Searching for SdB Binary Systems and Singles Using Pulsation Timing Variations

Binary stars are as common as single stars, and their interactions cause them to evolve in ways that are different from single stars. Although the binary evolution theory has been developed in the last two decades, observational studies of binaries are needed for testing and refining these theories. Subdwarf B (sdB) stars are post-main-sequence stars with high temperature and high surface gravity, and all subdwarf B stars are known to have undergone binary evolution with Common Envelope (CE), Roche Lobe Overflow (RLOF), and/or through mergers. Since the formation channels are well known for the sdB stars, observational studies of these stars can help further constrain binary evolution theory. Current observational studies focus on searching for binaries with short orbital periods, as these are more easily detected using common techniques such as the radial velocity (RV) and transit methods. As a consequence, sdB stars with orbital periods longer than 5-10 days remain underexplored, as well as single subdwarf B stars. Confirming a star as a single requires ruling out the presence of any low-mass companions. With increasing orbital period, the probability of finding a transit decreases. The RV method requires frequent observations using a large telescope covering more than one orbital period, which is inefficient for large surveys. About 30 % of the sdB stars exhibit stable pulsations, so it is possible to detect a companion and obtain the orbital solution by measuring the periodic change in pulse arrival times as the star’s reflex motion is manifested by the changing distance and light travel time along the line of sight. This method requires photometric observations, so we can use smaller telescopes compared with the radial velocity method. Therefore, this method is efficient for searching for long orbital period sdB binary systems as well as single sdB stars. In this talk, I will present our previous and ongoing search for companions to pulsating sdB stars using pulsation timing variations with data from the South African Astronomical Observatory (SAAO), Southeastern Association for Research in Astronomy (SARA), and Transiting Exoplanet Survey Satellite (TESS), and confirmation of the companions using other methods.