Interstellar Deflategate

Some exciting results out of the group this summer. Check out our paper led by rising fourth-year PhD student Eunkyu Han on the Kepler low-mass eclipsing binary T-Cyg1-12664.  The paper was recently accepted to The Astronomical Journal and posted to arXiv:

This eclipsing binary has an interesting history in the literature.  First discovered in the 2000s as part of the TrES survey, the system was originally believed to be an innocuous equal-mass M dwarf binary.  Later, data from NASA’s Kepler Spacecraft appeared to show an unequal-mass binary with a wildly inflated secondary star: twice the size it should be for its mass!  The authors ascribed the inflation to magnetic fields inhibiting convection deep inside the star.

The problem: A back-of-the-envelope calculation shows that Ohmic dissipation would limit the interior magnetic field strength before it could cause such high inflation.  Another explanation might be that the system is young, with the secondary component still undergoing contraction from formation.  Young low-mass eclipsing binaries are fantastic laboratories for studying stellar evolution, with only a handful found to date.

Earlier this year, another group reanalyzed the Kepler data and measured independent radial velocities.  They showed that the secondary star was not inflated, but the primary was!  Their results are broadly consistent with the magnetic inflation scenario, but there were still some questions.  Their work lacked independent radial velocity measurements of the secondary star, a caveat they openly discussed in their paper.

Enter our team.  By collecting data from the W.M. Keck Telescopes, Robo-AO and the Discovery Channel Telescope, including radial velocity measurements for both stars, Eunkyu  showed that neither star is inflated and that they are both consistent with predictions for main sequence stars.  In other words, we deflated the stars:

Interstellar Deflategate!  I wish I could take credit for this reference.  The group thought of it when I was on vacation.  For an explanation, this Wikipedia article does a comically thorough job, filled with Excel plots:

Tom Brady 2011

Future Hall-of-Famer Tom Brady in 2011. I once met his son’s hockey coach.
Credit: Jeffrey Beall, Creative Commons License

Following deflategate, people started to question the legitimacy of Brady’s previous wins.  Similarly, this result has us questioning whether other eclipsing binary stars have accurate masses and radii.  Will more eclipsing binaries be deflated?  We expect to have more results later this year.  Stay tuned!

Earlier this month, Eunkyu passed her Ph.D. Qualification Exam after presenting this research to the department.  She is now an official Ph.D. Candidate!  Congrats Eunkyu!

-Phil Muirhead