Infrared Studies of Epsilon Aurigae in Eclipse

Creators: Stencel, Robert E.; Kloppenborg, Brian K.; Wall, Randall E., Jr.; Hopkins, Jeffrey L.; Howell, Steve B.; Hoard, D. W.; Rayner, John; Bus, Schelte; Tokunaga, Alan; Sitko, Michael L.; Bradford, Suellen; Russell, Ray W.; Lynch, David K.; Hammel, Heidi; Whitney, Barbara; Orton, Glenn; Yanamandra-Fisher, Padma A.; Hora, Joseph L.; Hinz, Philip; Hoffmann, William; Skemer, Andrew

Abstract

We report here on a series of medium resolution spectro-photometric observations of the enigmatic long period eclipsing binary epsilon Aurigae, during its eclipse interval of 2009-2011, using near-infrared spectra obtained with SpeX on the Infrared Telescope Facility (IRTF), mid-infrared spectra obtained with BASS on AOES and IRTF, MIRSI on IRTF, and MIRAC4 on the MMT, along with mid-infrared photometry using MIRSI on IRTF and MIRAC4 on the MMT, plus 1995-2000 timeframe published photometry and data obtained with Denver's TNTCAM2 at WIRO. The goals of these observations included: (1) comparing eclipse depths with prior eclipse data, (2) confirming the re-appearance of CO absorption bands at and after mid-eclipse, associated with sublimation in the disk, (3) seeking evidence for any mid-infrared solid state spectral features from particles in the disk, and (4) providing evidence that the externally irradiated disk has azimuthal temperature differences. IR eclipse depths appear similar to those observed during the most recent (1983) eclipse, although evidence for post-mid-eclipse disk temperature increase is present, due to F star heated portions of the disk coming into view. Molecular CO absorption returned 57 days after nominal mid-eclipse, but was not detected at mid-eclipse plus 34 days, narrowing the association with differentially heated sub-regions in the disk. Transient He I 10830A absorption was detected at mid-eclipse, persisting for at least 90 days thereafter, providing a diagnostic for the hot central region. The lack of solid-state features in Spitzer Infrared Spectrograph, BASS, and MIRAC spectra to date suggests the dominance of large particles (micron-sized) in the disk. Based on these observations, mid-infrared studies out of eclipse can directly monitor and map the disk thermal changes, and better constrain disk opacity and thermal conductivity.

Additional Information

© 2011 The American Astronomical Society. Received 2011 July 7; accepted 2011 September 16; published 2011 October 17. This work was supported in part by the bequest of William Herschel Womble in support of astronomy at the University of Denver, by NSF grants AST 97-24506 and AST 10-16678, and JPL RSA 1414715 to the University of Denver, by NASA ADP grant NNX09AC73G to the University of Cincinnati, and by The Aerospace Corporation's Independent Research and Development Program. Observations reported here were obtained in part as Visiting Astronomers at the Infrared Telescope Facility, which is operated by the University of Hawaii under Cooperative Agreement NNX-08AE38A with the National Aeronautics and Space Administration, Science Mission Directorate, Planetary Astronomy Program. Observations reported here were obtained in part at the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona. Observations were also obtained in part at the University of Wyoming's Infrared Observatory (WIRO), involving access for which we are grateful. The first author thanks Dana Backman for the encouragement to obtain mid-IR data during the mid-1990s, and the many observers involved in those and all the data reported here. We also thank Jeff Hopkins, Brian McCandless, Thomas Rutherford, and the AAVSO for access to their visual observation records. Facilities: IRTF (SpeX), MMT (MIRAC4), Spitzer (IRAC)

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