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Stars Group Research Sample 2001-2002
Astrometric and parallax studies with Hubble Space Telescope.
The Hubble Space Telescope Astrometry Science Team was based at the University of Texas in 2002. The team finished
reducing and analyzing HST/FGS astrometry for two critical distance indicators, RR Lyrae and δ Cephei.
Space Astrometry at the University of Texas
press releases
Astronomers Re-measure the Universe with Hubble Space Telescope
Astronomers Precisely Measure Extra-solar World's Mass
Fritz Benedict,
Barbara McArthur,
R. Duncombe (Aerospace Engineering), Bill Jefferys,
Pete Shelus
Carbon and oxygen solar photospheric abundance.
A reference for chemical analyses of astronomical objects, the study found carbon and oxygen solar photospheric
abundances about 50% lower than previous determinations, and C/O in agreement with the ratios measured in the
solar corona from gamma-ray spectroscopy and solar energetic particles.
Carlos Allende Prieto,
David Lambert,
M. Asplund (Australia National University)
Recurrent novae U Sco and CI Aql.
Continuation of a program started in 1987 to time eclipses from recurrent novae U Sco and CI Aql. Old data
accurately measures orbital period before their eruptions in 1999 and 2000, respectively. Further post-eruption
timings will give an accurate dynamical measure of the mass ejected by the eruptions. Are white dwarfs in recurrent novae, on average,
gaining mass, and thereby becoming Type Ia supernova?
Brad Schaefer
Distances and metallicities of Cepheids in M31 and M33.
Using HET-HRS spectra of individual Cepheids in the nearby
spiral galaxies M31 and M33, we have determined radial velocity
curves and distances to several stars. Metallicities of the same
stars are in progress. These will be used to investigate the
dependence of the Cepheid PL relation upon [Fe/H].
Amy Forestell,
Tom Barnes,
Chris Sneden,
Tom Moffett (Purdue Univ.)
White dwarf asteroseismology.
Study of the fundamental structural and evolutionary parameters of white dwarf stars—rotation rates, magnetic
field strengths, total mass, compositional stratification of the envelope, core composition and more. Applying the
powerful theoretical machinery of asteroseismology to the intrinsic simplicity of these high gravity objects informs
diverse avenues of research, ranging from the behavior of matter under extreme conditions to galactic structure and
cosmochronology.
Whole Earth Telescope
Asteroseismology, Don Winget
Don Winget
Abundances and rotation velocities of evolved stars.
Brad Behr
Gravitational lensing in the Large Magellanic Cloud.
Near-IR imaging study to test whether line-of-site low mass main sequence stars are lenses.
Ted von Hippel,
A. Sarajedini (U. Florida)
Automation of stellar spectra analysis.
Brad Behr
Tight binaries.
Project to model the rotational line-broadening modulation of tidally-distorted secondary stars in tight binary systems.
Ed Robinson,
Brad Behr, Martin Bitner
Black hole and neutron star binaries.
Rob Hynes
Stellar metallicities and rotations in open clusters.
Precision study of the intrinsic width of the main sequence in open clusters, with collaborators in the WIYN Open
Cluster Study (WOCS). The goal of the project is to measure the dispersion of stellar metallicities and rotations in open
clusters to high precision. Also, continued study of the ages and abundances of open clusters, and work to constrain
stellar evolution theory for low mass stars.
WIYN Open Cluster Study
Ted von Hippel,
Rica French
Balmer line profiles: cool dwarfs and subgiants.
An analysis of Balmer line profiles in a sample of 30 cool dwarfs and subgiant stars based on the most recent
calculations of the line opacities.
Program stars span temperatures from 4800 to 7100 K and include a small number of population II stars.
Effective temperatures have been derived using a quantitative fitting method with a detailed error analysis, finding
a good agreement with those from the Infrared Flux Method (IRFM) at near solar metallicity. They find differences
at low metallicity where the two available IRFM determinations themselves are in disagreement.
Paul Barklem (and collegues, Uppsala Astronomical Observatory),
Carlos Allende Prieto
BaII line at 4554 Å of the metal-poor subgiant HD 140283.
Study shows that a solar-like r-process isotopic mixture provides a fair fit to ultra-high dispersion observations of
the 4554 Å profile from McDonald Observatory. This refutes a claim by P. Magain (U. de Liège) that a
pure r-process mix of the barium isotopes was inconsistent with the mix of odd to even barium isotopes derived from
a previous study. The new study shows that Magain's error bars were likely underestimated.
David Lambert,
Carlos Allende Prieto
Low mass stars and brown dwarfs in σ Orionis.
Aquisition of intermediate to low resolution optical spectra of low mass stars and brown dwarfs in the cluster
σ Orionis using telescopes in Calar Alto, the Roque de los Muchachos Observatory, Mauna Kea,
and McDonald.
Comparison of the observations to model atmosphere calculations of the Li line at 6708 Å, allowed the group to infer that no lithium
depletion has yet taken place in the cluster, and that the observed lines are consistent with a cluster initial lithium abundance
close to the cosmic value. Hence, the upper limit to the σ Orionis cluster age could be set at 8Myr, with a most likely value
around 2-4Myr.
M. Zapatero Osorio (Caltech) and collaborators,
Carlos Allende Prieto
Ultra-high resolution spectra of F-G-K stars.
Acquisition of ultra-high resolution spectra with the High Resolution Spectrograph and the HET for a set of nearby F-G-K stars.
The wavelength shifts of stellar lines relative to their laboratory positions were measured for more than a thousand Fe I lines
per star, finding a clear correlation with line depth. The observed patterns were interpreted as convective blueshifts that
become more prominent for weaker lines, which are formed in deeper atmospheric layers. A morphological sequence with
spectral type or effective temperature was apparent in the data. Two K giant stars were also studied for the first time. The
velocity span between weak and strong lines for these stars is larger than for the dwarfs and subgiants of similar spectral
types.
Carlos Allende Prieto,
David Lambert,
Bob Tull,
Phillip MacQueen
Spectroscopic survey: the solar neighborhood.
Observations have been completed of a sample representing all the stars brighter than Mv= 6.5 within
47 lightyears of the Sun, using the Mcdonald 2.7m telescope and the ESO 1.52m telescope at La Silla (Chile). A catalogue of
radial velocities, stellar parameters and chemical abundances for some 30 species will be released, providing the first
spectroscopically determined metallicity distribution for a complete sample of stars in the solar neighborhood. Regular monitoring
of the stars will look for life (carbon-based or not) on orbiting planets.
Spectroscopic Survey of Stars in the Solar Neighborhood
Carlos Allende Prieto,
David Lambert,
K. Cunha (Observatório Nacional, Rio de Janeiro),
Paul Barklem (Uppsala Astronomical Observatory)
R Coronae Borealis (R CrB) stars, hydrogen-deficient supergiants.
The dominant source of continuum opacity in the visible region is due to the photoionization of neutral carbon. As expected,
the CI line retains its equivalent width even as "metal" lines may vary considerably from star to star. But, the expectation is not
met in one crucial way. The predicted equivalent width of
a CI line exceeds the observed equivalent width by a considerable factor. This discrepancy is termed "the carbon problem".
Investigation of the [CI] 9850 Å line, expected to be unsaturated in the R CrB spectra, also shows the carbon problem. The
solution is concluded to be an appropriate photospheric temperature gradient.
Gajendra Pandey,
David Lambert,
N. Kameswara Rao (Indian Institute of Astrophysics, Bangalore)
Blue stragglers.
A survey of blue stragglers in nearby open clusters to determine how many were formed by collision, and how many by
mass transfer. This is the first complete spectroscopic survey of blue stragglers. The project includes observations with
the Mount Laguna 1m, McDonald 2.1m, McDonald 2.7m and Hobby-Eberly Telescope.
E. Sandquist (San Diego State U.),
Matthew Shetrone
Orbit of θ Draconis.
Using McDonald 2.1m telescope radial velocities, improved the orbit of the single-lined spectroscopic binary θ Draconis.
M. Slovak (Louisiana State U.),
Tom Barnes
Bayesian Analysis of Galactic Cepheids.
Determination of distances and radii for thirteen Galactic Cepheids using Bayesian statistical methods.
The study makes use of the surface brightness method newly calibrated by Cepheid interferometric angular diameters of T. Nordgren
(USNO) and collaborators. The approach fully accounts for errors in the data, provides unbiased distance estimates, provides objective
model selection for the photometric and velocity curves, and includes a Lutz-Kelker correction. The analysis uses Markov Chain
Monte Carlo simulations to sample the posterior probabilities of the individual models and then to properly weight the models.
A Bayesian Analysis of the Cepheid Distance Scale (pdf)
Tom Barnes,
Bill Jefferys,
J. Berger and P. Müller (Duke U.),
K. Orr and R. Rodriguez (UT Austin)
Distances to the Magellanic Clouds.
We have applied the Bayesian approach of Barnes et al. (2003,
ApJ, July 20), with modificiation to account for the different
priors on distance appropriate for other galaxies, to measure
distances to individual Cepheids in the Large Magellanic Cloud
and Small Magellanic Cloud.
Tom Barnes,
Tom Moffett (Purdue Univ.),
Bill Jefferys
OH and H2O in Arcturus.
Detections of pure rotation lines of OH and H2O in Arcturus using high-resolution, infrared spectra recorded
with the TEXES spectrometer used on NASA's IRTF.
Arcturus is the hottest star yet to show water-vapor features in its disk-averaged spectrum.
The argument
is made that the water vapor lines originate from the photosphere, albeit in the outer layers. Satisfactory prediction
can be made of the observed strengths of OH and H2O lines after lowering the temperature
structure of the very outer parts of the photosphere compared to a flux-constant, hydrostatic, standard model photosphere.
EXES: mid-IR spectrograph for SOFIA
N. Ryde,
David Lambert,
Matt Richter (UC Davis),
John Lacy
Near infrared spectra of supernovae.
Observing program with the SPEX instrument on the IRTF to obtain routine near infrared spectra of supernovae.
The focus of the observing program is on type Ia, using hydrodynamic simulations of the explosion and a
radiation transport code for the nucleosynthesis to learn more about their explosion dynamics and the systematic
variations that might affect the use of Type Ia as distance indicators. The spectral evolution suggests that the
intermediate mass elements are layered in a way that there is little mixing and that they result from a detonation.
The peculiar Type Ic SN 2002ap was shown to have no helium, but to form carbon monoxide at later epochs.
Howie Marion,
(supervised by Peter Höflich and
Craig Wheeler)
Routine spectropolarimetry of all accessible supernovae.
The continued observing program now concentrates on data from the ESO VLT. D. Baade and L. Wang take
the lead on reducing and analyzing the data in a target of opportunity program. Data on the peculiar Type Ic SN 2002ap
showed that it was significantly polarized with material moving as fast as 20,000 km s-1, but not higher,
as claimed in some preliminary work. The Type Ia SN 2001el showed a very distinct, highly polarized shell of Ca II that
might be some clue to the binary nature of the progenitor. The polarization of Type Ia suggests that their luminosity is
not emitted isotropically and hence has implications for their use as cosmological markers.
Peter Höflich,
Craig Wheeler,
Howie Marion,
D. Baade (PI/European Southern Observatory),
L. Wang (Lawrence Berkeley National Laboratory)
MHD processes in stellar core collapse.
Polarization studies suggest that core collapse supernovae are routinely strongly asymmetric, even commonly bi-polar. One means
to do this is to produce a jet as the neutron star forms. Akiyama et al. show that the magnetorotational instability may be a robust
mechanism to grow large magnetic fields (~ 1015 Gauss) in only several hundred milliseconds.
Craig Wheeler,
Shizuka Akiyama,
I. Lichtenstadt (Hebrew U.),
D. Meier (Jet Propulsion Laboratory)
Shock wave of SN 1987A.
Continued work of the Hubble Space Telescope SuperNovae INtensive Study examines the interaction of the shock
wave from SN 1987A with the circumstellar rings, and the shape of the debris. The asymmetry in the debris was shown to be
consistent with the expectations of jet models of the explosion and the coalignment of the ejecta image with the polarization
axis.
SINS: The Supernova INtensive Study
Craig Wheeler,
R. Kirshner (PI/Harvard)
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