Monday, May 23, 2011, 8:00 AM - 7:00 PM
125 Stellar Evolution, Stellar Populations Poster Session Essex Ballroom
125.01
Using High Precision Stellar Observations to Constrain the Physics of Convection in Stars
Timothy Carleton1, C. Meakin1
1Steward Observatory.
8:00 AM - 7:00 PM
Essex Ballroom
Arguably the most significant barrier to our full comprehension of stellar structure and evolution is the uncertainty in our understanding of stellar convection and its attendant mixing. Our current understanding of stellar convection, mixing length theory (MLT), describes convection as a process in which warmer pockets of fluid flow to the surface through a temperature gradient. The efficiency at which this transfers heat is dependent on the ratio of the surface area to the volume of the globule, gml. We use the stellar evolution simulation package MESA (Modules for Experiments in Stellar Astrophysics) together with new high precision observations of non-interacting binaries to constrain convection physics in low mass stars (M<1.2 Msun), specifically gml. Our data set contains 45 stars with precision mass, temperature and luminosity measurements (uncertainties at the few percent level) as well as observed relationships between turbulent surface velocity, surface gravity, and luminosity. This research was supported by the Arizona Space Grant Consortium.
125.02
The Physics of AGB Mass Loss
Lee Anne M. Willson1, Q. Wang1
1Iowa State Univ..
8:00 AM - 7:00 PM
Essex Ballroom
To investigate the importance of physical processes in the stellar atmosphere on the mass loss rates of AGB stars, we have run a substantial grid of dynamical atmosphere models using a code that approximates non-LTE, dust formation, and radiative transfer via one or two parameters each, and using R(L, M, Z, l/H) to investigate the importance of low gravity and metallicity. This gives us six parameters to investigate: Criticial density (for the onset of non-LTE), opacity kappa (determines the photospheric density), Tcondensation and ΔTcondensation (for dust formation), mixing length parameter l/H, and Z, M (for the initial stellar model). We find the location of the Deathline, where dlnM/dt = dlnL/dt, is quite stable, shifting by ΔlogLdeath < ~0.1 with variation of any of the parameters inside reasonable limits. We find that the biggest uncertainty in the model-based Deathline is introduced by the uncertainty in R(L, M, Z) represented by varying l/H in the models. The condensation of dust and the non-LTE transfer both have a great effect on the structure of the atmosphere, and affect the outflow velocity in the wind, but neither of these makes a large difference in the predicted Deathline. Observational constraints on the Deathline include the Mira P-L relation and a variety of published empirical mass loss formulae. Research supported by NSF AST0708143.
125.03
The Wfpc2 Uv Survey Of Globular Clusters: The Case Of Ngc 6229
Nicoletta Sanna1, R. T. Rood1, G. Beccari2, E. Dalessandro3, F. R. Ferraro3, B. Lanzoni3
1University of Virginia, 2European Southern Observatory, Germany, 3University of Bologna, Italy.
8:00 AM - 7:00 PM
Essex Ballroom
One of the valedictory projects undertaken by WFPC2 was a survey of UV bright objects in 30 globular clusters. Eventually these results will be
combined with similar results obtained by our group for 15 clusters. For most of these clusters observations were obtained with 4 or more filters.
For a subset of clusters we also have observations from GALEX which will allow us see if the sort radial variations previously found in blue
straggler stars (BSS) also exists in the hottest stellar populations.
Here we present the case of NGC 6229. The data set has been obtained by combining high-resolution (HST/WFPC2 and ACS) and wide-field space (GALEX)
observations and ground-based (MegaCam-CFHT) images. The photometric sample covers the entire cluster extension from the very
central regions up to the tidal radius and beyond. We determine the radial density profile and we study the BSS population and its radial distribution.
125.04
IRAS 20050+2720: Time Scales Of Pre-main Sequence Evolution
Hans Moritz Guenther1, S. J. Wolk1, B. Spitzbart1, R. A. Gutermuth2
1SAO, 2Smith College/UMass.
8:00 AM - 7:00 PM
Essex Ballroom
We present results of our multiwavelength study of IRAS 20050+2720, a young stellar cluster, which is thought to be located at 700 pc. IRAS 20050+2720 displays an exceptionally low 24 micron background, because no massive stars are present. We concentrate on Chandra and Spitzer data and compare cluster properties of an IR sample (as previously presented by Guthermuth et al. 2009) and an X-ray selected sample. Compared to previous works the IR coverage has been extended with new observations. Foreground X-ray sources are separated with optical photometry and we treat the remaining disk-less sources as the class III population of the cluster. It turns out, that the class III sources are much less clustered than class I and II sources.
The low 24 micron background allows us to achieve a more complete sample at this wavelength than in other star forming regions. Therefore, our census of transition disk objects between class II and class III should be more complete. We use this to put limits on the time scale of disk dispersal.
This work has been funded by Chandra award GO6-7017X.
125.05
Multi-wavelength Analysis of Young Stellar Objects in the W4 Star Forming Region
Micaela B. Bagley1, J. S. Kim1, W. H. Sherry2, M. R. Meyer3, M. M. Bagley1
1University of Arizona, 2NOAO/NSO, 3ETH Zurich, Switzerland.
8:00 AM – 7:00 PM
Essex Ballroom
We present our preliminary results of an optical survey of the W4 star forming region. W4 is an H II region located at a distance of about 2 kpc. Its central young star-forming cluster, IC 1805, contains well-studied massive stars making this an ideal region for studying the relationship between high- and low-mass star formation. As part of the W3/W4/W5 star-forming complex, stellar populations in the W4 region provide an opportunity to study the possibility of triggered star formation. We have performed an optical imaging survey of these regions using the 90Prime imager at the Bok telescope. Our preliminary results focus on intermediate to low-mass populations of W4. This work is part of a larger project to study the star-formation history, initial mass function, and circumstellar disk evolution of the W3/W4/W5 complex. Our observations are sensitive down to about 0.5 solar masses. We select candidate pre-main sequence stars based on their location in V-I, V color-magnitude diagrams compared to model isochrones. Preliminary tests have found about 1500 candidate stars with initial age estimates less than 3 Myr. We use infra-red data from the 2MASS catalog and the Spitzer Space Telescope to estimate the circumstellar disk frequency as a function of age and mass in this region. X-ray data from the Chandra X-ray Observatory also help select candidate young stars. These candidates will be targeted for optical spectroscopy to better determine stellar masses and ages. Here we present the spatial distribution of both confirmed and candidate young stars in the W4 star-forming region.
125.06
The Red and Yellow Supergiants in M33: Kinematics and Massive Star Evolution
Philip Massey1, M. Drout2, S. Tokarz3, N. Caldwell3
1Lowell Obs., 2University of Cambridge, United Kingdom, 3Smithsonian Astrophysical Observatory.
8:00 AM – 7:00 PM
Essex Ballroom
Massive star evolution is hard to model, owing to the complications of mass-loss, uncertainties over mixing and convection, the effects of rotation, and so on. It is generally agreed that the most massive stars spend their He-burning lives as Wolf-Rayet stars. Stars of slightly smaller masses spend most of their He-burning phase as red supergiants, after briefly passing through a yellow supergiant phase. We are interested in identifying the numbers and physical properties of these stars throughout the star-forming galaxies of the Local Group in an effort to test stellar evolutionary models at varying metallicities. However, foreground contamination by Milky Way dwarfs is severe for both the yellow supergiants (YSGs) and red supergiants (RSGs). Using the photometry of the Local Group Galaxy Survey, we have used two-color information (B-V vs V-R) to separate likely foreground dwarfs from bona fide RSGs in M33, and obtained radial velocities with Hectospec on the 6.5-m MMT. The radial velocities refine the rotation curves of previous studies, and demonstrate that the rotation curve is quite flat. With the new velocity data we then separate the yellow supergiant population from the foreground using radial velocities as well. Since the number of Wolf-Rayet stars is now known to a few percent in M33 (Neugent et al. 2011, ApJ, in press, as well as poster at this meeting) it is now possible to compare the numbers of RSGs, YSGs, and WRs in this nearby spiral. This work is supported by the National Science Foundation through AST-1008020.
125.07
Wolf-Rayet Stars in the Local Group
Kathryn Neugent1, P. Massey1
1Lowell Observatory.
8:00 AM – 7:00 PM
Essex Ballroom
The physics behind hot, massive stars is complicated, making the stars’ properties difficult to model. For this reason, we rely on observational tests to see how well stellar evolutionary theory predicts the relative numbers of various types of massive stars. The star-forming galaxies of the Local Group, with their varying metallicities, provide an excellent laboratory for such studies, as massive star evolution is strongly influenced by mass-loss rates, which in turn depend upon metallicity, at least on the main sequence. We’ve recently begun a far deeper, and more complete survey of the Wolf-Rayet (WR) content of Local Group galaxies compared to what has been done in the past. Here we discuss our candidate selection process, as well as the results from our most recent study of M33 which yielded 56 new WR stars. The relative number of WCs to WNs would support there being a strong metallicity gradient. This work was supported by the National Science Foundation under AST-1008020.
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