New radial velocity measurements w/interesting implications
We have a guest blog article from a coauthor of a recent paper published about epsilon Aurigae. The author describes the system overall for new participants, then describes what they discovered with their radial velocity data.
After 113 years of radial velocity measurements, epsilon Aurigae remains as mysterious as ever. 20 years of new radial velocity observations have been combined with historical data to improve our understanding of the orbital mechanics of the system, but nature of the objects themselves remains uncertain.
This eclipsing binary has the longest period on record – a whopping 27 years! There also seems to be no optical emission from the eclipsing object; but a two-year eclipse duration means this dark companion must be several AU wide. Its mass must also be similar to that of the star itself. There are models for the system, the most accepted being that the companion is a thick, dusty disk. The problem is that we don't have very good constraints on the spectral type of the primary. As you can imagine, in order to have a good idea of the size and mass scales involved we need to know what this primary object is!
In our paper appearing in the March 2010 edition of the Astronomical Journal, we use these radial velocity data to improve the existing orbital solution for the system. Whilst doing so we also identify short-term oscillations which may be due to motion in the stellar envelope. We present two orbital solutions; one based purely on radial velocities and one where the period is tied to the photometric eclipses. Interestingly, we see a nine-month difference in the predicted mid-eclipse. Whether the short-term oscillations or perhaps some other noise may be the source of this, we are unsure, but if not then this could imply that the eclipsing object and the gravitating companion are not one and the same.
The full article is now available at http://www.iop.org/EJ/
- Justin Lovegrove is a physics graduate student at the University of Southampton in the U.K and did some work on this paper while at the Harvard-Smithsonian Center for Astrophysics. He is a coauthor of the paper and presented a poster on the topic at the January 2009 meeting of the American Astronomical Society. A preprint of the paper is available here.