- Title: KIC 3858884: a hybrid δ Sct pulsator in a highly eccentric eclipsing binary
- Authors: C. Maceroni, H. Lehmann, R. da Silva, et al.
- First Authors Institution: INAF
- Paper Status: Accepted for publication in Astronomy & Astrophysics
If you read Astrobites regularly, or even semi-regularly, you understand the importance of the Kepler mission to discovering exoplanets. But Kepler, which observed ~100,000 stars continuously for over 3 years, has also uncovered many other interesting stellar systems and properties. Cataclysmic Variables and pulsating stars are just two examples, as well as a new way to measure surface gravity. The paper we will discuss today describes a pulsating Delta Scuti star in an eclipsing binary with another star.
Stellar pulsations are important because they can help shed light on the internal composition and structure of stars through the application of asteroseismology. Delta Scuti stars are one type of pulsating star that lie in the instability strip of the Hertzsprung-Russell Diagram, a nearly vertical region where nearly all pulsating stars are found. Other pulsating stars such as RR Lyrae and Cepheids are also found along the instability strip. Delta Scuti’s have both radial and non-radial pulsations. Radial pulsations occur when the star expands and contracts uniformly, like a beach ball you alternately inflate and deflate. Non-radial pulsations occur when the pulsations travel in other directions, such as around the star or alternating between hemispheres. For most Delta Scuti stars, their pulsations are between 0.03 and 0.3 days. Check out Zach’s post for more details on pulstions in Delta Scuti stars.
The authors studied a Delta Scuti star in an eclipsing binary, meaning one star passes in front of the other from our point of view. The Kepler data yields beautiful, uninterrupted photometry of the system that helps to disentangle the various pulsational modes. The authors also collected spectroscopy of the system to measure radial velocities and abundances of various elements. The photometry and spectroscopy were used to measure the mass, radius, orbital separation, pulsations, effective temperature, and surface gravities of the stars. It turned out that these two stars are very similar, with only small differences in radius and effective temperature.
Once the physical parameters of the two stars were determined, the authors tried to understand the evolutionary history of this system. They did this by examining simulations of stellar evolution in which they could vary multiple parameters, including the masses, abundances, temperatures, and radii. The photometry and spectroscopy place constraints on these parameters, which help the authors chose possible evolutionary tracks.
Figure 1 shows one of the possible evolutionary track from the models. The two lines represent the path each star is following. Both stars started in the bottom of the plot, then moved along the path indicated by the arrows to where they are today, represented by the red dots. In the future, they will continue to move along the lines. Despite how close they are in mass, the slightly more massive star is more evolved, as indicated by its more advanced position along the path.
Because of the similar properties, but slightly different evolutionary stages, this system will provide nice information on the evolution of stars in this mass range and around the instability strip. Further analysis of the pulsations of the Delta Scuti will enlighten whether some of the pulsations are caused by tidal forces from the other star.