Author name code: basri ADS astronomy entries on 2022-09-14 author:"Basri, Gibor" ------------------------------------------------------------------------ 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 Bibcode: 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. Title: An Introduction to Stellar Magnetic Activity Authors: Basri, Gibor Bibcode: 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. 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 Bibcode: 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. Title: Double-dipping to refine stellar rotation periods Authors: Tan, Joanne; Basri, Gibor Bibcode: 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. Title: Barriers to Equity, Inclusion, and Diversity in Astronomy Authors: Rudolph, A.; Basri, G.; Norman, D.; Wimberly, M. K. R. Bibcode: 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. 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 Bibcode: 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. Title: Chapter 11 - The Solar-Stellar Connection Authors: Basri, Gibor Bibcode: 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. 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 Bibcode: 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. Title: Calibration of Differential Light Curves for Physical Analysis of Starspots Authors: Basri, Gibor Bibcode: 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. Title: Double Dipping: A New Relation between Stellar Rotation and Starspot Activity Authors: Basri, Gibor; Nguyen, Hieu T. Bibcode: 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. Title: What is Kepler Really Telling Us about Starspots? Authors: Basri, Gibor Bibcode: 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. Title: Planets in Binary Star Systems: Keck/HIRES Search for Planets Around Sun-like Stars Within 25 pc Authors: Basri, Gibor Bibcode: 2017koa..prop..221B Altcode: No abstract at ADS 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 Bibcode: 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. Title: Planets in Binary Star Systems: Keck/HIRES Search for Planets Around Sun-like Stars Within 25 pc Authors: Basri, Gibor Bibcode: 2017koa..prop..116B Altcode: No abstract at ADS 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. Bibcode: 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. Title: Differential rotation as a model for starspots in magnetically active stars Authors: Agostino, Christopher James; Basri, Gibor S. Bibcode: 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. Title: Rotation-Activity-Age Relations For Solar-Type And Cooler Stars Authors: Basri, Gibor Bibcode: 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. Title: Planets in Binary Star Systems: Keck/HIRES Search for Planets Around Sun-like Stars Within 25 pc Authors: Basri, Gibor Bibcode: 2016koa..prop..358B Altcode: No abstract at ADS Title: The Structure and Dynamics of Multi-planet Systems Authors: Basri, Gibor Bibcode: 2016koa..prop..431B Altcode: No abstract at ADS 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. Bibcode: 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). Title: A Granulation "Flicker"-based Measure of Stellar Surface Gravity Authors: Bastien, Fabienne A.; Stassun, Keivan G.; Basri, Gibor; Pepper, Joshua Bibcode: 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 < Teff < 7150 K, 2.5 < {log}\g < 4.6, Kp ≤ 13.5, and overall photometric amplitudes <10 parts per thousand. 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 Bibcode: 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. 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 Bibcode: 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. 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. Bibcode: 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. Title: Brown Dwarf Authors: Basri, Gibor Bibcode: 2015enas.book..337B Altcode: No abstract at ADS Title: The Sun Among Stars: A Photometric Comparison from Kepler Authors: Basri, Gibor Bibcode: 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. 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. Bibcode: 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. Title: VizieR Online Data Catalog: Properties of KOI host stars (Walkowicz+, 2013) Authors: Walkowicz, L. M.; Basri, G. S. Bibcode: 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). Title: Rotation & differential rotation of the active Kepler stars Authors: Reinhold, Timo; Reiners, Ansgar; Basri, Gibor Bibcode: 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. 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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&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 Bibcode: 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 Bibcode: 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 < B - V < 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 http://www.aanda.orgA table with rotation periods is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/560/A4 Title: Rotation periods, variability properties and ages for Kepler exoplanet candidate host stars Authors: Walkowicz, Lucianne M.; Basri, Gibor S. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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 < 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 < 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 > 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. 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. Bibcode: 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. Title: Kepler Light Curves and Stellar Rotational Periods Authors: Reinhold, T.; Reiners, A.; Basri, G.; Walkowicz, L. M. Bibcode: 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. Title: Starspots and Stellar Rotation: Stellar Activity with Kepler Authors: Walkowicz, L. M.; Basri, G. S. Bibcode: 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. 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. Bibcode: 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). 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. Bibcode: 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). 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. Bibcode: 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. 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. Bibcode: 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. 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 Bibcode: 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 < 1.25 R ), 288 super-Earth-size (1.25 R <= R p < 2 R ), 662 Neptune-size (2 R <= R p < 6 R ), 165 Jupiter-size (6 R <= R p < 15 R ), and 19 up to twice the size of Jupiter (15 R <= R p < 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. Title: The Science in Science Fiction: Using Popular Entertainment as a Gateway Authors: Basri, Gibor S. Bibcode: 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. Title: Understanding Stellar Variability in Kepler Lightcurves Authors: Basri, Gibor S. Bibcode: 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. 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. Bibcode: 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. 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 Bibcode: 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 >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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/512/A37 Title: First thoughts on stellar variability from Kepler commissioning data Authors: Walkowicz, Lucianne M.; Basri, Gibor Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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 /L bol vprop 10-0.4×(SP-6) for SP >= 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 >= 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. Bibcode: 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 Bibcode: 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>=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 Bibcode: 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 Bibcode: 2009koa..prop..188B Altcode: No abstract at ADS Title: Magnetism and Rotation of Cool Dwarfs Authors: Basri, Gibor Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 2009astro2010S.262S Altcode: No abstract at ADS Title: The moderate magnetic field of the flare star Proxima Centauri Authors: Reiners, A.; Basri, G. Bibcode: 2008A&A...489L..45R Altcode: We report moderate magnetic flux of 450 G < Bf < 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. Bibcode: 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 Bibcode: 2008arXiv0808.2986R Altcode: We report moderate magnetic flux of 450G < Bf < 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. Bibcode: 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 (>1 mm). Title: Magnetism and Rotation of Cool Dwarfs Authors: Basri, Gibor Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 >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, <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 > 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. Bibcode: 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. Bibcode: 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 Bibcode: 2008koa..prop...53B Altcode: No abstract at ADS Title: Dynamo Action in Fully Convective Low-Mass Stars Authors: Browning, Matthew K.; Basri, Gibor Bibcode: 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 Bibcode: 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 Bibcode: 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 >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<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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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&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. Bibcode: 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&T Grant NNG05 GK48G. Title: Simulations of Convection and Magnetism in Fully Convective Stars Authors: Browning, Matthew K.; Basri, G. Bibcode: 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. Bibcode: 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&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. Bibcode: 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. Bibcode: 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 >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 Bibcode: 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. Bibcode: 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<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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 >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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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<~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 L/Lbol<~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 Bibcode: 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 <1 to ~10 Myr. The sample contains 41 brown dwarfs (spectral types >=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 >~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 Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Title: The Kepler Mission Authors: Basri, Gibor Bibcode: 2004wfis.confE..38B Altcode: No abstract at ADS Title: Magnetic Activity at Very Low Masses Authors: Basri, G. Bibcode: 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. Bibcode: 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. Bibcode: 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). Title: Brown Dwarfs: Up Close and Physical Authors: Basri, G. B. Bibcode: 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. Bibcode: 2003Mercu..32f..27B Altcode: Recent discoveries inside and outside the solar system have complicated our perception of what constitutes a "planet." Title: Rotation & Activity in Mid-M to L Dwarfs Authors: Mohanty, S.; Basri, G. Bibcode: 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. 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 >=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). 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 Bibcode: 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 Bibcode: 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. Title: Very Low Mass Stars and Brown Dwarfs in Taurus Authors: White, Russel; Basri, Gibor Bibcode: 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 Bibcode: 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. 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Title: Gravity & Mass Measurement in Young Substellar Objects Authors: Mohanty, Subhanjoy; Basri, Gibor; Jayawardhana, Ray; Allard, France; Hauschildt, Peter; Ardila, David Bibcode: 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. Bibcode: 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. Bibcode: 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 & Mass in Young Brown Dwarfs and Planemos Authors: Mohanty, Subhanjoy; Jayawardhana, Ray; Basri, Gibor; Allard, France; Hauschildt, Peter; Ardila, David Bibcode: 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 Bibcode: 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<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 >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<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 Bibcode: 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 F or L/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 (<~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 L/Lbol instead of F. 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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]<~ -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. Bibcode: 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. Bibcode: 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)<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 Bibcode: 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. Bibcode: 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 Bibcode: 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 (ApJ, 551, 833 [2001]), 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 Bibcode: 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 (<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. Bibcode: 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]<-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 Bibcode: 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 Bibcode: 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 & 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 & 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. Bibcode: 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. Bibcode: 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. Bibcode: 2001ASPC..223..261B Altcode: 2001csss...11..261B No abstract at ADS Title: Ultra-Cool Very Low-Mass Binaries Authors: Martín, Eduardo L.; Basri, Gibor Bibcode: 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. Bibcode: 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. Bibcode: 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<=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 & 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 >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 Bibcode: 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 Bibcode: 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 Bibcode: 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<2×10-6 (LX<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 Bibcode: 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 Bibcode: 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. Bibcode: 2000prpl.conf..457N Altcode: No abstract at ADS Title: The discovery of brown dwarfs. Authors: Basri, G. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 2000fepc.conf..446Z Altcode: We have obtained J photometry for a sample of 12 objects in the interval 16.0 < I <= 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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, & 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1999Sci...283.1718M Altcode: No abstract at ADS Title: The Nature of Young Brown Dwarf Candidates Authors: Martin, Eduardo; Ardila, David; Basri, Gibor Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 > I > 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. Bibcode: 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. Bibcode: 1998ASPC..134...51Z Altcode: 1998bdep.conf...51Z No abstract at ADS Title: Surveying low mass stars with SALT: newborn and stillborn. Authors: Basri, G. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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>I>=17.8, I-Z>= 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. Bibcode: 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 >=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 Bibcode: 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 < 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 < 50,000 K, many with M > 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 >~ 30,000 K as a result of differential cooling effects. Within the range Teff > 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 & 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. Bibcode: 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 >=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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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<logg<5.5 and 0<[M/H]<+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. Bibcode: 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. Bibcode: 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) >= 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. Bibcode: 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 & 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. Bibcode: 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 Bibcode: 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. Bibcode: 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, & 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, & 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 < υ < -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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 < 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. Bibcode: 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. Bibcode: 1991sepa.conf..189B Altcode: 1991IAUCo.129..189B No abstract at ADS Title: Properties and Models of T Tauri Stars Authors: Bertout, Claude; Basri, Gibor Bibcode: 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 Bibcode: 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. Bibcode: 1991iue..prop.3941B Altcode: We propose to complete the program which we began last year of observing the remaining hot (Teff > 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 1990iue..prop.3651B Altcode: We propose to continue our FUV observations of the known hot (Teff > 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. Bibcode: 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 Bibcode: 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. Bibcode: 1989BAAS...21.1102F Altcode: No abstract at ADS Title: Wild Spectral Variations in DF Tau Authors: Basri, G.; Misch, A. Bibcode: 1989BAAS...21.1084B Altcode: No abstract at ADS Title: Accretion Disks around T Tauri Stars. II. Balmer Emission Authors: Basri, Gibor; Bertout, Claude Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 1988BAAS...20Q1034B Altcode: No abstract at ADS Title: Accretion Disks around T Tauri Stars Authors: Bertout, Claude; Basri, Gibor; Bouvier, Jerome Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 1988BAAS...20..696W Altcode: No abstract at ADS Title: Supernova 1988H in NGC 5878 Authors: Filippenko, A. V.; Basri, G. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 1988ASIC..241..247B Altcode: 1988felm.conf..247B No abstract at ADS Title: High Quality Echelle Observations of T Tauri Stars Authors: Basri, G. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 1987BAAS...19..728I Altcode: No abstract at ADS Title: Stellar Activity - Causes and Effects Authors: Basri, G. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 1986BAAS...18R.984B Altcode: No abstract at ADS Title: Differential Activity Analysis Along the Pre-Main Sequence Authors: Basri, Gibor S. Bibcode: 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. Bibcode: 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 Bibcode: 1986LNP...254..442F Altcode: 1986csss....4..442F No abstract at ADS Title: Rossby or Not Rossby Authors: Basri, Gibor Bibcode: 1986LNP...254..184B Altcode: 1986csss....4..184B No abstract at ADS Title: T Tauri stars through the looking-glass. Authors: Finkenzeller, U.; Basri, G. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1983HiA.....6..650B Altcode: No abstract at ADS Title: Activity correlations in close binary systems Authors: Basri, G.; Laurent, R. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 &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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1981BAAS...13R.545A Altcode: No abstract at ADS Title: High resolution flux profiles of the Mg II h & k lines in evolved F8 to M5 stars. Authors: Stencel, R. E.; Mullan, D. J.; Basri, G. S.; Linsky, J. L. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1980BAAS...12R.805B Altcode: No abstract at ADS Title: The Chromospheric explanation of T Tauri spectra Authors: Basri, G.; Calvet, N.; Kuhi, L. V. Bibcode: 1980BAAS...12R.520B Altcode: No abstract at ADS Title: Outer atmospheres of cool stars. IV. A discussion of cool stellar wind models. Authors: Haisch, B. M.; Linsky, J. L.; Basri, G. S. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1979BAAS...11..472B Altcode: No abstract at ADS Title: Supergiant chromospheres Authors: Basri, Gibor Saul Bibcode: 1979PhDT.......249B Altcode: No abstract at ADS Title: Supergiant Chromospheres. Authors: Basri, G. S. Bibcode: 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. Bibcode: 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. Bibcode: 1978BAAS...10..729R Altcode: No abstract at ADS Title: Model Chromospheres for Supergiants: A Progress Report Authors: Basri, G. S.; Linsky, J. L. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1974BAAS....6..458L Altcode: No abstract at ADS