Infrared Studies of Epsilon Aurigae in Eclipse

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 20092011, using near-infrared spectra obtained with SpeX on IRTF, mid-infrared spectra obtained with BASS on AOES and IRTF, MIRSI on IRTF and MIRAC4 on MMT, along with mid-infrared photometry using MIRSI on IRTF and MIRAC4 on MMT, plus 19952000 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 that 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 IRS, 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. Subject headings: binaries: eclipsing stars: individual: epsilon Aurigae protoplanetary disks