Contributed Talk - Splinter Exoplanets

Wednesday, 23 September 2020, 17:05   (virtual room D)

The EXOTIME project: Using the stellar pulsation timing method to detect sub-stellar companions

Mackebrandt, Felix (1); Schuh, Sonja (1); Silvotti, Roberto (2)
(1) Max Planck Institute for Solar System Research; (2) INAF - Osservatorio Astrofisico di Torino

We investigate variations in the arrival time of coherent stellar pulsations due to the light travel time effect to test for the presence of sub-stellar companions. Those companions are the key to the possible formation scenario of apparently single subdwarf B stars (sdB). sdB stars are stripped He-burning cores of red giants with a thin hydrogen atmosphere. The canonical model to explain the existence of sdB stars is binary evolution. Formation scenarios for single sdB stars are more controversially discussed and can be hard to reconcile with observational properties. Besides the merger of two helium white dwarfs, an alternative formation channel involves planetary systems. During the RGB the star would develop a common envelope with a giant planet that leads to the loss of the envelope. This timing method is particularly sensitive to planets at large distances and complementary to other exoplanet detection methods which are not efficient for stars with small radii and high gravities. Examples of planetary candidates in sdB-systems are V391 Peg b, HW Vir b, c, HS 0705+67003 b and Kepler-429 b, c, d. We make use of an extensive set of ground based observations of the four large amplitude p-mode pulsators DW Lyn, V1636 Ori, QQ Vir and V541 Hya. Additionally, we use artificial light curves to analyse effects of mode beating on the apparent variations in arrival time. Thus, we can derive upper limits on sub-stellar companion masses from our observations. Our method allows us not only to probe evolved stars but also other pulsating stars such as main-sequence A stars as exoplanet host stars. We confirm previously detected exoplanets orbiting delta Scuti stars, using Kepler data. In consideration of photometric space missions like TESS or the planned PLATO mission it is essential to enhance the diversity of potential exoplanet host stars that can be probed.