Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 57, Number 11
Friday–Saturday, October 26–27, 2012; Socorro, New Mexico
Session E2: High Resolution Studies of the Sun and Stars I |
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Chair: Luke Schmidt, New Mexico Institute of Mining and Technology Room: Macey Center Copper |
Friday, October 26, 2012 4:30PM - 4:54PM |
E2.00001: Progress and Science with the Magdalena Ridge Observatory Interferometer Invited Speaker: Michelle Creech-Eakman The Magdalena Ridge Observatory Interferometer (MROI) is the most ambitious optical interferometer project in the world today (Creech-Eakman et al. 2012, SPIE). First funded in 2000, the project has gained significant momentum in the last few years, and is working closely with our collaborators from the University of Cambridge. We have completed the design, prototyped and tested most subsystems, begun installation of major infrastructure on the Ridge, and have a plan to complete and install four telescopes in four years. When completed, MROI will include 10 movable telescopes operating over 7.5 to 340m baselines and wavelengths (0.6-2.4 microns) which will allow astronomers to produce sub-milliarcsecond images of a large variety of astrophysical targets. I will present our completed design and give an overview of recent progress, our timeline to first light and some of the technical and scientific milestones anticipated as we enter our commissioning phase. First fringes are expected for MROI in approximately 2 years. [Preview Abstract] |
Friday, October 26, 2012 4:54PM - 5:06PM |
E2.00002: High Angular Resolution Investigations of Binary Stars Jenny Patience, Rob De Rosa, Lisa Prato, Gerard van Belle With long baseline optical/infrared interferometry, it is possible to probe uniquely high angular scales and investigate the frequency and properties of binary stars. The angular resolution provided by the Navy Prototype Optical Interferometer (NPOI) allows for the detection of close (5-700mas) binaries with a magnitude difference reaching approximately 3 magnitudes in R-band. Measurements of the binary fraction, mass ratio distribution, and separation distribution represent key statistical properties of binary stars which are important to understand the formation of stars and planets and the survivability of protoplanetary disks in binary systems. By mapping the orbits of young binary stars, it is possible to perform key empirical tests of evolutionary models. We detail the status of an ongoing volume-limited survey of nearby A- and B-type stars covering the important separation range between 1 and 15AU, complemented by AO observations to resolve wider companions. With our large, unbiased volume-limited sample, these observations will allow for the first constraint on the multiplicity of these massive stars over this separation range. A subset of these targets will also be included in upcoming extreme AO planet imaging searches, enabling a search for circumbinary planets. [Preview Abstract] |
Friday, October 26, 2012 5:06PM - 5:18PM |
E2.00003: Interferometric Imaging of Eclipsing Binaries Robert Stencel Multi-telescope interferometry has resulted in new horizons for near-infrared nano-radian imaging and spectro-interferometry (S-I). The CHARA Array has been increasingly productive, with the advent of MIRC and VEGA beam combiners, and the Magdalena Ridge Observatory Interferometer (MROI) holds similar promise. VLTI, NPOI and LBTI are discussed elsewhere. In this talk, I wish to highlight recent CHARA results on several eclipsing binary stars, and extend the prospects to a larger set of interacting binaries that can better reveal processes of mass loss, mass transfer and accretion disk physics. Stars imaged at high resolution in this manner include: the interacting hot stars in beta Lyr (Zhao+ arxiv.org/abs/0808.0932), the transiting disk in the epsilon Aurigae system (Kloppenborg+ arxiv.org/abs/1004.2464) and the famous ``Demon Star'' - Algol (Baron+ arxiv.org/abs/1205.0754). Epsilon Aurigae and its disk have also been studied with the VEGA S-I combiner (Mourard et al. 2012). The frontier for similar interferometric studies includes the next echelon of fainter eclipsing systems accessible to MROI, such as the symbiotic binaries which include white dwarf stars and are considered as possible precursors of cosmologically interesting Type Ia supernovae. [Preview Abstract] |
Friday, October 26, 2012 5:18PM - 5:30PM |
E2.00004: Epsilon Aurigae: Spectropolarimetric Characteristics of the Primary Star in and out of Eclipse Kathleen Geise, Robert Stencel Epsilon Aurigae is a single line binary system with an unusually long eclipse. The system consists of a variable F0 supergiant star, the primary, and a disk surrounding an unseen object, probably a B star. Many fundamental characteristics of the system, such as the mass and size of each object, origin and evolutionary nature of the disk material and the physical processes underlying the variability of the primary star, are poorly defined. We aim to characterize the polarization features of atomic and ionized gaseous species present in the F0 star atmosphere in order to identify anisotropies, to better understand the physical processes underlying the non-radial pulsation modes of the star. We obtained 50 epochs of high dispersion spectra from the ESPaDOnS spectropolarimeter at CFHT during 2008-2012. These spectra include eclipse and out-of-eclipse observations rich with polarization features attributable to both the F0 star and the disk. Polarization increased dramatically during eclipse, even for ionized species, suggesting that the B star engulfed in the disk contributes to the ionization of outer disk material. Pre-eclipse polarization signatures and position angles attributed to the F0 star indicate that anisotropies existed across the stellar disk. [Preview Abstract] |
Friday, October 26, 2012 5:30PM - 5:42PM |
E2.00005: Distance Determination to Binary Stars through Radiative Transfer Modeling Richard Pearson, Robert Stencel The epsilon Aurigae binary star system includes a F0 primary (7500 K) and an opaque accretion disk that engulfs the secondary star. The reported distance of the system falls around 800 +/- 200 pc. Uncertainty in the system's distance results in an observational parameter space that can be fitted by multiple evolutionary tracks. We explore a novel constraint to break this degeneracy. The accretion disk has an azimuthal temperature gradient, in response to the orbital phase of the primary star, plus disk rotation. Analysis of the thermal gradient with assumptions about the material properties of the disk, can constrain the distance. We use Monte Carlo radiative transfer methods to model the system. New constraints on physical parameters (binary separation, disk mass, disk composition, evolutionary state) are sought. Numerical models are created in HYPERION (Robitaille, http://arxiv.org/abs/1112.1071) by first defining a specific distance which parametrizes the model's inputs. The resulting disk temperatures are compared against the observed temperature range. Using a range of distances, we can match the disk temperature constraint with a smaller distance, and hence lower masses. The next step is to explore system response to a wider diversity of dust types. [Preview Abstract] |
Friday, October 26, 2012 5:42PM - 5:54PM |
E2.00006: Interferometric Observations of Rapidly Rotating Stars Gerard van Belle Interferometric observations of rapidly rotating stars are a powerful demonstration of the milliarcsecond imaging capabilities of these ultra-high-resolution facilities. These objects are typically rotating at greater than 80\% of their critical breakup velocity, and provide us with unique laboratories by which to test and confront common assumptions that underlie convention stellar modeling approaches. In particular, the departures from spherical symmetry in these stars allow us to probe internal structure in a unique and provocative way. [Preview Abstract] |
Friday, October 26, 2012 5:54PM - 6:06PM |
E2.00007: Disentangling Confused Stars at the Galactic Center with Long Baseline Infrared Interferometry Jordan Stone, Josh Eisner, John Monnier, Julien Woillez, Peter Wizinowich, Jorg-Uwe Pott, Andrea Ghez We present simulations of Keck Interferometer ASTRA and VLTI GRAVITY observations of mock star fields in orbit within $\sim50$ milliarcseconds of Sgr A*. Our results show an improvement in the confusion noise limit over current astrometric surveys, opening a window to study stellar sources in the region. For the Keck Interferometer, the improvement in the confusion limit depends on source position angles. The GRAVITY instrument will yield a more compact and symmetric PSF, providing an improvement in confusion noise which will not depend as strongly on position angle. Our Keck results show, we are able to detect and track a source down to $m_K\sim18$ through the least confused regions of our field of view at a precision of $\sim200~\mu$as along the baseline direction. Our GRAVITY results show the potential to detect and track multiple sources in the field. GRAVITY will perform $\sim10~\mu$as astrometry on a $m_K=16.3$ source and $\sim200~\mu$as astrometry on a $m_K=18.8$ source in six hours of monitoring a crowded field. Monitoring the orbits of several stars will provide the ability to distinguish between multiple post-Newtonian orbital effects, including those due to an extended mass distribution around Sgr A* and to low-order General Relativistic effects. (abridged) [Preview Abstract] |
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