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Searching for subdwarf B single stars and binary systems using TESS

Presentation #129.02 in the session Pulsating Variable and Symbiotic Stars.

Published onJul 01, 2023
Searching for subdwarf B single stars and binary systems using TESS

Subdwarf B (sdB) stars are extreme horizontal branch stars with high temperature and gravity. The most promising formation scenarios involve close binary star evolution with three different channels: (1) a Common Envelope (CE) channel, which can produce short-period (P=0.1–10 d) sdB + white dwarf (WD) or main sequence (MS) binaries, (2) a Roche lobe overflow (RLOF) channel, which results in a long-period (450 < P < 1400 d) sdB + MS binaries, and (2) a WD merger channel, which can produce single sdB stars. Estimating the percentage of members in each channel is essential to investigate the sdB formation scenarios. Prior observational studies focused mostly on the CE channel because the short period binaries produced by this channel are easier to detect and characterize using eclipse or radial velocity (RV) methods. Observational studies of the RLOF and merger channels are difficult because confirming long-period binary systems or single stars requires long-term observing campaigns, and the eclipse and RV methods are inefficient for such cases. Approximately 30% of sdB stars show stable pulsations and for these, the pulsation timing method remains the only effective tool to search for long-period binary systems or single stars. Positive detection of a binary system can be obtained from a periodic change of a pulsation mode phase, which is a consequence of a star’s reflex motion. Consequently, we can confirm single stars by non-detection of such a phase variation. TESS photometry is a powerful tool for this study because TESS data are continuous for 27 to as many as 324 days. We employed TESS light curves to search for candidates of sdB single stars and binary systems via this pulsating timing variation method. Our poster presents the results using TESS cycle 3, and 4 short cadence data.

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