explanation blue bibcodes open ADS page with paths to full text
Author name code: thompson-michael
ADS astronomy entries on 2022-09-14
author:"Thompson, Michael J."
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Title: Self-Reported Demographics of 2014–2021 Principle
Investigators Proposing to NASA Planetary Science Research Programs
Authors: Thompson, M.; Jensen, H. B.; Papas, L. L.; Taha, N.; New,
M. H.
2022LPICo2679.2049T Altcode:
The NASA Division of Planetary Science will present demographic data
of Principle Investigators proposing to Research Opportunities in
Space and Earth Sciences (ROSES) programs for the years 2014–2021.
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Title: Improving Idea Through Nasa's Planetary Science Division's
Proposal Processes
Authors: Daou, D.; Moore, L.; Nahm, A. L.; Rinehart, S. A.;
Santiago-Materese, D.; Thompson, M.; Vander Kaaden, K. E.; Watkins,
R. N.; Zellner, N.
2022LPICo2679.2043D Altcode:
NASA, including the Planetary Science Division, is strongly
committed to promoting a culture of inclusion, diversity, equity,
and accessibility. A multitude of actionable efforts are underway to
increase IDEA throughout the proposal process.
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Title: Possible Mechanism(s) in the Photo-Magnetic Production of
Enantiomer Excesses
Authors: Cooper, G.; Jackson, W.; Thompson, M.; Rios, A. C.; Yeung,
K.; Dateo, C.
2022LPICo2678.2843C Altcode:
Did early solar system photo-magnetic forces create enantiomer excesses
in organic compounds?
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Title: Outgassing Experiments on Carbonaceous Chondrites and Their
Implications for Titan's Secondary Atmosphere
Authors: Duncan, T.; Yu, X.; Thompson, M.; Kim, K.; Telus, M.; Joshi,
T.; Lederman, D.
2021LPI....52.2664D Altcode:
Outgassed organics / Inside Titan / May resupply / The mysterious
methane.
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Title: Pre-Flight Calibration of the Mars 2020 Rover Mastcam Zoom
(Mastcam-Z) Multispectral, Stereoscopic Imager
Authors: Hayes, Alexander G.; Corlies, P.; Tate, C.; Barrington,
M.; Bell, J. F.; Maki, J. N.; Caplinger, M.; Ravine, M.; Kinch,
K. M.; Herkenhoff, K.; Horgan, B.; Johnson, J.; Lemmon, M.; Paar,
G.; Rice, M. S.; Jensen, E.; Kubacki, T. M.; Cloutis, E.; Deen, R.;
Ehlmann, B. L.; Lakdawalla, E.; Sullivan, R.; Winhold, A.; Parkinson,
A.; Bailey, Z.; van Beek, J.; Caballo-Perucha, P.; Cisneros, E.;
Dixon, D.; Donaldson, C.; Jensen, O. B.; Kuik, J.; Lapo, K.; Magee,
A.; Merusi, M.; Mollerup, J.; Scudder, N.; Seeger, C.; Stanish, E.;
Starr, M.; Thompson, M.; Turenne, N.; Winchell, K.
2021SSRv..217...29H Altcode:
The NASA Perseverance rover Mast Camera Zoom (Mastcam-Z) system is a
pair of zoomable, focusable, multi-spectral, and color charge-coupled
device (CCD) cameras mounted on top of a 1.7 m Remote Sensing Mast,
along with associated electronics and two calibration targets. The
cameras contain identical optical assemblies that can range in focal
length from 26 mm (25.5<SUP>∘</SUP>×19.1<SUP>∘</SUP>FOV ) to 110
mm (6.2<SUP>∘</SUP>×4.2<SUP>∘</SUP>FOV ) and will acquire data
at pixel scales of 148-540 μm at a range of 2 m and 7.4-27 cm at 1
km. The cameras are mounted on the rover's mast with a stereo baseline
of 24.3 ±0.1 cm and a toe-in angle of 1.17 ±0.03<SUP>∘</SUP>
(per camera). Each camera uses a Kodak KAI-2020 CCD with 1600 ×1200
active pixels and an 8 position filter wheel that contains an IR-cutoff
filter for color imaging through the detectors' Bayer-pattern filters, a
neutral density (ND) solar filter for imaging the sun, and 6 narrow-band
geology filters (16 total filters). An associated Digital Electronics
Assembly provides command data interfaces to the rover, 11-to-8 bit
companding, and JPEG compression capabilities. Herein, we describe
pre-flight calibration of the Mastcam-Z instrument and characterize
its radiometric and geometric behavior. Between April 26t<SUP>h</SUP>
and May 9t<SUP>h</SUP>, 2019, ∼45,000 images were acquired during
stand-alone calibration at Malin Space Science Systems (MSSS) in San
Diego, CA. Additional data were acquired during Assembly Test and Launch
Operations (ATLO) at the Jet Propulsion Laboratory and Kennedy Space
Center. Results of the radiometric calibration validate a 5% absolute
radiometric accuracy when using camera state parameters investigated
during testing. When observing using camera state parameters not
interrogated during calibration (e.g., non-canonical zoom positions),
we conservatively estimate the absolute uncertainty to be <10 %
. Image quality, measured via the amplitude of the Modulation Transfer
Function (MTF) at Nyquist sampling (0.35 line pairs per pixel),
shows MTF<SUB>Nyquist</SUB>=0.26 -0.50 across all zoom, focus, and
filter positions, exceeding the >0.2 design requirement. We discuss
lessons learned from calibration and suggest tactical strategies that
will optimize the quality of science data acquired during operation
at Mars. While most results matched expectations, some surprises were
discovered, such as a strong wavelength and temperature dependence on
the radiometric coefficients and a scene-dependent dynamic component
to the zero-exposure bias frames. Calibration results and derived
accuracies were validated using a Geoboard target consisting of
well-characterized geologic samples.
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Title: Methane: the Ideal Biosignature for the JWST Era?
Authors: Thompson, M.; Krissansen-Totton, J.; Fortney, J.
2021BAAS...53c1024T Altcode:
The next phase of exoplanet science will focus on characterizing
exoplanet atmospheres, including those of low-mass, terrestrial
planets. A comprehensive understanding of possible biosignatures
that may be detected with the next generation of ground and space
telescopes is warranted. While some biosignature gases, such as
oxygen and phosphine, have recently been reviewed in depth (Meadows et
al. 2018 and Sousa-Silva et al. 2020), these will likely be extremely
difficult to detect with JWST. In contrast, while it has not been
thoroughly reviewed, methane at Earth-like biogenic fluxes is one
of the only biosignatures that may be readily detectable with JWST
(Krissansen-Totton et al. 2018a). In fact, an early Earth-like,
methane-rich atmosphere would be easier to detect with JWST than
modern Earth's oxygen-rich atmosphere (ibid). Here we present our
preliminary work on a comprehensive review of methane biosignatures
and false positives. Biogenic methane production, or methanogenesis,
is a simpler metabolism than oxygenic photosynthesis, that is carried
out by anaerobic microbes (i.e., those not requiring oxygen for
growth). Methanogens use either CO2 and H2 or acetate as substrates
(Schwieterman et al. 2018). This process could be widespread due to
the likely ubiquity of the CO2+H2 redox couple in terrestrial planet
atmospheres, and the antiquity of methanogenesis on Earth (Wolfe
and Fournier 2018). We briefly review the current understanding of
the origin and evolution of methanogens, the organisms responsible
for methanogenesis, and how this process relates to origins-of-life
theories. When CH4 is invoked as a possible biosignature it is
often included with a strongly oxidizing companion gas (e.g., CO2 or
O2/O3). This is because it is difficult to explain abundant CH4 if
a terrestrial planet atmosphere's redox state is more oxidizing so
that the thermodynamically stable form of carbon would not be CH4
(Schwieterman et al. 2018). However, even in atmospheres devoid
of oxygen, CH4 has a short photochemical lifetime on habitable
zone rocky planets, and the large fluxes required to sustain high
CH4 abundances are likely much greater than could be supplied by
abiotic processes (e.g., magmatic outgassing, serpentinization)
(Krissansen-Totton et al. 2018b, Wogan et al. 2020). In addition,
many abiotic, geological processes that produce CH4 are expected to
also produce abundant CO, which life readily consumes, so the presence
of CH4 and CO2 but absence of CO strengthens the case for biogenicity
(Krissansen-Totton et al. 2018b). Although CH4+CO2 (minus CO) might
coexist in thermodynamic equilibrium on planets without large surface
oceans (Woitke et al. 2020), in practice, such atmospheres would be
photochemically unstable and, in particular, the CH4 would have a short
lifetime (less than ~1 Myrs). In addition to briefly discussing methane
on Mars and Titan, we review the presence of methane in Jovian and
sub-Neptune planet atmospheres. In many giant planets, methane is the
most abundant carbon-bearing gas and can be replenished indefinitely
because, although methane is photodissociated in the upper atmosphere,
hydrogen is never depleted and carbon and hydrogen can recombine
deeper in the atmosphere where temperatures and pressures are high
enough for methane production to be thermodynamically favorable and
kinetically viable (Moses et al. 2013). On the other hand, terrestrial
planets with high mean molecular weight atmospheres do not have
deep enough atmospheres to replenish methane without an additional
source (abiotic or biotic). In terrestrial atmospheres without a
replenishment source, methane is photodissociated and hydrogen is
lost to space on short timescales (~10s of thousands of years for ~1
bar atmospheres). For planets in the sub-Neptune regime, we seek to
determine how much atmosphere is necessary for a planet to sustain
methane via thermodynamic recombination against photodissociation. In
summary, for terrestrial planets to have methane-rich atmospheres,
the methane must be constantly replenished. We explore to what extent
abiotic CH4 replenishment is possible based on prior work on abiotic
methane sources including water-rock reactions, volcanic outgassing,
and impacts (e.g., Etiope & Lollar 2013, Wogan et al. 2020, Kress
& McKay 2003). We review methane false positives on terrestrial
planets and determine if they are likely to produce methane fluxes
as large as those caused by known biogenic sources. Through this
comprehensive review, we will develop a framework for identifying
methane biosignatures and discuss detectability prospects with JWST.
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Title: VizieR Online Data Catalog: PGCCs in lambda Orionis
complex. II. Cores at 850um (Yi+, 2018)
Authors: Yi, H. -W.; Lee, J. -E.; Liu, T.; Kim, K. -T.; Choi, M.;
Eden, D.; Evans, N. J., II; di, Francesco J.; Fuller, G.; Hirano,
N.; Juvela, M.; Kang, S. -J.; Kim, G.; Koch, P. M.; Lee, C. W.;
Li, Di; Liu, H. -Y. B.; Liu, H. -L.; Liu, S. -Y.; Rawlings, M. G.;
Ristorcelli, I.; Sanhueza, P.; Soam, A.; Tatematsu, K.; Thompson,
M.; Toth, L. V.; Wang, Ke; White, G. J.; Wu, Y.; Yang, Y. -L.
2021yCat..22360051Y Altcode:
As part of the legacy survey, "SCUBA-2 Continuum Observations of
Pre-protostellar Evolution" (SCOPE; Liu+ 2018ApJS..234...28L and Eden+
2019MNRAS.485.2895E ; proposal code: M16AL003), we observed 58 Planck
Galactic Cold Clumps (PGCCs) in the "CV Daisy" mapping mode, which
is suitable for small and compact sources with sizes of less than 3'
at 450 and 850um with the Submillimetre Common-User Bolometer Array 2
(SCUBA-2) at the 15m James Clerk Maxwell Telescope (JCMT). <P />We also
included archival data of 38 PGCCs located in the Orion A and B clouds
from the JCMT Science Archive hosted by the Canadian Astronomical Data
Centre (CADC). <P />Table 1 lists information about the 96 PGCCs. <P
/>We also included data from the Wide-Field Infrared Survey Explorer
(WISE) AllWISE catalog (Wright+ 2010, see II/328). <P />Finally, we
obtained 119 cores within the 40 detected PGCCs in the Orion complex. In
the λ Orionis cloud, there are 8 detected PGCCs, from which 15 cores
are identified. The Orion A cloud has 74 cores in 23 PGCCs, and the
Orion B cloud has 30 cores in 9 PGCCs. The list of cores in each cloud
is found in Tables 2-4. <P />(4 data files).
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Title: Outgassing Experiments on Carbonaceous Chondrites to Understand
the Formation of Titan's Atmosphere
Authors: Duncan, T.; Yu, X.; Thompson, M.; Kim, K.
2020AGUFMP071...08D Altcode:
Titan is the only known moon in the Solar System with a substantial
atmosphere of N 2 and CH 4 , however, its origin and evolution
are not well understood. Titan's present amount of atmospheric
CH 4 was predicted to be destroyed photochemically on very short
timescales compared to the age of the Solar System suggesting a
resupply mechanism is necessary [1]. Cassini provided new insight
into the origin of Titan's atmosphere by measuring abundances of
primordial noble gases and found that instead of being incorporated
during formation, Titan's atmosphere is likely linked to its interior
[2][3]. Recent theoretical modeling of Titan's atmosphere and interior
[4][5] suggests that its atmosphere could have originated in part by
outgassing of primordial organics in its interior. Insoluble organic
matter (IOM) found in carbonaceous chondrites may serve as an analog
for the organic material in Titan's interior and provide experimental
constraints on the outgassed component of its atmosphere. Therefore,
outgassing experiments on carbonaceous chondrites can help inform how
Titan obtained its secondary atmosphere, and in particular reveal a
possible source for Titan's atmospheric CH 4 . By heating primitive
meteorite samples and measuring the abundances of their released
volatiles, we may be able to connect what we see in the lab to species
in Titan's atmosphere today. In this study, we use samples of Murchison,
a CM carbonaceous chondrite, which contains substantial amounts of
insoluble organic matter (IOM).We heated 3 mg of powdered (20-100 µm
and <20 µm) Murchison samples from room temperature to 1200° C
in a furnace and continuously monitored 10 outgassed volatile species
with a Residual Gas Analyzer (RGA). We plan to conduct additional
experiments with other primitive meteorites and their extracted IOM to
further investigate the link between outgassing of primitive materials
and the origin of Titan's atmosphere. <P />Yung, Y. L., et al. 1984 ,
Astrophys. J. , 55, 465 <P />Niemann, H. B., et al. 2005, Nature, 438,
779 <P />Niemann, H. B., et al. 2010, J. Geophys. Res. , 115, 65 <P
/>Miller, K. E., .et al. 2019, Astrophys. J. , 871, 59 <P />Neri, A.,
et al. 2019, Earth Planet. Sci. Letts , 530, 6
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Title: Carbonaceous Chondrite Outgassing Experiments to Constrain
the Formation of Titan's Atmosphere
Authors: Kim, K.; Thompson, M.; Yu, X.; Duncan, T.; Telus, M.; Joshi,
T.; Lederman, D.
2020DPS....5221803K Altcode:
The origin of Titan's thick N<SUB>2</SUB> and CH<SUB>4</SUB> dominated
atmosphere is an outstanding puzzle in planetary science. Photochemical
models predict that Titan's current atmospheric methane would be
quickly destroyed by photolysis in ~30 million years [1], suggesting
a possible need for a mechanism to replenish the methane [2]. One
potential mechanism has been linked to the interior composition and
structure of Titan, and to better understand this question of methane
persistence in the atmosphere, we turn to Titan's atmospheric formation
[3]. Titan's atmosphere may have been produced in part from interior
outgassing with evidence coming from the detection of outgassed
<SUP>40</SUP>Ar, a radiogenic decay product of <SUP>40</SUP>K, that
was detected by the Huygens Gas Chromatograph and Mass Spectrometer
[4]. Recent studies suggest that organic material similar to the
refractory organics found in comets may be a necessary component
of Titan's interior, and outgassing of such material could provide
significant amounts of N<SUB>2</SUB> and CH<SUB>4</SUB> to replenish
Titan's atmosphere [5][6]. For this study, we analyze carbonaceous
(CM) chondrites because they contain insoluble organic matter (IOM),
which is similar to cometary refractory organics and may serve as an
analog to part of the interior material of Titan. In particular, we
studied samples from the Murchison meteorite because it is a pristine
CM carbonaceous chondrite fall with a significant IOM component. We
performed a suite of stepped heating experiments that will help place
experimental constraints on the amounts of outgassed carbon and nitrogen
compounds from CM chondrites to help inform the outgassed origin and
composition of Titan's atmosphere. We performed these experiments on
powdered Murchison samples with two grain size distributions, one
including grains between 20-100 microns in diameter and the other
with grain diameters <20 microns. We present the results of our
stepped heating experiments in which we heated these powdered samples
up to 1200 C in a furnace connected to a residual gas analyzer (RGA)
that continuously monitored the partial pressures of 10 different
outgassed species (e.g., C, CO, CO<SUB>2</SUB>, CH<SUB>4</SUB>, N,
N<SUB>2</SUB>). By measuring the abundances of outgassed volatiles, we
compare our results to prior experimental work on IOM from carbonaceous
chondrites and discuss how these experiments will inform the outgassing
origin and composition of Titan's atmosphere. <P />1: Yung, Y. L.,
et al. 1984. ApJ., 55. ; 2: Hörst, S. M. 2017. J. Gphys Res., 122. ;
3: Nixon, C., et al, 2018. Pl. Sp. Sci., 155. ; 4: Niemann, H.B.,
et al. 2005. Nat. 438. ; 5: Miller, K. E., et al. 2019. ApJ., 871. ;
6: Néri, A., et al. 2019. E. Pl. Sci Lts, 530.
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Title: VizieR Online Data Catalog: Abundances of Gaia DR2 wide
binaries (Hawkins+, 2020)
Authors: Hawkins, K.; Lucey, M.; Ting, Y. -S.; Ji, A.; Katzberg, D.;
Thompson, M.; El-Badry, K.; Teske, J.; Nelson, T.; Carrillo, A.
2020yCat..74921164H Altcode:
Stellar parameters and abundances for 50 stars in 25 wide binaries
observed with McDonald Observatory in 2019. <P />(3 data files).
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Title: VizieR Online Data Catalog: SCUBA-2 Ambitious Sky Survey
(Nettke+, 2017)
Authors: Nettke, W.; Scott, D.; Gibb, A. G.; Thompson, M.;
Chrysostomou, A.; Evans, A.; Hill, T.; Jenness, T.; Joncas, G.; Moore,
T.; Serjeant, S.; Urquhart, J.; Vaccari, M.; Weferling, B.; White,
G.; Zhu, M.
2020yCat..74680250N Altcode:
This beam-sized source catalogue is based on scans of Scuba-2 imagery
obtained between 2012 May 15 and 2014 May 12 using the James Clerk
Maxwell Telescope. There are three catalogues as well as one PDF file
which details a source comparison of samples from each catalogue. <P
/>(4 data files).
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Title: Assessing the Threat of Major Outbreaks of Vector-Borne
Diseases Under a Changing Climate
Authors: Thompson, R. N.; Thompson, M. J.; Hurrell, J. W.; Sun, L.;
Obolski, U.
2020ASSP...57...25T Altcode:
Michael J. Thompson served as the Director of the High Altitude
Observatory at the National Center for Atmospheric Research (NCAR) in
Boulder, Colorado, where he was also a Senior Scientist. In September
2013, Michael became the Deputy Director and Chief Operating Officer
of NCAR, enjoying a very close working relationship with Director Jim
Hurrell. During this time, Michael oversaw an organisation conducting
research in a range of fields, including his own topics of solar and
stellar physics, as well as others such as atmospheric chemistry and
climate science. At the same time, his son Robin was completing a PhD
in mathematical epidemiology at the University of Cambridge, UK, after
which he was awarded an independent Junior Research Fellowship at the
University of Oxford. However, the work conducted at NCAR and Robin's
research have more overlap than might at first be expected. Here
we present results from a collaboration that was set up following
Michael's untimely death in October 2018, between climate scientists
(Jim Hurrell and Lantao Sun) and mathematical epidemiologists (Robin
Thompson and Uri Obolski). Specifically, we propose a framework for
studying the effect of climate variability and change on vector-borne
disease risk. We introduce a new quantity—the Instantaneous Outbreak
Risk (IOR)—which quantifies the risk posed by an invading pathogen
accounting for the climatic conditions when that pathogen enters the
population. We show how the IOR can be used to assess the threat from
vector-borne diseases under a changing climate.
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Title: The Impact of a Fossil Magnetic Field on Dipolar Mixed-Mode
Frequencies in Sub- and Red-Giant Stars
Authors: Bugnet, L.; Prat, V.; Mathis, S.; García, R. A.; Mathur,
S.; Augustson, K.; Neiner, C.; Thompson, M. J.
2020ASSP...57..251B Altcode: 2020arXiv201208684B
The recent discovery of low-amplitude dipolar oscillation mixed modes in
massive red giants indicates the presence of a missing physical process
inside their cores. Stars more massive than ∼ 1.3 M<SUB>⊙</SUB>
are known to develop a convective core during the main-sequence:
the dynamo process triggered by this convection could be the origin
of a strong magnetic field inside the core of the star, trapped when
it becomes stably stratified and for the rest of its evolution. The
presence of highly magnetized white dwarfs strengthens the hypothesis
of buried fossil magnetic fields inside the core of evolved low-mass
stars. If such a fossil field exists, it should affect the mixed
modes of red giants as they are sensitive to processes affecting
the deepest layers of these stars. The impact of a magnetic field
on dipolar oscillations modes was one of Pr. Michael J. Thompson's
research topics during the 90s when preparing the helioseismic SoHO
space mission. As the detection of gravity modes in the Sun is still
controversial, the investigation of the solar oscillation modes did
not provide any hint of the existence of a magnetic field in the solar
radiative core. Today we have access to the core of evolved stars thanks
to the asteroseismic observation of mixed modes from CoRoT, Kepler,
K2 and TESS missions. The idea of applying and generalizing the work
done for the Sun came from discussions with Pr. Michael Thompson in
early 2018 before we lost him. Following the path we drew together,
we theoretically investigate the effect of a stable axisymmetric mixed
poloidal and toroidal magnetic field, aligned with the rotation axis of
the star, on the mixed modes frequencies of a typical evolved low-mass
star. This enables us to estimate the magnetic perturbations to the
eigenfrequencies of mixed dipolar modes, depending on the magnetic
field strength and the evolutionary state of the star. We conclude
that strong magnetic fields of ∼ 1MG should perturb the mixed-mode
frequency pattern enough for its effects to be detectable inside
current asteroseismic data.
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Title: On the Limits of Seismic Inversions for Radial Differential
Rotation of Solar-Type Stars
Authors: Santos, Ângela R. G.; Mathur, Savita; García, Rafael A.;
Thompson, Michael J.
2020ASSP...57..269S Altcode:
Seismic data contains information on stellar internal rotation, which
plays an important role on dynamo models. Due to the uncertainties
on the observations and stellar models, determining internal rotation
of main-sequence solar-type stars has been challenging. Here, we use
artificial rotational splittings for two-zone profiles to explore the
limitations to constrain internal rotation profiles.
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Title: Meteorite Outgassing Experiments to Inform Chemical Abundances
of Super-Earth Atmospheres
Authors: Thompson, M.; Fortney, J. J.; Telus, M.; Lederman, D.;
Joshi, T.
2019AGUFM.P23B3487T Altcode:
At present, there is no first principles understanding of how to
connect a terrestrial planet's bulk composition to its atmospheric
properties. Since terrestrial exoplanets likely form their atmospheres
through degassing (Elkins-Tanton & Seager 2008), a logical first
step to build such a theory for superEarths is to assay meteorites,
the leftover building blocks of planets, by heating them to measure
the outgassed volatiles. Our Solar System presents a wide variety of
meteorite types, including chondrites which are primitive unaltered
rocks believed to be representative of the material that formed
the rocky planets. We present the current results of our meteorite
outgassing experiments in which we heated a variety of chondritic
meteorite samples, at carefully controlled rates to temperatures
from 200 to 1200 °C and measured the partial pressures and relative
abundances of the outgassed volatile species (e.g., CO2, H2O, CH4, H2,
O2, S, Na) as a function of temperature and time. Our experimental
setup consisted of a residual gas analyzer connected to a furnace
to heat samples at specified rates. We compare the results of these
experiments to Schaefer and Fegley's prior theoretical chemical
equilibrium and kinetics calculations which modeled thermal outgassing
for a wide variety of chondrites to predict the composition of
terrestrial atmospheres formed via outgassing of specific types of
meteorites (Schaefer & Fegley 2007, Schaefer & Fegley 2010). In
addition to testing and validating Schaefer and Fegley's models,
the results from our experiments inform the phase space of chemical
abundances used in atmospheric models of superEarth exoplanets.
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Title: Overview of the Search for Space Weathering Signals on the
Surface of Bennu: One Rock Type, or Two?
Authors: Clark, B. E.; Ferrone, S. M.; Kaplan, H. H.; Zou, X. -D.;
Trang, D.; DellaGiustina, D. N.; LeCorre, L.; Golish, D. R.; Li,
J. -Y.; Ballouz, R. -L.; Hergenrother, C. W.; Rizk, B.; Burke, K. N.;
Bennett, C. A.; Keller, L.; Howell, E. S.; Lantz, C.; Barucci, M. A.;
Fornasier, S.; Thompson, M.; Michel, P.; Molaro, J.; Jawin, E. R.;
Delbo, M.; Simon, A.; Reuter, D.; Pajola, M.; Lauretta, D. S.
2019LPICo2189.2125C Altcode:
We provide an overview of the evidence for space weathering on asteroid
(101955) Bennu, and summarize relevant findings from several ongoing
parallel studies of surface processes and surface properties.
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Title: Lightcurve Analysis and Rotation Period of 6372 Walker
Authors: Hayes-Gehrke, Melissa N.; Berk, Marley; Fatodu, Abisola;
Kanani, Bhargin; Kropschot, Quinn; Marks, Julia; Misangyi, Ella;
Nguyen, Matthew; Stone, Julie; Suniga, Joshua; Thompson, Michael;
Vorsteg, Matthew; Wagman, Timothy; Marchini, Alessandro; Banfi,
Massimo; Papini, Riccardo; Salvaggio, Fabio; Brincat, Stephen M.;
Galdies, Charles; Winston Grech
2019MPBu...46..388H Altcode:
From 2019 March-May, images of minor planet 6372 Walker were captured
to investigate its rotation period. Our analysis found a period of
44.25 ±0.01 h.
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Title: VizieR Online Data Catalog: Radio observations of G074.11+00.11
(Saajasto+, 2019)
Authors: Saajasto, M.; Harju, J.; Juvela, M.; Tie, L.; Zhang, Q.;
Liu, S. -Y.; Hirano, N.; Wu, Y.; Kim, K. -T.; Tatematsu, K.; Wang,
K.; Thompson, M.
2019yCat..36300069S Altcode:
This catalogue contains the radio observations of a cold clump
G074.11+00.11. The catalogue contains all of the observed molecular
lines, however, please note that not all of the observed molecules
were detected. The included data has been obtained from several
telescopes: Purple Mountain Observatory (PMO), Korean Very Long Baseline
Interferometry Network (KVN), the Submillimeter Telescope (SMT), and
the Submillimeter Array (SMA). For a more detailed description of the
data, velocity resolutions etc. please see the Section 2, Observations
of the main paper and the references therein. <P />(24 data files).
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Title: Space Weathering of Carbonaceous Asteroids and Meteorites
Authors: Loeffler, M. J.; Thompson, M.; Keller, L. P.
2018AGUFM.P21D3381L Altcode:
It is well known that solar wind particles and micrometeorite impacts
alter the surface regolith of airless bodies, such as the Moon and
asteroids. On the scale of the regolith grains, these alterations
are manifested through physical and chemical changes of the outer
layers, which can be due to a combination of direct irradiation or
redeposition of material evaporated during irradiation. Laboratory
studies focusing on simulating lunar- and asteroid-type space weathering
in iron-bearing minerals have been relatively successful at showing
that much of the changes in optical properties (spectral reddening
and darkening in the visible-near-infrared region) are driven by the
formation of chemically reduced iron produced through either solar wind
bombardment or micrometeorite impacts. However, a similar correlation
has not yet been made for carbonaceous asteroids and meteorites, as
laboratory experiments have shown a variety of trends, suggesting that
weathering in these types of minerals may be more complicated. Thus, we
have begun a systematic study where we are looking at space weathering
in diagnostic minerals found in carbonaceous asteroids and meteorites,
focusing on how the optical, structural and chemical properties of these
minerals' components are altered by ion and laser irradiation. Here we
present some of our most recent results on effects that micrometeorite
impacts, simulated with a pulsed laser, has on sulfide minerals, using
the our new ultra-high vacuum system at Northern Arizona University.
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Title: Solar Physics from Unconventional Viewpoints
Authors: Gibson, Sarah E.; Vourlidas, Angelos; Hassler, Donald M.;
Rachmeler, Laurel A.; Thompson, Michael J.; Newmark, Jeffrey; Velli,
Marco; Title, Alan; McIntosh, Scott W.
2018FrASS...5...32G Altcode: 2018arXiv180509452G
We explore new opportunities for solar physics that could be realized
by future missions providing sustained observations from vantage
points away from the Sun-Earth line. These include observations from
the far side of the Sun, at high latitudes including over the solar
poles, or from near-quadrature angles relative to the Earth (e.g.,
the Sun-Earth L4 and L5 Lagrangian points). Such observations fill
known holes in our scientific understanding of the three-dimensional,
time-evolving Sun and heliosphere, and have the potential to open new
frontiers through discoveries enabled by novel viewpoints.
---------------------------------------------------------
Title: The Coronal Solar Magnetism Observatory
Authors: Thompson, Michael J.; Tomczyk, Steven; Gibson, Sarah E.;
McIntosh, Scott W.; Landi, Enrico
2018IAUS..335..359T Altcode:
The Coronal Solar Magnetism Observatory (CoSMO) is a proposed new
facility led by the High Altitude Observatory and a consortium of
partners to measure magnetic field and plasma properties in a large
(one degree) field of view extending down to the inner parts of the
solar corona. CoSMO is intended as a research facility that will
advance the understanding and prediction of space weather. The
instrumentation elements of CoSMO are: a white-light coronagraph
(KCor), already operational at the Mauna Loa Solar Observatory
(MLSO); the Chromosphere and Prominence Magnetometer (ChroMag), due
for deployment to MLSO next year; and the CoSMO Large Coronagraph (LC)
which has completed Preliminary Design Review.
---------------------------------------------------------
Title: Design of a next generation synoptic solar observing network:
solar physics research integrated network group (SPRING)
Authors: Gosain, Sanjay; Roth, Markus; Hill, Frank; Pevtsov, Alexei;
Martinez Pillet, Valentin; Thompson, Michael J.
2018SPIE10702E..4HG Altcode:
Long-term synoptic observations of the Sun in different wavelength
regions are essential to understand its secular behavior. Such
observations have proven very important for discovery of 11 year
solar activity cycle, 22 year magnetic cycle, polar field reversals,
Hale's polarity law, Joy's law, that helped Babcock and Leighton
to propose famous solar dynamo model. In more recent decades, the
societal impact of the secular changes in Sun's output has been felt in
terms of solar inputs to terrestrial climate-change and space-weather
hazards. Further, it has been realized that to better understand the
activity phenomena such as flares and coronal mass ejections (CMEs)
one needs synoptic observations in multiple spectral lines to enable
tomographic inference of physical parameters. Currently, there are
both space and ground based synoptic observatories. However, given
the requirements for the long-term stability and reliability of such
synoptic datasets, ground-based facilities are more preferable. Also,
the ground based observatories are easy to maintain or upgrade while
detailed and frequent calibrations are easily possible. The only
ground-based facility that currently provides full-disk velocity and
magnetic field maps of the Sun around the clock and at good cadence,
is the Global Oscillations Network Group (GONG) network of National
Solar Observatory (NSO) which is operational since the mid 90s. Due
to its aging instrumentation, operating for nearly three decades, and
new requirements to obtain multiwavelength observations, a need is felt
in the solar community to build a next generation synoptic observatory
network. A group of international observatories have come together under
the auspices of SOLARNET program, funded by European Union (EU), to
carryout a preliminary design study of such a synoptic solar observing
facility called "SPRING", which stands for Solar Physics Research
Integrated Network Group. In this article we will present concept of
SPRING and the optical design concept of its major instruments.ts.
---------------------------------------------------------
Title: Signatures of Solar Cycle 25 in Subsurface Zonal Flows
Authors: Howe, R.; Hill, F.; Komm, R.; Chaplin, W. J.; Elsworth, Y.;
Davies, G. R.; Schou, J.; Thompson, M. J.
2018ApJ...862L...5H Altcode: 2018arXiv180702398H
The pattern of migrating zonal flow bands associated with the solar
cycle, known as the torsional oscillation, has been monitored with
continuous global helioseismic observations by the Global Oscillations
Network Group (GONG), together with those made by the Michelson
Doppler Imager (MDI) on board the Solar and Heliospheric Observatory
(SOHO) and its successor, the Helioseismic and Magnetic Imager (HMI)
on board the Solar Dynamics Observatory (SDO), since 1995, giving us
nearly two full solar cycles of observations. We report that the flows
now show traces of the mid-latitude acceleration that is expected to
become the main equatorward-moving branch of the zonal flow pattern for
Cycle 25. Based on the current position of this branch, we speculate
that the onset of widespread activity for Cycle 25 is unlikely to be
earlier than the middle of 2019.
---------------------------------------------------------
Title: Solar Observations Away from the Sun-Earth Line
Authors: Gibson, Sarah E.; McIntosh, Scott William; Rachmeler,
Laurel; Thompson, Michael J.; Title, Alan M.; Velli, Marco C. M.;
Vourlidas, Angelos
2018tess.conf40340G Altcode:
Observations from satellite missions have transformed the field of solar
physics. High-resolution observations with near-continuous temporal
coverage have greatly extended our capability for studying long-term
and transient phenomena, and the opening of new regions of the solar
spectrum has made detailed investigation of the solar atmosphere
possible. <P />However, to date most solar space-based missions
have been restricted to an observational vantage in the vicinity of
the Sun-Earth line, either in orbit around the Earth or from the L1
Lagrangian point. As a result, observations from these satellites
represent the same geometrical view of the Sun that is accessible
from the Earth. <P />Understanding the deep interior structure of the
Sun and the full development of solar activity would really benefit
from fully three-dimensional monitoring of the solar atmosphere and
heliosphere. On the one hand, simultaneous spacecraft observations
from multiple vantage points would allow studies of the deep interior
structure of the sun via stereoscopic helioseismology; on the other,
distributed observations would allow the understanding of the complete
evolution of activity complexes and enhance space weather predictions
dramatically. <P />Presently, observations of the Sun away from Earth
are obtained by the STEREO pair of satellites, which have provided
an unprecedented global view by orbiting around to the far side of
the Sun, and the Ulysses mission, which achieved a high-inclination
(80˚) near-polar orbit (but which, however, did not include any solar
imaging instruments). The forthcoming Solar Orbiter mission, which
will orbit the sun and reach a maximum inclination of 34˚ out of the
ecliptic should provide the first detailed mapping of the sun's polar
fields. In addition, Solar Probe Plus will explore the outer corona
and inner Heliosphere with very rapid solar encounters at a minimum
perihelion 9.86 solar radii from the center of the Sun. <P />We explore
some of the new opportunities for solar physics that can be realized
by future missions that provide sustained observations from vantage
points away from the Sun-Earth line (and in some cases the ecliptic
plane): observations from the far side of the Sun, over its poles,
or from the L5 Lagrangian point.
---------------------------------------------------------
Title: Flyby and Impact of Chariklo: A New Frontiers Class Centaur
Reconnaissance Mission Concept from the 2017 NASA-JPL Planetary
Science Summer Seminar
Authors: Bouchard, M. C.; Howell, S. M.; Chou, L.; Thompson, M.;
Cusson, S.; Marcus, M.; Brodsky Smith, H.; Bhattaru, S.; Balock,
J. J.; Brueshaber, S.; Eggl, S.; Jawin, E. R.; Miller, K. E.; Rizzo,
M.; Steakley, K.; Thomas, N. H.; Trent, K.; Ugelow, M.; Budney, C. J.;
Mitchell, K. L.
2018LPI....49.2087B Altcode:
This abstract summarizes a New Frontiers mission concept to the Centaur
Chariklo that was created during the 2017 NASA/JPL Planetary Science
Summer Seminar.
---------------------------------------------------------
Title: Solar Magnetic Fields
Authors: Balogh, André; Cliver, Edward; Petrie, Gordon; Solanki,
Sami; Thompson, Michael; von Steiger, Rudolf
2018smf..book.....B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Life Cycle of Active Region Magnetic Fields
Authors: Cheung, M. C. M.; van Driel-Gesztelyi, L.; Martínez Pillet,
V.; Thompson, M. J.
2018smf..book..317C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Life Cycle of Active Region Magnetic Fields
Authors: Cheung, M. C. M.; van Driel-Gesztelyi, L.; Martínez Pillet,
V.; Thompson, M. J.
2017SSRv..210..317C Altcode: 2016SSRv..tmp...46C
We present a contemporary view of how solar active region
magnetic fields are understood to be generated, transported and
dispersed. Empirical trends of active region properties that guide model
development are discussed. Physical principles considered important
for active region evolution are introduced and advances in modeling
are reviewed.
---------------------------------------------------------
Title: Prospects and Challenges for Helioseismology
Authors: Toomre, J.; Thompson, M. J.
2017hdsi.book....7T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Helioseismology and Dynamics of the Solar Interior
Authors: Thompson, M. J.; Brun, A. S.; Culhane, J. L.; Gizon, L.;
Roth, M.; Sekii, T.
2017hdsi.book.....T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Preface: Helioseismology and Dynamics of the Solar Interior
Authors: Gizon, Laurent; Thompson, Michael J.; Brun, A. Sacha; Culhane,
J. Len; Roth, Markus; Sekii, Takashi
2017hdsi.book....1G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Dynamics, Rotation, Convection and Overshoot
Authors: Hanasoge, S.; Miesch, M. S.; Roth, M.; Schou, J.; Schüssler,
M.; Thompson, M. J.
2017hdsi.book...85H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: MeerGAL: the MeerKAT Galactic Plane Survey
Authors: Thompson, M.; Goedhart, S.; Goedhart, S.; Benaglia,
P.; Beuther, H.; Blomme, R.; Chrysostomou, A. C.; Clark, J. S.;
Dickinson, C.; Ellingsen, S.; Fenech, D.; Hindson, L.; Longmore,
S. N.; van Langevelde, H. J.; MacLeod, G.; Molinari, S.; Prinja, R.;
Purcell, C. R.; Stevens, I.; Umana, G.; Urquhart, J. S.; Vlemmings,
W.; Walsh, A. J.; Yang, A. Y.; Zijlstra, A.
2016mks..confE..15T Altcode: 2016PoS...277E..15T
No abstract at ADS
---------------------------------------------------------
Title: Solar Dynamics, Rotation, Convection and Overshoot
Authors: Hanasoge, S.; Miesch, M. S.; Roth, M.; Schou, J.; Schüssler,
M.; Thompson, M. J.
2015SSRv..196...79H Altcode: 2015SSRv..tmp...24H; 2015arXiv150308539H
We discuss recent observational, theoretical and modeling progress
made in understanding the Sun's internal dynamics, including its
rotation, meridional flow, convection and overshoot. Over the past
few decades, substantial theoretical and observational effort has
gone into appreciating these aspects of solar dynamics. A review of
these observations, related helioseismic methodology and inference and
computational results in relation to these problems is undertaken here.
---------------------------------------------------------
Title: Prospects and Challenges for Helioseismology
Authors: Toomre, J.; Thompson, M. J.
2015SSRv..196....1T Altcode: 2015SSRv..tmp...22T
Helioseismology has advanced considerably our knowledge of the interior
of the Sun over the past three decades. Our understanding of the Sun's
internal structure, its dynamics, rotation, convection and magnetism,
have all been advanced. Yet there are challenges, areas where the
results from helioseismology are tantalizing but inconclusive, and
aspects where the interpretation of the data has still to be put on
a firm footing. In this paper we shall focus on a number of those
challenges and give our assessment of where progress needs to be made
in the next decade.
---------------------------------------------------------
Title: A helioseismic view of the Sun's internal structure and
dynamics
Authors: Basu, S.; Thompson, M. J.
2015exse.book..170B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Temporal evolution of the solar torsional oscillation and
implications for cycle 25
Authors: Hill, Frank; Howe, Rachel; Komm, Rudolf; Schou, Jesper;
Thompson, Michael; Larson, Timothy
2015TESS....110502H Altcode:
The zonal flow known as the torsional oscillation has been observed
on the Sun’s surface since 1980 and in its interior since 1995. It
has two branches that migrate during the solar cycle, with one moving
towards the equator and the other towards the poles. The rate at which
these branches migrate in latitude is tightly correlated with the
timing of the solar cycle, as seen during the long minimum between
cycles 23 and 24. The poleward branch generally becomes visible 10
to 12 years before the appearance of the magnetic activity associated
with the corresponding sunspot cycle as it did for the current cycle
24. However, the poleward flow for cycle 25, which was expected to
appear in 2008-2010, was not observed. Subsequent analysis showed
that it is a very weak flow, and is masked by an apparent change
in the background solar differential rotation rate. We will present
the latest observations of the zonal flow as determined from global
helioseismology, and will discuss the implications for the strength
and timing of cycle 25.
---------------------------------------------------------
Title: SKA tomography of Galactic star-forming regions and spiral arms
Authors: Loinard, L.; Thompson, M.; Hoare, M.; van Langevelde, H. J.;
Ellingsen, S.; Brunthaler, A.; Forbrich, J.; Rygl, K.; Rodríguez,
L. F.; Mioduszewski, A. J.; Torres-López, R. M.; Dzib, S. A.;
Ortiz-León, G. N.; Bourke, T.; Green, J. A.
2015aska.confE.166L Altcode: 2015PoS...215E.166L
No abstract at ADS
---------------------------------------------------------
Title: The ionised,radical and molecular Milky Way: spectroscopic
surveys with the SKA
Authors: Thompson, M.; Beuther, H.; Dickinson, C.; MOttram, J.;
Klaassen, P.; Ginsburg, A.; Longmore, S.; Remijan, A.; Menten, K. M.
2015aska.confE.126T Altcode: 2014arXiv1412.5554T; 2015PoS...215E.126T
The bandwith, sensitivity and sheer survey speed of the SKA offers
unique potential for deep spectroscopic surveys of the Milky Way. Within
the frequency bands available to the SKA lie many transitions that
trace the ionised, radical and molecular components of the interstellar
medium and which will revolutionise our understanding of many physical
processes. In this chapter we describe the impact on our understanding
of the Milky Way that can be achieved by spectroscopic SKA surveys,
including "out of the box" early science with radio recombination lines,
Phase 1 surveys of the molecular ISM using anomalous formaldehyde
absorption, and full SKA surveys of ammonia inversion lines.
---------------------------------------------------------
Title: The impact of SKA on Galactic Radioastronomy: continuum
observations
Authors: Umana, G.; Trigilio, C.; Cerrigone, L.; Cesaroni, R.;
Zijlstra, A. A.; Hoare, M.; Weis, K.; Beasley, A.; Bomans, D.;
Hallinan, G.; Molinari, S.; Taylor, R.; Testi, L.; Thompson, M.
2015aska.confE.118U Altcode: 2014arXiv1412.5833U; 2015PoS...215E.118U
The SKA will be a state of the art radiotelescope optimized for both
large area surveys as well as for deep pointed observations. In this
paper we analyze the impact that the SKA will have on Galactic studies,
starting from the immense legacy value of the all-sky survey proposed by
the continuum SWG but also presenting some areas of Galactic Science
that particularly benefit from SKA observations both surveys and
pointed. The planned all-sky survey will be characterized by unique
spatial resolution, sensitivity and survey speed, providing us with a
wide-field atlas of the Galactic continuum emission. Synergies with
existing, current and planned radio Galactic Plane surveys will be
discussed. SKA will give the opportunity to create a sensitive catalog
of discrete Galactic radio sources, most of them representing the
interaction of stars at various stages of their evolution with the
environment: complete census of all stage of HII regions evolution;
complete census of late stages of stellar evolution such as PNe and
SNRs; detection of stellar winds, thermal jets, Symbiotic systems,
Chemically Peculiar and dMe stars, active binary systems in both
flaring and quiescent states. Coherent emission events like Cyclotron
Maser in the magnetospheres of different classes of stars can be
detected. Pointed, deep observations will allow new insights into the
physics of the coronae and plasma processes in active stellar systems
and single stars, enabling the detection of flaring activity in larger
stellar population for a better comprehension of the mechanism of energy
release in the atmospheres of stars with different masses and age.
---------------------------------------------------------
Title: GONG, Helioseismology, and the Sun's internal dynamics
Authors: Thompson, Michael
2015TESS....121401T Altcode:
GONG has made remarkable contributions to the development of
helioseismology and our understanding of the solar interior. Even
before GONG produced any data, the teams of community scientists
formed under the auspices of the GONG project led to significant
advances in helioseismology, for example the development of helioseismic
inversion techniques. Once the network became operational and the first
observations started coming in, GONG data revealed as never before the
Sun's internal dynamics, in particular the solar internal rotation. In
this talk I shall review GONG's contribution to helioseismology and
the helioseismic results from the project.
---------------------------------------------------------
Title: Very low-luminosity Class I/Flat outflow sources in sigma
Orionis: Clues to alternative formation mechanisms for very low-mass
stars
Authors: Riaz, Basmah; Whelan, E.; Thompson, M.; Vorobyov, E.;
Lodieu, N.
2015AAS...22544907R Altcode:
We present an optical through sub-millimetre multi-wavelength study
of two very low-luminosity Class I/Flat systems, Mayrit 1701117 and
Mayrit 1082188, in the sigma Orionis cluster. We performed moderate
resolution (R 1000) optical ( 0.4-0.9mu) spectroscopy with the TWIN
spectrograph at the Calar Alto 3.5-m telescope. The spectra for both
sources show prominent emission in accretion- and outflow-associated
lines. The mean accretion rate measured from multiple line diagnostics
is 6.4x10^{-10} Msun/yr for Mayrit 1701117, and 2.5x10^{-10} Msun/yr
for Mayrit 1082188. The outflow mass loss rates for the two systems
are similar and estimated to be 1x10^{-9} Msun/yr. The activity rates
are within the range observed for low-mass Class I protostars. We
obtained sub-millimetre continuum observations with the Submillimetre
Common-User Bolometer Array (SCUBA-2) bolometer at the James Clerk
Maxwell Telescope. Both objects are detected at a >5-sigma level
in the SCUBA-2 850mu band. The bolometric luminosity of the targets as
measured from the observed spectral energy distribution over 0.8-850mu
is 0.18+/-0.04 Lsun for Mayrit 1701117, and 0.16+/-0.03 Lsun for Mayrit
1082188, and is in the very low-mass range. The total dust+gas mass
derived from sub-millimetre fluxes is 36 M_Jup and 22 M_Jup for Mayrit
1701117 and Mayrit 1082188, respectively. There is the possibility
that some of the envelope material might be dissipated by the strong
outflows driven by these sources, resulting in a final mass of the
system close to or below the sub-stellar limit. Given the membership
of these objects in a relatively evolved cluster of 3 Myr of age, we
consider an alternate formation mechanism in the context of the `hybrid'
model of disk fragmentation, followed by ejection of a gaseous clump.
---------------------------------------------------------
Title: The Sun's Interior Structure and Dynamics, and the Solar Cycle
Authors: Broomhall, A. -M.; Chatterjee, P.; Howe, R.; Norton, A. A.;
Thompson, M. J.
2015sac..book..191B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Very low-luminosity Class I/flat outflow sources in σ Orionis
Authors: Riaz, B.; Thompson, M.; Whelan, E. T.; Lodieu, N.
2015MNRAS.446.2550R Altcode: 2014arXiv1410.3377R
We present an optical to submillimetre multiwavelength study of two very
low-luminosity Class I/flat systems, Mayrit 1701117 and Mayrit 1082188,
in the σ Orionis cluster. We performed moderate-resolution (R ∼
1000) optical (∼0.4-0.9 μm) spectroscopy with the Cassegrain Twin
Spectrograph (TWIN) spectrograph at the Calar Alto 3.5-m telescope. The
spectra for both sources show prominent emission in accretion-
and outflow-associated lines. The mean accretion rate measured from
multiple line diagnostics is 6.4 × 10<SUP>-10</SUP> M<SUB>⊙</SUB>
yr<SUP>-1</SUP> for Mayrit 1701117 and 2.5 × 10<SUP>-10</SUP>
M<SUB>⊙</SUB> yr<SUP>-1</SUP> for Mayrit 1082188. The outflow
mass-loss rates for the two systems are similar and estimated to be
∼1 × 10<SUP>-9</SUP> M<SUB>⊙</SUB> yr<SUP>-1</SUP>. The activity
rates are within the range observed for low-mass Class I protostars. We
obtained submillimetre continuum observations with the Submillimetre
Common-User Bolometer Array (SCUBA-2) bolometer at the James Clerk
Maxwell Telescope. Both objects are detected at a ≥5σ level in
the SCUBA-2 850-μm band. The bolometric luminosity of the targets as
measured from the observed spectral energy distribution over ∼0.8-850
μm is 0.18 ± 0.04 L<SUB>⊙</SUB> for Mayrit 1701117 and 0.16 ±
0.03 L<SUB>⊙</SUB> for Mayrit 1082188 and is in the very low mass
range. The total dust+gas mass derived from submillimetre fluxes is
∼36 M<SUB>Jup</SUB> and ∼22 M<SUB>Jup</SUB> for Mayrit 1701117
and Mayrit 1082188, respectively. There is the possibility that some
of the envelope material might be dissipated by the strong outflows
driven by these sources, resulting in a final mass of the system close
to or below the substellar limit.
---------------------------------------------------------
Title: The Sun's Interior Structure and Dynamics, and the Solar Cycle
Authors: Broomhall, A. -M.; Chatterjee, P.; Howe, R.; Norton, A. A.;
Thompson, M. J.
2014SSRv..186..191B Altcode: 2014arXiv1411.5941B
The Sun's internal structure and dynamics can be studied with
helioseismology, which uses the Sun's natural acoustic oscillations
to build up a profile of the solar interior. We discuss how solar
acoustic oscillations are affected by the Sun's magnetic field. Careful
observations of these effects can be inverted to determine the
variations in the structure and dynamics of the Sun's interior as
the solar cycle progresses. Observed variations in the structure and
dynamics can then be used to inform models of the solar dynamo, which
are crucial to our understanding of how the Sun's magnetic field is
generated and maintained.
---------------------------------------------------------
Title: Deciphering Solar Magnetic Activity. I. On the Relationship
between the Sunspot Cycle and the Evolution of Small Magnetic Features
Authors: McIntosh, Scott W.; Wang, Xin; Leamon, Robert J.; Davey,
Alisdair R.; Howe, Rachel; Krista, Larisza D.; Malanushenko, Anna V.;
Markel, Robert S.; Cirtain, Jonathan W.; Gurman, Joseph B.; Pesnell,
William D.; Thompson, Michael J.
2014ApJ...792...12M Altcode: 2014arXiv1403.3071M
Sunspots are a canonical marker of the Sun's internal magnetic
field which flips polarity every ~22 yr. The principal variation of
sunspots, an ~11 yr variation, modulates the amount of the magnetic
field that pierces the solar surface and drives significant variations
in our star's radiative, particulate, and eruptive output over that
period. This paper presents observations from the Solar and Heliospheric
Observatory and Solar Dynamics Observatory indicating that the 11
yr sunspot variation is intrinsically tied to the spatio-temporal
overlap of the activity bands belonging to the 22 yr magnetic activity
cycle. Using a systematic analysis of ubiquitous coronal brightpoints
and the magnetic scale on which they appear to form, we show that the
landmarks of sunspot cycle 23 can be explained by considering the
evolution and interaction of the overlapping activity bands of the
longer-scale variability.
---------------------------------------------------------
Title: A New Ground-Based Network for Synoptic Solar Observations:
The Solar Physics Research Integrated Network Group (SPRING)
Authors: Hill, Frank; Roth, Markus; Thompson, Michael; Gusain, Sanjay
2014AAS...22412354H Altcode:
SPRING is a project to develop a geographically distributed network
of instrumentation to obtain synoptic solar observations. Building
on the demonstrated success of networks to provide nearly-continuous
long-term data for helioseismology, SPRING will provide data for a wide
range of solar research areas. Scientific objectives include internal
solar dynamics and structure; wave transport in the solar atmosphere;
the evolution of the magnetic field over the activity cycle; irradiance
fluctuations; and space weather origins. Anticipated data products
include simultaneous full-disk multi-wavelength Doppler and vector
magnetic field images; filtergrams in H-Alpha, CaK, and white light;
and PSPT-type irradiance support. The data will be obtained with a duty
cycle of around 90% and at a cadence no slower than one minute. The
current concept is a multi-instrument platform installed in at least
six locations, and which will also provide context information for
large-aperture solar telescopes such as EST and the DKIST. There is
wide support for the idea within the EU and the US solar research
communities. The project is in the early planning stages, and we are
open to and looking for participants in the science and instrument
definition.
---------------------------------------------------------
Title: Grand Challenges in the Physics of the Sun and Sun-like Stars
Authors: Thompson, Michael
2014FrASS...1....1T Altcode: 2014arXiv1406.4228T
The study of stellar structure and evolution is one of the main
building blocks of astrophysics, and the Sun has an importance both as
the star that is most amenable to detailed study and as the star that
has by far the biggest impact on the Earth and near-Earth environment
through its radiative and particulate outputs. Over the past decades,
studies of stars and of the Sun have become somewhat separate. But in
recent years, the rapid advances in asteroseismology, as well as the
quest to better understand solar and stellar dynamos, have emphasized
once again the synergy between studies of the stars and the Sun. In
this article I have selected two "grand challenges" both for their
crucial importance and because I thnk that these two problems are
tractable to significant progress in the next decade. They are (i)
understanding how solar and stellar dynamos generate magnetic field,
and (ii) improving the predictability of geo-effective space weather.
---------------------------------------------------------
Title: Future mmVLBI Research with ALMA: A European vision
Authors: Tilanus, R. P. J.; Krichbaum, T. P.; Zensus, J. A.; Baudry,
A.; Bremer, M.; Falcke, H.; Giovannini, G.; Laing, R.; van Langevelde,
H. J.; Vlemmings, W.; Abraham, Z.; Afonso, J.; Agudo, I.; Alberdi,
A.; Alcolea, J.; Altamirano, D.; Asadi, S.; Assaf, K.; Augusto, P.;
Baczko, A-K.; Boeck, M.; Boller, T.; Bondi, M.; Boone, F.; Bourda,
G.; Brajsa, R.; Brand, J.; Britzen, S.; Bujarrabal, V.; Cales, S.;
Casadio, C.; Casasola, V.; Castangia, P.; Cernicharo, J.; Charlot,
P.; Chemin, L.; Clenet, Y.; Colomer, F.; Combes, F.; Cordes, J.;
Coriat, M.; Cross, N.; D'Ammando, F.; Dallacasa, D.; Desmurs, J-F.;
Eatough, R.; Eckart, A.; Eisenacher, D.; Etoka, S.; Felix, M.; Fender,
R.; Ferreira, M.; Freeland, E.; Frey, S.; Fromm, C.; Fuhrmann, L.;
Gabanyi, K.; Galvan-Madrid, R.; Giroletti, M.; Goddi, C.; Gomez, J.;
Gourgoulhon, E.; Gray, M.; di Gregorio, I.; Greimel, R.; Grosso, N.;
Guirado, J.; Hada, K.; Hanslmeier, A.; Henkel, C.; Herpin, F.; Hess,
P.; Hodgson, J.; Horns, D.; Humphreys, E.; Hutawarakorn Kramer, B.;
Ilyushin, V.; Impellizzeri, V.; Ivanov, V.; Julião, M.; Kadler, M.;
Kerins, E.; Klaassen, P.; van 't Klooster, K.; Kording, E.; Kozlov,
M.; Kramer, M.; Kreikenbohm, A.; Kurtanidze, O.; Lazio, J.; Leite,
A.; Leitzinger, M.; Lepine, J.; Levshakov, S.; Lico, R.; Lindqvist,
M.; Liuzzo, E.; Lobanov, A.; Lucas, P.; Mannheim, K.; Marcaide, J.;
Markoff, S.; Martí-Vidal, I.; Martins, C.; Masetti, N.; Massardi,
M.; Menten, K.; Messias, H.; Migliari, S.; Mignano, A.; Miller-Jones,
J.; Minniti, D.; Molaro, P.; Molina, S.; Monteiro, A.; Moscadelli,
L.; Mueller, C.; Müller, A.; Muller, S.; Niederhofer, F.; Odert,
P.; Olofsson, H.; Orienti, M.; Paladino, R.; Panessa, F.; Paragi,
Z.; Paumard, T.; Pedrosa, P.; Pérez-Torres, M.; Perrin, G.; Perucho,
M.; Porquet, D.; Prandoni, I.; Ransom, S.; Reimers, D.; Rejkuba, M.;
Rezzolla, L.; Richards, A.; Ros, E.; Roy, A.; Rushton, A.; Savolainen,
T.; Schulz, R.; Silva, M.; Sivakoff, G.; Soria-Ruiz, R.; Soria, R.;
Spaans, M.; Spencer, R.; Stappers, B.; Surcis, G.; Tarchi, A.; Temmer,
M.; Thompson, M.; Torrelles, J.; Truestedt, J.; Tudose, V.; Venturi,
T.; Verbiest, J.; Vieira, J.; Vielzeuf, P.; Vincent, F.; Wex, N.;
Wiik, K.; Wiklind, T.; Wilms, J.; Zackrisson, E.; Zechlin, H.
2014arXiv1406.4650T Altcode:
Very long baseline interferometry at millimetre/submillimetre
wavelengths (mmVLBI) offers the highest achievable spatial
resolution at any wavelength in astronomy. The anticipated inclusion
of ALMA as a phased array into a global VLBI network will bring
unprecedented sensitivity and a transformational leap in capabilities
for mmVLBI. Building on years of pioneering efforts in the US and
Europe the ongoing ALMA Phasing Project (APP), a US-led international
collaboration with MPIfR-led European contributions, is expected to
deliver a beamformer and VLBI capability to ALMA by the end of 2014
(APP: Fish et al. 2013, arXiv:1309.3519). This report focuses on
the future use of mmVLBI by the international users community from
a European viewpoint. Firstly, it highlights the intense science
interest in Europe in future mmVLBI observations as compiled from
the responses to a general call to the European community for future
research projects. A wide range of research is presented that includes,
amongst others: - Imaging the event horizon of the black hole at the
centre of the Galaxy - Testing the theory of General Relativity an/or
searching for alternative theories - Studying the origin of AGN jets
and jet formation - Cosmological evolution of galaxies and BHs, AGN
feedback - Masers in the Milky Way (in stars and star-forming regions) -
Extragalactic emission lines and astro-chemistry - Redshifted absorption
lines in distant galaxies and study of the ISM and circumnuclear gas -
Pulsars, neutron stars, X-ray binaries - Testing cosmology - Testing
fundamental physical constants
---------------------------------------------------------
Title: On the shape of the mass-function of dense clumps in the Hi-GAL
fields . II. Using Bayesian inference to study the clump mass function
Authors: Olmi, L.; Anglés-Alcázar, D.; Elia, D.; Molinari, S.;
Pestalozzi, M.; Pezzuto, S.; Schisano, E.; Testi, L.; Thompson, M.
2014A&A...564A..87O Altcode: 2013arXiv1311.2736O
Context. Stars form in dense, dusty clumps of molecular clouds, but
little is known about their origin, their evolution, and their detailed
physical properties. In particular, the relationship between the mass
distribution of these clumps (also known as the "clump mass function",
or CMF) and the stellar initial mass function (IMF) is still poorly
understood. <BR /> Aims: To better understand how the CMF evolve toward
the IMF and to discern the "true" shape of the CMF, large samples of
bona-fide pre- and proto-stellar clumps are required. Two such datasets
obtained from the Herschel infrared GALactic Plane Survey (Hi-GAL)
have been described in Paper I. Robust statistical methods are needed
to infer the parameters describing the models used to fit the CMF and
to compare the competing models themselves. <BR /> Methods: In this
paper, we apply Bayesian inference to the analysis of the CMF of the
two regions discussed in Paper I. First, we determine the posterior
probability distribution for each of the fitted parameters. Then,
we carry out a quantitative comparison of the models used to fit
the CMF. <BR /> Results: We have compared several methods of sampling
posterior distributions and calculating global likelihoods, and we have
also analyzed the impact of the choice of priors and the influence
of various constraints on the statistical conclusions for the values
of model parameters. We find that both parameter estimation and model
comparison depend on the choice of parameter priors. <BR /> Conclusions:
Our results confirm our earlier conclusion that the CMFs of the two
Hi-GAL regions studied here have very similar shapes but different mass
scales. Furthermore, the lognormal model appears to better describe
the CMF measured in the two Hi-GAL regions studied here. However, this
preliminary conclusion is dependent on the choice of parameter priors.
---------------------------------------------------------
Title: Study of KIC 8561221 observed by Kepler: an early red giant
showing depressed dipolar modes
Authors: García, R. A.; Pérez Hernández, F.; Benomar, O.; Silva
Aguirre, V.; Ballot, J.; Davies, G. R.; Doğan, G.; Stello, D.;
Christensen-Dalsgaard, J.; Houdek, G.; Lignières, F.; Mathur, S.;
Takata, M.; Ceillier, T.; Chaplin, W. J.; Mathis, S.; Mosser, B.;
Ouazzani, R. M.; Pinsonneault, M. H.; Reese, D. R.; Régulo, C.;
Salabert, D.; Thompson, M. J.; van Saders, J. L.; Neiner, C.; De
Ridder, J.
2014A&A...563A..84G Altcode: 2013arXiv1311.6990G
Context. The continuous high-precision photometric observations
provided by the CoRoT and Kepler space missions have allowed us to
understand the structure and dynamics of red giants better using
asteroseismic techniques. A small fraction of these stars show
dipole modes with unexpectedly low amplitudes. The reduction in
amplitude is more pronounced for stars with a higher frequency of
maximum power, ν<SUB>max</SUB>. <BR /> Aims: In this work we want to
characterise KIC 8561221 in order to confirm that it is currently the
least evolved star among this peculiar subset and to discuss several
hypotheses that could help explain the reduction of the dipole mode
amplitudes. <BR /> Methods: We used Kepler short- and long-cadence
data combined with spectroscopic observations to infer the stellar
structure and dynamics of KIC 8561221. We then discussed different
scenarios that could contribute to reducing the dipole amplitudes,
such as a fast-rotating interior or the effect of a magnetic field
on the properties of the modes. We also performed a detailed study
of the inertia and damping of the modes. <BR /> Results: We have
been able to characterise 36 oscillations modes, in particular, a
few dipole modes above ν<SUB>max</SUB> that exhibit nearly normal
amplitudes. The frequencies of all the measured modes were used
to determine the overall properties and the internal structure of
the star. We have inferred a surface rotation period of ~91 days
and uncovered a variation in the surface magnetic activity during
the last 4 years. The analysis of the convective background did not
reveal any difference compared to "normal" red giants. As expected,
the internal regions of the star probed by the ℓ = 2 and 3 modes
spin 4 to 8 times faster than the surface. <BR /> Conclusions: With
our grid of standard models we are able to properly fit the observed
frequencies. Our model calculation of mode inertia and damping give
no explanation for the depressed dipole modes. A fast-rotating core
is also ruled out as a possible explanation. Finally, we do not have
any observational evidence of a strong deep magnetic field inside the
star. <P />Table 3 and Appendix A are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201322823/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: First Images from the Cript Muon Tomography System
Authors: Armitage, J.; Botte, J.; Boudjemline, K.; Erlandson, A.;
Robichaud, A.; Bueno, J.; Bryman, D.; Gazit, R.; Hydomako, R.; Liu,
Z.; Anghel, V.; Golovko, V. V.; Jewett, C.; Jonkmans, G.; Thompson,
M.; Charles, E.; Gallant, G.; Drouin, P. -L.; Waller, D.; Stocki,
T. J.; Cousins, T.; Noel, S.
2014IJMPS..2760129A Altcode:
The CRIPT Cosmic Ray Imaging and Passive Tomography system began
data taking in September 2012. CRIPT is a “proof of principle”
muon tomography system originally proposed to inspect cargo in
shipping containers and to determine the presence of special nuclear
materials. CRIPT uses 4 layers of 2 m x 2 m scintillation counter
trackers, each layer measuring two coordinates. Two layers are used
to track the incoming muon and two for the outgoing muon allowing
the trajectories of the muon to be determined. The target volume
is divided into voxels, and a Point of Closest Approach algorithm
is used to determine the number of scattering events in each voxel,
producing a 3D image. The system has been tested with various targets
of depleted uranium, lead bricks, and tungsten rods. Data on the
positional resolution has been taken and the intrinsic resolution
is unfolded with the help of a simulation using GEANT4. The next
steps include incorporation of data from the spectrometer section,
which will assist in determining the muon's momentum and improve the
determination of the density of the target.
---------------------------------------------------------
Title: Oscillations and Surface Rotation of Red Giant Stars
Authors: Hedges, C.; Mathur, S.; Thompson, M. J.; MacGregor, K. B.
2013ASPC..479..197H Altcode: 2013arXiv1308.0644H
More than 15000 red giants observed by Kepler for a duration of almost
one year became public at the beginning of this year. We analysed a
subsample of 416 stars to determine the global properties of acoustic
modes (mean large separation and frequency of maximum power). Using
the effective temperature from the Kepler Input Catalog, we derived
a first estimate of the masses and radii of these stars. Finally, we
applied wavelets to look for a signature of surface rotation, which
relies on the presence of spots or other surface features crossing
the stellar visible disk.
---------------------------------------------------------
Title: The Torsional Oscillation and the Timing of the Solar Cycle:
Is it Maximum Yet?
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
Larson, T. P.; Schou, J.; Thompson, M. J.
2013ASPC..478..303H Altcode:
After the late start to Cycle 24 there are some indications that
activity may have peaked as early as late 2011 and that the polar-field
reversal has already occurred in the North. We use helioseismic
measurements of the migrating zonal flow pattern known as the torsional
oscillation to estimate the length of the solar cycle, and find that
it has held steady at about 12.3 years since late 2009, which would
point to solar maximum in 2013 as expected.
---------------------------------------------------------
Title: The High-latitude Branch of the Solar Torsional Oscillation
in the Rising Phase of Cycle 24
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
Larson, T. P.; Rempel, M.; Schou, J.; Thompson, M. J.
2013ApJ...767L..20H Altcode:
We use global heliseismic data from the Global Oscillation Network
Group, the Michelson Doppler Imager on board the Solar and Heliospheric
Observatory, and the Helioseismic and Magnetic Imager on board the Solar
Dynamics Observatory, to examine the behavior, during the rising phase
of Solar Cycle 24, of the migrating zonal flow pattern known as the
torsional oscillation. Although the high-latitude part of the pattern
appears to be absent in the new cycle when the flows are derived by
subtracting a mean across a full solar cycle, it can be seen if we
subtract the mean over a shorter period in the rising phase of each
cycle, and these two mean rotation profiles differ significantly
at high latitudes. This indicates that the underlying high-latitude
rotation has changed; we speculate that this is in response to weaker
polar fields, as suggested by a recent model.
---------------------------------------------------------
Title: A New Multi-Wavelength Synoptic Network for Solar Physics
and Space Weather
Authors: Hill, Frank; Roth, Markus; Thompson, Michael
2013EGUGA..1511892H Altcode:
Continuous solar observations are important for many research topics
in solar physics, such as magnetic field evolution, flare and CME
characteristics, and p-mode oscillation measurements. In addition,
space weather operations require constant streams of solar data as
input. The deployment of a number of identical instruments around
the world in a network has proven to be a very effective strategy for
obtaining nearly continuous solar observations. The financial costs of
a network are 1-2 orders of magnitude lower than space-based platforms;
network instrumentation can be easily accessed for maintenance and
upgrades; and telemetry bandwidth is readily available. Currently,
there are two solar observing networks with consistent instruments:
BiSON and GONG, both designed primarily for helioseismology. In
addition, GONG has been augmented with continual magnetic field
measurements and H-alpha imagery, with both being used for space
weather operational purposes. However, GONG is now 18 years old and
getting increasingly more challenging to maintain. There are also at
least three scientific motivations for a multi-wavelength network:
Recent advances in helioseismology have demonstrated the need for
multi-wavelength observations to allow more accurate interpretation
of the structure and dynamics below sunspots. Vector magnetometry
would greatly benefit from multi-wavelength observations to provide
height information and resolve the azimuthal ambiguity. Finally,
space weather operations always need a consistent reliable source of
continual solar data. This presentation will outline the scientific
need for a multi-wavelength network, and discuss some concepts for
the design of the instrumentation. A workshop on the topic will be
held in Boulder this April.
---------------------------------------------------------
Title: On the shape of the mass-function of dense clumps in the
Hi-GAL fields . I. Spectral energy distribution determination and
global properties of the mass-functions
Authors: Olmi, L.; Anglés-Alcázar, D.; Elia, D.; Molinari, S.;
Montier, L.; Pestalozzi, M.; Pezzuto, S.; Polychroni, D.; Ristorcelli,
I.; Rodon, J.; Schisano, E.; Smith, M. D.; Testi, L.; Thompson, M.
2013A&A...551A.111O Altcode: 2012arXiv1209.4465O
Context. Stars form in dense, dusty clumps of molecular clouds, but
little is known about their origin and evolution. In particular, the
relationship between the mass distribution of these clumps (also known
as the clump mass function or CMF) and the stellar initial mass function
(IMF), is still poorly understood. <BR /> Aims: To discern the "true"
shape of the CMF and to better understand how the CMF may evolve toward
the IMF, large samples of bona-fide pre- and proto-stellar clumps are
required. The sensitive observations of the Herschel Space Observatory
(HSO) are now allowing us to look at large clump populations in various
clouds with different physical conditions. <BR /> Methods: We analyze
two fields in the Galactic plane mapped by HSO during its science
demonstration phase (SDP), as part of the more complete and unbiased
Herschel infrared GALactic Plane Survey (Hi-GAL). These fields underwent
a source-extraction and flux-estimation pipeline, which allowed us to
obtain a sample with thousands of clumps. Starless and proto-stellar
clumps were separated using both color and positional criteria to find
those coincident with MIPS 24 μm sources. We describe the probability
density functions of the power-law and lognormal models that were used
to fit the CMFs. For the lognormal model we applied several statistical
techniques to the data and compared their results. <BR /> Results: The
CMFs of the two SDP fields show very similar shapes, but very different
mass scales. This similarity is confirmed by the values of the best-fit
parameters of either the power-law or lognormal model. The power-law
model leads to almost identical CMF slopes, whereas the lognormal
model shows that the CMFs have similar widths. <BR /> Conclusions:
The similar CMF shape but different mass scale represents an evidence
that the overall process of star formation in the two regions is very
different. When comparing with the IMF, we find that the width of the
IMF is narrower than the measured widths of the CMF in the two SDP
fields. This may suggest that an additional mass selection occurs in
later stages of gravitational collapse.
---------------------------------------------------------
Title: Minor Planet Observations [J13 La Palma-Liverpool Telescope]
Authors: Foster, P.; Ashcroft, H.; Robinson, D.; Ellender, N.; Hill,
S.; Browne, J.; Thompson, M.; Thomas, H.; Mill, C.; Edwards, J.;
Martin, S.; Thorpe, C.; Llewellyn-Davies, S.; Hewitt, J.; Kettle,
P.; Woodruff, K.; Edwar, J.; Emmett, J.; Culshaw, B.
2013MPC..82706...1B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Coral Sea Rehearsal for the Eclipse Megamovie
Authors: Hudson, H. S.; Davey, A. R.; Ireland, J.; Jones, L.; Mcintosh,
S. W.; Paglierani, R.; Pasachoff, J. M.; Peticolas, L. M.; Russell,
R. M.; Suarez Sola, F. I.; Sutherland, L.; Thompson, M. J.
2012AGUFMSH11C..06H Altcode:
The "Eclipse on the Coral Sea" - 13/14 November 2012 (GMT/Australia)
- will have happened already. Our intention is to have used this
opportunity as a trial run for the eclipse in 2017, which features
1.5 hours of totality across the whole width of the continental
US. Conceived first and foremost as an education and public outreach
activity, the plan is to engage the public in solar science and
technology by providing a way for them to include images they have taken
of the solar eclipse, into a movie representation of coronal evolution
in time. This project will assimilate as much eclipse photography as
possible from the public. The resulting movie(s) will cover all ranges
of expertise, and at the basic smartphone or hand-held digital camera
level, we expect to have obtained a huge number of images in the case
of good weather conditions. The capability of modern digital technology
to handle such a data flow is new. The basic purpose of this and the
2017 Megamovie observations is to explore this capability and its
ability to engage people from many different communities in the solar
science, astronomy, mathematics, and technology. The movie in 2017,
especially, may also have important science impact because of the
uniqueness of the corona as seen under eclipse conditions. In this
presentation we will describe our smartphone application development
(see the "Transit of Venus" app for a role model here). We will also
summarize data acquisition via both the app and more traditional web
interfaces. Although for the Coral Sea eclipse event we don't expect to
have a movie product by the time of the AGU, for the 2017 event we do
intend to assemble the heterogenous data into beautiful movies within a
short space of time after the eclipse. These movies may have relatively
low resolution but would extend to the base of the corona. We encourage
participation in the 2012 observations, noting that no total eclipse,
prior to 2017, will occur in a region with good infrastructure for
extended observations. The National Center for Atmospheric Research is
sponsored by the National Science Foundation. The Megamovie project
is supported by NSF grant AGS-1247226, and JMP's eclipse work about
the eclipses of 2012 is supported by NSF grant AGS-1047726.
---------------------------------------------------------
Title: Fundamental Properties of Stars Using Asteroseismology from
Kepler and CoRoT and Interferometry from the CHARA Array
Authors: Huber, D.; Ireland, M. J.; Bedding, T. R.; Brandão, I. M.;
Piau, L.; Maestro, V.; White, T. R.; Bruntt, H.; Casagrande, L.;
Molenda-Żakowicz, J.; Silva Aguirre, V.; Sousa, S. G.; Barclay,
T.; Burke, C. J.; Chaplin, W. J.; Christensen-Dalsgaard, J.; Cunha,
M. S.; De Ridder, J.; Farrington, C. D.; Frasca, A.; García, R. A.;
Gilliland, R. L.; Goldfinger, P. J.; Hekker, S.; Kawaler, S. D.;
Kjeldsen, H.; McAlister, H. A.; Metcalfe, T. S.; Miglio, A.; Monteiro,
M. J. P. F. G.; Pinsonneault, M. H.; Schaefer, G. H.; Stello, D.;
Stumpe, M. C.; Sturmann, J.; Sturmann, L.; ten Brummelaar, T. A.;
Thompson, M. J.; Turner, N.; Uytterhoeven, K.
2012ApJ...760...32H Altcode: 2012arXiv1210.0012H
We present results of a long-baseline interferometry campaign using
the PAVO beam combiner at the CHARA Array to measure the angular
sizes of five main-sequence stars, one subgiant and four red
giant stars for which solar-like oscillations have been detected
by either Kepler or CoRoT. By combining interferometric angular
diameters, Hipparcos parallaxes, asteroseismic densities, bolometric
fluxes, and high-resolution spectroscopy, we derive a full set of
near-model-independent fundamental properties for the sample. We
first use these properties to test asteroseismic scaling relations
for the frequency of maximum power (ν<SUB>max</SUB>) and the large
frequency separation (Δν). We find excellent agreement within the
observational uncertainties, and empirically show that simple estimates
of asteroseismic radii for main-sequence stars are accurate to <~
4%. We furthermore find good agreement of our measured effective
temperatures with spectroscopic and photometric estimates with mean
deviations for stars between T <SUB>eff</SUB> = 4600-6200 K of -22 ±
32 K (with a scatter of 97 K) and -58 ± 31 K (with a scatter of 93 K),
respectively. Finally, we present a first comparison with evolutionary
models, and find differences between observed and theoretical properties
for the metal-rich main-sequence star HD 173701. We conclude that
the constraints presented in this study will have strong potential
for testing stellar model physics, in particular when combined with
detailed modeling of individual oscillation frequencies.
---------------------------------------------------------
Title: Measurements of CO Redshifts with Z-Spec for Lensed
Submillimeter Galaxies Discovered in the H-ATLAS Survey
Authors: Lupu, R. E.; Scott, K. S.; Aguirre, J. E.; Aretxaga, I.; Auld,
R.; Barton, E.; Beelen, A.; Bertoldi, F.; Bock, J. J.; Bonfield, D.;
Bradford, C. M.; Buttiglione, S.; Cava, A.; Clements, D. L.; Cooke,
J.; Cooray, A.; Dannerbauer, H.; Dariush, A.; De Zotti, G.; Dunne,
L.; Dye, S.; Eales, S.; Frayer, D.; Fritz, J.; Glenn, J.; Hughes,
D. H.; Ibar, E.; Ivison, R. J.; Jarvis, M. J.; Kamenetzky, J.; Kim,
S.; Lagache, G.; Leeuw, L.; Maddox, S.; Maloney, P. R.; Matsuhara,
H.; Murphy, E. J.; Naylor, B. J.; Negrello, M.; Nguyen, H.; Omont,
A.; Pascale, E.; Pohlen, M.; Rigby, E.; Rodighiero, G.; Serjeant,
S.; Smith, D.; Temi, P.; Thompson, M.; Valtchanov, I.; Verma, A.;
Vieira, J. D.; Zmuidzinas, J.
2012ApJ...757..135L Altcode: 2010arXiv1009.5983L
We present new observations from Z-Spec, a broadband 185-305 GHz
spectrometer, of five submillimeter bright lensed sources selected
from the Herschel-Astrophysical Terahertz Large Area Survey science
demonstration phase catalog. We construct a redshift-finding algorithm
using combinations of the signal to noise of all the lines falling
in the Z-Spec bandpass to determine redshifts with high confidence,
even in cases where the signal to noise in individual lines is low. We
measure the dust continuum in all sources and secure CO redshifts for
four out of five (z ~ 1.5-3). In one source, SDP.17, we tentatively
identify two independent redshifts and a water line, confirmed at z =
2.308. Our sources have properties characteristic of dusty starburst
galaxies, with magnification-corrected star formation rates of 10<SUP>2
- 3</SUP> M <SUB>⊙</SUB> yr<SUP>-1</SUP>. Lower limits for the dust
masses (~ a few 10<SUP>8</SUP> M <SUB>⊙</SUB>) and spatial extents
(~1 kpc equivalent radius) are derived from the continuum spectral
energy distributions, corresponding to dust temperatures between 54
and 69 K. In the local thermodynamic equilibrium (LTE) approximation,
we derive relatively low CO excitation temperatures (lsim 100 K)
and optical depths (τ <~ 1). Performing a non-LTE excitation
analysis using RADEX, we find that the CO lines measured by Z-Spec
(from J = 4 → 3 to 10 → 9, depending on the galaxy) localize the
best solutions to either a high-temperature/low-density region or a
low/temperature/high-density region near the LTE solution, with the
optical depth varying accordingly. Observations of additional CO lines,
CO(1-0) in particular, are needed to constrain the non-LTE models.
---------------------------------------------------------
Title: Fast Rotating Solar-like Stars Using Asteroseismic Datasets
Authors: García, R. A.; Ceillier, T.; Campante, T. L.; Davies, G. R.;
Mathur, S.; Suárez, J. C.; Ballot, J.; Benomar, O.; Bonanno, A.;
Brun, A. S.; Chaplin, W. J.; Christensen-Dalsgaard, J.; Deheuvels,
S.; Elsworth, Y.; Handberg, R.; Hekker, S.; Jiménez, A.; Karoff, C.;
Kjeldsen, H.; Mathis, S.; Mosser, B.; Pallé, P. L.; Pinsonneault, M.;
Régulo, C.; Salabert, D.; Silva Aguirre, V.; Stello, D.; Thompson,
M. J.; Verner, G.; PE11 Team of Kepler WG#1
2012ASPC..462..133G Altcode: 2011arXiv1109.6488G
The NASA Kepler mission is providing an unprecedented set of
asteroseismic data. In particular, short-cadence light-curves (∼ 60
s samplings), allow us to study solar-like stars covering a wide range
of masses, spectral types and evolutionary stages. Oscillations have
been observed in around 600 out of 2000 stars observed for one month
during the survey phase of the Kepler mission. The measured light
curves can present features related to the surface magnetic activity
(starspots) and, thus we are able to obtain a good estimate of the
surface (differential) rotation. In this work we establish the basis
of such research and we show a potential method to find stars with
fast surface rotation.
---------------------------------------------------------
Title: Seismic Analysis of Four Solar-like Stars Observed during
More Than Eight Months by Kepler
Authors: Mathur, S.; Campante, T. L.; Handberg, R.; García, R. A.;
Appourchaux, T.; Bedding, T. R.; Mosser, B.; Chaplin, W. J.; Ballot,
J.; Benomar, O.; Bonanno, A.; Corsaro, E.; Gaulme, P.; Hekker,
S.; Régulo, C.; Salabert, D.; Verner, G.; White, T. R.; Brandão,
I. M.; Creevey, O. L.; Dogan, G.; Bazot, M.; Cunha, M. S.; Elsworth,
Y.; Huber, D.; Hale, S. J.; Houdek, G.; Karoff, C.; Lundkvist, M.;
Metcalfe, T. S.; Molenda-Zakowicz, J.; Monteiro, M. J. P. F. G.;
Thompson, M. J.; Stello, D.; Christensen-Dalsgaard, J.; Gilliland,
R. L.; Kawaler, S. D.; Kjeldsen, H.; Clarke, B. D.; Girouard, F. R.;
Hall, J. R.; Quintana, E. V.; Sanderfer, D. T.; Seader, S. E.
2012ASPC..462..180M Altcode: 2011arXiv1110.0135M
Having started science operations in May 2009, the Kepler photometer
has been able to provide exquisite data for solar-like stars. Five
out of the 42 stars observed continuously during the survey phase
show evidence of oscillations, even though they are rather faint
(magnitudes from 10.5 to 12). In this paper, we present an overview
of the results of the seismic analysis of 4 of these stars observed
during more than eight months.
---------------------------------------------------------
Title: Solar and stellar activity: diagnostics and indices
Authors: Judge, Philip G.; Thompson, Michael J.
2012IAUS..286...15J Altcode: 2012arXiv1201.4625J
We summarize the fifty-year concerted effort to place the “activity”
of the Sun in the context of the stars. As a working definition of solar
activity in the context of stars, we adopt those globally-observable
variations on time scales below thermal time scales, of ~10<SUP>5</SUP>
yr for the convection zone. So defined, activity is dominated by
magnetic-field evolution, including the 22-year Hale cycle, the typical
time it takes for the quasi-periodic reversal in which the global
magnetic-field takes place. This is accompanied by sunspot variations
with 11 year periods, known since the time of Schwabe, as well as faster
variations due to rotation of active regions and flaring. “Diagnostics
and indices” are terms given to the indirect signatures of varying
magnetic-fields, including the photometric (broad-band) variations
associated with the sunspot cycle, and variations of the accompanying
heated plasma in higher layers of stellar atmospheres seen at special
optical wavelengths, and UV and X-ray wavelengths. Our attention is
also focussed on the theme of the Symposium by examining evidence for
deep and extended minima of stars, and placing the 70-year long solar
Maunder Minimum into a stellar context.
---------------------------------------------------------
Title: Latest Results on the Torsional Oscillation and Solar Cycle 25
Authors: Hill, Frank; Howe, R.; Schou, J.; Thompson, M.; Larson, T.;
Komm, R.
2012AAS...22012302H Altcode:
The Torsional Oscillation in the Sun is a zonal (East-West) flow
that is slightly faster than the background differential rotation
profile. The location of this flow slowly migrates in latitude over
a period of several years. There are two branches of the flow: an
equatorward branch that underlies the active regions, and a poleward
branch. The timing of the equatorward migration is correlated with the
timing of the solar cycle such that the activity for a cycle appears
when the center of the flow reaches latitude 25 degrees. In addition,
the poleward branch appears about 12 years prior to the activity for
a cycle. Thus we should have observed the onset of Cycle 25 in 2008,
but did not. This poster will update the observations to 2012, and
present a new analysis that shows that the Cycle 25 flow appeared
in 2010, but was hidden by a change in the background differential
rotation profile. These results suggest that the next minimum will be
two years longer than average, and that Cycle 25 will begin in 2022.
---------------------------------------------------------
Title: A Uniform Asteroseismic Analysis of 22 Solar-type Stars
Observed by Kepler
Authors: Mathur, S.; Metcalfe, T. S.; Woitaszek, M.; Bruntt, H.;
Verner, G. A.; Christensen-Dalsgaard, J.; Creevey, O. L.; Doǧan, G.;
Basu, S.; Karoff, C.; Stello, D.; Appourchaux, T.; Campante, T. L.;
Chaplin, W. J.; García, R. A.; Bedding, T. R.; Benomar, O.; Bonanno,
A.; Deheuvels, S.; Elsworth, Y.; Gaulme, P.; Guzik, J. A.; Handberg,
R.; Hekker, S.; Herzberg, W.; Monteiro, M. J. P. F. G.; Piau, L.;
Quirion, P. -O.; Régulo, C.; Roth, M.; Salabert, D.; Serenelli, A.;
Thompson, M. J.; Trampedach, R.; White, T. R.; Ballot, J.; Brandão,
I. M.; Molenda-Żakowicz, J.; Kjeldsen, H.; Twicken, J. D.; Uddin,
K.; Wohler, B.
2012ApJ...749..152M Altcode: 2012arXiv1202.2844M
Asteroseismology with the Kepler space telescope is providing not
only an improved characterization of exoplanets and their host stars,
but also a new window on stellar structure and evolution for the
large sample of solar-type stars in the field. We perform a uniform
analysis of 22 of the brightest asteroseismic targets with the highest
signal-to-noise ratio observed for 1 month each during the first year
of the mission, and we quantify the precision and relative accuracy
of asteroseismic determinations of the stellar radius, mass, and age
that are possible using various methods. We present the properties
of each star in the sample derived from an automated analysis of the
individual oscillation frequencies and other observational constraints
using the Asteroseismic Modeling Portal (AMP), and we compare them to
the results of model-grid-based methods that fit the global oscillation
properties. We find that fitting the individual frequencies typically
yields asteroseismic radii and masses to ~1% precision, and ages to
~2.5% precision (respectively, 2, 5, and 8 times better than fitting
the global oscillation properties). The absolute level of agreement
between the results from different approaches is also encouraging,
with model-grid-based methods yielding slightly smaller estimates of
the radius and mass and slightly older values for the stellar age
relative to AMP, which computes a large number of dedicated models
for each star. The sample of targets for which this type of analysis
is possible will grow as longer data sets are obtained during the
remainder of the mission.
---------------------------------------------------------
Title: Estimating stellar mean density through seismic inversions
Authors: Reese, D. R.; Marques, J. P.; Goupil, M. J.; Thompson, M. J.;
Deheuvels, S.
2012A&A...539A..63R Altcode: 2012arXiv1201.1844R
Context. Determining the mass of stars is crucial both for improving
stellar evolution theory and for characterising exoplanetary
systems. Asteroseismology offers a promising way for estimating the
stellar mean density. When combined with accurate radii determinations,
such as are expected from Gaia, this yields accurate stellar masses. The
main difficulty is finding the best way to extract the mean density
of a star from a set of observed frequencies. <BR /> Aims: We seek to
establish a new method for estimating the stellar mean density, which
combines the simplicity of a scaling law while providing the accuracy
of an inversion technique. <BR /> Methods: We provide a framework in
which to construct and evaluate kernel-based linear inversions that
directly yield the mean density of a star. We then describe three
different inversion techniques (SOLA and two scaling laws) and apply
them to the <ASTROBJ>Sun</ASTROBJ>, several test cases and three stars,
<ASTROBJ>α Cen B</ASTROBJ>, <ASTROBJ>HD 49933</ASTROBJ> and <ASTROBJ>HD
49385</ASTROBJ>, two of which are observed by CoRoT. <BR /> Results:
The SOLA (subtractive optimally localised averages) approach and the
scaling law based on the surface correcting technique described by
Kjeldsen et al. (2008, ApJ, 683, L175) yield comparable results that
can reach an accuracy of 0.5% and are better than scaling the large
frequency separation. The reason for this is that the averaging kernels
from the two first methods are comparable in quality and are better
than what is obtained with the large frequency separation. It is also
shown that scaling the large frequency separation is more sensitive
to near-surface effects, but is much less affected by an incorrect
mode identification. As a result, one can identify pulsation modes by
looking for an ℓ and n assignment which provides the best agreement
between the results from the large frequency separation and those from
one of the two other methods. Non-linear effects are also discussed,
as is the effects of mixed modes. In particular, we show that mixed
modes bring little improvement to the mean density estimates because
of their poorly adapted kernels.
---------------------------------------------------------
Title: Disc frequencies for brown dwarfs in the Upper Scorpius OB
association: implications for brown dwarf formation theories
Authors: Riaz, B.; Lodieu, N.; Goodwin, S.; Stamatellos, D.;
Thompson, M.
2012MNRAS.420.2497R Altcode: 2011arXiv1111.3929R
We have investigated the brown dwarf (BD) and stellar disc fractions
in the Upper Scorpius (USco) OB association and compared them with
several other young regions. We have compiled the most complete
sample of all spectroscopically confirmed BDs in USco and have made
use of the Wide-field Infrared Survey Explorer (WISE) catalogue to
identify the disc candidates. We report on the discovery of 12 new
BD discs in USco, with spectral types between M6 and M8.5. The WISE
colours for the new discs are similar to the primordial (transition)
discs earlier detected in USco. Combining with previous surveys,
we find the lowest inner disc fractions (∼20-25 per cent) for a
wide range in stellar masses (∼0.01-4.0 M<SUB>⊙</SUB>) in the
USco association. The low disc fractions for high-mass stars in USco
(and the other clusters) are consistent with an evolutionary decline
in inner disc frequency with age. However, BD disc fractions are
higher than those for the stars in 1-3 Myr clusters, but very low in
the ∼5 Myr old USco. Also, primordial BD discs are still visible
in the ∼10 Myr old TW Hydrae association, whereas the higher mass
stars have all transitioned to the debris stage by this age. The disc
frequencies for BDs and low-mass stars do not show any dependence on
the stellar density or the BD/star number ratio in a cluster. We also
find no convincing evidence that any of the well-known disc dispersal
mechanisms for stars are active in BD discs. We suggest that the large
differences in the observed BD disc fractions between regions may well
be due to different BD formation mechanisms and therefore different
initial disc fractions/properties. <P />We also present a WISE spectral
energy distribution classification scheme, based on the K<SUB>s</SUB>
and WISE bands of 3.4-12 μm. We have determined certain thresholds in
the WISE spectral slope versus spectral type diagrams to distinguish
between the red population of Class I/II systems and the Class III
sequence. We have found the WISE [3.4] - [12] colour to provide the
best distinction between the photospheric and the disc population. Our
work includes a comparison of the sensitivities of WISE and Spitzer
disc surveys. We estimate that WISE can be incomplete for discs at
spectral type later than M8 in distant clusters such as SOri. WISE
should be able to recover the M8-M9 discs in the nearby young clusters.
---------------------------------------------------------
Title: Kepler-21b: A 1.6 R <SUB>Earth</SUB> Planet Transiting the
Bright Oscillating F Subgiant Star HD 179070
Authors: Howell, Steve B.; Rowe, Jason F.; Bryson, Stephen T.; Quinn,
Samuel N.; Marcy, Geoffrey W.; Isaacson, Howard; Ciardi, David R.;
Chaplin, William J.; Metcalfe, Travis S.; Monteiro, Mario J. P. F. G.;
Appourchaux, Thierry; Basu, Sarbani; Creevey, Orlagh L.; Gilliland,
Ronald L.; Quirion, Pierre-Olivier; Stello, Denis; Kjeldsen, Hans;
Christensen-Dalsgaard, Jörgen; Elsworth, Yvonne; García, Rafael
A.; Houdek, Günter; Karoff, Christoffer; Molenda-Żakowicz, Joanna;
Thompson, Michael J.; Verner, Graham A.; Torres, Guillermo; Fressin,
Francois; Crepp, Justin R.; Adams, Elisabeth; Dupree, Andrea; Sasselov,
Dimitar D.; Dressing, Courtney D.; Borucki, William J.; Koch, David
G.; Lissauer, Jack J.; Latham, David W.; Buchhave, Lars A.; Gautier,
Thomas N., III; Everett, Mark; Horch, Elliott; Batalha, Natalie M.;
Dunham, Edward W.; Szkody, Paula; Silva, David R.; Mighell, Ken;
Holberg, Jay; Ballot, Jerôme; Bedding, Timothy R.; Bruntt, Hans;
Campante, Tiago L.; Handberg, Rasmus; Hekker, Saskia; Huber, Daniel;
Mathur, Savita; Mosser, Benoit; Régulo, Clara; White, Timothy R.;
Christiansen, Jessie L.; Middour, Christopher K.; Haas, Michael R.;
Hall, Jennifer R.; Jenkins, Jon M.; McCaulif, Sean; Fanelli, Michael
N.; Kulesa, Craig; McCarthy, Don; Henze, Christopher E.
2012ApJ...746..123H Altcode: 2011arXiv1112.2165H
We present Kepler observations of the bright (V = 8.3), oscillating
star HD 179070. The observations show transit-like events which
reveal that the star is orbited every 2.8 days by a small, 1.6 R
<SUB>Earth</SUB> object. Seismic studies of HD 179070 using short
cadence Kepler observations show that HD 179070 has a frequency-power
spectrum consistent with solar-like oscillations that are acoustic
p-modes. Asteroseismic analysis provides robust values for the mass
and radius of HD 179070, 1.34 ± 0.06 M <SUB>⊙</SUB> and 1.86 ±
0.04 R <SUB>⊙</SUB>, respectively, as well as yielding an age of
2.84 ± 0.34 Gyr for this F5 subgiant. Together with ground-based
follow-up observations, analysis of the Kepler light curves and
image data, and blend scenario models, we conservatively show at the
>99.7% confidence level (3σ) that the transit event is caused by
a 1.64 ± 0.04 R <SUB>Earth</SUB> exoplanet in a 2.785755 ± 0.000032
day orbit. The exoplanet is only 0.04 AU away from the star and our
spectroscopic observations provide an upper limit to its mass of ~10 M
<SUB>Earth</SUB> (2σ). HD 179070 is the brightest exoplanet host star
yet discovered by Kepler. <P />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, the Mayall
telescope at Kitt Peak National Observatory, and the WIYN Observatory
which is a joint facility of NOAO, University of Wisconsin-Madison,
Indiana University, and Yale University.
---------------------------------------------------------
Title: Solar-cycle variation of oscillation frequencies and surface
magnetic field
Authors: Tan, S.; Thompson, M. J.; Centeno, R.
2011AGUFMSH13B1933T Altcode:
We investigate the relationship between solar oscillation frequencies
and surface magnetic fields over the course of the last solar
cycle. Using MDI and GONG data, we study the variation in the even
frequency-splitting coefficients a<SUB>k</SUB> (describing solar
asphericity and effects of the magnetic field), and the variation in the
coefficients B<SUB>k</SUB> of the latitudinal Lengendre decomposition
of the surface magnetic field, during the period 1996 - 2010. We find
a strong linear correlation between the a and B coefficients, during
both the rising and declining phases of the solar cycle, consistent
with results published in 2001 (Antia et al.). We also investigated
different ways to handle the magnetic field decomposition at the poles,
and find that the linear correlation persists, though with varying
intercepts. The variation of slope with coefficient index that we find
is non-monotonic, which disagrees with the previous study by Antia et
al. (2001).
---------------------------------------------------------
Title: Asteroseismic Diagrams from a Survey of Solar-like Oscillations
with Kepler
Authors: White, Timothy R.; Bedding, Timothy R.; Stello, Dennis;
Appourchaux, Thierry; Ballot, Jérôme; Benomar, Othman; Bonanno,
Alfio; Broomhall, Anne-Marie; Campante, Tiago L.; Chaplin, William
J.; Christensen-Dalsgaard, Jørgen; Corsaro, Enrico; Doǧan, Gülnur;
Elsworth, Yvonne P.; Fletcher, Stephen T.; García, Rafael A.; Gaulme,
Patrick; Handberg, Rasmus; Hekker, Saskia; Huber, Daniel; Karoff,
Christoffer; Kjeldsen, Hans; Mathur, Savita; Mosser, Benoit; Monteiro,
Mario J. P. F. G.; Régulo, Clara; Salabert, David; Silva Aguirre,
Victor; Thompson, Michael J.; Verner, Graham; Morris, Robert L.;
Sanderfer, Dwight T.; Seader, Shawn E.
2011ApJ...742L...3W Altcode: 2011arXiv1110.1375W
Photometric observations made by the NASA Kepler Mission have led to a
dramatic increase in the number of main-sequence and subgiant stars with
detected solar-like oscillations. We present an ensemble asteroseismic
analysis of 76 solar-type stars. Using frequencies determined from the
Kepler time-series photometry, we have measured three asteroseismic
parameters that characterize the oscillations: the large frequency
separation (Δν), the small frequency separation between modes of
l = 0 and l = 2 (δν<SUB>02</SUB>), and the dimensionless offset
(epsilon). These measurements allow us to construct asteroseismic
diagrams, namely the so-called Christensen-Dalsgaard diagram of
δν<SUB>02</SUB> versus Δν, and the recently re-introduced epsilon
diagram. We compare the Kepler results with previously observed
solar-type stars and with theoretical models. The positions of
stars in these diagrams places constraints on their masses and
ages. Additionally, we confirm the observational relationship
between epsilon and T <SUB>eff</SUB> that allows for the unambiguous
determination of radial order and should help resolve the problem of
mode identification in F stars.
---------------------------------------------------------
Title: Constructing a One-solar-mass Evolutionary Sequence Using
Asteroseismic Data from Kepler
Authors: Silva Aguirre, V.; Chaplin, W. J.; Ballot, J.; Basu,
S.; Bedding, T. R.; Serenelli, A. M.; Verner, G. A.; Miglio, A.;
Monteiro, M. J. P. F. G.; Weiss, A.; Appourchaux, T.; Bonanno,
A.; Broomhall, A. M.; Bruntt, H.; Campante, T. L.; Casagrande, L.;
Corsaro, E.; Elsworth, Y.; García, R. A.; Gaulme, P.; Handberg,
R.; Hekker, S.; Huber, D.; Karoff, C.; Mathur, S.; Mosser, B.;
Salabert, D.; Schönrich, R.; Sousa, S. G.; Stello, D.; White, T. R.;
Christensen-Dalsgaard, J.; Gilliland, R. L.; Kawaler, S. D.; Kjeldsen,
H.; Houdek, G.; Metcalfe, T. S.; Molenda-Żakowicz, J.; Thompson,
M. J.; Caldwell, D. A.; Christiansen, J. L.; Wohler, B.
2011ApJ...740L...2S Altcode: 2011arXiv1108.2031S
Asteroseismology of solar-type stars has entered a new era of
large surveys with the success of the NASA Kepler mission, which
is providing exquisite data on oscillations of stars across the
Hertzsprung-Russell diagram. From the time-series photometry, the two
seismic parameters that can be most readily extracted are the large
frequency separation (Δν) and the frequency of maximum oscillation
power (ν<SUB>max</SUB>). After the survey phase, these quantities
are available for hundreds of solar-type stars. By scaling from solar
values, we use these two asteroseismic observables to identify for the
first time an evolutionary sequence of 1 M <SUB>sun</SUB> field stars,
without the need for further information from stellar models. Comparison
of our determinations with the few available spectroscopic results
shows an excellent level of agreement. We discuss the potential of the
method for differential analysis throughout the main-sequence evolution
and the possibility of detecting twins of very well-known stars.
---------------------------------------------------------
Title: Herschel-ATLAS: rapid evolution of dust in galaxies over the
last 5 billion years
Authors: Dunne, L.; Gomez, H. L.; da Cunha, E.; Charlot, S.; Dye,
S.; Eales, S.; Maddox, S. J.; Rowlands, K.; Smith, D. J. B.; Auld,
R.; Baes, M.; Bonfield, D. G.; Bourne, N.; Buttiglione, S.; Cava, A.;
Clements, D. L.; Coppin, K. E. K.; Cooray, A.; Dariush, A.; de Zotti,
G.; Driver, S.; Fritz, J.; Geach, J.; Hopwood, R.; Ibar, E.; Ivison,
R. J.; Jarvis, M. J.; Kelvin, L.; Pascale, E.; Pohlen, M.; Popescu, C.;
Rigby, E. E.; Robotham, A.; Rodighiero, G.; Sansom, A. E.; Serjeant,
S.; Temi, P.; Thompson, M.; Tuffs, R.; van der Werf, P.; Vlahakis, C.
2011MNRAS.417.1510D Altcode: 2010arXiv1012.5186D; 2011MNRAS.tmp.1395D
We present the first direct and unbiased measurement of the evolution
of the dust mass function of galaxies over the past 5 billion
years of cosmic history using data from the Science Demonstration
Phase of the Herschel-Astrophysical Terahertz Large Area Survey
(Herschel-ATLAS). The sample consists of galaxies selected at 250 ?m
which have reliable counterparts from the Sloan Digital Sky Survey
(SDSS) at z < 0.5, and contains 1867 sources. Dust masses are
calculated using both a single-temperature grey-body model for the
spectral energy distribution and also a model with multiple temperature
components. The dust temperature for either model shows no trend with
redshift. Splitting the sample into bins of redshift reveals a strong
evolution in the dust properties of the most massive galaxies. At z=
0.4-0.5, massive galaxies had dust masses about five times larger than
in the local Universe. At the same time, the dust-to-stellar mass ratio
was about three to four times larger, and the optical depth derived
from fitting the UV-sub-mm data with an energy balance model was also
higher. This increase in the dust content of massive galaxies at high
redshift is difficult to explain using standard dust evolution models
and requires a rapid gas consumption time-scale together with either a
more top-heavy initial mass function (IMF), efficient mantle growth,
less dust destruction or combinations of all three. This evolution
in dust mass is likely to be associated with a change in overall
interstellar medium mass, and points to an enhanced supply of fuel
for star formation at earlier cosmic epochs.
---------------------------------------------------------
Title: OT2_mthomp01_2: Confirming a sample of massive and luminous
debris disks identified in the Herschel-ATLAS
Authors: Thompson, M.
2011hers.prop.2085T Altcode:
Debris disks are the remains of planetary system formation, tracing
the existence of planetesimal-sized objects in orbit around main
sequence stars. Current and planned surveys of debris disks (including
the Herschel Key Projects DEBRIS and DUNES) are deep surveys aimed
at characterising the typical population of disks and targeted at
samples of a few hundred nearby objects. These deep narrow surveys are
relatively insensitive to the rarities in the debris disk population,
some of which may be luminous and/or massive disks that have undergone
recent disruptive collisional events. We have recently shown that the
primarily extragalactic Key Project, the Herschel-ATLAS, can be used as
a wide and shallow survey of debris disks by combining its excellent
optical coverage and statistical techniques more commonly employed to
identify galaxies. The combination of Herschel-ATLAS, DEBRIS and DUNES
thus forms a powerful nested tier of surveys that will be sensitive
to disks across the spectrum from exosolar analogues to rare disks
that cannot be inferred from local populations. In this proposal we
seek time to image 23 candidate disks that we have discovered in the
Herschel-ATLAS with PACS so that we may confirm them as true debris
disks and model their SEDs to extract mass, temperature and fractional
luminosity. We will confirm whether these disk candidates are in fact
the most luminous disks yet detected.
---------------------------------------------------------
Title: Stellar hydrodynamics caught in the act: Asteroseismology
with CoRoT and Kepler
Authors: Christensen-Dalsgaard, Jørgen; Thompson, Michael J.
2011IAUS..271...32C Altcode: 2011arXiv1104.5191C
Asteroseismic investigations, particularly based on data on stellar
oscillations from the CoRoT and Kepler space missions, are providing
unique possibilities for investigating the properties of stellar
interiors. This constitutes entirely new ways to study the effects
of dynamic phenomena on stellar structure and evolution. Important
examples are the extent of convection zones and the associated mixing
and the direct and indirect effects of stellar rotation. In addition,
the stellar oscillations themselves show very interesting dynamic
behaviour. Here we discuss examples of the results obtained from such
investigations, across the Hertzsprung-Russell diagram.
---------------------------------------------------------
Title: Minor Planet Observations [F65 Haleakala-Faulkes Telescope
North]
Authors: Fitzsimmons, A.; Roche, P.; Micheli, M.; Guido, E.; Lister,
T.; Miller, P.; Tripp, A.; Holmes, R.; Miles, R.; Buzzi, L.; Fogl,
S.; Howes, N.; Sostero, G.; Blyth, H.; Foglia, S.; Armstrong, J. D.;
Sobaje, C. S.; Boaz, R. Z.; Thompson, M.; Pfluke, A.
2011MPC..75687...1F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Probing Subsurface Flows Around Sunspots with 3-Dimensional
Ring Inversions
Authors: Featherstone, Nicholas Andrew; Hindman, Bradley W.; Thompson,
Michael J.; Toomre, Juri
2011shin.confE...7F Altcode:
We examine convective flows around sunspots as inferred through
ring-analysis helioseismology of MDI Dopplergrams. These flow
measurements were obtained using a novel 3-D inversion procedure
termed Adaptively Resolved Ring-Diagram Inversions, or ARRDI, which
uses sensitivity kernels based on the Born approximation. The ARRDI
algorithm is multi-scale in nature, folding together information from
tiles located at different positions on the solar surface and from
tiles of different sizes, thus enabling fine control of the horizontal
resolution and the probing depth. When we apply ARRDI to sunspots,
we measure outflows persisting to depths of at least 7 Mm. In many
instances, the surface outflow diminishes within the upper 3 Mm
of the convection zone. Beyond 3 Mm, such outflows strengthen and
attain peak amplitudes of 200 m/s at depths of 5-7 Mm. We discuss the
implications of such a two-component outflow for understanding the
magneto-hydrodynamic behavior and evolution of sunspots.
---------------------------------------------------------
Title: Solar-like Oscillations in KIC 11395018 and KIC 11234888 from
8 Months of Kepler Data
Authors: Mathur, S.; Handberg, R.; Campante, T. L.; García, R. A.;
Appourchaux, T.; Bedding, T. R.; Mosser, B.; Chaplin, W. J.; Ballot,
J.; Benomar, O.; Bonanno, A.; Corsaro, E.; Gaulme, P.; Hekker,
S.; Régulo, C.; Salabert, D.; Verner, G.; White, T. R.; Brandão,
I. M.; Creevey, O. L.; Doǧan, G.; Elsworth, Y.; Huber, D.; Hale,
S. J.; Houdek, G.; Karoff, C.; Metcalfe, T. S.; Molenda-Żakowicz,
J.; Monteiro, M. J. P. F. G.; Thompson, M. J.; Christensen-Dalsgaard,
J.; Gilliland, R. L.; Kawaler, S. D.; Kjeldsen, H.; Quintana, E. V.;
Sanderfer, D. T.; Seader, S. E.
2011ApJ...733...95M Altcode: 2011arXiv1103.4085M
We analyze the photometric short-cadence data obtained with the Kepler
mission during the first 8 months of observations of two solar-type
stars of spectral types G and F: KIC 11395018 and KIC 11234888,
respectively, the latter having a lower signal-to-noise ratio (S/N)
compared with the former. We estimate global parameters of the acoustic
(p) modes such as the average large and small frequency separations, the
frequency of the maximum of the p-mode envelope, and the average line
width of the acoustic modes. We were able to identify and to measure
22 p-mode frequencies for the first star and 16 for the second one
even though the S/N of these stars are rather low. We also derive some
information about the stellar rotation periods from the analyses of the
low-frequency parts of the power spectral densities. A model-independent
estimation of the mean density, mass, and radius is obtained using the
scaling laws. We emphasize the importance of continued observations
for the stars with low S/N for an improved characterization of the
oscillation modes. Our results offer a preview of what will be possible
for many stars with the long data sets obtained during the remainder
of the mission.
---------------------------------------------------------
Title: A more realistic representation of overshoot at the base of
the solar convective envelope as seen by helioseismology
Authors: Christensen-Dalsgaard, J.; Monteiro, M. J. P. F. G.; Rempel,
M.; Thompson, M. J.
2011MNRAS.414.1158C Altcode: 2011MNRAS.tmp..440C; 2011arXiv1102.0235C
The stratification near the base of the Sun's convective envelope
is governed by processes of convective overshooting and element
diffusion, and the region is widely believed to play a key role in
the solar dynamo. The stratification in that region gives rise to
a characteristic signal in the frequencies of solar p modes, which
has been used to determine the depth of the solar convection zone
and to investigate the extent of convective overshoot. Previous
helioseismic investigations have shown that the Sun's spherically
symmetric stratification in this region is smoother than that in a
standard solar model without overshooting, and have ruled out simple
models incorporating overshooting, which extend the region of adiabatic
stratification and have a more-or-less abrupt transition to subadiabatic
stratification at the edge of the overshoot region. In this paper we
consider physically motivated models which have a smooth transition
in stratification bridging the region from the lower convection zone
to the radiative interior beneath. We find that such a model is in
better agreement with the helioseismic data than a standard solar model.
---------------------------------------------------------
Title: Preparation of Kepler light curves for asteroseismic analyses
Authors: García, R. A.; Hekker, S.; Stello, D.; Gutiérrez-Soto,
J.; Handberg, R.; Huber, D.; Karoff, C.; Uytterhoeven, K.;
Appourchaux, T.; Chaplin, W. J.; Elsworth, Y.; Mathur, S.; Ballot,
J.; Christensen-Dalsgaard, J.; Gilliland, R. L.; Houdek, G.; Jenkins,
J. M.; Kjeldsen, H.; McCauliff, S.; Metcalfe, T.; Middour, C. K.;
Molenda-Zakowicz, J.; Monteiro, M. J. P. F. G.; Smith, J. C.; Thompson,
M. J.
2011MNRAS.414L...6G Altcode: 2011arXiv1103.0382G
The Kepler mission is providing photometric data of exquisite
quality for the asteroseismic study of different classes of pulsating
stars. These analyses place particular demands on the pre-processing
of the data, over a range of time-scales from minutes to months. Here,
we describe processing procedures developed by the Kepler Asteroseismic
Science Consortium to prepare light curves that are optimized for the
asteroseismic study of solar-like oscillating stars in which outliers,
jumps and drifts are corrected.
---------------------------------------------------------
Title: On the effects of rotation on acoustic stellar pulsations:
validity domains of perturbative methods and close frequency pairs
Authors: Burke, K. D.; Reese, D. R.; Thompson, M. J.
2011MNRAS.414.1119B Altcode: 2011MNRAS.tmp..475B; 2011arXiv1102.0382B
Pulsation frequencies of acoustic modes are calculated for realistic
rotating stellar models using both a perturbative and a two-dimensional
approach. A comparison between the two yields validity domains which
are similar to those previously obtained in Reese et al. for polytropic
models. One can also construct validity domains based on polynomial
fits to the frequencies from the two-dimensional approach, and these
also turn out to be similar, thus further confirming the agreement
between the perturbative and the two-dimensional approaches at low
rotation rates. Furthermore, as was previously shown in Espinosa
et al., adjacent frequencies in multiplets come close together,
thus forming pairs. This phenomenon, exclusive to two-dimensional
calculations, is shown to be an unlikely explanation of the close
frequency pairs observed in δ Scuti stars. A systematic search for
all close frequency pairs in the calculated spectrum is also carried
out. The number of close frequency pairs is shown to agree with what is
expected based on a Poisson distribution, but does not match the number
or distribution of close pairs in stars such as FG Vir. Furthermore,
a lack of close frequency pairs appears at low rotation rates, where
frequency multiplets do not overlap. δ Scuti stars currently reported
as having close frequency pairs do not fall in this interval.
---------------------------------------------------------
Title: Predicting the Detectability of Oscillations in Solar-type
Stars Observed by Kepler
Authors: Chaplin, W. J.; Kjeldsen, H.; Bedding, T. R.;
Christensen-Dalsgaard, J.; Gilliland, R. L.; Kawaler, S. D.;
Appourchaux, T.; Elsworth, Y.; García, R. A.; Houdek, G.; Karoff, C.;
Metcalfe, T. S.; Molenda-Żakowicz, J.; Monteiro, M. J. P. F. G.;
Thompson, M. J.; Verner, G. A.; Batalha, N.; Borucki, W. J.;
Brown, T. M.; Bryson, S. T.; Christiansen, J. L.; Clarke, B. D.;
Jenkins, J. M.; Klaus, T. C.; Koch, D.; An, D.; Ballot, J.; Basu,
S.; Benomar, O.; Bonanno, A.; Broomhall, A. -M.; Campante, T. L.;
Corsaro, E.; Creevey, O. L.; Esch, L.; Gai, N.; Gaulme, P.; Hale,
S. J.; Handberg, R.; Hekker, S.; Huber, D.; Mathur, S.; Mosser, B.;
New, R.; Pinsonneault, M. H.; Pricopi, D.; Quirion, P. -O.; Régulo,
C.; Roxburgh, I. W.; Salabert, D.; Stello, D.; Suran, M. D.
2011ApJ...732...54C Altcode: 2011arXiv1103.0702C
Asteroseismology of solar-type stars has an important part to play
in the exoplanet program of the NASA Kepler Mission. Precise and
accurate inferences on the stellar properties that are made possible
by the seismic data allow very tight constraints to be placed on the
exoplanetary systems. Here, we outline how to make an estimate of the
detectability of solar-like oscillations in any given Kepler target,
using rough estimates of the temperature and radius, and the Kepler
apparent magnitude.
---------------------------------------------------------
Title: Evidence for the Impact of Stellar Activity on the
Detectability of Solar-like Oscillations Observed by Kepler
Authors: Chaplin, W. J.; Bedding, T. R.; Bonanno, A.; Broomhall,
A. -M.; García, R. A.; Hekker, S.; Huber, D.; Verner, G. A.;
Basu, S.; Elsworth, Y.; Houdek, G.; Mathur, S.; Mosser, B.; New,
R.; Stevens, I. R.; Appourchaux, T.; Karoff, C.; Metcalfe, T. S.;
Molenda-Żakowicz, J.; Monteiro, M. J. P. F. G.; Thompson, M. J.;
Christensen-Dalsgaard, J.; Gilliland, R. L.; Kawaler, S. D.; Kjeldsen,
H.; Ballot, J.; Benomar, O.; Corsaro, E.; Campante, T. L.; Gaulme,
P.; Hale, S. J.; Handberg, R.; Jarvis, E.; Régulo, C.; Roxburgh,
I. W.; Salabert, D.; Stello, D.; Mullally, F.; Li, J.; Wohler, W.
2011ApJ...732L...5C Altcode: 2011arXiv1103.5570C
We use photometric observations of solar-type stars, made by the NASA
Kepler Mission, to conduct a statistical study of the impact of stellar
surface activity on the detectability of solar-like oscillations. We
find that the number of stars with detected oscillations falls
significantly with increasing levels of activity. The results present
strong evidence for the impact of magnetic activity on the properties
of near-surface convection in the stars, which appears to inhibit
the amplitudes of the stochastically excited, intrinsically damped
solar-like oscillations.
---------------------------------------------------------
Title: Large-scale Zonal Flows During the Solar Minimum -- Where Is
Cycle 25?
Authors: Hill, Frank; Howe, R.; Komm, R.; Christensen-Dalsgaard, J.;
Larson, T. P.; Schou, J.; Thompson, M. J.
2011SPD....42.1610H Altcode: 2011BAAS..43S.1610H
The so-called torsional oscillation is a pattern of migrating zonal flow
bands that move from mid-latitudes towards the equator and poles as the
magnetic cycle progresses. Helioseismology allows us to probe these
flows below the solar surface. The prolonged solar minimum following
Cycle 23 was accompanied by a delay of 1.5 to 2 years in the migration
of bands of faster rotation towards the equator. During the rising phase
of Cycle 24, while the lower-level bands match those seen in the rising
phase of Cycle 23, the rotation rate at middle and higher latitudes
remains slower than it was at the corresponding phase in earlier cycles,
perhaps reflecting the weakness of the polar fields. In addition,
there is no evidence of the poleward flow associated with Cycle 25. We
will present the latest results based on nearly sixteen years of global
helioseismic observations from GONG and MDI, with recent results from
HMI, and discuss the implications for the development of Cycle 25.
---------------------------------------------------------
Title: Ensemble Asteroseismology of Solar-Type Stars with the NASA
Kepler Mission
Authors: Chaplin, W. J.; Kjeldsen, H.; Christensen-Dalsgaard, J.;
Basu, S.; Miglio, A.; Appourchaux, T.; Bedding, T. R.; Elsworth, Y.;
García, R. A.; Gilliland, R. L.; Girardi, L.; Houdek, G.; Karoff,
C.; Kawaler, S. D.; Metcalfe, T. S.; Molenda-Żakowicz, J.; Monteiro,
M. J. P. F. G.; Thompson, M. J.; Verner, G. A.; Ballot, J.; Bonanno,
A.; Brandão, I. M.; Broomhall, A. -M.; Bruntt, H.; Campante, T. L.;
Corsaro, E.; Creevey, O. L.; Doğan, G.; Esch, L.; Gai, N.; Gaulme,
P.; Hale, S. J.; Handberg, R.; Hekker, S.; Huber, D.; Jiménez, A.;
Mathur, S.; Mazumdar, A.; Mosser, B.; New, R.; Pinsonneault, M. H.;
Pricopi, D.; Quirion, P. -O.; Régulo, C.; Salabert, D.; Serenelli,
A. M.; Silva Aguirre, V.; Sousa, S. G.; Stello, D.; Stevens, I. R.;
Suran, M. D.; Uytterhoeven, K.; White, T. R.; Borucki, W. J.; Brown,
T. M.; Jenkins, J. M.; Kinemuchi, K.; Van Cleve, J.; Klaus, T. C.
2011Sci...332..213C Altcode: 2011arXiv1109.4723C
In addition to its search for extrasolar planets, the NASA Kepler
mission provides exquisite data on stellar oscillations. We report the
detections of oscillations in 500 solar-type stars in the Kepler field
of view, an ensemble that is large enough to allow statistical studies
of intrinsic stellar properties (such as mass, radius, and age) and
to test theories of stellar evolution. We find that the distribution
of observed masses of these stars shows intriguing differences to
predictions from models of synthetic stellar populations in the Galaxy.
---------------------------------------------------------
Title: Wave absorption and moat flow in AR9787
Authors: Roth, M.; Thompson, M. J.
2011JPhCS.271a2022R Altcode:
We present the results of a study of the wave absorption and the moat
flow around the sunspot in AR9787 (the "HELAS sunspot", so-called
because it has been the object of in-depth study at a HELAS workshop)
using Fourier-Hankel decomposition of the oscillatory wave field. We
carry out inversions both for the flow speed and for the sound speed
perturbation as a function of depth. The results are compared with
results from time-distance helioseismology.
---------------------------------------------------------
Title: Ring-analysis flow measurements of sunspot outflows
Authors: Featherstone, Nicholas A.; Hindman, Bradley W.; Thompson,
Michael J.
2011JPhCS.271a2002F Altcode:
We present a local helioseismological analysis of the convective
flows around sunspots. The flow deductions were obtained from MDI
Dopplergrams using ring-analysis techniques to measure Doppler
shifts induced in solar acoustic oscillations. A novel multi-scale
3-D inversion procedure was used to self-consistently combine all
ring-analysis data taken from a mosaic of analysis tiles spanning the
solar disk. The inversion is multi-scale because in addition to folding
together information from tiles located at different positions on the
solar surface, it is capable of incorporating tiles of different sizes,
thus, enabling fine control of the horizontal resolution and the probing
depth. The inversion is based on sensitivity kernels computed with
the Born approximation. Our inversion results indicate that outflow
observed at the surface surrounding sunspots persists to unexpectedly
deep depths (~ 7 Mm). These outflows appear to have two components,
being comprised of a superficial moat flow and a deeper outflow whose
strength peaks around 5 Mm.
---------------------------------------------------------
Title: First Global Rotation Inversions of HMI Data
Authors: Howe, R.; Larson, T. P.; Schou, J.; Hill, F.; Komm, R.;
Christensen-Dalsgaard, J.; Thompson, M. J.
2011JPhCS.271a2061H Altcode:
We present the first 2-dimensional global rotational inversions of
medium-degree p-mode data from the Helioseismic and Magnetic Imager,
and compare the results with inversions of Michelson Doppler Imager
data for the same time period. The inferred rotation profiles show
good agreement between the two instruments.
---------------------------------------------------------
Title: Helioseismic Tests With the FLASH Simulation Code
Authors: González-Morales, Pedro A.; Jain, Rekha; Thompson, Michael J.
2011JPhCS.271a2013G Altcode:
We show our first results from local helioseismic simulations using
the numerical code FLASH by testing its suitability for simulating
subphotospheric wave motions in helioseismology. In order to check
the capability of this code for different sources of waves, we have
implemented a non-magnetic plane-parallel atmosphere adding a source
term to the energy equation. We confirm the capabilities of FLASH code
for investigating the propagation of sound waves into a realistically
stratified solar interior.
---------------------------------------------------------
Title: Progress on the Baker Observatory Sub-minute Survey
Authors: Reed, Mike; Gilker, J.; Thompson, M.; Hicks, L.; Quint, A.;
Metzger, A.
2011AAS...21733408R Altcode: 2011BAAS...4333408R
The Baker Observatory Sub-minute Survey is designed to look for
phenomena with short-period variability. Typical exposure times are
under 15 seconds, surveying a magnitude range of 10-13 in white
light. Known short-period phenomena include pulsating subdwarf B
stars, white dwarfs, rapidly oscillating Ap stars and Delta Scuti
stars. Currently, most sky surveys are interested in observing
the entire sky and as such, the temporal cadence is best suited
for variations of several hours or longer. Our survey observes
single fields for four hour spans on two separate (non-adjacent)
nights. During Phase I of our survey, we have selected 40 fields
which contain at least one known variable star. It is then a blind
study to determine if we can recover the known variable and search for
new variables within each field. Observations for Phase I are nearly
complete and we are enhancing our procedures and detection algorithms to
optimize sensitivity to variations over many time scales. Our data are
excellent for detecting variability shorter than two hours, even down
to amplitudes of a millimagnitude (depending on S/N). This material
is based upon work supported by the National Science Foundation under
Grant No. Any opinions, findings, and conclusions or recommendations
expressed in this material are those of the author(s) and do not
necessarily reflect the views of the National Science Foundation. This
work was partially funded by the Missouri Space Grant Consortium,
funded by NASA and Missouri State University.
---------------------------------------------------------
Title: The torsional oscillation and the new solar cycle
Authors: Howe, R.; Hill, F.; Komm, R.; Christensen-Dalsgaard, J.;
Larson, T. P.; Schou, J.; Thompson, M. J.; Ulrich, R.
2011JPhCS.271a2074H Altcode:
We present updated observations of the pattern of migrating solar
zonal flows known as the torsional oscillation, covering 15 years of
helioseismic measurements with GONG and MDI and 30 years of surface
Doppler observations from Mount Wilson. We compare the behavior of the
flows during the extended solar minimum following Cycle 23 with that in
earlier minima. We demonstrate that the timing of the migration of the
zonal flow belts may be of some use in predicting the start of the new
cycle. We also note that the behavior of the high-latitude part of the
pattern currently differs from that seen early in the previous cycle,
with the high-latitude poleward-migrating branch still not established.
---------------------------------------------------------
Title: Rotation-rate variations at the tachocline: An update
Authors: Howe, R.; Komm, R.; Hill, F.; Christensen-Dalsgaard, J.;
Larson, T. P.; Schou, J.; Thompson, M. J.; Toomre, J.
2011JPhCS.271a2075H Altcode:
After 15 years of GONG and MDI observations of the solar interior
rotation, we revisit the issue of variations in the rotation rate near
the base of the convection zone. The 1.3-year period seen in the first
few years of the observations disappeared after 2000 and has still
not returned. On the other hand, the agreement between GONG and MDI
observations suggests that variations seen in this region have some
solar origin, whether a true rotation-rate change or possibly mere
stochastic variation; we present a numerical experiment supporting
this contention.
---------------------------------------------------------
Title: A new code for Fourier-Legendre analysis of large datasets:
First results and a comparison with ring-diagram analysis
Authors: Doerr, H. -P.; Roth, M.; Zaatri, A.; Krieger, L.; Thompson,
M. J.
2010AN....331..911D Altcode: 2010arXiv1011.4152D
Fourier-Legendre decomposition (FLD) of solar Doppler imaging data is a
promising method to estimate the sub-surface solar meridional flow. FLD
is sensible to low-degree oscillation modes and thus has the potential
to probe the deep meridional flow. We present a newly developed code to
be used for large scale FLD analysis of helioseismic data as provided
by the Global Oscillation Network Group (GONG), the Michelson Doppler
Imager (MDI) instrument, and the upcoming Helioseismic and Magnetic
Imager (HMI) instrument. First results obtained with the new code are
qualitatively comparable to those obtained from ring-diagram analyis
of the same time series.
---------------------------------------------------------
Title: Asteroseismology of solar-type stars with Kepler I: Data
analysis
Authors: Karoff, C.; Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.;
Garcia, R. A.; Houdek, G.; Metcalfe, T. S.; Molenda-Żakowicz, J.;
Monteiro, M. J. P. F. G.; Thompson, M. J.; Christensen-Dalsgaard, J.;
Gilliland, R. L.; Kjeldsen, H.; Basu, S.; Bedding, T. R.; Campante,
T. L.; Eggenberger, P.; Fletcher, S. T.; Gaulme, P.; Handberg, R.;
Hekker, S.; Martic, M.; Mathur, S.; Mosser, B.; Regulo, C.; Roxburgh,
I. W.; Salabert, D.; Stello, D.; Verner, G. A.; Belkacem, K.; Biazzo,
K.; Cunha, M. S.; Gruberbauer, M.; Guzik, J. A.; Kupka, F.; Leroy,
B.; Ludwig, H. -G.; Mathis, S.; Noels, A.; Noyes, R. W.; Roca Cortes,
T.; Roth, M.; Sato, K. H.; Schmitt, J.; Suran, M. D.; Trampedach,
R.; Uytterhoeven, K.; Ventura, R.
2010AN....331..972K Altcode: 2010arXiv1005.0507K
We report on the first asteroseismic analysis of solar-type stars
observed by Kepler. Observations of three G-type stars, made at
one-minute cadence during the first 33.5 days of science operations,
reveal high signal-to-noise solar-like oscillation spectra in all three
stars: About 20 modes of oscillation can clearly be distinguished
in each star. We discuss the appearance of the oscillation spectra,
including the presence of a possible signature of faculae, and the
presence of mixed modes in one of the three stars.
---------------------------------------------------------
Title: Four years of HELAS
Authors: Roth, M.; Lühe, O. v. d.; Aerts, C.; Christensen-Dalsgaard,
J.; Corbard, T.; Daszyńska-Daszkiewicz, J.; Di Mauro, M. P.; Gizon,
L.; Jiménez-Reyes, S.; Monteiro, M. J. P. F. G.; Pallé, P. L.;
Thompson, M. J.
2010AN....331.1084R Altcode:
The European Coordination Action on HELio- and ASteroseismology
(HELAS) has completed its fourth and final year of initial funding by
the European Commission. Set up as a network which combines solar and
stellar physics communities in the important and vigorously evolving
field of seismology, HELAS has been able to coordinate the efforts of
European astronomers with remarkable success. Four large international
conferences including the HELAS-IV conference on Lanzarote as well as
many workshops were organized with a substantial contribution from
HELAS. About a dozen workshops, addressing specialized questions in
global and local helioseismology and asteroseismology were entirely
organized by HELAS. Data analysis tools to prepare the European
communities for the upcoming influx of data from new missions have
been prepared, tested and demonstrated. Lecture notes and outreach
material have been assembled and prepared for general access. As a
result, HELAS has an important impact on the scientific output of the
astrophysics seismology communities and significantly increased the
visibility of European research in this field. This paper summarizes
the activities and accomplishments of HELAS.
---------------------------------------------------------
Title: Asteroseismology of solar-type stars with Kepler: II. Stellar
modeling
Authors: Metcalfe, T. S.; Monteiro, M. J. P. F. G.; Thompson, M. J.;
Chaplin, W. J.; Basu, S.; Bonanno, A.; Di Mauro, M. P.; Doğan, G.;
Eggenberger, P.; Karoff, C.; Stello, D.; WG1, KASC
2010AN....331..977M Altcode: 2010arXiv1006.5695M
Observations from the Kepler satellite were recently published for
three bright G-type stars, which were monitored during the first 33.5
days of science operations. One of these stars, KIC 11026764, exhibits
a characteristic pattern of oscillation frequencies suggesting that the
star has evolved significantly. We have derived initial estimates of the
properties of KIC 11026764 from the oscillation frequencies observed
by Kepler, combined with ground-based spectroscopic data. We present
preliminary results from detailed modeling of this star, employing a
variety of independent codes and analyses that attempt to match the
asteroseismic and spectroscopic constraints simultaneously.
---------------------------------------------------------
Title: A Precise Asteroseismic Age and Radius for the Evolved Sun-like
Star KIC 11026764
Authors: Metcalfe, T. S.; Monteiro, M. J. P. F. G.; Thompson, M. J.;
Molenda-Żakowicz, J.; Appourchaux, T.; Chaplin, W. J.; Doǧan, G.;
Eggenberger, P.; Bedding, T. R.; Bruntt, H.; Creevey, O. L.; Quirion,
P. -O.; Stello, D.; Bonanno, A.; Silva Aguirre, V.; Basu, S.; Esch,
L.; Gai, N.; Di Mauro, M. P.; Kosovichev, A. G.; Kitiashvili, I. N.;
Suárez, J. C.; Moya, A.; Piau, L.; García, R. A.; Marques, J. P.;
Frasca, A.; Biazzo, K.; Sousa, S. G.; Dreizler, S.; Bazot, M.; Karoff,
C.; Frandsen, S.; Wilson, P. A.; Brown, T. M.; Christensen-Dalsgaard,
J.; Gilliland, R. L.; Kjeldsen, H.; Campante, T. L.; Fletcher, S. T.;
Handberg, R.; Régulo, C.; Salabert, D.; Schou, J.; Verner, G. A.;
Ballot, J.; Broomhall, A. -M.; Elsworth, Y.; Hekker, S.; Huber, D.;
Mathur, S.; New, R.; Roxburgh, I. W.; Sato, K. H.; White, T. R.;
Borucki, W. J.; Koch, D. G.; Jenkins, J. M.
2010ApJ...723.1583M Altcode: 2010arXiv1010.4329M
The primary science goal of the Kepler Mission is to provide
a census of exoplanets in the solar neighborhood, including the
identification and characterization of habitable Earth-like planets. The
asteroseismic capabilities of the mission are being used to determine
precise radii and ages for the target stars from their solar-like
oscillations. Chaplin et al. published observations of three bright
G-type stars, which were monitored during the first 33.5 days of science
operations. One of these stars, the subgiant KIC 11026764, exhibits a
characteristic pattern of oscillation frequencies suggesting that it
has evolved significantly. We have derived asteroseismic estimates of
the properties of KIC 11026764 from Kepler photometry combined with
ground-based spectroscopic data. We present the results of detailed
modeling for this star, employing a variety of independent codes and
analyses that attempt to match the asteroseismic and spectroscopic
constraints simultaneously. We determine both the radius and the age
of KIC 11026764 with a precision near 1%, and an accuracy near 2%
for the radius and 15% for the age. Continued observations of this
star promise to reveal additional oscillation frequencies that will
further improve the determination of its fundamental properties.
---------------------------------------------------------
Title: Modeling the Subsurface Structure of Sunspots
Authors: Moradi, H.; Baldner, C.; Birch, A. C.; Braun, D. C.; Cameron,
R. H.; Duvall, T. L.; Gizon, L.; Haber, D.; Hanasoge, S. M.; Hindman,
B. W.; Jackiewicz, J.; Khomenko, E.; Komm, R.; Rajaguru, P.; Rempel,
M.; Roth, M.; Schlichenmaier, R.; Schunker, H.; Spruit, H. C.;
Strassmeier, K. G.; Thompson, M. J.; Zharkov, S.
2010SoPh..267....1M Altcode: 2009arXiv0912.4982M; 2010SoPh..tmp..171M
While sunspots are easily observed at the solar surface, determining
their subsurface structure is not trivial. There are two main
hypotheses for the subsurface structure of sunspots: the monolithic
model and the cluster model. Local helioseismology is the only means
by which we can investigate subphotospheric structure. However, as
current linear inversion techniques do not yet allow helioseismology to
probe the internal structure with sufficient confidence to distinguish
between the monolith and cluster models, the development of physically
realistic sunspot models are a priority for helioseismologists. This
is because they are not only important indicators of the variety of
physical effects that may influence helioseismic inferences in active
regions, but they also enable detailed assessments of the validity of
helioseismic interpretations through numerical forward modeling. In
this article, we provide a critical review of the existing sunspot
models and an overview of numerical methods employed to model wave
propagation through model sunspots. We then carry out a helioseismic
analysis of the sunspot in Active Region 9787 and address the serious
inconsistencies uncovered by Gizon et al. (2009a, 2009b). We find that
this sunspot is most probably associated with a shallow, positive
wave-speed perturbation (unlike the traditional two-layer model)
and that travel-time measurements are consistent with a horizontal
outflow in the surrounding moat.
---------------------------------------------------------
Title: Erratum: Erratum to: Helioseismology of Sunspots: A Case
Study of NOAA Region 9787
Authors: Gizon, L.; Schunker, H.; Baldner, C. S.; Basu, S.; Birch,
A. C.; Bogart, R. S.; Braun, D. C.; Cameron, R.; Duvall, T. L.;
Hanasoge, S. M.; Jackiewicz, J.; Roth, M.; Stahn, T.; Thompson, M. J.;
Zharkov, S.
2010SSRv..156..257G Altcode: 2010SSRv..tmp...99G
No abstract at ADS
---------------------------------------------------------
Title: VISTA Variables in the Vía Láctea (VVV): Current Status
and First Results
Authors: Saito, R.; Hempel, M.; Alonso-García, J.; Toledo, I.;
Borissova, J.; González, O.; Beamin, J. C.; Minniti, D.; Lucas, P.;
Emerson, J.; Ahumada, A.; Aigrain, S.; Alonso, M. V.; Amôres, E.;
Angeloni, R.; Arias, J.; Bandyopadhyay, R.; Barbá, R.; Barbuy, B.;
Baume, G.; Bedin, L.; Bica, E.; Bronfman, L.; Carraro, G.; Catelan,
M.; Clariá, J.; Contreras, C.; Cross, N.; Davis, C.; de Grijs, R.;
Dékány, I.; Janet Drew, J. D.; Fariña, C.; Feinstein, C.; Fernández
Lajús, E.; Folkes, S.; Gamen, R.; Geisler, D.; Gieren, W.; Goldman,
B.; Gosling, A.; Gunthardt, G.; Gurovich, S.; Hambly, N.; Hanson, M.;
Hoare, M.; Irwin, M.; Ivanov, V.; Jordán, A.; Kerins, E.; Kinemuchi,
K.; Kurtev, R.; Longmore, A.; López-Corredoira, M.; Maccarone, T.;
Martín, E.; Masetti, N.; Mennickent, R.; Merlo, D.; Messineo, M.;
Mirabel, F.; Monaco, L.; Moni Bidin, C.; Morelli, L.; Padilla, N.;
Palma, T.; Parisi, M. C.; Parker, Q.; Pavani, D.; Pietrukowicz, P.;
Pietrzynski, G.; Pignata, G.; Rejkuba, M.; Rojas, A.; Roman Lopes,
A.; Ruiz, M. T.; Sale, S.; Saviane, I.; Schreiber, M.; Schröder,
A.; Sharma, S.; Smith, M.; Sodré, L., Jr.; Soto, M.; Stephens,
A.; Tamura, M.; Tappert, C.; Thompson, M.; Valenti, E.; Vanzi, L.;
Weidmann, W.; Zoccali, M.
2010Msngr.141...24S Altcode:
VISTA Variables in the Vía Láctea (VVV) is a public ESO near-IR
variability survey aimed at scanning the Milky Way Bulge and an adjacent
section of the mid-plane. VVV observations started in October 2009
during ESO science verification. Regular observations for the first
year of the survey have been conducted since February 2010 and will
cover a total area of 520 square degrees in five passbands and five
epochs. Here we address the first results obtained from the VVV Survey
as well as the current status of the observations.
---------------------------------------------------------
Title: Herschel ATLAS: The cosmic star formation history of quasar
host galaxies
Authors: Serjeant, S.; Bertoldi, F.; Blain, A. W.; Clements, D. L.;
Cooray, A.; Danese, L.; Dunlop, J.; Dunne, L.; Eales, S.; Falder,
J.; Hatziminaoglou, E.; Hughes, D. H.; Ibar, E.; Jarvis, M. J.;
Lawrence, A.; Lee, M. G.; Michałowski, M.; Negrello, M.; Omont, A.;
Page, M.; Pearson, C.; van der Werf, P. P.; White, G.; Amblard, A.;
Auld, R.; Baes, M.; Bonfield, D. G.; Burgarella, D.; Buttiglione, S.;
Cava, A.; Dariush, A.; de Zotti, G.; Dye, S.; Frayer, D.; Fritz, J.;
Gonzalez-Nuevo, J.; Herranz, D.; Ivison, R. J.; Lagache, G.; Leeuw,
L.; Lopez-Caniego, M.; Maddox, S.; Pascale, E.; Pohlen, M.; Rigby,
E.; Rodighiero, G.; Samui, S.; Sibthorpe, B.; Smith, D. J. B.; Temi,
P.; Thompson, M.; Valtchanov, I.; Verma, A.
2010A&A...518L...7S Altcode: 2010arXiv1005.2410S
We present a derivation of the star formation rate per comoving volume
of quasar host galaxies, derived from stacking analyses of far-infrared
to mm-wave photometry of quasars with redshifts 0 < z < 6 and
absolute I-band magnitudes -22 > I<SUB>AB</SUB> > -32 We use the
science demonstration observations of the first ~16 deg<SUP>2</SUP>
from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS)
in which there are 240 quasars from the Sloan Digital Sky Survey (SDSS)
and a further 171 from the 2dF-SDSS LRG and QSO (2SLAQ) survey. We
supplement this data with a compilation of data from IRAS, ISO, Spitzer,
SCUBA and MAMBO. H-ATLAS alone statistically detects the quasars in its
survey area at >5σ at 250,350 and 500 μm. From the compilation as
a whole we find striking evidence of downsizing in quasar host galaxy
formation: low-luminosity quasars with absolute magnitudes in the range
-22 > I<SUB>AB</SUB> > -24 have a comoving star formation rate
(derived from 100 μm rest-frame luminosities) peaking between redshifts
of 1 and 2, while high-luminosity quasars with I<SUB>AB</SUB> <
-26 have a maximum contribution to the star formation density at z ~
3. The volume-averaged star formation rate of -22 > I<SUB>AB</SUB>
> -24 quasars evolves as (1 + z)<SUP>2.3±0.7</SUP> at z < 2,
but the evolution at higher luminosities is much faster reaching (1 +
z)<SUP>10±1</SUP> at -26 > I<SUB>AB</SUB> > -28. We tentatively
interpret this as a combination of a declining major merger rate with
time and gas consumption reducing fuel for both black hole accretion
and star formation. <P />Herschel is an ESA space observatory with
science instruments provided by European-led Principal Investigator
consortia with important participation from NASA.
---------------------------------------------------------
Title: Herschel-ATLAS: The dust energy balance in the edge-on spiral
galaxy UGC 4754
Authors: Baes, M.; Fritz, J.; Gadotti, D. A.; Smith, D. J. B.; Dunne,
L.; da Cunha, E.; Amblard, A.; Auld, R.; Bendo, G. J.; Bonfield, D.;
Burgarella, D.; Buttiglione, S.; Cava, A.; Clements, D.; Cooray,
A.; Dariush, A.; de Zotti, G.; Dye, S.; Eales, S.; Frayer, D.;
Gonzalez-Nuevo, J.; Herranz, D.; Ibar, E.; Ivison, R.; Lagache, G.;
Leeuw, L.; Lopez-Caniego, M.; Jarvis, M.; Maddox, S.; Negrello, M.;
Michałowski, M.; Pascale, E.; Pohlen, M.; Rigby, E.; Rodighiero,
G.; Samui, S.; Serjeant, S.; Temi, P.; Thompson, M.; van der Werf,
P.; Verma, A.; Vlahakis, C.
2010A&A...518L..39B Altcode: 2010arXiv1005.1773B
We use Herschel PACS and SPIRE observations of the edge-on spiral galaxy
UGC 4754, taken as part of the H-ATLAS SDP observations, to investigate
the dust energy balance in this galaxy. We build detailed SKIRT
radiative models based on SDSS and UKIDSS maps and use these models to
predict the far-infrared emission. We find that our radiative transfer
model underestimates the observed FIR emission by a factor of two to
three. Similar discrepancies have been found for other edge-on spiral
galaxies based on IRAS, ISO, and SCUBA data. Thanks to the good sampling
of the SED at FIR wavelengths, we can rule out an underestimation of the
FIR emissivity as the cause for this discrepancy. Instead we support
highly obscured star formation that contributes little to the optical
extinction as a more probable explanation. <P />Herschel is an ESA space
observatory with science instruments provided by European-led principal-
investigator consortia and with important participation from NASA.
---------------------------------------------------------
Title: Herschel-ATLAS: Extragalactic number counts from 250 to
500 microns
Authors: Clements, D. L.; Rigby, E.; Maddox, S.; Dunne, L.; Mortier,
A.; Pearson, C.; Amblard, A.; Auld, R.; Baes, M.; Bonfield, D.;
Burgarella, D.; Buttiglione, S.; Cava, A.; Cooray, A.; Dariush, A.;
de Zotti, G.; Dye, S.; Eales, S.; Frayer, D.; Fritz, J.; Gardner,
Jonathan P.; Gonzalez-Nuevo, J.; Herranz, D.; Ibar, E.; Ivison, R.;
Jarvis, M. J.; Lagache, G.; Leeuw, L.; Lopez-Caniego, M.; Negrello,
M.; Pascale, E.; Pohlen, M.; Rodighiero, G.; Samui, S.; Serjeant,
S.; Sibthorpe, B.; Scott, D.; Smith, D. J. B.; Temi, P.; Thompson,
M.; Valtchanov, I.; van der Werf, P.; Verma, A.
2010A&A...518L...8C Altcode: 2010arXiv1005.2409C
<BR /> Aims: The Herschel-ATLAS survey (H-ATLAS) will be the largest
area survey to be undertaken by the Herschel Space Observatory. It
will cover 550 sq. deg. of extragalactic sky at wavelengths of 100,
160, 250, 350 and 500 μm when completed, reaching flux limits (5σ)
from 32 to 145 mJy. We here present galaxy number counts obtained
for SPIRE observations of the first ~14 sq. deg. observed at 250,
350 and 500 μm. <BR /> Methods: Number counts are a fundamental
tool in constraining models of galaxy evolution. We use source
catalogs extracted from the H-ATLAS maps as the basis for such an
analysis. Correction factors for completeness and flux boosting are
derived by applying our extraction method to model catalogs and then
applied to the raw observational counts. <BR /> Results: We find a
steep rise in the number counts at flux levels of 100-200 mJy in all
three SPIRE bands, consistent with results from BLAST. The counts are
compared to a range of galaxy evolution models. None of the current
models is an ideal fit to the data but all ascribe the steep rise to a
population of luminous, rapidly evolving dusty galaxies at moderate to
high redshift. <P />Herschel is an ESA space observatory with science
instruments provided by European-led Principal Investigator consortia
and with important participation from NASA.
---------------------------------------------------------
Title: Herschel-ATLAS: Blazars in the science demonstration phase
field
Authors: González-Nuevo, J.; de Zotti, G.; Andreani, P.; Barton,
E. J.; Bertoldi, F.; Birkinshaw, M.; Bonavera, L.; Buttiglione, S.;
Cooke, J.; Cooray, A.; Danese, G.; Dunne, L.; Eales, S.; Fan, L.;
Jarvis, M. J.; Klöckner, H. -R.; Hatziminaoglou, E.; Herranz, D.;
Hughes, D. H.; Lapi, A.; Lawrence, A.; Leeuw, L.; Lopez-Caniego, M.;
Massardi, M.; Mauch, T.; Michałowski, M. J.; Negrello, M.; Rawlings,
S.; Rodighiero, G.; Samui, S.; Serjeant, S.; Vieira, J. D.; White,
G.; Amblard, A.; Auld, R.; Baes, M.; Bonfield, D. G.; Burgarella, D.;
Cava, A.; Clements, D. L.; Dariush, A.; Dye, S.; Frayer, D.; Fritz,
J.; Ibar, E.; Ivison, R. J.; Lagache, G.; Maddox, S.; Pascale, E.;
Pohlen, M.; Rigby, E.; Sibthorpe, B.; Smith, D. J. B.; Temi, P.;
Thompson, M.; Valtchanov, I.; Verma, A.
2010A&A...518L..38G Altcode: 2010arXiv1005.2407G
To investigate the poorly constrained sub-mm counts and spectral
properties of blazars we searched for these in the Herschel-ATLAS
(H-ATLAS) science demonstration phase (SDP) survey catalog. We
cross-matched 500 μm sources brighter than 50 mJy with the FIRST radio
catalogue. We found two blazars, both previously known. Our study is
among the first blind blazar searches at sub-mm wavelengths, i.e.,
in the spectral regime where little is still known about the blazar
SEDs, but where the synchrotron peak of the most luminous blazars
is expected to occur. Our early results are consistent with educated
extrapolations of lower frequency counts and question indications of
substantial spectral curvature downwards and of spectral upturns at
mm wavelengths. One of the two blazars is identified with a Fermi/LAT
γ-ray source and a WMAP source. The physical parameters of the two
blazars are briefly discussed. These observations demonstrate that the
H-ATLAS survey will provide key information about the physics of blazars
and their contribution to sub-mm counts. <P />Herschel is an ESA space
observatory with science instruments provided by European-led Principal
Investigator consortia and with important participation from NASA.
---------------------------------------------------------
Title: Herschel-ATLAS: The angular correlation function of
submillimetre galaxies at high and low redshift
Authors: Maddox, S. J.; Dunne, L.; Rigby, E.; Eales, S.; Cooray, A.;
Scott, D.; Peacock, J. A.; Negrello, M.; Smith, D. J. B.; Benford,
D.; Amblard, A.; Auld, R.; Baes, M.; Bonfield, D.; Burgarella, D.;
Buttiglione, S.; Cava, A.; Clements, D.; Dariush, A.; de Zotti, G.;
Dye, S.; Frayer, D.; Fritz, J.; Gonzalez-Nuevo, J.; Herranz, D.; Ibar,
E.; Ivison, R.; Jarvis, M. J.; Lagache, G.; Leeuw, L.; Lopez-Caniego,
M.; Pascale, E.; Pohlen, M.; Rodighiero, G.; Samui, S.; Serjeant,
S.; Temi, P.; Thompson, M.; Verma, A.
2010A&A...518L..11M Altcode: 2010arXiv1005.2406M
We present measurements of the angular correlation function of galaxies
selected from the first field of the H-ATLAS survey. Careful removal
of the background from galactic cirrus is essential, and currently
dominates the uncertainty in our measurements. For our 250 μm-selected
sample we detect no significant clustering, consistent with the
expectation that the 250 μm-selected sources are mostly normal
galaxies at z ⪉ 1. For our 350 μm and 500 μm-selected samples
we detect relatively strong clustering with correlation amplitudes
A of 0.2 and 1.2 at 1', but with relatively large uncertainties. For
samples which preferentially select high redshift galaxies at z~2-3
we detect significant strong clustering, leading to an estimate of
r<SUB>0</SUB> ~ 7-11 h<SUP>-1</SUP> Mpc. The slope of our clustering
measurements is very steep, δ ~ 2. The measurements are consistent
with the idea that sub-mm sources consist of a low redshift population
of normal galaxies and a high redshift population of highly clustered
star-bursting galaxies. <P />Herschel is an ESA space observatory with
science instruments provided by European-led Principal Investigator
consortia and with important participation from NASA.
---------------------------------------------------------
Title: OT1_mthomp01_1: Confirming a sample of luminous debris disk
candidates identified in the Herschel ATLAS
Authors: Thompson, M.
2010hers.prop.1318T Altcode:
Debris disks are the remains of planetary system formation, tracing
the existence of planetesimal-sized objects in orbit around main
sequence stars. Current and planned surveys of debris disks (including
the Herschel Key Projects DEBRIS and DUNES) are deep surveys aimed
at characterising the typical population of disks and targeted at
samples of a few hundred nearby objects. These deep narrow surveys are
relatively insensitive to the rarities in the debris disk population,
some of which may be luminous and/or massive disks that have undergone
recent disruptive collisional events. We have recently shown that the
primarily extragalactic Key Project, the Herschel-ATLAS, can be used as
a wide and shallow survey of debris disks by combining its excellent
optical coverage and statistical techniques more commonly employed to
identify galaxies. The combination of Herschel-ATLAS, DEBRIS and DUNES
thus forms a powerful nested tier of surveys that will be sensitive
to disks across the spectrum from exosolar analogues to rare disks
that cannot be inferred from local populations. In this proposal we
seek time to image the three candidate disks that we discovered in
the Herschel-ATLAS Science Demonstration Phase with PACS so that we
may confirm them as true debris disks and model their SEDs to extract
mass, temperature and fractional luminosity. We will confirm whether
these disk candidates are in fact the most luminous disks yet detected.
---------------------------------------------------------
Title: Helioseismology over the Solar Cycle
Authors: Thompson, M. J.
2010ASPC..428...23T Altcode: 2010arXiv1003.3888T
Helioseismology has produced unprecedented measurements of the Sun's
internal structure and dynamics over the past 25 years. Much of this
work has been based on global helioseismology. Now local helioseismology
too is showing its great promise. This review summarizes very briefly
the principal global results that may be relevant to an understanding of
the origins of solar magnetism. Recent results regarding the variation
of frequencies over the solar cycle and the temporal variations of
subsurface flows are briefly summarized.
---------------------------------------------------------
Title: Developing Physics-Based Procedures for Local Helioseismic
Probing of Sunspots and Magnetic Regions
Authors: Birch, Aaron; Braun, D. C.; Crouch, A.; Rempel, M.; Fan,
Y.; Centeno, R.; Toomre, J.; Haber, D.; Hindman, B.; Featherstone,
N.; Duvall, T., Jr.; Jackiewicz, J.; Thompson, M.; Stein, R.; Gizon,
L.; Cameron, R.; Saidi, Y.; Hanasoge, S.; Burston, R.; Schunker, H.;
Moradi, H.
2010AAS...21630805B Altcode:
We have initiated a project to test and improve the local helioseismic
techniques of time-distance and ring-diagram analysis. Our goals are
to develop and implement physics-based methods that will (1) enable the
reliable determinations of subsurface flow, magnetic field, and thermal
structure in regions of strong magnetic fields and (2) be quantitatively
tested with realistic solar magnetoconvection simulations in the
presence of sunspot-like magnetic fields. We are proceeding through a
combination of improvements in local helioseismic measurements, forward
modeling of the helioseismic wavefield, kernel computations, inversions,
and validation through numerical simulations. As improvements over
existing techniques are made they will be applied to the SDO/HMI
observations. This work is funded through the the NASA Heliophysics
Science Division through the Solar Dynamics Observatory (SDO) Science
Center program.
---------------------------------------------------------
Title: The Solar Dynamo
Authors: Jones, Chris A.; Thompson, Michael J.; Tobias, Steven M.
2010SSRv..152..591J Altcode:
Observations relevant to current models of the solar dynamo are
presented, with emphasis on the history of solar magnetic activity
and on the location and nature of the solar tachocline. The problems
encountered when direct numerical simulation is used to analyse the
solar cycle are discussed, and recent progress is reviewed. Mean field
dynamo theory is still the basis of most theories of the solar dynamo,
so a discussion of its fundamental principles and its underlying
assumptions is given. The role of magnetic helicity is discussed. Some
of the most popular models based on mean field theory are reviewed
briefly. Dynamo models based on severe truncations of the full MHD
equations are discussed.
---------------------------------------------------------
Title: The Asteroseismic Potential of Kepler: First Results for
Solar-Type Stars
Authors: Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.; García,
R. A.; Houdek, G.; Karoff, C.; Metcalfe, T. S.; Molenda-Żakowicz,
J.; Monteiro, M. J. P. F. G.; Thompson, M. J.; Brown, T. M.;
Christensen-Dalsgaard, J.; Gilliland, R. L.; Kjeldsen, H.; Borucki,
W. J.; Koch, D.; Jenkins, J. M.; Ballot, J.; Basu, S.; Bazot, M.;
Bedding, T. R.; Benomar, O.; Bonanno, A.; Brandão, I. M.; Bruntt,
H.; Campante, T. L.; Creevey, O. L.; Di Mauro, M. P.; Doǧan,
G.; Dreizler, S.; Eggenberger, P.; Esch, L.; Fletcher, S. T.;
Frandsen, S.; Gai, N.; Gaulme, P.; Handberg, R.; Hekker, S.; Howe,
R.; Huber, D.; Korzennik, S. G.; Lebrun, J. C.; Leccia, S.; Martic,
M.; Mathur, S.; Mosser, B.; New, R.; Quirion, P. -O.; Régulo, C.;
Roxburgh, I. W.; Salabert, D.; Schou, J.; Sousa, S. G.; Stello, D.;
Verner, G. A.; Arentoft, T.; Barban, C.; Belkacem, K.; Benatti, S.;
Biazzo, K.; Boumier, P.; Bradley, P. A.; Broomhall, A. -M.; Buzasi,
D. L.; Claudi, R. U.; Cunha, M. S.; D'Antona, F.; Deheuvels, S.;
Derekas, A.; García Hernández, A.; Giampapa, M. S.; Goupil, M. J.;
Gruberbauer, M.; Guzik, J. A.; Hale, S. J.; Ireland, M. J.; Kiss,
L. L.; Kitiashvili, I. N.; Kolenberg, K.; Korhonen, H.; Kosovichev,
A. G.; Kupka, F.; Lebreton, Y.; Leroy, B.; Ludwig, H. -G.; Mathis, S.;
Michel, E.; Miglio, A.; Montalbán, J.; Moya, A.; Noels, A.; Noyes,
R. W.; Pallé, P. L.; Piau, L.; Preston, H. L.; Roca Cortés, T.;
Roth, M.; Sato, K. H.; Schmitt, J.; Serenelli, A. M.; Silva Aguirre,
V.; Stevens, I. R.; Suárez, J. C.; Suran, M. D.; Trampedach, R.;
Turck-Chièze, S.; Uytterhoeven, K.; Ventura, R.; Wilson, P. A.
2010ApJ...713L.169C Altcode: 2010arXiv1001.0506C
We present preliminary asteroseismic results from Kepler on three G-type
stars. The observations, made at one-minute cadence during the first
33.5 days of science operations, reveal high signal-to-noise solar-like
oscillation spectra in all three stars: about 20 modes of oscillation
may be clearly distinguished in each star. We discuss the appearance of
the oscillation spectra, use the frequencies and frequency separations
to provide first results on the radii, masses, and ages of the stars,
and comment in the light of these results on prospects for inference
on other solar-type stars that Kepler will observe.
---------------------------------------------------------
Title: The Smallest Lunar Grains: Analytical TEM Characterization
of the Sub-Micron Size Fraction of a Mare Soil
Authors: Thompson, M.; Christoffersen, R.
2010LPI....41.2191T Altcode:
Analytical TEM observations show the sub-micron size fraction of
a mature mare soil is highly enriched in glass grains, including
spherules, relative to the larger size fractions, including the sub
10 micron size fraction as a whole.
---------------------------------------------------------
Title: The Solar Dynamo
Authors: Jones, Chris A.; Thompson, Michael J.; Tobias, Steven M.
2010plma.book..591J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Baker Observatory Subminute Survey
Authors: Gilker, Justin; Reed, M.; Doennig, A.; Quint, A.; Hicks,
L.; Thompson, M.
2010AAS...21541805G Altcode: 2010BAAS...42..275G
We are conducting a small-scale short-period stellar variability
survey using our 16-inch telescope at Baker Observatory. The goal is
to search for previously undetected variability types and to increase
membership of known pulsation classes. We are currently in the first
portion of this survey which is to understand the sensitivity of
our observations. Our strategy is to have four hour runs with short
integrations and observe each field twice. We have begun collecting
data with at least one known type of variable star in each field
and are doing a blind study to recover the known variable and seek
new variable stars. Our initial strategy for detecting variability
is to use Fourier techniques for short-period (1 - 30 minutes)
variability, phase-dispersion techniques for mid-period (0.5 to 4
hours) and a brightness comparator between the runs for long-period
(4 hours to days) variations. <P />This research is sponsored by the
National Science Foundation grant 0913175 and The Missouri Space Grant
Consortium, funded by NASA. Any opinions, findings, and conclusions
or recommendations expressed in this material are those of the authors
and do not necessarily reflect views of the National Science Foundation.
---------------------------------------------------------
Title: Analysis of Acoustic Wave Propagation in the Subphotosphere
with Localized Magnetic Field Concentration
Authors: Zharkov, S.; Shelyag, S.; Thompson, M. J.
2009ASPC..416...75Z Altcode:
We present the time-distance analysis of numerical simulations of
acoustic wave propagation and dispersion in the solar subphotosphere
with a localized magnetic field concentration.
---------------------------------------------------------
Title: Iterative Inversion for Solar and Stellar Internal Rotation
Authors: Sudnik, M.; Thompson, M. J.
2009ASPC..416..411S Altcode:
We investigate the feasibility and efficiency of using an iterative
method used in geophysics for solving the inverse problem of inferring
from frequency splittings the internal rotation of the Sun or other
stars.
---------------------------------------------------------
Title: The internal dynamics and magnetism of the sun -- the
perspective from global helioseismology (Invited)
Authors: Howe, R.; Hill, F.; Komm, R.; Christensen-Dalsgaard, J.;
Schou, J.; Thompson, M. J.
2009AGUFMSH11B..04H Altcode:
Helioseismology allows us to probe the interior dynamics of the
Sun. Observations over the past three decades reveal the interior
rotation profile, with a near-surface shear layer, differential
rotation throughout the convection zone, a strong shear layer -- the
tachocline -- at the base of the convection zone, and approximately
uniform rotation in the radiative interior. Since the mid 1990's,
continuous observations from the Global Oscillations Network Group and
the Michelson Doppler Imager have allowed the study of subtle temporal
variations in the rotation within the convection zone. The so-called
"torsional oscillation" pattern of migrating zonal flows accompanying
the surface activity migration during the solar cycle has been shown to
penetrate deep within the convection zone. During the current extended
solar minimum, the flow bands can be seen to migrate more slowly towards
the equator than was seen in the previous minimum. There have also been
(still unconfirmed) findings of shorter-term variations in the rotation
rate close to the tachocline during the early years of the previous
solar cycle. This review will describe the important results and give
an update on the most recent observations of the interior dynamics as
we await the rise of solar cycle 24.
---------------------------------------------------------
Title: The Herschel ATLAS Key Project
Authors: Serjeant, S.; Eales, S.; Dunne, L.; Clements, D.; Cooray, A.;
de Zotti, G.; Dye, S.; Ivison, R.; Jarvis, M.; Lagache, G.; Maddox,
S.; Negrello, M.; Thompson, M.; Herschel Atlas Consortium
2009ASPC..418..523S Altcode:
The Herschel Astrophysical Terahertz Large Area Survey (ATLAS) is the
largest Open Time Key Project on the Herschel Space Observatory. This
legacy survey will cover 550 deg<SUP>2</SUP>, an order of magnitude
larger than all other Herschel extragalactic surveys combined, and
will provide more extragalactic sources than all other Herschel
surveys combined. Herschel ATLAS builds on the ground-breaking
AKARI All-Sky Survey and has six primary science themes, described
here. More information can be found on the consortium web site,
http://h-atlas.astro.cf.ac.uk .
---------------------------------------------------------
Title: Numerical Simulation of Acoustic Wave Propagation in the
Solar Sub-Photosphere with Localized Magnetic Field Concentration
Authors: Shelyag, S.; Zharkov, S.; Fedun, V.; Erdélyi, R.; Thompson,
M. J.
2009ASPC..416..167S Altcode:
The results of numerical simulations of acoustic wave propagation and
dispersion in the solar sub-photosphere with a localised magnetic
field concentration are presented. The initial equilibrium density
and pressure stratifications are derived from a standard solar
model and adjusted to maintain magnetohydrostatic and convective
stability. Acoustic waves are generated by a perturbation located
at the height corresponding to the visible surface of the Sun. The
time-distance diagram of the vertical velocity perturbation at the level
corresponding to the visible solar surface shows that the magnetic
field perturbs and scatters acoustic waves and absorbs the acoustic
power of the wave packet.
---------------------------------------------------------
Title: The Torsional Oscillation and the Solar Minimum
Authors: Howe, R.; Hill, F.; Komm, R.; Christensen-Dalsgaard, J.;
Schou, J.; Thompson, M. J.
2009AGUFM.U34A..03H Altcode:
The so-called torsional oscillation is a pattern of zonal flow bands,
detected at the solar surface by direct Doppler measurements and within
the convection zone by helioseismic measurements such as those carried
out by the Global Oscillations Network Group and the Michelson Doppler
Imager, that migrates from mid-latitudes towards the equator and poles
with each solar cycle. In the current minimum the low-latitude branch
of the pattern can be seen to have taken at least a year longer to
migrate towards the equator than was the case in the previous minimum. A
flow configuration matching that of the previous minimum was reached
during 2008, and by early 2009 the fast-rotating belt associated with
the new cycle had reached the latitude at which the onset of activity
was seen in Cycle 23, but magnetic activity has remained low. We will
present the most recent results and consider the implications for the
new solar cycle.
---------------------------------------------------------
Title: The Torsional Oscillation and the Solar Cycle: Is it Minimum
Yet?
Authors: Howe, R.; Komm, R.; Hill, F.; Larson, T.; Schou, J.; Thompson,
M. J.; Ulrich, R. K.
2009ASPC..416..269H Altcode:
The torsional oscillation pattern of migrating zonal flows is related to
the solar activity cycle. In the approach to solar minimum, we compare
the current flow profile with that seen at the previous minimum, using
Global Oscillation Network Group (GONG) and Michelson Doppler Imager
(MDI) data as well as Mount Wilson Doppler observations that reach
further back in time. Will the flow pattern at the upcoming minimum
match that for the previous one?
---------------------------------------------------------
Title: Mode identification in rapidly rotating stars
Authors: Reese, D. R.; Thompson, M. J.; MacGregor, K. B.; Jackson,
S.; Skumanich, A.; Metcalfe, T. S.
2009A&A...506..183R Altcode: 2009arXiv0905.4889R
Context: Recent calculations of pulsation modes in rapidly rotating
polytropic models and models based on the Self-Consistent Field method
have shown that the frequency spectrum of low degree pulsation modes can
be described by an empirical formula similar to Tassoul's asymptotic
formula, provided that the underlying rotation profile is not too
differential. <BR />Aims: Given the simplicity of this asymptotic
formula, we investigate whether it can provide a means by which to
identify pulsation modes in rapidly rotating stars. <BR />Methods:
We develop a new mode identification scheme which consists in scanning
a multidimensional parameter space for the formula coefficients which
yield the best-fitting asymptotic spectra. This mode identification
scheme is then tested on artificial spectra based on the asymptotic
formula, on random frequencies and on spectra based on full numerical
eigenmode calculations for which the mode identification is known
beforehand. We also investigate the effects of adding random frequencies
to mimic the effects of chaotic modes which are also expected to show
up in such stars. <BR />Results: In the absence of chaotic modes,
it is possible to accurately find a correct mode identification
for most of the observed frequencies provided these frequencies are
sufficiently close to their asymptotic values. The addition of random
frequencies can very quickly become problematic and hinder correct mode
identification. Modifying the mode identification scheme to reject the
worst fitting modes can bring some improvement but the results still
remain poorer than in the case without chaotic modes.
---------------------------------------------------------
Title: Photospheric high-frequency acoustic power excess in sunspot
umbra: signature of magneto-acoustic modes
Authors: Zharkov, S.; Shelyag, S.; Fedun, V.; Erdélyi, R.; Thompson,
M. J.
2009arXiv0909.5332Z Altcode:
We present observational evidence for the presence of MHD waves in
the solar photosphere deduced from SOHO/MDI Dopplergram velocity
observations. The magneto-acoustic perturbations are observed as
acoustic power enhancement in the sunspot umbra at high-frequency bands
in the velocity component perpendicular to the magnetic field. We use
numerical modelling of wave propagation through localised non-uniform
magnetic field concentration along with the same filtering procedure
as applied to the observations to identify the observed waves. Guided
by the results of the numerical simulations we classify the observed
oscillations as magneto-acoustic waves excited by the trapped
sub-photospheric acoustic waves. We consider the potential application
of the presented method as a diagnostic tool for magnetohelioseismology.
---------------------------------------------------------
Title: A Note on the Torsional Oscillation at Solar Minimum
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
Schou, J.; Thompson, M. J.
2009ApJ...701L..87H Altcode: 2009arXiv0907.2965H
We examine the evolution of the zonal flow pattern in the upper solar
convection zone during the current extended solar minimum, and compare
it with that during the previous minimum. The results suggest that
a configuration matching that at the previous minimum was reached
during 2008, but that the flow band corresponding to the new cycle has
been moving more slowly toward the equator than was observed in the
previous cycle, resulting in a gradual increase in the apparent length
of the cycle during the 2007-2008 period. The current position of the
lower-latitude fast-rotating belt corresponds to that seen around the
onset of activity in the previous cycle.
---------------------------------------------------------
Title: Acoustic wave propagation in the solar sub-photosphere with
localised magnetic field concentration: effect of magnetic tension
Authors: Shelyag, S.; Zharkov, S.; Fedun, V.; Erdélyi, R.; Thompson,
M. J.
2009A&A...501..735S Altcode: 2009arXiv0901.3680S
Aims: We analyse numerically the propagation and dispersion of acoustic
waves in the solar-like sub-photosphere with localised non-uniform
magnetic field concentrations, mimicking sunspots with various
representative magnetic field configurations. <BR />Methods: Numerical
simulations of wave propagation through the solar sub-photosphere
with a localised magnetic field concentration are carried out using
SAC, which solves the MHD equations for gravitationally stratified
plasma. The initial equilibrium density and pressure stratifications
are derived from a standard solar model. Acoustic waves are generated
by a source located at the height corresponding approximately to
the visible surface of the Sun. By means of local helioseismology we
analyse the response of vertical velocity at the level corresponding
to the visible solar surface to changes induced by magnetic field in
the interior. <BR />Results: The results of numerical simulations of
acoustic wave propagation and dispersion in the solar sub-photosphere
with localised magnetic field concentrations of various types are
presented. Time-distance diagrams of the vertical velocity perturbation
at the level corresponding to the visible solar surface show that the
magnetic field perturbs and scatters acoustic waves and absorbs the
acoustic power of the wave packet. For the weakly magnetised case, the
effect of magnetic field is mainly thermodynamic, since the magnetic
field changes the temperature stratification. However, we observe
the signature of slow magnetoacoustic mode, propagating downwards,
for the strong magnetic field cases.
---------------------------------------------------------
Title: VISTA Milky Way Public Survey
Authors: Minniti, D.; Lucas, P.; Ahumada, A. V.; Zoccali, M.; Catelan,
M.; Morelli, L.; Tappert, C.; Pignata, G.; Toledo, I.; Ruiz, M. T.;
Carraro, G.; Casassus, S.; Bronfman, L.; Barbá, R. H.; Gamen, R.;
Gieren, W.; Geisler, D.; Pietrzynski, G.; Mennickent, R. E.; Kurtev,
R.; Borissova, J.; Mirabel, F.; Ivanov, V. D.; Saviane, I.; Vanzi, L.;
Monaco, L.; Rejkuba, M.; Messineo, M.; Bedin, L.; Stephens, A.; Barbuy,
B.; Bica, E.; Clariá, J. J.; CASU (VDFS) Team; WFAU (VDFS) Team;
Emerson, J.; Drew, J.; López-Correidora, M.; Martin, E.; Goldman,
B.; Gianinni, T.; Eisloeffel, J.; Groot, P.; Fabregat, J.; Hambly,
N.; Longmore, A.; Walton, N.; de Grijs, R.; Hoare, M.; Schroeder,
A.; Naylor, T.; Barlow, M.; Zijlstra, A.; White, G.; Gosling, A.;
McGowan, K.; Adamson, A.; Bandyopadhyay, R.; Thompson, M.; Cropper,
M.; Lucey, J.; Kerins, E.; Hodgkin, S.; Pinfield, D.
2009RMxAC..35..263M Altcode:
We propose a public IR variability survey, named “Vista Variables
in the Vía Láctea” (VVV), of the Milky Way bulge and an adjacent
section of the mid-plane where star formation activity is high. This
would take 1920 hours, covering ∼ 10^9 point sources within an area
of 520 sq deg, including 33 known globular clusters and ∼ 350 open
clusters. The final products will be a deep IR atlas in 5 passbands and
a catalogue of ∼ 10^6 variable point sources. These will produce a
3-D map of the surveyed region (unlike single-epoch surveys that only
give 2-D maps) using well-understood primary distance indicators such
as RR Lyrae stars. It will yield important information on the ages
of the populations. The observations will be combined with data from
MACHO, OGLE, EROS, VST, SPITZER, HST, CHANDRA, INTEGRAL, and ALMA for
a complete understanding of the variable sources in the inner Milky
Way. Several important implications for the history of the Milky Way,
for globular cluster evolution, for the population census of the bulge
and center, and for pulsation theory would follow from this survey.
---------------------------------------------------------
Title: Helioseismology of Sunspots: A Case Study of NOAA Region 9787
Authors: Gizon, L.; Schunker, H.; Baldner, C. S.; Basu, S.; Birch,
A. C.; Bogart, R. S.; Braun, D. C.; Cameron, R.; Duvall, T. L.;
Hanasoge, S. M.; Jackiewicz, J.; Roth, M.; Stahn, T.; Thompson, M. J.;
Zharkov, S.
2009SSRv..144..249G Altcode: 2008SSRv..tmp..188G; 2010arXiv1002.2369G
Various methods of helioseismology are used to study the subsurface
properties of the sunspot in NOAA Active Region 9787. This sunspot
was chosen because it is axisymmetric, shows little evolution during
20-28 January 2002, and was observed continuously by the MDI/SOHO
instrument. AR 9787 is visible on helioseismic maps of the farside
of the Sun from 15 January, i.e. days before it crossed the East
limb. Oscillations have reduced amplitudes in the sunspot at all
frequencies, whereas a region of enhanced acoustic power above 5.5 mHz
(above the quiet-Sun acoustic cutoff) is seen outside the sunspot and
the plage region. This enhanced acoustic power has been suggested to
be caused by the conversion of acoustic waves into magneto-acoustic
waves that are refracted back into the interior and re-emerge as
acoustic waves in the quiet Sun. Observations show that the sunspot
absorbs a significant fraction of the incoming p and f modes around 3
mHz. A numerical simulation of MHD wave propagation through a simple
model of AR 9787 confirmed that wave absorption is likely to be due
to the partial conversion of incoming waves into magneto-acoustic
waves that propagate down the sunspot. Wave travel times and mode
frequencies are affected by the sunspot. In most cases, wave packets
that propagate through the sunspot have reduced travel times. At
short travel distances, however, the sign of the travel-time shifts
appears to depend sensitively on how the data are processed and,
in particular, on filtering in frequency-wavenumber space. We carry
out two linear inversions for wave speed: one using travel-times
and phase-speed filters and the other one using mode frequencies
from ring analysis. These two inversions give subsurface wave-speed
profiles with opposite signs and different amplitudes. The travel-time
measurements also imply different subsurface flow patterns in the
surface layer depending on the filtering procedure that is used. Current
sensitivity kernels are unable to reconcile these measurements, perhaps
because they rely on imperfect models of the power spectrum of solar
oscillations. We present a linear inversion for flows of ridge-filtered
travel times. This inversion shows a horizontal outflow in the upper
4 Mm that is consistent with the moat flow deduced from the surface
motion of moving magnetic features. From this study of AR 9787, we
conclude that we are currently unable to provide a unified description
of the subsurface structure and dynamics of the sunspot.
---------------------------------------------------------
Title: The Solar Dynamo
Authors: Weiss, N. O.; Thompson, M. J.
2009SSRv..144...53W Altcode: 2008SSRv..tmp..155W
It is generally accepted that the strong toroidal magnetic fields that
emerge through the solar surface in sunspots and active regions are
formed by the action of differential rotation on a poloidal field,
and then stored in or near the tachocline at the base of the Sun’s
convection zone. The problem is how to explain the generation of
a reversed poloidal field from this toroidal flux—a process that
can be parametrised in terms of an α-effect related to some form
of turbulent helicity. Here we first outline the principal patterns
that have to be explained: the 11-year activity cycle, the 22-year
magnetic cycle and the longer term modulation of cyclic activity,
associated with grand maxima and minima. Then we summarise what has
been learnt from helioseismology about the Sun’s internal structure
and rotation that may be relevant to our subject. The ingredients
of mean-field dynamo models are differential rotation, meridional
circulation, turbulent diffusion, flux pumping and the α-effect:
in various combinations they can reproduce the principal features
that are observed. To proceed further, it is necessary to rely on
large-scale computation and we summarise the current state of play.
---------------------------------------------------------
Title: Introduction to Solar Magnetism: The Early Years
Authors: Balogh, A.; Thompson, M. J.
2009SSRv..144....1B Altcode:
The year 2008 marked the one hundredth anniversary of the observational
discovery by George Ellery Hale of magnetic field in sunspots (Hale
in Astrophys. J. 28:315-343, 1908). This observation, the first to
suggest a direct link between the best-known variable features on
the Sun and magnetism, started a line of research that has widened
considerably over the last 100 years and is continuing today. Knowledge
about all aspects of the Sun has increased in a remarkable way over
the past few decades. Variations in the appearance of the Sun and its
corona, as well as deeper sources of quasi-regular and chaotic changes
that make up solar variability have been extensively documented by
both ground-based and space-based solar observatories. It has been
recognized that solar magnetism is the key phenomenon that drives
solar variability. The workshop devoted to the origin and dynamics of
solar magnetism held in the International Space Science Institute in
Bern, Switzerland, from 21 to 25 January 2008 reviewed the status of
the field and has led to this volume that brings together the best
available knowledge and understanding of solar magnetism 100 years
after Hale’s pioneering paper. This introductory paper gives an
outline of the history of research into solar variability up to the
work of Hale and his colleagues. The achievements of the past decades
are discussed extensively in the other contributions to this volume.
---------------------------------------------------------
Title: Introduction to Solar Magnetism: The Early Years
Authors: Balogh, A.; Thompson, M. J.
2009odsm.book....1B Altcode:
The year 2008 marked the one hundredth anniversary of the observational
discovery by George Ellery Hale of magnetic field in sunspots (Hale
in Astrophys. J. 28:315-343, 1908). This observation, the first to
suggest a direct link between the best-known variable features on
the Sun and magnetism, started a line of research that has widened
considerably over the last 100 years and is continuing today. Knowledge
about all aspects of the Sun has increased in a remarkable way over
the past few decades. Variations in the appearance of the Sun and its
corona, as well as deeper sources of quasi-regular and chaotic changes
that make up solar variability have been extensively documented by
both ground-based and space-based solar observatories. It has been
recognized that solar magnetism is the key phenomenon that drives
solar variability. The workshop devoted to the origin and dynamics
of solar magnetism held in the International Space Science Institute
in Bern, Switzerland, from 21 to 25 January 2008 reviewed the status
of the field and has led to this volume that brings together the best
available knowledge and understanding of solar magnetism 100 years after
Hale's pioneering paper. This introductory paper gives an outline of
the history of research into solar variability up to the work of Hale
and his colleagues. The achievements of the past decades are discussed
extensively in the other contributions to this volume.
---------------------------------------------------------
Title: The Solar Dynamo
Authors: Weiss, N. O.; Thompson, M. J.
2009odsm.book...53W Altcode:
It is generally accepted that the strong toroidal magnetic fields that
emerge through the solar surface in sunspots and active regions are
formed by the action of differential rotation on a poloidal field,
and then stored in or near the tachocline at the base of the Sun's
convection zone. The problem is how to explain the generation of
a reversed poloidal field from this toroidal flux—a process that
can be parametrised in terms of an α-effect related to some form
of turbulent helicity. Here we first outline the principal patterns
that have to be explained: the 11-year activity cycle, the 22-year
magnetic cycle and the longer term modulation of cyclic activity,
associated with grand maxima and minima. Then we summarise what has
been learnt from helioseismology about the Sun's internal structure
and rotation that may be relevant to our subject. The ingredients
of mean-field dynamo models are differential rotation, meridional
circulation, turbulent diffusion, flux pumping and the α-effect:
in various combinations they can reproduce the principal features
that are observed. To proceed further, it is necessary to rely on
large-scale computation and we summarise the current state of play.
---------------------------------------------------------
Title: The Origin and Dynamics of Solar Magnetism
Authors: Thompson, M. J.; Balogh, A.; Culhane, J. L.; Nordlund, Å.;
Solanki, S. K.; Zahn, J. -P.
2009odsm.book.....T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Helioseismology of Sunspots: A Case Study of NOAA Region 9787
Authors: Gizon, L.; Schunker, H.; Baldner, C. S.; Basu, S.; Birch,
A. C.; Bogart, R. S.; Braun, D. C.; Cameron, R.; Duvall, T. L.;
Hanasoge, S. M.; Jackiewicz, J.; Roth, M.; Stahn, T.; Thompson, M. J.;
Zharkov, S.
2009odsm.book..249G Altcode:
Various methods of helioseismology are used to study the subsurface
properties of the sunspot in NOAA Active Region 9787. This sunspot
was chosen because it is axisymmetric, shows little evolution during
20-28 January 2002, and was observed continuously by the MDI/SOHO
instrument. AR 9787 is visible on helioseismic maps of the farside of
the Sun from 15 January, i.e. days before it crossed the East limb.
---------------------------------------------------------
Title: Recent Developments in Local Helioseismology
Authors: Thompson, M. J.; Zharkov, S.
2008SoPh..251..225T Altcode: 2008SoPh..tmp...42T
Local helioseismology is providing new views of subphotospheric flows
from supergranulation to global-scale meridional circulation and for
studying structures and dynamics in the quiet Sun and active regions. In
this short review we focus on recent developments, and in particular
on a number of current issues, including the sensitivity of different
measures of travel time and testing the forward modelling used in local
helioseismology. We discuss observational and theoretical concerns
regarding the adequacy of current analyses of waves in sunspots and
active regions, and we report on recent progress in the use of numerical
simulations to test local helioseismic methods.
---------------------------------------------------------
Title: Time Distance Analysis of the Emerging Active Region
NOAA 10790
Authors: Zharkov, S.; Thompson, M. J.
2008SoPh..251..369Z Altcode: 2008arXiv0807.3000Z; 2008SoPh..tmp..140Z
We investigate the emergence of Active Region NOAA 10790 by means of
time - distance helioseismology. Shallow regions of increased sound
speed at the location of increased magnetic activity are observed,
with regions becoming deeper at the locations of sunspot pores. We also
see a long-lasting region of decreased sound speed located underneath
the region of the flux emergence, possibly relating to a temperature
perturbation due to magnetic quenching of eddy diffusivity, or to
a dense flux tube. We detect and track an object in the subsurface
layers of the Sun characterised by increased sound speed which could
be related to emerging magnetic-flux and thus obtain a provisional
estimate of the speed of emergence of around 1 km s<SUP>−1</SUP>.
---------------------------------------------------------
Title: Editors' note
Authors: Jiménez Reyes, S. J.; Reese, D. R.; Thompson, M. J.
2008AN....329..439J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Views of the Solar Torsional Oscillation
Authors: Howe, R.; Komm, R. W.; Hill, F.; Schou, J.; Thompson, M. J.
2008AGUSMSP41A..05H Altcode:
The pattern of zonal flows migrating towards the equator over the
solar cycle, known as the torsional oscillation, is well established
from both helioseismology and surface Doppler measurements. However,
the exact appearance of the pattern will vary depending on the form of
the overall rotation profile that has been subtracted, even when the
data cover a full eleven-year cycle. Here we compare the appearance
of the flow pattern when applying several different methods to the
MDI and GONG data for Solar Cycle 23.
---------------------------------------------------------
Title: Stellar Astrophysical Fluid Dynamics
Authors: Thompson, Michael J.; Christensen-Dalsgaard, Jørgen
2008safd.book.....T Altcode:
Preface; 1. A selective overview Jørgen Christensen-Dalsgaard and
Michael J. Thompson; Part I. Stellar Convection and Oscillations:
2. On the diversity of stellar pulsations Wojciech A. Dziembowski;
3. Acoustic radiation and mode excitation by turbulent convection
Günter Houdek; 4. Understanding roAp stars Margarida S. Cunha; 5. Waves
in the magnetised solar atmosphere Colin S. Rosenthal; Part II. Stellar
Rotation and Magnetic Fields: 6. Stellar rotation: a historical survey
Leon Mestel; 7. The oscillations of rapidly rotating stars Michel
Rieutord; 8. Solar tachocline dynamics: eddy viscosity, anti-friction,
or something in between? Michael E. McIntyre; 9. Dynamics of the solar
tachocline Pascale Garaud; 10. Dynamo processes: the interaction of
turbulence and magnetic fields Michael Proctor; 11. Dynamos in planets
Chris Jones; Part III. Physics and Structure of Stellar Interiors:
12. Solar constraints on the equation of state Werner Däppen;
13. 3He transport and the solar neutrino problem Chris Jordinson;
14. Mixing in stellar radiation zones Jean-Paul Zahn; 15. Element
settling and rotation-induced mixing in slowly rotating stars Sylvie
Vauclair; Part IV. Helio- and Asteroseismology: 16. Solar structure
and the neutrino problem Hiromoto Shibahashi; 17. Helioseismic data
analysis Jesper Schou; 18. Seismology of solar rotation Takashi Sekii;
19. Telechronohelioseismology Alexander Kosovichev; Part V. Large-Scale
Numerical Experiments: 20. Bridges between helioseismology and models
of convection zone dynamics Juri Toomre; 21. Numerical simulations of
the solar convection zone Julian R. Elliott; 22. Modelling solar and
stellar magnetoconvection Nigel Weiss; 23. Nonlinear magnetoconvection
in the presence of a strong oblique field Keith Julien, Edgar Knobloch
and Steven M. Tobias; 24. Simulations of astrophysical fluids Marcus
Brüggen; Part VI. Dynamics: 25. A magic electromagnetic field Donald
Lynden-Bell; 26. Continuum equations for stellar dynamics Edward
A. Spiegel and Jean-Luc Thiffeault; 27. Formation of planetary systems
Douglas N. C. Lin; 28. The solar-cycle global warming as inferred from
sky brightness variation Wasaburo Unno and Hiromoto Shibahashi.
---------------------------------------------------------
Title: Meridional flow profile measurements with SOHO/MDI
Authors: Mitra-Kraev, U.; Thompson, M. J.
2007AN....328.1009M Altcode: 2007arXiv0711.4968M
We present meridional flow measurements of the Sun using a novel
helioseismic approach for analyzing SOHO/MDI data in order to push
the current limits in radial depth. Analyzing three consecutive months
of data during solar minimum, we find that the meridional flow is as
expected poleward in the upper convection zone, turns equatorward at a
depth of around 40 Mm (∼0.95 R_⊙), and possibly changes direction
again in the lower convection zone. This may indicate two meridional
circulation cells in each hemisphere, one beneath the other.
---------------------------------------------------------
Title: Varied Mechanisms for Star Formation in Bright-Rimmed Clouds
Authors: Morgan, Larry; Urquhart, J.; Thompson, M.; White, G.;
Figura, C.
2007AAS...211.8914M Altcode: 2007BAAS...39..880M
Bright-rimmed clouds (BRCs) are potential examples of triggered
star-formation regions, in which photoionisation driven shocks caused
by the expansion of HII regions induce protostellar collapse within the
clouds. A sample of optically bright BRCs at the edge of HII regions
has been observed at multiple wavelengths in order to investigate the
possibility that star-formation is present. Such activity may be related
to photoionisation induced shocks caused by the massive stars powering
the HII regions. <P />The sample has been observed at radio, infrared
and submillimetre wavelengths, these observations reveal dense cores
present within the heads of 44 observed BRCs drawn from a catalogue of
IRAS sources embedded within HII regions, supportive of the scenario
proposed by radiatively driven implosion (RDI) models. The physical
properties of these cores indicate the presence of star formation
across the majority of our sample. This star-formation appears to
be predominately in the regime of intermediate to high mass and may
indicate the formation of clusters. IR observations indicate the
association of early star forming sources with the sample. <P />A
fundamental difference appears to exist between different morphological
types of BRC. Morphological variations in BRCs have previously been
attributed to an evolutionary scenario of RDI. However, the physical
properties of cores found within different types of BRC indicate that
the strength of the ambient ionisation field is highly correlated with
the attributes of certain cores, and not with others. The suggestion
is that different morphological types of BRC have followed different
evolutionary pathways, this is supported by the mass distributions of
cores associated with the different morphologies.
---------------------------------------------------------
Title: Asteroseismology and interferometry
Authors: Cunha, M. S.; Aerts, C.; Christensen-Dalsgaard, J.;
Baglin, A.; Bigot, L.; Brown, T. M.; Catala, C.; Creevey, O. L.;
Domiciano de Souza, A.; Eggenberger, P.; Garcia, P. J. V.; Grundahl,
F.; Kervella, P.; Kurtz, D. W.; Mathias, P.; Miglio, A.; Monteiro,
M. J. P. F. G.; Perrin, G.; Pijpers, F. P.; Pourbaix, D.; Quirrenbach,
A.; Rousselet-Perraut, K.; Teixeira, T. C.; Thévenin, F.; Thompson,
M. J.
2007A&ARv..14..217C Altcode: 2007arXiv0709.4613C
Asteroseismology provides us with a unique opportunity to improve
our understanding of stellar structure and evolution. Recent
developments, including the first systematic studies of solar-like
pulsators, have boosted the impact of this field of research within
astrophysics and have led to a significant increase in the size of
the research community. In the present paper we start by reviewing
the basic observational and theoretical properties of classical and
solar-like pulsators and present results from some of the most recent
and outstanding studies of these stars. We centre our review on those
classes of pulsators for which interferometric studies are expected
to provide a significant input. We discuss current limitations to
asteroseismic studies, including difficulties in mode identification
and in the accurate determination of global parameters of pulsating
stars, and, after a brief review of those aspects of interferometry
that are most relevant in this context, anticipate how interferometric
observations may contribute to overcome these limitations. Moreover,
we present results of recent pilot studies of pulsating stars involving
both asteroseismic and interferometric constraints and look into the
future, summarizing ongoing efforts concerning the development of
future instruments and satellite missions which are expected to have
an impact in this field of research.
---------------------------------------------------------
Title: Joint Discussion 17 Highlights of recent progress in the
seismology of the Sun and Sun-like stars
Authors: Bedding, Timothy R.; Brun, Allan S.; Christensen-Dalsgaard,
Jørgen; Crouch, Ashley; De Cat, Peter; García, Raphael A.; Gizon,
Laurent; Hill, Frank; Kjeldsen, Hans; Leibacher, John W.; Maillard,
Jean-Pierre; Mathis, S.; Rabello-Soares, M. Cristina; Rozelot,
Jean-Pierre; Rempel, Matthias; Roxburgh, Ian W.; Samadi, Réza; Talon,
Suzanne; Thompson, Michael J.
2007HiA....14..491B Altcode:
The seismology and physics of localized structures beneath the surface
of the Sun takes on a special significance with the completion in
2006 of a solar cycle of observations by the ground-based Global
Oscillation Network Group (GONG) and by the instruments on board the
Solar and Heliospheric Observatory (SOHO). Of course, the spatially
unresolved Birmingham Solar Oscillation Network (BiSON) has been
observing for even longer. At the same time, the testing of models of
stellar structure moves into high gear with the extension of deep probes
from the Sun to other solar-like stars and other multi-mode pulsators,
with ever-improving observations made from the ground, the success of
the MOST satellite, and the recently launched CoRoT satellite. Here
we report the current state of the two closely related and rapidly
developing fields of helio- and asteroseimology.
---------------------------------------------------------
Title: Forward modelling of sub-photospheric flows for time-distance
helioseismology
Authors: Shelyag, S.; Erdélyi, R.; Thompson, M. J.
2007A&A...469.1101S Altcode: 2007astro.ph..3067S
Context: The results of forward modelling of acoustic wave propagation
in a realistic solar sub-photosphere with two cases of steady
horizontal flows are presented and analysed by the means of local
helioseismology. <BR />Aims: This paper is devoted to an analysis
of the influence of steady flows on the propagation of sound waves
through the solar interior. <BR />Methods: The simulations are based
on fully compressible ideal hydrodynamical modelling in a Cartesian
grid. The initial model is characterised by solar density and pressure
stratifications taken from the standard Model S and is adjusted in
order to suppress convective instability. Acoustic waves are excited
by a non-harmonic source located below the depth corresponding to
the visible surface of the Sun. Numerical experiments with coherent
horizontal flows of linear and Gaussian dependences of flow speed on
depth are carried out. These flow fields may mimic horizontal motions
of plasma surrounding a sunspot, differential rotation or meridional
circulation. An inversion of the velocity profiles from the simulated
travel time differences is carried out. The inversion is based on
the ray approximation. The results of inversion are then compared
with the original velocity profiles. <BR />Results: The results
of forward modelling of acoustic wave propagation in a realistic
solar sub-photosphere with two cases of steady horizontal flows are
presented. The influence of steady flow on the propagation of sound
waves through the solar interior is analysed. A time-distance analysis
technique is applied to compute the direct observable signatures of
the background bulk motions on travel times and phase shifts. This
approach allows direct comparison with observational data. Further,
we propose a method of obtaining the travel-time differences for the
waves propagating in sub-photospheric solar regions with horizontal
flows. The method employs directly the difference between travel-time
diagrams of waves propagating with and against the background flow. <BR
/>Conclusions: The analysis shows that the flow speed profiles obtained
from inversion based on the ray approximation differ from the original
ones. The difference between the original and observed profiles is
caused by the fact that the wave packets propagate along the ray
bundle, which has a finite extent, and thus reach deeper regions of
the sub-photosphere in comparison with ray theory.
---------------------------------------------------------
Title: Optimized data masks for focussed solar tomography: background
and artificial diagnostic experiments
Authors: Hughes, S. J.; Pijpers, F. P.; Thompson, M. J.
2007A&A...468..341H Altcode:
Context: The use of solar tomography for detecting subsurface
features in the Sun is now well established. It customarily proceeds
from an analysis of data on the solar surface given weightings in
a predetermined geometric (e.g. centre-annulus) configuration. <BR
/>Aims: We seek to improve these weightings by developing a scheme for
choosing optimal combinations of data that maximise the contribution
from signal at a desired horizontal and depth location. <BR />Methods:
We employ a subtractive optimally localized averaging (SOLA) scheme
to pick weights for particular data points and analyse the quality of
the results. <BR />Results: We show in this work that particularly by
using wave kernels instead of rays for modelling purposes, one can do
well at localizing a measurement through our techniques while achieving
desirable error-magnification properties.
---------------------------------------------------------
Title: Solar Cycle Changes Over 11 Years of Medium-Degree Helioseismic
Observations
Authors: Howe, Rachel; Komm, R. W.; Hill, F.; Christensen-Dalsgaard,
J.; Schou, J.; Thompson, M. J.
2007AAS...210.2218H Altcode: 2007BAAS...39..127H
The Global Oscillations Network Group (GONG) has now completed, and
the Michelson Doppler Imager (MDI) aboard SOHO will soon complete,
a full eleven years of continuous observations of the medium-degree
solar oscillations. This enables us to follow changes in the acoustic
mode parameters and interior dynamics over a full solar cycle. We
present results from observations of convection-zone dynamics, in
which the torsional oscillation pattern seen at the surface can be
followed throughout most of the bulk of the convection zone, and also
changes in the frequency, lifetime and amplitude of the modes which
can be shown to be closely related in space and time to the migrating
pattern of surface activity. <P />This work utilizes data obtained by
the Global Oscillation Network Group (GONG) program, managed by the
National Solar Observatory, which is operated by AURA, Inc. under a
cooperative agreement with the National Science Foundation. SOHO is
a mission of international cooperation between ESA and NASA.
---------------------------------------------------------
Title: Time distance study of isolated sunspots
Authors: Zharkov, S.; Nicholas, C. J.; Thompson, M. J.
2007AN....328..240Z Altcode: 2008arXiv0802.2524Z
We present a comparative seismic study of conditions around and beneath
isolated sunspots. Using the European Grid of Solar Observations'
Solar Feature Catalogue of sunspots derived from SOHO/MDI continuum and
magnetogram data, 1996-2005, we identify a set of isolated sunspots by
checking that within a Carrington Rotation there were no other spots
detected in the vicinity. We then use level-2 tracked MDI Dopplergrams
available from SOHO website to investigate wave-speed perturbations
of such sunspots using time-distance helioseismology.
---------------------------------------------------------
Title: A procedure for the inversion of f-mode travel times for
solar flows
Authors: Jackiewicz, J.; Gizon, L.; Birch, A. C.; Thompson, M. J.
2007AN....328..234J Altcode: 2007astro.ph..2345J
We perform a two-dimensional inversion of f-mode travel times
to determine near-surface solar flows. The inversion is based on
optimally localized averaging of travel times. We use finite-wavelength
travel-time sensitivity functions and a realistic model of the data
errors. We find that it is possible to obtain a spatial resolution
of 2 Mm. The error in the resulting flow estimate ultimately depends
on the observation time and the number of travel distances used in
the inversion.
---------------------------------------------------------
Title: Outstanding problems in local helioseismology
Authors: Gizon, L.; Thompson, M. J.
2007AN....328..204G Altcode: 2010arXiv1002.2347G
Time-distance helioseismology and related techniques show great promise
for probing the structure and dynamics of the subphotospheric layers
of the Sun. Indeed time-distance helioseismology has already been
applied to make inferences about structures and flows under sunspots
and active regions, to map long-lived convective flow patterns, and
so on. Yet certainly there are still many inadequacies in the current
approaches and, as the data get better and the questions we seek to
address get more subtle, methods that were previously regarded as
adequate are no longer acceptable. Here we give a short and partial
description of outstanding problems in local helioseismology, using
time-distance helioseismology as a guiding example.
---------------------------------------------------------
Title: The Effect of Abnormal Granulation on Acoustic Wave Travel
Times and Mode Frequencies
Authors: Petrovay, K.; Erdélyi, R.; Thompson, M. J.
2007SoPh..240..197P Altcode: 2007astro.ph..2076P
Observations indicate that in plage areas (i.e. in active regions
outside sunspots) acoustic waves travel faster than in the quiet Sun,
leading to shortened travel times and higher p-mode frequencies. Coupled
with the 11-year variation of solar activity, this may also explain the
solar cycle variation of oscillation frequencies. While it is clear
that the ultimate cause of any difference between the quiet Sun and
plage is the presence of magnetic fields of order 100 G in the latter,
the mechanism by which the magnetic field exerts its influence has
not yet been conclusively identified. One possible such mechanism is
suggested by the observation that granular motions in plage areas tend
to be slightly "abnormal", dampened compared to the quiet Sun.
---------------------------------------------------------
Title: A Magnetometer For The Solar Orbiter Mission
Authors: Carr, C. M.; Horbury, T. S.; Balogh, A.; Baumjohann, W.;
Bavassano, B.; Breen, A.; Burgess, D.; Cargill, P. J.; Brooker, N.;
Erdõs, G.; Fletcher, L.; Forsyth, R. J.; Giacalone, J.; Glassmeier,
K. -H.; Hoeksema, J. T.; Goldstein, M. L.; Lockwood, M.; Magnes, W.;
Masimovic, M.; Marsch, G.; Matthaeus, W. H.; Murphy, N.; Nakariakov,
V. M.; Pacheco, J. R.; Pincon, J. -L.; Riley, P.; Russell, C. T.;
Schwartz, S. J.; Szabo, A.; Thompson, M.; Vainio, R.; Velli, M.;
Vennerstrom, S.; Walsh, R.; Wimmer-Schweingruber, R.; Zank, G.
2007ESASP.641E..41C Altcode:
The magnetometer is a key instrument to the Solar Orbiter mission. The
magnetic field is a fundamental parameter in any plasma: a precise
and accurate measurement of the field is essential for understanding
almost all aspects of plasma dynamics such as shocks and stream-stream
interactions. Many of Solar Orbiter's mission goals are focussed
around the links between the Sun and space. A combination of in situ
measurements by the magnetometer, remote measurements of solar magnetic
fields and global modelling is required to determine this link and
hence how the Sun affects interplanetary space. The magnetic field
is typically one of the most precisely measured plasma parameters and
is therefore the most commonly used measurement for studies of waves,
turbulence and other small scale phenomena. It is also related to the
coronal magnetic field which cannot be measured directly. Accurate
knowledge of the magnetic field is essential for the calculation of
fundamental plasma parameters such as the plasma beta, Alfvén speed
and gyroperiod. We describe here the objectives and context of magnetic
field measurements on Solar Orbiter and an instrument that fulfils those
objectives as defined by the scientific requirements for the mission.
---------------------------------------------------------
Title: The Parkes methanol multibeam survey
Authors: Cohen, R. J.; Caswell, J. L.; Brooks, K.; Burton, M. G.;
Chrysostomou, A.; Cox, J.; Diamond, P. J.; Ellingsen, S.; Fuller,
G. A.; Gray, M. D.; Green, J. A.; Hoare, M. G.; Masheder, M. R. W.;
McClure-Griffiths, N.; Pestalozzi, M.; Phillips, C.; Thompson, M.;
Voronkov, M.; Walsh, A.; Ward-Thompson, D.; Wong-McSweeney, D.; Yates,
J. A.
2007IAUS..237..403C Altcode: 2006IAUS..237E..89B
A new 7-beam methanol multibeam receiver was successfully commissioned
at Parkes in January, and has begun surveying the Milky Way for newly
forming stars, that are pinpointed by strong methanol maser emission
at 6.7 GHz. The Parkes survey of the Milky Way for methanol masers is
two orders of magnitude faster than previous systematic surveys using
30-m class dishes. The first 26 days of observations have yielded
377 methanol sources, of which 150 are new discoveries. Preliminary
results will be presented.
---------------------------------------------------------
Title: Observational results and issues concerning the tachocline
Authors: Christensen-Dalsgaard, Jørgen; Thompson, Michael J.
2007sota.conf...53C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Temporal variations in solar rotation at the bottom of the
convection zone: The current status
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
Schou, J.; Thompson, M. J.; Toomre, J.
2007AdSpR..40..915H Altcode:
We present the most recent results on the short-period variations
in the solar rotation rate near the base of the convection zone. The
1.3-year period which was reported in the early years of solar cycle 23
appears not to persist after 2001, but there are hints of fluctuations
at a different period during the declining phase of the cycle.
---------------------------------------------------------
Title: T he Solar Dynamo - What Have We Learned From Helioseismology?
Authors: Thompson, M. J.
2007ESASP.641E..25T Altcode: 2006ESASP.641E..25T
Helioseismology provides a unique tool for probing the solar dynamo by
observing the evolution of the solar interior over the solar activity
cycle. In particular, helioseismology has now imaged the subphotospheric
large-scale flows (solar subsurface weather), differential rotation
and meridional circulation. It has also probed the stratifica- tion
and flows under active regions and sunspots. Here I briefly review the
recent advances from helioseismology in probing aspects of the solar
interior relevant to an understanding of the solar dynamo problem, and
assess the current state of theoretical modelling of the solar dynamo.
---------------------------------------------------------
Title: The Pulsation Properties of the Double-Mode RR Lyrae Variable
V79 in Messier 3
Authors: Clement, C. M.; Thompson, M.
2007JAVSO..35..336C Altcode:
The double-mode RR Lyrae variable V79 in M3 was observed on seven nights
in April 2006 with a 14-inch Schmidt-Cassegrain telescope. A total
of 275 CCD frames were obtained. An analysis of these observations
indicates that the first overtone period P1 was 0.3590 day, the
fundamental period P0 was 0.4834 day, and the amplitude ratio A1 /A0
was 1.00 ± 0.22. These results imply that the fundamental period
increased and that the strength of the fundamental mode oscillations
relative to the first-overtone may have increased since 1998 when the
star was previously observed. The data also indicate that the periods
may fluctuate from cycle to cycle.
---------------------------------------------------------
Title: Forward Modeling of Acoustic Wave Propagation in the Quiet
Solar Subphotosphere
Authors: Shelyag, S.; Erdélyi, R.; Thompson, M. J.
2006ApJ...651..576S Altcode:
The results of numerical simulations of acoustic wave propagation
and dispersion in the nonmagnetic solar subphotosphere are
presented. Initial equilibrium density and pressure stratifications are
taken from a standard solar model but modified to suppress convective
instabilities in fully compressible two-dimensional ideal hydrodynamical
modeling. Acoustic waves are generated by sources located below the
height corresponding to the visible solar surface. The dynamic response
of the solar interior to two acoustic source types, namely a harmonic
source and one representing downward-propagating photospheric plumes,
is studied. A large number of randomly distributed localized cooling
sources with random amplitudes is also introduced. The methods used to
analyze the simulation data are similar to ones used in observational
studies in local helioseismology. Time-distance diagrams of the pressure
and vertical velocity perturbations at the level corresponding to the
solar surface show the appearance of wave packets propagating with
different speeds, which are reflected at different depths beneath the
subphotosphere. The (ω, k<SUB>h</SUB>) power spectra, derived from the
vertical velocity data, show the existence of g-, f-, and p-modes p-mode
ridges are identifiable up to high radial orders of n~11 g-modes appear
in the simulations, unlike in the real Sun, where they cannot propagate
in the convectively unstable solar subphotosphere. Cross-correlation
analysis of vertical velocity perturbations shows a good correspondence
with the observed time-distance helioseismic data for quiet Sun. Thus,
the ability of the implemented approach of forward modeling to
investigate propagation of acoustic, internal, and surface gravity
waves in a realistic solar interior model is shown.
---------------------------------------------------------
Title: Helioseismology of sub-photospheric flows
Authors: Shelyag, S.; Erdélyi, R.; Thompson, M. J.
2006ESASP.624E.123S Altcode: 2006soho...18E.123S
No abstract at ADS
---------------------------------------------------------
Title: The DynaMICS perspective
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
Thompson, M.; Vauclair, S.; Zahn, J. P.
2006ESASP.624E..24T Altcode: 2006soho...18E..24T
No abstract at ADS
---------------------------------------------------------
Title: The effects of rotation on frequency of stellar oscillations
Authors: Burke, K. D.; Thompson, M. J.
2006ESASP.624E.107B Altcode: 2006soho...18E.107B
No abstract at ADS
---------------------------------------------------------
Title: European helio- and asteroseismology network HELAS
Authors: Roth, M.; Luhe, O. v. d.; Palle, P.; Thompson, M. J.;
Christensen-Dalsgaard, J.; Monteiro, M. J. P. F. G.; Gizon, L.;
Di Mauro, M. P.; Aerts, C.; Daszynska-Daszkiewicz, J.; Corbard, T.
2006ESASP.624E.130R Altcode: 2006soho...18E.130R
The Helio- and Asteroseismology Network (HELAS) is a Coordinated
Action funded by the FP6-Infrastructure-Programme of the European
Commission. Currently, HELAS consists of ten members. The objective
of HELAS is to co-ordinate European activities in helio- and
asteroseismology. HELAS will transfer knowledge and data analysis
techniques, and will prepare the European research community for
important missions in the immediate future.
---------------------------------------------------------
Title: Effect of sunspot structure from p-modes scattering
Authors: Gordovskyy, M.; Jain, R.; Thompson, M. J.
2006ESASP.624E..14G Altcode: 2006soho...18E..14G
No abstract at ADS
---------------------------------------------------------
Title: Meridional flow measurements with statistical waveform analysis
Authors: Mitra-Kraev, U.; Thompson, M. J.; Woodard, M. F.
2006ESASP.624E..57M Altcode: 2006soho...18E..57M
No abstract at ADS
---------------------------------------------------------
Title: Comparative study of isolated sunspots using time-distance
helioseismology
Authors: Zharkov, S.; Nicholas, C. J.; Thompson, M. J.
2006ESASP.624E..61Z Altcode: 2006soho...18E..61Z
No abstract at ADS
---------------------------------------------------------
Title: Solar Convection Zone Dynamics: How Sensitive Are Inversions
to Subtle Dynamo Features?
Authors: Howe, R.; Rempel, M.; Christensen-Dalsgaard, J.; Hill, F.;
Komm, R.; Larsen, R. M.; Schou, J.; Thompson, M. J.
2006ApJ...649.1155H Altcode:
The nearly 10 year span of medium-degree helioseismic data from the
Global Oscillation Network Group and the Michelson Doppler Imager has
allowed us to study the evolving flows in the solar convection zone
over most of solar cycle 23. Using two independent two-dimensional
rotation inversion techniques and extensive studies of the resolution
using artificial data from different assumed flow profiles, including
those generated from sample mean field dynamo models, we attempt to
assess the reality of certain features seen in the inferred rotation
profiles. Our results suggest that the findings from observations of
a substantial depth dependence of the phase of the zonal flow pattern
in the low latitudes, and the penetration of the flows deep into the
convection zone, are likely to be real rather than artifacts of the
inversion process.
---------------------------------------------------------
Title: SOHO 18/GONG 2006/HELAS I, Beyond the spherical Sun
Authors: Fletcher, Karen; Thompson, Michael
2006ESASP.624E....F Altcode: 2006soho...18E....F
No abstract at ADS
---------------------------------------------------------
Title: Time-Distance Measurements of Cross-Correlation Asymmetries
around NOAA AR 10486
Authors: Jensen, Jesper M.; Pijpers, Frank P.; Thompson, Michael J.
2006ApJ...648L..75J Altcode:
We apply time-distance helioseismology to NOAA AR 10486 in order
to examine the effect the presence of magnetic fields has on the
resulting cross-correlations. Large-amplitude asymmetries between waves
propagating in opposite directions are observed. The asymmetries can
be attributed to suppression and absorption of seismic waves by the
magnetic field. Unraveling the effects of magnetic field on the waves
from the effects of sound-speed perturbations and flows is one of the
major challenges facing time-distance helioseismology.
---------------------------------------------------------
Title: Vista Variables in the Via Lactea (VVV)
Authors: Ahumada, A. V.; Minniti, D.; Adamson, A.; Bandyopadhyay, R.;
Barbá, R.; Barbuy, B.; Barlow, M.; Bedin, L.; Bica, E.; Borissova,
J.; Bronfman, L.; Carraro, G.; Casassus, S.; Catelan, M.; Clariá,
J.; Cropper, M.; Dalton, N.; de Grijs, R.; Drew, J.; Eisloeffel, J.;
Emerson, J.; Fabregat, J.; García, P.; Geisler, D.; Giannini, T.;
Gieren, W.; Goldman, B.; Gosling, A.; Groot, P.; Hambly, N.; Hoare,
M.; Irwin, M.; Ivanov, V.; Kerber, L.; Kurtev, R.; Longmore, A.;
López-Corredoira, M.; Lucas, P.; Lucey, J.; McGowan, K.; Mennickent,
R.; Messineo, M.; Mirabel, F.; Monaco, L.; Morelli, L.; Naylor, T.;
Pietrzynski, G.; Pignata, G.; Rejkuba, M.; Ruiz, M. T.; Saviane, I.;
Schreiber, M.; Schroeder, A.; Stephens, A.; Tappert, C.; Thompson,
M.; Vanzi, L.; Walton, N.; White, G.; Zijlstra, A.; Zoccali, M.
2006IAUJD..13E..50A Altcode:
We describe a proposal for a public IR variability survey of the entire
Milky Way Bulge and a large portion of the Southern Galactic Plane
with VISTA at ESO Paranal Observatory. The survey will take about 180
nights, covering 5×10^8 point sources within an area of about 600 sq
deg, including 40 known globular clusters and more than one hundred
known open clusters. The final products of our VVV survey will be a
deep IR atlas of the bulge and inner disk, along with a catalogue of
more than a million variable point sources. These will allow to map
the 3-D structure of the bulge and inner disk (unlike single epoch
surveys that only give 2-D maps) using well understood primary distance
indicators such as RR-Lyrae stars, and to obtain important information
on the age of the Milky Way stellar populations. The survey will also
detect hundreds of star formation regions, and allow to examine the
environmental dependence of star formation. The VISTA observations
will be combined with data from MACHO, OGLE, EROS, 2MASS, DENIS, VST,
SPITZER, HST, CHANDRA, INTEGRAL and ALMA for a complete understanding
of the variable sources in the inner Milky Way. Several important
implications for the history of the Milky Way, for globular cluster
evolution, for the population census of the bulge and center, and for
pulsation theory would follow from this survey.
---------------------------------------------------------
Title: Scientific Objectives of the Novel Formation Flying Mission
Aspiics
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
Thompson, M.; Vauclair, S.; Zahn, J. P.
2006ESASP.617E.164L Altcode: 2006soho...17E.164L
No abstract at ADS
---------------------------------------------------------
Title: On the Choice of Phase-Speed Filters For Helioseismic
Travel-Time Measurements
Authors: Zharkov, S.; Jensen, J. M.; Thompson, M. J.
2006ESASP.617E..48Z Altcode: 2006soho...17E..48Z
No abstract at ADS
---------------------------------------------------------
Title: The EUV Variability Experiment (EVE) on the Solar Dynamics
Observatory (SDO): Science Plan and Instrument Overview
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
Thompson, M.; Vauclair, S.; Zahn, J. P.
2006ESASP.617E.165W Altcode: 2006soho...17E.165W
No abstract at ADS
---------------------------------------------------------
Title: Sound Wave Travel Times in Plage Areas - The Effect of
Abnormal Granulation
Authors: Petrovay, K.; Erdélyi, R.; Thompson, M. J.
2006ESASP.617E..73P Altcode: 2006soho...17E..73P
No abstract at ADS
---------------------------------------------------------
Title: Helas-European Helio- and Asteroseismology Network
Authors: Roth, M.; Lühe, O. v. d.; Pallé, P.; Thompson, M.;
Christensen-Dalsgaard, J.; Monteiro, M. J. P. F. G; Gizon, L.; Di
Mauro, M. P.; Aerts, C.; Daszynska-Daszkiewicz, J.; Corbard, T.
2006ESASP.617E.157R Altcode: 2006soho...17E.157R
No abstract at ADS
---------------------------------------------------------
Title: Sensitivity of Time-Distance Helioseismic Measurements to
Spatial Variation of Oscillation Amplitudes. I. Observations and a
Numerical Model
Authors: Rajaguru, S. P.; Birch, A. C.; Duvall, T. L., Jr.; Thompson,
M. J.; Zhao, J.
2006ApJ...646..543R Altcode: 2006astro.ph..4048R
It is well known that the observed amplitude of solar oscillations is
lower in sunspots than in quiet regions of the Sun. We show that this
local reduction in oscillation amplitudes, combined with the phase-speed
filtering procedure in time-distance helioseismic analyses, could be
a source of systematic errors in the range of 5%-40% in the measured
travel-time anomalies of acoustic waves around sunspots. Removing
these travel-time artifacts is important for correctly inferring the
subsurface structure of sunspots. We suggest an empirical correction
procedure and illustrate its usage for a small sunspot. This work uses
data from SOHO MDI.
---------------------------------------------------------
Title: The Dynamics Project
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
Thompson, M.; Vauclair, S.; Zahn, J. P.
2006ESASP.617E.162T Altcode: 2006soho...17E.162T
No abstract at ADS
---------------------------------------------------------
Title: Triggered star formation in bright-rimmed clouds: the Eagle
nebula revisited
Authors: Miao, J.; White, Glenn J.; Nelson, R.; Thompson, M.;
Morgan, L.
2006MNRAS.369..143M Altcode: 2006astro.ph..3230M; 2006MNRAS.tmp..464M
A three-dimensional smoothed particle hydrodynamics model has been
extended to study the radiation-driven implosion effect of massive stars
on the dynamical evolution of surrounding molecular clouds. The new
elements in the upgraded code are the inclusion of Lyman continuum in
the incident radiation flux and the treatment of hydrogen ionization
process; the introduction of ionization heating and recombination
cooling effects; and the addition of a proper description of the
magnetic and turbulent pressures to the internal pressure of the
molecular cloud. This extended code not only provides a realistic model
to trace the dynamical evolution of a molecular cloud, but also can be
used to model the kinematics of the ionization and shock fronts and the
photoevaporating gas surrounding the molecular cloud, which the previous
code is unable to handle. <P />The application of this newly developed
model to the structure of the middle Eagle nebula finger suggests that
the shock induced by the ionizing radiation at the front side of the
head precedes an ionization front moving towards the centre of the core,
and that the core at the fingertip is at a transition stage evolving
toward a state of induced star formation. The dynamical evolution
of the velocity field of the simulated cloud structure is discussed
to illustrate the role of the self-gravity and the different cloud
morphologies which appear at different stages in the evolutionary
process of the cloud. The motion of the ionization front and the
evaporating gas are also investigated. The modelled gas evaporation
rate is consistent with that of other current models and the density,
temperature and chemical profiles are in agreement with the observed
values. <P />The relative lifetimes of different simulated cloud
morphologies suggest a possible answer to the question of why more
bright-rimmed clouds are observed to possess a flat-core than an
elongated-core morphology.
---------------------------------------------------------
Title: Large-Scale Zonal Flows Near the Solar Surface
Authors: Howe, R.; Komm, R.; Hill, F.; Ulrich, R.; Haber, D. A.;
Hindman, B. W.; Schou, J.; Thompson, M. J.
2006SoPh..235....1H Altcode:
Migrating bands of weak, zonal flow, associated with the activity
bands in the solar cycle, have been observed at the solar surface for
some time. More recently, these flows have been probed deep within the
convection zone using global helioseismology and examined in more detail
close to the surface with the techniques of local helioseismology. We
compare the near-surface results from global and local helioseismology
using data from the Michelson Doppler Imager and the Global Oscillation
Network Group with surface Doppler velocity measurements from the Mount
Wilson 150-foot tower and find that the results are in reasonable
agreement, with some explicable differences in detail. All of the
data sets show zones of faster rotation approaching the equator from
mid-latitudes during the solar cycle, with a variation at any given
location that can be approximately, but not completely, described by a
single sinusoid and an amplitude that does not drop off steeply below
the surface.
---------------------------------------------------------
Title: Magnetohelioseismology
Authors: Thompson, Michael J.
2006RSPTA.364..297T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An introduction to astrophysical fluid dynamics
Authors: Thompson, Michael J.
2006iafd.book.....T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Jets in the Solar Tachocline as Diagnostics of Global MHD
Processes
Authors: Christensen-Dalsgaard, J.; Corbard, T.; Dikpati, M.; Gilman,
P. A.; Thompson, M. J.
2005ASPC..346..115C Altcode:
Multiple theories predict the existence of prograde fluid jets in the
solar tachocline. We find helioseismic evidence of a prograde jet near
60° latitude in N and S hemispheres that persists through almost all
of the current solar cycle. This evidence favors a hydrodynamic origin
for the jet, from global instability of the differential rotation of
the tachocline. We see no evidence for jets that migrate toward the
equator with the advancing solar cycle, which tends to rule out jets
associated with toroidal field bands in the tachocline.
---------------------------------------------------------
Title: Solar Convection-Zone Dynamics, 1995-2004
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
Schou, J.; Thompson, M. J.
2005ApJ...634.1405H Altcode:
The nine-year span of medium-degree helioseismic data from the Global
Oscillation Network Group (GONG) and the Michelson Doppler Imager (MDI)
allows us to study the evolving zonal flows in the solar convection
zone over the rising phase, maximum, and early declining phase
of solar cycle 23. Using two independent two-dimensional rotation
inversion techniques, we investigate the depth profile of the flow
pattern known as the torsional oscillation. The observations suggest
that the flows penetrate deep within the convection zone-perhaps to
its base-even at low latitudes, and that the phase of the pattern is
approximately constant along lines of constant rotation rather than
lines of constant latitude.
---------------------------------------------------------
Title: Acoustic Wave Propagation in the Solar Subphotosphere
Authors: Shelyag, S.; Erdelyi, R.; Thompson, M. J.
2005AGUFMSH53A1237S Altcode:
Local time-distance helioseismology aims to get an information about the
internal structure of subphotospheric region of the Sun, like flows and
sound speed perturbations, by investigation of observed travel times
of the oscillatory responses of subphotosphere to a perturbation. We
present the results of simulations of acoustic wave propagation and
dispersion in the non-magnetic solar subphotosphere. We use methods
similar to the observational ones to produce results aiming to reproduce
observational data from local helioseismology. The VAC code (G. Toth)
is used to carry out the simulations. The code can solve the full system
of ideal hydrodynamic equations in two or three dimensions. All the
results presented are carried out in 2D. The simulations use realistic
solar density and pressure stratifications and are based on fully
compressible ideal hydrodynamical model. Acoustic waves are produced
by perturbations located near the layer corresponding to the visible
surface of the Sun. The simulation domain is 150 Mm wide and 52.6 Mm
deep, and has a resolution of 600x4000 grid points; the upper boundary
of the domain is near the temperature minimum. The density profile for
the initial plane-parallel model is taken from Christensen-Dalsgaard's
standard Model S. We suppress convective motions of the fluid in the
domain by slight change of adiabatic index γ_1. This approach has
an advantage among other approaches because the waves we study, while
they propagate through the quiescent medium, can be clearly observed
far from the source undisturbed by convective fluid motions. First
we study the propagation of acoustic waves produced by a harmonic
pressure perturbation, then, in order to follow the criteria of realism
we introduce more involved perturbation source, described as a source
in the energy equation of the HD system of equations. The source used
corresponds to a localized cooling event causing mass inflow and
sound waves extinction (M. Rast, 1999). In order to reproduce the
helioseismogram of the quiet Sun we introduce a number of randomly
distributed sources with random amplitudes and present a comparison
of the simulated data with the observations.
---------------------------------------------------------
Title: How Sensitive are Rotation Inversions to Subtle Features of
the Dynamo?
Authors: Howe, R.; Rempel, M.; Christensen-Dalsgaard, J.; Schou, J.;
Thompson, M. J.; Komm, R.; Hill, F.
2005ASPC..346...99H Altcode:
Global rotation inversions can probe the pattern of zonal flows
well into the convection zone. In this paper, we test the ability
of the inversions to constrain the predictions of dynamo models. A
flux-transport dynamo model, including a mean-field theory of
differential rotation and allowing for feedback of the Lorentz force
on differential rotation and meridional flow, was used to produce a
22-year cycle of simulated rotation profiles. These were then subjected
to simulated inversions with realistic mode sets and errors, in order
to test how well the subtle subsurface features of the input profile
could be recovered. The preliminary results are quite encouraging.
---------------------------------------------------------
Title: Preface (Advances in astronomy. From the big bang to the
solar system)
Authors: Thompson, Michael
2005aabb.bookD..11T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Seismic analysis of the second ionization region of helium
in the Sun - I. Sensitivity study and methodology
Authors: Monteiro, Mário J. P. F. G.; Thompson, Michael J.
2005MNRAS.361.1187M Altcode: 2005astro.ph..6286M; 2005MNRAS.tmp..632M
The region of the second ionization of helium in the Sun is a narrow
layer near the surface. Ionization induces a local change in the
adiabatic exponent Γ<SUB>1</SUB>, which produces a characteristic
signature in the frequencies of p modes. By adapting the method
developed by Monteiro, Christensen-Dalsgaard & Thompson, we propose
a methodology for determining the properties of this region by studying
such a signature in the frequencies of oscillation. <P />Using solar
data we illustrate how the signal from the helium ionization zone can
be isolated. Using solar models which each use different physics - the
theory of convection, equation of state and low-temperature opacities -
we establish how the characteristics of the signal depend on the various
physical processes contributing to the structure in the ionization
layer. We further discuss how the method can be used to measure the
solar helium abundance in the envelope and to constrain the physics
affecting this region of the Sun. <P />The potential usefulness of the
method we propose is shown. It may complement other inversion methods
developed to study the solar structure and to determine the envelope
helium abundance.
---------------------------------------------------------
Title: Comparison of GONG and MDI: Sound-Speed Anomalies beneath
Two Active Regions
Authors: Hughes, S. J.; Rajaguru, S. P.; Thompson, M. J.
2005ApJ...627.1040H Altcode:
Travel times of acoustic waves are calculated from Dopplergrams of solar
oscillations obtained using the Global Oscillation Network Group (GONG)
ground-based network and the Michelson Doppler Imager (MDI) instrument
on board the SOHO satellite. These travel times are inverted using
a standard ray approximation to ascertain the sound-speed anomalies
below two active regions. Some simple methods for ignoring the possibly
corrupted measurements from within a sunspot are considered, as are
diagnostics for optimizing the inversion. Results are then presented
for two different spot regions, and the results of the instruments
are compared: both regions behave in similar ways, and the agreement
between the two instruments is good. First-skip and second-skip data
are found to produce similar results for deeper layers of the model,
but the significance of the shallower results from second-skip data
is questionable. We conclude that GONG data are appropriate for
time-distance analysis.
---------------------------------------------------------
Title: Global, Local and Surface Measurements of Large-Scale Zonal
Flows Near the Solar Surface
Authors: Howe, R.; Komm, R. W.; Haber, D. A.; Hindman, B. W.; Ulrich,
R. K.; Schou, J.; Thompson, M. J.; Hill, F.
2005AGUSMSP32A..03H Altcode:
Migrating bands of weak zonal flow, associated with the activity
bands in the solar cycle, have been observed at the solar surface
for some time. More recently, these flows have been probed deep
within the convection zone using global helioseismology, and
examined in more detail close to the surface with the techniques of
local helioseismology. We compare the results from global and local
helioseismology using data from the Michelson Doppler Imager and the
GONG network and also Doppler measurements from Mount Wilson, and find
that the results are in reasonable agreement, with some explicable
differences in detail. This was work was supported by the National
Science Foundation and NASA.
---------------------------------------------------------
Title: Helioseismic Ring Analyses of Artificial Data Computed for
Two-dimensional Shearing Flows
Authors: Hindman, Bradley W.; Gough, Douglas; Thompson, Michael J.;
Toomre, Juri
2005ApJ...621..512H Altcode:
The local helioseismological technique of ring analysis has been
crucial in the discovery of complex large-scale flows in the Sun's
near-surface shear layer. However, current implementations of
ring-analysis procedures assume that the flow field is horizontally
homogeneous over the analysis region. This assumption is certainly
incorrect, and in the present paper we assess the significance of this
approximation by analyzing artificial data sets computed from models of
horizontal shear flows. We consider the simple case of purely horizontal
and unidirectional flow that varies solely in the horizontal direction
orthogonal to the flow in a piecewise-constant manner. An ensemble
of plane waves is incident on the flow, and the scattered wave field
produced by the prescribed two-dimensional flow is computed to generate
an artificial helioseismic power spectrum. The artificial spectrum
is processed in a manner similar to standard ring analysis, and the
flow field that is thereby inferred is compared with the known imposed
flow. We find that the inferred flow velocity is essentially an average
of the true flow velocity over the region of the analysis, weighted by
the square of the spatial apodization function used in processing the
oscillation signal. Furthermore, the shape of a p-mode line profile
is determined by the distribution of speeds across the analysis region.
---------------------------------------------------------
Title: The use of frequency-separation ratios for asteroseismology
Authors: Otí Floranes, H.; Christensen-Dalsgaard, J.; Thompson, M. J.
2005MNRAS.356..671O Altcode: 2005MNRAS.356..671F
The systematic patterns of separations between frequencies of modes of
different degree and order are a characteristic of p-mode oscillations
of stars. The frequency separations depend on the internal structure
of the star and so measuring them in the observed oscillation spectra
of variable stars gives valuable diagnostics of the interior of a
star. Roxburgh & Vorontsov proposed using the ratio of the so-called
small frequency separation to the large frequency separation as a
diagnostic of the stellar interior, and demonstrated that this ratio
was less sensitive than the individual frequency separations themselves
to uncertain details of the near-surface structure. Here we derive
kernels relating the frequency separation ratio to structure, and show
why the ratio is relatively insensitive to the near-surface structure
in terms of the very small amplitude of the kernels in the near-surface
layers. We also investigate the behaviour of the separation ratio for
stars of different masses and ages, and demonstrate the usefulness of
the ratio in the so-called asteroseismic Hertzsprung-Russell diagram.
---------------------------------------------------------
Title: Local Modulation of Solar Oscillations by Magnetic Fields
Authors: Nicholas, C. J.; Thompson, M. J.; Rajaguru, S. P.
2004SoPh..225..213N Altcode:
The amplitudes of solar oscillations measured in Doppler velocity are
modulated by the presence of a strong photospheric magnetic field. Here
we show that the amount of modulation cannot be predicted solely
on the local photospheric magnetic field strength. Qualitatively,
magnetic fields of similar strength have similar effects on the
oscillations. Quantitatively, however, we find a `neighborhood effect',
so that the presence of a nearby sunspot affects oscillations in
the area in its vicinity that has normal quiet-Sun magnetic field
strength. Thus, different types of magnetic regions alter the
oscillatory power to a varying degree, and the p-mode power within
regions of similar magnetic field strength is more reduced if there is
a sunspot present. The neighborhood effect falls off with distance from
the sunspot. We also show that our measurements of the power modulation,
in which we look at the effects on oscillations pixel by pixel, can
be made consistent with results of amplitude modulation of modes as
obtained from ring-diagram analysis of active regions, but only if
the neighborhood effect on quiet-Sun regions is taken into account.
---------------------------------------------------------
Title: Comparison of GONG and MDI Sound-Speed Anomalies Beneath Two
Active Regions
Authors: Hughes, S. J.; Rajaguru, S. P.; Thompson, M. J.
2004ESASP.559..493H Altcode: 2004soho...14..493H
No abstract at ADS
---------------------------------------------------------
Title: Detection of Jets and Associated Toroidal Fields in the
Solar Tachocline
Authors: Christensen-Dalsgaard, J.; Corbard, T.; Dikpati, M.; Gilman,
P. A.; Thompson, M. J.
2004ESASP.559..376C Altcode: 2004soho...14..376C
No abstract at ADS
---------------------------------------------------------
Title: How Sensitive are Rotation Inversions to Subtle Features of
the Dynamo?
Authors: Howe, R.; Rempel, M.; Christensen-Dalsgaard, J.; Hill, F.;
Komm, R. W.; Schou, J.; Thompson, M. J.
2004ESASP.559..468H Altcode: 2004soho...14..468H
No abstract at ADS
---------------------------------------------------------
Title: The Effect of Strong Magnetic Fields on Acoustic Power in
Their Surroundings at the Surface of the Sun
Authors: Nicholas, C. J.; Thompson, M. J.; Rajaguru, S. P.
2004ESASP.559..590N Altcode: 2004soho...14..590N
No abstract at ADS
---------------------------------------------------------
Title: Optimal Masks for Deep Focussing
Authors: Hughes, S. J.; Pijpers, F. P.; Thompson, M. J.
2004ESASP.559..488H Altcode: 2004soho...14..488H
No abstract at ADS
---------------------------------------------------------
Title: Subphotospheric Flows Near Active Region NOAA 10486
Authors: Haber, D. A.; Hindman, B. W.; Toomre, J.; Bogart, R. S.;
Thompson, M. J.
2004ESASP.559..148H Altcode: 2004soho...14..148H
No abstract at ADS
---------------------------------------------------------
Title: The Phase of the Torsional Oscillation Pattern
Authors: Howe, R.; Komm, R. W.; Hill, F.; Christensen-Dalsgaard, J.;
Schou, J.; Thompson, M. J.
2004ESASP.559..476H Altcode: 2004soho...14..476H
No abstract at ADS
---------------------------------------------------------
Title: Asteroseismology: Asteroseismology of Sun-like stars
Authors: Elsworth, Yvonne P.; Thompson, Michael J.
2004A&G....45e..14E Altcode:
Seismology has become a powerful tool for analysis of the interior
of the Sun; it has great potential for the study of oscillations in
solar-like stars. Asteroseimology could provide direct information
about detailed properties of stellar interiors, bringing the potential
for testing theories of stellar evolution and structure. Current
stellar models are simple with few direct observational constraints;
consequences such as age estimates are uncertain to a factor of two. A
recent attempt at asteroseismology on Procyon, a likely candidate
star, found no detectable oscillations. In this paper we discuss the
asteroseismology of solar-like stars in the context of studies of the
Sun and then indicate possible reasons for the Procyon results.
---------------------------------------------------------
Title: Application of Local-Area Helioseismic Methods as Predictors
of Space Weather
Authors: Jensen, J. M.; Lundstedt, H.; Thompson, M. J.; Pijpers,
F. P.; Rajaguru, S. P.
2004ESASP.559..497J Altcode: 2004soho...14..497J
No abstract at ADS
---------------------------------------------------------
Title: Convection-Zone Dynamics from GONG and MDI, 1995-2004
Authors: Howe, R.; Komm, R. W.; Hill, F.; Christensen-Dalsgaard, J.;
Haber, D. A.; Schou, J.; Thompson, M. J.
2004ESASP.559..472H Altcode: 2004soho...14..472H
No abstract at ADS
---------------------------------------------------------
Title: Solar interior: Helioseismology and the Sun's interior
Authors: Thompson, Michael J.
2004A&G....45d..21T Altcode:
Helioseismology is the study of the solar interior using observations
of waves on the Sun's surface. It has done much to improve our
understanding of the interior of the Sun, testing the physical
inputs used to model stellar interiors and providing a detailed map
of the Sun's structure and internal rotation. This in turn has greatly
influenced theories of the solar magnetic dynamo. These interior studies
thus make a valuable bridge between solar physics and studies of the
structure and evolution of other stars. Recent developments include new
local techniques for unprecedented studies of subsurface structures
and flows in emerging active regions, under sunspots, and even of
active regions on the far side of the Sun. These developments hold
the possibility of a real understanding of how the interior links to
solar magnetic activity in the corona and heliosphere. Finally, studies
such as those of the deep solar interior are on the verge of becoming
possible for other stars exhibiting similar multimode oscillations.
---------------------------------------------------------
Title: Subphotospheric Flows Around Active Region NOAA 10486
Authors: Haber, D. A.; Hindman, B. W.; Toomre, J.; Bogart, R. S.;
Thompson, M. J.; LoHCo Team
2004AAS...204.0211H Altcode: 2004BAAS...36Q.669H
We have used MDI Dynamics Program Doppler data taken between October
18th and November 15th 2003 to study the interaction of solar subsurface
flows with NOAA 10486, one of the most dynamic active regions of the
past solar cycle. Using the local helioseismic techniques of ring and
time-distance analyses, we assess the horizontal flows that surrounded
and permeated this region and how they varied with depth in the upper
14 Mm of the convection zone. We examine and identify structures in the
flow field that may have been associated with the energetic flares that
occurred during the period of observation. This research is in part
supported by NASA through grants NAG5-11920, NAG5-10917, and NAG5-12491.
---------------------------------------------------------
Title: Comparison OF Noise Properties Of GONG And MDI Time-Distance
Helioseismic Data
Authors: Rajaguru, S. P.; Hughes, S. J.; Thompson, M. J.
2004SoPh..220..381R Altcode:
The recently upgraded system of the ground-based Global Oscillation
Network Group (GONG) network of helioseismic observatories has started
to provide higher-resolution solar oscillation measurements suitable
for local helioseismic studies. Selecting simultaneously observed
regions on the Sun by both GONG and the space-borne Michelson Doppler
Imager (MDI) instrument on board the Solar and Heliospheric Observatory
(SOHO), we perform a comparative analysis of time-distance measurements
focussing on the noise properties.
---------------------------------------------------------
Title: Organized Subsurface Flows near Active Regions
Authors: Haber, D. A.; Hindman, B. W.; Toomre, J.; Thompson, M. J.
2004SoPh..220..371H Altcode:
Local helioseismic techniques, such as ring analysis and time-distance
helioseismology, have already shown that large-scale flows near the
surface converge towards major active regions. Ring analysis has further
demonstrated that at greater depths some active regions exhibit strong
outflows. A critique leveled at the ring-analysis results is that the
Regularized Least Squares (RLS) inversion kernels on which they are
based have negative sidelobes near the surface. Such sidelobes could
result in a surface inflow being misidentified as a diverging outflow
at depth. In this paper we show that the Optimally Located Averages
(OLA) inversion technique, which produces kernels without significant
sidelobes, generates flows markedly similar to the RLS results. Active
regions are universally zones of convergence near the surface, while
large complexes evince strong outflows deeper down.
---------------------------------------------------------
Title: ENEAS: the European Network of Excellence in AsteroSeismology
Authors: Aerts, C.; Baglin, A.; Christensen-Dalsgaard, J.; Goupil,
M. J.; Houdek, G.; Kjeldsen, H.; Kollath, Z.; Kurtz, D.; Lebreton,
Y.; Maceroni, C.; Noels, A.; Schwarzenberg-Czerny, A.; Škoda, P.;
Solano, E.; Thompson, M. J.
2004ESASP.538..247A Altcode: 2004sshp.conf..247A
Asteroseismology is one of the major important science topics in
astrophysics in the coming decade. Several recent breakthroughs have
indeed been made in Europe in this field. The observational data will
improve significantly in the near future, as upgraded ground-based
instruments are being built and two European asteroseismic space
missions are planned for launch between 2005 and 2008. They will
provide us for the first time with ultra-high-accuracy, high-temporal
resoluton data from space for stars other than the Sun. A successful
asteroseismic study involves many different steps, from state-of-the-art
raw data treatment to theoretical physical modelling of the oscillation
frequencies. Our network is set up to meet the needs of combining and
exchanging the different expertises of the participating institutes, of
training PhD students and of both training and exchanging post-doctoral
researchers. This will guarantee the most fruitful and efficient
exploitation of the very substantial investments that are being made in
Europe in future observations of stellar oscillations, strengthening
Europe's leading position in this research field. Also, it will be a
test-bed for the development of efficient procedures for collaboration
across the internet, involving a vast range of procedures and skills,
as well as extensive common use of a broad variety of data. Furthermore,
procedures will be incorporated for the joint training of students,
which is an essential part of our project.
---------------------------------------------------------
Title: Application of local-area helioseismic methods as predictors
of spaceweather
Authors: Jensen, J. M.; Lundstedt, H.; Thompson, M. J.; Pijpers,
F. P.; Rajaguru, S. P.
2004cosp...35.2195J Altcode: 2004cosp.meet.2195J
Many of the phenomena observed on the Sun are of magnetic origin. The
solar wind, Coronal Mass Ejections and flares are all phenomena
closely linked to Sun's magnetic field. The technology based society
of today can be strongly influences by these phenomena. The high
energetic particles emitted in connection with CMEs and flares are
able to cause enough damage to satellites to render them useless. It
is therefore of great interest to understand the physical processes
behind these phenomena. During the last three decades helioseismology
has investigated the solar interior by measurements of the global
eigenmode frequencies. The global nature of these data makes it
impossible to resolve phenomena which are highly localized in the
Sun. Within the last decade local-area helioseismic methods have emerged
as powerful tools for investigating localized phenomena in the solar
convection zone such as flows and magnetic activity. With these methods
it has become possible to study structures around and below active
regions. Observations have been made of flows and temperature variations
surrounding and extending below sunspots thereby enabling the study of
dynamical processes below the solar surface in actice regions. These
studies can help to understand the processes behind phenomena such
as flares and CMEs which can influence the Earth. With local-area
helioseismic methods a wealth of new information has or will become
available, which hopefully can be used to increase the reliability
of space weather predictions. With the data available from the SOHO
satellite and the GONG network it is possible to monitor large-scale
flows in the Sun in connection with magnetic active regions using
local-area helioseismic methods. We propose to use these observed flows
as indicators for future space weather. If observations of the magnetic
configuration in active regions are supplemented with information of
the flow fields surrounding the active region it might be possible to
improve on flare prediction. To this end we propose to use physics-based
neural network to investigate if the flow fields can be used to predict
flares and space weather. The goal is to incorporate these data into
the space weather forecast models developed at the Swedish Institute
of Space Physics in Lund. A space weather forecast service prototype
was developed within the ESA Space Weather Programme Study and an ESA
Pilot Project is in progress. The Lund division of the institute also
runs the RWC-Sweden of ISES. Here we present preliminary results of
this new approach of using helioseismological data.
---------------------------------------------------------
Title: The Significance of Density and Attenuation in the Local
Helioseismology
Authors: Tong, C. H.; Thompson, M. J.; Warner, M. R.; Pain, C. C.
2003ApJ...596L.263T Altcode:
We present results from numerical simulations in order to demonstrate
the significance of density and attenuation in helioseismic
data modeling and in the interpretation of reconstructed solar
models. Attenuation beneath active regions causes significant dispersion
as well as temporal shifts of the helioseismic signals. These effects
can be considerably more significant than those caused by sound-speed
anomalies. On the basis of the differential changes in the waveform
of the signals as a function of density, we propose the modeling of
density for the estimation of the relative contribution from buoyancy
and magnetic fields toward the origin of the fluid flows in the solar
interior.
---------------------------------------------------------
Title: Helioseismic Signals and Wave Field Helioseismology
Authors: Tong, C. H.; Thompson, M. J.; Warner, M. R.; Pain, C. C.
2003ApJ...593.1242T Altcode:
We investigate the effect of sound-speed perturbations on the
characteristics of helioseismic signals in order to demonstrate
the feasibility and desirability of wave field helioseismology. The
oscillatory nature of the signals with varying frequency content allows
us to characterize the waveform of the signals by the amplitudes of the
peaks and troughs as well as by the time lags between successive peaks
and troughs. Sinusoidal sound-speed perturbations with an amplitude
of 1% of the local sound speed produce more than +/-10% changes in the
amplitudes of the peaks and troughs. The same sound-speed perturbations
produce changes in the time lags between successive peaks and troughs
of the signals that are comparable with the variations of first-break
travel times of the oscillatory wave packet. The vertical and horizontal
sound-speed perturbations result in distinct patterns of changes in
the shape of the helioseismic signals. These changes in the amplitudes
and travel-time lags are differential for the successive peaks and
troughs: the magnitude is higher for the later peaks and troughs. We
also observe that these variations in the amplitude and travel-time
lags are more sensitive to shorter wavelength sound-speed perturbations
at relatively small source-receiver offsets. Therefore, our results
indicate that the waveform of the signals is variable and sensitive to
sound-speed perturbations. These observations can be explained by the
more dispersive nature of the low-frequency components in the seismic
signals at shallow depths. The relatively high sensitivity of these
perturbations in the waveform of the signals to sound speed, density,
and vertical density gradient at shallow depths due to dispersion is
an important modeling consideration.
---------------------------------------------------------
Title: A Comparison of Solar p-Mode Parameters from MDI and GONG:
Mode Frequencies and Structure Inversions
Authors: Basu, S.; Christensen-Dalsgaard, J.; Howe, R.; Schou, J.;
Thompson, M. J.; Hill, F.; Komm, R.
2003ApJ...591..432B Altcode:
Helioseismic analysis of solar global oscillations allows investigation
of the internal structure of the Sun. One important test of the
reliability of the inferences from helioseismology is that the
results from independent sets of contemporaneous data are consistent
with one another. Here we compare mode frequencies from the Global
Oscillation Network Group and Michelson Doppler Imager on board SOHO
and resulting inversion results on the Sun's internal structure. The
average relative differences between the data sets are typically less
than 1×10<SUP>-5</SUP>, substantially smaller than the formal errors in
the differences; however, in some cases the frequency differences show
a systematic behavior that might nonetheless influence the inversion
results. We find that the differences in frequencies are not a result
of instrumental effects but are almost entirely related to the data
pipeline software. Inversion of the frequencies shows that their
differences do not result in any significant effects on the resulting
inferences on solar structure. We have also experimented with fitting
asymmetric profiles to the oscillation power spectra and find that,
compared with the symmetric fits, this causes no significant change
in the inversion results.
---------------------------------------------------------
Title: First results from Time-Distance inversions of GONG+ data.
Authors: Rajaguru, S. P.; Hughes, S. J.; Thompson, M. J.
2003SPD....34.0801R Altcode: 2003BAAS...35..821R
We present first results from time-distance helioseismic analysis
of a few active regions using the new merged sequences of data from
GONG+ instruments. In particular we focus on issues related to the
resolution achievable from GONG+ data and also estimate their noise
properties.Results from inversions for sound speed changes beneath
active regions will be presented with initial comparisons between
first and second bounce time-distance data for acoustic rays passing
under a spot. We acknowledge support from the UK Particle Physics and
Astronomy Research Council.
---------------------------------------------------------
Title: Stellar Astrophysical Fluid Dynamics
Authors: Thompson, Michael J.; Christensen-Dalsgaard, Jørgen
2003safd.book.....T Altcode:
Preface; 1. A selective overview Jørgen Christensen-Dalsgaard and
Michael J. Thompson; Part I. Stellar Convection and Oscillations:
2. On the diversity of stellar pulsations Wojciech A. Dziembowski;
3. Acoustic radiation and mode excitation by turbulent convection
Günter Houdek; 4. Understanding roAp stars Margarida S. Cunha; 5. Waves
in the magnetised solar atmosphere Colin S. Rosenthal; Part II. Stellar
Rotation and Magnetic Fields: 6. Stellar rotation: a historical survey
Leon Mestel; 7. The oscillations of rapidly rotating stars Michel
Rieutord; 8. Solar tachocline dynamics: eddy viscosity, anti-friction,
or something in between? Michael E. McIntyre; 9. Dynamics of the solar
tachocline Pascale Garaud; 10. Dynamo processes: the interaction of
turbulence and magnetic fields Michael Proctor; 11. Dynamos in planets
Chris Jones; Part III. Physics and Structure of Stellar Interiors:
12. Solar constraints on the equation of state Werner Däppen;
13. 3He transport and the solar neutrino problem Chris Jordinson;
14. Mixing in stellar radiation zones Jean-Paul Zahn; 15. Element
settling and rotation-induced mixing in slowly rotating stars Sylvie
Vauclair; Part IV. Helio- and Asteroseismology: 16. Solar structure
and the neutrino problem Hiromoto Shibahashi; 17. Helioseismic data
analysis Jesper Schou; 18. Seismology of solar rotation Takashi Sekii;
19. Telechronohelioseismology Alexander Kosovichev; Part V. Large-Scale
Numerical Experiments: 20. Bridges between helioseismology and models
of convection zone dynamics Juri Toomre; 21. Numerical simulations of
the solar convection zone Julian R. Elliott; 22. Modelling solar and
stellar magnetoconvection Nigel Weiss; 23. Nonlinear magnetoconvection
in the presence of a strong oblique field Keith Julien, Edgar Knobloch
and Steven M. Tobias; 24. Simulations of astrophysical fluids Marcus
Brüggen; Part VI. Dynamics: 25. A magic electromagnetic field Donald
Lynden-Bell; 26. Continuum equations for stellar dynamics Edward
A. Spiegel and Jean-Luc Thiffeault; 27. Formation of planetary systems
Douglas N. C. Lin; 28. The solar-cycle global warming as inferred from
sky brightness variation Wasaburo Unno and Hiromoto Shibahashi.
---------------------------------------------------------
Title: Asteroseismology Across the HR Diagram
Authors: Thompson, M. J.; Cunha, M. S.; Monteiro, M. J. P. F. G.
2003aahd.conf.....T Altcode:
Ground-based observations have detected solar-like oscillations
on Sun-like stars, and diagnostics similar to those used in
helioseismology are now being used to test and constrain the physics
and evolutionary state of these stars. Multi-mode oscillations are
being observed in an abundance of other stars, including slowly
pulsating B stars (SPB stars), delta-Scuti stars, Ap stars and the
pulsating white dwarfs. New classes of pulsators continue to be
discovered across the Herzsprung-Russell diagram. Yet the chances
still to be faced to make asteroseismology across the HR diagram
a reality are formidable. Observation, data analysis and theory
all pose hard problems to be overcome. This book, reflecting the
goal of the meeting, aims to facilitate a cross-fertilisation of
ideas and approaches between fields covering different pulsators
and with different areas of expertise. The book successfully covers
most known types of pulsators, reflecting a highly productive and
far reaching interchange of ideas which we believe is conveyed
by the papers and posters published, making it a reference for
researchers and postgraduate students working on stellar structure and
evolution. <P />Link: <A href="http://www.wkap.nl/prod/b/1-4020-1173-3">
http://www.wkap.nl/prod/b/1-4020-1173-3</A>
---------------------------------------------------------
Title: Time-distance analysis of GONG+ data
Authors: Rajaguru, S. P.; Hughes, S. J.; Thompson, M. J.
2003ESASP.517...75R Altcode: 2003soho...12...75R
We show our first time-distance analyses of data from GONG+. We
present details of our method of analysing the data and travel-time
anomalies measured over an active region when compared to that over a
quiet region. The dataset used for studying the active region is from
a merged sequence of GONG+ Doppler images.
---------------------------------------------------------
Title: Time-distance helioseismology of subsurface flows
Authors: Hughes, Stephen J.; Thompson, Michael J.
2003ESASP.517..307H Altcode: 2003soho...12..307H
We revisit the work of Giles (1999) in an attempt to extend the
work on large scale flows using the technique of time-distance
helioseismology. The basic process and techniques are discussed and some
initial results are shown. The behaviour of the meridional and zonal
flows is found to be similar to that found by Giles and separately by
ring diagram methods (Haber et al. 2002).
---------------------------------------------------------
Title: Transient oscillations near the solar tachocline
Authors: Toomre, Juri; Christensen-Dalsgaard, Jorgen; Hill, Frank;
Howe, Rachel; Komm, Rudolf W.; Schou, Jesper; Thompson, Michael J.
2003ESASP.517..409T Altcode: 2003soho...12..409T
We report on further developments in the 1.3-yr quasi-periodic
oscillations reported by Howe et al. (2000). These are small (6 to 8
nHz peak-to-peak) oscillations in the inferred rotation rate near the
bottom of the convection zone and in the outer part of the radiative
interior. The oscillations are strongest and most coherent at about a
fractional radius of 0.72 in the equatorial region. Further monitoring
of the oscillations near the equator shows that they continued for a
period after the end of the data analyzed by Howe et al., but appear to
have now diminished in amplitude. This is reminiscent of the transient
behavior of similar (1.3 to 1.4 yr) periodicities in solar-wind and
geomagnetic datasets previously reported. We speculate that the near
tachocline oscillation is associated with the rising phase of the
solar cycle. We discuss tests performed to eliminate various possible
explanations of the oscillations due to systematic errors in the data
and in their analyses.
---------------------------------------------------------
Title: On variation of the latitudinal structure of the solar
convection zone
Authors: Antia, H. M.; Chitre, S. M.; Thompson, M. J.
2003A&A...399..329A Altcode: 2002astro.ph.12095A
The latitudinal sound-speed structure of the Sun's convection zone gives
insight into the physical processes occurring there, specifically the
cellular convection and possibly the presence of magnetic fields. Using
helioseismic data from the GONG network and MDI instrument on SOHO,
we map the latitudinal acoustic structure of the convection zone from
1995 to 2002. The temporally averaged structure confirms previous
findings of an excess in sound speed at the 10<SUP>-4</SUP> level at
60 degrees latitude. There also appear to be some variation with time,
with the peak in sound-speed asphericity at 60 degrees growing towards
the maximum of solar activity according to the MDI data. However,
we present some evidence that such variation may be associated with
instrumental variation between the epochs before and after SOHO was
temporarily lost in 1998. Nonetheless, some genuine temporal variation
may be present, and we discuss the possible physical causes of that.
---------------------------------------------------------
Title: Helioseismology present and future
Authors: Thompson, Michael J.
2003ESASP.517..209T Altcode: 2003soho...12..209T
The subject of helioseismology is in a exciting phase of expansion. In
terms of the methods being developed and applied, the new and
challenging results coming out from the high-quality data that
present observational campaigns, networks and missions are providing,
the arrival of GONG+, the prospects for new missions including Solar
Dynamics Observatory, and the recent ground-based results and exciting
prospects for asteroseismology of other solar-like stars. I pick up
on some themes of the conference, and expand on the above developments
and activities.
---------------------------------------------------------
Title: Acoustic Wave Propagation in the Sun: Implications for Wave
Field and Time-Distance Helioseismology
Authors: Tong, C. H.; Thompson, M. J.; Warner, M. R.; Rajaguru, S. P.;
Pain, C. C.
2003ApJ...582L.121T Altcode:
We present results of the numerical simulation of acoustic wave
propagation in the Sun's subphotospheric layers. A finite-difference
code is used to calculate the pressure perturbation in the frequency
domain. We show that the oscillatory seismic signals are closely
associated with the solar density and sound speed structures. Owing
to the acoustic cutoff frequency, the reduction in the group velocity
relative to the background sound speed varies significantly with
frequency, especially at low frequencies. This variation causes
acoustic wave dispersion, which results in the nonuniform frequency
content in the oscillatory signals in the wave packets. An asymptotic
arrival generated by the constructive interference of the high-order
bounces is observed in the synthetic seismic traces. The synthetic
seismic traces presented in this study can provide the basis for wave
field tomography, in which phase and amplitude information (including
the nonresonant frequencies) is exploited, to enhance the spatial
resolution of the reconstructed solar models.
---------------------------------------------------------
Title: Rotation of the solar interior
Authors: Christensen-Dalsgaard, J.; Thompson, M. J.
2003dysu.book...55C Altcode:
Helioseismology allows us to infer the rotation in the greater part
of the solar interior with high precision and resolution. The results
show interesting conflicts with earlier theoretical expectations,
indicating that the Sun is host to complex dynamical phenomena, so
far hardly understood. This has important consequences for our ideas
about the evolution of stellar rotation, as well as for models for
the generation of the solar magnetic field. An overview of our current
knowledge about solar rotation is given, much of it obtained from the
SOHO spacecraft, and the broader implications are discussed.
---------------------------------------------------------
Title: Preface (Stellar astrophysical fluid dynamics)
Authors: Thompson, Michael J.; Christensen-Dalsgaard, Jørgen
2003safd.bookD...9T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On Asteroseismic Constraints for Modelling the δ Scuti Stars
V480 Tau and θ<SUP>2</SUP> Tau A
Authors: Di Mauro, M. P.; Pijpers, F.; Christensen-Dalsgaard, J.;
Paternò, L.; Teixeira, T.; Thompson, M. J.
2003ASPC..305..161D Altcode: 2003mfob.conf..161D
We investigate the structure and evolution of δ Scuti stars and
discuss how basic properties as well as global oscillation frequencies
are modified by moderate rotation. We present theoretical analyses of
V480 Tau, observed during the MUSICOS 1996 campaign (Hao et al. 2001),
and of θ<SUP>2</SUP> Tau A, monitored by the WIRE satellite (Poretti
et al. 2002). We compare the observed spectra of frequencies with the
theoretical oscillation frequencies calculated by including rotational
effects.
---------------------------------------------------------
Title: Seismological analysis of the Helium ionization zones in low-
and moderate-mass stars
Authors: Miglio, A.; Christensen-Dalsgaard, J.; di Mauro, M. P.;
Monteiro, M. J. P. F. G.; Thompson, M. J.
2003aahd.conf..537M Altcode:
The region of the second ionization of helium in solar-like stars is a
narrow subsurface layer whose thermodynamic properties are responsible
for the presence of a characteristic signature in the oscillation
frequencies of the p modes. Here, with the aim of detecting the acoustic
depth of the second helium ionization zone, we consider two methods
of analysing the signal generated in the oscillation frequencies by
the sharp decrease in the first adiabatic exponent Γ<SUB>1</SUB>,
which occurs where ionization takes place. The properties of the
ionization zone, once determined by seismological means, may be used
to put constraints on the structure of the stars, in particular on
the envelope helium abundance.
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Title: Seismic Study of Temporal Variations of Solar Magnetic Field
Authors: Antia, H. M.; Chitre, S. M.; Thompson, M. J.
2003IAUJD..12E..30A Altcode:
The temporal variations of acoustic frequencies of solar oscillations
with the solar activity cycle are studied with a view to understanding
the changes in the Sun's internal magnetic field. The data used are
even a-coefficients from the GONG and MDI observations of the Sun's
p-mode oscillations. These coefficients describe the modification of the
frequencies by agents such as magnetic fields or latitudinal thermal
perturbations that break the spherical symmetry of the Sun but that -
unlike rotational advection and Coriolis forces - do not distinguish
eastward- and westward-propagating acoustic waves. It is hoped that
such a study will shed light on the mechanism of the solar dynamo.
---------------------------------------------------------
Title: A selective overview
Authors: Christensen-Dalsgaard, Jørgen; Thompson, Michael J.
2003safd.book....1C Altcode:
Contents: 1. Introduction. 2. On taking mixing-length
theory seriously. 3. The solar spoon. 4. Deep roots of solar
cycles. 5. Helioseismology: oscillations as a diagnostic of
the solar interior. 6. Inverting helioseismic data. 7. On the
detection of subphotospheric convective velocities and temperature
fluctuations. 8. Prospects for asteroseismic inference.
---------------------------------------------------------
Title: The Internal Rotation of the Sun
Authors: Thompson, Michael J.; Christensen-Dalsgaard, Jørgen; Miesch,
Mark S.; Toomre, Juri
2003ARA&A..41..599T Altcode:
Helioseismology has transformed our knowledge of the Sun's
rotation. Earlier studies revealed the Sun's surface rotation,
but now a detailed observational picture has been built up of the
internal rotation of our nearest star. Unlike the predictions of
stellar-evolution models, the radiative interior is found to rotate
roughly uniformly. The rotation within the convection zone is also
very different from prior expectations, which had been that the
rotation rate would depend primarily on the distance from the rotation
axis. Layers of rotational shear have been discovered at the base of
the convection zone and in the subphotospheric layers. Studies of the
time variation of rotation have uncovered zonal-flow bands, extending
through a substantial fraction of the convection zone, which migrate
over the course of the solar cycle, and there are hints of other
temporal variations and of a jet-like structure. At the same time,
building on earlier work with mean-field models, researchers have made
great progress in supercomputer simulations of the intricate interplay
between turbulent convection and rotation in the Sun's interior. Such
studies are beginning to transform our understanding of how rotation
organizes itself in a stellar interior.
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Title: A Sub-mm Imaging Survey of Ultracompact HII Regions
Authors: Thompson, M.; Hatchell, J.; MacDonald, G.; Millar, T.
2002ASPC..267..429T Altcode: 2001astro.ph.12444T; 2002hsw..work..429T
Ultracompact (UC) H II regions are currently the best known tracer of
massive YSOs and represent the earliest confirmed stage of massive star
formation. In excess of 150 UC HII regions have been detected, mainly
by radio surveys. Whilst the environments of UC HII regions are known
very well on the small scale (a few arcseconds) they are not well known
on scales over 40 arcsec. This is because most UC HII's have, to date,
been observed using either interferometers (to gain information on small
scales at the expense of large scales) or by single-position large-beam
(typically 40 arcsec or worse) spectroscopy. To redress this issue we
recently undertook an imaging survey of over 100 UC HII regions using
SCUBA on the JCMT, which enables us to rapidly map with high-resolution
the dust emission from the clumps in which the UC HII's are embedded.
---------------------------------------------------------
Title: Induced Star Formation Near HII Regions: the Fate of Three
Clouds in IC 1848
Authors: Thompson, M.; White, G.; Miao, J.; Fridlund, M.; Huldtgren, M.
2002ASPC..267..431T Altcode: 2002hsw..work..431T
From a combination of NVSS archive radio continuum data and JCMT
<SUP>12</SUP>CO and <SUP>13</SUP>CO maps we have evaluated the pressure
balance between the ionised exterior and molecular interior of three
bright-rimmed clouds. We predict that photo-ionisation shocks are
currently being driven into two of the clouds whilst the third is
likely to be in a pre-shock state.
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Title: Flux Transport Solar Dynamos with Near-Surface Radial Shear
Authors: Dikpati, Mausumi; Corbard, Thierry; Thompson, Michael J.;
Gilman, Peter A.
2002ApJ...575L..41D Altcode:
Corbard & Thompson analyzed quantitatively the strong radial
differential rotation that exists in a thin layer near the solar
surface. We investigate the role of this radial shear in driving a flux
transport dynamo operating with such a rotation profile. We show that
despite being strong, near-surface radial shear effectively contributes
only ~1 kG (~30% of the total) to the toroidal fields produced there
unless an abnormally high, surface α-effect is included. While 3 kG
spot formation from ~1-2 kG toroidal fields by convective collapse
cannot be ruled out, the evolutionary pattern of these model fields
indicates that the polarities of spots formed from the near-surface
toroidal field would violate the observed polarity relationship with
polar fields. This supports previous results that large-scale solar
dynamos generate intense toroidal fields in the tachocline, from which
buoyant magnetic loops rise to the photosphere to produce spots. Polar
fields generated in flux transport models are commonly much higher
than observed. We show here that by adding enhanced diffusion in the
supergranulation layer (originally proposed by Leighton), near-surface
toroidal fields undergo large diffusive decay preventing spot formation
from them, as well as reducing polar fields closer to the observed
values. However, the weaker polar fields lead to the regeneration of
a toroidal field of less than ~10 kG at the convection zone base,
too weak to produce spots that emerge in low latitudes, unless an
additional poloidal field is produced at the tachocline. This is
achieved by a tachocline α-effect, previously shown to be necessary
for coupling the north and south hemispheres to ensure toroidal and
poloidal fields that are antisymmetric about the equator.
---------------------------------------------------------
Title: Solar internal rotation as seen from SOHO MIDI data
Authors: Vorontsov, S. V.; Christensen-Dalsgaard, J.; Schou, J.;
Strakhov, V. N.; Thompson, M. J.
2002ESASP.508..111V Altcode: 2002soho...11..111V
We report results of inverting the rotational splittings of solar
p-mode frequencies measured from the MDI data, using an adaptive
regularization technique as described by Strakhov & Vorontsov
(2001). We analyse the spatial and temporal structure of the variations
in the internal rotation, which constitute the 11-yr solar torsional
oscillations. We employ all the data collected over half a solar cycle
to analyse further the time-independent component of the differential
rotation, particularly focusing on the solar tachocline region. We
address systematic errors in the rotational splitting measurements,
as indicated by the inversion residuals, which appear to restrict the
accuracy of the current helioseismic measurements.
---------------------------------------------------------
Title: Effect of subsurface radial differential rotation on
flux-transport solar dynamo
Authors: Corbard, T.; Dikpati, M.; Gilman, P. A.; Thompson, M. J.
2002ESASP.508...75C Altcode: 2002soho...11...75C
A near-surface radial gradient of rotation was recently inferred and
quantified from MDI f-modes observations by Corbard & Thompson
(2001). We show, from our preliminary simulation of the large-scale
solar magnetic field, by using a flux-transport type dynamo, that
despite being strong, this gradient plays only a small role compared
to the tachocline in shearing the poloidal fields to produce toroidal
fields. This happens primarily because the turbulent diffusivity near
the surface wins in the competition of generation versus decay of
the magnetic fields unless an abnormally high α-effect is considered
there. This supports the results of previous flux-transport as well
as interface and overshoot layer dynamo models that the major toroidal
fields of the Sun are generated in the tachocline.
---------------------------------------------------------
Title: Helioseismic Measurement of Solar Torsional Oscillations
Authors: Vorontsov, S. V.; Christensen-Dalsgaard, J.; Schou, J.;
Strakhov, V. N.; Thompson, M. J.
2002Sci...296..101V Altcode:
Bands of slower and faster rotation, the so-called torsional
oscillations, are observed at the Sun's surface to migrate in latitude
over the 11-year solar cycle. Here, we report on the temporal variations
of the Sun's internal rotation from solar p-mode frequencies obtained
over nearly 6 years by the Michelson Doppler Imager (MDI) instrument
on board the Solar and Heliospheric Observatory (SOHO) satellite. The
entire solar convective envelope appears to be involved in the torsional
oscillations, with phase propagating poleward and equatorward from
midlatitudes at all depths throughout the convective envelope.
---------------------------------------------------------
Title: A Comparison of Solar p-Mode Parameters from the Michelson
Doppler Imager and the Global Oscillation Network Group: Splitting
Coefficients and Rotation Inversions
Authors: Schou, J.; Howe, R.; Basu, S.; Christensen-Dalsgaard, J.;
Corbard, T.; Hill, F.; Komm, R.; Larsen, R. M.; Rabello-Soares, M. C.;
Thompson, M. J.
2002ApJ...567.1234S Altcode:
Using contemporaneous helioseismic data from the Global Oscillation
Network Group (GONG) and Michelson Doppler Imager (MDI) onboard SOHO,
we compare frequency-splitting data and resulting inversions about the
Sun's internal rotation. Helioseismology has been very successful in
making detailed and subtle inferences about the solar interior. But
there are some significant differences between inversion results
obtained from the MDI and GONG projects. It is important for making
robust inferences about the solar interior that these differences are
located and their causes eliminated. By applying the different analysis
pipelines developed by the projects not only to their own data but
also to the data from the other project, we conclude that the most
significant differences arise not from the observations themselves
but from the different frequency estimation analyses used by the
projects. We find that the GONG pipeline results in substantially fewer
fitted modes in certain regions. The most serious systematic differences
in the results, with regard to rotation, appear to be an anomaly in
the MDI odd-order splitting coefficients around a frequency of 3.5 mHz
and an underestimation of the low-degree rotational splittings in the
GONG algorithm.
---------------------------------------------------------
Title: The subsurface radial gradient of solar angular velocity from
MDI f-mode observations
Authors: Corbard, T.; Thompson, M. J.
2002SoPh..205..211C Altcode: 2001astro.ph.10361C
We report quantitative analysis of the radial gradient of solar
angular velocity at depths down to about 15 Mm below the solar surface
for latitudes up to 75° using the Michelson Doppler Imager (MDI)
observations of surface gravity waves (fmodes) from the Solar and
Heliospheric Observatory (SOHO). A negative outward gradient of around
−400 nHz/R<SUB>⊙</SUB>, equivalent to a logarithmic gradient of
the rotation frequency with respect to radius which is very close
to −1, is found to be remarkably constant between the equator and
30° latitude. Above 30° it decreases in absolute magnitude to a
very small value at around 50°. At higher latitudes the gradient may
reverse its sign: if so, this reversal takes place in a thin layer
extending only 5 Mm beneath the visible surface, as evidenced by the
most superficial modes (with degrees l>250). The signature of the
torsional oscillations is seen in this layer, but no other significant
temporal variations of the gradient and value of the rotation rate
there are found.
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Title: SOLA inversions for the core structure of solar-type stars
Authors: Basu, S.; Christensen-Dalsgaard, J.; Thompson, M. J.
2002ESASP.485..249B Altcode: 2002sshp.conf..249B; 2001astro.ph.10446B
The Subtractive Optimally Localized Averages (SOLA) method, developed
and extensively used in helioseismology, is applied to artificial data
to obtain measures of the sound speed inside a solar-type star. In
contrast to inversion methods which fit models to some aspect of
the data, methods such as SOLA provide an honest assessment of
what can truly be resolved using seismic data, without introducing
additional assumptions such as that the space of admissible stellar
models is small. The resulting measures obtained from SOLA inversion
can subsequently be used to eliminate putative stellar models. Here
we present results of experiments to test the reliability of SOLA
inferences using solar models and models of solar-type stars.
---------------------------------------------------------
Title: On inverting asteroseismic data
Authors: Thompson, M. J.; Christensen-Dalsgaard, J.
2002ESASP.485...95T Altcode: 2002sshp.conf...95T; 2001astro.ph.10447T
Some issues of inverting asteroseismic frequency data are discussed,
including the use of model calibration and linearized inversion. An
illustrative inversion of artificial data for solar-type stars,
using least-squares fitting of a small set of basis functions, is
presented. A few details of kernel construction are also given.
---------------------------------------------------------
Title: Asteroseismic inference for solar-type stars
Authors: Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.; Thompson,
M. J.
2002ESASP.485..291M Altcode: 2001astro.ph.10445M; 2002sshp.conf..291M
The oscillation spectra of solar-type stars may in the not-too-distant
future be used to constrain certain properties of the stars. The C-D
diagram of large versus small frequency separations is one of the
powerful tools available to infer the properties - including perhaps
masses and ages - of stars which display a detectable spectrum of
oscillation. Also, the border of a convective region in a solar-type
star gives rise to a characteristic periodic signal in the star's
low-degree p-mode frequencies. Such a signature contains information
about the location and nature of the transition between convective and
non-convective regions in the star. In this work we address some of
the uncertainties associated with the direct use of the C-D diagram to
evaluate the mass and age of the star due to the unknown contributions
that make the stars different from the evolutionary models used to
construct our reference grid. We also explore the possibility of
combining an amplitude versus period diagram with the C-D diagram to
evaluate the properties of convective borders within solar-type stars.
---------------------------------------------------------
Title: Rotation of the solar interior
Authors: Christensen-Dalsgaard, J.; Thompson, M. J.
2001astro.ph.10607C Altcode:
Helioseismology has allowed us to infer the rotation in the greater part
of the solar interior with high precision and resolution. The results
show interesting conflicts with earlier theoretical expectations,
indicating that the the Sun is host to complex dynamical phenomena,
so far hardly understood. This has important consequences for our
ideas about the evolution of stellar rotation, as well as for models
for the generation of the solar magnetic field. Here we provide an
overview of our current knowledge about solar rotation, much of it
obtained from observations from the SOHO spacecraft, and discuss the
broader implications.
---------------------------------------------------------
Title: Variations of the solar interior with the cycle: observational
aspects.
Authors: Corbard, Thierry; Jimenez-Reyes, S. J.; Thompson, M. J.;
Tomczyk, S.
2001sf2a.conf..109C Altcode:
Helioseismic observations of long duration now open the possibility of
studying the variation of the interior of the Sun during its cycle of
activity. In particular, the possible dynamic or structure variations of
the interface between the convective zone and the radiative interior,
or tachocline, is of great interest to constrain solar dynamo models
and to understand the phenomena at the origin of the cycle of activity
observed at the surface. We have analysed the observations obtained
during the 6 last years by the LOWL instrument located at Mauna Loa,
Hawaii as well as the observations in integrated disc covering more
than one solar cycle (1984-2000) by MARK-I instrument at the Peak del
Teide, Tenerife. The results concerning the signature of the solar
activity on the pressure modes of low and medium degrees and seeks for
possible variations of the dynamic of the tachocline will be presented
and replaced in the theoretical context.
---------------------------------------------------------
Title: Comparing Global Solar Rotation Results from MDI and GONG
Authors: Howe, R.; Komm, R. W.; Hill, F.; Christensen-Dalsgaard, J.;
Schou, J.; Thompson, M. J.; Corbard, T.
2001AGUSM..SP31A14H Altcode:
The GONG (Global Oscillations Network Group) project and the Solar
Oscillations Investigation (SOI) using the Michelson Doppler Imager
(MDI) instrument aboard the SOHO spacecraft have jointly accumulated
more than five years of data on medium-degree solar p-modes, including
nearly four years of contemporaneous observations. The inferences of
interior solar rotation from the two projects are broadly consistent
and show similar temporal variations, but there are also significant
systematic differences. We report here on the results of an ongoing
attempt to cross-compare the results and analysis techniques of the
two projects. Three 108-day periods, at low, medium and high solar
activity epochs, have been analysed, with both MDI and GONG analysis
being applied to each data set, and the results are compared.
---------------------------------------------------------
Title: Variations in Rotation Rate Within the Solar Convection Zone
From GONG and MDI 1995-2000
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Schou, J.; Thompson, M. J.; Toomre, J.
2001AGUSM..SP31A15H Altcode:
Helioseismic measurements with the Michelson Doppler Imager (MDI)
instrument aboard SOHO, and complementary measurements from the Global
Oscillation Network Group (GONG) project, are revealing changes deep
within the Sun as the solar cycle progresses. We will present the
latest results based on recent data from both experiments, including
flows in the upper part of the convection zone and variations in the
rotation rate near its base.
---------------------------------------------------------
Title: Seismology of solar-type stars
Authors: Basu, S.; Christensen-Dalsgaard, J.; Monteiro, M. J. P. F. G.;
Thompson, M. J.
2001ESASP.464..407B Altcode: 2001soho...10..407B
Seismology of solar-type stars other than the Sun becomes a realistic
possibly with the upcoming MOST, COROT and MONS missions, and the
ESA mission Eddington. We report on the results of experiments with
artificial data from models of solar-type stars to assess further what
we might learn about the internal structure of such stars.
---------------------------------------------------------
Title: Inversion for the solar internal rotation with an adaptive
regularization technique
Authors: Vorontsov, S. V.; Christensen-Dalsgaard, J.; Schou, J.;
Strakhov, V. N.; Thompson, M. J.
2001ESASP.464..559V Altcode: 2001soho...10..559V
We report the first preliminary results of applying the adaptive
regularization technique (Strakhov and Vorontsov 2000) to the inversion
for the solar internal rotation. The 360d SOHO MDI data set with 18-th
degree fit to the rotational splittings is used in the 1.5-D and 2-D
inversions, and we used the 72d data sets (Schou 1999) to trace the
possible variations with solar activity.
---------------------------------------------------------
Title: Comparing mode frequencies from MDI and GONG
Authors: Howe, R.; Hill, F.; Basu, S.; Christensen-Dalsgaard, J.;
Komm, R. W.; Munk Larsen, R.; Roth, M.; Schou, J.; Thompson, M. J.;
Toomre, J.
2001ESASP.464..137H Altcode: 2001soho...10..137H
We present results of analyses of MDI and GONG time series covering
the same time intervals, and using both the MDI and GONG peakbagging
algorithms. We discuss some of the likely causes of differences between
the inferred frequencies and frequency splittings. In addition, we
consider the effect of these differences on the results of inversions
for the solar internal rotation and sound speed.
---------------------------------------------------------
Title: Solar cycle changes in convection zone dynamics from MDI and
GONG 1995 - 2000
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Munk Larsen, R.; Schou, J.; Thompson, M. J.; Toomre, J.
2001ESASP.464...19H Altcode: 2001soho...10...19H
The combined GONG and MDI medium-degree helioseismic data sets now cover
just over 5 years and allow us to probe the changing dynamics of the
convection zone in unprecedented detail. Here we present the latest
results from both projects, showing the evolution of the migrating
zonal flows close to the surface and also changes close to and below
the base of the convection zone.
---------------------------------------------------------
Title: Temporal variations of the Sun's internal structure and
dynamics: a theoretical perspective
Authors: Thompson, Michael J.
2001ESASP.464...39T Altcode: 2001soho...10...39T
As is well known from surface observations of magnetic fields, flow
fields and radiation fluxes, the Sun is a highly dynamical object
and varies on many timescales, one of the most prominent being the
22-year period of the solar activity cycle. Recently there has been
much direct evidence from helioseismology (e.g. the many contributions
to this Session) for temporal variations also in the solar interior,
on timescales of months and years. In this review talk I consider
the theoretical expectations of how the solar interior (structure,
magnetic field, velocity field) might change over the solar cycle and
on other timescales, how these changes can be expected to influence
the measurable properties of the oscillations, and possible theoretical
interpretations of some of the recent helioseismic results on temporal
variations of the solar interior.
---------------------------------------------------------
Title: Interior Solar-Cycle Changes Detected by Helioseismology
Authors: Howe, R.; Hill, F.; Komm, R. W.; Christensen-Dalsgaard, J.;
Munk Larsen, R.; Schou, J.; Thompson, M. J.; Toomre, J.
2001IAUS..203...40H Altcode:
Helioseismic measurements with the MDI instrument aboard SOHO,
and complementary measurements from the GONG network, are revealing
changes deep within the Sun as the solar cycle progresses. We will
present results based on recent data from both experiments, including
variations in the rotation rate deep inside the convection zone.
---------------------------------------------------------
Title: On the signature of the solar activity at the base of the
convective envelope
Authors: Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.; Schou,
J.; Thompson, M. J.
2001ESASP.464..535M Altcode: 2001soho...10..535M
A we approach the solar maximum for the current cycle it is timely to
establish what helioseismology can tell us about the internal changes
the Sun undergoes as the cycle progresses. In this work we use SOI-MDI
data in order to identify changes occurring to the stratification of
the Sun at the base of the convective envelope. Both changes with
time (averaged over colatitude) and changes over time at different
colatitudes are addressed. These are discussed in terms of the changes
in the properties of the convection at the base of the envelope in
the region where the tachocline is present. Those variations could
be attributed to the interaction between convection, rotation and
magnetic fields, which must be intrinsically time-dependent phenomena,
possibly correlated with the observed changes occurring over the cycle
in the envelope up to the surface.
---------------------------------------------------------
Title: The Sun's acoustic asphericity and magnetic fields in the
solar convection zone
Authors: Antia, H. M.; Chitre, S. M.; Thompson, M. J.
2000A&A...360..335A Altcode: 2000astro.ph..5587A
The observed splittings of solar oscillation frequencies can be employed
to separate the effects of internal solar rotation and to estimate
the contribution from a large-scale magnetic field or any latitude-
dependent thermal perturbation inside the Sun. The surface distortion
estimated from the rotation rate in the solar interior is found to be
in good agreement with the observed oblateness at solar surface. After
subtracting out the estimated contribution from rotation, there is
some residual signal in the even splitting coefficients, which may be
explained by a magnetic field of approximately 20 kG strength located
at a depth of 30000 km below the surface or an equivalent aspherical
thermal perturbation. An upper limit of 300 kG is derived for a toroidal
field near the base of the convection zone.
---------------------------------------------------------
Title: Seismic study of stellar convective regions: the base of the
convective envelope in low-mass stars
Authors: Monteiro, Mário J. P. F. G.; Christensen-Dalsgaard, Jørgen;
Thompson, Michael J.
2000MNRAS.316..165M Altcode:
The possibility of observing solar-type oscillations on other stars
is of great relevance to investigating the uncertain aspects of the
internal structure of stars. One of these aspects is the convective
overshoot that takes place at the borders of the envelopes of
stars of mass similar to, or lower than, the Sun. It affects the
temperature stratification, mixing, rotation and magnetic-field
generation. Asteroseismology can provide an observational test for the
studies of the structure of such overshoot regions. The seismic study of
the transition in the Sun, located at the base of the convection zone,
has been successful in determining the characteristics of this layer
in the Sun. In this work we consider the extension of the analysis to
other solar-type stars (of mass between 0.85 and 1.2M<SUB>solar</SUB>)
in order to establish a method for determining the characteristics
of their convective envelopes. In particular, we hope to be able to
establish seismologically that a star does indeed possess a convective
envelope, to measure the size of the convective region and also to
constrain the properties of an overshoot layer at the bottom of the
envelope. The limitations in terms of observational uncertainties and
stellar characteristics, and the detectability of an overshoot layer,
are discussed.
---------------------------------------------------------
Title: Helioseismic Search for Magnetic Field in the Solar Interior
Authors: Antia, H. M.; Chitre, S. M.; Thompson, M. J.
2000JApA...21..343A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar-Cycle Changes in Convection-Zone Dynamics from SOI and
GONG Data
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J.
2000SPD....31.0113H Altcode: 2000BAAS...32..803H
The combined GONG and MDI medium-degree helioseismic data sets now cover
more than 4.5 years and allow us to probe the changing dynamics of the
convection zone in unprecedented detail. Here we present the latest
results from both projects, showing the evolution of the migrating zonal
flows close to the surface and also changes close to and below the base
of the convection zone. This work utilizes data obtained by the Global
Oscillation Network Group (GONG) project, managed by the National Solar
Observatory, a Division of the National Optical Astronomy Observatories,
which is operated by AURA, Inc. under a cooperative agreement with the
National Science Foundation. SOHO is a joint project of ESA and NASA.
---------------------------------------------------------
Title: Seismology of solar-type stars
Authors: Thompson, M. J.
2000mons.proc...15T Altcode:
I review the asteroseismology of solar-type stars. The emphasis is on
the theory of what may be learned and how. I draw on our experience
of performing low-degree seismology on the Sun.
---------------------------------------------------------
Title: Deeply Penetrating Banded Zonal Flows in the Solar Convection
Zone
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J.
2000ApJ...533L.163H Altcode: 2000astro.ph..3121H
Helioseismic observations have detected small temporal variations
of the rotation rate below the solar surface that correspond to the
so-called “torsional oscillations” known from Doppler measurements of
the surface. These appear as bands of slower- and faster-than-average
rotation moving equatorward. Here we establish, using complementary
helioseismic observations over 4 yr from the GONG network and from
the MDI instrument on board SOHO, that the banded flows are not
merely a near-surface phenomenon: rather, they extend downward at
least 60 Mm (some 8% of the total solar radius) and thus are evident
over a significant fraction of the nearly 200 Mm depth of the solar
convection zone.
---------------------------------------------------------
Title: Solar shear flows deduced from helioseismic dense-pack
samplings of ring diagrams
Authors: Haber, D. A.; Hindman, B. W.; Toomre, J.; Bogart, R. S.;
Thompson, M. J.; Hill, F.
2000SoPh..192..335H Altcode:
We report on large-scale horizontal flows in the solar convection zone
and their variability in time and space using a local-helioseismology
technique known as ring-diagram analysis. By performing this analysis
on a dense mosaic of individual regions on the solar disk, i.e.,
a `Dense-Pack' sampling, and repeating the analysis periodically on
several time scales, we are able to assess the variation of horizontal
flows from day-to-day, week-to-week, and year-to-year. We find that
although there are changes in the flows on all these time scales,
there are also basic patterns that persist. On a daily time scale we
observe that the flow is reduced in those areas which are occupied
by large active regions. On somewhat longer time-scales we see bands
of persistent fast and slow zonal flow that are identifiable as
torsional oscillations. As we examine these bands during a series of
years, we find that these bands migrate toward the equator as solar
activity increases. Similarly, the latitudes at which the meridional
flow reaches maximum follow these regions of fast zonal flow as they
migrate equatorwards. These Dense-Pack samplings also reveal substantial
differences in the zonal and meridional flow patterns in the northern
and southern hemispheres.
---------------------------------------------------------
Title: Time Variability of Rotation in Solar Convection Zone From
soi-mdi
Authors: Toomre, J.; Christensen-Dalsgaard, J.; Howe, R.; Larsen,
R. M.; Schou, J.; Thompson, M. J.
2000SoPh..192..437T Altcode:
The variation of rotation in the convection zone over a period of two
years from mid-1996 is studied using inversions of SOI-MDI data. We
confirm the existence of near-surface banded zonal flows migrating
towards the equator from higher latitudes, and reveal that these banded
flows extend substantially beneath the surface, possibly to depths
as great as 70 Mm (10% of the solar radius). Our results also reveal
apparently significant temporal variations in the rotation rate at
high latitudes and in the vicinity of the tachocline over the period
of study.
---------------------------------------------------------
Title: Dynamic Variations at the Base of the Solar Convection Zone
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J.
2000Sci...287.2456H Altcode:
We have detected changes in the rotation of the sun near the base of
its convective envelope, including a prominent variation with a period
of 1.3 years at low latitudes. Such helioseismic probing of the deep
solar interior has been enabled by nearly continuous observation of
its oscillation modes with two complementary experiments. Inversion of
the global-mode frequency splittings reveals that the largest temporal
changes in the angular velocity Ω are of the order of 6 nanohertz
and occur above and below the tachocline that separates the sun's
differentially rotating convection zone (outer 30% by radius) from
the nearly uniformly rotating deeper radiative interior beneath. Such
changes are most pronounced near the equator and at high latitudes and
are a substantial fraction of the average 30-nanohertz difference in Ω
with radius across the tachocline at the equator. The results indicate
variations of rotation close to the presumed site of the solar dynamo,
which may generate the 22-year cycles of magnetic activity.
---------------------------------------------------------
Title: Helioseismic detection of temporal variations of solar rotation
rate near the base of the convection zone
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J.
1999AAS...19510702H Altcode: 1999BAAS...31R1530H
The differential rotation of the Sun and its ability to generate
large-scale magnetic fields through cyclic dynamo action appear to be
intimately linked. It is now commonly thought that the global dynamo
behavior responsible for the emergence of active regions is derived
from strong organized toroidal magnetic fields generated by rotational
shear in a thin region (the tachocline) at the base of the convection
zone. The magnetic field could well have a feedback effect on the fluid
motions in the region. We are thus motivated to use helioseismology
to look for changes in rotation profiles near the tachocline as the
Sun's magnetic cycle progresses. This approach has become possible
using frequency-splitting data for p- and f-mode oscillations derived
over four years (from May 1995 to Sept 1999) of full-disk Doppler
observations from the ground-based Global Oscillation Network Group
(GONG) project and from the Michelson Doppler Imager (MDI) experiment
aboard the SOHO spacecraft. Inversions using two different methods of
the splittings from these two independent data sets reveal systematic
variations of the rotation rate close to the base of the convection
zone, with different behavior at low and high latitudes. Notable
are variations of order 6 nHz in rotation rates near the equator,
to be compared with the radial angular velocity contrast across the
tachocline of about 30 nHz. These exhibit several nearly repetitive
changes with a period of about 1.2-1.4 years and appear to be real
changes in the deep convection zone and tachocline rotation rates that
need to be followed as the solar cycle progresses. The GONG project is
managed by the National Solar Observatory, a Division of the National
Optical Astronomy Observatories, which is operated by AURA, Inc. under
a cooperative agreement with the National Science Foundation. SOHO is
a joint project of ESA and NASA.
---------------------------------------------------------
Title: Helioseismic Constraints on the Structure of the Solar
Tachocline
Authors: Charbonneau, P.; Christensen-Dalsgaard, J.; Henning, R.;
Larsen, R. M.; Schou, J.; Thompson, M. J.; Tomczyk, S.
1999ApJ...527..445C Altcode:
This paper presents a series of helioseismic inversions aimed at
determining with the highest possible confidence and accuracy the
structure of the rotational shear layer (the tachocline) located
beneath the base of the solar convective envelope. We are particularly
interested in identifying features of the inversions that are robust
properties of the data, in the sense of not being overly influenced
by the choice of analysis methods. Toward this aim we carry out
two types of two-dimensional linear inversions, namely Regularized
Least-Squares (RLS) and Subtractive Optimally Localized Averages
(SOLA), the latter formulated in terms of either the rotation rate or
its radial gradient. We also perform nonlinear parametric least-squares
fits using a genetic algorithm-based forward modeling technique. The
sensitivity of each method is thoroughly tested on synthetic data. The
three methods are then used on the LOWL 2 yr frequency-splitting
data set. The tachocline is found to have an equatorial thickness
of w/R<SUB>solar</SUB>=0.039+/-0.013 and equatorial central radius
r<SUB>c</SUB>/R<SUB>solar</SUB>=0.693+/-0.002. All three techniques
also indicate that the tachocline is prolate, with a difference in
central radius Δr<SUB>c</SUB>/R<SUB>solar</SUB>~=0.024+/-0.004 between
latitude 60° and the equator. Assuming uncorrelated and normally
distributed errors, a strictly spherical tachocline can be rejected
at the 99% confidence level. No statistically significant variation
in tachocline thickness with latitude is found. Implications of these
results for hydrodynamical and magnetohydrodynamical models of the
solar tachocline are discussed.
---------------------------------------------------------
Title: Rotation of the solar interior
Authors: Christensen-Dalsgaard, Jørgen; Thompson, Michael J.
1999CSci...77.1460C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Effects of line asymmetries on the determination of solar
internal structure
Authors: Rabello-Soares, M. C.; Christensen-Dalsgaard, J.; Rosenthal,
C. S.; Thompson, M. J.
1999A&A...350..672R Altcode: 1999astro.ph..8250R
Despite the strong evidence that the peaks in the spectrum of solar
oscillations are asymmetric, most determinations of mode frequencies
have been based on fits of symmetric Lorentzian profiles to the Fourier
or power spectra of oscillation time strings. The systematic errors
resulting from neglecting the line asymmetry could have serious effects
on inversions for the solar internal structure and rotation. Here we
analyse artificial data based on simple models of the intrinsic line
asymmetry, using GONG mode parameters with asymmetries found by one
of us (Rosenthal \cite{rosenthal2}). By fitting Lorentzians to the
resulting spectra, we estimate the likely properties of the errors
introduced in the frequencies. We discuss whether these frequency
shifts have a form similar to the near-surface layers uncertainties
and are therefore suppressed in the solar structure inversion. We also
estimate directly their contribution, if any, in the solar sound-speed
and density determinations using the SOLA technique.
---------------------------------------------------------
Title: A note on Saio's estimate of second-order effects of rotation
on stellar oscillation frequencies
Authors: Christensen-Dalsgaard, J.; Thompson, M. J.
1999A&A...350..852C Altcode:
In many cases, oscillating stars rotate so rapidly that second-order
effects must be taken into account in analyses of the oscillation
frequencies. Such investigations have commonly been based on results
provided by Saio (1981) for a polytropic model. Here we compare those
with frequency changes for more realistic models; we point out that
a simple correction to Saio's data allows them to be used in the
observationally relevant case of comparing models at fixed luminosity
and effective temperature.
---------------------------------------------------------
Title: Rotation of the solar core from BiSON and LOWL frequency
observations
Authors: Chaplin, W. J.; Christensen-Dalsgaard, J.; Elsworth, Y.;
Howe, R.; Isaak, G. R.; Larsen, R. M.; New, R.; Schou, J.; Thompson,
M. J.; Tomczyk, S.
1999MNRAS.308..405C Altcode:
Determination of the rotation of the solar core requires very accurate
data on splittings for the low-degree modes which penetrate to the core,
as well as for modes of higher degree to suppress the contributions
from the rest of the Sun to the splittings of the low-degree modes. Here
we combine low-degree data based on 32 months of observations with the
BiSON network and data from the LOWL instrument. The data are analysed
with a technique that specifically aims at obtaining an inference of
rotation that is localized to the core. Our analysis provides what we
believe is the most stringent constraint to date on the rotation of
the deep solar interior.
---------------------------------------------------------
Title: Strange baryon production in p-Pb collisions at 158 GeV
img1.gif: a comparison with VENUS model
Authors: Virgili, T.; WA97 Collaboration; Andersen, E.; Antinori,
F.; Armenise, N.; Bakke, H.; Bán, J.; Barberis, D.; Beker, H.;
Beusch, W.; Bloodworth, I. J.; Böhm, J.; Caliandro, R.; Campbell,
M.; Cantatore, E.; Carrer, N.; Catanesi, M. G.; Chesi, E.; Dameri,
M.; Darbo, G.; Diaczek, A.; Di Bari, D.; Di Liberto, S.; Earl, B. C.;
Elia, D.; Evans, D.; Fanebust, K.; Fini, R. A.; Fontaine, J. C.;
Ftácnik, J.; Ghidini, B.; Grella, G.; Guida, M.; Heijne, E. H. M.;
Helstrup, H.; Holme, A. K.; Huss, D.; Jacholkowski, A.; Jones,
G. T.; Jovanovic, P.; Jusko, A.; Kachelhoffer, T.; Kinson, J. B.;
Kirk, A.; Klempt, W.; Knudsen, B. T. H.; Knudson, K.; Králik, I.;
Lenti, V.; Lietava, R.; Loconsole, R. A.; Løvhøiden, G.; Lupták,
M.; Mack, V.; Manzari, V.; Martinengo, P.; Mazzoni, M. A.; Meddi, F.;
Michalon, A.; Michalon-Mentzer, M. E.; Middelkamp, P.; Morando, M.;
Muciaccia, M. T.; Nappi, E.; Navach, F.; Norman, P. I.; Osculati,
B.; Pastircák, B.; Pellegrini, F.; Piska, K.; Posa, F.; Quercigh,
E.; Ricci, R. A.; Romano, G.; Rosa, G.; Rossi, L.; Rotscheidt, H.;
Safarik, K.; Saladino, S.; Salvo, C.; Sándor, L.; Scognetti, T.;
Segato, G.; Sené, M.; Sené, R.; Simone, S.; Snoeys, W.; Staroba,
P.; Szafran, S.; Thompson, M.; Thorsteinsen, T. F.; Tomasicchio, G.;
Torrieri, G. D.; Tveter, T. S.; Urbán, J.; Venables, M.; Villalobos
Baillie, O.; Virgili, T.; Volte, A.; Votruba, M. F.; Závada, P.
1999JPhG...25..345V Altcode:
img2.gif, img3.gif, and img4.gif yields measured by the WA97 experiment
at central rapidity in p-Pb interactions at 158 GeV/c are compared to
those predicted by VENUS 4.12. The VENUS model, although in reasonable
agreement with the img2.gif and the negative particle data, fails to
reproduce the data on multistrange baryons and anti-baryons.
---------------------------------------------------------
Title: Time-Variability of the Inferred Rotation in the Upper
Convection Zone
Authors: Toomre, J.; Christensen-Dalsgaard, J.; Howe, R.; Larsen,
R. M.; Schou, J.; Thompson, M. J.
1999soho....9E..87T Altcode:
We present results of inverting for the rotation of the upper convection
zone, using frequency splittings derived from successive 72-day time
series of SOI-MDI observations. Schou (1999; also Schou et al. 1998)
has studied the evolution of the pattern of small-scale zonal flows
in the near-surface layers using f-mode splittings and has found that
this flow pattern migrates equatorward in a manner similar to that seen
in the so-called torsional oscillation observed in surface Doppler
measurements. In the present work we look at the time variability
of the rotation at greater depth, in the upper convection zone, by
inverting both f- and p-mode splittings. The evolution of the flow is
less regular than is seen at the surface, but we do observe apparently
significant variations in the inferred flow pattern, on latitudinal
scales similar to those seen at the surface. In particular, in the
subsurface shear layer we see intriguing variations, with the first
year's data showing apparent emergence of zonal flows of some 10-15
m/s amplitude at around 20 degrees latitude.
---------------------------------------------------------
Title: Convective Envelopes in Solar-Type Stars: What Can We Learn
from their Seismic Study?
Authors: Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.; Thompson,
M. J.
1999ASPC..173..273M Altcode: 1999sstt.conf..273M
No abstract at ADS
---------------------------------------------------------
Title: Simulation of Wave Fields to Assess the Sensitivity of
Ring-Diagram Analyses to Shearing Flows
Authors: Hindman, B. W.; Gough, D. O.; Haber, D. A.; Thompson, M. J.;
Toomre, J.
1999soho....9E..64H Altcode:
Ring-diagram analyses of acoustic-wave distortion by flows map
horizontal motions within the solar convection beneath the localized
regions where the observations are taken. To leading order, the
flow field responsible for the advection of waves is taken to be
horizontally uniform across the region. Current ring-diagram analyses
are only carried out to this order, although in reality the flow
is likely to vary across the local patch of the Sun. It is crucial
for the interpretation of the results of ring-diagram analyses that
the effects of shearing flows be assessed. Furthermore, the present
analyses ignore any influence on the ring parameters of flows exterior
to the region being studied. We present a progress report on the
forward calculation of the modification of ring parameters produced
by spatially varying flow fields. We examine effects of flow fields
both inside and outside the region of observation. Additionally,
we assess the influence of the non-uniform flow on the maps of the
velocity field obtained by inverting the ring-parameter data. The
effect of the inhomogeneous flow can be studied as a scattering
problem. We have developed Green functions connecting an underlying
inhomogeneous horizontal flow to the scattered wave field that results
when an incident plane wave encounters the flow. By considering an
ensemble of such incident waves, ring parameters can be inferred from
the wave field. One application is to analyze artificial data sets,
computed from models that contain horizontal shear flows. The scattered
wave field produced by a prescribed 3-D shearing flow is computed,
and the original and scattered wave fields are combined to generate an
artificial helioseismic data set. The artificial data so produced should
then be passed through a ring-diagram analysis and the deduced velocity
field compared to the known imposed flow. Another application is to
compute 3-D kernels relating the ring parameters to the underlying flow:
these will in the future permit 3-D inversions for the flows within
the solar convection zone, using mosaics of many ring-diagram samplings.
---------------------------------------------------------
Title: Helioseismic Studies of Differential Rotation in the Solar
Envelope by the Solar Oscillations Investigation Using the Michelson
Doppler Imager
Authors: Schou, J.; Antia, H. M.; Basu, S.; Bogart, R. S.; Bush,
R. I.; Chitre, S. M.; Christensen-Dalsgaard, J.; Di Mauro, M. P.;
Dziembowski, W. A.; Eff-Darwich, A.; Gough, D. O.; Haber, D. A.;
Hoeksema, J. T.; Howe, R.; Korzennik, S. G.; Kosovichev, A. G.;
Larsen, R. M.; Pijpers, F. P.; Scherrer, P. H.; Sekii, T.; Tarbell,
T. D.; Title, A. M.; Thompson, M. J.; Toomre, J.
1998ApJ...505..390S Altcode:
The splitting of the frequencies of the global resonant acoustic modes
of the Sun by large-scale flows and rotation permits study of the
variation of angular velocity Ω with both radius and latitude within
the turbulent convection zone and the deeper radiative interior. The
nearly uninterrupted Doppler imaging observations, provided by the
Solar Oscillations Investigation (SOI) using the Michelson Doppler
Imager (MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft
positioned at the L<SUB>1</SUB> Lagrangian point in continuous sunlight,
yield oscillation power spectra with very high signal-to-noise ratios
that allow frequency splittings to be determined with exceptional
accuracy. This paper reports on joint helioseismic analyses of
solar rotation in the convection zone and in the outer part of the
radiative core. Inversions have been obtained for a medium-l mode set
(involving modes of angular degree l extending to about 250) obtained
from the first 144 day interval of SOI-MDI observations in 1996. Drawing
inferences about the solar internal rotation from the splitting data
is a subtle process. By applying more than one inversion technique
to the data, we get some indication of what are the more robust
and less robust features of our inversion solutions. Here we have
used seven different inversion methods. To test the reliability and
sensitivity of these methods, we have performed a set of controlled
experiments utilizing artificial data. This gives us some confidence
in the inferences we can draw from the real solar data. The inversions
of SOI-MDI data have confirmed that the decrease of Ω with latitude
seen at the surface extends with little radial variation through much
of the convection zone, at the base of which is an adjustment layer,
called the tachocline, leading to nearly uniform rotation deeper
in the radiative interior. A prominent rotational shearing layer in
which Ω increases just below the surface is discernible at low to
mid latitudes. Using the new data, we have also been able to study the
solar rotation closer to the poles than has been achieved in previous
investigations. The data have revealed that the angular velocity
is distinctly lower at high latitudes than the values previously
extrapolated from measurements at lower latitudes based on surface
Doppler observations and helioseismology. Furthermore, we have found
some evidence near latitudes of 75° of a submerged polar jet which
is rotating more rapidly than its immediate surroundings. Superposed
on the relatively smooth latitudinal variation in Ω are alternating
zonal bands of slightly faster and slower rotation, each extending
some 10° to 15° in latitude. These relatively weak banded flows
have been followed by inversion to a depth of about 5% of the solar
radius and appear to coincide with the evolving pattern of “torsional
oscillations” reported from earlier surface Doppler studies.
---------------------------------------------------------
Title: A strategy for fitting partially blended ridges in GONG solar
p-mode spectra
Authors: Howe, R.; Thompson, M. J.
1998A&AS..131..539H Altcode:
Observations of solar oscillations by the Global Oscillation Network
Group (GONG) using a network of telescopes deployed around the Earth
eliminate temporal aliases from the oscillation power spectra to a
very substantial extent, making the measurement of oscillation mode
parameters much cleaner than with single-site observations. However,
the problem of spatial aliasing, which arises from the fact that we see
only one side of the Sun, still causes some problems. We discuss some
of the issues affecting the estimation of medium-l solar acoustic mode
parameters from the data obtained by the GONG network, and in particular
the contamination by spatial leakage. We determine the areas in the
l-nu plane in which such leakage is a problem, and finally we describe
a method for improving the mode frequency estimation in such regions,
thus extending the range of modes for which useful frequency estimates
can be obtained.
---------------------------------------------------------
Title: The Rotation of the Solar Core Inferred by Genetic Forward
Modeling
Authors: Charbonneau, P.; Tomczyk, S.; Schou, J.; Thompson, M. J.
1998ApJ...496.1015C Altcode:
Genetic forward modeling is a genetic algorithm-based modeling technique
that can be used to perform helioseismic inversions of the Sun's
internal angular velocity profile. The method can easily accommodate
constraints such as positivity and monotonicity and readily lends itself
to the use of robust statistical goodness-of-fit estimators. After
briefly describing the technique, we ascertain its performance
by carrying out a series of inversions for artificial splitting
data generated from a set of synthetic internal rotation profiles
characterized by various small inward increases in angular velocity in
the deep solar core (r/R<SUB>⊙</SUB> <= 0.5). These experiments
indicate that the technique is accurate down to r/R<SUB>⊙</SUB>
~= 0.2, and retains useful sensitivity down to r/R<SUB>⊙</SUB> ~=
0.1. <P />We then use genetic forward modeling in conjunction with the
LOW degree L (LOWL) 2 year frequency-splitting data set to determine
the rotation rate in the deep solar core. We perform a large set
of one-dimensional and 1.5-dimensional inversions using regularized
least-squares minimization, conventional least-squares minimization
with a monotonicity constraint (∂Ω/∂r <= 0), and inversions
using robust statistical estimators. These calculations indicate that
the solar core rotates very nearly rigidly down to r/R<SUB>⊙</SUB> ~
0.1. More specifically, on spatial scales >~0.04 R<SUB>⊙</SUB> we
can rule out inward increases by more than 50% down to r/R<SUB>⊙</SUB>
= 0.2, and by more than a factor of 2 down to r/R<SUB>⊙</SUB> =
0.1. Thorough testing of various possible sources of bias associated
with our technique indicates that these results are robust with respect
to intrinsic modeling assumptions. Consequences of our results for
models of the rotational evolution of the Sun and solar-type stars
are discussed.
---------------------------------------------------------
Title: Slow Poles and Shearing Flows from Heliospheric Observations
with MDI and GONG Spanning a Year
Authors: Schou, J.; Christensen-Dalsgaard, J.; Howe, R.; Larsen,
R. M.; Thompson, M. J.; Toomre, J.
1998ESASP.418..845S Altcode: 1998soho....6..845S
We invert one year of coeval high-resolution rotational splitting data
(up to degree l 250) from GONG and SOI-MDI. The first 4 months of
MDI data uncovered several new features in the rotation of the solar
convective envelope: surface and subsurface zonal bands corresponding
to the so-called torsional oscillations, superimposed on the overall
smooth latitudinal surface rotation; a drop in the near-polar surface
rotation rate below the rate extrapolated from lower latitudes; and an
indication of a prograde jet-like feature at high latitudes at a depth
of about 5 percent of the solar radius. Using the 1 year of data from
the MDI and GONG instruments, we test the robustness and stationarity of
these features. As an aid to testing the robustness of our inferences,
we use two independent inversion methods (2-D regularized least squares
and SOLA) and apply them to the splitting data obtained from both GONG
and MDI.
---------------------------------------------------------
Title: Seismic Constraints on Sound Speed in the Solar Core
Authors: Rabello-Soares, M. C.; Christensen-Dalsgaard, J.; Thompson,
M. J.
1998ESASP.418..511R Altcode: 1998soho....6..511R
Direct seismic information about the structure of the solar core from
measured p-mode frequencies is based on only a modest number of modes
of low degree. Hence it is difficult to obtain local measures of,
for example, the variation of the sound speed in the core. However,
even averages of the central sound-speed difference between the Sun
and a model would be of considerable diagnostic value, provided that
these averages could be effectively restricted to a sufficiently
small region. Chaplin et al. (1998) developed a technique, based on
the method of optimally localized averages introduced by Backus &
Gilbert, to construct an average of the rotation of the solar core,
and this was applied with some success to combined BiSON and LOWL
data. Here we investigate a similar procedure for constructing averages
of the sound-speed difference between the Sun and a reference model,
localized to the core. These provide seismic constraints on core
structure that are only minimally sensitive to uncertainties in other
regions of the Sun.
---------------------------------------------------------
Title: The Base of the Convection Zone and the Solar Magnetic Cycle:
Seismic Detection of Their Connection
Authors: Monteiro, Mario J. P. F. G.; Christensen-Dalsgaard, Jorgen;
Thompson, Michael J.
1998ESASP.418..495M Altcode: 1998soho....6..495M
It is now possible to detect small variations with time of the
characteristics of the transition at the bottom of the solar convection
zone, as determined from the periodic signal in the frequencies
(Christensen-Dalsgaard et.al. 1995, Basu 1997). Such measurements may
allow us to establish whether and in what manner the deeper convection
zone changes with the solar magnetic cycle. This would be important
for understanding the dynamics at the base of the convection zone and
the origin of the solar cycle. It will also help in understanding
the physics of convective overshoot, its interaction with rotation
and magnetic fields, and the effects on the stratification. In this
work we investigate the limits on the detectability of small changes
in the stratification at the base of the convection zone, and attempt
to constrain the amplitude of the changes from currently available
seismic data.
---------------------------------------------------------
Title: On the seismic signature of the HeII ionization zone in
stellar envelopes
Authors: Monteiro, M. J. P. F. G.; Thompson, M. J.
1998IAUS..185..317M Altcode:
The method developed for the seismic measurement of convective overshoot
(Christensen-Dalsgaard et al 1995, MNRAS 276, 283) can be extended in
order to study the layer where the second ionization of helium takes
place in a star's envelope. Because this zone is confined to a very thin
region the effects on the structure can be treated as the result of a
localized perturbation to an otherwise smooth behaviour. Therefore,
we may hope to be able to use the characteristic periodic signal
in the frequencies of oscillation, arising from such a localized
perturbation, to determine important aspects of this region. In this
poster we present the theoretical analysis of such a signal showing
how its different characteristics are associated with the different
physical aspects contributing for the zone of the second ionization
of helium. Some of these aspects we consider are the envelope helium
abundance and the properties of the equation of state (EOS). In this
way we attempt to establish how such a characteristic signal can be
used to study seismologically the Sun and other stars.
---------------------------------------------------------
Title: Asteroseismology and Stellar Rotation
Authors: Kjeldsen, H.; Arentoft, T.; Bedding, T.;
Christensen-Dalsgaard, J.; Frandsen, S.; Thompson, M. J.
1998ESASP.418..385K Altcode: 1998soho....6..385K
Δ Scuti stars are observed to rotate with surface velocities of the
order 100-200 km/s corresponding to a rotation period of about one
day. Rotation removes the frequency degeneracy in the azimuthal order m
of the modes and thus allows the possibility of determining the angular
velocity inside the star. Rotation also perturbs the internal structure
of the star, making the star oblate, as well as changing the internal
stratification. Such perturbations will result in a systematic change of
all frequencies, if compared with a non-rotating star of similar mass
and age. In this way even the radial (l = 0) mode frequencies will be
affected by the rotation of the star. We discuss how basic properties
as well as frequencies of δ Scuti stars are affected by fast rotation
and we investigate the impact of these changes on our interpretation
of observed frequencies used in an asteroseismic analysis. We discuss
the results in the light of the currently available frequency data
for δ Scuti stars in the Praesepe cluster.
---------------------------------------------------------
Title: Looking for Variations with Latitude of the Base of the Solar
Convection Zone
Authors: Monteiro, M. J. P. F. G.; Thompson, M. J.
1998ESASP.418..819M Altcode: 1998soho....6..819M
The Sun's m-averaged frequencies of global oscillations have been used
successfully in determining the basic characteristics of the base of the
solar convective region (e.g. Christensen-Dalsgaard et.al. 1995, Basu
1997). In particular, it has been possible to constrain its location
and more particularly the extent of convective overshoot. With higher
quality data now available it is becoming possible to isolate the
properties of this region at different latitudes. This is important
for the modelling aspects such as mixing and convective overshoot
occurring at the base of the convection zone. It can also have
interesting interplay with the rotation profile around the region of
the tachocline and the generation of magnetic fields. Such properties
as deeper penetration of the convection at certain latitudes may be
intimately connected with the angular velocity profile there, and the
identification of such characteristics in the thermal stratification
is therefore important to complement the information from the rotation
inversions (Schou et al. 1998). Here we present an analysis of SOI--MDI
data to try to detect such latitudinal variations.
---------------------------------------------------------
Title: Space Asteroseismology on Later-type Stars
Authors: Roxburgh, Ian W.; Thompson, Michael J.
1998Ap&SS.261...13R Altcode: 1999Ap&SS.261...13R
No abstract at ADS
---------------------------------------------------------
Title: Inversion Methods
Authors: Thompson, M. J.
1998IAUS..185..125T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: What We Have Learned from Helioseismology
Authors: Thompson, Michael J.
1998Ap&SS.261...23T Altcode: 1999Ap&SS.261...23T
The Sun's global oscillations, which are studied both in spatially
unresolved ("Sun-as-a-star") and resolved observations of the
solar disk, have enabled helioseismology to probe in detail the
solar interior. I review first what is learned from the unresolved
measurements, since this gives an idea of what we may in the not too
distant future be able to learn about the interiors of other stars
undergoing solar-type oscillations. I then look at the main results
from resolved observations, which have begun to reveal the structure
and dynamics of the interior of a star in exquisite detail.
---------------------------------------------------------
Title: Effects of Line Asymmetries on the Determination of Solar
Oscillation Frequencies
Authors: Christensen-Dalsgaard, J.; Rabello-Soares, M. C.; Rosenthal,
C. S.; Thompson, M. J.
1998ESASP.418..147C Altcode: 1998soho....6..147C
Despite the strong evidence that the peaks in the spectrum of solar
oscillations are asymmetric, most determinations of mode frequencies
have been based on fits of symmetric Lorentzian profiles to the Fourier
or power spectra of oscillation time strings. The systematic errors
resulting from neglecting the line asymmetry could have serious effects
on inversions for the solar internal structure and rotation. Here we
analyze artificial data based on simple models of the intrinsic line
asymmetry. By fitting Lorentzians to the resulting spectra, we estimate
the likely properties of the errors introduced in the frequencies and
consider the possible effects on the inversions.
---------------------------------------------------------
Title: Seismic detection of boundaries of stellar convective regions
Authors: Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.; Thompson,
M. J.
1998IAUS..185..315M Altcode:
The seismic study of the base of the convection zone in the Sun (eg
Christensen-Dalsgaard et al 1995, MNRAS 276, 283) has been successful
in determining not only the position of the base of the convective
envelope, but also the characteristics of this transition layer. In
this poster we consider other types of star possessing convective
envelopes or cores and seek to establish the conditions under which we
may determine important characteristics of their convective regions. In
particular we may hope to establish seismologically that a star does
indeed posess a convective envelope or core and to measure the size
of that convective region. The method used consists in identifying a
signal in the observed frequencies whose characteristics depend on
the location of the border of a convective region in the star. The
limitations in terms of observational uncertainties and stellar
characteristics are presented.
---------------------------------------------------------
Title: Detection of the Lower Boundary of Stellar Convective Envelopes
from Seismic Data
Authors: Monteiro, Mário J. P. F. G.; Christensen-Dalsgaard, Jørgen;
Thompson, Michael J.
1998Ap&SS.261...41M Altcode: 1999Ap&SS.261...41M
No abstract at ADS
---------------------------------------------------------
Title: Diagnostic Potential of the Solar f Modes
Authors: Chitre, S. M.; Christensen-Dalsgaard, J.; Thompson, M. J.
1998ESASP.418..141C Altcode: 1998soho....6..141C
The frequencies of f modes of intermediate and high degree l of a
stellar model in hydrostatic equilibrium are essentially given by ω
= square root {g k<SUB>h</SUB>}, where to a good first approximation
g is the surface gravitational acceleration G M / R<SUP>2</SUP> and
k<SUB>h</SUB> = square root {l(l+1)}/R, M and R being the mass and
radius respectively of the model. More precisely, the frequency is
determined not simply by the surface values of these quantities but
by a weighted average over the region where the mode has appreciable
amplitude. Thus the frequencies of the f modes depend on the density
stratification in the near-surface region (Gough 1985, 1993). Given
the very high accuracy to which the f-mode frequencies can now
be determined, in particular from the SOI/MDI experiment on SOHO,
this sensitivity may provide an important diagnostic of the Sun's
near-surface structure. We investigate this sensitivity, in terms of
numerical kernels and the simple analytical approximation derived by
Gough. In addition, we consider the possibilities for investigating
time variations and asphericity in solar structure on the basis of
f-mode observations.
---------------------------------------------------------
Title: The SOI-MDI High-Latitude Jet: the Evidence For and Against
Authors: Howe, R.; Antia, H.; Basu, S.; Christensen-Dalsgaard, J.;
Korzennik, S. G.; Schou, J.; Thompson, M. J.
1998ESASP.418..803H Altcode: 1998soho....6..803H
The apparent detection of a prograde jet at latitude 75-circ and at a
radius of about 0.95R<SUB>odot</SUB> in some inversions of rotation data
from SOI--MDI (Schou et al., 1998) has excited considerable interest,
but whether the jet really exists in the solar interior is certainly not
yet firmly established. The detection of the feature is sensitive both
to the inversion techniques used and to the methods of mode parameter
estimation used to generate the input data. In particular, the feature
is much more apparent in Regularized Least-Squares inversions than
in inversions using an Optimally Localized Average approach, and is
not detected at all in the present GONG data when analysed with the
GONG peakfinding algorithm, or indeed in SOI data when analysed with
the GONG algorithm. Therefore in this poster we examine critically
the current evidence for the source and existence of this jet in the
light of forward and inverse analyses.
---------------------------------------------------------
Title: Solar internal sound speed as inferred from combined BiSON
and LOWL oscillation frequencies
Authors: Basu, Sarbani; Christensen-Dalsgaard, J.; Chaplin, W. J.;
Elsworth, Y.; Isaak, G. R.; New, R.; Schou, J.; Thompson, M. J.;
Tomczyk, S.
1997MNRAS.292..243B Altcode: 1997astro.ph..2105B
Observations of the Sun with the LOWL instrument provide a homogeneous
set of solar p-mode frequencies from low to intermediate degree that
allow one to determine the structure of much of the solar interior
avoiding systematic errors that are introduced when different data sets
are combined, i.e., principally the effects of solar cycle changes on
the frequencies. Unfortunately, the LOWL data set contains very few of
the lowest-degree modes, which are essential for determining reliably
the structure of the solar core - in addition, these lowest-degree data
have fairly large associated uncertainties. However, observations made
by the Birmingham Solar-Oscillations Network (BiSON) in integrated
sunlight provide high-accuracy measurements of a large number of
low-degree modes. In this paper we demonstrate that the low-degree mode
set of the LOWL data can be successfully combined with the more accurate
BiSON data, provided the observations are contemporaneous for those
frequencies where the solar cycle induced effects are important. We
show that this leads to a factor of 2 decrease in the error on the
inferred sound speed in the solar core. We find that the solar sound
speed is higher than in solar models for r<0.2Rsolar. The density
of the solar core is, however, lower than that in solar models.
---------------------------------------------------------
Title: Rotation and Zonal Flows in the Solar Envelope from the
SOHO/MDI Observations
Authors: Scherrer, P. H.; Schou, J.; Bogart, R. S.; Bush, R. I.;
Hoeksema, J. T.; Kosovichev, A. G.; Antia, H. M.; Chitre, S. M.;
Christensen-Dalsgaard, J.; Larsen, R. M.; Pijpers, F. P.; Eff-Darwich,
A.; Korzennik, S. G.; Gough, D. O.; Sekii, T.; Howe, R.; Tarbell,
T.; Title, A. M.; Thompson, M. J.; Toomre, J.
1997AAS...191.7310S Altcode: 1997BAAS...29.1322S
We report on the latest inferences concerning solar differential
rotation that have been drawn from the helioseismic data that are now
available from the Solar Oscillations Investigation (SOI) using the
Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory
(SOHO). That spacecraft is positioned in a halo orbit near the Sun-Earth
Lagrangian point L_1, in order to obtain continuous Doppler-imaged
observations of the sun with high spatial fidelity. Doppler velocity,
intensity and magnetic field images are recorded, based on modulations
of the 676.8 nm Ni I solar absorption line. The high spatial resolution
of MDI thereby permits the study of many millions of global resonant
modes of solar oscillation. Determination and subsequent inversion
of the frequencies of these modes, including the degeneracy-splitting
by the rotation of the sun, enables us to infer how the sun's angular
velocity varies throughout much of the interior. The current MDI data
are providing substantial refinements to the helioseismic deductions
that can be made about differential rotation both within the convection
zone and in its transition to the radiative interior. The shearing
layer evident in the angular velocity Omega just below the solar
surface is becoming better defined, as is the adjustment layer or
tachocline near the base of the convection zone. The MDI data are also
revealing a prominent decrease in Omega at high latitudes from the
rotation rate expressed by a simple three-term expansion in latitude
that was originally deduced from surface Doppler measurements. Further,
there are indications that a submerged polar vortex involving somewhat
faster Omega than its surroundings exists at about 75(deg) in latitudes.
---------------------------------------------------------
Title: SVD preprocessing of helioseismic data for solar structure
inversion.
Authors: Basu, S.; Christensen-Dalsgaard, J.; Thompson, M. J.
1997A&A...321..634B Altcode:
Helioseismic inversion to determine solar structure is based on the
analysis of very substantial numbers of modes and hence may involve
considerable computational expense. This is particularly true for
inversions using methods of optimally localised averages, which
require inversion of matrices whose order is the number of modes in
the set; yet such methods are desirable to make the full use of the
data. On the other hand, there is considerable redundancy in the
data, different modes carrying almost the same information about
solar structure. Thus, in the unavoidable presence of data errors,
the number of independent pieces of information is generally much
less than the number of modes. This suggests that the mode-set can
be reduced by forming suitable combinations of the data before the
more computationally intensive inversion is performed. We show that
such combinations may be based on singular value decomposition (SVD)
of the problem, leading to a drastically reduced inverse problem whose
solution is essentially indistinguishable from the solution of the
original problem. In addition, the results of the SVD provide insight
into the information content of the helioseismic data.
---------------------------------------------------------
Title: Structure and Rotation of the Solar Interior: Initial Results
from the MDI Medium-L Program
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.;
Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.; de
Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.; Scott,
K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard, J.; Dappen,
W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.; Thompson, M. J.;
Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.; Title, A. M.;
Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson, C. J.; Zayer, I.;
Milford, P. N.
1997SoPh..170...43K Altcode:
The medium-l program of the Michelson Doppler Imager instrument on board
SOHO provides continuous observations of oscillation modes of angular
degree, l, from 0 to ∽ 300. The data for the program are partly
processed on board because only about 3% of MDI observations can be
transmitted continuously to the ground. The on-board data processing,
the main component of which is Gaussian-weighted binning, has been
optimized to reduce the negative influence of spatial aliasing of the
high-degree oscillation modes. The data processing is completed in a
data analysis pipeline at the SOI Stanford Support Center to determine
the mean multiplet frequencies and splitting coefficients. The initial
results show that the noise in the medium-l oscillation power spectrum
is substantially lower than in ground-based measurements. This enables
us to detect lower amplitude modes and, thus, to extend the range of
measured mode frequencies. This is important for inferring the Sun's
internal structure and rotation. The MDI observations also reveal the
asymmetry of oscillation spectral lines. The line asymmetries agree
with the theory of mode excitation by acoustic sources localized in the
upper convective boundary layer. The sound-speed profile inferred from
the mean frequencies gives evidence for a sharp variation at the edge
of the energy-generating core. The results also confirm the previous
finding by the GONG (Gough et al., 1996) that, in a thin layer just
beneath the convection zone, helium appears to be less abundant than
predicted by theory. Inverting the multiplet frequency splittings from
MDI, we detect significant rotational shear in this thin layer. This
layer is likely to be the place where the solar dynamo operates. In
order to understand how the Sun works, it is extremely important to
observe the evolution of this transition layer throughout the 11-year
activity cycle.
---------------------------------------------------------
Title: Internal structure and rotation of the Sun: First results
from MDI data
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.;
Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.;
De Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.;
Scott, K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard,
J.; Däppen, W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.;
Thompson, M. J.; Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.;
Title, A. M.; Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson,
C. J.; Zayer, I.; Milford, P. N.
1997IAUS..181..203K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Internal rotation and dynamics of the Sun from GONG data
Authors: Korzennik, S.; Thompson, M. J.; Toomre, J.; GONG Internal
Rotation Team
1997IAUS..181..211K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On solar p-mode frequency shifts caused by near-surface
model changes
Authors: Christensen-Dalsgaard, J.; Thompson, M. J.
1997MNRAS.284..527C Altcode:
The effect on p-mode frequencies of changing the near-surface structure
of solar models is investigated. As is well known, changes confined
to the near-surface region have little effect on the low-frequency p
modes: this is as one would expect from a simple asymptotic description
which shows that these modes have upper turning points located well
beneath the photosphere. However, some examples of structural changes
show that, if the changes are viewed at fixed fractional radius (an
Eulerian description), the small frequency shifts at low frequency
come about through near-cancellation of different contributions which
are individually much larger than the resultant shifts themselves;
the reason is that even so-called near-surface changes extend
substantially below the upper turning points of these modes. We
demonstrate that the corresponding changes at fixed fractional mass
(a Lagrangian description) are confined much closer to the surface,
so that the small frequency shifts come about in a natural way.
---------------------------------------------------------
Title: The seismic structure of the Sun from GONG
Authors: Anderson, E.; Antia, H. M.; Basu, S.; Chaboyer, B.; Chitre,
S. M.; Christensen-Dalsgaard, J.; Eff-Darwich, A.; Elliott, J. R.;
Giles, P. M.; Gough, D. O.; Guzik, J. A.; Harvey, J. W.; Hill,
F.; Leibacher, J. W.; Kosovichev, A. G.; Monteiro, M. J. P. F. G.;
Richard, O.; Sekii, T.; Shibahashi, H.; Takata, M.; Thompson, M. J.;
Toomre, J.; Vauclair, S.; Vorontsov, S. V.
1997IAUS..181..151A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the use of the error correlation function in helioseismic
inversions
Authors: Howe, R.; Thompson, M. J.
1996MNRAS.281.1385H Altcode:
A diagnostic of helioseismic inversions that has not so far been
greatly used is the correlation function describing how the errors
in the solutions at different points in the solar interior are
correlated. Even if the errors in the input data are uncorrelated,
the solution errors will in general be correlated. We investigate the
correlation functions for a variety of inversion methods commonly
used in helioseismology, using the estimation of a one-dimensional
rotation profile as a prototypical example. As we demonstrate, there
are characteristic length scales over which the errors are correlated,
which are similar among different inversion methods. However, there
can also be dramatic differences in the error correlations among
otherwise similar looking inversions if the parameters are chosen
inappropriately. It is therefore advisable to consider the correlation
function, as well as other diagnostics, when assessing the reliability
of an inversion solution.
---------------------------------------------------------
Title: Solar structure as revealed by 1 year LOWL data
Authors: Basu, Sarbani; Christensen-Dalsgaard, J.; Schou, J.; Thompson,
M. J.; Tomczyk, S.
1996BASI...24..147B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Results from the LOWL instrument
Authors: Schou, J.; Tomczyk, S.; Thompson, M. J.
1996BASI...24..375S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Low-degree frequency splitting measurements and the rotation
rate of the solar core
Authors: Tomczyk, S.; Schou, J.; Thompson, M. J.
1996BASI...24..245T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Current State of Solar Modeling
Authors: Christensen-Dalsgaard, J.; Dappen, W.; Ajukov, S. V.;
Anderson, E. R.; Antia, H. M.; Basu, S.; Baturin, V. A.; Berthomieu,
G.; Chaboyer, B.; Chitre, S. M.; Cox, A. N.; Demarque, P.; Donatowicz,
J.; Dziembowski, W. A.; Gabriel, M.; Gough, D. O.; Guenther, D. B.;
Guzik, J. A.; Harvey, J. W.; Hill, F.; Houdek, G.; Iglesias, C. A.;
Kosovichev, A. G.; Leibacher, J. W.; Morel, P.; Proffitt, C. R.;
Provost, J.; Reiter, J.; Rhodes, E. J., Jr.; Rogers, F. J.; Roxburgh,
I. W.; Thompson, M. J.; Ulrich, R. K.
1996Sci...272.1286C Altcode:
Data from the Global Oscillation Network Group (GONG) project and
other helioseismic experiments provide a test for models of stellar
interiors and for the thermodynamic and radiative properties, on which
the models depend, of matter under the extreme conditions found in the
sun. Current models are in agreement with the helioseismic inferences,
which suggests, for example, that the disagreement between the predicted
and observed fluxes of neutrinos from the sun is not caused by errors in
the models. However, the GONG data reveal subtle errors in the models,
such as an excess in sound speed just beneath the convection zone. These
discrepancies indicate effects that have so far not been correctly
accounted for; for example, it is plausible that the sound-speed
differences reflect weak mixing in stellar interiors, of potential
importance to the overall evolution of stars and ultimately to estimates
of the age of the galaxy based on stellar evolution calculations.
---------------------------------------------------------
Title: Filtering out near-surface uncertainties from helioseismic
inversions
Authors: Basu, Sarbani; Christensen-Dalsgaard, J.; Perez Hernandez,
F.; Thompson, M. J.
1996MNRAS.280..651B Altcode:
The differences between observed solar p-mode frequencies and the
frequencies of a reference model can be inverted to infer the structure
of the Sun using a variety of linear inversion techniques. However, it
is well known that the adiabatic description, which is often employed
in frequency calculations, breaks down in the outermost layers of the
Sun. This and other uncertainties in the treatment of the superficial
layers introduce a slowly varying frequency-dependent function
into the frequency differences. <P />We present here a technique to
pre-process the frequency differences prior to applying any of the
standard inversion techniques in order to eliminate the frequency
dependent component which arises from the near-surface uncertainties,
suppressing also the corresponding contributions from the kernels
relating frequency differences to differences in structure. This
is achieved by applying suitable linear filters to the frequency
differences and to the mode kernels. We obtain the filtered kernels
and demonstrate that the surface contribution can be successfully
suppressed. We also present the results of the inversions performed
after the data and mode kernels have been filtered.
---------------------------------------------------------
Title: The Seismic Structure of the Sun
Authors: Gough, D. O.; Kosovichev, A. G.; Toomre, J.; Anderson,
E.; Antia, H. M.; Basu, S.; Chaboyer, B.; Chitre, S. M.;
Christensen-Dalsgaard, J.; Dziembowski, W. A.; Eff-Darwich, A.;
Elliott, J. R.; Giles, P. M.; Goode, P. R.; Guzik, J. A.; Harvey,
J. W.; Hill, F.; Leibacher, J. W.; Monteiro, M. J. P. F. G.; Richard,
O.; Sekii, T.; Shibahashi, H.; Takata, M.; Thompson, M. J.; Vauclair,
S.; Vorontsov, S. V.
1996Sci...272.1296G Altcode:
Global Oscillation Network Group data reveal that the internal
structure of the sun can be well represented by a calibrated standard
model. However, immediately beneath the convection zone and at the
edge of the energy-generating core, the sound-speed variation is
somewhat smoother in the sun than it is in the model. This could be a
consequence of chemical inhomogeneity that is too severe in the model,
perhaps owing to inaccurate modeling of gravitational settling or to
neglected macroscopic motion that may be present in the sun. Accurate
knowledge of the sun's structure enables inferences to be made about
the physics that controls the sun; for example, through the opacity,
the equation of state, or wave motion. Those inferences can then be
used elsewhere in astrophysics.
---------------------------------------------------------
Title: Measurement of the Rotation Rate in the Deep Solar Interior
Authors: Tomczyk, S.; Schou, J.; Thompson, M. J.
1996AAS...188.6903T Altcode: 1996BAAS...28..935T
We present a measurement of the rotation rate in the interior of the
Sun based on two years of observations with the LOWL instrument. LOWL
allows the observation of solar oscillations with degrees from 0
to 100, thus providing a homogeneous low- and intermediate-degree
dataset. Significantly, it is able to make spatially resolved
observations of low degree modes, thereby making it possible to separate
the different modes within a given multiplet. This reduces the potential
for systematic errors compared to observations using integrated
sunlight. We have used observations of the frequency splittings
of modes with degrees from 1 to 100 to infer the rotation rate in
the solar interior with some radial resolution and without excessive
errors. Over most of the interior we have also been able to estimate
the latitudinal variation of the rotation rate. We confirm earlier
findings that near the base of the convection zone the solar rotation
profile undergoes a transition from surface-like differential rotation
to a rotation rate that is independent of latitude. Additionally,
we find that below the base of the convection zone our measurement is
consistent with rigid body rotation at a rate somewhat lower than the
surface equatorial rate. This measurement provides strong constraints
on the theories of angular momentum transport in solar-type stars.
---------------------------------------------------------
Title: Differential Rotation and Dynamics of the Solar Interior
Authors: Thompson, M. J.; Toomre, J.; Anderson, E. R.; Antia, H. M.;
Berthomieu, G.; Burtonclay, D.; Chitre, S. M.; Christensen-Dalsgaard,
J.; Corbard, T.; De Rosa, M.; Genovese, C. R.; Gough, D. O.; Haber,
D. A.; Harvey, J. W.; Hill, F.; Howe, R.; Korzennik, S. G.; Kosovichev,
A. G.; Leibacher, J. W.; Pijpers, F. P.; Provost, J.; Rhodes, E. J.,
Jr.; Schou, J.; Sekii, T.; Stark, P. B.; Wilson, P. R.
1996Sci...272.1300T Altcode:
Splitting of the sun's global oscillation frequencies by large-scale
flows can be used to investigate how rotation varies with radius
and latitude within the solar interior. The nearly uninterrupted
observations by the Global Oscillation Network Group (GONG) yield
oscillation power spectra with high duty cycles and high signal-to-noise
ratios. Frequency splittings derived from GONG observations confirm
that the variation of rotation rate with latitude seen at the surface
carries through much of the convection zone, at the base of which is
an adjustment layer leading to latitudinally independent rotation at
greater depths. A distinctive shear layer just below the surface is
discernible at low to mid-latitudes.
---------------------------------------------------------
Title: Solar Internal Rotation and Dynamics from GONG Frequency
Splittings
Authors: Thompson, M. J.; Toomre, J.; GONG Dynamics Inversion Team
1996AAS...188.5305T Altcode: 1996BAAS...28..903T
The splitting of the Sun's global mode frequencies by large-scale flows
can be used to investigate the rotation profile in both radius and
latitude within the convection zone and deeper radiative interior. The
inversion of GONG data confirms that the surface latitudinal variation
of the rotation rate carries through much of the convection zone. At the
base of the convection zone there is a currently unresolved adjustment
layer with latitudinally independent rotation at greater depths. A
shearing layer just below the surface is discernable at low to mid
latitudes. Such global investigations are supplemented by local area
analyses via ring diagrams, which enable us to probe the subsurface
variation of rotation with depth beneath selected regions of the Sun.
---------------------------------------------------------
Title: The Solar Acoustic Spectrum and Eigenmode Parameters
Authors: Hill, F.; Stark, P. B.; Stebbins, R. T.; Anderson, E. R.;
Antia, H. M.; Brown, T. M.; Duvall, T. L., Jr.; Haber, D. A.;
Harvey, J. W.; Hathaway, D. H.; Howe, R.; Hubbard, R. P.; Jones,
H. P.; Kennedy, J. R.; Korzennik, S. G.; Kosovichev, A. G.; Leibacher,
J. W.; Libbrecht, K. G.; Pintar, J. A.; Rhodes, E. J., Jr.; Schou, J.;
Thompson, M. J.; Tomczyk, S.; Toner, C. G.; Toussaint, R.; Williams,
W. E.
1996Sci...272.1292H Altcode:
The Global Oscillation Network Group (GONG) project estimates
the frequencies, amplitudes, and linewidths of more than 250,000
acoustic resonances of the sun from data sets lasting 36 days. The
frequency resolution of a single data set is 0.321 microhertz. For
frequencies averaged over the azimuthal order m, the median formal
error is 0.044 microhertz, and the associated median fractional error
is 1.6 x 10<SUP>-5</SUP>. For a 3-year data set, the fractional error
is expected to be 3 x 10<SUP>-6</SUP>. The GONG m-averaged frequency
measurements differ from other helioseismic data sets by 0.03 to 0.08
microhertz. The differences arise from a combination of systematic
errors, random errors, and possible changes in solar structure.
---------------------------------------------------------
Title: The Sun's Hydrostatic Structure from LOWL Data
Authors: Basu, Sarbani; Christensen-Dalsgaard, J.; Schou, J.; Thompson,
M. J.; Tomczyk, S.
1996ApJ...460.1064B Altcode:
Recent observations with the LOWL (Low-Degree [l] Oscillations
Experiment) instrument have for the first time provided a uniform set of
frequencies that allow detailed inversion for the structure of much of
the Sun's deep interior. We present the results of inverting the LOWL
data and compare them with the corresponding results obtained using
inhomogeneous data sets from more than one instrument. Furthermore,
improvements in the description of the required physics motivates the
calculation of new solar models. Thus, we present results of inversions
of the LOWL data against several reference models using up-to-date
physics. In models including the gravitational settling of helium, the
sound speed and density agree with the Sun to within substantially
better than 1%. We test various modifications to the physics of
the models in order to see if the remaining small (but significant)
discrepancy between the Sun and the models can be removed. We find
that none of the modifications tested can adequately account for the
remaining discrepancy, though a small increase in helium diffusion
in the core gives a modest improvement over the standard diffusion
model. Finally, we find that the seismic data support theoretical
calculations that indicate that settling of heavier elements has
reduced the present surface value of Z by about 8% relative to its
mean interior value.
---------------------------------------------------------
Title: The Sun's rotation rate in its equatorial plane.
Authors: Antia, H. M.; Chitre, S. M.; Thompson, M. J.
1996A&A...308..656A Altcode:
We investigate the Sun's rotation rate in its equatorial plane, as
a function of depth, using Big Bear data for the years 1986, 1988,
1989 and 1990. One novel feature of this investigation is that we
have used an iterative inversion technique, based upon the regularized
least-squares method. Such methods generally have one or more adjustable
parameters, and the details of the inferred rotation profile depend
upon the values chosen for those parameters. We find that the iterative
technique produces results that are much less sensitive to the values of
the parameters, which may be seen as one advantage of our procedure. Our
results exhibit various features, including a secular decrease in the
rotation rate beneath the convection zone, a locally enhanced rotation
rate near 0.9R<SUB>sun</SUB>_ (R<SUB>sun</SUB>_ being the photospheric
radius), and a local minimum near 0.6R<SUB>sun</SUB>_. Not only are
these features apparently fairly robust from year to year, they have
all variously been seen in inversions of other datasets. However,
we demonstrate that some caution should be exercised in interpreting
such features in the Sun's equatorial rotation rate.
---------------------------------------------------------
Title: Seismic properties of the Sun's superadiabatic
layer. I. Theoretical modelling and parametrization of the
uncertainties.
Authors: Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.; Thompson,
M. J.
1996A&A...307..624M Altcode:
Some alternatives to the traditional mixing-length theory (MLT)
have recently been proposed for modelling convective heat transport
inside stars. The ideal formulation is one that does not involve
any free parameters. However, in our present state of ignorance we
still need at least one free parameter in order to build solar models
with the correct radius. Having adjusted this parameter (e.g. the
mixing-length parameter α_c_) to obtain the observed radius, we cannot
discriminate non-seismically between different convective theories,
regardless of how low-efficiency convection is treated. In this paper
we consider how the additional information provided by global p-mode
frequencies can be used to investigate low-efficiency convection at
the top of the solar convective envelope and discriminate between
different theories. We consider a parametrization which in addition
to the mixing length has two further parameters: one (β_c_) which
regulates the relative degree of overadiabaticity (or inefficiency) of
convection, and a second (m) that affects the transition between the
regimes of efficient and inefficient convection. Our parametrization
includes traditional MLT__ and the theory of Canuto & Mazzitelli
as particular cases. We study the effect of varying these parameters
by constructing a series of envelope models with the same depth of
the convection zone and computing their oscillation frequencies. We
discuss our results in terms of kernels relating frequency changes to
changes in the structure of the superadiabatic region.
---------------------------------------------------------
Title: A modified R^1∘xR^1 method for helioseismic rotation
inversions
Authors: Pijpers, F. P.; Thompson, M. J.
1996MNRAS.279..498P Altcode: 1995astro.ph.10143P
We present an efficient method for two-dimensional (2D) inversions
for the solar rotation rate using the Subtractive Optimally Localized
Averages (SOLA) method and a modification of the R^1∘xR^1 technique
proposed by Sekii. The SOLA method is based on explicit construction of
averaging kernels similar to the Backus-Gilbert method. The versatility
and reliability of the SOLA method in reproducing a target form for
the averaging kernel, in combination with the idea of the R^1∘xR^1
decomposition, results in a computationally very efficient inversion
algorithm. This is particularly important for full 2D inversions of
helioseismic data in which the number of modes runs into at least tens
of thousands.
---------------------------------------------------------
Title: On constructing seismic models of the Sun.
Authors: Basu, S.; Thompson, M. J.
1996A&A...305..631B Altcode:
Observed p-mode frequencies have been extensively used to determine
the the Sun's radial structure. The results of such inversions are
often called "seismic models" of the Sun. In this work we investigate
whether one can in fact construct models that match the measured solar
frequencies to within observational errors. We invert linearized
equations, relating frequency differences between the Sun and a
reference model to differences in their structure, using a Regularized
Least Squares (RLS) technique with second derivative smoothing. As a
test, we first invert frequencies from test models. Random noise is
added to these to simulate the observers' quoted errors for solar
data. We investigate how the goodness of fit to the data, and the
acceptability of the solution, depend upon the number of spline
knots in the solution functions and upon the amount of smoothing
used. With this artificial data, we can obtain a chi-squared per
degree of freedom (χ<SUB>nu</SUB>_^2^) of order unity even when the
differences between the reference and test models are quite large. In
contrast, using the most widely used compilation of observed solar
frequencies, we are unable to get the value of χ<SUB>nu</SUB>_^2^
close to one. Replacing the low degree data with recent data from the
BISON network, and omitting frequencies determined by the ridge-fitting
method (which could be more susceptible to systematic error), the value
χ<SUB>nu</SUB>_^2^ can be reduced substantially. We discuss possible
causes for the small remaining excess in χ<SUB>nu</SUB>_^2^.
---------------------------------------------------------
Title: Filtering in Inversion for Solar Internal Structure
Authors: Basu, Sarbani; Christensen-Dalsgaard, J.; Pérez Hernández,
F.; Thompson, M. J.
1996imie.conf...32B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Averaging Kernels, Error Correlation Functions and Linear
Methods in Helioseismology
Authors: Howe, Rachel; Thompson, Michael J.
1996imie.conf...40H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Results From the LOWL Instrument
Authors: Schou, J.; Tomczyk, S.; Thompson, M. J.
1995AAS...18710101S Altcode: 1995BAAS...27.1426S
In this poster we will present various results from one year of
observations with the LOWL instrument. The LOWL instrument is designed
to observe oscillations with degrees l from 0 to about 100 providing a
homogeneous dataset for inversions. Given the spatial resolution of the
instrument it is possible to separate different azimuthal orders m even
for the lowest degree modes, hopefully giving more accurate splittings
than those determined using integrated sunlight for a similar time
period. We will show the results of an inversion for the solar rotation
rate between 0.1R_sun and 0.95R_sun. Given the long duration and the
large number of terms used to describe the m-dependence of the mode
frequencies we have been able to obtain very good resolution in both
the radial direction and in latitude while keeping the statistical
errors low, thereby obtaining more accurate results than previously
possible. We will also present results of analyzing different parts of
the time-series and compare the temporal variations in mode frequencies
and splittings with variations in the solar activity.
---------------------------------------------------------
Title: Helioseismic estimation of convective overshoot in the Sun
Authors: Christensen-Dalsgaard, Jorgen; Monteiro, Mario J. P. F. G.;
Thompson, Michael J.
1995MNRAS.276..283C Altcode:
By using the periodic signal present in the frequencies of
oscillation due to the base of the solar convection zone, Monteiro,
Christensen-Dalsgaard & Thompson gave an upper limit to the
extent of a layer of convective overshooting in the Sun. Alternative
studies have suggested that it may not be possible to do so since the
amplitude of the signal does not vary monotonically with the extent
of the layer. <P />In this work a new more complete set of models is
used to compare the values of the amplitude obtained from the fitting
of the signal with the expected amplitudes. These are determined using
the assumption that the rapid variation occurring at the base of the
convection zone and creating the periodic signal can be described as
discontinuities of the sound-speed derivatives. The amplitude of the
signal due to the discontinuity of the third derivative of the sound
speed is then proportional to the derivative of the radiative gradient,
while the amplitude resulting from the discontinuity of the second
derivative is proportional to the difference between radiative and
adiabatic gradients at the position where the transition occurs. The
latter is non-zero only if overshoot is present. <P />Asymptotic
predictions of the amplitudes of the signal in the p-mode frequencies
are in good agreement with the values found from fitting models with
substantial overshoot regions; as was also found by Monteiro et al.,
the observed solar frequencies place severe limits on the extent of
overshoot of this nature.
---------------------------------------------------------
Title: Linear inversions for the Sun's internal rotation
Authors: Thompson, M. J.
1995InvPr..11..709T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Measurement of the Rotation Rate in the Deep Solar Interior
Authors: Tomczyk, S.; Schou, J.; Thompson, M. J.
1995ApJ...448L..57T Altcode:
We present a measurement of solar internal rotation based
on observations obtained over 3 months in early 1994 with a new
instrument called LOWL. This instrument allows for the simultaneous
observation of low- and intermediate-degree solar oscillations with
spatial resolution. We have measured the frequency splitting of 673
multiplets with degrees ranging from 1 to 80 and inverted these to
derive an estimate of the solar internal rotation profile between 0.2
and 0.85 R⊙. The accuracy of this measurement ranges from ~1% in the
outer regions to ~5% at 0.2 R⊙ and thus places better constraints than
hitherto on the rotation in the deep solar interior. We confirm earlier
findings that near the base of the convection zone the solar rotation
profile undergoes a transition from surface-like differential rotation
to a rotation rate that is independent of latitude. In addition, we
find that from the base of the convection zone down to 0.2 R⊙ our
measurement is consistent with rigid body rotation at a rate somewhat
lower than the surface equatorial rate. The accuracy of our measurement
in the deep solar interior provides a strong constraint to theories
of solar and stellar angular momentum transport.
---------------------------------------------------------
Title: A Measurement of the Rotation Rate in the Deep Solar Interior
Authors: Schou, J.; Tomczyk, S.; Thompson, M. J.
1995ESASP.376b.275S Altcode: 1995soho....2..275S; 1995help.confP.275S
No abstract at ADS
---------------------------------------------------------
Title: The Sensitivity of Various Mode Sets for Probing Differential
Rotation Shear Zones
Authors: Christensen-Dalsgaard, J.; Schou, J.; Thompson, M. J.;
Toomre, J.
1995ESASP.376b..41C Altcode: 1995soho....2...41C; 1995help.confP..41C
The potential of forthcoming datasets from GONG and SOI for resolving
long-lived azimuthal jets and shearing flows is investigated. The
authors construct various artificial datasets, containing noise
resembling that for a one-year observing run. These are then inverted,
using a 2-D regularized least squares (RLS) inversion. In particular,
the authors investigate the ability of the RLS method to form
well-localized averages of the rotation rate, as measured by the
averaging kernels, using an extensive mode set as well as subsets
thereof. The authors show that it is possible to keep the noise in
the solution down to a few nanohertz in much of the solar interior,
while obtaining very reasonable resolution, for a GONG-like dataset.
---------------------------------------------------------
Title: Solar Structure Inversion with LOWL Data
Authors: Basu, S.; Christensen-Dalsgaard, J.; Schou, J.; Thompson,
M. J.; Tomczyk, S.
1995ESASP.376b..25B Altcode: 1995help.confP..25B; 1995soho....2...25B
Presents inversion results for the radial hydrostatic structure of
the Sun, using six months of oscillation data obtained with the LOWL
instrument. Using modes with degrees from 0 to 90 and frequencies
between 1.5 and 3.5 mHz, the authors have inferred the variation with
depth of the sound speed, density ρ and u = p/ρ (p being pressure)
from r = 0.05 R<SUB>sun</SUB> to 0.85 R<SUB>sun</SUB>. They find that
in this region the sound speed in the Sun is within 0.15% of that of a
model constructed using the MHD equation of state and OPAL opacities
and incorporating helium diffusion. The density difference between
Sun and model is less than 0.8%. Given the small error bars on the
inversion results these small differences are significant, however. The
solar sound speed appears to be higher than in the model for r <
0.2 R<SUB>sun</SUB> . The authors speculate that this might indicate
interesting physics in the inner core.
---------------------------------------------------------
Title: Constraining Solar Core Rotation with Genetic Forward Modelling
Authors: Tomczyk, S.; Charbonneau, P.; Schou, J.; Thompson, M. J.
1995ESASP.376b.271T Altcode: 1995soho....2..271T; 1995help.confP.271T
No abstract at ADS
---------------------------------------------------------
Title: Uncertainties for Two-dimensional Models of Solar Rotation
from Helioseismic Eigenfrequency Splitting
Authors: Genovese, Christopher R.; Stark, Philip B.; Thompson,
Michael J.
1995ApJ...443..843G Altcode:
Observed solar p-mode frequency splittings can be used to estimate
angular velocity as a function of position in the solar interior. Formal
uncertainties of such estimates depend on the method of estimation
(e.g., least-squares), the distribution of errors in the observations,
and the parameterization imposed on the angular velocity. We obtain
lower bounds on the uncertainties that do not depend on the method
of estimation; the bounds depend on an assumed parameterization, but
the fact that they are lower bounds for the 'true' uncertainty does
not. Ninety-five percent confidence intervals for estimates of the
angular velocity from 1986 Big Bear Solar Observatory (BBSO) data, based
on a 3659 element tensor-product cubic-spline parameterization, are
everywhere wider than 120 nHz, and exceed 60,000 nHz near the core. When
compared with estimates of the solar rotation, these bounds reveal that
useful inferences based on pointwise estimates of the angular velocity
using 1986 BBSO splitting data are not feasible over most of the Sun's
volume. The discouraging size of the uncertainties is due principally
to the fact that helioseismic measurements are insensitive to changes in
the angular velocity at individual points, so estimates of point values
based on splittings are extremely uncertain. Functionals that measure
distributed 'smooth' properties are, in general, better constrained than
estimates of the rotation at a point. For example, the uncertainties
in estimated differences of average rotation between adjacent blocks
of about 0.001 solar volumes across the base of the convective zone
are much smaller, and one of several estimated differences we compute
appears significant at the 95% level.
---------------------------------------------------------
Title: Results from the LOWL Instrument
Authors: Schou, J.; Tomczyk, S.; Thompson, M. J.
1995SPD....26..402S Altcode: 1995BAAS...27..954S
No abstract at ADS
---------------------------------------------------------
Title: Optimally Localized Kernels for 2D Helioseismic Inversion
Authors: Christensen-Dalsgaard, J.; Larsen, R. M.; Schou, J.; Thompson,
M. J.
1995ASPC...76...70C Altcode: 1995gong.conf...70C
No abstract at ADS
---------------------------------------------------------
Title: SOLA Inversions for the Radial Structure of the Sun
Authors: Christensen-Dalsgaard, J.; Thompson, M. J.
1995ASPC...76..144C Altcode: 1995gong.conf..144C
No abstract at ADS
---------------------------------------------------------
Title: Some Aspects of Helioseismic Time-Series Analysis
Authors: Schou, J.; Christensen-Dalsgaard, J.; Thompson, M. J.
1995ASPC...76..528S Altcode: 1995gong.conf..528S
No abstract at ADS
---------------------------------------------------------
Title: A Self-Consistent Approach to Filtering Out Near-Surface
Uncertainties from Helioseismic Inversions
Authors: Basu, S.; Thompson, M. J.; Christensen-Dalsgaard, J.; Perez
Hernandez, F.
1995ASPC...76..152B Altcode: 1995gong.conf..152B
No abstract at ADS
---------------------------------------------------------
Title: Helioseismic Constraints on Theories of Convection
Authors: Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.; Thompson,
M. J.
1995ASPC...76..128M Altcode: 1995gong.conf..128M
No abstract at ADS
---------------------------------------------------------
Title: On Constructing Seismic Models of the Sun's Radial Structure
Authors: Basu, S.; Thompson, M. J.
1995ASPC...76..148B Altcode: 1995gong.conf..148B
No abstract at ADS
---------------------------------------------------------
Title: Hunting for Azimuthal Jets and Shearing Flows in the Solar
Convection Zone
Authors: Christensen-Dalsgaard, J.; Schou, J.; Thompson, M. J.;
Toomre, J.
1995ASPC...76..212C Altcode: 1995gong.conf..212C
No abstract at ADS
---------------------------------------------------------
Title: A Measurement of the Rotation Rate in the Deep Solar Interior
Authors: Schou, J.; Tomczyk, S.; Thompson, M. J.
1994AAS...185.4401S Altcode: 1994BAAS...26Q1377S
Measurements of the rotation rate in the deep solar interior using
helioseismology have given inconsistent results, presumably due to
problems with the algorithms used for the analysis of spatially
unresolved observations of the oscillations. Here we present a
measurement of the rotation rate in the interior of the Sun based
on observations with a new instrument called LOWL. Unlike earlier
instruments this instrument allows the observation of oscillations
with degrees from 0 to ~ 80. In particular it is able to make spatially
resolved observations of low degree modes, thereby making it possible to
spatially separate the different modes within a given multiplet. This
reduces the potential for systematic errors compared to observations
using integrated sunlight. We have used observations of the frequency
splittings of modes with degrees from 1 to 80 to infer the rotation rate
in the solar interior down to ~ 0.2 R_⊙ with some radial resolution
and without excessive errors. Over part of the range we have also been
able to estimate the latitudinal variation of the rotation rate. This
measurement provides strong constraints on the theories of solar and
stellar angular momentum transport.
---------------------------------------------------------
Title: On Comparing Helioseismic Two-dimensional Inversion Methods
Authors: Schou, J.; Christensen-Dalsgaard, J.; Thompson, M. J.
1994ApJ...433..389S Altcode:
We consider inversion techniques for investigating the structure and
dynamics of the solar interior as functions of radius and latitude. In
particular, we look at the problem of inferring the radial and
latitudinal dependence of the Sun's internal rotation, using a fully
two-dimensional least-squares inversion algorithm. Concepts such as
averaging kernels, measures of resolution, and trade-off curves, which
have previously been used in the one-dimensional case, are generalized
to facilitate a comparison of two-dimensional methods. We investigate
the weighting given to different modes and discuss the implications of
this for observational strategies. As an illustration we use a mode
set whose properties are similar to those expected for data from the
GONG network.
---------------------------------------------------------
Title: Conceptual Astronomy
Authors: Thompson, M. J.
1994ConPh..35..289T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Seismic study of overshoot at the base of the solar convective
envelope
Authors: Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.; Thompson,
M. J.
1994A&A...283..247M Altcode:
Sharp transitions in the internal stratification of a star give rise to
a characteristic signature in normal-mode frequencies. In particular,
if in the Sun such a feature were located well inside the acoustic
cavity of many solar p modes, it would give rise to a signal that was a
periodic function of the frequency of the modes. We use this signature
to detect the base of the solar convection zone and to investigate the
existence of convective overshoot into the radiative interior. Two
methods are considered. The 'absolute' method obtains the residuals
in the frequencies after making a smooth fit in mode order n, and
then uses an asymptotic description of the eigenfunctions to make a
fit to the residuals. The 'differential' method makes an asymptotic
fit to the differences between solar frequencies and the frequencies
of a theoretical model. Various theoretical models of overshoot at
the base of the convection zone predict the existence of a rather
abrupt transition to subadiabatic stratification at the base of the
overshoot region. We find no strong evidence for the existence of an
overshoot region of this kind. Indeed if the overshoot consists of an
essentially adiabatic extension of the convection zone followed by an
abrupt transition to radiative stratification then we may (at the 95%
confidence level) put an upper limit of 0.07 local pressure scale
heights on the extent of the overshoot layer.
---------------------------------------------------------
Title: Recent results from helioseismology.
Authors: Thompson, M. J.
1994LNP...432...19T Altcode: 1994LNPM...11...19T
The very accurately measured frequencies of the Sun's global oscillation
are providing us with a detailed picture of the solar interior. The
adiabatic sound speed is of foremost importance in determining
the observed p-mode frequencies and hence is readily accessible to
seismic analysis of the frequency data. It has thus been known for
some time that the sound speed in the bulk of the radiative interior
is greater than in theoretical models. Much of this discrepancy is
removed by the latest Livermore opacities, but a significant discrepancy
remains. The cause of this discrepancy may be settling and diffusion of
helium in the solar interior. This would also explain the discrepancy
between seismic measurements of the envelope helium abundance and the
abundance required to produce correctly calibrated evolution models. The
frequencies also enable to pinpoint the base of the convection zone and
to investigate the extent of overshoot into the underlying convectively
stable region. The variation of the p-mode frequencies with time is
discussed, as are the current helioseismic determinations of the Sun's
internal rotation. Finally future prospects are considered.
---------------------------------------------------------
Title: The SOLA method for helioseismic inversion
Authors: Pijpers, F. P.; Thompson, M. J.
1994A&A...281..231P Altcode:
The Subtractive Optimally Localized Averages (SOLA) method is a
versatile and efficient technique for inverting helioseismic data. The
SOLA method is based on explicit construction of Backus-Gilbert
averaging kernels, but whereas the more usual formulations of the
optimally localized averages (OLA) method use a multiplicative penalty
function to localize the kernels, the distinctive idea of SOLA is that
one specifies a desired target form for the kernels and then minimizes
the integrated squared difference between the kernels and the target
form. This allows great versatility in the choice of target form, and
furthermore SOLA has the significant advantage of being computationally
more efficient than the usual OLA formulations. A Gaussian target
function is a useful choice, and we use the example of determining
the Sun's internal rotation to explore how the parameter values (such
as the Gaussian's width) should best be chosen. Some alternatives to
using a Gaussian function as target function are discussed and applied
to artificial data in a blind experiment. In particular we show that it
is possible to invert directly for the gradient of the rotation. This
may be of interest if there are localized large gradients in the
rotation rate.
---------------------------------------------------------
Title: The Depth of the Solar Convection Zone
Authors: Christensen-Dalsgaard, J.; Gough, D. O.; Thompson, M. J.
1994snft.book..427C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Generalized Singular Value Decomposition Analysis of
Helioseismic Inversions
Authors: Christensen-Dalsgaard, J.; Hansen, P. C.; Thompson, M. J.
1993MNRAS.264..541C Altcode:
We present the generalized singular value decomposition (GSVD) as a
powerful tool for the analysis of 111-conditioned inversion problems,
such as arise in helioseismology and other areas of astronomy. The
GSVD provides rather natural bases with which to express the
various properties of the inversion, in particular the solution,
the inversion coefficients (which relate the solution to the data)
and the averaging kernels (which relate the solution to the underlying
unknown function). These facilitate an analysis of resolution and error
properties. We apply the theory to a helioseismic example and find inter
alia that, for our prototypical problem, there is an effective limit to
the information content of the mode set in the presence of reasonable
data errors which is much less than might have been expected from the
number of modes. We show that various popular inversion methods can be
analysed using the tools developed here. We find in our helioseismic
application that the methods make very similar use of the data.
---------------------------------------------------------
Title: Resonant Alfvén wave excitation in two-dimensional systems:
Singularities in partial differential equations
Authors: Thompson, Michael J.; Wright, Andrew N.
1993JGR....9815541T Altcode:
The resonant excitation of Alfvén waves is considered in a cold plasma
embedded in a uniform magnetic field Bẑ. All wave fields are assumed
to vary as exp[i(λy-ωt)], and the background medium is invariant in
y. The background density distribution ρ<SUB>0</SUB>(x,z) is otherwise
completely arbitrary. Regular and singular solutions for the waves are
derived systematically in the vicinity of a resonance by considering a
generalized Frobenius series, and we are able to recover many results
found in earlier studies. Some new features of our work include a
generalization of the overlap integral determining the efficiency
with which any resonance may be excited, and the possibility that
ξ<SUB>y</SUB>~1/x<SUP>N</SUP> (N=1,2,3...) at the resonance. Hitherto
only the solution with N=1 has been considered.
---------------------------------------------------------
Title: A preprocessing strategy for helioseismic inversions
Authors: Christensen-Dalsgaard, J.; Thompson, M. J.
1993A&A...272L...1C Altcode:
Helioseismic inversion in general involves considerable
computational expense, due to the large number of modes that is
typically considered. This is true in particular of the widely used
optimally localized averages (OLA) inversion methods, which require
the inversion of one or more matrices whose order is the number of
modes in the set. However, the number of practically independent
pieces of information that a large helioseismic mode set contains
is very much less than the number of modes, suggesting that the set
might first be reduced before the expensive inversion is performed. We
demonstrate with a model problem that by first performing a singular
value decomposition the original problem may be transformed into a
much smaller one, reducing considerably the cost of the OLA inversion
and with no significant loss of information.
---------------------------------------------------------
Title: Effects of Diffusion on Solar Models and Their Oscillation
Frequencies
Authors: Christensen-Dalsgaard, J.; Proffitt, C. R.; Thompson, M. J.
1993ApJ...403L..75C Altcode:
Settling and diffusion of helium have significant effects on the
structure of solar models and their oscillation frequencies. We examine
these effects in considerably more detail than has been done before,
and we compare the computed frequencies with an extensive set of
observed frequencies. We find that inclusion of diffusion results
in a significant improvement in the agreement between theory and
observations.
---------------------------------------------------------
Title: On Detecting Overshoot Below the Sun's Convective Envelope
Authors: Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.; Thompson,
M. J.
1993ASPC...42..253M Altcode: 1993gong.conf..253M
No abstract at ADS
---------------------------------------------------------
Title: Two-dimensional helioseismic inversions
Authors: Schou, J.; Christensen-Dalsgaard, J.; Thompson, M. J.
1993ASPC...40...72S Altcode: 1993IAUCo.137...72S; 1993ist..proc...72S
No abstract at ADS
---------------------------------------------------------
Title: Detecting convective overshoot in solar-type stars
Authors: Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.; Thompson,
M. J.
1993ASPC...40..557M Altcode: 1993IAUCo.137..557M; 1993ist..proc..557M
No abstract at ADS
---------------------------------------------------------
Title: Faster Formulations of the Ola Method
Authors: Pijpers, F. P.; Thompson, M. J.
1993ASPC...42..245P Altcode: 1993gong.conf..245P
No abstract at ADS
---------------------------------------------------------
Title: Tests and Applications of the SOLA Inversion Method - a New
Determination of the Solar Rotation Rate
Authors: Pijpers, F. P.; Thompson, M. J.
1993ASPC...42..241P Altcode: 1993gong.conf..241P
No abstract at ADS
---------------------------------------------------------
Title: Two-Dimensional Helioseismic Inversions
Authors: Schou, J.; Christensen-Dalsgaard, J.; Thompson, M. J.
1993ASPC...42..205S Altcode: 1993gong.conf..205S
No abstract at ADS
---------------------------------------------------------
Title: A Hands-On IDL Program for Helioseismic Inversion
Authors: Christensen-Dalsgaard, J.; Thompson, M. J.
1993ASPC...42..249C Altcode: 1993gong.conf..249C
No abstract at ADS
---------------------------------------------------------
Title: Seismic Investigation of the Sun's Internal Structure and
Rotation
Authors: Thompson, M. J.
1993ASPC...42..141T Altcode: 1993gong.conf..141T
No abstract at ADS
---------------------------------------------------------
Title: Sources of uncertainty in direct seismological measurements
of the solar helium abundance
Authors: Kosovichev, A. G.; Christensen-Dalsgaard, J.; Daeppen, W.;
Dziembowski, W. A.; Gough, D. O.; Thompson, M. J.
1992MNRAS.259..536K Altcode:
The methods by which Dappen et al. (1988, 1990, 1991) and Dziembowski
et al. (1990, 1991, 1992) recently obtained discrepant estimates of
the helium abundance in the solar convection zone are compared. The
aim of the investigation reported in this paper is to identify the
main source of the discrepancy. Using as proxy data eigenfrequencies
of a set of modes of a theoretical solar model, computed with the
same physics as were the frequencies of a reference model with which
these data are compared, the two methods yield similar results. Thus
we ascertain that the principal source of the discrepancy is not in
the inversions themselves, which yield essentially a measure of the
variation of the adiabatic exponent gamma of the material in the He II
ionization zone. Instead it is in the approximations adopted in the
treatment of heavy elements in the equation of state used to relate
the variation of gamma to chemical composition. We obtain acceptably
consistent results when inverting solar data by two methods using the
same equation of state. We attempt to identify the likely residual
sources of uncertainty.
---------------------------------------------------------
Title: On the rate of destruction of lithium in late-type
main-sequence stars
Authors: Christensen-Dalsgaard, J.; Gough, D. O.; Thompson, M. J.
1992A&A...264..518C Altcode:
It it shown that the rate of destruction of lithium by nuclear reactions
in the outer mixed layers of late-type main-sequence stars depends on
both the depth of the region where mixing occurs and the stratification
within it. The mixed region includes and probably extends beneath the
base of the convection zone. As the star evolves on the main sequence,
the properties of the convection zone vary in a simple manner. If
the mixed layer behaves similarly, then the mean destruction rate
can easily be related to the present local value evaluated at the
base of the mixed layer. In the case of the sun, it is found that if
mixing is rapid compared with the nuclear destruction rate, then the
mean destruction rate is approximately equal to one-half the present
local value.
---------------------------------------------------------
Title: On the effects of chromospheric magnetic perturbations on
solar oscillation frequencies
Authors: Wright, A. N.; Thompson, M. J.
1992A&A...264..701W Altcode:
A perturbation method is developed for calculating the effect
on the frequencies of solar global oscillations of changes in the
chromosphere. We show that the frequency perturbation depends on the
subphotospheric structure of the solar model only through the mode
inertia (or mode mass). The effects of changing the chromosphere can
first be calculated independently of any particular model of the solar
interior; and the frequency perturbations for any given model then
obtained by scaling with mode inertia. In particular we apply the
method to changes in chromospheric magnetic field.
---------------------------------------------------------
Title: Faster formulations of the optimally localized averages method
for helioseismic inversions
Authors: Pijpers, F. P.; Thompson, M. J.
1992A&A...262L..33P Altcode:
Much use is made in helioseismology of the optimally localized averages
method of inversion, introduced by Backus and Gilbert. However,
the method is computationally expensive for large data sets. Here we
present a class of alternative formulations of that method which are
more efficient computationally and yet they retain the advantages of
the method in its usual form.
---------------------------------------------------------
Title: The Effect of an Inclined Magnetic Field on Solar Oscillation
Frequencies
Authors: Goode, Philip R.; Thompson, Michael J.
1992ApJ...395..307G Altcode:
The radiative interior of the sun could be hiding a large-scale magnetic
field, which might not be axisymmetric about the observed rotation
axis. Using helioseismic data, we estimate that the strength of any such
relic field must be less than about 30 MG, if the field is axisymmetric
about the rotation axis. The shape oblateness caused by a field at
this limiting strength is about 5-10 x 10 exp -6. Stronger fields can
be accommodated by the helioseismic data if they are inclined to the
rotation axis. We further conclude that the convention zone and at
least the outer part of the radiative interior rotate on the same axis.
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Title: The Resolving Power of Current Helioseismic Inversions for
the Sun's Internal Rotation
Authors: Schou, J.; Christensen-Dalsgaard, J.; Thompson, M. J.
1992ApJ...385L..59S Altcode:
An inversion of the currently available rotational splitting data
which is representative of other recent inversions for the sun's
internal rotation is analyzed. The so-called polar rate is found to be
an extrapolation from lower latitudes. The basic conclusion that the
average radial gradient of the rotation rate in the solar convection
zone is small is corroborated.
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Title: Does the Sun Rotate on a Single Axis?
Authors: Goode, Philip R.; Thompson, Michael J.
1992ASPC...27..182G Altcode: 1992socy.work..182G
No abstract at ADS
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Title: The Depth of the Solar Convection Zone
Authors: Christensen-Dalsgaard, J.; Gough, D. O.; Thompson, M. J.
1991ApJ...378..413C Altcode:
The transition of the temperature gradient between being subadiabatic
and adiabatic at the base of the solar convection zone gives rise to
a clear signature in the sound speed. Helioseismic measurements of the
sound speed therefore permit a determination of the location of the base
of the convection zone. Two techniques were tested by applying them
to artifical data, obtained by adding simulated noise to frequencies
computed from two different solar models. The determinations appear to
be relatively insensitive to uncertainties of the physics of the solar
interior. From an analysis of observed frequencies of solar oscillation
it is concluded that the depth of the solar convection zone is (0.287 +
or - 0.003) solar radii.
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Title: The Response of the Adiabatic Exponent Gamma 1 to Modifications
of Solar Models
Authors: Christensen-Dalsgaard, J.; Thompson, M. J.
1991ApJ...367..666C Altcode:
Guenther et al. (1989) investigated the effet of varying the abundance
of elemental Ne on solar models and found that the changes in some
aspects of these models in the ionization zones of helium and hydrogen
were nonmonotonic functions of the assumed Ne abundance. In this paper,
the results of Guenther et al. are examined, and it is found that
the apparent nonmonotonic behavior of the models was caused by slight
errors in the radii of their models, combined with the fact that the
adiabatic exponent Gamma(1) was compared at fixed distance r from the
center of the model. When the models are compared at fixed fractional
radius r/R, the differences in the values of Gamma(1) were found to
behave in a much more regular way.
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Title: Helioseismic Inversion
Authors: Thompson, M. J.
1991LNP...388...61T Altcode: 1991ctsm.conf...61T
The application of inverse theory enables us to use the measured
frequencies of normal modes of oscillation of the Sun to make inferences
about the structure and dynamics of the solar interior. Some basic
concepts and a few inversion techniques are discussed. Results on
solar rotation and radial stratification are reviewed, and finally the
potential for investigating other moderate-mass stars seismologically
is considered.
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Title: The inversion problem.
Authors: Gough, D. O.; Thompson, M. J.
1991sia..book..519G Altcode:
The authors discuss some fundamental problems associated with inverting
helioseismic data to infer properties of the solar interior, and
review various methods used to invert frequencies of normal modes of
oscillation. After discussing linear methods, the authors present and
compare different asymptotic methods that have been used to infer the
internal solar sound speed. They also discuss numerical inversions
for solar structure, and address the issue of inverting for more than
one function. Methods of inverting for the nonspherically symmetric
structure of the Sun are presented.
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Title: A New Inversion for the Hydrostatic Stratification of the Sun
Authors: Däppen, W.; Gough, D. O.; Kosovichev, A. G.; Thompson, M. J.
1991LNP...388..111D Altcode: 1991ctsm.conf..111D
Inversions for the spherically symmetric component of the hydrostatic
stratification of the Sun are presented. These employ the Backus-Gilbert
optimally localized averaging procedure applied to oscillation multiplet
frequencies in the range 1.5 - 3 mHz of modes with 4 l 140 determined
by Libbrecht et al. (1990) from observations carried out in 1986. We
also obtain an estimate of the helium abundance in the solar convective
envelope.
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Title: A comparison of methods for inverting helioseismic data
Authors: Christensen-Dalsgaard, J.; Schou, J.; Thompson, M. J.
1990MNRAS.242..353C Altcode:
Consideration is given to the inversion techniques used to study the
properties of the solar interior with observed frequencies of solar
oscillation. Linear inversion schemes for helioseismic problems are
compared in terms of resolutions and error properties. Measures of the
error amplification resulting from the inversion and the resolution
achieved are defined. Although the study includes only inversions for
a spherically symmetric angular velocity distribution, it is suggested
that the methods may be used to study kernels for other properties of
the solar interior.
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Title: The effect of rotation and a buried magnetic field on stellar
oscillations
Authors: Gough, D. O.; Thompson, M. J.
1990MNRAS.242...25G Altcode:
A perturbation method is presented for calculating the frequency
modification of stellar oscillations caused by rotation and internal
magnetic field. A short-wavelength asymptotic analysis derived from
ray theory is also presented. The effects on high-order solar acoustic
modes of various hypothetical angular velocity and magnetic field
configurations are investigated using both methods of calculation. The
asymptotic formulas provide a good estimate for the frequency splitting
of five-minute modes when the field and the rotation vary sufficiently
smoothly. On the other hand, a localized magnetic field, for example at
the base of the convection zone, produces a characteristic oscillatory
perturbation to the eigenfrequencies.
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Title: A New Inversion of Solar Rotational Splitting Data
Authors: Thompson, M. J.
1990SoPh..125....1T Altcode:
The fine structure of the solar p-mode spectrum is used to obtain
an estimate of the Sun's internal rotation rate, as a function of
both latitude and depth, for fractional radii in the range 0.55 <
r/R < 0.85. Because each piece of data is a weighted average of
the rotation rate over an extended region of the solar interior and
because the number of such measurements is finite, such an inversion
unavoidably has limited resolution and suffers from other systematic
errors. Accordingly, the results of the inversion presented here
and other published inversions should be interpreted with this in
mind. These problems are discussed in detail for the present inversion.
---------------------------------------------------------
Title: What are the Observed High-Frequency Solar Acoustic Modes?
Authors: Kumar, P.; Duvall, T. L., Jr.; Harvey, J. W.; Jefferies,
S. M.; Pomerantz, M. A.; Thompson, M. J.
1990LNP...367...87K Altcode: 1990psss.conf...87K
Jefferies et al. (1988) observe discrete peaks up to 7mHz in the power
spectra of their intermediate degree solar intensity oscillation data
obtained at South Pole. This is perhaps surprising since waves with
frequency greater than the acoustic cut-off frequency at the temperature
minimum ( 5.5mHz), unlike their lower frequency counterparts, are not
trapped in the solar interior. We propose that the observed peaks are
associated with what are principally progressive waves emanating from
a broad-band acoustic source. The geometrical effect of projecting
observations of these progressive waves onto spherical harmonics
then gives rise to peaks in the power spectra. The frequencies and
amplitudes of the peaks will depend on the spatial characteristics of
the source. Partial reflections in the solar atmosphere modify the power
spectra, but in this picture they are not the primary reason for the
appearance of the peaks. We estimate the frequency and power which would
be expected from this model and compare it with the observations. We
argue that these high frequency mock-modes are not overstable, and
that they are excited by acoustic emission from turbulent convection.
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Title: Differential asymptotic sound-speed inversions
Authors: Christensen-Dalsgaard, J.; Thompson, M. J.; Gough, D. O.
1989MNRAS.238..481C Altcode:
An asymptotic method for determining the internal solar sound speed
from the differences between observed p-mode frequencies and those
of a standard reference solar model is presented. In order to test
the method, it has been applied to the frequency differences between
pairs of solar models, where in each case one takes the part of the
reference model and the other the role of the sun. The results of
these numerical experiments indicate that by using this simple method
one may in principle be able to determine the sound speed from the
energy-generating core to the helium ionization zone.
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Title: Determination of the solar internal sound speed by means of
a differential asymptotic inversion.
Authors: Christensen-Dalsgaard, J.; Gough, Douglas O.; Thompson, M. J.
1988ESASP.286..493C Altcode: 1988ssls.rept..493C
The authors present a simple asymptotic inversion method for
obtaining an estimate of the difference in internal sound speed from
differences between five-minute p-mode oscillation frequencies. Thus,
given a known model and a set of frequencies of a model of unknown
structure, or of the Sun, the internal sound speed of the latter can be
estimated. Numerical experiments with error-free frequencies indicate
that this method can provide an estimate of the sound speed, from the
energy-generating core to the helium ionization zone, with smaller
fractional error than any previously published results. The authors
have applied the method to real solar data, and find that the solar
sound speed is indeed broadly as determined by an earlier investigation
at those depths for which the earlier inversion should be reliable.
---------------------------------------------------------
Title: Evidence for a thin perturbative layer near the base of the
solar convection zone.
Authors: Thompson, M. J.
1988ESASP.286..321T Altcode: 1988ssls.rept..321T
Low-degree solar p-mode frequencies hint at the presence of a thin
perturbative layer at the base of the Sun's convection zone. Magnetic
flux stored in an overshoot region could constitute such a perturbative
layer.
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Title: Further progress on the helium abundance determination.
Authors: Daeppen, W.; Gough, Douglas O.; Thompson, M. J.
1988ESASP.286..505D Altcode: 1988ssls.rept..505D
The authors report on further progress in attempting to determine the
helium abundance in the solar convection zone by analysing the position
and shape of the "helium hump" in a thermodynamic quantity Θ which
can be inferred from the sound speed in the vicinity of the He II
ionization zone. At present they are estimating the sound speed from
frequencies of high-degree oscillations by a differential asymptotic
technique. The helium abundance Y is then determined by fitting the hump
inferred to one obtained by interpolation in a grid of theoretical model
envelopes. They have tested the procedure by carrying out a double-blind
experiment on artificial data, and have found that accurate knowledge
of the equation of state is essential for a useful determination. The
authors have also carried out the procedure on real solar data, but
they judge that the frequencies are at present too poorly determined
to enable us to obtain a reliable estimate of Y in the sun.
---------------------------------------------------------
Title: On the Implications of the Symmetric Component of the
Frequency Splitting
Authors: Gough, D. O.; Thompson, M. J.
1988IAUS..123..175G Altcode:
The component of the frequency splitting of solar five-minute
oscillations observed by Duvall, Harvey and Pomerantz that is even
in azimuthal degree measures latitudinal and depth variations in the
structure of the sun. The authors indicate how the data hint that there
is a shallow perturbation, possibly associated with a magnetic field,
that is concentrated at low latitudes.
---------------------------------------------------------
Title: Magnetic Perturbations to Stellar Oscillation Eigenfrequencies
Authors: Gough, D. O.; Thompson, M. J.
1988IAUS..123..155G Altcode:
Magnetic fields contribute to the splitting of the degeneracy of modes
of like order and degree. The splitting is estimated for some simple
hypothetical toroidal magnetic field configurations in the sun, and
the results are compared with previous asymptotic estimates. Splitting
by a field confined to a thin layer at the base of the convection zone
is found not to agree with recent measurements.
---------------------------------------------------------
Title: Problems in helioseismology
Authors: Thompson, Michael John
1987PhDT........98T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Communication. Enhanced sensitivity in the determination of
mercury by inductively coupled plasma atomic-emission spectrometry
Authors: Thompson, Michael; Coles, Barry J.
1984Ana...109..529T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Post-Newtonian collapse calculations
Authors: Thompson, M.
1983PASA....5..179T Altcode: 1983PASAu...5..179T
The dynamical collapse of a rotating body (with a mass less than the
critical mass) from white dwarf densities down toward neutron star
densities is examined with a view to resolving some of the effects of
rotation on the evolution. In the approach used here, the post-Newtonian
equations for continuity and momentum (Chandrasekhar, 1964) for a
perfect fluid are modeled with the smoothed particle hydrodynamics of
Gingold and Monagham (1982). The version of the code used conserves
both linear and angular momentum exactly. Collapse calculations are
carried out using a 1000-particle code. The results obtained are
briefly discussed, and improvements to the code are suggested.
