolution of free-floating brown dwarfs.

---------------------------------------------------------
Title: Evidence for a T Tauri Phase in Young Brown Dwarfs
Authors: Jayawardhana, Ray; Mohanty, Subhanjoy; Basri, Gibor
2003ApJ...592..282J Altcode: 2003astro.ph..3565J
As part of a multifaceted program to investigate the origin and early
evolution of substellar objects, we present high-resolution Keck optical
spectra of 14 very low mass sources in the IC 348 young cluster and
the Taurus star-forming cloud. All of our targets, which span a range
of spectral types from M5 to M8, exhibit moderate to very strong Hα
emission. In half of the IC 348 objects, the Hα profiles are broad and
asymmetric, indicative of ongoing accretion. Of these, IC 348-355 (M8)
is the lowest mass object to date to show accretion-like Hα. Three of
our ~M6 IC 348 targets with broad Hα also harbor broad O I (8446 Å)
and Ca II (8662 Å) emission, and one shows broad He I (6678 Å)
emission; these features are usually seen in strongly accreting
classical T Tauri stars. We find that in very low mass accretors,
the Hα profile may be somewhat narrower than that in higher mass
stars. We propose that low accretion rates combined with small infall
velocities at very low masses can conspire to produce this effect. In
the nonaccretors in our sample, Hα emission is commensurate with,
or higher than, saturated levels in field M dwarfs of similar spectral
type. Our results constitute the most compelling evidence to date that
young brown dwarfs undergo a T Tauri-like accretion phase similar
to that in stars. This is consistent with a common origin for most
low-mass stars, brown dwarfs, and isolated planetary mass objects.

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Title: Very Low Mass Stars and Brown Dwarfs in Taurus
Authors: White, Russel; Basri, Gibor
2003IAUS..211..143W Altcode:
We present high resolution optical spectra obtained with the Keck I
telescope of low mass T Tauri stars and brown dwarfs in the Taurus star
forming region. Based on the inferred photospheric and circumstellar
properties, we conclude that objects in Taurus with masses as low as 50
Jupiters form and evolve in the same way as higher-mass T Tauri stars,
but with smaller disks and shorter disk lifetimes.

---------------------------------------------------------
Title: Multiplicity of Nearby Free-floating Late M and L Dwarfs:
HST-WFPC2 Observations of Candidates and Bona Fide Binary Brown Dwarfs
Authors: Bouy, Hervé; Brandner, Wolfgang; Martín, Eduardo L.;
Delfosse, Xavier; Allard, France; Basri, Gibor
2003IAUS..211..245B Altcode:
We review the results of HST/WFPC2 observations of a sample of
50 very-low-mass objects in the solar neighborhood (30 from our
own program and 20 from the archive). Using high spatial resolution
HST/WFPC2 images, we observed these objects in two filters (F814W and
F675W) in order to identify close companions, measure their colours,
and obtain first epoch data of the newly discovered binaries. In
addition to 3 previously known binaries we discovered 3 new multiple
systems. Second epoch data are required to confirm that they are
real common proper motion pairs. Binary properties like multiplicity,
distribution of binary separations and brightness ratios hold clues
on the origin and evolution of free-floating brown dwarf binaries.

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Title: Nomenclature: Brown Dwarfs, Gas Giant Planets, and ?
Authors: Boss, Alan P.; Basri, Gibor; Kumar, Shiv S.; Liebert, James;
Martín, Eduardo L.; Reipurth, Bo; Zinnecker, Hans
2003IAUS..211..529B Altcode:
The question of what sort of guidelines should be used to classify
substellar mass objects was considered and debated during an evening
panel discussion at the IAU 211 Symposium on Brown Dwarfs.

---------------------------------------------------------
Title: Magnetic Activity and Rotation in Brown Dwarfs and Low
Mass Stars
Authors: Basri, Gibor; Mohanty, Subanjoy
2003IAUS..211..427B Altcode:
One of the triumphs of the last 2 decades has been the establishment
of the relation between stellar rotation and magnetic activity in
solar-type stars. Rapid rotation produces strong activity, which in turn
provides magnetic braking to reduce rotation. A solar-type dynamo cannot
operate in fully convective stars, so it is of interest to study mid
and late M stars. Hints that a dramatic change occurs in very low-mass
stars and substellar objects appeared in 1995. The past 7 years have
seen substantial progress on this question, with the conclusion that
the rotation-activity connection indeed breaks down. As one goes to the
bottom of the main sequence and below, the amount of magnetic activity
takes a sudden fall, with a concomitant increase in the spindown times
of the objects. We summarize these results, and some theoretical work
which helps explain them. We also present some remaining mysteries,
such as why very young objects seem excessively active, and flaring
in objects with no other signs of magnetic activity.

---------------------------------------------------------
Title: The Kepler mission: a wide-field-of-view photometer designed to
determine the frequency of Earth-size planets around solar-like stars
Authors: Borucki, William J.; Koch, David G.; Lissauer, Jack J.;
Basri, Gibor B.; Caldwell, John F.; Cochran, William D.; Dunham,
Edward W.; Geary, John C.; Latham, David W.; Gilliland, Ronald L.;
Caldwell, Douglas A.; Jenkins, Jon M.; Kondo, Yoji
2003SPIE.4854..129B Altcode:
NASA's Kepler Mission is designed to determine the frequency of
Earth-size and larger planets in the habitable zone of solar-like
stars. It uses transit photometry from space to determine planet size
relative to its star and orbital period. From these measurements, and
those of complementary ground-based observations of planet-hosting
stars, and from Kepler's third law, the actual size of the planet,
its position relative to the habitable zone, and the presence of other
planets can be deduced. The Kepler photometer is designed around a
0.95 m aperture wide field-of-view (FOV) Schmidt type telescope with a
large array of CCD detectors to continuously monitor 100,000 stars in a
single FOV for four years. To detect terrestrial planets, the photometer
uses differential relative photometry to obtain a precision of 20 ppm
for 12th magnitude stars. The combination of the number of stars that
must be monitored to get a statistically significant estimate of the
frequency of Earth-size planets, the size of Earth with respect to
the Sun, the minimum number of photoelectrons required to recognize
the transit signal while maintaining a low false-alarm rate, and the
areal density of target stars of differing brightness are all critical
to the photometer design.

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Title: Gravity &amp; Mass Measurement in Young Substellar Objects
Authors: Mohanty, Subhanjoy; Basri, Gibor; Jayawardhana, Ray; Allard,
France; Hauschildt, Peter; Ardila, David
2003IAUJD..20E..29M Altcode:
We present an analysis of optical high-resolution spectra of very
young ultra-low mass stellar and substellar objects in Upper Scorpius
and Taurus. We show that a multi-feature spectral analysis combined
with the latest synthetic spectra can yield accurate surface gravities
(+/- 0.25 dex) and effective temperatures (+/- 50K). This represents
the most stringent observational constraint so far on gravity in young
ultra-low mass objects. Combining our gravity and temperature results
with observed and synthetic photometry and known cluster distance
we also derive masses and radii for our objects. These are the first
mass and radii measurements in young ultra-low mass objects that are
INDEPENDENT of theoretical evolutionary tracks. We find that two of our
faintest targets have planetary mass (~ 6 Jupiters). We also find that
significant discrepancies exist between our results and the theoretical
tracks for the coolest objects: our derived radii are substantially
larger than predicted. Recent studies of M dwarf eclipsing binaries
also show the theoretical radii to be underestimations. We conclude that
high-resolution spectroscopy is invaluable for guiding the evolutionary
modeling of young low-mass stars and brown dwarfs.

---------------------------------------------------------
Title: Observational Clues to Brown Dwarf Origins
Authors: Jayawardhana, Ray; Mohanty, Subhanjoy; Basri, Gibor; Ardila,
David R.; Stelzer, Beate; Haisch, Karl E., Jr.
2003ASSL..299..251J Altcode: 2003oils.conf..251J
No abstract at ADS

---------------------------------------------------------
Title: The Kepler Mission: Finding the Sizes, Orbits and Frequencies
of Earth-size and Larger Extrasolar Planets
Authors: Borucki, W. J.; Koch, D. G.; Basri, G. B.; Caldwell, D. A.;
Caldwell, J. F.; Cochran, W. D.; Devore, E.; Dunham, E. W.; Geary,
J. C.; Gilliland, R. L.; Gould, A.; Jenkins, J. M.; Kondo, Y.; Latham,
D. W.; Lissauer, J. J.
2003ASPC..294..427B Altcode:
The first step in discovering the extent of life in our galaxy is to
determine the number of terrestrial planets in circumstellar habitable
zones (HZ). The Kepler Mission is designed around a 0.95 m aperture
Schmidt-type telescope with an array of 42 CCDs. The photometer is
designed to continuously monitor the brightness of 100,000 solar-like
stars to detect the transits of Earth-size and larger planets. It is
scheduled to be launched into a heliocentric orbit in 2007. Measurements
of the depth and repetition time of transits provide the size of the
planet relative to the star and its orbital period. When combined with
ground-based spectroscopy of these stars to fix the stellar parameters,
the true planet radius and orbit, semi-major axis, hence the position
relative to the HZ, are determined. The spectra are also used to
discover the relationships between the characteristics of planets and
the stars that they orbit. In particular, the association of planetary
size and occurrence frequency with stellar mass and metallicity will
be investigated. At the end of the four year mission, hundreds of
terrestrial planets should be discovered in and near the HZ of their
stars if such planets are common. Extending the mission to six years
doubles the expected number of Earth-size planets in the HZ. A null
result would imply that terrestrial planets in the HZ occur in less than
1% of the stars and that habitable planets might be quite rare. Based
on the results of the current Doppler velocity discoveries, detection
of the reflected light from several hundred short-period giant planets
is also expected. Information on the albedos and densities of those
giants showing transits will be obtained.

---------------------------------------------------------
Title: Surface Gravity &amp; Mass in Young Brown Dwarfs and Planemos
Authors: Mohanty, Subhanjoy; Jayawardhana, Ray; Basri, Gibor; Allard,
France; Hauschildt, Peter; Ardila, David
2003ASSL..299..259M Altcode: 2003oils.conf..259M
No abstract at ADS

---------------------------------------------------------
Title: Very Low Mass Stars and Brown Dwarfs in Taurus-Auriga
Authors: White, Russel J.; Basri, Gibor
2003ApJ...582.1109W Altcode: 2002astro.ph..9164W
We present high-resolution optical spectra obtained with the HIRES
spectrograph on the W. M. Keck I Telescope of seven low-mass T Tauri
stars (LMTTs) and brown dwarfs in Taurus-Auriga. The observed Li I 6708
Å absorption, low surface gravity signatures, and radial velocities
confirm that all are members of the Taurus star-forming region; no
new spectroscopic binaries are identified. Four of the seven targets
observed appear to be T Tauri brown dwarfs. Of particular interest is
the previously classified “continuum T Tauri star” GM Tau, which has a
spectral type of M6.5 and possibly a substellar mass. These spectra, in
combination with previous high-resolution spectra of LMTTs, are used to
understand the formation and early evolution of objects in Taurus-Auriga
with masses near and below the stellar/substellar boundary. None of the
LMTTs in Taurus are rapidly rotating (vsini&lt;30 km s-1),
unlike low-mass objects in Orion. Many of the slowly rotating,
nonaccreting stars and brown dwarfs exhibit prominent Hα emission
(equivalent widths of 3-36 Å), indicative of active chromospheres. We
demonstrate empirically that the full width at 10% of the Hα emission
profile peak is a more practical and possibly more accurate indicator
of accretion than either the equivalent width of Hα or optical veiling:
10% widths &gt;270 km s-1 are classical T Tauri stars (i.e.,
accreting), independent of stellar spectral type. Although LMTTs can
have accretion rates comparable to that of more typical, higher mass
T Tauri stars (e.g., K7-M0 spectral types), the average mass accretion
rate appears to decrease with decreasing mass. A functional form of M~M
is consistent with the available data, but the dependence is difficult
to establish because of both selection biases in observed samples
and the decreasing frequency of active accretion disks at low masses
(M&lt;0.2 Msolar). The diminished frequency of accretion
disks for LMTTs, in conjunction with their lower, on average, mass
accretion rates, implies that they are formed with less massive disks
than higher mass T Tauri stars. The radial velocities, circumstellar
properties, and known binaries do not support the suggestion that many
of the lowest mass members of Taurus have been ejected from higher
stellar density regions within the cloud. Instead, LMTTs appear to have
formed and are evolving in the same way as higher mass T Tauri stars,
but with smaller disks and shorter disk lifetimes.

---------------------------------------------------------
Title: Rotation and Activity in Mid-M to L Field Dwarfs
Authors: Mohanty, Subhanjoy; Basri, Gibor
2003ApJ...583..451M Altcode: 2002astro.ph..1455M
We analyze rotation velocities and chromospheric (Hα) activity,
derived from high-resolution spectra, in a large sample of mid-M to
L field dwarfs. The projected rotation velocity is found to increase
from mid-M to L. This is consistent with a lengthening of spin-down
timescale with later type, although in the L types the trend may also
be a function of the observational bias toward younger objects. From
M4 to M8.5 a saturation-type rotation-activity relation is seen,
similar to that in earlier types, when activity is measured through
either FHα or LHα/Lbol. However,
we find that activity saturates at a significantly higher velocity
(~10 km s-1) in the M5.5-M8.5 dwarfs than in the M4-M5
ones (&lt;~4 km s-1). This may result from a change in
the dynamo behavior with later type (see also below). We note that
the saturation level in Hα emission appears to vary somewhat less
with spectral type (from M4 to M8.5) when activity is measured through
LHα/Lbol instead of FHα. In M9 and
later dwarfs, we observe a drastic drop in activity and a sharp break
in the rotation-activity connection: Hα emission levels in these
dwarfs are much lower than in earlier types, and often undetectable,
in spite of very rapid rotation. This may be caused by the very
high resistivities in the predominantly neutral atmospheres of these
dwarfs, which would damp the magnetic energy available for supporting a
chromosphere. It is also possible that the rapid formation of dust in
these cool atmospheres exacerbates this effect, as charged particles
are soaked up by (more massive) dust grains. Finally, we note that
spectral type determination from low-resolution spectra may be affected
by gravity effects: cooler, lower gravity objects may mimic hotter,
higher gravity ones. Therefore, it is possible that the few unsaturated
fast rotators from M5.5 to M8.5 (whose presence leads us to ascribe a
higher saturation velocity to these spectral types, as noted above)
may actually be very low mass objects, with lower Teff
(and gravity) than their spectral types suggest. If so, their behavior
(low activity, fast rotation) would be compatible with that of the
cool M9 and later dwarfs (and no change in dynamo behavior would have
to be postulated in the M5.5-M8.5 dwarfs). This interpretation is
supported by a preliminary analysis of the high-resolution spectra
of these anomolous objects. It is also bolstered by the fact that
a saturation-type Rossby number-activity relation is seen in the
M5.5-M8.5 dwarfs when these anomalous objects are removed from the
sample, while the relationship is much weaker when they are included.

---------------------------------------------------------
Title: Lithium Abundances in Wide Binaries with Solar-Type Twin
Components
Authors: Martín, Eduardo L.; Basri, Gibor; Pavlenko, Yakiv; Lyubchik,
Yuri
2002ApJ...579..437M Altcode: 2002astro.ph..6473M
We present high-resolution spectroscopic observations of the Li I
resonance line in a sample of 62 stars that belong to 31 common proper
motion pairs with twin F- or G-type components. Photospheric abundances
of lithium were derived by spectral synthesis analysis. For seven of
the pairs, we have measured large lithium abundance differences. Eleven
other pairs have components with similar lithium abundances. We cannot
determine if the remaining 13 pairs have lithium differences because
we did not detect the Li I lines, and hence we can only provide upper
limits to the abundances of both stars. Our results demonstrate that
twin stars do not always share the same lithium abundances. Lithium
depletion in solar-type stars does not only depend on age, mass,
and metallicity. This result is consistent with the spread in lithium
abundances among solar-type stars in the solar-age open cluster M67. Our
stars are brighter than the M67 members of similar spectral type,
making them good targets for detailed follow-up studies that could shed
light on the elusive mechanism responsible for the depletion of lithium
during the main-sequence evolution of the Sun and solar-type stars.

---------------------------------------------------------
Title: Probing Disk Accretion in Young Brown Dwarfs
Authors: Jayawardhana, Ray; Mohanty, Subhanjoy; Basri, Gibor
2002ApJ...578L.141J Altcode: 2002astro.ph..9275J
We present high-resolution optical spectra of 15 objects near or below
the substellar limit in the Upper Scorpius and ρ Ophiuchus star-forming
regions. These spectra, obtained with the High Resolution Echelle
Spectrometer on the Keck I telescope, are used to investigate disk
accretion, rotation, and activity in young very low mass objects. We
report the detection of a broad, asymmetric Hα emission line in the
ρ Oph source GY 5, which is also known to harbor mid-infrared excess,
consistent with the presence of an accreting disk. The Hα profiles
of the Upper Sco objects suggest little or no ongoing accretion. Our
results imply that if most brown dwarfs are born with disks, their
accretion rates decrease rapidly, at timescales comparable to or smaller
than those for T Tauri disks. The Upper Sco brown dwarfs appear to be
rotating faster than their somewhat younger counterparts in Taurus,
consistent with spin-up due to contraction following disk unlocking. The
Hα activity is comparable to saturated activity levels in field M
dwarfs with similar spectral type and rotation rates. Comparison of
our data with published (albeit lower resolution) spectra of a few of
the same objects from other epochs suggests possible variability in
accretion/activity indicators.

---------------------------------------------------------
Title: Activity in Very Cool Stars: Magnetic Dissipation in Late M
and L Dwarf Atmospheres
Authors: Mohanty, Subhanjoy; Basri, Gibor; Shu, Frank; Allard, France;
Chabrier, Gilles
2002ApJ...571..469M Altcode: 2002astro.ph..1518M
Recent observations show that chromospheric Hα activity in late M and L
dwarfs is much lower than in the earlier M types. This is particularly
surprising given that the late M and L dwarfs are comparatively very
rapid rotators: in the early M dwarfs, rapid rotation is associated
with high activity levels. One possibility is that the drop-off
in activity in the late M and L dwarfs is a result of very high
electrical resistivities in their dense, cool, and predominantly
neutral atmospheres.We calculate the magnetic field diffusivity in the
atmospheres of objects with Teff in the range 3000-1500 K
(mid M to late L) using the atmospheric structure models of Allard
and Hauschildt. We find that the combination of very low ionization
fraction and high density in these atmospheres results in very large
resistivities and thus efficient field diffusion. While both ambipolar
diffusion and Ohmic decay of currents due to ion-electron collisions
occur, the primary diffusion effects are due to current decay through
collisions of charged particles with neutrals. Moreover, the latter
resistivity is a strong function of both effective temperature and
optical depth, increasing rapidly as either Teff or optical
depth decreases. This has two implications: (1) Any magnetic field
present is increasingly decoupled from atmospheric fluid motions as one
moves from mid M to L. In the late M and L dwarfs, atmospheric motions
cannot lead to equilibrium field configurations very different from
potential ones. That is, the magnitude of magnetic stresses generated
by atmospheric motions is very small in these objects. We quantify
this effect by a simple Reynolds number calculation. (2) Even if
magnetic stresses are easily produced by fluid motions in the hot
interior (where the coupling between field and matter is good), their
propagation up through the atmosphere will be increasingly hampered
by the growing atmospheric resistivity as one moves from mid M to
late L. Thus both the generation and propagation of magnetic stresses
are increasingly damped with decreasing Teff in these cool
dwarfs. As a result, the magnetic free energy available for the support
of a chromosphere, and activity becomes smaller and smaller with later
type. This can account for the observed drop in Hα activity from mid M
to L, assuming that activity in these dwarfs is magnetically driven. To
check the latter assumption, we estimate the emergent acoustic fluxes
in these objects through a Lighthill-Proudman calculation. While
the acoustic fluxes also decrease with decreasing Teff,
they appear inadequate to explain the observed Hα fluxes in mid M to
L dwarfs. In the absence of acoustic heating, magnetic heating indeed
seems the most viable way of generating activity. We emphasize that our
calculations are equilibrium ones and do not address time-dependent
phenomena. We also do not examine the highest atmospheric layers,
where correction is not expected, but which we show are rarefied enough
to permit charged particles to remain coupled to the field. Finally,
while our calculations do not address flares in late M and L dwarfs,
we speculate that the latter could be created by buoyant flux tubes that
are generated in the interior and rise rapidly through the atmosphere,
dissipating their associated currents in the upper atmospheric layers.

---------------------------------------------------------
Title: Observations of T Tauri Stars Using the Hubble Space Telescope
GHRS. II. Optical and Near-Ultraviolet Lines
Authors: Ardila, David R.; Basri, Gibor; Walter, Frederick M.; Valenti,
Jeff A.; Johns-Krull, Christopher M.
2002ApJ...567.1013A Altcode:
We have analyzed GHRS data of eight classical T Tauri stars (CTTSs)
and one weak T Tauri star (WTTS). The GHRS data consist of a spectral
range 40 Å wide centered on 2800 Å. For four of the CTTSs, we have
nearly simultaneous optical observations that contain Hα, Hβ, He I,
Na D, and the Ca II infrared triplet. The Mg II resonance doublet is
the strongest feature in the 2800 Å range. This line has a fairly
wide and symmetric emission component (~200-300 km s-1 for
the CTTSs), with a narrow central absorption and a wide blueshifted
absorption superimposed to it. The narrow central absorption width and
equivalent width are inconsistent with being due only to interstellar
medium clouds described in the literature, which leads us to conclude
that it is partially due to non-LTE processes in the emission-line
region itself. The emission profile closely follows Hα. Its large
width in CTTSs cannot be due to the Stark effect, and we suggest that
it is due to supersonic turbulence. All the stars show blueshifted
absorptions that are evidence of outflows (terminal velocities ~300
km s-1), with multiple flows observed in two stars. We
show evidence that the wind is not spherical, with wind signatures
being stronger for lower inclinations at a given accretion rate. We
briefly compare other optical lines with the hot transition region
lines observed in CTTS.

---------------------------------------------------------
Title: Observations of T Tauri Stars using Hubble Space Telescope
GHRS. I. Far-Ultraviolet Emission Lines
Authors: Ardila, David R.; Basri, Gibor; Walter, Frederick M.; Valenti,
Jeff A.; Johns-Krull, Christopher M.
2002ApJ...566.1100A Altcode: 2001astro.ph.10436A
We have analyzed Goddard High Resolution Spectrograph data of
eight classical T Tauri stars (CTTSs) and one weak-lined T Tauri
star (WTTS). The GHRS data consist of spectral ranges 40 Å wide
centered on 1345, 1400, 1497, 1550, and 1900 Å. These UV spectra
show strong Si IV and C IV emission and large quantities of sharp
(~40 km s-1) H2 lines. All the H2
lines belong to the Lyman band, and all the observed lines are single
peaked and optically thin. The averages of all the H2 lines
centroids for each star are negative, which may indicate that they come
from an outflow. We interpret the emission in H2 as being the
result of fluorescence, mostly by HLyα, and identify seven
excitation routes within 4 Å of that line. We obtain column densities
(1012-1015 cm-2) and optical depths (~1
or less) for each exciting transition. We conclude that the populations
are far from being in thermal equilibrium. We do not observe any lines
excited from the far blue wing of HLyα, which implies that
the molecular features are excited by an absorbed profile. Si IV and
C IV (corrected for H2 emission) have widths of ~200 km
s-1 and an array of centroids (blueshifted lines, centered,
redshifted). These characteristics are difficult to understand in
the context of current models of the accretion shock. For DR Tau we
observe transient strong blueshifted emission, perhaps the result
of reconnection events in the magnetosphere. We also see evidence of
multiple emission regions for the hot lines. While C IV is optically
thin in most stars in our sample, Si IV is not. However, C IV is a
good predictor of Si IV and H2 emission. We conclude that
most of the flux in the hot lines may be caused by accretion processes,
but the line profiles can have multiple and variable components.

---------------------------------------------------------
Title: Oxygen abundances derived from UV OH and O I IR lines in very
metal-poor stars
Authors: García López, Ramón J.; Israelian, Garik; Rebolo, Rafael;
Bonifacio, Piercarlo; Molaro, Paolo; Basri, Gibor; Shchukina, Natalya
2002HiA....12..413G Altcode:
Oxygen abundances have been derived in a sample of very metal-poor
stars using the O I triplet at λλ7771-5 Å and OH lines in the near
UV. A detailed NLTE analysis of iron lines has been carried out for
one of the observed stars, BD +23°3130, providing consistent values
of effective temperature and surface gravity that are in very good
agreement with independent estimates from the infrared flux method and
Hipparcos parallaxes, respectively. These parameters, especially the
higher gravity obtained with respect to previous analyses, reduce the
discrepancies claimed between the oxygen abundances determined from OH,
O I triplet and [O I] λ6300 Å lines, and give consistent abundances
to within 0.16 dex for BD +23°3130 ([Fe/H]NLTE = -2.43). The
oxygen abundances derived for this new sample confirm previous findings
for a progressive linear increase in the oxygen-to-iron ratio with a
slope -0.33±0.02 (including NLTE corrections to the iron abundances
for all the stars considered) from solar metallicity to [Fe/H]~ -3, and
[O/Fe] values as high as ~1.1 for stars with [Fe/H]&lt;~ -2.5. These
results can be interpreted as evidence for oxygen overproduction in
the very early epoch of the formation of the Galactic halo, possibly
associated with supernova events with very massive progenitor stars.

---------------------------------------------------------
Title: Stellar variability and its implications for photometric
planet detection with Kepler
Authors: Batalha, N. M.; Jenkins, J.; Basri, G. S.; Borucki, W. J.;
Koch, D. G.
2002ESASP.485...35B Altcode: 2002sshp.conf...35B
Kepler is one of three candidates for the next NASA Discovery
Mission and will survey the extended solar neighborhood to detect and
characterize hundreds of terrestrial (and larger) planets in or near the
habitable zone. Its strength lies in its ability to detect large numbers
of Earth-sized planets - planets which produced a 10-4
change in relative stellar brightness during a transit across the disk
of a sun-like parent star. Such a detection requires high instrumental
relative precision and is facilitated by observing stars which are
photometrically quiet on hourly timescales. Probing stellar variability
across the HR diagram, one finds that many of the photometrically
quietest stars are the F and G dwarfs. The Hipparcos photometric
database shows the lowest photometric variances among stars of this
spectral class. Our own Sun is a prime example with RMS variations
over a few rotational cycles of typically (3 - 4)×10-4
(computed from VIRGO/DIARAD data taken Jan-Mar 2001). And variability
on the hourly time scales crucial for planet detection is significantly
smaller: just (2 - 5)×10-5. This bodes well for planet
detection programs such as Kepler and Eddington. With significant
numbers of photometrically quiet solar-type stars, Earth-sized planets
should be readily identified provided they are abundant in the solar
neighborhood. In support of the Kepler science objectives, we have
initiated a study of stellar variability and its implications for
planet detection. Herein, we summarize existing observational and
theoretrical work with the objective of determining the percentage
of stars in the Kepler field of view expected to be photometrically
stable at a level which allows for Earth-sized planet detection.

---------------------------------------------------------
Title: Analysis of the spectra of two solar-like binaries
Authors: Lyubchik, Yu. P.; Martin, E.; Basri, G.; Pavlenko, Ya. V.
2001KFNT...17..530L Altcode: 2001KFNT...17f.530L
Procedure and results of Li, Ca, Al, Si, and Fe abundance determinations
in the atmospheres of the solar-type components of the binaries HD
6872 A, HD 6872 B and HD 224984, HD 224994 are described. These stars
are dwarfs of spectral types G and F. Synthetic spectrum method was
used to analyse their spectra. Kurucz's (2000) model atmospheres of
metallicities [mu] = 0...-0.2 and the atomic line list VALD veryfied
by the solar spectrum are used for computations of the synthetic
spectra. Theoretical spectra were fitted to the observed HD 6872 A,
HD 6872 B and HD 224984, HD 224994 spectra (lambda/deltalambda =
55000). We determined the same lithium abundances (logN(Li) = 2.3)
in the atmospheres of HD 224984 and HD 224994. For HD 6872 A and HD
6872 B we determined different lithium abundances- logN(Li)&lt;1.8,
and logN(Li) = 2.6, respectively. For HD 6872 A we determined vsin i =
14 km/s.

---------------------------------------------------------
Title: The Spectral Variability of the Classical T Tauri Star DR Tauri
Authors: Alencar, Silvia H. P.; Johns-Krull, Christopher M.; Basri,
Gibor
2001AJ....122.3335A Altcode:
We present the analysis of 103 spectra, collected over more than
a decade, of the classical T Tauri star DR Tau observed with the
Hamilton echelle spectrograph at Lick Observatory. The star exhibits
strong emission lines that show substantial variety and variability
in their profile shapes. The emission lines show signatures of both
outflow and infall, which vary on multiple timescales. The system
shows quasi-periodic variations in line intensity and wavelength,
but we are unable to recover a unique period that describes all the
data. The Balmer and He I line changes are well correlated and appear to
result from real variations in the accretion and wind flows, as opposed
to apparent variations caused by changes in the veiling continuum
flux. The Balmer line profiles are generally strongly peaked in the red
(v~100 km s-1) and do not resemble published theoretical
magnetospheric accretion profiles. We suggest that the system is seen
nearly pole-on. Coupled with a line emissivity that increases strongly
near the stellar surface, this can explain the strongly asymmetric
Balmer line profiles. The Ca II and He I emission-line components are
found to be very symmetric and Gaussian in shape, suggesting production
in a turbulent (possibly magnetic) region. An additional sporadic
high-velocity outflow component is seen in the Balmer lines and He
I. The main characteristic of the lines is their dramatic variability,
which indicates a very dynamic interaction between the star and the
disk. This is illustrated in several MPEGs animations showing the line
profile variations of DR Tau, which are available on CD-ROM and the
World Wide Web.6 Based on observations obtained at Lick Observatory.

---------------------------------------------------------
Title: Observations of T-Tauri Stars using HST-GHRS: II. Optical
and Near UV lines
Authors: Ardila, David R.; Basri, Gibor; Walter, Frederick M.; Valenti,
Jeff A.; Johns-Krull, Christopher M.
2001astro.ph.11182A Altcode:
We have analyzed GHRS data of eight Classical T Tauri stars (CTTSs)
and one Weak T Tauri star (WTTS). The GHRS data consist of an spectral
range 40 A wide centered on 2800 A. For 4 of the CTTS we have nearly
simultaneous optical observations which contain Halpha, Hbeta, HeI,
NaD, and the CaII infrared triplet. The MgII resonance doublet is the
strongest feature in the 2800 A range. This line has a fairly wide
and symmetric emission component (~200 to \~300 km/s for the CTTSs),
with a narrow central absorption and a wide blueshifted absorption
superimposed to it. The narrow central absorption width and equivalent
width are inconsistent with being due only to ISM clouds described in
the literature, which lead us to conclude that it is partially due to
non-LTE processes in the emission line region itself. The emission
profile closely follows Halpha. Its large width in CTTS cannot be
due to the Stark effect and we suggest that it is due to supersonic
turbulence. All the stars show blueshifted absorptions that are
evidence of outflows (terminal velocities \~300 km/s), with multiple
flows observed in two stars. We show evidence that the wind is not
spherical, with wind signatures being stronger for lower inclinations
at a given accretion rate. We briefly compare other optical lines with
the hot transition region lines observed in CTTS.

---------------------------------------------------------
Title: Erratum: Oxygen in the Very Early Galaxy
Authors: Israelian, Garik; Rebolo, Rafael; García López, Ramón J.;
Bonifacio, Piercarlo; Molaro, Paolo; Basri, Gibor; Shchukina, Nataliya
2001ApJ...560..535I Altcode:
In the paper “Oxygen in the Very Early Galaxy” by Garik
Israelian, Rafael Rebolo, Ramón J. García López, Piercarlo
Bonifacio, Paolo Molaro, Gibor Basri, and Nataliya Shchukina (<A
href="/abs/2001ApJ...551..833">ApJ, 551, 833 [2001]</A>), in Figures 7,
8, 9, 10, and 11 the OH oxygen abundance for BD +23°3130 is slightly
misplaced. The correct figures, which were not included because of
an error at the Press during the production process, are displayed
here. The legends are not changed. The Press sincerely regrets this
error.

---------------------------------------------------------
Title: X-ray Flare from an Old Brown Dwarf
Authors: Rutledge, Robert E.; Basri, Gibor
2001tysc.confE.238R Altcode:
An X-ray flare from the brown dwarf LP 944-20 is described. This
observation is distinguished from earlier X-ray detections of brown
dwarfs by two facts: (1) the detection is of a flare (approximately 90
min in duration), and not of persistent emission, indicating strong
magnetic activity, and (2) this object is 500 Myr old and therefore
fully collapsed, while previous detections were of young objects
(&lt;10 Myr) and may be powered by accretion collapse, such as in
T Tauri stars. The idea that an unusual process is taking place is
further reinforced by the later detection with the VLA (by Berger
et al) of strong radio flares - up to a factor 10,000 stronger than
expected from the radio/X-ray correlation from active stellar coronae
by Guedel and Benz. Either this object is unusual to itself, or there
is an unexpected physical process which dominates coronal emission at
the end of the main sequence.

---------------------------------------------------------
Title: Oxygen abundances derived in unevolved very metal-poor stars
Authors: García López, R. J.; Israelian, G.; Rebolo, R.; Bonifacio,
P.; Molaro, P.; Basri, G.; Shchukina, N.
2001NewAR..45..519G Altcode:
Oxygen abundances have been derived in a sample of very metal-poor
stars from observations of the O I triplet at λλ 7771-5 Å and OH
lines in the near UV. Iron abundances derived in LTE were corrected
for NLTE effects following Thévenin and Idiart [ApJ 521 (1999)
753]. Furthermore, a detailed NLTE analysis of iron lines has been
carried out for one of the observed stars, BD +23° 3130 ([Fe/H]
NLTE=-2.43), providing consistent values of effective
temperature, surface gravity and metallicity, that are in good agreement
with independent estimates from the infrared flux method, Hipparcos
parallaxes and recent NLTE work in the literature, respectively. These
parameters, especially the higher gravity obtained with respect to
previous analyses, reduce the discrepancies claimed by Fulbright and
Kraft [AJ 118 (1999) 527] between the oxygen abundances determined
from OH and [O I] λ 6300 Å lines, and give a similar abundance from
the O I triplet for BD+23° 3130. A mean value of the oxygen-to-iron
ratio [O/Fe]=0.78±0.16 for this star is fully consistent with the
abundances derived from the three sets of features. This consistency,
which is found using 1D hydrostatic model atmospheres, strongly
constrains the effects predicted by 3D hydrodynamical models on
these three indicators. The oxygen abundances derived for this new
sample confirm previous findings for a progressive linear increase
in the oxygen-to-iron ratio with a slope -0.33±0.02 (including NLTE
corrections to the iron abundances for all the stars considered)
from solar metallicity to [Fe/H]∼-3, and [O/Fe] values as high as
∼1.1 for stars with [Fe/H]&lt;-2.5. These results can be interpreted
as evidence for oxygen overproduction in the very early epoch of the
formation of the Galactic halo, possibly associated with supernova
events with very massive progenitor stars.

---------------------------------------------------------
Title: Astronomy: Young stars go cruising by
Authors: Basri, Gibor
2001Natur.411..145B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Oxygen in the Very Early Galaxy
Authors: Israelian, Garik; Rebolo, Rafael; García López, Ramón J.;
Bonifacio, Piercarlo; Molaro, Paolo; Basri, Gibor; Shchukina, Nataliya
2001ApJ...551..833I Altcode: 2001astro.ph..1032I
Oxygen abundances in a sample of ultra-metal-poor subdwarfs have
been derived from measurements of the oxygen triplet at 7771-5 Å
and OH lines in the near-UV performed in high-resolution and high
signal-to-noise ratio spectra obtained with WHT/UES, Keck I/HIRES,
and VLT/UVES. Our Fe abundances were derived in LTE and then corrected
for non-LTE (NLTE) effects. The new oxygen abundances confirm previous
findings for a progressive linear rise in the oxygen-to-iron ratio
with a slope -0.33+/-0.02 from solar metallicity to [Fe/H]~-3. A
slightly higher slope would be obtained if the Fe NLTE corrections
were not considered. Below [Fe/H]=-2.5 our stars show [O/Fe] ratios
as high as ~1.17 (G64-12), which can be interpreted as evidence
for oxygen overproduction in the very early epoch of the formation
of the halo, possibly associated with supernova events with very
massive progenitor stars. We show that the arguments against this
linear trend given by Fulbright &amp; Kraft in 1999, based on the
LTE Fe analysis of two metal-poor stars, cannot be sustained when an
NLTE analysis is performed. We discuss how the Fulbright &amp; Kraft
LTE ionization balance of Fe lines underestimates the gravity of the
very metal-poor star BD +23°3130 ([Fe/H]=-2.43) and how this leads to
an underestimation of the oxygen abundance derived from the forbidden
line. Gravities from Hipparcos appear to be in good agreement with those
determined in NLTE, giving higher values than previously assumed, which
reduces the discrepancies between the oxygen abundances determined from
OH, triplet, and forbidden lines. Using one-dimensional models, our
analysis of three oxygen indicators available for BD +23°3130 gives
an average [O/Fe] ratio of 0.78+0.15-0.18. The
high oxygen abundances at very low metallicities do not pose a
problem to theoretical modeling since there is a range of parameters
in the calculations of nucleosynthesis yields from massive stars at
low metallicities that can accommodate our results. Based on data
collected at the Keck I, VLT, and William Herschel telescopes.

---------------------------------------------------------
Title: Effective Temperatures for Very Cool Objects, from Resonance
Lines of Cs I and Rb I (CD-ROM Directory: contribs/mohanty)
Authors: Mohanty, S.; Basri, G.; Allard, F.; Hauschildt, P. H.;
Delfosse, X.; Martín, E. L.; Forveille, T.; Goldman, B.
2001ASPC..223..838M Altcode: 2001csss...11..838M
No abstract at ADS

---------------------------------------------------------
Title: Oxygen abundances in very metal-poor stars
Authors: García López, R. J.; Israelian, G.; Rebolo, R.; Bonifacio,
P.; Molaro, P.; Basri, G.; Shchukina, N.
2001hsa..conf..221G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Rotation and Hα Emission Above and Below the Substellar
Boundary (CD-ROM Directory: contribs/basri)
Authors: Basri, G.
2001ASPC..223..261B Altcode: 2001csss...11..261B
No abstract at ADS

---------------------------------------------------------
Title: Ultra-Cool Very Low-Mass Binaries
Authors: Martín, Eduardo L.; Basri, Gibor
2001IAUS..200...55M Altcode:
Observations of ultra-cool (spectral type later than M6) binaries are
summarized. Only a few systems are known, and all have been discovered
in the past few years. We describe each of these discoveries. Despite
their small numbers, some interesting trends among the binaries may be
emerging. Ultra-cool binaries have a frequency similar to but perhaps
a little less than stars (binary fraction ~20%) and have mass ratios
closer to unity, with respect to solar-type stars. Neither of these
results can be considered firm, as there are far too few systems
known, and observational biases would tend to move trends in these
directions. There also seems to be a trend towards smaller separations
in lower mass systems, which is less subject to observational biases. We
discuss how these results fit into current ideas about binary formation,
and favor a fragmentation scenario.

---------------------------------------------------------
Title: Chemical Abundances in Binaries with Twin Components
Authors: Lyubchik, Yu.; Martin, E.; Basri, G.; Pavlenko, Ya.
2001OAP....14..244L Altcode:
Procedure and some preliminary results of abundances determination
in binaries with twin components from solar neighborhood are
discussed. Numerical analysis were carried out by fits of synthetical
spectra and COG to high resolution (R=50000) observed data. To fit
the observations we used model atmospheres of Kurucz with different
metallicities and (modified) VALD line list.

---------------------------------------------------------
Title: Membership and Multiplicity among Very Low Mass Stars and
Brown Dwarfs in the Pleiades Cluster
Authors: Martín, E. L.; Brandner, W.; Bouvier, J.; Luhman, K. L.;
Stauffer, J.; Basri, G.; Zapatero Osorio, M. R.; Barrado y Navascués,
D.
2000ApJ...543..299M Altcode: 2000astro.ph..4174M
We present near-infrared photometry and optical spectroscopy of
very low mass stars and brown dwarf candidates in the Pleiades open
cluster. The membership status of these objects is assessed using
color-magnitude diagrams, lithium and spectral types. Eight objects
out of 45 appear to be nonmembers. A search for companions among 34
very low mass Pleiades members (M&lt;=0.09 Msolar) in high
spatial resolution images obtained with the Hubble Space Telescope (HST)
and the adaptive optics system of the Canada-France-Hawaii telescope
produced no resolved binaries with separations larger than 0.2" (a~27 AU
P~444 yr). Nevertheless, we find evidence for a binary sequence in the
color-magnitude diagrams, in agreement with the results of Steele &amp;
Jameson for higher mass stars. We apply the lithium test to two objects:
CFHT-Pl-16, which lies in the cluster binary sequence but is unresolved
in images obtained with the Hubble Space Telescope; and CFHT-Pl-18,
which is binary with 0.33" separation. The first object passes the
test, but the second object does not. We conclude that CFHT-Pl-16 is
an Pleiades brown dwarf binary with separation less than 11 AU and
that CFHT-Pl-18 is a foreground system. We compare the multiplicity
statistics of the Pleiades very low mass stars and brown dwarfs with
that of G- and K-type main-sequence stars in the solar neighborhood. We
find that there is some evidence for a deficiency of wide binary systems
(separation &gt;27 AU) among the Pleiades very low mass members. We
briefly discuss how this result can fit with current scenarios of brown
dwarf formation. We correct the Pleiades substellar mass function for
the contamination of cluster nonmembers found in this work. We find a
contamination level of 33% among the brown dwarf candidates identified
by Bouvier et al. Assuming a power-law IMF across the substellar
boundary, we find a slope dN/dM~M-0.53, implying that the
number of objects per mass bin is still rising but the contribution
to the total mass of the cluster is declining in the brown dwarf
regime. Based in part on observations made with the NASA/ESA Hubble
Space Telescope, obtained at the Space Telescope Science Institute,
which is operated by the Association of Universities for Research in
Astronomy, Inc., under NASA contract NAS 5-26555. These observations
are associated with proposal ID 7952.

---------------------------------------------------------
Title: Rotation and H-alpha Emission Above and Below the Substellar
Boundary
Authors: Basri, Gibor
2000astro.ph..9252B Altcode:
I present the results of a multiyear survey of very low mass stars
and brown dwarfs, at high spectral resolution. The spectra were
gathered with the HIRES echelle at the Keck Observatory. Some of these
objects are stellar and others are substellar (or ambiguous). Early
indications that such objects can be rapidly rotating but display
little H-alpha emission turn out to be commonly true. This is the
opposite of the relation between rotation and activity in solar-type
stars. The H-alpha surface flux drops precipitously at the bottom
of the main sequence, and seems to be related to the luminosity
or temperature of the objects. There is a general trend to higher
rotation velocities as one looks at objects of lower luminosity. I
discuss several possible explanations for these results. The dynamos
for these objects are probably fully turbulent, driven by convection,
and thus more directly related to the object's luminosity. They may be
quenched when the rotational velocities become too fast in comparison
to the convective velocities (supersaturation). Another possibility is
that the atmospheres of the cooler objects are becoming sufficiently
neutral to decouple atmospheric motions from the field. Either of
these could explain why young brown dwarfs can be magnetically active
while older brown dwarfs are not. A final possibility is that instead
of being quenched, the field configuration in rapid rotators changes
to a less conducive form for dissipative heating. This could explain
why flares are occasionally seen on generally inactive objects.

---------------------------------------------------------
Title: The Balmer Wavelength Range of BP Tauri
Authors: Ardila, David R.; Basri, Gibor
2000ApJ...539..834A Altcode: 2000astro.ph..3313A
We have analyzed all the observations of BP Tauri taken by the
International Ultraviolet Explorer (IUE) in the low-resolution (Δλ~6
Å), long-wavelength (λ=1850-3350 Å) range. This data set contains
61 spectra. We observe variability in the ultraviolet continuum of
Δmcont.~1 mag and variability in the Mg II line flux
of ΔmMgII~0.8 mag. Moreover, these spectra do not show
any correlation between the continuum flux and the Mg II line flux,
thus resolving a standing controversy in the literature concerning
the origin of the Mg II line flux. There is no correlation between
the color temperature of the UV continuum and the average value of its
flux. Using models of the accretion process recently developed by other
authors, we obtain energy fluxes, accretion spot sizes, and accretion
rates from the IUE observations of BP Tauri. We find average energy
fluxes of 5.0×1011 ergs cm-2 s- 1,
average spot sizes of 4.4×10-3 times the stellar surface,
and average accretion rates of 1.6×10-8 Msolar
yr-1. Our analysis shows that the particle energy flux and
the UV flux in the stellar surface are proportional to each other. Most
strikingly, we observe a correlation between accretion rate and spot
size, with the spot size increasing as the square of the accretion
rate. Based on the results of a simulation, we conclude that geometrical
effects (i.e., the varying inclination of the spot with respect to the
observer) are not enough to account for this effect. Current models
of the accretion process fail to reproduce such an effect, suggesting
the need of using more realistic descriptions of the stellar field
when treating magnetospheric accretion. There may also be an unmodeled
efficiency factor that determines how matter is loaded into the field
lines. Nondipole fields, geometry, oblique shocks, and the possibility
of “limb brightening” should be taken into account when creating
models and explaining the results of observations of T Tauri stars.

---------------------------------------------------------
Title: Chandra Detection of an X-Ray Flare from the Brown Dwarf
LP 944-20
Authors: Rutledge, Robert E.; Basri, Gibor; Martín, Eduardo L.;
Bildsten, Lars
2000ApJ...538L.141R Altcode: 2000astro.ph..5559R
We have detected a bright X-ray flare from the nearby (d=5.0 pc)
brown dwarf LP 944-20 with the Chandra Advanced CCD Imaging
Spectrometer-S. This is an old (500 Myr), rapidly rotating,
lithium-bearing M9 object, with a bolometric luminosity of
~6×1029 ergs s-1. It was detected
only by Chandra during an X-ray flare of duration 1-2 hr near
the end of a 12.1 hr observation. The peak X-ray luminosity
was 1.2+0.5-0.3×1026
ergs s-1 in the brightest ~550 s, corresponding
to LX/Lbol~2×10-4. A
total of 2×1029 ergs was released during
the 43,773 s observation, giving a time-averaged
LX/Lbol~7×10-6. LP 944-20 was
not detected before the flare, with a 3 σ upper limit on the
emission at LX/Lbol&lt;2×10-6
(LX&lt;1×1024 ergs s-1). This is
faint for a rapidly rotating late-type star and establishes a record
lower limit to the quiescent flux about an order of magnitude below the
flux limit (and a factor of 5 below the LX/Lbol
limit) placed on quiescent X-ray emission from the M8 dwarf VB 10. The
inferred flaring duty cycle is comparable to that measured via variable
Hα emission for other late M-type, fully convective stars.

---------------------------------------------------------
Title: An Effective Temperature Scale for Late-M and L Dwarfs,
from Resonance Absorption Lines of Cs I and Rb I
Authors: Basri, Gibor; Mohanty, Subhanjoy; Allard, France; Hauschildt,
Peter H.; Delfosse, Xavier; Martín, Eduardo L.; Forveille, Thierry;
Goldman, Bertrand
2000ApJ...538..363B Altcode: 2000astro.ph..3033B
We present Keck HIRES spectra of six late-M dwarfs and 11 L dwarfs. Our
goal is to assign effective temperatures to the objects using detailed
atmospheric models and fine analysis of the alkali resonance absorption
lines of Cs I and Rb I. These yield mutually consistent results (+/-50
K) when we use “cleared-dust” models, which account for the removal
of refractory species from the molecular states but do not include dust
opacities. We find a tendency for the Rb I line to imply a slightly
higher temperature, which we ascribe to an incomplete treatment of
the overlying molecular opacities. The final Teff we adopt
are based on the Cs I fits alone, though the Rb I fits support the Cs
I temperature sequence. This work, in combination with results from
the infrared, hints that dust in these atmospheres has settled out of
the high atmosphere but is present in the deep photosphere. We also
derive radial and rotational velocities for all the objects, finding
that the previously discovered trend of rapid rotation for very low
mass objects is quite pervasive. To improve on our analysis, there
is a clear need for better molecular line lists and a more detailed
understanding of dust formation and dynamics.

---------------------------------------------------------
Title: A Survey for Low-Mass Stars and Brown Dwarfs in the Upper
Scorpius OB Association
Authors: Ardila, David; Martín, Eduardo; Basri, Gibor
2000AJ....120..479A Altcode: 2000astro.ph..3316A
The Upper Scorpius association is the OB association nearest to the Sun
(145 pc). Its young age (~5 Myr) makes it an ideal place to search for
low-mass stars and brown dwarfs, as these objects should be relatively
bright. We have performed a photometric search for the low-mass members
of the association, using the R, I, and Z filters. The completeness
limit is I~18.5, and the saturation limit is I~13. We obtain 138
candidate members, covering nearly the entire M spectral type range. We
find an excess of brown dwarf candidates over the number predicted by
a Miller-Scalo initial mass function. In addition, we have performed
infrared imaging and low-resolution optical spectroscopy of selected
candidates. We find that the infrared observations confirm the spectral
types obtained with the optical photometry. Furthermore, we find Hα
in emission in 20 of the 22 objects observed spectroscopically. As Hα
is an indicator of youth, we believe that these 20 objects may belong
to the association. One of them, UScoCTIO 128, has a very strong and
constant Hα line (equivalent width -130 Å), and its position in the
color-magnitude diagram suggests that it is a brown dwarf with mass
0.02 Msolar. Confirmation of this and the other candidates
will have to wait for higher resolution observations that can reveal
spectroscopic mass indicators such as Li I and gravity indicators such
as K I and the subordinate lines of Na I.

---------------------------------------------------------
Title: Spectroscopy of Inner Protoplanetary Disks and the Star-Disk
Interface
Authors: Najita, J. R.; Edwards, S.; Basri, G.; Carr, J.
2000prpl.conf..457N Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The discovery of brown dwarfs.
Authors: Basri, G.
2000SciAm.282d..76B Altcode:
Less massive than stars but more massive than planets, brown dwarfs
were long assumed to be rare. New sky surveys, however, show that the
objects may be as common as stars.

---------------------------------------------------------
Title: Profiles of Strong Permitted Lines in Classical T Tauri Stars
Authors: Alencar, Silvia H. P.; Basri, Gibor
2000AJ....119.1881A Altcode: 2000astro.ph..1322A
We present a spectral analysis of 30 T Tauri stars observed with the
Hamilton echelle spectrograph over more than a decade. One goal is to
test magnetospheric accretion model predictions. Observational evidence
previously published supporting the model, such as emission-line
asymmetry and a high frequency of redshifted absorption components,
are considered. We also discuss the relation between different
line-forming regions and search for good accretion rate indicators. In
this work we confirm several important points of the models, such
as the correlation between accretion and outflow, broad emission
components that are mostly central or slightly blueshifted, and
only the occasional presence of redshifted absorption. We also show,
however, that the broad emission components supposedly formed in the
magnetospheric accretion flow only partially support the models. Unlike
the predictions, they are sometimes redshifted and are mostly found to
be symmetric. The published theoretical profiles do not have a strong
resemblance to our observed ones. We emphasize the need for accretion
models to include a strong turbulent component before their profiles
will match the observations. The effects of rotation, as well as the
outflow components, will also be needed to complete the picture. Based
on observations obtained at Lick Observatory.

---------------------------------------------------------
Title: Accretion-induced Lithium Line Enhancements in Classical T
Tauri Stars: RW Aurigae
Authors: Stout-Batalha, N. M.; Batalha, C. C.; Basri, G. S.
2000ApJ...532..474S Altcode: 1999astro.ph.11508S
It is widely accepted that much of the stochastic variability of T Tauri
stars is due to accretion by a circumstellar disk. The emission-line
spectrum as well as the excess continuum emission are common probes
of this process. In this communication, we present additional probes
of the circumstellar environment in the form of resonance lines of
low ionization potential elements. Using a set of 14 high-resolution
echelle observations of the classical T Tauri star (CTTS) RW Aur, taken
between 1986 and 1996, we carefully measure the continuum veiling at
each epoch by comparing more than 500 absorption lines with those of
an appropriate template. This allows us to accurately subtract out
the continuum emission and to recover the underlying photospheric
spectrum. In doing so, we find that selected photospheric lines are
enhanced by the accretion process, namely, the resonance lines of Li I
and K I. A resonance line of Ti I and a low excitation potential line of
Ca I also show weak enhancements. Simple slab models and computed line
bisectors lead us to propose that these line enhancements are markers
of cool gas at the beginning of the accretion flow which provides an
additional source of line opacity. These results suggest that published
values of surface lithium abundances of classical T Tauri stars are
likely to be overestimated. This would account for the various reports
of surface lithium abundances in excess of meteoritic values among the
extreme CTTSs. Computing LTE lithium abundances of RW Aur in a low and
then high accretion state yields abundances which vary by 1 order of
magnitude. The low accretion state lithium abundance is consistent with
theoretical predictions for a star of this age and mass, while the high
accretion state spectrum yields a supermeteoritic lithium abundance.

---------------------------------------------------------
Title: Approaching the Deuterium Burning Limit in the σ Orionis
Young Cluster
Authors: Zapatero Osorio, M. R.; Béjar, V.; Martín, E. L.; Rebolo,
R.; Basri, G.
2000fepc.conf..446Z Altcode:
We have obtained J photometry for a sample of 12 objects in the
interval 16.0 &lt; I &lt;= 20.5 which are member candidates in the
young σ Orionis cluster. Our data confirms that 11 of them do fit the
photometric sequence expected for the cluster implying their very likely
membership in σ Orionis. Their masses span from 0.09 Modot
down to the very low-mass brown dwarf regime at the very young age
(1--5 Myr) of the cluster. We have also obtained low-resolution
spectroscopy for the faintest object in our sample, SOri 47 (I =
20.5). We classify it as an early L-type young brown dwarf with a
very likely mass around the deuterium burning limit. SOri 47 provides
evidence that the initial mass function extends down to masses of the
order of 0.015 Modot and serves as a guide for the study
of the new L-class discoveries in the field.

---------------------------------------------------------
Title: Aspects of the Substellar Mass Function
Authors: Basri, Gibor
2000fepc.conf..429B Altcode:
The best method we have at the moment for finding the substellar mass
function is the study of young clusters. These have the advantages
that 1) the stellar mass function for the same environment is known, 2)
the brown dwarfs are all at the same (known) age as are the stars, 3)
effects of dynamical evolution are minimized the younger the cluster
(and the brightness of brown dwarfs is maximized). Rather than
concentrate on this method, I consider issues relevant to two other
methods that are also being employed to study the substellar mass
function: brown dwarfs as companions to stars, and brown dwarfs in the
field. I argue that the impression of a brown dwarf "desert" that arose
from radial velocity studies of solar-type stars is misleading (although
there is a "desert island" associated with this class ofobject). I also
discuss the difficulties in finding a mass function in the field, and
the use of lithium and luminosity distributions to help constrain it.

---------------------------------------------------------
Title: Observations of Brown Dwarfs
Authors: Basri, Gibor
2000ARA&A..38..485B Altcode:
The brown dwarfs occupy the gap between the least massive star and
the most massive planet. They begin as dimly stellar in appearance and
experience fusion (of at least deuterium) in their interiors. But they
are never able to stabilize their luminosity or temperature and grow
ever fainter and cooler with time. For that reason, they can be viewed
as a constituent of baryonic "dark matter." Indeed, we currently have
a hard time directly seeing an old brown dwarf beyond 100 pc. After 20
years of searching and false starts, the first confirmed brown dwarfs
were announced in 1995. This was due to a combination of increased
sensitivity, better search strategies, and new means of distinguishing
substellar from stellar objects. Since then, a great deal of progress
has been made on the observational front. We are now in a position to
say a substantial amount about actual brown dwarfs. We have a rough idea
of how many of them occur as solitary objects and how many are found
in binary systems. We have obtained the first glimpse of atmospheres
intermediate in temperature between stars and planets, in which dust
formation is a crucial process. This has led to the proposal of the
first new spectral classes in several decades and the need for new
diagnostics for classification and setting the temperature scale. The
first hints on the substellar mass function are in hand, although all
current masses depend on models. It appears that numerically, brown
dwarfs may well be almost as common as stars (though they appear not
to contain a dynamically interesting amount of mass).

---------------------------------------------------------
Title: VizieR Online Data Catalog: Keck/HIRES Sky Line Atlas
(Osterbrock+ 1997)
Authors: Osterbrock, D. E.; Fulbright, J. P.; Martel, A. R.; Keane,
M. J.; Trager, S. C.; Basri, G.
2000yCat.3211....0O Altcode:
This catalog provides a list of atmospheric OH and O2 lines that are
useful for wavelength calibration of high resolution spectra. Tables
of observed OH lines, and calculated wavelengths for molecular oxygen
(O2) are given; the journal of the observations is found in the "Tables
1" section below, and spectra with identified lines are provided as
postscript figures, which are summarized in the "figs.dat" file. (3
data files).

---------------------------------------------------------
Title: The discovery of brown dwarfs.
Authors: Basri, G.
2000SciAm.282d..57B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High Resolution Spectra of L Type Stars and Brown Dwarfs
Authors: Basri, G.; Allard, F.; Hauschildt, P.; Mohanty, S.
2000vlms.conf..133B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Spectroscopic Classification of Late-M and L Field Dwarfs
Authors: Martín, Eduardo L.; Delfosse, Xavier; Basri, Gibor; Goldman,
Bertrand; Forveille, Thierry; Zapatero Osorio, Maria Rosa
1999AJ....118.2466M Altcode:
We present spectra for 12 new ultracool dwarfs found in the DENIS
infrared survey. Seven of them have spectral types at the bottom of
the M-class (M8-M9.5), and the other five belong to the cooler “L”
class. We also present spectra for the two new L dwarfs found by
the EROS 2 proper-motion survey. We introduce a scheme for L dwarf
classification that is based on an extension to cooler spectra of a
pseudocontinuum ratio previously defined for M dwarfs. For calibrating
the spectral subclasses, we use a temperature scale for late-M and
L dwarfs recently obtained by Basri et al. from synthetic spectrum
fitting of high-resolution profiles of Cs I and Rb I resonance
lines. We define that the subclass range from L0 to L6 corresponds
to the temperature range from 2200 K to 1600 K. Our subclasses L0,
L1, and L2 agree with recent findings by Kirkpatrick et al., but then
they diverge such that our L6 is equivalent to their L8. We find that
late-M and L dwarf subclasses can be assigned either in the optical
with the PC3 index or in the near-infrared with the H2O
H-band index. We discuss the main photospheric features present in L
dwarf spectra, in particular in the region 400-650 nm, which has never
been shown before. The TiO bands at 549.7, 559.7, 615.9, and 638.4 nm
fade with decreasing temperature, but do not vanish until well inside
the L domain (~L5). The Na I 589.0, 589.6 nm resonance doublet in
our latest object (L6) becomes the broadest atomic feature ever seen
in any cool dwarf. We do not detect Hα emission in our L
dwarfs later than L3. We discuss the ages and masses of our objects
using their temperatures and absence or presence of lithium. Finally,
we compare two L1 dwarfs with different gravities (one with lithium
and one without it) and discuss differences in spectral features.

---------------------------------------------------------
Title: PPL 15: The First Brown Dwarf Spectroscopic Binary
Authors: Basri, Gibor; Martín, Eduardo L.
1999AJ....118.2460B Altcode: 1999astro.ph..8015B
PPl 15 is the first object to have been confirmed as a brown dwarf
by the lithium test (in 1995), though its inferred mass was very
close to the substellar limit. It is a member of the Pleiades open
cluster. Its position in a cluster color-magnitude diagram suggested
that it might be binary, and preliminary indications that it is a
double-lined spectroscopic binary were reported by us in 1997. Here we
report on the results of a consecutive week of Keck HIRES observations
of this system, which yield its orbit. It has a period of about 5.8
days, and an eccentricity of 0.4+/-0.05. The rotation of the stars
is slow for this class of objects. Because the system luminosity is
divided between two objects with a mass ratio of 0.85, each of them is
rendered an incontrovertible brown dwarf, with masses between 60 and
70 MJ. We show that component B is a little redder than A by
studying their wavelength-dependent line ratios and that this variation
is compatible with the mass ratio. We confirm that the system has
lithium but cannot support the original conclusion that it is depleted
(which would be surprising, given the new masses). This is a system of
very close objects, which, if they had combined, would have produced
a low-mass star. We discuss the implications of this discovery for
the theories of binary formation and formation of very low mass objects.

---------------------------------------------------------
Title: An L-Type Substellar Object in Orion: Reaching the Mass
Boundary between Brown Dwarfs and Giant Planets
Authors: Zapatero Osorio, M. R.; Béjar, V. J. S.; Rebolo, R.; Martín,
E. L.; Basri, G.
1999ApJ...524L.115Z Altcode: 1999astro.ph..8223Z; 1999astro.ph..8223O
We present near-infrared photometry (J band) and low-resolution
optical spectroscopy (600-1000 nm) for one of the faintest substellar
member candidates in the young σ Orionis cluster, S Ori 47 (I=20.53;
Béjar, Zapatero Osorio, &amp; Rebolo). Its very red (I-J) = 3.3+/-0.1
color and its optical spectrum allow us to classify S Ori 47 as an
L1.5-type object that fits the low-luminosity end of the cluster
photometric and spectroscopic sequences. It also displays atmospheric
features indicative of low gravity, such as weak alkaline lines and
hydride and oxide bands, consistent with the expectation for a very
young object still undergoing gravitational collapse. Our data lead
us to conclude that S Ori 47 is a true substellar member of the σ
Orionis cluster. Additionally, we present the detection of Li I in
its atmosphere, which provides an independent confirmation of youth
and substellarity. Using current theoretical evolutionary tracks and
adopting an age interval of 1-5 Myr for the σ Orionis cluster, we
estimate the mass of S Ori 47 to be 0.015+/-0.005 Msolar,
i.e., at the minimum mass for deuterium burning, which has been
proposed as a definition for the boundary between brown dwarfs and
giant planets. S Ori 47 could well be the result of a natural extension
of the process of cloud fragmentation down to the deuterium-burning
mass limit; a less likely alternative is that it has originated from
a protoplanetary disk around a more massive cluster member and was
later ejected from its orbit because of interacting effects within
this rather sparse (~12 objects pc-3) young cluster. The
study of this object serves as a guide for future deep searches for
free-floating objects with planetary masses.

---------------------------------------------------------
Title: The End of Stellar Coronae?
Authors: Basri, Gibor
1999cxo..prop...98B Altcode:
Almost all stars are X-ray emitters. Convective stars are thought to
have analogs of the solar corona, caused by magnetic activity which in
turn is produced by a dynamo. There are reasons to believe that the
dynamo and coronal heating could change character near the bottom of
the main sequence. We get to the heart of this by going to the very
bottom of the main sequence, and below to the brown dwarf regime. We
test 2 of the nearest known such objects to see if they lie beyond
the end of the realm of stellar coronae.

---------------------------------------------------------
Title: Evidence of a supernova origin for the black hole in the
system GRO J1655 - 40
Authors: Israelian, G.; Rebolo, R.; Basri, G.; Casares, J.; Martín,
E. L.
1999Natur.401..142I Altcode:
Stars with masses greater than about ten solar masses are thought to end
their lives either in a supernova or in a direct gravitational collapse
process, either of which could have a black hole as a remnant. But
there is as yet no direct observational evidence to support either
gravitational collapse in general or the formation of black hole
remnants in particular. Here we report a large overabundance of oxygen,
magnesium, silicon and sulphur in the atmosphere of the star orbiting
a probable black hole in the binary system GRO J1655-40 (also known as
Nova Scorpii 1994). These α-elements are six to ten times more abundant
in the star's atmosphere than they are in the Sun's. We interpret
these high abundances as evidence for supernova ejecta captured by the
companion star. The relative abundances of these elements suggest that
the supernova progenitor was in the mass range 25-40 solar masses.

---------------------------------------------------------
Title: The Lithium Test in Young Brown Dwarf Candidates
Authors: Martín, E. L.; Basri, G.; Zapatero Osorio, M. R.
1999AJ....118.1005M Altcode:
We present high-, mid-, and low-resolution spectroscopy of the field
brown dwarf candidate PC 0025+0447 (M9.5) spanning a 4 yr baseline
(1994-1998). The strength of the emission lines and the amount of
optical veiling are very variable. Our spectra taken at an epoch
of low veiling allow us to detect the lithium resonance line, which
was not detected when the veiling was high. The presence of lithium
proves that PC 0025+0447 is a substellar object less massive than
~0.06 M_solar and younger than ~1 Gyr. We also present mid-resolution
spectra of three brown dwarf candidates in star-forming regions, namely
rho Oph 162349.8-242601 (M8.5), V410 Tau X3 (M6.5), and V410 Tau X6
(M6). Lithium is detected in all of them, supporting their very young
age. Of these three objects, only the one in rho Oph is sufficiently
cool to warrant an unambiguous substellar status. The spectroscopic
characteristics that PC 0025+0447 and rho Oph 162349.8-242601 have in
common are moderately strong Li I lines (pseudo-equivalent width ~1 Å),
persistent Hα emission with equivalent width greater than 50 Å, and
weaker K I and Na I lines than field dwarfs of the same spectral type.

---------------------------------------------------------
Title: Rapid Rotation Above and Below the Substellar Boundary
Authors: Basri, G.
1999AAS...194.8208B Altcode: 1999BAAS...31..968B
I present the results of a multiyear survey of very low mass stars and
brown dwarfs, at high spectral resolution. The echelle spectra were
gathered with the HIRES spectrometer at the Keck Observatory. One
primary purpose was to determine rotational velocities for many
objects of the late M and L spectral classes. Some of these objects
are confirmed brown dwarfs, others are stars near the bottom of the
main sequence, and some might be either. I show that the initial
indication provided by BRI 0021, that such objects tend to be rapidly
rotating and display little H-alpha emission, proves to be a common
characteristic. There is a general trend to higher rotation velocities
as one looks to objects of lower luminosity; the fastest rotator found
so far is the brown dwarf Kelu-1 at 80 km/s (which implies a rotation
period of about 90 minutes!). The most active object, PC 0025 (which
may well be a brown dwarf), is a relatively slow rotator and probably
very young. I discuss a possible explanation for these results: the
dynamos for these objects are fully turbulent, driven by convection (and
therefore indirectly by the object's luminosity), and quenched when the
rotational velocities become too fast in comparison to the convective
velocities. I thank the NSF for its support through grant AST96-18439.

---------------------------------------------------------
Title: A Search for Companions to Nearby Brown Dwarfs: The Binary
DENIS-P J1228.2-1547
Authors: Martin, E. L.; Brandner, W.; Basri, G.
1999Sci...283.1718M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Nature of Young Brown Dwarf Candidates
Authors: Martin, Eduardo; Ardila, David; Basri, Gibor
1999noao.prop...20M Altcode:
We want to study the nature of brown dwarf (BD) candidates that
we have found in a wide CCD survey of the open clusters IC 2391
and IC2602 and the OB association Upper Sco. Our BD candidates are
interesting because they are expected to be much younger and thus
brighter than in the Pleiades, where most cluster BDs have been
found so far. We will thus constrain the substellar mass function
in different environments. Furthermore, we will be able to compare
the new brown dwarfs with those found in the Pleiades to study
evolutionary effects. The near-IR observations will help to establish
the luminosity and thus place the objects in the HR diagram and compare
with evolutionary tracks and isochrones. The spectroscopic observations
will be used to determine membership. This is the most important step
towards asserting the BD status of the candidates.

---------------------------------------------------------
Title: The Mass and Age of Very Low Mass Members of the Open Cluster
α Persei
Authors: Basri, Gibor; Martín, Eduardo L.
1999ApJ...510..266B Altcode: 1998astro.ph..7145B
We present spectroscopic optical and photometric infrared observations
of 12 faint candidate members of the young open cluster α Persei
found by Prosser in 1994. Keck HIRES echelle spectra provide radial
and rotational velocity measurements for five objects, two of which
are clearly nonmembers based on the radial velocities. These kinematic
nonmembers also do not fit well in the (V-I) versus (I-J) cluster
sequence. One additional faint object is likely a nonmember based
on a low-resolution spectrum. Using HIRES, we have searched for the
Li I resonance line. Combining the absence/presence of lithium and
photometry of the faint α Persei targets with confirmed membership
constrains their ages and masses. The lack of lithium in AP J0323+4853
implies that its age is greater than about 65 Myr, which is older
than the cluster classical upper main-sequence turnoff age of 50
Myr. A similar age discrepancy is found in the Pleiades. We detect
lithium in the faintest of our program stars, AP 270, which implies a
mass for it just at the substellar mass limit, given our adopted age
and its luminosity. The membership of AP 281 is in question because
of its high radial velocity compared with the cluster mean. On the
other hand, AP 281 lies on the photometric cluster sequence and has
a very high rotation velocity and Hα emission, indicating youth. If
it is a member, its lack of lithium would push the minimum age of the
cluster to 75 Myr, in agreement with a very recent upper main-sequence
determination. In that case, AP 270 would not be a brown dwarf.

---------------------------------------------------------
Title: Brown Dwarfs: The First Three Years
Authors: Basri, Gibor B.
1999RvMA...12..187B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Discovery of a Very Low Mass Binary with the Hubble Space
TelescopeNear-Infrared Camera and Multiobject Spectrometer
Authors: Martín, E. L.; Basri, G.; Brandner, W.; Bouvier, J.; Zapatero
Osorio, M. R.; Rebolo, R.; Stauffer, J.; Allard, F.; Baraffe, I.;
Hodgkin, S. T.
1998ApJ...509L.113M Altcode:
Hubble Space Telescope Near-Infrared Camera and Multiobject Spectrometer
(NICMOS) observations of six brown dwarf candidates in the Pleiades
open cluster are presented. One of them, namely CFHT-Pl-18, is clearly
resolved as a binary with an angular separation of 0.33". The very
low density of contaminating background stars in our images and the
photometry of the components support that this system is a physical
binary rather than a chance projection. All of the available photometric
and spectroscopic data indicate that the CFHT-Pl-18 system is likely
a member of the Pleiades cluster, but a final confirmation will have
to wait until lithium can be detected. Assuming cluster membership,
we compare our NICMOS photometry with evolutionary models and find that
the inclusion of the effects of dust grains is necessary for fitting the
data. We estimate that the masses of the components are about 0.045 and
0.035 Msolar. The binary system has a projected separation of
42 AU (for a distance of 125 pc) that is common among stellar binaries.

---------------------------------------------------------
Title: The First L-Type Brown Dwarf in the Pleiades
Authors: Martín, E. L.; Basri, G.; Zapatero-Osorio, M. R.; Rebolo,
R.; López, R. J. García
1998ApJ...507L..41M Altcode: 1998astro.ph..9031M
We have obtained low-resolution optical spectra of three faint brown
dwarf candidates in the Pleiades open cluster. The objects observed
are Roque 12 (IC=18.5), Roque 5 (IC=19.7),
and Roque 25 (IC=21.2). The spectrum of Roque 25 does not
show the strong TiO band heads that characterize the optical spectra
of M-type stars, but molecular bands of CaH, CrH, and VO are clearly
present. We classify Roque 25 as an early L-type brown dwarf. Using
current theoretical evolutionary tracks we estimate that the transition
from M type to L type in the Pleiades (age ~120 Myr) takes place
at Teff~2200 K or M~0.04 Msolar. Roque 25 is a
benchmark brown dwarf in the Pleiades because it is the first known one
that belongs to the L-type class. It provides evidence that the initial
mass function (IMF) extends down to about 0.035 Msolar
and serves as a guide for future deep searches for even less massive
young brown dwarfs.

---------------------------------------------------------
Title: Discovery of a Very Low-Mass Binary with HST/NICMOS
Authors: Martin, E. L.; Basri, G.; Brandner, W.; Bouvier, J.; Zapatero
Osorio M., R.; Rebolo, R.; Stauffer, J.; Allard, F.; Baraffe, I.;
Hodgkin, S. T.
1998astro.ph.10387M Altcode: 1998astro.ph.10387L
Hubble Space Telescope NICMOS observations are presented of six brown
dwarf candidates in the Pleiades open cluster. One of them, namely
CFHT-Pl-18, is clearly resolved as a binary with an angular separation
of 0".33. The very low density of contaminating background stars in our
images and the photometry of the components support that this system
is a physical binary rather than a chance projection. All the available
photometric and spectroscopic data indicate that the CFHT-Pl-18 system
is likely a member of the Pleiades cluster, but a final confirmation
will have to wait until lithium can be detected. Assuming cluster
membership, we compare our NICMOS photometry with evolutionary models,
and find that the inclusion of the effects of dust grains is necessary
for fitting the data. We estimate that the masses of the components
are about 0.045 Msol and 0.035 Msol. The binary system has a projected
separation of 42 AU (for a distance of 125 pc) that is common among
stellar binaries.

---------------------------------------------------------
Title: A New Pleiades Member at the Lithium Substellar Boundary
Authors: Martín, E. L.; Basri, G.; Gallegos, J. E.; Rebolo, R.;
Zapatero-Osorio, M. R.; Bejar, V. J. S.
1998ApJ...499L..61M Altcode: 1998physics...3026M
We present the discovery of an object in the Pleiades open cluster,
named Teide 2, with optical and infrared photometry that places it
on the cluster sequence slightly below the expected substellar mass
limit. We have obtained low- and high-resolution spectra that allow us
to determine its spectral type (M6), radial velocity, and rotational
broadening and to detect Hα in emission and Li I in absorption. All
the observed properties strongly support the membership of Teide 2
in the Pleiades. This object has an important role in defining the
reappearance of lithium below the substellar limit in the Pleiades. The
age of the Pleiades' very low mass members, based on their luminosities
and the absence or presence of lithium, is constrained to be in the
range 100-120 Myr.

---------------------------------------------------------
Title: Brown Dwarfs in the Pleiades Cluster
Authors: Zapatero Osorio, M. R.; Rebolo, R.; Martin, E. L.; Basri,
G.; Magazzu, A.; Hodgkin, S. T.; Cossburn, M. R.; Jameson, R. F.
1998ASPC..154.1912Z Altcode: 1998csss...10.1912Z
We have discovered a relatively large number of brown dwarf candidates
in the Pleiades young open cluster as a result of a deep CCD IZ survey
covering 1 deg^2 down to limiting magnitudes I ~22 and Z ~21. Follow-up
infrared photometry and low/intermediate-resolution spectroscopy of
seven of our candidates in the interval 20 &gt; I &gt; 17.8 allow us
to investigate their membership in the Pleiades. The observed spectra
show that these objects are very cool dwarfs (M6-M9). Five of them can
be considered as cluster members on the basis of their spectroscopic
and photometric properties. Given their low luminosity and according
to current evolutionary models, we estimate their masses to range
from roughly 80 M_Jup for the hottest object, down to 45 M_Jup for
Roque 4, the coolest and faintest confirmed member. We observe some
differences in the spectra of our least massive Pleiades brown dwarfs
in comparison to field stars of very late spectral types and similar
effective temperatures. They may be related to gravity effects and the
presence of dust in the atmospheres. The brown dwarfs discovered in
the Pleiades prove that the process of fragmentation of clouds extend
well into the substellar realm, suggesting a rise in the inital mass
function below the star-BD boundary.

---------------------------------------------------------
Title: PPL 15: the First Binary Brown Dwarf System?
Authors: Basri, G.; Martin, E. L.
1998ASPC..134..284B Altcode: 1998bdep.conf..284B
No abstract at ADS

---------------------------------------------------------
Title: Revealing the Brown Dwarf Population in the Pleiades Open
Cluster
Authors: Zapatero Osorio, M. R.; Rebolo, R.; Martin, E. L.; Hodgkin,
S. T.; Jameson, R. F.; Cossburn, M. R.; Magazzu, A.; Basri, G.;
Steele, I. A.
1998ASPC..134...51Z Altcode: 1998bdep.conf...51Z
No abstract at ADS

---------------------------------------------------------
Title: Surveying low mass stars with SALT: newborn and stillborn.
Authors: Basri, G.
1998salt.conf..127B Altcode:
The SALT/HET telescopes are unique for several reasons. One of them is
the need for queue scheduling, given the visibility characteristics of
targets. The author argues here that this can be viewed as a virtue,
allowing exploration of the time domain in Astronomy. Traditional
scheduling on very large telescopes has practically precluded such
programs, giving SALT/HET a valuable niche to perform truly unique
science. While there are many subjects which would greatly benefit from
time coverage, the author concentrates here on the subject of low mass
star formation. He shows that only through synoptic observations can
one hope to gain an understanding of the crucial star-disk interface
zone, where disk material is both loaded down onto the star and is
flung out in bipolar outflows, solving and regulating the buildup
of both mass and angular momentum in the new star. The author also
discusses the use of SALT/HET in the new area of substellar objects,
both brown dwarfs and extrasolar planets.

---------------------------------------------------------
Title: The First Line Profiles from Cool Field Brown Dwarfs
Authors: Basri, G.; Martin, E.; Ruiz, M. T.; Delfosse, X.; Forveille,
T.; Epchtein, N.; Allard, F.; Leggett, S. K.
1998ASPC..154.1819B Altcode: 1998csss...10.1819B
The empirical study of confirmed brown dwarfs began in 1995. Until
this year, however, no ironclad examples of free-floating field brown
dwarfs have been confirmed. Recently three excellent candidates have
been discovered --- bright enough to obtain high resolution spectra
with the Keck 10-m telescope. Two of our targets clearly show the
lithium resonance line which, given their temperatures, ensures that
they are true brown dwarfs. We discuss several line profiles from these
exciting new objects. We provide constraints on their mass and age based
on simple arguments involving their lithium content and temperatures.

---------------------------------------------------------
Title: The Lithium Test for Young Brown Dwarfs (invited review)
Authors: Basri, G.
1998ASPC..134..394B Altcode: 1998bdep.conf..394B
I discuss the successful application of the "lithium test" to the
problem of distinguishing young brown dwarfs from true stars, given
that they occupy overlapping regions of effective temperature and
luminosity. In simple terms, stars will burn lithium in at most 100
Myr, while brown dwarfs may never reach the core temperature required
to do so. The minimum lithium burning mass is not the same as the
minimum stellar mass however, introducing some subtleties into the
lithium test. I discuss the history of this subject, leading up to
its successful application in the Pleiades. In addition to verifying
substellar status, observations of lithium can be used to assess the
age of stars in clusters, which is helpful in the proper usage of the
lithium test itself. I also discuss how lithium observations of very
cool objects can be useful in constraining the nature of brown dwarf
candidates both in the field and in star forming regions.

---------------------------------------------------------
Title: New Brown Dwarfs in the Pleiades Cluster
Authors: Zapatero Osorio, M. R.; Rebolo, R.; Martín, E. L.; Basri,
G.; Magazzù, A.; Hodgkin, S. T.; Jameson, R. F.; Cossburn, M. R.
1997ApJ...491L..81Z Altcode: 1997astro.ph.10300O; 1997astro.ph.10300Z
We present intermediate- and low-resolution optical spectroscopy
(650-915 nm) of seven faint, very red objects (20&gt;I&gt;=17.8,
I-Z&gt;= 0.5) discovered in a CCD-based IZ survey covering an area of 1
deg2 in the central region of the Pleiades open cluster. The
observed spectra show that these objects are very cool dwarfs having
spectral types in the range M6-M9. Five out of the seven objects can
be considered Pleiades members on the basis of their radial velocities,
Hα emissions, and other gravity-sensitive atomic features like the Na I
doublet at 818.3 and 819.5 nm. According to current evolutionary models,
the masses of these new objects range from roughly 80 MJup
for the hottest in the sample down to 45 MJup for Roque 4,
the coolest and faintest confirmed member. These observations prove
that the cloud fragmentation process extends well into the brown
dwarf realm, suggesting a rise in the initial mass function below the
substellar limit.

---------------------------------------------------------
Title: Keck HIRES spectra of the brown dwarf DENIS-P J1228.2-1547
Authors: Martin, E. L.; Basri, G.; Delfosse, X.; Forveille, T.
1997A&A...327L..29M Altcode:
We report Keck high-resolution echelle spectroscopic observations
of two very cool field dwarfs discovered by the near-IR photometric
survey DENIS. DENIS-P J1228.2-1547 shows a conspicuous LiI resonance
line that confirms it as an incontrovertible brown dwarf (BD). From
the presence of Li, and its low surface temperature, we estimate from
theoretical models a mass and an age upper limit of ~ 60 jupiters and ~
10(9) years. The other DENIS object shows no detectable LiI line in our
data, and thus we infer a mass &gt;=60 jupiters for it. It could be a
high-mass BD or very low-mass star. Both objects have modest radial
velocities that suggest they are kinematically young. They show the
strongest and broadest resonance line profiles from low ionization
species ever seen. The extreme breadth of the KI lines are good further
indicators of the expected high gravity in very low-mass dwarfs. We
suggest a new spectral class, “L”, for objects cooler than M-type
(as these are) that do not show TiO molecular bands. The confirmation
of at least one field BD in only ~ 1% of the final DENIS survey is a
strong indication of the presence of a numerous population of these
objects in the solar neighborhood. Based on observations obtained at
the W.M. Keck Observatory, which is operated jointly by the University
of California and the Californian Institute of Technology.

---------------------------------------------------------
Title: The Temperature Scale and Mass Distribution of Hot DA White
Dwarfs
Authors: Finley, David S.; Koester, Detlev; Basri, Gibor
1997ApJ...488..375F Altcode:
Results are presented from a comprehensive spectroscopic survey of DA
white dwarfs hotter than ~25,000 K. The observations consisted of CCD
spectra with signal-to-noise ratios of ~100 in the blue, with ~5 Å
resolution. The majority of the spectra covered the wavelength range of
3500-7500 Å, allowing the detection of a number of cool companions. To
date, spectra have been obtained and analyzed for 174 DA stars. The
spectra were analyzed using our model atmospheres, which are described
in detail here, resulting in temperatures and gravities with average
internal errors of 1% and 0.04 dex, respectively. Comparisons with
previously published results showed that temperature determinations
for Teff &lt; 30,000 K were generally consistent at the 1%
or better level, while spectroscopic gravity determinations based on the
latest models were consistent at the 0.02 dex level. Wood's evolutionary
sequences were used to derive masses for the observed stars with average
internal errors of 0.02 M⊙. The mass distribution for this
hot sample peaked at 0.570 M⊙, consistent with previous
spectroscopic results for cooler samples. One salient feature of
this hot sample is the presence of a significant number of massive
DA stars with Teff &lt; 50,000 K, many with M &gt; 1.1
M⊙. The ultramassive DA's comprise a much larger fraction
of the total than was the case for cooler samples. Calculations based
on white dwarf evolutionary models showed that a higher proportion
of massive white dwarfs is expected to be found in samples with
Teff &gt;~ 30,000 K as a result of differential cooling
effects. Within the range Teff &gt; 40,000 K, the
EUV-selected subsample did have proportionately more massive stars
than the optically selected subsample. However, a detailed comparison
showed that EUV and optical surveys were equally capable of detecting
relatively nearby massive white dwarfs. On the other hand, interstellar
EUV absorption eliminated from the EUV sample many of the more distant
stars that were detectable optically. Therefore, the apparent excess of
massive DA white dwarfs in the EUV sample is largely due to a relative
deficit of stars with more typical masses. Results are presented
for individual stars, including a number of subdwarf identifications
and reports of detections of cool companions. Properties of some of the
more interesting binaries are discussed. We also report on some stars
in the sample that evidently have varying He abundances. WD 0612+177
(G104-27) had been observed, at one point, to have photospheric He I;
we confirm that He has remained absent since then. WD 0718-316 (RE
0720-314) is in a post-common-envelope binary and has photospheric He
II, the abundance of which appears to vary by more than an order of
magnitude over timescales of months.

---------------------------------------------------------
Title: Hamilton Echelle Spectroscopy of the 1993 March 6 Solar Flare
Authors: Johns-Krull, Christopher M.; Hawley, Suzanne L.; Basri,
Gibor; Valenti, Jeff A.
1997ApJS..112..221J Altcode:
We report on a successful program that used the Hamilton echelle
spectrograph and the coudé auxiliary telescope at Lick Observatory
to take spectra of solar flares. Our observations consist of
high-resolution (λ/δλ ~ 48,000) spectra covering the entire optical
region from approximately 3800 to 9000 Å in each exposure. These
are the first time-resolved high-resolution optical spectra of this
type obtained for a solar flare. On 1993 March 6 we observed a
relatively large (GOES class M7.7) solar flare event. Our sequence of
observations began before flare maximum and continued for more than 1
hr. We present our high signal-to-noise spectra and compare them with
similar stellar flare observations. We find that the hydrogen-emitting
layers in flares on the Sun differ markedly from those in flares on dMe
stars, though the total energy emitted in various emission lines can be
rather similar. We also find that the amount of energy released in the
optical emission lines is similar to that emitted in soft X-rays. We
find evidence for Stark broadening in the Balmer lines for members
lower in the series than reported in earlier studies. This appears to
have occurred because the optical depth in the Balmer lines is lower
than in previously reported flares. Early in the flare, the Hα and
Hβ line profiles appear to be asymmetric as a result of absorption
by chromospheric material expanding upward into the corona. We also
examine solar flare model atmospheres synthesized with the non-LTE
code MULTI and find that our observations can be generally understood
in terms of equilibrium models of electron-beam- and X-ray-heated
chromospheres in equilibrium with coronal loops in which the pressure
is rather high; however, there remain marked differences between
the theoretical predictions and our observations, implying that
substantial refinement of the models is in order. Several photospheric
lines show flare enhancements as well. The temporal behavior of these
line enhancements is identical to that of the chromospheric lines,
but there is no indication that significant flare heating penetrates
to continuum formation depths. Based on observations obtained at
Lick Observatory, which is operated by the University of California.

---------------------------------------------------------
Title: The Classical T Tauri Spectroscopic Binary DQ Tau. II. Emission
Line Variations with Orbital Phase.
Authors: Basri, Gibor; Johns-Krull, Christopher M.; Mathieu, Robert D.
1997AJ....114..781B Altcode:
We report on echelle observations of a variety of line profiles taken
throughout the orbit of the close, eccentric binary T Tauri system
DQ Tau. The stars themselves exhibit puzzling inconsistencies in the
spectral types inferred from atomic vs. molecular lines. The system
shows clear evidence of an extensive circumbinary disk. The binary is
expected to clear a central hole in the disk, however the line profiles
are similar to those from single classical T Tauri stars. This indicates
that similar infall and outflow activities are taking place. The
implication is that material is flowing through the supposed gap
in the disk. It also means that these “classical” profiles do not
require a stable circumstellar disk for their formation, since the
stellar separation at periastron is too small to allow such disks. We
present evidence that accretion increases (sometimes dramatically) as
the stars approach each other. Both continuum veiling and emission line
intensities can increase. In one outburst the \caII IR lines brighten
by a factor of 5. We discuss the line profiles during such outbursts
in some detail. Along with increased accretion, the lines sometimes
also imply high velocity outflows. Given the fact that outbursts
can occur as much as 0.15 in phase away from closest approach, we
favor accretion over direct magnetospheric interactions as the power
source of the outbursts. Away from each other, the stars resemble
moderate- to low-activity classical T Tauri stars. There is evidence
that some material is stored near the stars and ingested throughout
the orbit. These observations are generally consistent with a model
for disks in binary systems proposed by \cite{al96}. The importance
of this system is that it provides empirical support for continuing
accretion through dynamical tidal gaps in disks. It demonstrates that
very close binaries can be classical T Tauri systems.

---------------------------------------------------------
Title: Ultraviolet Line Eclipses by Extrasolar Planets
Authors: Basri, Gibor
1997hst..prop.7508B Altcode:
One of the most exciting events in Astronomy last year was the discovery
of extrasolar planets. Even more exciting was the character of these
planets. Several were found to be around the mass of Jupiter, yet
located extremely close to their stars {4 day orbital periods}. While
no other plausible explanation for the Doppler variations which signal
their presence has been found, it would obviously be very important if
we could confirm the presence of physical bodies in orbit, and begin
to study their properties. Though there is reason to believe these
systems are seen almost edge on, direct eclipses by the planets have
been ruled out. The planets are likely to be losing a lot of hydrogen
from their exospheres due to their proximity to the stars. We will
look for eclipses due to Lyman alpha clouds around the short period
planets orbiting 51 Peg and Tau Boo. The expected size of the Lyman-
alpha clouds gives us 4 times the range of orbital inclination in which
to see eclipses. We will observe the stars during two consecutive
transits to distinguish between intrinsic variability and perodic
phenomena. This experiment has a plausible chance of succeeding,
with very exciting results if it does.

---------------------------------------------------------
Title: The Classical T Tauri Spectroscopic Binary DQ Tau.I.Orbital
Elements and Light Curves
Authors: Mathieu, Robert D.; Stassun, Keivan; Basri, Gibor; Jensen,
Eric L. N.; Johns-Krull, Christopher M.; Valenti, J. A.; Hartmann,
L. W.
1997AJ....113.1841M Altcode:
We report the discovery that the classical T Tauri star DQ Tan is
a double-lined spectroscopic binary. The orbital period is 15.804
days, with a large orbital eccentricity e=0.556. The mass ratio is
0.97±0.15. We have monitored DQ Tau photometrically over two observing
seasons and observed recurring episodes during which the stars get
brighter (≍0.5 mag in V) and bluer (≍-0.2 mag in V-I). When
combined with photometry in the literature (time span ≍5000 days),
a Scargle periodogram analysis reveals a highly significant periodicity
of 15.80 days, essentially identical to the binary orbital period. These
brightening events occur shortly before or at periastron passage. They
occur during at least 65% of periastron passages, but not during all
periastron passages. DQ Tau is surrounded by a circumbinary disk with
mass of 0.002-0.02 Msun. The infrared spectral energy
distribution resembles a power law from 1 to 60 μm. Remarkably,
there is no paucity of near-infrared emission indicative of the inner
disk having been cleared by the binary; there is clearly warm material
within the binary orbit. We interpret the brightening events as due to a
variable mass accretion rate regulated by the binary orbit. The periodic
brightenings, the associated increases in emission line strength and
veiling reported in an accompanying paper [Basri et al., submitted
(1997)], and the circumstellar material together are consistent with a
recent theoretical finding that circumbinary disk material can stream
across a binary orbit at certain orbital phases, resulting in a pulsed
accretion flow onto the stars [Artymowicz &amp; Lubow, ApJ, 467, L77
(1996)]. The theoretically predicted phase of maximum accretion rate is
shortly before periastron, in good agreement with the phasing of the
brightenings of DQ Tan. At the same time the periastron separation is
smaller than the inferred stellar magnetospheric radii of classical
T Tauri stars, so that such magnetospheres would interact at each
periastron passage. The magnetic energies are plausibly adequate
to power the brightenings. However, the strongly enhanced continuum
veiling and long duration of some of the brightenings are not naturally
explained in a pure flaring scenario. Nonetheless, magnetospheres
likely play a role in the detailed accretion flow near the stars.

---------------------------------------------------------
Title: Dynamic Processes in Be Star Atmospheres. V. Helium Line
Emissions from the Outer Atmosphere of λ Eridani
Authors: Smith, Myron A.; Cohen, D. H.; Hubeny, I.; Plett, K.; Basri,
G.; Johns-Krull, C. M.; MacFarlane, J. J.; Hirata, R.
1997ApJ...481..467S Altcode:
The He I lines of the mild B2e star λ Eri often exhibit rapid,
small-amplitude emissions that can occur at random places in
their photospheric lines, even when the star is in a “nonemission
state.” New simultaneous observations of the triplet λ5876 and singlet
λ6678 lines show that the emission ratio for these lines is near unity,
contrary to the predictions of either non-LTE model atmospheres or
nebular recombination theory. Several He I emission events point to
the formation of short-lived structures near the star's surface. On 1995
September 12 the line λ6678 exhibited a strong (0.13Icont)
emission lasting some 20 minutes. The rapid decay of this feature
implies a density of &gt;=1011.5 cm-3 for an
emitting plasma structure near the star. This value is consistent with
density estimates for slabs which may be responsible for ephemeral
“dimples” in this star's He I lines on other occasions. We argue that
photospheric helium emissions during Hα-quiescent phases are caused
by foreground material and ask what mechanism might produce these
features against the stellar background. To answer this question
we have simulated He I line emission from model slabs having various
properties and suspended over the star. We find that illumination by
a source of extreme-ultraviolet (EUV) or X-ray flux depletes the He I
column density so that it is difficult to form observable He I lines. A
more interesting set of conditions occur for slabs with high densities
(~1012 cm-3) and moderately large optical
thicknesses in optical He I lines. Under these modified assumptions
modest amounts of emission can be reproduced in singlet and triplet
lines, and in the observed ratio. The key to producing this emission is
for the slab to feel its own Lyman continuum radiation. This condition
causes λ584 and other resonance lines to partially depopulate the
ground state and to overpopulate the first few excited levels, ensuring
that the departure coefficients of relevant atomic levels approach
common values. The second necessary ingredient is a high density,
which tends to equalize the departure coefficients of excited levels
through recombinations and through redistribution of electrons among the
l-sublevels. The combination is a kind of “Lyman-pumped recombination”
because it relies on the Lyman continuum being marginally optically
thick. Our results are consistent with studies of He I emission from
planetary nebulae, symbiotic variables, and active galactic nuclei
(AGNs), and may have a bearing on other “detached atmospheres”
problems as well. This study appears to be the first application of
such a recombination mechanism to a quasi-photospheric setting.

---------------------------------------------------------
Title: Early hints on the substellar mass function
Authors: Basri, Gibor; Marcy, Geoffrey W.
1997AIPC..393..228B Altcode: 1997sfnf.conf..228B
The study of substellar objects, which had no solid empirical basis as
little as two years ago, has now achieved remarkable progress. Three
indisputable brown dwarfs have been discovered, and six Doppler
companions to solar-type stars appear very convincingly to be extrasolar
planets. A number of other Doppler companions are almost certainly
substellar. We begin by defining the classes of substellar objects
on a physical basis. Then we discuss the discoveries of the past two
years, and the methods which led to success. We make a preliminary
estimation of the substellar mass function, based on the Doppler
results and the cluster searches. We use these to predict the success
rate of various continuing searches. We must emphasize that these
predictions are based on very few objects, and are likely to change
in the coming years. Nonetheless, the number of substellar objects
is already reasonably constrained, and it is unlikely that they are
a major constituent of the baryonic dark matter.

---------------------------------------------------------
Title: The Spectral Variability of the T Tauri Star DF Tauri
Authors: Johns-Krull, Christopher M.; Basri, Gibor
1997ApJ...474..433J Altcode:
We analyze 117 echelle spectra of the T Tauri star DF Tau,
concentrating on variations in the optical continuum veiling and the
strong emission lines. Although this star was the inspiration for
the original suggestion of magnetospheric accretion in T Tauri stars
(TTSs), this hypothesis is only partially supported in our data. We
find that variations in the Ca II infrared triplet lines correlate
with the veiling variations; there is some evidence that the broad
component of the He I line does, too. The narrow component of He I
is shown to arise at the stellar surface, but it correlates with the
broad component. There is a surprising lack of periodicity in the lines,
and it does not occur where expected when seen. The correlation between
continuum veiling and the line components expected to be most related
to the veiling is poor. There is a great deal of variability in all
the lines and line components; a snapshot spectrum is a poor way to
characterize the star as a whole. The total Balmer line fluxes are
poorly correlated with the veiling, unlike previous results on a large
sample of TTSs. Redshifted absorption components are found in the weaker
lines but are not common. The strength of the blueshifted absorption
feature in Hα is correlated with the veiling, but changes in it perhaps
occur before veiling changes by about one day. This time delay supports
the idea that the wind originates at some distance from the stellar
surface and is related to accretion. Spherically symmetric wind models
are unable to reproduce well the relative absorption levels on the blue
side of the Hα and Hβ lines simultaneously. Hα does not display the
asymmetries expected of magnetospheric accretion, but it is sometimes
suggestive of azimuthally asymmetric corotating structures. The line
wings indicate that the formation region of the Hα line is dominated
by high turbulence. Hβ does show more of the asymmetry expected of
magnetospheric accretion. Based on observations obtained at the
Lick Observatory operated by the University of California.

---------------------------------------------------------
Title: Lithium near the substellar boundary: a new age diagnostic.
Authors: Basri, G.
1997MmSAI..68..917B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Lithuim in Very Low-Mass Stars in the Pleiades
Authors: Oppenheimer, B. R.; Basri, G.; Nakajima, T.; Kulkarni, S. R.
1997AJ....113..296O Altcode:
High-resolution, Keck Telescope echelle observations from 630 nm
to 850 nm of seven Pleiads with spectral types from M5 to M6.5
reveal rather rapid rotation, with an average v sin i ~ 52 km s(-1)
, and chromospheric activity in Hα emission. The activity in these
stars is not any stronger than that of other Pleiades low-mass stars,
despite the expected high contrast of Hα with their cool photospheres
and their rapid rotation. This shows that the “levelling off” of Hα
equivalent widths previously noted in low-mass stars in young clusters
is not related to the conventional rotation-activity connection. None
of the stars previously categorized as brown dwarf candidates have
lithium signatures in their spectra. They are, therefore, very low-mass
stars and not brown dwarfs. However, two stars, HHJ 339 and HHJ 430,
1 and 2 magnitudes above the Pleiades zero-age main sequence, do show
absorption due to Li 1 at 670.8 nm and in the subordinate feature at
812.6 nm. These two stars are also rotating very rapidly. These facts
strongly suggest that these stars are rather young. Their proper motions
and radial velocities agree with those measured for the Pleiades as a
whole. We discuss various explanations for these stars, none of which
is completely satisfactory. In one scenario they represent very late
star formation in the Pleiades cluster (implying a huge range in the
ages of Pleiads). This seems unpalatable given the lack of matter dense
enough to form stars in the Pleiades at present. Another possibility is
that these stars formed in a nearby, more recent star formation site
and drifted into the Pleiades. Although the cluster recently passed
through a clump of young Taurus stars, we do not see how it could
“accrete” two of them. In our most feasible explanation, we posit
that a cloud which was a member of the “Pleiades Supercluster”
recently formed stars, which are now scattered between us and the
Pleiades. HHJ 339 and HHJ 430 could be members of this group whose
motion has now brought them near the older open star cluster.

---------------------------------------------------------
Title: Analysis of Keck high-resolution spectra of VB 10
Authors: Schweitzer, Andreas; Hauschildt, Peter H.; Allard, France;
Basri, G.
1996MNRAS.283..821S Altcode: 1996astro.ph..6150S
We use a preliminary version of our `NextGen' grid of cool star
model atmospheres to compute synthetic line profiles which fit
high-resolution Keck spectra of the cool M dwarf VB10 satisfactorily
well. We show that the parameters derived from the Keck data are
consistent with the parameters derived from lower resolution spectra
with larger wavelength coverage. We discuss the treatment of van der
Waals broadening in cool stellar atmospheres that are dominated by
molecules (mostly H_2). The line profiles are dominated by van der Waals
pressure broadening and are a sensitive indicator for the gravity and
metallicity. Therefore the high-resolution Keck spectra are useful for
determining the parameters of M dwarfs. There is some ambiguity between
the metallicity and gravity. For VB10, we find from the high-resolution
spectra that 5.0&lt;logg&lt;5.5 and 0&lt;[M/H]&lt;+0.5 for an adopted
fixed effective temperature of 2700 K, which is consistent with recent
interior calculations.

---------------------------------------------------------
Title: The T Tauri Double-Lined Spectroscopic Binary DQ Tau
Authors: Stassun, K.; Mathieu, R. D.; Basri, G.; Johns-Krull, C. M.;
Valenti, J. A.; Jensen, E. L. N.; Hartmann, L. W.
1996AAS...188.4006S Altcode: 1996BAAS...28R.884S
We report the results of spectroscopic and photometric monitoring of
the classical T Tauri star (CTTS) DQ Tau. Radial-velocity variations
show DQ Tau to be a double-lined spectroscopic binary, one of only
three spectroscopic binaries known amongst CTTSs (see also abstract
on UZ Tau E by Mathieu et al.). We have determined an orbit solution
for DQ Tau characterized by a large eccentricity (e = 0.58) and an
orbital period of 15.8 days. The mass ratio is indistinguishable from
unity. During our photometric monitoring of this system over three
observing seasons, we observed recurring flare-like brightening events
( ~ 0.5 mag in V). A Scargle periodogram analysis of these brightenings
reveals a highly significant period that is, remarkably, identical to
the binary orbital period. These brightening events are phased at or
near periastron. Furthermore, as the system brightens, it becomes bluer
(Delta V-I ~ -0.2 mag). We find this periodic photometric signature
throughout our data, spanning ~ 5000 days. We find continuum veiling at
low levels throughout the orbit. There is a suggestion in our data that
enhanced continuum veiling accompanies the photometric brightening. The
emission lines also sometimes brighten near periastron. In one case, the
CaII IR triplet shows spectacular brightening and blue-shifted emission
just after periastron. DQ Tau's large infrared excess (K-N = 4.2 mag),
IRAS fluxes, and millimeter-wave emission attest to the presence of
a massive circumbinary disk. Thus, one possible interpretation for
the photometric brightening and veiling is periodic accretion events
fueled by the circumbinary disk. Recent theory suggests that accretion
streams may occur in such highly eccentric systems. Alternatively,
the flaring may be due to interacting magnetospheres; at periastron
the stars are only a few stellar radii apart. In any case, our data
strongly imply that the activity is directly connected to the orbital
kinematics of the system.

---------------------------------------------------------
Title: Brown Dwarfs in the Pleiades Cluster Confirmed by the
Lithium Test
Authors: Rebolo, R.; Martin, E. L.; Basri, G.; Marcy, G. W.;
Zapatero-Osorio, M. R.
1996ApJ...469L..53R Altcode: 1996astro.ph..7002R
We present Keck Observatory 10 m telescope spectra of the two Pleiades
brown dwarfs, Teide 1 and Calar 3, showing a clear detection of the Li
670.8 nm resonance line. In Teide 1, we have also obtained evidence for
the presence of the subordinate line at 812.6 nm. A high Li abundance
[log N(Li) &gt;= 2.5], consistent with little if any depletion,
is inferred from the observed lines. Since Pleiades brown dwarfs are
unable to burn Li, the significant preservation of this fragile element
confirms the substellar nature of our two objects. Regardless of their
age, their low luminosities and Li content place Teide 1 and Calar 3
comfortably in the genuine brown dwarf realm. Given the probable age
of the Pleiades cluster, their masses are estimated at 55 +/- 15 MJ.

---------------------------------------------------------
Title: Dynamic Processes in Be Star Atmospheres. IV. Common Attributes
of Line Profile “Dimples”
Authors: Smith, Myron A.; Plett, K.; Johns-Krull, C. M.; Basri, G. S.;
Thomson, J. R.; Aufdenberg, J. P.
1996ApJ...469..336S Altcode:
"Dimples" are transient central absorption features flanked by weak
emissions commonly seen in the He I λ6678 line profile of the mild B2e
star λ Eridani. Smith &amp; Polidan have found that these features can
be reproduced with a model in which line photons are scattered within
an optically thick (in the line) slab elevated over the surface of a
rapidly rotating star. We have undertaken a series of simultaneous
He I multiline observations of this star at the McMath, McDonald,
Lick, David Dunlap, and Ritter Observatories to search for dimples
in weak blue He ilines when they appear in λ6678. Four dimples were
found during 15 hr of multiobservatory monitoring. In three cases,
a dimple was observed in a weak blue line of the same absorption
series as λ6678. In the fourth instance, a dimple was observed only
in λ5876 and λ5015 lines that, like λ6678, are strong and have weak
wings. A joint lUE/optical campaign demonstrated that the He II λ1640
line shows decreases in absorption and possible weak emissions just as
new dimples appear in the λ6678 line. Our observations confirm a
previous report that dimples appear in the λ6678 line of four other
Be stars. We also find that the resonance C iv double weakens when
dimples appear, a result similar to that found for λ Eri. Our data
also disclosed that "migrating subfeatures" similar to those found in
γ Cas are present in the λ6678 line of the B5 star HR 1011. These
features appear to be a more vigorous form of dimple activity than
observed in λ Eri and other mild Be stars. These findings lend support
to the slab model as an explanation for the dimple phenomenon. They
also suggest that this activity is endemic to the class of mild Be
stars. The appearance of dimples in the weak blue He I lines suggests
slab masses of at least 7 x 10-13 Msun for most
dimples. The greatest enigma that characterizes classical Be
stars is their highly variable and episodic mass-loss histories. Our
estimates of dimple-slab masses are high enough that this problem may
be removed if the magnetic paradigm for Be activity is correct. In
this picture, exospheric flares trigger explosive ablations of plasma
from the upper photosphere. The evaporated mass is trapped by overlying
closed magnetic field loops, where it cools, taking on characteristics
of prominence-like structures. If the loops were opened for any reason,
this mass would be free to escape from the star at a rate consistent
with massloss rates during active Be episodes. Then the essential
difference between Be stars in active and inactive phases would be
understood not as a difference in their mass release rates but rather
in the prevailing geometries of their surface fields.

---------------------------------------------------------
Title: The Narrow Emission Lines of T Tauri Stars
Authors: Batalha, C. C.; Stout-Batalha, N. M.; Basri, G.; Terra,
M. A. O.
1996ApJS..103..211B Altcode:
We present the first comprehensive study of the narrow emission
lines of T Tauri stars (TTS). These narrow lines have been reported
in the literature as originating in the stellar atmosphere and having
Gaussian-type profiles centered at the stellar rest velocity, with a
base width not larger than 50 km s-1. Here, we concentrate
on the Ca II lines λλ8498, 8542, and 8662 and the helium line
λ5876. After applying veiling corrections, the average narrow
component line emission is found to be larger than that found in
active main-sequence stars: up to several times larger for classical
T Tauri stars with strong rates of disk accretion. More striking is
the finding that the resulting line emission strengths of these lines
correlate with veiling. The correlation is confirmed on individual
stars for which observations at several epochs exist and for which
veiling varies widely on relatively short timescales. We also find a
correlation between the narrow emission fluxes and the near-infrared
excesses for stars with low levels of veiling, which includes the
few weak-lined TTS of the sample. We discuss possible formation
sites for the narrow emission lines in the classical TTS, and we
present simple models to explain the observations. In these models,
the excess line emission found for the stars with higher accretion
rates is assumed to originate in localized regions near the magnetic
footpoints of the accretion column. We refer to these hypothetical
regions in the atmosphere collectively as the "hot chromosphere" since
we assume they are additionally heated by the reprocessed energy of the
colliding gas in the accretion process. Computing two chromospheric
models, one representing the typical weak TTS chromosphere and the
other representing the best guess at the "hot chromosphere," we find
the following. The "hot chromosphere" is characterized by a steep
temperature gradient beginning at low continuum optical depths in
order to give simultaneously the large observed central flux and the
relatively narrow baselines (50-60 km s-1). The chromosphere
temperature rise is not similar to the earlier deep chromosphere models
in which a sudden chromospheric temperature rise is appended to the
photosphere at relatively large mass column. For the most extreme cases
(i.e., largest line fluxes), 20%, at most, of the star's surface must
be covered by "hot chromospheric" regions.

---------------------------------------------------------
Title: Night-Sky High-Resolution Spectral Atlas of OH and O2 Emission
Lines for Echelle Spectrograph Wavelength Calibration
Authors: Osterbrock, Donald E.; Fulbright, Jon P.; Martel, Andre R.;
Keane, Michael J.; Trager, Scott C.; Basri, Gibor
1996PASP..108..277O Altcode:
The potential of night-sky emission lines recorded on every
long-exposure astronomical spectrum, for wavelength calibration, is
emphasized. A high-resolution atlas, based on spectra obtained with
the Keck 10-meter telescope on Mauna Kea and the HIRES high-resolution
echelle spectrograph is presented. This atlas shows OH, O2, and a
few other night-sky lines, and will make it possible to identify them
easily on high-resolution spectra. Accurate wavelengths and references
to their sources are given. (SECTION: Atmospheric Phenomena and Seeing)

---------------------------------------------------------
Title: Lithium in Brown Dwarf Candidates: The Mass and Age of the
Faintest Pleiades Stars
Authors: Basri, Gibor; Marcy, Geoffrey W.; Graham, James R.
1996ApJ...458..600B Altcode:
We present high-resolution optical spectroscopy and infrared photometry
of one of the lowest luminosity Pleiades stars, PPL 15. Its cluster
membership is strengthened by both its measured radial velocity and
Hα strength. Its reported mass is 0.06 Msun, based on
its I-band luminosity and the Pleiades age of 75 Myr as reported by
Stauffer, Hamilton, &amp; Probst in 1994. We confirm its luminosity
with JHK photometry. Such a low mass for PPL 15 implies that it should
currently retain lithium, unlike all low-mass Pleiades stars tested
so far. Our Keck HIRES spectrum of PPL 15 indeed exhibits the lithium
absorption feature with an equivalent width of 0.5 Å. We estimate the
likelihood this detection is spurious to be less than 1%. Thus, PPL 15
passes the lithium test for brown dwarf status. Calculations of the
luminosity as a function of mass and age for very low mass stars, along
with the history of lithium depletion, have been provided by Nelson,
Rappaport, &amp; Chiang in 1993. Lithium is depleted in HHJ 3, which is
only a little brighter than PPL 15. The self-consistent interpretation
with both observations and theory is that the age of the Pleiades is
∼115 Myr. If so, the derived mass for PPL 15 increases to ∼0.078
Msun. The canonical 75 Myr age was derived from the upper
main-sequence turnoff, but it substantially increases if core convective
overshoot is included. Such mixing could bring the two methods of age
determination into agreement. It is therefore possible that the ages
of young clusters have generally been underestimated. The luminosity
of brown dwarfs in these clusters would thus have been overestimated.

---------------------------------------------------------
Title: Spectroscopic variability of the T Tauri star DF Tau
Authors: Johns-Krull, C. M.; Basri, G.
1996ASPC..109..431J Altcode: 1996csss....9..431J
No abstract at ADS

---------------------------------------------------------
Title: C IV in classical T Tauri stars
Authors: Calvet, N.; Hartmann, L.; Hewett, R.; Valenti, J. A.; Basri,
G.; Walter, F.
1996ASPC..109..419C Altcode: 1996csss....9..419C
No abstract at ADS

---------------------------------------------------------
Title: Rotation and activity in the coolest stars
Authors: Basri, G.; Marcy, G.; Oppenheimer, B.; Kulkari, S. R.;
Nakajima, T.
1996ASPC..109..587B Altcode: 1996csss....9..587B
No abstract at ADS

---------------------------------------------------------
Title: EUVE and VLA Observations of the Eclipsing Pre-Cataclysmic
Variable V471 Tauri
Authors: Cully, S. L.; Dupuis, J.; Rodriguez-Bell, T.; Basri, G.;
Siegmund, O. H. W.; Lim, J.; White, S. M.
1996aeu..conf..349C Altcode: 1996IAUCo.152..349C
No abstract at ADS

---------------------------------------------------------
Title: Stellar Population and Abundance Studies at High Resolution
with Very Large Telescopes
Authors: Sneden, C.; Basri, G.; Boesgaard, A. M.; Brown, J. A.;
Carney, B. W.; Kraft, R. P.; Smith, V. V.; Suntzeff, N. B.
1995PASP..107..997S Altcode:
New opportunities for exploring stellar populations at high spectral
resolution with the new generation of very large optical telescopes
are reviewed. This summary will discuss papers presented at the Tucson
workshop, High Resolution Spectroscopy with Very Large Telescopes, on
abundance and kinematic information for relatively cool stars of the
field and clusters of our Galaxy and in the Magellanic Clouds. (SECTION:
Workshop on High-Resolution Spectroscopy)

---------------------------------------------------------
Title: The Line Profile Variability of SU Aurigae
Authors: Johns, Christopher M.; Basri, Gibor
1995ApJ...449..341J Altcode:
We analyze approximately 100 echelle spectra of the T Tauri star
SU Aur. The photospheric lines appear unveiled and show little
variability. We find evidence for periodic intensity variations in the
blue wing of Hβ between -170 &lt; υ &lt; -110 km s-1 from
line center with a period of approximately 3 days, the rotation period
of the star. Both the period and velocity are the same as previously
reported for Hα in SU Aur. Furthermore, evidence for unsteady accretion
is found in the presence of a variable red displaced absorption
feature with a velocity of υ +100 km s-1 in Hβ. This
feature is also periodic at 3 days (unlike in Hα). Several spectra
indicate simultaneous mass inflow and outflow. The Ca II infrared and
He 1 5876 lines show modest variability and imply that the structure
of the chromosphere on SU Aur is very different than solar plage
regions. Variations of the Ca II lines and the He I line are well
correlated with each other but only poorly correlated with Balmer line
variability. We use spherically symmetric radiative transfer codes to
calculate the line profiles for SU Aur. The equations of statistical
equilibrium are solved using the general purpose program CLOUDY. By
simultaneously fitting the Balmer lines in SU Aur, we determine to
what extent these lines can be produced in a spherically symmetric
wind and constrain the parameters of this wind. We find that large
turbulent velocities are required at the base of such a wind, where
the bulk of the emission is produced. The steady absorption feature
seen at υ ≍ -50 km s-1 must form in the outer portions
of the stellar wind, implying a terminal velocity of the wind much
below the stellar escape velocity. The mass-loss rate is determined
to be about 4.5 × 10-9 Msun yr-1.

---------------------------------------------------------
Title: Hot Winds in T Tauri Stars?
Authors: Basri, Gibor
1995hst..prop.5875B Altcode: 1995hst..prop.2348B
Interest in T Tauri stars is high because they are surrounded by
accretion disks like the solar nebula, and because they provide the
best view of the mass loss mechanism responsible for bipolar outflows,
protostellar jets, and the winds which play a big role in fixing the
angular momentum and possibly the mass of the newly formed star. In
Cycle 2 we obtained the first good high resolution observations of the
ultraviolet emission lines formed in the interface between star and
disk. These demonstrated that emission arises both in narrow components
likely confined by the stellar magnetic field, and in broad components
diagnostic of the accretion disk interaction with the star. There were
several surprises; we did not expect material at 10^5K to so closely
resemble the optical profiles. Especially tantalizing are hints that
the wind itself may contain such hot material, possibly even optically
thick. This has strong implications for the mechanism driving the
outflow. In particular it may be difficult to produce such material
in the magnetocentifugally driven winds which currently hold favor. We
propose a program aimed specifically at the question of to what extent
hot material exists in T Tauri winds. We will examine stars selected
specifically for their wind diagnostics, and expand our coverage of
stellar masses. We will also examine for the first time pre--main
sequence stars without disks, to disentangle purely stellar phenomena.

---------------------------------------------------------
Title: Hamilton Echelle Spectra of Young Stars. II. Time Series
Analysis of H(alpha) Variations
Authors: Johns, Christopher M.; Basri, Gibor
1995AJ....109.2800J Altcode:
We present the results of time series analysis on the Hα profile
variations in 7 T Tauri stars (TTS). All stars show strong line profile
variability. Included in the data are 37 almost fully contiguous nights
of profile data on 5 TTS. For these stars (T Tau, RY Tau, DF Tau,
DR Tau, and RW Aur) our temporal sampling is adequate to look for
periodicities. We detect periodic variations on the red side of the
profile near the peak of the line in two of our stars (7.3 days in DF
Tau and 5.1 days in DR Tau). The periods recovered and the location
in the line profiles displaying the periodicity do not provide the
convincing support for magnetocentrifugally controlled accretion and
wind generation which SU Aur exhibited. The other stars show no evidence
for periodic profile behavior. Correlation analysis shows that the
blue-shifted absorption component of the line profile visible in most of
these stars varies on a longer time scale and is basically uncorrelated
with the rest of the line profiles. We interpret this as evidence for
this feature forming far from the star and that the velocity of this
feature indicates the terminal velocity of the flow from TTS seen in
Ra, which is substantially below escape velocity. We find that TTS
Hα profile variations are not due to global changes in the physical
parameters of the wind and accretion flows surrounding these stars but
instead represent smaller- scale stochastic variability. Changes in
the profiles tend to occur in discrete velocity patches rather than
across the whole line. Over most of the profile the time scale for
this tends to be less than two days. While of the general nature of a
"stochastic wind," the variations differ substantially in detail from
a model which has been proposed for this. A new result is the common
appearance of variance peaks on the red side of Hα as well. These peaks
are likely indirect evidence of variable accretion seen in this line,
which rarely shows overt red-shifted absorption.

---------------------------------------------------------
Title: The First Lithium Brown Dwarf: PPL 15
Authors: Basri, Gibor; Marcy, Geoffrey W.; Graham, James R.
1995AAS...186.6003B Altcode: 1995BAAS...27.1214B
No abstract at ADS

---------------------------------------------------------
Title: HST/GHRS Observations of Molecular H_2 Lyman Band Emission
in Pre-Main Sequence Stars
Authors: Walter, F. M.; Basri, G. S.; Brown, A.; Lissauer, J. J.;
Millar, T. J.
1995AAS...186.0906W Altcode: 1995BAAS...27..825W
We will present HST/GHRS spectra of 9 low mass PMS stars. All 7
classical T Tauri stars show evidence for H_2 Lyman band emission
lines. Emission in the Lyman band arises from either shock-excited
gas or in gas at temperatures of 2000-4000K. In the latter case, the
emission can be used to probe the innermost portion of the circumstellar
gaseous disks (within about 10 stellar radii). Comparison of large
and small aperture spectra show that all the H_2 emission from T Tauri
arises within 15 AU of the star. Two naked T Tauri stars, with ages of
~ 2 Myr, do not show evidence of H_2 emission. This has implications
for the clearing times of the gaseous components of the circumstellar
disks of PMS stars.

---------------------------------------------------------
Title: Infrared Zeeman Analysis of epsilon Eridani
Authors: Valenti, Jeff A.; Marcy, Geoffrey W.; Basri, Gibor
1995ApJ...439..939V Altcode:
We analyze high-resolution infrared FTS spectra near 1.6 micrometers to
obtain the most accurate measurement to date of the magnetic field on
a typical active star. A total of 16 infrared Fe I lines are analyzed,
including the geff = 3 line at 1.56485 micrometers. We find
the 8.8% of the deep photosphere of the active star epsilon Eridiani
(K2 V) is covered with a 1.44 kG magnetic field. This corresponds to
an absolute magnetic flux of absolute value of B f = 0.13 kG, which is
about half the value found in all recent optical studies but agrees with
one existing infrared upper limit. We discuss possible explanations for
this discrepancy in terms of models with different atmospheres for the
quiet and magnetic components. We carefully assess the impact of random
noise on our derived mmagnetic parameters and find that the quantity
absolute value of B f0.8 is most accurately known, witha
formal uncertainty of 0.1%. The 1 sigma confidence interval along this
curve ranges between (absolute value of B, f) = (1.31 kG, 10.0%) and
(1.60 kG, 7.8%). We also study various sources of systematic errors,
and find a 35% uncertainty in f, primarily because the structure of
stellar flux tubes is poorly known, but also because of uncertainty
in log g. Systematic errors in absolute value of B are smaller (less
than 15%) because the sigma components of the 1.56485 micrometer line
are resolved. We place low upper limits on the surface magnetic flux
on two inactive stars, 40 Eri (Ki V) and sigma Dra (KO V), reinforcing
the significance of our magnetic field detection for epsilon Eri. As a
byproduct of the Zeeman analysis, we have derived accurate effective
temperatures, iron abundances, and macroturbulences for all three
stars. In addition, we have determined oscillator strengths (most
previously unmeasured) for 21 Fe I transitions near 1.6 micrometers
by matching models to the observed solar sprectrum.

---------------------------------------------------------
Title: A Surprise at the Bottom of the Main Sequence: Rapid Rotation
and NO H(alpha) Emission
Authors: Basri, Gibor; Marcy, Geoffrey W.
1995AJ....109..762B Altcode:
We report Kech Observatory high-resolution echelle spectra from 640-850
nm for eight stars near the faint end of the main sequence. These
spectra are the highest resolution spectra of such late-type stars,
and clearly resolve the TiO, VO, and atomic lines. The sample
includes the field brown-dwarf candidate, BRI 0021-0214 (M9.5+). Very
unexpectedly, it shows the most rapid rotation in the entire samples,
v sin i approximately 40 km/s, which is 20x faster than typical field
nonemission M stars. Equally surprising is that BRI 0021 exhibits
no emission or absorptionat H-alpha. We argue that this absence is
not simply due to its cool photosphere, but that stellar activity
declines in a fundamental way at the end of the main sequence. As it
is the first very late M dwarf observed at high spectral resolution,
BRI 0021 may be signaling a qualitative change in the angular momentum
loss rate among the lowest mass stars. Conventionally, its rapid
rotation would have marked BRI 0021 as very young, consistent with the
selection effect which arises if the latest-type dwarfs are really
brown dwarfs on cooling curves. In any case, it is unprecedented to
find no sign of stellar activity in such a rapidly rotating convective
star. We also discuss the possible conflict between this observation
and the extremely strong H-alpha seen in another very cool star,
PC 0025+0447. Extrapolation of M-L relations for BRI 0021 yields M
approximately 0.065 solar mass, and the other sample objects have
expected masses near the H-burning limit. These include two Pleiades
brown-dwarf candidates, four field M6 dwarfs and one late-type T
Tauri star. The two Pleiades M6 dwarfs have v sin i of 26 and 37 km/s,
H-alpha in emission, and radial velocities consistent with Pleiades
M6 dwarfs have v sin i of 26 and 37 km/s, H-alpha in emission, and
radial velocities consistent with Pleiades membership. Similarly,
the late-type T Tauri star has v sin i approximately 30 km/s and
H alpha emission indicate of its youth. Two of the four late-type
field dMe star also exhibit rotation above 5 km/s, consistent with
expectations. BRI 0021 has no measurable absoprtion due to lithium,
indicating that it is likely to be more massive than 0.065 solar mass.

---------------------------------------------------------
Title: Zeeman Enhancement of Lines in Extremely Active K Dwarfs
Authors: Basri, Gibor; Marcy, Geoffrey W.
1994ApJ...431..844B Altcode:
We have searched for the predicted enhancement of the equivalent widths
of Zeeman-sensitive lines in five chromospherically active K dwarfs,
by direct comparison with inactive dwarfs of similar spectral type. In
two active stars, EQ Vir and HD 82558, the equivalent widths indeed
exhibit enhancements (of up to 30%) which correlate with the Zeeman
sensitivity of the individual lines. HD 17925 barely shows the effect,
and epsilon Eri does not show it. The amount of the Zeeman effect is
related to the enhancement of the emission cores of the Ca II infrared
triplet lines. Radiative transfer models including magnetic fields
permit estimates of Bf, the product of field strength (B) and surface
filling factor (f). Our detections imply Bf approximately equals 2kG to
3kG, in agreement with Saar. Difficulties in predicting line strengths
from active stars arise due to surface inhomogeneities. These render
the method ineffective in our most active case, GI 171.2.

---------------------------------------------------------
Title: A Search for Lithium in Pleiades Brown Dwarf Candidates Using
the Keck HIRES Echelle
Authors: Marcy, Geoffrey W.; Basri, Gibor; Graham, James R.
1994ApJ...428L..57M Altcode:
We report Keck Observatory high-resolution echelle spectra of lithium
at 670.8 nm in two of the lowest luminosity brown dwarf candidates in
the Pleiades. These objects have estimated masses of 0.055 to 0.059
solar mass from their location on a color-magnitude diagram relative
to theoretical isochrones. Stellar interior models predict that Li
has not burned in them. However, we find no evidence of the Li line,
at limits 100 to 1000 times below the initial abundance. This indicates
that Li has in fact been depleted, presumably by nuclear processing as
occurs in Pleiades stars. Interior models suggest that such large Li
depletion occurs only for objects with M greater than 0.09 solar mass
at the age of the Pleiades. Thus, it is unlikely that the candidates
are brown dwarfs. The brown dwarf candidates present a conflict:
either they have masses greater than suggested from their placement
on the H-R diagram, or they do have the very low suggested masses but
are nonetheless capable of destroying Li, in only 70 Myr. Until this
dilemma is resolved, the photometric identification of brown dwarfs
will remain difficult. Resolution may reside in higher Teff
derived from optical and IR colors or in lower Teff in the
interior models.

---------------------------------------------------------
Title: Sleuthing the Dynamo: HST/FOS Observations of UV Emissions
of Solar-Type Stars in Young Clusters
Authors: Ayres, T.; Basri, G.; Simon, T.; Stauffer, J.; Stern, R.;
Antiochos, S.; Bookbinder, J.; Brown, A.; Doschek, G.; Linsky, J.;
Ramsey, L.; Walter, F.
1994ASPC...64...53A Altcode: 1994csss....8...53A
No abstract at ADS

---------------------------------------------------------
Title: A Far-Ultraviolet Flare on a Pleiades G Dwarf
Authors: Ayres, T. R.; Stauffer, J. R.; Simon, Theodore; Stern, R. A.;
Antiochos, S. K.; Basri, G. S.; Bookbinder, J. A.; Brown, A.; Doschek,
G. A.; Linsky, J. L.; Ramsey, L. W.; Walter, F. M.
1994ApJ...420L..33A Altcode:
The Hubble Space Telescope/Faint Object Spectrograph (HST/FOS) recorded
a remarkable transient brightening in the C IV lambda lambda 1548,50
emissions of the rapidly rotating Pleiades G dwarf H II 314. On the one
hand the 'flare' might be a rare event luckily observed; on the other
hand it might be a bellwether of the coronal heating in very young
solar-mass stars. If the latter, flaring provides a natural spin-down
mechanism through associated sporadic magnetospheric mass loss.

---------------------------------------------------------
Title: The Spectral Variability of BP Tauri
Authors: Simon, Theodore; Imhoff, C. L.; Basri, G. S.; Ayres, T. R.
1994ASPC...64..729S Altcode: 1994csss....8..729S
No abstract at ADS

---------------------------------------------------------
Title: A Search for Periodicities in Balmer Line Profiles of Six T
Tauri Stars
Authors: Johns, Christopher M.; Basri, Gibor
1994ASPC...64..190J Altcode: 1994csss....8..190J
No abstract at ADS

---------------------------------------------------------
Title: Multiline Zeeman Analysis of epsilon Eridani in the Near IR
Authors: Valenti, J. A.; Marcy, G. W.; Basri, G.
1994ASPC...64..489V Altcode: 1994csss....8..489V
No abstract at ADS

---------------------------------------------------------
Title: Periodicities in T Tauri Star Line Profiles
Authors: Johns, C. M.; Basri, G.
1993AAS...183.4006J Altcode: 1993BAAS...25.1351J
Between 1986 and 1993 we have carried out repeated observations of
several T Tauri stars (TTS) with the Hamilton echelle spectrometer
at Lick Observatory. During several intensive campaigns, the longest
occurring in Fall 1992, we obtained sufficient temporal coverage to look
for periodicity in the line profiles. We have such data for 11 TTS. Here
we present periodogram analyses of several of our targets, concentrating
on the Hα line profile. As of the writing of this abstract, 3 of 6
stars show evidence for periodic behavior in some portion of their line
profiles. In one case (SU Aur) the detected period in the line profile
variations is in good agreement with the rotation period of the star
(3 days). The remaining 2 stars with detected periods in their line
profile variations (DF Tau and DR Tau) do not match known photometric
periods. The velocities at which the periodicities occur are quite
different in each case, and correspond to different physical regions
of profile formation. The stars which have not shown periodic profile
variations so far are RW Aur, RY Tau, and T Tau.

---------------------------------------------------------
Title: GHRS Profiles of Hot UV Lines in T Tauri Stars
Authors: Valenti, J. A.; Basri, G.; Walter, F.; Hartmann, L.;
Calvet, N.
1993AAS...183.4007V Altcode: 1993BAAS...25.1351V
We present the first good line profiles of “transition region”
lines in “typical” T Tauri stars. In particular, we discuss the C
IV and Si IV doublets at 1400 Angstroms and 1550 Angstroms for BP Tau,
DF Tau, DR Tau, and RW Aur. These line profiles were obtained with the
GHRS on HST, and they are supplemented with concurrent observations
of the Mg II doublet at 2800 Angstroms and various optical lines such
as Hα , Hβ , the Ca II infrared triplet, Na D, and He I at 5876
Angstroms. The C IV emission profiles have broad wings indicative of
high velocity gas (+/-200 km/s). For DR Tau and RW Aur the velocity
structure seen in C IV is similar to that seen in Hα and Mg II. Line
flux ratios imply that the gas is close to optically thin in the C IV
lines. In addition, blueshifted absorption may be present in 3 of the
4 stars. The Si IV profiles are narrower than the C IV profiles, but
still broader than expected from a classical transition region. There
is also evidence of a “stellar” (very narrow) component in several
of the profiles. This is particularly striking for RW Aur, where
the weaker line has a distinct narrow core, while the stronger line
is broad and has a flat top. Furthermore, the broad (500 km/s) Si IV
emission in RW Aur is significantly redshifted. In each of the stars,
the Mg II profile looks very similar to the Hα profile, and C IV and
Ca II bear an intriguing relation to each other. We do not claim to
fully understand these profiles yet, but it is obvious that they are
primarily formed outside the stellar atmosphere.

---------------------------------------------------------
Title: A Synoptic Study of H alpha Line Profile Variability in the
T Tauri Star SU Aurigae
Authors: Giampapa, Mark S.; Basri, Gibor S.; Johns, Christopher M.;
Imhoff, Catherine
1993ApJS...89..321G Altcode:
We present a catalog of 106 high spectral resolution observations of the
H-alpha line profile in the T Tauri star SU Aurigae, obtained during
the period from 1986 October through 1990 November. The spectra were
acquired during joint synoptic programs to observe selected T Tauri
stars using the Hamilton Echelle Spectrometer of the Lick Observatory
and the solar-stellar spectrograph at the McMath telescope of the
National Solar Observatory on Kitt Peak. A restricted set of Mg II h
and k line profiles was also obtained in a coordinated program involving
the International Ultraviolet Explorer (IUE) satellite observatory and
the McMath solar-stellar facility. Striking variability is evident on
a nightly basis. A key result is that the relative intensity in the
blue wing of H-alpha spanning a range of velocities bear -150 km/s is
modulated at a period of 2.98 +/- 0.4 days. We identify the 2.98 day
period with the rotation period of the star. We also find that the
occurrence of the periodic modulation of the mass outflow is episodic
and most evident during a 2 week sequence of nightly observations. We
find two other intervals where the periodic spectroscopic variability
is likely present, although at a lower level of significance at a
lower level of significance. The variability is otherwise stochastic in
nature. The Mg II resonance lines exhibit clear variability that is most
pronounced in the blue wing of the k line. A comparison of the Mg II k
line profile with H-alpha profiles obtained nearly simultaneous yields
no apparent correlation between the variable features in each line. The
profile shapes of the Mg II h and k lines are generally indicative
of formation in a wind. An analysis of the principal features that
appear in the H-alpha profile set suggests that the line is composed of
contributions from an enhanced chromosphere; a relatively slow moving,
dense, optically thick component of a stellar wind formed relatively
close to the star; and an optically thin, high-velocity, expanding
stellar wind located further away from the star. An investigation of
possible correlations among the principal features in the series of
H-alpha profiles suggests that as the density in the wind increases,
the wind may become more unstable to large turbulence. This may lead to
a reduction in the wind bulk velocity, thus regulating the mass-loss
rate. We also find that the position of the main absorption feature
which is always present in the H-alpha profiles is not correlated
with its depth, indicating that optical depth and wind velocity are
not correlated in the denser portions of the wind.

---------------------------------------------------------
Title: T Tauri Stars in Blue
Authors: Valenti, Jeff A.; Basri, Gibor; Johns, Christopher M.
1993AJ....106.2024V Altcode:
We present an atlas of 96 low dispersion spectra of T Tauri stars, both
classical and weak-lined. The flux-calibrated spectra extend from H-Beta
to well blueward of the Balmer jump. Observed equivalent widths and
rough blue veilings are presented. We model stars with excess emission
as a combination of a weak-lined T Tauri star of a similar spectral
type and a slab of hot hydrogen. We tabulate the physical parameters of
the slab, and give both intrinsic and observed Balmer jumps. The region
responsible for the excess blue continuum has a high density and small
surface area, in agreement with previous work. This is consistent with
the boundary layer hypothesis, but not unique to it. We suggest that
the emission region may actually be the stellar photosphere, heated by
accretion shocks at the footprints of magnetic loops extending to the
disk. We find that observed infrared excesses are often many times
higher than predicted by simple accretion disk models (including
reprocessing). The blue excess is more likely to be diagnostic of
the actual accretion rate onto the star than the infrared. Typical
values for this are a few 10-8 solar mass/yr. Some accreting
material may not make it to the star, but is turned around into a wind
near the star. The line strengths from the model agree qualitatively
with observations of the upper Balmer lines, but are increasingly
underestimated for the lower Balmer lines. Including both low and high
optical depth components yields better agreement. No weak-lined stars
are found to have a Balmer emission jump, confirming that an accretion
disk is required to produce this feature in pre-main-sequence stars.

---------------------------------------------------------
Title: The Atmospheres of T Tauri Stars. II. Chromospheric Line
Fluxes and Veiling
Authors: Batalha, C. C.; Basri, Gibor
1993ApJ...412..363B Altcode:
A set of high-resolution calibrated spectra of southern T Tauri Stars
(TTS), comprising objects with H-alpha equivalent widths ranging from 3
to 40 A are used to derive one-component plane-parallel chromospheric
models. Our motivation is to discover how much emission activity
can truly be ascribed to stellar activity, using real calibrated
stellar data. We find that simple models can reproduce the Ca II line
at 8542 A for most of the stars. The chromospheric enhancements are
comparable to the ones found among active main-sequence stars of similar
spectral type. These models cannot account for the veiling observed in
TTS. Likewise, realistic TTS chromospheres are unable to create the
observed Balmer jumps. The targets have a range of H-alpha strength
that allow us to study possible correlations among narrow symmetric
emission lines, and H-alpha which probes nonstellar regions. On the
basis of their stellar vs systemic luminosities, Sz 77, Sz 82, and Sz
19 present signatures of disk accretion, in addition to the previously
reported case of Sz 98. By correlating the fluxes of the Ca II IR line,
H-alpha and the near-IR excess, we conclude that disk accretion may
enhance the luminosity of typical chromospheric emission lines.

---------------------------------------------------------
Title: Echelle Spectra of the 6 March 1993 Solar Flare
Authors: Johns, C. M.; Basri, G. S.; Hawley, S. L.
1993BAAS...25.1189J Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High Resolution Spectroscopy in the Non-thermal Infrared:
Use of an Existing Coude System
Authors: Basri, Gibor; Marcy, Geoffrey W.
1993AAS...182.5104B Altcode: 1993BAAS...25..886B
We describe a recent effort to use a NICMOS 3 chip as the detector
on the 160" coude spectrograph camera at Lick Observatory. This new
instrument (IRCS) has a useful spectral range of 1-2mu with spectral
coverage in one exposure of about 25 Angstroms, and resolutions up
to 75000. We have successfully obtained astronomical observations
with essentially no modification of the (uncooled) spectrograph,
using an existing grating blazed at 1.22mu , and a dewar without
optics (but containing a filter) easily mounted at the position of
the old photographic plates. The throughput of the system is very
high. Its sensitivity is primarily limited by the background from the
warm spectrograph. Using filters with 0.1mu bandwidth, the expected
background is negligible below 1.5mu , but limits exposures to one
minute near 2mu . With an optimized dewar, one can remain photon
(rather than background) limited down to 10th magnitude even at 2mu
. Our current system (using a test dewar and engineering grade chip)
has been tested at 1.6mu . We have operated with and without an
image slicer. We show spectra and discuss the current successes and
problems. Our first application is to study the Zeeman--sensitive line
at 1.56mu at high resolution. We expect to be able to achieve S/N of
200:1 in 10 minutes on 6th magnitude stars now, and eventually 100:1 in
one hour on 10th magnitude stars using the 3-m telescope. This opens
the possibility of measuring magnetic fields for large numbers of RS
CVN and dM(e) stars (in addition to many G,K dwarfs), and even perhaps
a few pre-main sequence stars. There is a lot of potential for science
in the 1-2mu range at high resolution, which cannot be done as easily
with any other type of instrument. This includes: (1) molecular lines in
giants and winds, (2) lines from the ISM for abundances and kinematics,
(3) detailed atmospheric analysis of embedded stars (and disks?).

---------------------------------------------------------
Title: A Remarkable FUV Flare on the Pleiades G Dwarf HZ 314
Authors: Ayers, T.; Basri, G.; Simon, T.; Stauffer, J.; Stern, R.;
Antiochon, S.; Bookbinger, J.; Brown, A.; Doschek, G.; Linsky, J.;
Ramsey, L.; Walter, F.
1993AAS...182.4611A Altcode: 1993BAAS...25..875A
No abstract at ADS

---------------------------------------------------------
Title: High Resolution Spectral Variability of SU Aur
Authors: Johns, C. M.; Basri, G. S.
1993AAS...182.6211J Altcode: 1993BAAS...25..904J
No abstract at ADS

---------------------------------------------------------
Title: Magnetic Fields on epsilon Eridani from High Quality FTS
Spectra near 1.6 microns
Authors: Valenti, Jeff A.; Marcy, Geoffrey W.; Basri, Gibor
1993AAS...182.4609V Altcode: 1993BAAS...25..875V
We present outstanding infrared spectra of the active star epsilon
Eridani (K2V) and two inactive reference stars, 40 Eridani (K1V)
and sigma Draconis (K0V). The spectra are the result of 9 hours of
observations per star with the IR FTS at the 4--m Mayall Telescope
at Kitt Peak National Observatory. The noise is 0.5--1.0% with an
unapodized spectral resolution of 120,000. The wavelength range covered
is 1.54-1.59 microns (6290--6490 cm(-1) ) in air, which includes two
dozen moderate strength lines, notably the Lande--g=3 line at 1.5649
microns. This line is a superior magnetic diagnostic because of its high
Lande--g factor, long wavelength, and large depth of formation. The
Zeeman sensitivity of this line is at least a factor of 2--3 times
greater than any optical line. We employ a polarized radiative tranfer
code to simultaneously model the profiles of clean neutral iron lines
in our infrared spectra and high quality optical spectra. The inactive
stars are used to determine and check oscillator strengths and to assess
the accuracy of our models. We then model epsilon Eridani both with
and without a magnetic field. The observed wings of the magnetically
sensitive 1.5649 microns line are clearly deeper than predicted by
the B=0 model. No such discrepency is observed in the insensitive
lines or in inactive stars. We then fit the epsilon Eridani profiles
with various magnetic models. A model with depth independent magnetic
fields yields a (preliminary) field strength of 1.9 kG covering 12%
of the stellar surface. We also consider the observable effects of
magnetic fields that vary with depth or across the stellar surface.

---------------------------------------------------------
Title: T-Tauri Stars and Their Accretion Disks
Authors: Basri, Gibor; Bertout, Claude
1993prpl.conf..543B Altcode:
The T Tauri stars are both more rapidly rotating and more convective
than their main-sequence counterparts, which leads to increased magnetic
activity, a partner in producing the 'T Tauri phenomena'. Evidence is
presented for accretion through a disk as the source of the emission
excesses, particularly those seen in the continuum between 0.1 and 10
microns and in the strong permitted emission lines. We present a brief
overview of the classical T Tauri phenomena, and a detailed discussion
of how accretion-disk models can explain them. We explore their relation
to the weak-lined T Tauri stars, and mention some effects disk accretion
could have on the evolutionary status of young stars. We suggest some
directions that research in this area should take in the near future.

---------------------------------------------------------
Title: Automated CCD Photometry of T Tauri Stars
Authors: Richter, Matthew; Basri, Gibor; Perlmutter, Saul; Pennypacker,
Carl
1992PASP..104.1144R Altcode:
T Tauri stars have long been known to undergo irregular variations in
brightness. Extended monitoring of these pre-main-sequence solar-type
stars is important to understanding the sources of variations. Using
an automated telescope at Leuschner Observatory, we have developed
a procedure to acquire differential photometry of classical T
Tauri stars in Taurus and Auriga. It is almost fully automatic,
dramatically reducing the time necessary to process the data. We
achieved accuracy of 0.02 mag in eight fields containing target stars
down to 13th magnitude. Although most of the T Tauri stars did vary,
we find possible but not definitive periods for several targets. The
variations in general are complex but often are correlated over a few
days. (SECTION: Stars)

---------------------------------------------------------
Title: He I D3 Line in T Tauri Stars
Authors: Stout, N. M.; Batalha, C. C.; Basri, G. S.
1992AAS...18110310S Altcode: 1992BAAS...24R1288S
We present the results of a study of variations in the narrow emission
component of the He I D3 line at 5875.68 Angstroms in T Tauri Stars
of spectral types K5 to M3. 20 stars with representation from the
extreme, classical, and weak subclasses of TTS were observed at up to
6 different epochs between October 1986 and January 1989. Almost all
of these observations contain, to some degree, narrow (average FWHM of
38 km/s), generally symmetric He I D3 emission at rest velocity with
respect to the star superimposed on a broad (average FWHM of 177 km/s),
asymmetric emission component apparently slightly blueshifted with
respect to the star. The goal of this study is to measure line strengths
representing only chromospheric radiative losses in the D3 line in
order to gain insight as to the mechanisms of He I line formation in
TTS. All observations are corrected for any veiling effects of excess
continuum emission. Veiling measurements for this data set already
exist in the literature. We adopt these values except in cases of high
uncertainty estimates or apparent discrepancies which we find for the
extreme TTS in our sample. In these cases, we recalculate the veiling
by fitting analytic gaussians to weak absorption lines and comparing
line depths to those of appropriate photospheric templates. We make
the following conclusions: 1) Gaussian fits to weak absorption lines
give lower veiling values than those in the literature due to enhanced
stellar activity in the TTS whose effects are generally more pronounced
in stronger lines. 2) The lithium line at 6707 Angstroms is not a good
indicator of continuum veiling since it shows variable strengths even
after correcting for veiling. We find a correlation between Li I 6707
Angstroms line strength and veiling for RW Aur suggesting that this
line is enhanced by accretion processes. 3) We find a correlation
between the chromospheric radiative losses in the D3 line and veiling
for veilings up to approximately 1.0 suggesting that this line as well
is enhanced by accretion processes.

---------------------------------------------------------
Title: EUVE Deep Survey Observations of a Large Flare on AU MIC
Authors: Cully, S. L.; Siegmund, O. H. W.; Basri, G.; Vedder, P. W.;
Vallerga, J. V.
1992AAS...181.8009C Altcode: 1992BAAS...24.1251C
We have made the first observation of a stellar flare in the EUV at
100 second time resolution. The flare was first detected on AU Mic by
the EUVE Deep Survey Instrument at 12:38 UT on July 15, 1992, during
a four-day observation from July 14 to 18, 1992. This was a large
flare detected in the Lexan/boron band (centered at 100 Angstroms)
with an observed peak count rate of approximately 7 counts per second,
corresponding to a peak luminousity of 10(30) ergs sec(-1) in our
bandpass. This is significantly above the measured quiescent level of
0.4 +/- 0.2 counts per second. The flare consisted of a peak lasting
approximately 2 hours, followed by a decaying tail that lasted over a
day. We compare this EUV observation with stellar flare observations in
other bandpasses and discuss the implications of this long decay. This
work has been supported by NASA grant NAGW-1290 and NASA contracts
NAS5-30180 and NAS5-29298.

---------------------------------------------------------
Title: Balmer Jumps in T Tauri Stars
Authors: Valenti, Jeff A.; Basri, G. B.
1992AAS...18110311V Altcode: 1992BAAS...24.1288V
Using well measured Balmer jumps and emission line strengths, we
discuss the origin of excess optical emission from classical T Tauri
stars. We present a selection of moderate resolution, moderate S/N,
flux--calibrated, blue spectra from our sample of 97 T Tauri stars. They
illustrate the range of observed emission levels. The spectra extend
from 3400 Angstroms to 5000 Angstroms, and they include the Balmer
jump and the entire Balmer series except for Hα . We detail a new
method of measuring Balmer jumps that uses a spectral model to infer
the true jump, rather than attempting to measure it directly from
the spectrum. A weak T Tauri star of similar spectral type is used
to remove the photospheric contribution from our CTTS spectra. The
remaining “excess” emission is then modelled as an isothermal
rectangular slab of hydrogen projected against the star. A simple
slab of hydrogen does a remarkably good job of explaining continuum
and high Balmer line (beyond Hdelta ) emission. The continuum shape
and flux, including the magnitude of the Balmer jump are well matched
for most of the CTTS in our sample. The role of H(-) \ is critical
in mediating the size of the Balmer jump. Because H(-) \ emission is
sensitive to density, we believe that most of the continuous optical
excess emission in CTTS arises from gas at a density of roughly 10(14)
\ cm(-3) . The continuous emission from the hydrogen slab also serves
to weaken or “veil” photospheric absorption lines in accordance
with our observations. The general behavior and strength of the high
Balmer lines can be reproduced by a slab model. The low Balmer lines,
however, have considerable excess emission beyond that arising from
the isothermal slab, which we take as evidence for a lower density
component, perhaps arising in a wind. We also discuss the relationship
between the Balmer jump and various other measures of excess emission.

---------------------------------------------------------
Title: Mg II Line Profiles in the T Tauri Stars
Authors: Imhoff, C. L.; Giampapa, M. S.; Basri, G.
1992AAS...180.4310I Altcode: 1992BAAS...24..798I
No abstract at ADS

---------------------------------------------------------
Title: Limits on the Magnetic Flux of Pre--Main-Sequence Stars
Authors: Basri, Gibor; Marcy, Geoffrey W.; Valenti, Jeff A.
1992ApJ...390..622B Altcode:
Magnetic fields on two weak-emission-line T Tauri stars were
detected by searching for the enhancement of the equivalent widths
of Zeeman-sensitive absorption lines. For both stars, 26 observed
Fe I lines, which represent a wide range of Zeeman sensitivities,
are synthesized using an LTE Stokes line-transfer calculation. The
theoretical growth of equivalent width with magnetic field is discussed
for lines with various Zeeman patterns. Oscillator strengths for all
lines are empirically determined a priori using a magnetically quiet
star of similar spectral type. The iron abundances of both T Tauri
stars are established by synthesizing lines that are insensitive to
Zeeman splitting. The observed equivalent widths of Zeeman-sensitive
lines in TAP 35 are found to be systematically enhanced relative to
those calculated for no magnetic field, while such an enhancement is
not seen in Zeeman-insensitive lines.

---------------------------------------------------------
Title: Synoptic Studies of the T Tauri Star SU AUR
Authors: Johns, C. M.; Basri, G. S.; Giampapa, M. S.; Defonso, E.
1992ASPC...26..441J Altcode: 1992csss....7..441J
No abstract at ADS

---------------------------------------------------------
Title: The lithium resonance line in T Tauri stars.
Authors: Basri, G.; Martin, E. L.; Bertout, C.
1991A&A...252..625B Altcode:
High-resolution spectra provide evidence of the Li-I 6707 line in 28 of
the stars, and the significance of the results is discussed. The Li-I
equivalent widths are presented after correcting for continuum veiling
with actual measurements of the veiling itself. Surface spots are found
to have a complex effect on the width of the photospheric lines, and
the width of the line for V 410 Tau does not appear to change with spot
coverage. The results indicate that the model atmospheres and stellar
parameters for the T-Tauri stars lead to errors in calculating the Li
abundances. The stars have higher Li abundances than meteorites and the
local ISM if the T-Tauri stars are hotter than late K. Several effects
are discussed which are of an unusual nature including the Li depletion
among young low-mass Taurus-Auriga objects and the homogeneous nature
of Li depletion among stars with strong and weak emission lines.

---------------------------------------------------------
Title: Deciphering the UV Emission Lines in T Tauri Systems
Authors: Basri, Gibor
1991hst..prop.3845B Altcode:
Currently there is complete confusion as to the physical origin of the
UV emission lines in T Tauri stars, although they are the strongest
known UV emissions from cool stars. Possibilities include closed
magnetic field loops in analogy to active main sequence stars, a hot
region in an Alfven wind, the accretion boundary layer between star
and disk, accretion columns in the stellar magnetic field, or some
other region associated with a disk-generated wind. Emission measure
analyses have been unable to distinguish between the possibilities
listed above. What is clearly needed is line profile information:
in particular a good measurement of the breadth of the profiles
and a reasonable idea of their symmetry. Narrow lines will indicate
plasma originating either on the stellar surface or in closed magnetic
loops. Broad lines will indicate a turbulent boundary layer or wind
region. The asymmetry of the lines will indicate whether they arise in
accretion, outflow, or relatively static plasma, and something about the
size of the region (via occulation effects). Taken with some emission
measures, density diagnostics, and wind diagnostic information, the
current mystery about the origin of these strong hot emission lines
can be illuminated. We propose to measure enough profiles and emission
measures in a representative small sample of stars to constrain,
support or eliminate the above hypotheses.

---------------------------------------------------------
Title: EUVE Observations of Hot DA White Dwarfs
Authors: Basri, G.; Finley, D. S.; Jelinsky, P.
1991BAAS...23..970B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Limits on the Magnetic Flux of a Pre-Main Sequence Star
Authors: Basri, G.; Marcy, G. W.
1991LNP...380..401B Altcode: 1991IAUCo.130..401B; 1991sacs.coll..401B
We attempt to detect a magnetic field on the weak T Tauri star, TAP35,
via the enhanced equivalent widths of Zeeman-broadened absorption
lines. We synthesize 25 Fe I lines, having a range of Zeeman
sensitivities, using an LTE Stokes line-transfer calculation. The
oscillator strengths of all lines are empirically determined a priori
using the same line-transfer code applied to the spectrum of the
magnetically quiet star, Ceti. The Fe abundance of TAP35 was established
by synthesizing lines that are insensitive to Zeeman splitting. We find
that the equivalent widths, W eq, of Zeeman-sensitive lines in TAP35
are systematically enhanced relative to the Zeeman-insensitive lines,
consistent with the presence of widespread, kilogauss fields. The
excess W eq can be explained by a product of field strength and
surface filling factor (B f) of 1 kiloGauss. A strong upper limit can
be placed on the product of those two quantities, B f &lt; 2 kG. This
measurement bears on the physics of T Tauri coronae, chromospheres,
dynamos, and accretion-disk boundary layers.

---------------------------------------------------------
Title: Stellar Zeeman Analyses - Effects of Multi-Component
Atmospheres
Authors: Marcy, G. W.; Basri, G.; Valenti, J. A.
1991LNP...380..407M Altcode: 1991IAUCo.130..407M; 1991sacs.coll..407M
We simulate the radiative transfer of Zeeman-broadened lines in an
active star containing both quiet and flux-tube regions. A traditional
one-atmosphere Zeeman analysis of these synthetic lines yields magnetic
field measurements systematically inaccurate by up to 40%. However,
two atmospheric components alone cannot reproduce the observed line
strengths, luminosities or photometric constancy of active stars.

---------------------------------------------------------
Title: Disks around T Tauri Stars.
Authors: Basri, G.; Bertout, C.
1991sepa.conf..189B Altcode: 1991IAUCo.129..189B
No abstract at ADS

---------------------------------------------------------
Title: Properties and Models of T Tauri Stars
Authors: Bertout, Claude; Basri, Gibor
1991ASIC..342..649B Altcode: 1991psfe.conf..649B
Historical Background and Key Observations Basic Physics of Accretion
Disks Comparisons with Observations The Evolutionary Status of CTTS
and WTTS Summary

---------------------------------------------------------
Title: The Classical T Tauri Stars: Future Solar Systems?
Authors: Bertout, Claude; Basri, Gibor; Cabrit, Sylvie
1991suti.conf..682B Altcode:
Observed properties of low-mass young stellar objects are reviewed with
emphasis on their circumstellar (possibly) protoplanetary disks and on
their powerful winds. Proposed theoretical wind mechanisms are proposed
in the light of observational constraints, and it is concluded that
although none of the existing mass-loss theories is entirely convincing,
they demonstrate that both the disk and the magnetic field must play
key roles in protostellar and T Tauri mass ejection.

---------------------------------------------------------
Title: Temperatures of Hot DA White Dwarfs
Authors: Basri, Gibor S.
1991iue..prop.3941B Altcode:
We propose to complete the program which we began last year of observing
the remaining hot (Teff &gt; 30,000 K) DA white dwarfs which are
observable with IUE. The main purpose is to obtain the effective
temperatures of the targets. The temperatures will be needed for
successful analysis of the extreme ultraviolet (EUV) data which will be
obtained for numerous hot DA white dwarfs by the EUV Explorer sky survey
mission. The IUE observations include small aperture SWP observations
which are being used for temperature and gravity determinations based on
fitting the Lyman-alpha line profile. Ground-based observations are also
being made of the Balmer lines of these stars, giving an independent
temperature and gravity measurement. With the complete data sets, we
will be able to detect attenuation due to dust absorption, and in some
cases may be able to directly measure the neutral hydrogen column. We
also intend to use the combined Balmer and Lyman-alpha line profile
measurements to attempt to detect the presence of stratification of the
atmospheres of the white dwarfs. Determination of HeII 1640 A and 4686 A
line strengths (or upper limits) will also be used as a stratification
indicator. Half of the 24 targets are expected to be observed during
the 13th Episode (three, to date). The time being requested for the
14th Episode is required to observe the remainder of the targets.

---------------------------------------------------------
Title: Lithium Abundances as a Probe of the Early Evolution of
Solar-type Stars
Authors: Martin, Eduardo L.; Basri, Gibor; Bertout, Claude
1991LNP...390...63M Altcode: 1991beb..conf...63M; 1991bioa.conf...63M
No abstract at ADS

---------------------------------------------------------
Title: The Young Star Cluster in NGC 1275: H-alpha Linewidth and
Star Formation Properties
Authors: Shields, Joseph C.; Filippenko, Alexei V.; Basri, Gibor
1990AJ....100.1805S Altcode:
High spectral resolution observations of the massive young star cluster
in the filaments of NGC 1275 reveal that the associated Hα emission
line ]as a velocity width comparable to, or somewhat less than,
that of Hα in typical giant H II regions of similar emission-line
luminosity. If this linewidth reflects virial motions of matter within
the star-forming region, as has been suggested for other giant H II
regions, the mass fraction represented by massive, ionizing stars is not
unusually small in this object, and may actually be somewhat larger than
average. This behavior is contrary to scenarios of preferential low-mass
star formation that have been invoked to reconcile x-ray and optical
indications of mass accretion in this object and other cooling-flow
galaxies. The observations also confirm that the cluster emission
connects smoothly in projected location and velocity with emission
from a low-ionization nebular filament. If this region is typical of
star formation in cooling flows, it provides strong evidence that the
mass accretion rate is less than that predicted from estimates based
on x-ray cooling.

---------------------------------------------------------
Title: Hamilton Echelle Spectra of Young Stars. I. Optical Veiling
Authors: Basri, Gibor; Batalha, Celso
1990ApJ...363..654B Altcode:
An extensive set of veiling measurements of T Tauri stars covering
almost the entire optical spectrum is presented. These are based on
Hamilton echelle spectra obtained during 1987-1989. A full range
of T Tauri stars, from 'weak' to 'continuum' stars is studied;
in some cases, several spectra of a given target are seen in which
the veiling has changed, occasionally dramatically. Veilings are
determined using two new methods: one which concentrates on the
residual intensities of selected spectral lines, and the other which
compares the autocorrelation functions for a T Tauri star and a veiled
standard. The general shape of the veiling is often as predicted by
accretion disk models: almost flat in the red and increasing in the
blue. Cooler stars have generally higher veiling, implying that the
veiling power is relatively independent of stellar mass. The relation
between veiling and the narrow and broad emission lines supports a
nonstellar origin for the veiling and broad line components, and a
stellar origin for the narrow lines.

---------------------------------------------------------
Title: Physical Realism in the Analysis of Stellar Magnetic
Fields. III. Flux Tubes and Multicomponent Atmospheres
Authors: Basri, Gibor; Marcy, Geoffrey W.; Valenti, Jeff A.
1990ApJ...360..650B Altcode:
Several important tests of likely systematic effects in the analysis
of Zeeman broadening on cool stars have been performed. The effects
of different atmospheric structures inside and outside of magnetic
regions are considered, and the effects of field gradients within
flux tubes and of errors in the assumed spectral type of a star are
considered. It is found that substantial effects are possible which
render the results of one-component analyses somewhat uncertain,
with systematic errors potentially as great as 40 percent in the
derived magnetic flux. However, it appears that two-component models
consisting of quiet and flux tube regions may be oversimplified, since
the predicted line profiles tend to be shallower than those observed.

---------------------------------------------------------
Title: Solar systems in the making
Authors: Basri, Gibor
1990Natur.346..515B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Temperature Scale of Hot DA White Dwarfs: Temperatures
from Far-Ultraviolet Continuum Fluxes
Authors: Finley, David S.; Basri, Gibor; Bowyer, Stuart
1990ApJ...359..483F Altcode:
Observed far-UV to visible flux ratios of all DA white dwarfs hotter
than about 25,000 K are compared with ratios predicted by models in
order to derive effective temperatures for the stars. All suitable IUE
spectra of seven hot DA white dwarfs for which accurate temperatures
based on hydrogen line profiles were available are used to derive
a flux correction to the 1980 IUE absolute calibration. Application
of the corrections to the IUE spectra results in derived temperature
which are consistent with the line profile temperatures.

---------------------------------------------------------
Title: Strong emission line profiles from T Tauri stars.
Authors: Basri, Gibor
1990MmSAI..61..707B Altcode:
This paper reviews spectroscopic observations available on the classical
T Tauri stars, including observations of the Balmer lines and other
strong lines such as those from singly ionized Ca and the He I 5876 A
line and, in the more extreme stars, Fe I and Fe II. The explanations
for the production of various line profiles (such as spherical line
formation, axisymmetric line formation, and turbulent line formation)
from various physical scenarios are examined.

---------------------------------------------------------
Title: Observations of Photospheric Activity in Cool Dwarfs
Authors: Basri, Gibor S.
1990iue..prop.3660B Altcode:
IUE spectra have been used to greatly enhance the information on stellar
chromospheric activity compared with ground-based observations. This
is because the brightness contrast between the hot chromosphere and
the cooler photosphere is substantially larger in the ultraviolet
than in the optical. The same advantage can be used in the analysis of
photospheric activity nonradiative heating of the upper photosphere),
which has received scant attention to date, due to the extreme subtlety
of its observational consequences in the optical. Nevertheless,
a majority of the nonradiative heating of stellar atmospheres
occurs in the upper photosphere, not the chromosphere. We propose a
differential analysis of ultraviolet absorption lines in active and
inactive cool dwarfs of the same spectral type, using high dispersion
IUE spectra. This should allow assessment of whether sources of heating
are the same at photospheric and chromospheric levels, and clarify the
role of acoustic waves. Adequate IUE spectra of active stars already
exist, but observations of inactive stars are very sparse, and more
are needed for a meaningful differential analysis.

---------------------------------------------------------
Title: Temperatures of Hot DA White Dwarfs
Authors: Basri, Gibor S.
1990iue..prop.3651B Altcode:
We propose to continue our FUV observations of the known hot (Teff
&gt; 25,000 K) DA (predominantly hydrogen atmosphere) white dwarfs
for the purpose of obtaining their effective temperatures. Accurate
temperatures for these objects serve several purposes: determination
of the upper temperature limit, better definition of the luminosity
function/cooling sequence, and the theoretical interpretation of trace
element abundances. The temperatures will also be needed for analysis
of extreme ultraviolet (EUV) data which will be obtained for numerous
hot DA white dwarfs in upcoming sky survey missions. Our previous
FUV data analysis efforts resulted in a substantial improvement in
the absolute calibration of the IUE instruments, and showed that
the IUE continuum fluxes could be used to determine the effective
temperatures of the hot DA's to an accuracy of typically 5% or
better. The proposed new observations will include (when feasible)
small aperture observations with the SWP camera which will be used for
temperature and gravity determinations based on fitting the Lyman a
line profile. Independent ground-based observations will also be made
of the Balmer lines of these stars, giving another temperature and
gravity measurement. The complete data sets will provide unambiguous
determinations of the properties of the targets. For example, the
FUV continuum fluxes may in some cases be attenuated due to dust
absorption. The use of the FUV continuum alone would then result in an
erroneously low temperature. However, a comparison of the measured FUV
flux with the predicted flux based on the line profile temperatures
would give a measurement of the attenuation. If the star is very hot
and the reddening is significant, the absorption in the damping wings
of interstellar Lyman cc can be used for a direct measurement of the
neutral hydrogen column, thereby giving the dust-to-gas ratio in that
line of sight. The primary usage of the interstellar medium properties
will be for subsequent EUV data analysis. We also intend to use the
combined Balmer and Lyman-alpha fine profile measurements to attempt to
detect the presence of stratification of the atmospheres of the white
dwarfs. Determination of HeII 1640 A line strengths (or upper limits)
will also be used as a stratification indicator. Our examination of
the published data for spectroscopically identified white dwarfs and
of the IUE Log has resulted in the identification of -25 white dwarfs
hotter than 30,000 K which it is feasible and worth while to either
observe for the first time or else reobserve with TUE. In the case of
targets which have previously been observed, we only intend to take
spectra in a different configuration than that used previously (such
as small aperture SWP), except for those cases in which the previous
exposures were not of suitable quality for the analyses which we are
carrying out. All observations will be made in low dispersion mode;
none of the proposed targets are bright enough for high dispersion
observations. The lengths of the exposures required are such that the
preponderance of the observations should be done during US1 shifts, in
order to obtain spectra of sufficient quality. We are asking for only
half the time necessary for performing the full set of observations; we
anticipate proposing again for the following year in order to complete
the work. The complete target list is being submitted at this time in
order to achieve the maximum flexibility in scheduling the observations.

---------------------------------------------------------
Title: Optical Veiling from Accretion onto T-Tauri Stars
Authors: Batalha, C.; Basri, G.
1989PASP..101..878B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Physical Realism in the Analysis of Stellar Magnetic
Fields. II. K Dwarfs
Authors: Marcy, Geoffrey W.; Basri, Gibor
1989ApJ...345..480M Altcode:
Evidence for the Zeeman broadening was searched for in the absorption
line profiles of 11 large G and K dwarfs. The analysis employed was
different from past efforts in that it is closely tied to the actual
physical processes that produce Zeeman-broadened absorption lines in
these stars. The radiative line transfer in all Stokes parameters is
computed for a model stellar atmosphere and the resulting intensity
profiles are disk-integrated to model the stellar rotation and
macroturbulence. Zeeman-sensitive profile was constructed, and Zeeman
broadening was detected as an excess broadening between the synthesized
8468 profile and the observed profile. Six of the 11 stars were shown
to exhibit clear Zeeman broadening, the most extreme being Epsilon
Eri and Xi Boo A; Cyg A was found among the stars showing clear Zeeman
broadening, contrary to expectations for an old slow rotator. Two stars,
Sigma Dra and 54 Psc were found with no Zeemen broadening at all,
showing that magnetically weak stars exist later than K0.

---------------------------------------------------------
Title: The Temperature Scale of Hot DA White Dwarfs Based on FUV
Spectrophotometry
Authors: Finley, D.; Basri, G.; Bowyer, S.
1989BAAS...21.1102F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Wild Spectral Variations in DF Tau
Authors: Basri, G.; Misch, A.
1989BAAS...21.1084B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Accretion Disks around T Tauri Stars. II. Balmer Emission
Authors: Basri, Gibor; Bertout, Claude
1989ApJ...341..340B Altcode: 1989ApJ...341..341B
Original models of T Tauri systems, which assumed them to be composed of
a premain-sequence low-mass star similar to the 'naked' T Tauri stars,
along with an accreting circumstellar disk, have been refined. The
main extension of the models has been to incorporate the possibility
of optically thin emission from the accretion boundary layer in
order to explain the Balmer continuum emission jumps observed in
many such systems. This is done by treating the boundary-layer size
(and possibly the disk viscosity) as additional free parameters. It
is shown that this produces a very satisfactory explanation for the
Balmer emission found in new blue spectra, while preserving the ability
to explain the continuum distribution from the ultraviolet to the
midinfrared. The problem of how unique the parameters determined from
these disk models are, is discussed, and it is concluded that further
independent constraints on the stellar parameters would be very helpful.

---------------------------------------------------------
Title: Photospheric Activity in Main-Sequence Stars
Authors: Basri, Gibor; Wilcots, Eric; Stout, Natalie
1989PASP..101..528B Altcode:
High-resolution echelle spectra were obtained for early K dwarfs
in order to study the effects of stellar activity on photospheric
absorption lines. Two classes of effects are noted in the ratio spectra:
simple pseudoemission profiles resulting from the filling in of the
line core, and profiles indicating that lines in some active stars have
broader wings but shallower cores than their inactive counterparts. It
is suggested that the present stellar activity effects may be the
result of a shallower average photospheric temperature gradient due to
nonradiative heating in the upper photosphere and additional effects
inside the magnetic flux tubes.

---------------------------------------------------------
Title: Synoptic Observations of RW Aurigae
Authors: Stout, N. M.; Basri, G. B.; Misch, T.
1989BAAS...21..716S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Profiles of Strong Lines in T Tauri Stars
Authors: Basri, G. B.; Rumph, T. F.; Batalha, C. C.; Stout, N. M.
1989BAAS...21..716B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations of the Type II Supernova 1986I in M99
Authors: Pennypacker, C. R.; Burns, M. S.; Crawford, F. S.; Friedman,
P. G.; Graham, J. R.; Kare, J. T.; Muller, R. A.; Perlmutter, S.;
Smith, C. K.; Treffers, R. R.; Williams, R. W.; Basri, G.; Bixler,
J.; Filippenko, A. V.; Foltz, C.; Garnett, D. R.; Harkness, R. P.;
Junkkarinen, V.; Kennicutt, R.; McCarthy, P. J.; Spinrad, H.; Wheeler,
J. C.; Willick, H.; Wills, B. J.
1989AJ.....97..186P Altcode:
We report spectra for the first seven weeks and photometry for the
first seven months of supernova SN 1986I in M99. This object was below
our detection threshold of about 16.6 mag on 8 May (UT), and was first
detected in an image obtained on 17 May (UT). From its first spectrum
(taken on 20 May UT), SN 1986I exhibited strong Hα emission. During
the first three months after detection, the light curves in V, R,
and I dropped slowly (+0.01 mag/day or less), indicating a Type II
plateau supernova. The SN then disappeared behind the Sun for 75 days,
re-emerging about 1.5 mag dimmer than predicted by linear extrapolation
of the light curves of the first three months. We have measured the
wavelengths and velocities of the stronger emission and absorption
features, with standard identifications.

---------------------------------------------------------
Title: Far ultraviolet observations of hot DA white dwarfs
Authors: Finley, David; Basri, Gibor; Bowyer, Stuart
1989LNP...328..138F Altcode: 1989IAUCo.114..138F; 1989whdw.coll..138F
Far ultraviolet (FUV) fluxes have been used for determining the
effective temperatures of a number of DA white dwarfs hotter than
20,000 K. The analysis consisted of comparing the observed FUV
fluxes with model fluxes scaled to the V-band flux. After suitable
corrections were performed for the time-dependent sensitivity
degradation of the IUE, it was found that the available flux
calibrations for the IUE were insufficiently accurate for precise
temperature determinations. Accordingly, seven white dwarfs for which
accurate, independent temperature determinations were made from line
profile analyses were used to improve the accuracy of the IUE flux
calibration. The correction to the original calibration was as great as
20 percent in individual 5-A wavelength bins, while the average over
the IUE wavelength range was 5 percent. Both the IUE flux correction
and the temperatures obtained for the hot white dwarfs are presented.

---------------------------------------------------------
Title: Modelling T Tauri systems.
Authors: Bertout, Claude; Bouvier, Jerome; Basri, Gibor
1989mse..proc..189B Altcode:
There is now compelling evidence that T Tauri stars are systems made
up of a late-type active central star surrounded by an extended,
probably proto-planetary accretion disk. Besides a description of the
stellar photospheric and chromospheric radiation fields, models of these
objects must therefore also include a description of disk emission and
of the interaction between star and disk in the equatorial boundary
layer. The authors review the current state-of-the-art in T Tauri
star/disk models and discuss observational and theoretical areas in
which improvements are both needed and possible.

---------------------------------------------------------
Title: Far Ultraviolet Observations of Hot DA White Dwarfs
Authors: Finley, David; Basri, Gibor; Bowyer, Stuart
1989LNP...328..139F Altcode: 1989IAUCo.114..139F; 1989whdw.coll..139F
Far ultraviolet (FUV) fluxes have been used for determining the
effective temperatures of a number of DA white dwarfs hotter than
20,000 K. The spectra were obtained with the International Ultraviolet
Explorer (IUE). The analysis consisted of comparing the observed FUV
fluxes with model fluxes scaled to the V-band flux. After suitable
corrections were performed for the time-dependent sensitivity
degradation of the IUE, it was found that the available flux
calibrations for the IUE were insufficiently accurate for precise
temperature determinations. Accordingly, we used seven white dwarfs
for which accurate, independent temperature determinations have been
made from line profile analyses to improve the accuracy of the IUE flux
calibration. The correction to the original calibration was as great
as 20% in individual 5-A wavelength bins, while the average over the
IUE wavelength range was 5%. We present both our IUE flux correction
and the temperatures obtained for the hot white Dwarfs

---------------------------------------------------------
Title: Accretion Disks and T Tauri Stars
Authors: Basri, Gibor S.
1989iue..prop.3385B Altcode:
The T Tauri stars represent the first time during a young star's
evolution that we can directly observe its surface. There is increasing
evidence that circumstellar disks remain around the classical T Tauri
stars. These are manifested through infrared excesses which both cannot
be easily explained any other way and can be easily explained with
simple disk models. In the event the disk is still accreting onto the
star, there might be a violent boundary layer at the interface between
the disk and star which can produce as much luminosity as the infrared
excess from the disk, but in the ultraviolet. Is this the source of some
or all of the ultraviolet and emission line activity associated with T
Tauri stars? Our research with previous IUE observations has strongly
supported this possibility, providing a major leap in the understanding
of young stars. The biggest remaining ambiguity arises because there
is also strong magnetic activity on these stars. If the boundary layer
model is relevant, there should be correlated variations between the
excess UV and IR emission measured at the same time; this would not be
the case if classical chromospheres supply the UV luminosity. Our recent
Work on optically thin boundary layers suggests that the UV variations
due to chromospheres and boundary layers will produce different veiling
effects as well. We propose to extend the number of disks studied,
and to make a direct test of whether accretion is the explanation for
many of the spectral peculiarities of classical T Tauri stars using
coordinated UV, visible, and infrared observations. This proposal is
a continuation of last year's proposal for which the main criticism
by the peer review panel was that it should have been a 2-year proposal!

---------------------------------------------------------
Title: Observations of Young Stars
Authors: Basri, G. B.
1988BAAS...20Q1034B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Accretion Disks around T Tauri Stars
Authors: Bertout, Claude; Basri, Gibor; Bouvier, Jerome
1988ApJ...330..350B Altcode:
The authors examine the proposition that many T Tauri stars are still
actively accreting material from a surrounding disk of material formed
at the same time as the star. It is shown that the observations are both
unified and explained if classical T Tauri stars are chromospherically
active pre-main-sequence stars with accretion disks. Contemporaneous
optical and ultraviolet observations, along with extensive photometric
monitoring in the optical and infrared, are used to test disk
models and to show that there is evidence for accretion in the range
5×10-8 - 5×10-7M_sun;yr-1 from stars
exhibiting strong ultraviolet excesses. These models also explain the
infrared spectrum shortward of 10 μm and the total system luminosities.

---------------------------------------------------------
Title: Physical Realism in the Analysis of Stellar Magnetic Fields
Authors: Basri, Gibor; Marcy, Geoffrey W.
1988ApJ...330..274B Altcode:
The detection and analysis of magnetic fields on cool stars have been
reexamined using improved theoretical and observational methods. Lines
in the near-infrared are employed which are both accessible at high
signal-to-noise and resolution with CCD detectors, and more sensitive
to Zeeman broadening than optical lines. The analysis of these is
treated with a model atmosphere code which includes all relevant line
and stellar physics (in LTE) instead of the approximate treatment of
transfer that has been previously used. The possibility that observed
broadenings could be due to deficiencies in past or present methods
of analysis is carefully examined, and it is concluded that magnetic
fields are really being detected. In particular, for Epsilon Eri an
average field strength of 1000 G covering 35 percent of the stellar
surface is derived and for Boo A a field of 1200 G covering 40 percent
of the surface is derived. The analysis of fields from observations
of spectral line profiles is discussed in detail, and some future
improvements which could be made in it are mentioned.

---------------------------------------------------------
Title: Observations of interstellar absorption lines toward hot
white dwarfs
Authors: Jelinsky, Patrick; Bowyer, Stuart; Basri, Gibor
1988ESASP.281b.235J Altcode: 1988uvai....2..235J; 1988IUE88...2..235J
A method of detecting and determining parameters for narrow
absorption lines in IUE high-resolution spectra of hot white dwarfs
was developed. It provides a statistical estimate of the variance
of the parameters measured. The statistical accuracy of narrow
line measurements with IUE spectra is discussed. The method was
employed to determine the column densities of low-ionization species
(including N I, Si II, and C II) in the line of sight to seven hot white
dwarfs. High-ionization species (N V, Si IV, and C IV) are detected
towards four of the stars. The temperature of the low-ionization
gas towards 4 of the stars is constrained to be less than 50,000
K. The temperature of the high-ionization gas to two of the stars is
constrained to be under 100,000 K, which is well below the equilibrium
ionization temperature of a collisionally ionized gas. This suggests
that this gas is either in a photoionized region (most likely near
the star) or is produced in the photosphere of the star.

---------------------------------------------------------
Title: Temperature determinations of hot DA white dwarfs using IUE
continuum flares
Authors: Finley, David; Basri, Gibor; Bowyer, Stuart
1988ESASP.281a.267F Altcode: 1988IUE88...1..267F; 1988uvai....1..267F
Effective temperatures of 15 DA white dwarfs hotter than 20,000 K
were derived from low-dispersion far ultraviolet spectra obtained
with IUE. The analysis was carried out by comparing the observed
far ultraviolet fluxes with model fluxes scaled to the V-band
flux. Accurate calibration of the IUE spectra is critical for this
analysis. Observations at all epochs were corrected to the 1980
IUE calibration using the time-dependent corrections of Bohlin
(1988). Taking advantage of the smooth and well-defined continuum
fluxes provided by DA white dwarfs, seven white dwarfs for which
accurate, independent temperature determinations were made from line
profile analyses were used to improve the accuracy of the IUE flux
calibration. The correction to the original calibration is as great
as 20 percent in individual 5 A wavelength bins, while the average
over the IUE wavelength range is 5 percent. The final calibration
correction and the temperatures for the hot white dwarfs are presented.

---------------------------------------------------------
Title: Photospheric Activity in Cool Main Sequence Stars
Authors: Wilcots, E. M.; Basri, G. B.; Stout, N. M.
1988BAAS...20..696W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Supernova 1988H in NGC 5878
Authors: Filippenko, A. V.; Basri, G.
1988IAUC.4561....1F Altcode: 1988IAUC.4561....0F
A. V. Filippenko and G. Basri, University of California at Berkeley,
report that spectra (range 390-700 nm, resolution 1-2 nm) obtained
by Basri on Mar. 8 UT with a CCD spectrograph on the 3-m Shane
reflector at Lick Observatory show that the new object in NGC 5878
(IAUC 4560) is a type-II supernova, probably a few weeks past maximum
brightness. Strong, broad (FWHM about 8000 km/s) H-alpha emission is
present, as is a blueshifted H-alpha absorption trough.

---------------------------------------------------------
Title: Magnetic Field Measurements on Late-Type Stars : a New
Technique
Authors: Marcy, G. W.; Basri, G.
1988IAUS..132..301M Altcode:
A new technique for detecting and measuring magnetic fields on cool
stars is presented, incorporating both an improved observational
approach and a rigorous LTE theoretical treatment. The authors have
identified two lines in the near infrared, one of which is very
sensitive to Zeeman broadening and the other relatively insensitive,
that are easily accessible to CCD and Reticon detectors. The authors
have obtained high resolution, high S/N spectroscopic observations
of several G and K dwarfs and have synthesized the two lines using
two free parameters, namely, the average field strength, B, and the
fraction, f, of the surface covered by fields.

---------------------------------------------------------
Title: Accretion Disks and T Tauri Stars
Authors: Basri, Gibor
1988iue..prop.3074B Altcode:
The T Tauri stars represent the first time during a young star's
evolution that we can directly observe its surface. They display extreme
activity with far-UV emission lines up to 3 orders of magnitude stronger
than in the quiet sun. There is increasing evidence that circumstellar
disks remain around the classical T Tauri stars. These are manifested
through infrared excesses which both cannot be easily explained any
other way and can be easily explained with simple disk models. In a
number of systems, the bolometric luminosity is substantially higher
than the best estimate of what can be produced by the star: the best
explanation is that accretion luminosity is still being produced in the
disk. If so, there might be a violent boundary layer at the interface
between the disk and star which can produce as much luminosity as
the infrared excess from the disk, but in the ultraviolet. Is this
be the source of some or all of the ultraviolet and emission line
activity associated with T Tauri stars? Our research with previous
IUE observations has strongly supported this possibility, providing a
major leap in the understanding of young stars. The biggest remaining
ambiguity arises because there is also strong magnetic activity on
these stars. If the boundary layer model is relevant, there should be
correlated variations between the excess UV and IR emission measured
at the same time; this would not be the case if classical chromospheres
supply the UV luminosity. We propose a direct test of whether accretion
is the explanation for many of the spectral peculiarities of classical T
Tauri stars using coordinated UV, visible, and infrared observations. We
also extend our ground-breaking research on T Tauri accretion begun
last year.

---------------------------------------------------------
Title: Emission Activity on T Tauri Stars
Authors: Basri, G.
1988ASIC..241..247B Altcode: 1988felm.conf..247B
No abstract at ADS

---------------------------------------------------------
Title: High Quality Echelle Observations of T Tauri Stars
Authors: Basri, G.
1988IAUS..132...99B Altcode:
This is a very brief review of the high resolution line profile work
that has been done on very young stars. The spectral anomalies peculiar
to these stars are mentioned, with some discussion of what may give rise
to them. The Hα line is discussed most extensively, as the most work
has been done with it. While progress has been made in understanding
the general nature of T Tauri spectra, there are very large gaps in
our current understanding of the emission lines from these stars.

---------------------------------------------------------
Title: The Atmospheres of T Tauri Stars. I. High-Resolution Calibrated
Observations of Moderately Active Stars
Authors: Finkenzeller, Ulrich; Basri, Gibor
1987ApJ...318..823F Altcode:
Calibrated optical spectra from 3700 to 8700 Å with high resolution
and signal-to-noise ratio have been obtained quasi-simultaneously
for three pairs of cool low- and intermediate-activity southern T
Tauri stars and one G2 T Tauri star with well-defined photospheric
spectra. Together with observations of spectral standards, these are
used to obtain spectral types, reddening corrections, radial velocities,
v sin i, and in combination with near-IR and IRAS data, photospheric and
systemic luminosities. From positions in the H-R diagram, the authors
determine the mass, radius, and surface gravity for each object. Surface
fluxes in the emission lines are discussed. For all targets, ratio or
difference plots versus appropriate standards are analyzed and show
that important features of T Tauri spectra are clearly chromospheric.

---------------------------------------------------------
Title: Stellar Activity in Synchronized Binaries. II. A Correlation
Analysis with Single Stars
Authors: Basri, Gibor
1987ApJ...316..377B Altcode:
The interdependences between various measures of activity and a number
of relevant stellar parameters are explored for a sample of largely
post-main-sequence, late-type binaries with orbital periods from one
to 100 days. This paper examines the relations between diagnostics
formed at various heights in the atmospheres, and between activity
and stellar parameters expected to have a bearing on the level of
activity. The stars are compared with single dwarfs having similar
periods. It is found that the binaries closely resemble the single
stars in the way the various activity diagnostics are related to each
other. The primary dependence of activity is confirmed to be on stellar
rotation. Tidal coupling is ruled out as a direct factor for increasing
activity in binaries. The binaries and single stars exhibit similar
and clear dependences of activity on either their rotation periods or
Rossby numbers.

---------------------------------------------------------
Title: A Catalog of Mg II Emission Line Fluxes for T Tauri Stars
Authors: Imhoff, C. L.; Basri, G.; Giampapa, M. S.
1987BAAS...19..728I Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Stellar Activity - Causes and Effects
Authors: Basri, G.
1987penm.conf..211B Altcode:
This paper is a review of the progress made in understanding stellar
activity in the last decade, a summary of the important results and a
description of some of the current exciting work underway in this field.

---------------------------------------------------------
Title: The circumstellar environment of chromospherically active T
Tauri stars.
Authors: Finkenzeller, U.; Basri, G.
1987IAUS..122..103F Altcode:
The authors discuss new spectroscopic material on 7 T Tauri stars of
low intermediate activity level which have envelopes of low optical
thickness and small circumstellar/interstellar extinction. They show
that difference plots between the target star and appropriate standards
are a powerful tool to probe the stellar envelope structure. In this
sample the authors find 1 object with a P Cyg type, 3 with inverse P
Cyg type, and 3 with symmetrical Balmer line profiles. They conclude
that the physical processes in these T Tauri stars do not differ
qualitatively from the ones found in extremely active ones. In
particular, the inverse P Cyg type profiles are not restricted to
stars with very opaque envelopes and are possibly a much more common
attribute of young stellar objects.

---------------------------------------------------------
Title: The T Tauri Stars (Invited review)
Authors: Basri, Gibor
1987LNP...291..411B Altcode: 1987LNP87.291..411B; 1987csss....5..411B
The T Tauri stars have always been somewhat mysterious, displaying a
bewildering variety of spectral peculiarities and variability. They
are relatively faint, yet demand the highest quality observations
to help unravel their puzzles. In the last few years they have been
studied with a new level of detail and in a developing context of star
formation theory. This has begun to clarify the reasons behind their
many interesting characteristics. A coherent picture is emerging,
although many major problems are yet unsolved. I try to summarize the
results of many new and old observations and. theoretical viewpoints
into a current cohesive overview of this exciting area.

---------------------------------------------------------
Title: Improved Analysis of Stellar Magnetic Fields
Authors: Basri, G.; Marcy, G.
1986BAAS...18R.984B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Differential Activity Analysis Along the Pre-Main Sequence
Authors: Basri, Gibor S.
1986iue..prop.2418B Altcode:
The T Tauri stars represent the first time during a young star's
evolution that we can directly observe its surface. We find them
covered by extreme activity with far-UV emission lines up to 3 orders of
magnitude stronger than in the quiet sun. These stars also seem to be
going through a phase of relatively strong mass loss. Previous studies
with the IUE have begun to constrain physical conditions in the stellar
atmosphere. They have concentrated on the brightest targets, however,
and it is now clear that these may be misleading objects with which
to study chromospheric activity in its early phases, since many of the
emission line diagnostics are formed in the wind rather than near the
stellar surface. This proposal continues work begun last year to examine
a more "normal" set of targets. Last year we concentrated on concurrent
observations of Ca II and Mg II in lower luminosity stars. This year we
wish to obtain complementary UV coverage for by far the most complete
set of optical observations ever made on T Tauri stars. We have recently
obtained essentially all the optical information possible (resolved,
calibrated spectra over the entire visible and near IR region) on stars
selected to sample the pre-main sequence differentially with matched
pairs. When augmented by UV coverage, the crucial but somewhat neglected
effort to obtain data suitable for the construction of physical model
atmospheres will be greatly enhanced for the stars most representative
of the early evolution of stellar chromospheres.

---------------------------------------------------------
Title: Upper limits to ultraviolet line emission in fully convective
M-dwarfs
Authors: Ambruster, C. W.; Kunkel, W. E.; Moreno, H.; Basri, G. B.
1986AdSpR...6h.199A Altcode: 1986AdSpR...6..199A
Theoretical stellar structure models find that stars later than ~dM3
are fully convective. It is widely believed that this should result
in reduced non-radiative heating and activity levels, however, the
observational evidence is sparse and somewhat contradictory. In order
to expand the number of atmospheric diagnostics for these stars,
we have obtained deep short wavelength (SWP) IUE spectra of 5 M
dwarfs later than spectral type dM5. Exposure times ranged from 4
to 7 hours. Only upper limits were measured for chromospheric and
transition region lines, thus appearing to rule out enhanced line
emission activity. The fractional luminosities of C IV (λ1550), C II
(λ1335), and C I (λ1657) relative to Lbol indicate that
emission lines in the temperature range 6000 K to ~1 × 105
K are up to an order of magnitude weaker than in earlier M dwarfs
having radiative cores. The lower limits on line fluxes for Barnard's
star are significantly below those of the other stars in the program.

---------------------------------------------------------
Title: Calibrated High Resolution Full Spectral Coverage of T
Tauri Stars
Authors: Finkenzeller, Ulrich; Basri, Gibor
1986LNP...254..442F Altcode: 1986csss....4..442F
No abstract at ADS

---------------------------------------------------------
Title: Rossby or Not Rossby
Authors: Basri, Gibor
1986LNP...254..184B Altcode: 1986csss....4..184B
No abstract at ADS

---------------------------------------------------------
Title: T Tauri stars through the looking-glass.
Authors: Finkenzeller, U.; Basri, G.
1985Msngr..42...20F Altcode:
It is pointed out that the Caspec on the 3.6 m telescope is a very
powerful new instrument for high dispersion spectroscopy. It has
been used to obtain optical information on a number of T Tauri stars,
taking into account calibrated resolved full spectral coverage. Seven
low to intermediately active T Tauri stars from the spectral catalog
of Appenzeller et al. (1983) have been selected. Two different
spectrographs have been used concurrently, including the ESO echelle
spectrograph with CCD (Caspec) at the 3.6 m telescope and the IDS at
the 1.5 m telescope. It was attempted to cover the most important
lines of Ca II and hydrogen along with photospheric lines of all
strengths. Attention is also given to details of data processing, line
ratios, absolute line and continuum fluxes, the study of chromospheric
structure, and a schematic representation of the Eddington-Barbier
relation in a spectral line.

---------------------------------------------------------
Title: Stellar activity in synchronized binaries. I. Dependence
on rotation.
Authors: Basri, G.; Laurent, R.; Walter, F. M.
1985ApJ...298..761B Altcode:
The authors have examined a large sample of late-type binaries with
orbital periods from 1 to 100 days for relationships between stellar
activity and rotation period, which is assumed to be synchronized
with the stellar orbital period. Most of the systems are in the RS
Canum Venaticorum class of close binaries. The activity diagnostics
were observed with the IUE and the Einstein Observatory and range
from the mid-chromosphere to the corona. There is a dependence of
activity on rotation in the synchronized binaries; surface flux is
the preferable measure of activity. This dependence is approximately
linear in the corona and rather weak in the chromosphere (intermediate
for the transition region). These results for binaries are compared
with those for single stars.

---------------------------------------------------------
Title: Simultaneous observations of CA II K and MG II K in T TAuri
stars.
Authors: Calvet, N.; Basri, G.; Imhoff, C. L.; Giampapa, M. S.
1985ApJ...293..575C Altcode:
The first simultaneous, calibrated observations of the Ca II K and
Mg II k resonance lines in T Tauri stars are presented. It is found
that for T Tauri stars with mass greater than 1.5 solar mass, which
have radiative cores and tend to be fast rotators, the k line seems to
arise in an extended region (probably also responsible for the H-alpha
emission), whereas the K line apparently originates closer to the highly
inhomogeneous stellar surface. The lower mass stars, which are fully
convective and tend to be slow rotators, are more easily described by
a largely chromospheric model, consistent with main-sequence activity
structures but at greater values of the nonradiative flux. The strongest
emission-line stars in the low-mass group, however, are also likely
to have extended k line regions.

---------------------------------------------------------
Title: IUE spectra of GO V-G5 V solar-type stars.
Authors: Haisch, B. M.; Basri, G.
1985ApJS...58..179H Altcode:
An atlas of IUE short-wavelength spectra for a set of 14 bright G0
V-G5 V stars are presented, and it is shown that these manifest a
range of qualitatively different chromospheric and transition region
spectra and significant differences in radiative flux originating at
the temperature minimum level. A comprehensive survey of observational
data and physical parameters of these stars has been performed, and
tabular summaries of the data are presented. It is concluded that
the UV continuum longward of about 1600 A is a diagnostic of the
temperature minimum. A considerable range of minimum temperature for
stars of similar effective temperature and spectral type is found. The
temperature minimum of the sun is highly structured on spatial scales
of about one arcsec.

---------------------------------------------------------
Title: An analysis of scattered light in low dispersion IUE spectra.
Authors: Basri, G.; Clarke, J. T.; Haisch, B. M.
1985A&A...144..161B Altcode:
A detailed numerical simulation of light scattering from the
low-resolution grating in the short wavelength spectrograph of the
IUE Observatory was developed, in order to quantitatively analyze the
effects of scattering on both continuum and line emission spectra. It
is found that: (1) the redistribution of light by grating scattering
did not appreciably alter either the shape or the absolute flux level
of continuum spectra for A-F stars; (2) late-type stellar continua
showed a tendency to flatten when observed in scattered light toward
the shorter wavelengths; and (3) the effect of grating scattering
on emission lines is to decrease measured line intensities by an
increasing percentage toward the shorter wavelengths. The spectra
obtained from scattering experiments for solar-type and late type
stars are reproduced in graphic form.

---------------------------------------------------------
Title: Atmospheric Structures in High and Low Mass T Tauri Stars
Authors: Basri, Gibor S.
1985iue..prop.2116B Altcode:
The effort to understand the origin of the emission features seen in
very young stars has been making good progress, in no small part due
to the ultraviolet window opened by the IUE. Physical models have been
produced for both generic chromospheres and winds for this class of
stars, which reproduce the gross features of the observed emission
line fluxes and continuum. This work is currently being extended to
simultaneous observations of optical and UV spectra of particular stars,
with the goal of producing full self-consistent models for specific
cases. It is clear, however, that a very significant physical aspect
of the atmospheres is being left out. The velocity fields can only be
observed with high resolution line profiles, but are among the most
interesting properties of these stars. Though a few profiles have been
obtained, simultaneous observations of enough diagnostics in specific
objects to produce relatively unique interpretations of the profiles
are conspicuously absent. This has lead to recurring questions about
even the most elementary conclusions on the profile appearances (such
as the true direction of the flow). We propose to utilize the unique
information available in Mg II profiles along with other calibrated
profiles to construct physically meaningful atmospheres for a selected
set of T Tauri stars. In this way we will be able to directly assess
the mass loss rates, structure and acceleration of the wind, and
relative importance of the chromospheric vs. wind region contributions
to emission spectra.

---------------------------------------------------------
Title: Chromospheric Activity in Solar Mass Pre-Main Sequence Stars
Authors: Basri, Gibor S.
1985iue..prop.2119B Altcode:
The T Tauri stars represent the first time during a young star's
evolution that we can directly observe its surface. We find that it
is covered by extreme activity with far-UV emission lines 3 orders of
magnitude stronger than in the quiet sun. These stars also seem to be
going through a phase of relatively strong mass loss. Previous studies
with the IUE have begun to constrain physical conditions on the stellar
surface and have been very helpful in starting to disentangle surface
emission from wind emission. IUE programs have concentrated on the
brightest targets, however, and we have begun to understand that these
may be misleading objects with which to study chromospheric activity
in its early phases as many of the emission line diagnostics may be
formed in the wind rather than near the stellar surface. This proposal
concentrates on looking at a more "normal" set of targets to measure
their Mg II and UV continuum emission concurrently with a full set
of optical observations at similar resolution. It therefore extends
the crucial effort to obtain data suitable for the construction of
physical model atmospheres to the stars most representative of the
early evolution of stellar chromospheres.

---------------------------------------------------------
Title: Self-consistent recalibration of IUE and determination of
hot DA white dwarf effective temperatures.
Authors: Finley, D. S.; Basri, G.; Bowyer, S.
1984NASCP2349..277F Altcode: 1984IUE84......277F; 1984fiue.rept..277F
Using low dispersion short and long wavelength camera observations,
the spectra of over twenty stars identified as DA white dwarfs,
with temperatures in the range 20,000 to 70,000 K were analyzed. In
addition to the IUE data were collected, all other available data on
these stars from which temperature estimates may be made. The observed
IUE fluxes were compared with the FUV fluxes predicted by using the
observed V magnitudes and temperatures obtained from non-IUE data. These
comparisons indicate a need to revise the overall IUE calibration by
+10% in Flambda. The appropriate correction as a function
of wavelength was computed, and this correction was applied to the
measured IUE fluxes. Temperatures with significantly more accuracy
than is achievable with optical photometry were obtained.

---------------------------------------------------------
Title: A Transition from Chromosphere to Wind for MgII in T Tauri
Stars
Authors: Basri, G.; Calvet, N.; Imhoff, C. L.; Giampapa, M. S.
1984BAAS...16..938B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The chromospheric hypothesis for the T Tauri phenomenon.
Authors: Calvet, N.; Basri, G.; Kuhi, L. V.
1984ApJ...277..725C Altcode:
A number of model atmospheres for T Tauri stars are constructed which
are characterized by a late-type photosphere plus a chromosphere with a
deep-lying temperature minimum. Parameter studies of these models show
that they reproduce reasonably well the Ca II, Mg II emission-line
fluxes, the continuous energy distribution, the absorption lines,
and the ultraviolet lines. The presence of a chromosphere also likely
accounts for the veiling phenomenon but is not sufficient to produce
the large observed H alpha fluxes in many T Tauri stars, which require
a much larger extended emitting region. However, it seems adequate to
account for many spectral features of the average T Tauri star which
are qualitatively similar to a normal active late-type star.

---------------------------------------------------------
Title: IUE Observations of Hot DA White Dwarfs
Authors: Finley, D. S.; Basri, G. S.; Bowyer, S.
1983BAAS...15R.984F Altcode: 1983BAAS...15..984F
No abstract at ADS

---------------------------------------------------------
Title: Coordinated Multi-Spectral Coverage of T-Tauri Stars
Authors: Basri, G.; Kuhi, L.
1983RMxAA...7Q.198B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: First observations of stellar coronal structure : the coronae
of AR Lacertae.
Authors: Walter, F. M.; Gibson, D. M.; Basri, G. S.
1983ApJ...267..665W Altcode:
In connection with the present investigation, X-ray, radio, and
ultraviolet observations of AR Lacertae over one orbital cycle have
been obtained. The X-ray light curve shows a deep primary minimum and
a broad, shallow secondary minimum. The quiescent corona of the G2
IV component is small and asymmetric. This corona extends some 0.02
stellar radii above the photosphere; the leading, spotted hemisphere is
brighter in X-rays than the trailing hemisphere. The K0 IV component
has two coronal components. The extended, presumably hotter component
extends to one stellar radius above the photosphere and exhibits a
brighter leading hemisphere. There is an inner coronal component which
is small relative to the stellar radius, but the lack of coverage past
mid-eclipse severely limits the possibility to deduce the nature of
this component. The UV observations also imply a nonuniform surface
distribution of plage regions.

---------------------------------------------------------
Title: Coronal and chromospheric structures in AR Lac. I - Data
and models
Authors: Gibson, D. M.; Walter, F. M.; Basri, G. S.
1983IAUS..102..369G Altcode:
The first X-ray, UV, and radio observations above the photosphere
of an eclipsing binary are reported, together with geometrical and
physical interpretations that allow the determination of coronal and
chromospheric properties, for the case of stars in the RS CVn binary
AR Lac. Attention is given to Einstein observations which yield an
X-ray light curve, IUE data that allow inferred coronal features to
be related to the surfaces and radio observations that facilitate the
separation of geometric and intrinsic variations by acting as a flare
monitor. Also noted is the construction of a simple coronal model
applicable to the X-ray light curve to yield coronae sizes and shapes.

---------------------------------------------------------
Title: An Absorption Line Study of High Latitude Diffuse Clouds
Authors: Basri, Gibor S.
1983iue..prop.1407B Altcode:
We propose to study diffuse clouds at high latitudes that have been
identified in uvby beta photometric surveys. We will study absorption
lines in the spectra of thirteen stars in two small (4 x 4) fields
that contain these clouds. The ultraviolet absorption line data, when
combined with the reddening and distance information gained from the
photometry, and the optical absorption line study that we have already
initiated, will provide a very complete evaluation of the physical
state of these diffuse clouds. With this information, we will be able
to assess quantitatively the accuracy of the photometric technique
for detecting very small excesses. We will estimate abundances and
depletions, and relate these to reddening values. By using stars at
different distances, we will probe the structure of the ISM along the
line of sight, and determine the location of components of different
velocity and ionization. We may detect highly ionized species and
determine their association with the clouds. Finally, we will initiate
a long term study of the transition region between the very local ISM
and the global ISM.

---------------------------------------------------------
Title: Period-activity relations in close binary systems
Authors: Basri, G.; Laurent, R.; Walter, F.
1983IAUS..102..199B Altcode:
The question as to whether the amount of activity observed in stars with
the same fundamental stellar parameters depends on rotational velocity
is considered in view of close binary systems, making use of their
orbital rather than their rotational period. It is noted that the main
sequence G star binaries lie systematically lower than the K subgiants
for the same rotational periods, so that relations including a variety
of spectral classes cannot be used to directly deduce correlations
between magnetic fields and activity without suitable correction. The
behavior of the present sample suggests that activity increases with
later spectral type and with evolution off the main sequence. The
chromosphere shows a minor reaction to rotational velocity increase.

---------------------------------------------------------
Title: The geometrical structure of activity in the AR Lac system.
Authors: Basri, G.; Gibson, D.; Walter, F.
1983HiA.....6..650B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Activity correlations in close binary systems
Authors: Basri, G.; Laurent, R.
1983ASSL..102..439L Altcode: 1983ASSL..102..439B; 1983ards.proc..439B; 1983IAUCo..71..439B
The IUE satellite is used to observe a homogeneous sample of stars
for which there is extensive coronal data. It is noted that the X-ray
studies of close binaries by Walter and Bowyer (1981) and Walter (1982)
provide such a sample; what is more, these stars are accessible to the
IUE owing to their tendency to strong activity. To study the relations
among the diagnostics, correlation plots are constructed in which
the normalized flux in each diagnostic is plotted in a log-log plane
against various canonical diagnostic normalized to the bolometric
flux measured at the earth (corrected for inactive components in the
binary system). Three canonical diagnostics are chosen for making
the correlations: MgII for the chromosphere, CIV for the transition
region, and X rays for the corona. It is found that the behavior of the
diagnostics would best be explained by an increasingly greater pressure
at the transition region (and thus also in the corona) with increasing
activity. Something like a P-squared dependence of diagnostics might be
expected in this region but not the midchromosphere owing to both the
increasing populations of ions and increasing collisional excitation
of the resonance lines.

---------------------------------------------------------
Title: Coronal and chromospheric structure in AR Lac. II - Physical
characteristics of the atmosphere
Authors: Walter, F. M.; Gibson, D. M.; Basri, G. S.
1983ASSL..102..445W Altcode: 1983ards.proc..445W; 1983IAUCo..71..445W
An effort to deduce the morphology of the chromosphere and corona of
AR Lacertae, an eclipsing RS CVn system (Hall, 1976), by means of
observations at UV, radio, and X-ray wavelengths during a complete
orbital cycle is discussed. The corona is modeled as a volume of
uniform volume emissivity rather than as individual loops. The model
is symmetric about the equator, and it confines the emission to within
a band in latitude. From the observed emission measure N(e-squared)V,
the coronal temperatures and the emitting volume V inferred from the
model, the mean densities (Ne) and pressures (2 Ne
kT) are computed. The derived pressure scale heights are much larger
than the observed extent of the corona, which implies the necessity
of active confinement of the gas.

---------------------------------------------------------
Title: Fk-Comae - a Coalescing Binary System
Authors: Walter, F. M.; Basri, G. S.
1983S&T....65..323W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Ultraviolet and X-ray detection of the 56 Peg system (K0
II p+WD) : evidence for accretion of a cool stellar wind onto a
white dwarf.
Authors: Schindler, M.; Stencel, R. E.; Linsky, J. L.; Basri, G. S.;
Helfand, D. J.
1982ApJ...263..269S Altcode:
IUE spectra of the slowly rotating mild barium star 56 Peg (HD 218356;
K0 IIp) show excess continuum emission from 1300 to 2000 Å, a broad
Lyα absorption feature, and emission lines usually associated with a
l04-(2 × l05) K plasma. The best fit blackbody
curve to the dereddened continuum gives a temperature of 32000 ± 4000
K and a radius for the object of (2.7 ± 1.0) × l09 cm,
consistent with that of a white dwarf. Einstein IPC observations of this
system yield Lx ≍ 3 × 1O31 ergs s-1,
which is as bright as the RS CVn binary systems. The X-rays can be
fitted to a bremsstrahlung spectrum with kT = 0.45 ± 0.3 keV, or a
blackbody spectrum with kT ≍ 0.2 keV. Since bright X-ray and high
temperature emission lines are unusual for single stars in this region
of the H-R diagram, we do not believe that the 56 Peg primary has a
hot corona and transition region. Instead, we propose that the observed
X-ray luminosity is due to accretion onto the white dwarf of ∼0.1% of
the wind from the primary, which we assume has a reasonable mass loss
rate of 2 × 10-7 to 4 × l0-9 Msun
yr-1. The ultraviolet emission lines likely result from
reprocessed X-radiation absorbed by the wind. The Mg II K line exhibits
a time-varying emission core, that may be explained by ionization of
Mg+ in the wind by X-rays from the white dwarf.

---------------------------------------------------------
Title: Extreme ultraviolet spectrophotometry of He II in the stellar
atmosphere.
Authors: Malina, R. F.; Bowyer, S.; Basri, G.
1982ApJ...262..717M Altcode:
A We report a spectrum of the hot white dwarf Hz 43 in the extreme
ultraviolet band from 170-500 with a resolution of 15 &amp;Å ring;. The
spectrum is marked by a prominent absorption edge at 225 Å ± 15 Å
with Nλ (220 Å)/N(236 Å) = 0.51 ± O.13. The observed
edge is attributed to absorption at the 228 Å Lyman edge of singly
ionized helium. A grid of blanketed LTE model atmospheres with uniform
compositions of hydrogen with trace helium were used to interpret the
data. We find that we are able to obtain satisfactory fits to our data
for effective temperatures in the range 45,000-60,000 K either for pure
hydrogen models with an interstellar He II column density in the range
(2.8-6) × 1017 ions cm-2, or for models with a
photospheric helium fractional number densities in the range (1.5-6)
× 10-5 of hydrogen. Our results, combined with observations
at other wavelengths, yield a best estimate of 55,000-60,000 K for the
effective temperature. We derive an upper limit on the interstellar
column densities of N(H) ≤ 2 × 1017 cm-2for
neutral hydrogen, of N(He I) for neutral helium and of N(He II) 6 ×
1017 cm-2 for singly ionized helium. However, no
single pure hydrogen or uniform trace helium model will simultaneously
fit the available optical to soft X-ray data. We have evaluated possible
sources of He ii in the interstellar medium and conclude that they
are unlikely to contribute the entire observed column density. Hence
the observations provide the first detection of helium in Hz 43.

---------------------------------------------------------
Title: The soft X-ray spectrum of Sirius B : evidence for the
photospheric hypothesis.
Authors: Martin, C.; Basri, G.; Lampton, M.; Kahn, S. M.
1982ApJ...261L..81M Altcode:
The soft X-ray spectrum of Sirius obtained by the HEAO 1 A-2
experiment is used to investigate the origin of the X-radiation
from that system. It is shown that, if the emission is coronal,
then the coronal temperature must be less than 150,000 K, and the
coronal luminosity must be greater than 10 to the 33rd ergs/s. Such
a corona conflicts severely with EUV observations and is physically
untenable. White dwarf atmosphere models are fitted to the spectrum and
it is shown that a photospheric temperature of 28,000 K is much more
consistent with the data. The relative consistency of the soft X-ray,
EUV, and UV observations of Sirius B is discussed and it is concluded
that the evidence favors the white dwarf photosphere as the origin of
the soft X-rays.

---------------------------------------------------------
Title: The enigmatic Half line of FK COM : last stages of a coalescing
binary ?
Authors: Walter, F. M.; Basri, G. S.
1982ApJ...260..735W Altcode:
The apparently single, rapidly rotating G giant FK Comae displays an
unusual hydrogen alpha emission line which is very broad, strong, and
variable. Extensive high-resolution studies of this line with complete
phase coverage are presented. The alpha hydrogen emission centroid
shows a radial velocity modulation on the 2.4 days stellar rotation
period with a semiamplitude identical to the photospheric rotational
velocity. These data, when phased with optical photometry, indicate that
the star has a bright, rather than dark, region on its surface and that
the phase may have been stable for seven years. A qualitative model
wherein the bright spot is caused by accretion from a low mass unseen
companion onto the surface of the G giant is considered. Such a model
explains many of the observed characteristics of the stellar spectrum
and hydrogen alpha feature, and it is concluded that FK Comae is not yet
a single star, but is still evolving toward coalescence of the system.

---------------------------------------------------------
Title: Outer atmospheres of cool stars. XI. High-dispersion IUE
spectra of five late-type dwarfs and giants.
Authors: Ayres, T. R.; Linsky, J. L.; Basri, G. S.; Landsman, W.;
Henry, R. C.; Moos, H. W.; Stencel, R. E.
1982ApJ...256..550A Altcode:
We present high-dispersion, far-ultraviolet (1150-2000 Å) spectra
of five late-type dwarfs and giants obtained with the International
Ultraviolet Explorer. The chromospheric (T ≲104K)
emission lines in the giants tend to be about twice as broad as
the corresponding features of the dwarf star spectra, suggesting a
width-luminosity relation similar to the Wilson-Bappu effect for Ca
II H and K. The Si III λ1892 and C III λ1909 intercombination lines
formed in hotter layers (T ≍ 5 × 104K) also broaden
by a factor of 2 from the main-sequence stars to the evolved stars,
and the permitted resonance doublets of C II(3 × 104
K), Si IV (6 × 104 K), and C IV (105 K) are as much as
a factor of 4 broader in the giants than in the dwarfs. However, we
find no evidence for asymmetric or shifted emission profiles that
might indicate the presence of warm (T≪105K) stellar
winds. We conclude that broad C iv profiles, in particular, are typical
of active chromosphere giant stars and are unlikely to be a unique
signature of an extended, expanding warm wind. Since the resonance
lines tend to be wider than the intersystem lines formed at similar
temperatures in the chromosphere and in hotter layers, we conclude
that opacity must be an important broadening enhancement mechanism in
active chromosphere giant stars. Nevertheless, the intercombination
line widths do indicate a general increase in the outer atmosphere
Doppler motions from the dwarfs to the giants. Application of
the density sensitive line ratio C III λ1909/Si III λ1892 suggests
that the outer atmosphere pressures (T ≍ 5 × 104K)
are similar in the active chromosphere subgiant λ And and the quiet
chromosphere dwarfs, α Cen A and B. However, the pressures derived
for the Capella secondary and β Dra are factors of 3 or more lower
than the dwarfs, suggesting geometrically extended, low-density outer
atmosphere structures qualitatively different from the high-pressure,
compact structures typical of solar magnetic active regions. Finally, we have isolated the He II λ1640 emission component
from contaminant blends, and we find that the line strength is well
correlated with soft X-ray fluxes of the sample stars, as predicted
by photoionization-recombination models of the He II Bα formation.

---------------------------------------------------------
Title: On the enigma of FK Comae.
Authors: Walter, F.; Basri, G.
1982SAOSR.392A.219W Altcode: 1982csss....2..219W
Stellar chromospheric and coronal activity appears ubiquitous among
late type stars to the left of the TR-wind boundary line (Linksy and
Haisch 1979). The level of activity as measured by the X-ray surface
flux is linearly proportional to the stellar angular velocity, with
the exception of slowly rotating dwarfs (Walter 1981, 1982; Walter and
Bowyer 1981). The peculiar rapidly rotating G giant FK Comae (Merrill
1948) appears to fit into this pattern. Line widths indicate V sin i =
120 + or - 20 km s(-1) (Bopp and Stencel 1981). FK Comae has strong Ca
II H and K and H alpha emission, strong transition region UV lines (Bopp
and Stencel 1981), and an X-ray surface flux in good agreement with its
rapid rotation (Walter 1981). Yet, FK Comae is an enigmatic star. It is
a rapid rotator, but it is not clear why it is a rapid rotator. There is
no direct evidence for duplicity; indeed, the upper limit of 20 km s(-1)
on the K velocity puts tight constraints on any binary configuration,
especially if sin i approx 1, as indicated by the large V sin i. Bopp
and Stencel (1981) have suggested that FK Comae is an example of a
coalesced W UMa system (Webbink 1976), wherein the orbital angular
momentum has become rotational angular momentum of the coalesced star.

---------------------------------------------------------
Title: Ultraviolet and X-ray detection of the 56 Peg system (K0 IIp
+ WD).
Authors: Schindler, M.; Stencel, R. E.; Linsky, J. L.; Basri, G.;
Helfand, D.
1982SAOSR.392B.125S Altcode: 1982STIN...8234317S
Both IUE short and long wavelength exposures of the 56 Peg system are
discussed. This mild barium star has an X-ray luminosity of 3 x 10 to
the 31st power ergs/1, comparable to the rapidly rotating RS CVn binary
systems, yet lies in a region of the HR diagram where stellar X-rays
are generally not observed. This cool, bright giant is not a rapid
rotator and the key to understanding its emission lies in the recent
discovery of its white dwarf companion. Accretion onto the white dwarf
of approximately 0.1% of the stellar wind of the primary is sufficient
to power an X-ray source of the observed luminosity. Reprocessing of
the X-rays in the cool dense stellar wind explains the origin of the
UV emission line spectrum, and may explain the time varying asymmetry
of the Mg 2 kappa line profile that is observed. Graphs which show
observed fluxes and wavelengths are discussed.

---------------------------------------------------------
Title: Comparative chromospheric and coronal emission from close
binaries.
Authors: Basri, G.; Walter, F.; Laurent, R.
1982SAOSR.392B..87B Altcode: 1982csss....2...87B
No abstract at ADS

---------------------------------------------------------
Title: The chromospheric rotation-activity relation in late type
close binary systems.
Authors: Walter, F. M.; Basri, G. S.; Laurent, R.
1982NASCP2238..566W Altcode: 1982auva.nasa..566W; 1982NASCP2338..566W; 1982IUE82......566W
The IUE data on 36 late type close binary stars are presented. It is
shown that the chromospheric and TR line fluxes increase with decreasing
stellar rotation period, though not as rapidly as does the X-ray
flux. There is an increasing dependence upon rotation with increasing
line temperature. The data are consistent with the hypothesis that
there exists a critical rotation rate, which depends on temperature,
below which the emission flux is independent of rotation and above
which it increases linearly with increasing angular velocity omega.

---------------------------------------------------------
Title: Outer atmospheres of cool stars. VIII. IUE observations
and chromospheric models for the supergiant stars beta Draconis,
epsilon Geminorum and alpha Orionis.
Authors: Basri, G. S.; Linsky, J. L.; Eriksson, K.
1981ApJ...251..162B Altcode:
A semiempirical modeling of stellar chromospheres is extended to
late-type supergiants, where computations match high-resolution,
absolute-flux profiles of the Ca II K and Mg II h and k lines. IUE
UV spectra of Epsilon Gem and Alpha Ori show no evidence of emission
lines formed at temperatures greater than 10,000 K, leading to the
computation of chromospheric models extending to 10 to the -6th g/sq cm
at temperatures that rise to 6500 K for the former star and 7000 K for
the latter. By contrast, the C II-IV, Si IV, and He II and N V strong
emission lines of Beta Dra lead to a tentative chromospheric model
extension to 16,000 K at 0.012 dynes/sq cm. It is pointed out that
the Ca II and Mg II line analyses presented, which assume hydrostatic
equilibrium with only thermal and turbulent components to the pressure,
imply nearly plane-parallel chromospheres even in the case of Alpha Ori.

---------------------------------------------------------
Title: High-resolution spectra of five late-type dwarfs and giants
obtained with the IUE satellite.
Authors: Ayres, T. R.; Basri, G. S.; Henry, R. C.; Landsman, W.;
Linsky, J. L.; Moos, H. W.; Stencel, R. E.
1981BAAS...13..546A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The unusual outer atmosphere of 56 Pegasi (K0 IIp).
Authors: Schindler, M.; Stencel, R. E.; Linsky, J. L.; Helfand, D. J.;
Basri, G.
1981BAAS...13..547S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: HeII in the Spectrum of the Hot White Dwarf HZ43: Photospheric
or Interstellar?
Authors: Malina, R. F.; Basri, G.; Bowyer, S.
1981BAAS...13..873M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Evidence for Photospheric Soft X-Ray Emission from Sirius B
Authors: Martin, C.; Basri, G.; Lampton, M.; Kahn, S.
1981BAAS...13R.810M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Structure of the Coronae of AR Lacertae
Authors: Walter, F.; Gibson, D. M.; Basri, G. S.
1981BAAS...13..833W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Relation Between Coronal, Chromospheric and Magnetic
Activity: A Case Study
Authors: Basri, G. S.; Walter, F. M.; Marcy, G.
1981BAAS...13..828B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Unusual Outer Atmosphere of 56 Pegasi (KO IIp)
Authors: Schindler, M.; Stencel, R.; Linsky, J.; Helfand, D.; Basri, G.
1981BAAS...13Q.545S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High-Resolution Spectra of Five Late-Type Dwarfs and Giants
Obtained with the IUE Satellite
Authors: Ayres, T. R.; Basri, G. S.; Henry, R. C.; Landsman, W.;
Linsky, J. L.; Moos, H. W.; Stencel, R. E.
1981BAAS...13R.545A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High resolution flux profiles of the Mg II h &amp; k lines
in evolved F8 to M5 stars.
Authors: Stencel, R. E.; Mullan, D. J.; Basri, G. S.; Linsky, J. L.
1981NASCP2171..317S Altcode: 1980IUE80......317S; 1981uviu.nasa..317S; 1981NASCP3171..317S
The central results of a survey of the Mg II resonance line
emission in a sample of over 50 evolved late type stars, including
spectral-luminosity type F8 to M5 and La to IV are presented. Observed
and surface fluxes are derived and correlations noted. The major
findings include: (1) Mg II k emission core asymmetry transition near
K1 III, analogous to that known for Ca II K; (2) a small gravity and
temperature dependence of the Mg II chromospheric radiative loss rate.

---------------------------------------------------------
Title: Formation of chromospheric resonance line profiles in
supergiants.
Authors: Basri, G. S.
1980ApJ...242.1133B Altcode:
The formation of chromospheric resonance line profiles is examined
for the case of the relatively low-density atmospheres appropriate
to late-type supergiants. The effects of partial frequency
redistribution control the emergent line profiles, to the extent
that even an isothermal atmosphere can give rise to apparent emission
features. Schematic model chromospheres are used to demonstrate the
effects of different velocity fields and temperature-density structures
on the line profiles, as a first step toward a clearer understanding
of the chromospheric line profiles and why supergiants have broad
emission lines (the Wilson-Bappu effect). Neither the Doppler nor the
mass column density explanation alone can explain the Wilson-Bappu
effect in supergiants, but both theories may play a role.

---------------------------------------------------------
Title: The outher atmospheres of cool stars. VII. High resolution,
absolute flux profiles of the MG II H and K lines in stars of spectral
types F8 to M5.
Authors: Stencel, R. E.; Mullan, D. J.; Linsky, J. L.; Basri, G. S.;
Worden, S. P.
1980ApJS...44..383S Altcode:
We present high-resolution lUE spectra of the emission cores of the
Mg II resonance doublet at 280 nm in a selection of 54 stars covering
a range of spectral type from F8 to MS and of luminosity class from
supergiant (Ia) to subgiant (IV). These spectra were obtained with the
LWR echelle system onboard the IUE satellite, and have been calibrated
in absolute flux units using OAO 2 photometry of Eta UMa as a standard,
plus the Barnes and Evans relations for stellar angular diameters. The
uncertainty in flux is probably of order 20%. We discuss the qualitative
line profile groupings, as determined by Basri and Linsky, and derive
chromospheric radiative losses in the h and k lines; we discuss
these loss rates as functions of effective temperature and luminosity
class. We make further comparisons of these rates with rates derived
for the Ca II H and K lines by Linsky and his colleagues. Chromospheric
velocity fields and indicators of circumstellar envelopes are discussed
in terms of profile asymmetries and other diagnostics. Line width
measures and velocity shifts of the central reversals are tabulated,
among other quantities, and several correlations noted. Finally, we
discuss the relation of the Wilson K index and stellar coronae to Mg
II emission, and note the occurrence of Fe II emission lines in the
middle range of the UV of late-type stars.

---------------------------------------------------------
Title: Determination of Physical Parameters of the Envelopes Around
T Tauri Stars
Authors: Calvet, N.; Basri, G.
1980BAAS...12R.827C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Onset of Mass-Loss Among G Supergiants
Authors: Basri, G. S.; Stencel, R. E.; Linsky, J. L.
1980BAAS...12R.805B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Chromospheric explanation of T Tauri spectra
Authors: Basri, G.; Calvet, N.; Kuhi, L. V.
1980BAAS...12R.520B Altcode:
No abstract at ADS

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Title: Outer atmospheres of cool stars. IV. A discussion of cool
stellar wind models.
Authors: Haisch, B. M.; Linsky, J. L.; Basri, G. S.
1980ApJ...235..519H Altcode:
Possible wind models for late-type stars which appear not to have hot
coronae and transition regions are investigated; taking Arcturus and
the prototypical star, models with T less than approximately 20,000
K are considered, and solutions with mass loss rates of 10 to the
-9th solar masses per year are sought. The radiation pressure of
L-alpha resonance scattering can exceed the force of gravity in
the chromosphere and initiate a net outflow, but is insufficient
to sustain a wind, except perhaps in the presence of an additional
momentum input term such as Alfven wave pressure. It is concluded that
L-alpha radiation-pressure-initiated winds can occur in stars to the
right of the Linsky-Haisch dividing line in the H-R diagram between
stars with and without transition regions and presumably hot coronae,
and that the existence of these winds may explain energetically the
absence of hot coronae in these stars.

---------------------------------------------------------
Title: Formation of Strong Resonance Line Wings
Authors: Basri, G. S.
1979BAAS...11..625B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Outer atmospheres of cool stars. II. MG II flux profiles and
chromospheric radiative loss rates.
Authors: Basri, G. S.; Linsky, J. L.
1979ApJ...234.1023B Altcode:
International Ultraviolet Explorer high-resolution spectra of the Mg
II lines at 2796, 2803 A in 15 stars of spectral type G2-M2 including a
wide range of luminosities are presented. These spectra are calibrated
in absolute flux units at earth and at the stellar surface, and the
chromospheric radiative loss rates in the Mg II lines are compared with
corresponding rates in the Ca II H, K, and 8542 lines. The ratio of
Mg II surface flux to total surface flux is found to be independent
of stellar luminosity and thus gravity; may decrease slowly with
decreasing effective temperature, and increases with decreasing period
among RS Canum Venaticorum binaries. The factor of 10 range in this
ratio at each effective temperature may be due to differences in the
fractional surface area covered by plages and may indicate that stars
of all luminosity classes have chromospheric plages. In this small
data sample no evidence is found that the Mg II line surface fluxes
indicate whether a star possesses a transition region and hot corona.

---------------------------------------------------------
Title: Lyman-alpha rocket spectra and models of the quiet and active
solar chromosphere based on partial redistribution diagnostics.
Authors: Basri, G. S.; Linsky, J. L.; Bartoe, J. -D. F.; Brueckner,
G.; van Hoosier, M. E.
1979ApJ...230..924B Altcode:
Absolute intensity Lyman-alpha profiles with a spatial resolution
of 0.8 min and a spectral resolution of 50 mA were obtained for
network and cell regions in the quiet sun, umbral and penumbral
areas of a sunspot, two plages, and a quiescent prominence of the
limb. Weak limb brightening shown by the Lyman-alpha cores and wings
are consistent with predictions derived from partial redistribution
line transfer calculations. Through use of a comoving two-level partial
redistribution code which conserves mass flux, unequal red and blue
Lyman-alpha peak intensities may be interpreted as flow velocities
near 20,000 K. Outflows in the plages and downflows in the network
are also noted. A model of a mean quiet sun chromosphere consistent
with the Lyman-alpha integrated intensity, the Lyman continuum slope,
and the millimeter continuum is presented.

---------------------------------------------------------
Title: Resonance Line Formation and the Wilson-Bappu Relation in
Supergiants
Authors: Basri, G. S.
1979BAAS...11..472B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Supergiant chromospheres
Authors: Basri, Gibor Saul
1979PhDT.......249B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Supergiant Chromospheres.
Authors: Basri, G. S.
1979PhDT.........9B Altcode:
Observations with high spectral resolution that are calibrated in
absolute flux units at the stellar surface are used to construct
preliminary models of three late-type supergiants; beta Dra (G211)
equal to Gem (G8Ib)), and Ori(M2Iab). The details of chromospheric
emission formation in the low density atmospheres of supergiants are
studied using partial redistribution radiative transfer codes. The
strong coherency of the resonance line wings has a profound effect
on the appearance of the emergent line profile and on the physical
properties of the atmosphere that can be derived from it.

---------------------------------------------------------
Title: IUE observations of cool stars : alf Aur, HR 1099, lam and
EPS Eri.
Authors: Linsky, J. L.; Ayres, T. R.; Basri, G. S.; Morrison, N. D.;
Boggess, A.; Schiffer, F. H., III; Holm, A.; Cassatella, A.; Heck,
A.; Macchetto, F.; Stickland, D.; Wilson, R.; Blanco, C.; Dupree,
A. K.; Jordan, C.; Wing, R. F.
1978Natur.275..389L Altcode:
Initial IUE observations of four cool stars are reported. Observed
fluxes and surface fluxes are given for several UV emission lines in
the spectral range 1175-2000 A, obtained at low and high dispersion with
the short-wavelength spectrograph and camera. These lines are formed in
the outer atmospheres of these stars, in regions presumably analogous to
the solar chromosphere and transition region. The surface fluxes in the
lines increase along the sequence: quiet sun, Epsilon Eri, Lambda And,
Alpha Aur, and HR1099. The 2.8-d RS CVn-type binary HR1099, observed on
1 March 1978 near the end of a major flaring episode, has line surface
fluxes roughly 100 times that of the quiet sun, similar to those seen in
solar flares. Line profiles and flux ratios in multiplets for Capella
are presented, and comments given on the opacity of the lines and on
a tendency of line width to increase with temperature of formation.

---------------------------------------------------------
Title: The effect of the frequency dependent Stark broadening
parameter on partial redistribution (PRD) calculations.
Authors: Roussel-Dupre, D.; Basri, G. S.
1978BAAS...10..729R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Model Chromospheres for Supergiants: A Progress Report
Authors: Basri, G. S.; Linsky, J. L.
1978BAAS...10..647B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A First Look at IUE Far Ultraviolet Spectra of K and M Stars -
α Ori, α Boo, and ɛ Eri
Authors: Basri, G. S.; Linsky, J. L.
1978BAAS...10R.443B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Stellar model chromospheres. VII. Capella (G5 III+), Pollux
(K0 III), and Aldebaran (K5 III).
Authors: Kelch, W. L.; Linsky, J. L.; Basri, G. S.; Chiu, H. -Y.;
Chang, S. -H.; Maran, S. P.; Furenlid, I.
1978ApJ...220..962K Altcode:
Data from high-resolution SEC vidicon spectroscopy with a ground-based
telescope (for the Ca II K line) and from spectral scans made with the
BUSS ultraviolet balloon spectrograph (for the Mg II h and k lines)
are used to derive models of the chromospheres and upper photospheres
of three G-K giants. The models are based on partial-redistribution
analyses of the Ca II K line wings and cores and on the fluxes in the
Mg II lines. The photospheres thus computed are hotter than predicted
by radiative-equilibrium models. The minimum-to-effective temperature
ratio is found to decrease with decreasing effective temperature,
while the mass column density at the top of the chromosphere increases
with decreasing stellar surface gravity. The computed pressure at the
chromosphere top in the primary member of the Capella spectroscopic
binary system is 70 times smaller than the transition-region pressure
derived by Haisch and Linsky (1976), which suggests that additional
terms must be included in the transition-region energy equations for
giant stars. Estimates of the Ca II and hydrogen column densities are
made for the circumstellar envelope of Aldebaran.

---------------------------------------------------------
Title: Evidence for Outward Acceleration of the Circumstellar Shell
of α Orionis Determined by High Resolution Vidicon Spectrocopy.
Authors: Linsky, J. L.; Basri, G. S.; Chiu, H. Y.; Chang, S. W.;
Maran, S. P.
1977BAAS....9R.345L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High-resolution stellar vidicon spectrophotometry. I. Variable
mass loss from Arcturus and the hypothesis of giant convective
elements.
Authors: Chiu, H. Y.; Adams, P. J.; Linsky, J. L.; Basri, G. S.;
Maran, S. P.; Hobbs, R. W.
1977ApJ...211..453C Altcode:
High-resolution spectrophotometry of the variable Ca II K line in the
K2 IIIp star Alpha Boo was performed with the McMath Solar Telescope
at Kitt Peak National Observatory and an experimental SEC vidicon
camera. The results are compared with Copernicus observations of the Mg
II h and k lines and with earlier Ca II data. It is found that either
of two states may typically occur in the Arcturus chromosphere. From
comparison with the results of model calculations for expanding
chromospheres, it is concluded that these correspond respectively to a
'normal' state in which the mass loss is less than one billionth of
a solar mass per year and an 'abnormal' state in which the mass loss
is about 8 billionths of a solar mass per year. In the latter case,
the expansion velocity is around 13 km/s at optical depth unity in the
K-line, which exceeds the local sound speed. It is suggested that the
abnormal state represents the rise to the photosphere of a very large
convective element, as hypothesized for red giants by Schwarzschild
(1975).

---------------------------------------------------------
Title: Model Chromospheres and Photospheres of Selected G and
K Giants.
Authors: Kelch, W. L.; Linsky, J. L.; Basri, G. S.; Chiu, H. Y.;
Maran, S. P.; Furenlid, I.
1976BAAS....8..518K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Models of Solar Chromosphere Structures Implied by Lyman-α
Rocket Spectra.
Authors: Basri, G.; Linsky, J. L.; Bartoe, J. -D. F.; Brueckner, G.;
van Hoosier, M. E.
1976BAAS....8..534B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Preliminary Analysis of NRL Rocket Spectra of the Lα Line
Wings
Authors: Basri, G.; Bartoe, J. -D. F.; Brueckner, G.; Linsky, J.;
van Hoosier, M. E.
1976BAAS....8..331B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Recent Studies of the Chromospheres and Coronae of K-Type
Stars and the Local Interstellar Medium using the Copernicus Satellite
Authors: Linsky, J. L.; McClintock, W.; Henry, R. C.; Moos, H. W.;
Basri, G. S.
1976BAAS....8Q.354L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Simultaneous High-Dispersion Stellar Spectroscopy with
Copernicus and the McMath Solar Telescope
Authors: Maran, S. P.; Chiu, H. Y.; Linsky, J. L.; Henry, R. C.;
Moos, W.; McClintock, W.; Basri, G. S.
1976BAAS....8R.353M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Changes in the K-Line of Arcturus Observed at High Resolution
by SEC Vidicon Spectroscopy.
Authors: Chiu, H. Y.; Adams, P.; Linsky, J. L.; Basri, G. S.; Maran,
S. P.; Hobbs, R. W.
1975BAAS....7..469C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Mass Loss and Winds in K-type Stars ad Derived from
"Copernicus" Spectra.
Authors: Linsky, J. L.; Basri, G.; McClintock, W.; Henry, R. C.;
Moos, H. W.
1974BAAS....6..458L Altcode:
No abstract at ADS