Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 59, Number 11
Friday–Saturday, October 17–18, 2014; Orem, Utah
Session D5: Stellar Astrophysics |
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Chair: Michael Joner, Brigham Young University Room: Science Building 260 |
Friday, October 17, 2014 1:50PM - 2:14PM |
D5.00001: Calibrated H-Alpha Monitoring of Astrophysically Interesting Objects Invited Speaker: Eric Hintz Given that the normal matter in the Universe is predominately hydrogen it makes sense that monitoring the first Balmer line of hydrogen would be a very common practice in astronomy. As an absorption line it can be used to monitor the surface temperature of stars, or examine open star clusters. As an emission line it is used to study emission line stars, nebulae, and active galaxies. Many different photometric systems have been developed over the years to monitor the H-alpha line. However, when many research teams each develop their own filter system it is very difficult to compare one data set to another, or to merge data sets to examine long period variations. Over the last 9 years we have been spectrophotometrically calibrating a new H-alpha index that can be used to monitor a variety of objects in both absorption and emission. The photometric index will be defined and its early application to a wide variety of objects will be presented. Some early monitoring efforts on High Mass X-ray Binaries, Be stars, Cepheids, RR Lyrae, $\delta$ Scuti variable, YSO's, and nearby Active Galaxies will be addressed. [Preview Abstract] |
Friday, October 17, 2014 2:14PM - 2:26PM |
D5.00002: Getting the Most Out of Stellar Spectrum Fits Timothy Anderton Stellar spectra can be rich sources of information including effective temperature, surface gravity, rotation rate, and chemical enrichment of various elements. However what quantities are derivable from a spectrum is a complex question. A prime example is the potential to measure chemical enrichment which is a complex function of temperature, surface gravity, level and type of enrichment, observed spectral range, signal-to-noise, and spectrograph resolution. One solution is to attempt to measure all potentially measurable quantities and throw away quantities determined with low precision. However in practice this can introduce large undesirable covariances into our set of measurements. Moreover this strategy is inapplicable when dealing with nuisance parameters for which it is difficult or impossible to know a priori what a good parameterization might be. We present a method to automatically determine the optimal parameterization for both physical and nuisance parameters to use in fitting stellar spectra based on the adoption of a fit metric which takes into account both goodness of fit and model complexity combined with a search methodology which slowly expands the number and type of parameters being fit until an optimum is found. [Preview Abstract] |
Friday, October 17, 2014 2:26PM - 2:38PM |
D5.00003: Development of Stellar Intensity Interferometry techniques using twin 3 meter telescopes at \textit{StarBase}-Utah Nolan Matthews, David Kieda, Stephan LeBohec The emergence of large air Cherenkov telescope arrays have opened up the potential for high-resolution imaging of stellar surfaces using Intensity Interferometry techniques. Stellar Intensity Interferometry (SII) allows coverage into the optical and ultraviolet frequency bands which are traditionally inaccessible to classical Michelson interferometry. The relative insensitivity to atmospheric turbulence allows for unprecedented angular resolution scales as the baselines between telescopes can be made very large (\textgreater 100m) without the need for precise spatial resolution as required by Michelson interferometry. In this talk I will illustrate the science capabilities of the SII technique and describe the progress achieved in developing a modern Stellar Intensity Interferometry system with a pair of 3 m diameter optical telescopes located at \textit{StarBase}-Utah. In particular, observations of the optical Crab pulsar are being performed as a proof-of-concept for intensity interferometry measurements. [Preview Abstract] |
Friday, October 17, 2014 2:38PM - 2:50PM |
D5.00004: Analyzing solar-type stars in the infrared with APOGEE Jessica Galbraith-Frew, Inese I. Ivans The Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a high resolution spectroscopic survey aimed at understanding the chemical and kinematic properties of stars in our galaxy, and is one of four experiments in the Sloan Digital Sky Survey III (SDSSIII). The APOGEE data is the first high resolution spectra collected in the infrared (IR), and contains features for more than 15 elements. The APOGEE spectra are run through an automated pipeline to determine the stars effective temperature, surface gravity, metallicity (stellar parameters), and the stars chemical composition. These parameters are required for modeling a stars atmosphere and spectrum. A majority of the stars observed by APOGEE are in a different evolutionary state than the sun, and have calibration relations. For solar-type stars, further analysis is needed to provide parameters for calibration relations. To this end we are studying the sensitivity of different spectral features to the stellar properties, to find a technique to independently determine temperature, surface gravity, and metallicity. Once the properties of these stars are determined, we can determine the chemical composition of the star using standard spectroscopic techniques. Over 200 of the APOGEE solar-type stars have planetary candidates from the Kepler spacecraft. The chemical composition of solar-type stars can be used to study how the composition of a host star impacts its planetary companions or lack thereof. [Preview Abstract] |
Friday, October 17, 2014 2:50PM - 3:02PM |
D5.00005: Core Convection, A Possible Driving Mechanism for Gamma Doradus-Delta Scuti Pulsations Taylor Morgan, Joyce Guzik, Nicholas Nelson Delta Scuti stars lie on the instability strip of the Hertzsprung-Russell diagram where stars undergo self-excited oscillations, pulsating in radial and non-radial acoustic modes with periods of one to several hours. Gamma Doradus stars are nonradial gravity-mode pulsators that lie just at the red edge of the delta Scuti instability strip. They pulsate with periods in the range of 0.3 to 3.0 days. It was originally thought that convective blocking at the bottom of the envelope convection zone was the sole mechanism for driving g-modes. However, recent Kepler data shows that stars that are either too hot or too cold for this mechanism to work also exhibit these pulsations. We propose that core convection within gamma Doradus - delta Scuti type stars contributes to driving gravity-mode pulsations. We show results for a 1.62 solar mass model developed to investigate a Kepler gamma Doradus - delta Scuti hybrid, and simulate its core convection using the 3D hydrodynamics code ASH (Anelastic Spherical Harmonic). In order to generate the initial conditions for ASH, we evolve a model using a 1D Lagrangian code MESA (Modules for Experiments in Stellar Astrophysics). [Preview Abstract] |
Friday, October 17, 2014 3:02PM - 3:14PM |
D5.00006: The Morphology and Uniformity of Circumstellar Shells Surrounding OH/IR Stars Derek Felli, Victor Migenes OH/IR stars are asymptotic giant branch stars that have circumstellar envelopes with rich chemistry. These envelopes form from the mass loss process in these stars. Although we understand that this mass loss process drives the formation of proto-planetary nebulae, the uniformity of this process is not well understood. This is because there is not a compilation of multi-wavelength high resolution data on individual OH/IR stars to improve the models. Current scientific models of these processes assume uniform mass loss and spherical symmetry; this is an oversimplification that must be corrected in order to further understand how planetary nebulae achieve bipolar or irregular shapes as well as spherical forms. We are using high resolution optical, infrared and radio observations to image various circumstellar shells to understand the uniformity of the mass loss process. These observations will provide the layout for better models. The models will lead to a better understanding of how late-type stars evolve into planetary nebulae. [Preview Abstract] |
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