Discovery Of Strong Helium 10830A Absorption In The Mid-eclipse Disk Of Epsilon Aurigae

Details Discovery Of Strong Helium 10830A Absorption In The Mid-eclipse Disk Of Epsilon Aurigae Discovery Of Strong Helium 10830A Absorption In The Mid-eclipse Disk Of Epsilon Aurigae

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21822504s&link_type=abstract

American Astronomical Society, AAS Meeting #218, #225.04; Bulletin of the American Astronomical Society, Vol. 43, 2011

Astronomy and Astrophysics

Astronomy

Scientific paper

During the 2010 eclipse of the enigmatic binary, epsilon Aurigae (F0p + B5?), we obtained a series of near-infrared spectra with the SpeX instrument at NASA's IRTF, primarily to detect the re-appearance of CO (2-0) at 2.29 microns after nominal mid-eclipse, 2010 August 4 (JD 2,455,400). To our surprise, the well-known He I 10830A line appeared in absorption, in the spectrum closest to mid-eclipse (Aug.24, RJD 55433), persisting in spectra Sep.27 (55467), Oct.24 and 29 (55494, 55499). The line weakened by Nov.12 (55513), and was gone Dec.7 (55537) and 2011 Jan.7 (55569). The extra absorption, up to 6A equivalent width, appeared atop a weaker, persistent 1A equivalent width feature. With Van de Kamp's distance (580 pc) and orbital velocities during eclipse phase, the duration of the extra absorption implies a region 1.0 +/- 0.2 AU in radial extent, in the middle of the eclipse-causing dark disk with its 3.8 +/- 0.2 AU radius. He I 10830 arises from a metastable triplet from a lower level at 19.82 volts, representing plasma in excess of 25,000K. If the disk-center star were B5V type and experiencing a modest amount of accretion, it would create a 1 AU Stromgren He+ sphere. This assumes a mean gas density of 10^{10} cm^{-3}, which is the lower limit to the column density established by non-detection of soft Xrays. This heated region could represent the presence of an upper main sequence object and accretion onto the hidden star inside the disk, in analogy to Be stars, symbiotics, zeta Aurs and YSOs. This work was supported in part by the bequest of William Herschel Womble in support of astronomy at the University of Denver, by NSF grant 1016678 and JPL RSA 1414715 to the University of Denver, and by NASA ADP grant NNX09AC73G to the University of Cincinnati.

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