Institute of Astronomy

A Spectroscopic Hunt for RR Lyrae Pulsators in Binary Systems

SpeakerTalk DateTalk Series
Elisabeth Guggenberger28 July 2016Binary Stars Talks


RR Lyrae stars are evolved pulsating stars burning helium in their cores. Their high-amplitude radial pulsation can lead to radial velocity changes of tens of km/s and brightness changes of about 1 mag. Since its discovery more than a century ago this class of stars has increased our knowledge of, among others, stellar pulsation theory, stellar evolution, and Milky Way structure. As standard candles RR Lyrae stars also serve as an important part of the cosmic distance ladder. Thanks to large surveys, ten thousands of RR Lyraes are known today. In spite of this large number only a handful of them have been found to reside in binary systems. Having an independent constraint of the mass from an orbit solution would be a crucial test for pulsation theory. The only eclipsing RR Lyrae pulsator that was found so far turned out to be an exotic object with an unexpectedly low mass - too low to ignite helium. 

We present here a spectroscopic study of RR Lyrae stars that are suspected to be binaries.  Extracting orbital parameters for RR Lyraes is very challenging due to their large intrinsic variability which can be an order of magnitude larger than the signal we are aiming to detect. We have been awarded 28 nights at the 2.1m telescope at McDonald observatory for our project. We present the pulsational RV curves and the derived center of mass RVs which we compare to previous measurements from the literature in order to find long-term changes induced by orbital motions.