Report from the Interferometry meeting
Bounce during totality: have you noticed that epsilon is a bit brighter this month compared to last? Totality is with us, but the Out of Eclipse variations continue. We anticipate a significant brightening starting next month as the central opening in the disk begins crossing in front of the F star...
It's been a pleasure to attend the 5 year science review meeting of the CHARA collaboration (http://www.chara.gsu.edu/CHARA/ ) an amazing group that runs the interferometer atop Mt. Wilson, CA. This 300 meter baseline telescope is capable of delivering milli-arcsecond imaging that has made the details of the epsilon Aur eclipse much more obvious, as has been reported in recent popular articles in Sky & Telescope, Astronomy and Astronomy Now.
More news is to be announced soon, but among the informative talks at the meeting that relate well to epsilon Aur was that by Gail Schaefer (CHARA/GSU) describing high resolution studies of the Be star, zeta Tau [Be stars are characterized by having hydrogen emission lines present in their spectra, see Gies 2007 "
CHARA Array K'-Band Measurements of the Angular Dimensions of Be Star Disks" - http://adsabs.harvard.edu/abs/2007ApJ...654..527G ]. Important results that lead to her newest work at CHARA includes the discovery that H-alpha V/R variations correlate with the disk rotation period - see Pollmann and Rivinius 2008 "Cyclic variability of the circumstellar disk of the Be star ζ Tauri" -
http://adsabs.harvard.edu/abs/2008IBVS.5813....1P - and -
http://adsabs.harvard.edu/abs/2009A%26A...504..915C . Also see Stefl et al. 2009 "Structure and Evolution of Pre-main-sequence Circumstellar Disks" - http://adsabs.harvard.edu/abs/2009A%26A...504..929S . Both report it is possible to characterize the periodic changes in the H-alpha V/R emission wing ratio ("horns") with disk rotational period! We should look for this effect with epsilon Aurigae spectra on both the ~100 day out of eclipse variation and ~3 year anticipated disk periods.
Even more fun is the growing evidence that Be star disks can be asymmetric or even contain spiral structure. Does the B star inside the epsilon Aurigae disk do this? For a reading list on this topic, visit these papers and references therein: The classic paper: Hanuschick 1994 "Observational evidence for global oscillations in Be star disks" -
2009 Kervella "The environment of the fast rotating star Achernar" -
2009 AAS abstract, The Asymmetric Disk of The Be Star ζ Tauri - http://adsabs.harvard.edu/abs/2009AAS...21340904Y .
There was a set of good discussions of disk models based on observations. Yamina Touhami (CHARA/GSU) spoke about disk models she's constructed to compute and fit the spectral energy distribution near-infrared excess in Be stars, using IDL calcuations that begin with these equations: density: rho(r,z) = rho(o)*(r/ro)^(-n)*exp[-1/2*(z/H)^2] for r>r(o) the inner rim of the disk; T(r) = T(o)*(r/ro)^(-q) for the temperature structure, and, for the total flux: F(nu) = kappa(nu)/D * Integral integral Integral B(nu,T(r)) rho(r/z)^2 r dr dtheta dz. For those interested in some of the important papers concerning models for astrophysical disks, a good starting point is the "classic" paper by Hillenbrand et al. 1992 "Herbig Ae/Be stars - Intermediate-mass stars surrounded by massive circumstellar accretion disks" -
This was elaborated into a flared disk (atmosphere) by Chiang and Goldreich 1997 "
Spectral Energy Distributions of T Tauri Stars with Passive Circumstellar Disks" - http://adsabs.harvard.edu/abs/1997ApJ...490..368C .
Among the interesting updates are those by Isella et al. 2005 "Large dust grains in the inner region of circumstellar disks" -
and 2009 "Structure and Evolution of Pre-main-sequence Circumstellar Disks" - http://adsabs.harvard.edu/abs/2009ApJ...701..260I .
Much more to follow. ;-D