Aavso paper Session I sunday Sunday, May 22, 2011, 9: 30 am – 12: 00 pm
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323Stellar Atmospheres, WindsPoster SessionEssex Ballroom323.01
Theoretical Near-IR Spectra for Surface Abundance Studies of Massive Stars George Sonneborn1, J. Bouret1 1NASA's GSFC. 8:00 AM - 7:00 PM Essex Ballroom We present initial results of a study of abundance and mass loss properties of O-type stars based on theoretical near-IR spectra computed with state-of-the-art stellar atmosphere models. The James Webb Space Telescope (JWST) will be a powerful tool to obtain high signal-to-noise ratio near-IR (1-5 micron) spectra of massive stars in different environments of local galaxies. Our goal is to analyze model near-IR spectra corresponding to those expected from NIRspec on JWST in order to map the wind properties and surface composition across the parameter range of O stars and to determine projected rotational velocities. As a massive star evolves, internal coupling, related mixing, and mass loss impact its intrinsic rotation rate. These three parameters form an intricate loop, where enhanced rotation leads to more mixing which in turn changes the mass loss rate, the latter thus affecting the rotation rate. Since the effects of rotation are expected to be much more pronounced at low metallicity, we pay special attention to models for massive stars in the the Small Magellanic Cloud. This galaxy provides a unique opportunity to probe stellar evolution, and the feedback of massive stars on galactic evolution in conditions similar to the epoch of maximal star formation. 323.02
8:00 AM - 7:00 PM Essex Ballroom We derived the elemental abundances of the sharp-lined B3IV star iota Herculis from high quality optical region spectra (Δλ/λ = 67000, signal-to-noise ≥ 750) obtained with the long camera of the coude spectrograph of the 1.22-m telescope of the Dominion Astrophysical Observatory, Victoria, BC. Canada. The 4096 pixel long SITe4 CCD was used. Generally, two or three one-hour spectra of the same region taken on the same night were co-added to increase the S/N. Twenty-one central wavelength settings covered the entire spectrum (λλ3827-8976) where the desired S/N could be obtained. The regions selected were not seriously affected by telluric lines were not observed. The spectrum was measured using the REDUCE family of programs of Graham Hill. H I, He I, C II, C III, N I, N II, O I, O II, Ne I, Mg II, Al II, Al III, Si II, Si III, P II, P III, S II, S III, Ar II, Fe II, Fe III, and Ni II lines are used to derive the elemental abundances in an LTE fine analysis using Kurucz’s ATLAS9 and WIDTH9 programs. Lines of additional species might be present. Initial estimates of the effective temperature, surface gravity, and microturbulence are 17400 K, 3.85 dex, and 1.9 km s-1, respectively. The He/H ratio is found to be near solar as are the other derived abundances. However, abundances of the same element derived from two species can be different. This probably indicates that some adjustments of these parameters and non-LTE physics are needed to get ionization equilibrium. In addition to our fine analysis we performed a synthesized spectra analysis to refine the results. SJA and AFG are Guest Observers at the Dominion Astrophysical Observatory. 323.03
Surface Abundance Patterns in A-Type Stars from UV Spectral Synthesis Edward L. Fitzpatrick1 1Villanova University. 8:00 AM - 7:00 PM Essex Ballroom In this poster, we present results from a program whose goals are to (1) examine the degree to which current LTE atmosphere models can reproduce the complex UV spectra (1200-3200 A) of the A-type stars; in order to (2) develop better estimates of the physical properties, including composition, for specific target stars with available archival UV data; and (3) examine the abundance patterns revealed from a large group of normal and peculiar A-type stars to gain insight into the processes driving the compositional anomalies often observed in this spectral domain. We use the ATLAS9 atmospheric structure models from R.L. Kurucz, the spectral synthesis program SPECTRUM from R. Gray, and a new atomic line list developed from data in the VALD and NIST archives. For most of the stars, the data are high-dispersion spectrophotometry from the IUE satellite, although in several cases very high quality HST spectroscopy from GHRS and STIS are available. In addition to measurements of effective temperature, surface gravity, mictrotubulence velocity, and rotational velocity, we are also able to determine abundances for over 30 elements per star, including CNO, the light metals, the Fe group, and a number of heavy elements. We illustrate the striking abundance patterns for a number of stars, including members of the Am and HgMn classes, along with several ``normal’’ and ``superficially normal’’ stars. This research has been supported by NASA Astrophysics Data Program grant NX08AJ62G. 323.04
Line Identifications in the Far Ultraviolet Spectrum of the Eclipsing Binary System 31 Cygni Wendy Hagen Bauer1, P. D. Bennett2 1Wellesley College, 2Eureka Scientific. 8:00 AM - 7:00 PM Essex Ballroom The eclipsing binary system 31 Cygni (K4 Ib + B3 V) was observed at several phases with the Far Ultraviolet Spectrosocopic Explorer (FUSE) satellite. During total eclipse, a rich emission spectrum was observed, produced by scattering of hot star photons in the extended wind of the K supergiant. The system was observed during deep chromospheric eclipse, and ~2.5 months after total eclipse ended. We present an atlas of line identifications in these spectra. During total eclipse, emission features from C II , C III, N I, N II, N III, O I, Si II, P II, P III, S II, S III, Ar I, Cr III, Fe II, Fe III, and Ni II were detected. The strongest emission features arise from N II. These lines appear strongly in absorption during chromospheric eclipse, and even 2.5 months after total eclipse, the absorption bottoms out on the underlying emission seen during total eclipse. The second strongest features in the emission spectrum arise from Fe III. Any chromospheric Fe III absorption is buried within strong chromospheric absorption from other species, mainly Fe II. The emission profiles of most of the doubly-ionized species are red-shifted relative to the systemic velocity, with asymmetric profiles with a steeper long-wavelength edge. Emission profiles from singly-ionized species tend to be more symmetric and centered near the systemic velocity. In deep chromospheric eclipse, absorption features are seen from neutral and singly-ionized species, arising from lower levels up to ~3 eV. Many strong chromospheric features are doubled in the observation obtained during egress from eclipse. The 31 Cygni spectrum taken 2.5 months after total eclipse ended ws compared to single-star B spectra from the FUSE archives. There was still some additional chromospheric absorption from strong low-excitation Fe II, O I and Ar I. 323.05
Comparing High-Precision Stellar Diameters From the Navy Prototype Optical Interferometer With Stellar Atmosphere Models as a Function of Wavelength Anders M. Jorgensen1, J. T. Armstrong2, H. R. Schmitt2, E. K. Baines2, D. Mozurkewich3, C. Tycner4, D. J. Hutter5, T. Hall1, D. Paiton1, M. Brown1, B. Curtis1 1New Mexico Tech, 2Naval Research Laboratory, 3Seabrook Engineering, 4Central Michigan University, 5Naval Observatory Flagstaff Station. 8:00 AM - 7:00 PM Essex Ballroom In this paper we use the coherent integration technique to obtain extremely high precision stellar diameters as a function of wavelength in the visible band using observations from the Navy Prototype Optical Interferometer (NPOI). We then compare these diameters with stellar atmosphere models as a function of wavelength. Coherent integration is a post-processing technique which corrects for atmospheric optical-path-difference shifts in interferometric data and allows, effectively, to increase the integration time of optical interferometric data indefinitely by summing many short exposures suitably phase-shifted. This is significant because coherent integration, which allows the complex visibilities to be summed in phase, greatly improves the signal-to-noise ratio over traditional techniques which average squared visibilities. The improvement is particularly dramatic for faint targets, and/or when the visibility amplitude is very small. This is important when measuring stellar diameters on resolving baselines that include visibility nulls. Those baselines best constrain the diameters. However in order to take full advantage of the null as a diameter measure it is necessary to obtain high-SNR measurements around the null, which is possible with coherent integration. We present wavelength-dependent uniform disk diameter measurements with precision up to 1:500 to 1:1000. We then compare these with the corresponding uniform-disk diameters obtained from stellar atmosphere models 323.06
Diameters and Temperatures of Main-Sequence Stars Tabetha S. Boyajian1, H. McAlister1, K. von Braun2, G. van Belle3, D. Gies1, T. ten Brummelaar1, C. Farrington1, P. Goldfinger1, S. Ridgway4, L. Sturmann1, J. Sturmann1, G. Schaefer1, N. Turner1 1Georgia State UNIV./CHARA, 2NExScI/Caltech, 3ESO, Germany, 4NOAO. 8:00 AM - 7:00 PM Essex Ballroom We present the current status of the survey to measure accurate diameters of nearby, main-sequence stars with the CHARA Array, a long baseline optical/infrared interferometer. This project is the source of the largest homogeneous data set that provides direct measurements of the stellar linear radius and effective temperature for stars of this type. We discuss the challenges these data bring to current stellar atmospheric and evolutionary models, as well as the development of empirically based relations and calibrations to the stellar effective temperature scale. Download 2.63 Mb. Share with your friends:
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