College of Arts & Sciences Research

Our group, which includes both graduate and undergraduate students, studies the formation of subdwarf B (sdB) stars by investigating their binarity through stellar pulsations. We use photometry data from the TESS space telescope to measure precise pulsation frequencies, distinguish between binary and single-star systems, and determine orbital solutions for candidate binaries. This research is supported by NASA funding.

Subdwarf B (sdB) stars are very hot, compact stars that have already left the main sequence, but how they form is still not fully understood. The main ideas are: (1) a common-envelope (CE) phase, which makes close sdB binaries with white dwarfs (WDs) or main-sequence (MS) stars; (2) Roche-lobe overflow (RLOF), which creates wider sdB+MS binaries; and (3) white-dwarf mergers, which leave a single sdB star. About 200 CE systems have been found, but only ~26 RLOF systems are well studied because their long orbital periods and small radial-velocity signals are difficult to measure, and mergers are even harder to confirm. GAIA data help in some cases, but most sdB stars are too hot or faint for their spectroscopic solutions. Another way to look for companions is through pulsation timing, since about 30% of sdBs show stable pulsations. As the star moves in its orbit, the pulses arrive a little early or late, revealing unseen companions—including planets. This method needs two types of data: long, continuous observations to measure pulsations precisely, and repeated observations over years to find orbits. The TESS space telescope provides the first type of data, while ground-based telescopes can add the second. By combining these, we can find more sdB binaries and singles, test how they form, and better understand the stars that contribute to the ultraviolet light in galaxies.