AAS Meeting report: new solutions for epsilon Aurigae

This morning, Donald Hoard (Spitzer Science Center) reported on an analysis of a large set of multi-wavelength measurements (ultraviolet, optical and infrared) that provide important insight into the components that comprise the epsilon Aurigae system.  Dr.Hoard spoke about this work at the Adler meeting of Citizen Sky August 2009 and you can find the video of his talk on the website.

Appearing at a "Mysterious Stars" press briefing Tues Jan.5th 2010 at the American Astronomical Society meeting in DC, Dr. Hoard told reporters that the wealth of data from ground based and space telescopes working during the past two decades have provided the details necessary to begin to clearly separate the components of the star system we call epsilon Aurigae: in addition to the very large F star, a middle B dwarf star 15000K hot and with 5.9 solar masses, appears to be present (based on far-ultraviolet output) and a 550K disk of material, 8 AU long and 0.5 AU thick, but probably less than one solar mass in total. 

With the adopted distance (625pc), inclination (89 degrees) and orbital separation (18-20AU), the implied mass range for the F star is only 2-3 solar masses.  That is far smaller in mass than a true supergiant star (as previously assumed) and resembles what is called a Post-AGB star - a state occurring after the Red Giant and Asymptotic Giant Branch portions of stellar evolution.  The F star is super-giant in size however, nearly 300 Suns across!  If confirmed, epsilon Aurigae's primary star offers insight into this unusual stage in stellar evolution.  This "turning the tables" reverse the mass ratio often presumed in the past, and avoids complications like needing a binary inside the disk to offset the huge supergiant mass (~15 solar masses).  Drs. Saito and Lambert anticipated this result after the 1983 eclipse, and the new work seems to support their conclusions.

Each of the components in the system offer unique astrophysical insights: why does the F star behave the way it does in terms of out of eclipse light variations (if indeed it is the source thereof)?  What is the disk made of and how massive is it?  Other "debris disks" around young stars often amount to only earth mass totals.  What does the interface between the inner disk and the B star look like?  Could there be ultraviolet lightning bolts on the scale presumed in our own early proto-solar nebular disk? 

These questions will keep researchers busy, but success still depends on gathering as detailed an eclipse light curve as we've already developed here at Citizen Sky, so keep up your efforts on looking at and reporting the visual brightness of epsilon Aurigae - in eclipse all of 2010!