The ε aurigae secondary: A hydrostatically supported disk

Jack J. Lissauer, Scott J. Wolk, Caitlin A. Griffith, Dana E. Backman

Research output: Contribution to journalArticle

22 Scopus citations

Abstract

Epsilon Aurigae is an F supergiant in a spectroscopic binary system that undergoes a flat-bottomed partial eclipse of 2 yr duration every 27 yr. The spectrum appears to be single-lined, aside from extra absorption features detected during and shortly after eclipse. Eclipse characteristics indicate that the secondary is a very elongated object 5-10 AU in dimension parallel to its orbit. Orbital characteristics and the spectral properties of the primary are consistent with two different models of the system, with the secondary having a mass of either ∼15 M or ∼4 M. We have modeled the cool, dark secondary in the ε Aurigae system as a geometrically thin circumstellar disk of gas and dust (surrounding one or two unseen stars, at or near its center), which is rotationally supported about its short axis and pressure supported perpendicular to its midplane. We assume that the midplane of the disk is coplanar with the orbital plane of the system. The gross features of the eclipse light curve observed at any single wavelength are easily reproduced, using a variety of disk scale heights and optical depths, provided that we are viewing within ∼3° of the symmetry plane of the system. Central holes in the disk only affect the eclipse profile for models with low optical depth (and correspondingly large pressure scale height). The observed grayness of the eclipse in the visible and near-IR implies that the particles in the disk are significantly larger than those in the typical ISM. Either particles of radius ≲ 5 μm are almost completely absent, or the disk must be very opaque. If the disk is very opaque, then the observed eclipse depth implies a small scale height for the disk, equal to roughly 3% of the disk's radius at the outer edge. This is a factor of ∼ 1.5-2 smaller than the value expected for the low-mass model from hydrostatic balance with the disk temperature measured in the thermal-IR, suggesting that the high-mass model of the system is correct and/or the dust particles have settled into a thinner disk than the pressure-supported gas. We have also constructed a quasi-hydrodynamic model of the expansion of the material in the outermost edge of the disk secondary in response to the heating that it receives as it rotates into view of the luminous primary. Light curves computed using this model reproduce the basic features of absorption lines, which are observed to be deepest subsequent to the middle of the continuum eclipse and to persist after fourth contact.

Original languageEnglish (US)
Pages (from-to)371-384
Number of pages14
JournalAstrophysical Journal
Volume465
Issue number1 PART I
DOIs
StatePublished - Jan 1 1996

Keywords

  • Binaries: Eclipsing
  • Circumstellar matter
  • Stars: Individual (ε Aurigae)
  • Stars: Supergiants

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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