Interferometric Studies of the extreme binary, ϵ\epsilon Aurigae: Pre-eclipse Observations

We report new and archival K-band interferometric uniform disk diameters obtained with the Palomar Testbed Interferometer for the eclipsing binary star $\epsilon$ Aurigae, in advance of the start of its eclipse in 2009. The observations were inteded to test whether low amplitude variations in the system are connected with the F supergiant star (primary), or with the intersystem material connecting the star with the enormous dark disk (secondary) inferred to cause the eclipses. Cepheid-like radial pulsations of the F star are not detected, nor do we find evidence for proposed 6% per decade shrinkage of the F star. The measured 2.27 +/- 0.11 milli-arcsecond K band diameter is consistent with a 300 times solar radius F supergiant star at the Hipparcos distance of 625 pc. These results provide an improved context for observations during the 2009-2011 eclipse.Comment: Accepted for Ap.J. Letters, Oct. 200

SIFTIR: Spectro-polarimetric Imaging Fourier Transform Spectrometer for the InfraRed

Observations of evolved stars in the infrared are well suited for studies of dusty environments, providing a wealth of absorption and emission bands with which to diagnose grain characteristics. We are currently developing an instrument that will employ a Fourier transform spectrometer in conjunction with TNTCAM2 (Klebe et al. 1998), an imaging polarimeter. The FTS component will enhance TNTCAM2, giving the instrument a maximum resolution of 2000 at 10 11m. The FTS is capable of operating between 2-15 11m, but polarimetry for the instrument is limited to the 8-15 11m region due to waveplate/wiregrid characteristics. SIFTIR, the Spectro-polarimetric Imaging Fourier Transform spectrometer for the InfraRed, will build upon the results of TNTCAM2 (Jurgenson et al. 2003). Imaging polarimetry has the potential to trace polarization magnitude and P.A. changes throughout an extended region of interest. TNTCAM2, though capable of a fair degree of spatial resolution, lacked spectral resolution needed to carry out the analysis for approximating grain shapes (e.g. Hildebrand & Dragovan 1995). Holloway et al. (2002), established correlations in polarization magnitude and position angle between the 10 11m silicate feature and the 3 11m water ice feature in a small sample ofYSO\u27s. The existence of a correlation makes plausible the argument that silicate grains might provide nucleation sites for grain growth in a core-mantle arrangement. SIFTIR not only has the capability to cover both the near and mid-IR spectral regions to check for polarization correlations, but will also have the resolution necessary to characterize the grain shapes

Stellar Geometries with Spectro-Interferometry

The most massive stars are important contributors to their host galaxies. During their stellar lifetimes, and even in their demise as supernovae, they deposit a great deal of material and energy into their galactic neighborhood, thus providing the building blocks for the next generation of stars. Near the end of their lives, they begin to shed their outer layers into space via a stellar wind, creating what astronomers call a circumstellar envelope. These envelopes are thus cosmic fossils of the stars themselves. The physics of stellar winds- more generally referred to as mass loss, is poorly understood. The geometric structure and molecular composition of this circumstellar material can provide important clues to the mass loss process as well as constrain models of stellar evolution. This information can also help inform models of supernova ejecta by providing detailed information about the pre-existing material that the ejecta will slam into as it expands. Previously, these envelopes have been too small to observe from ground or space-based telescopes. The advent of near infrared interferometry has allowed us to resolve these structures for the ¯rst time. A survey of massive stars called Supergiants has been measured using such an instrument; the results of that study are presented here. Support for this work has been generously provided in part by the Rocky Mountain NASA Space Grant Consortium

ROSAT-IUE observations of symbiotic stars. The x ray morphology of high latitude associations

The purposes of this grant included: to provide for continuing investigations of the x-ray properties of a class of interacting binaries known as symbiotic stars through analysis of their detection statistics in the ROSAT All-Sky Survey and simultaneous IUE observations; and to obtain and analyze ROSAT images of selected high latitude OB star associations, in order to permit multi-wavelength dissection of their contents and energetics. The first study is expected to result in enhanced information on mass transfer and accretion in such systems, and provide a more quantitative basis for interpretation of the spectra of these and similar stellar and extragalactic systems. This particular effort represents NASA support for an approved collaboration between the PI and the ROSAT Team at MPE Garching. In the second study, we seek to correlate the strength with which the diffuse clouds have been shocked and the recent star formation triggered, namely, the O and B stars of the Association, as well as nearby T Tauri stars. The large scale X-ray emission in deep ROSAT PSPC images will be compared with the optical, infrared, and radio topology of nearby supernova remnants, molecular clouds, and the distribution of massive stars in the regions. This should enable us to test whether the star formation triggering shocks originate from in the galactic plane (nearby supernovae) or from the collision of infalling matter with the disk material (galactic fountain dynamics)

Supernova Progenitors: Theory, Observation and Outstanding Questions

Supernovae play a prominent role in current theories of cosmology, galaxy evolution and stellar evolution. Key to understanding supernovae is a characterization of their progenitors. A robust body of theoretical work predicts the nature of these stars, but direct observations are lacking. Current theory and observations to date are summarized, as well as open questions in the field. Interferometric methods are proposed for the resolution of some of these questions

VVNRS: Variable phenomena in VV Cephei

The current research project (VVNRS) involves VV Cephei, which is a binary system in which a 20 solar mass main sequence star orbits within the extended atmosphere of the 40 solar mass M-type supergiant primary. Although the period of the system is 20.3 years, the components are close enough for a stream of matter from the primary to form an accretion disk around the hot secondary. We had previously completed an ADP-sponsored study of twelve years of archival spectra of this system and were surprised to find intermittent changes in the line profiles of the chromosphere-like absorption spectrum. This we think may be related to the accretion process. The previously existing spectra were not closely spaced enough in time to clearly delineate the nature of these changes. Therefore, we proposed and were granted eleven half-shifts to obtain closely spaced IUE spectra during IUE's 14th year of operations (1991/1992)