Tomomi Otani | Searcharxiv

arXiv2025

Binary Systems Search with TESS

Hot subdwarf B (sdB) stars are post-main-sequence stars of high temperature and gravity. Approximately 30$\%$ of sdBs exhibit stable pressure and/or gravity-mode pulsations, which can be used via the timing method to test for companion stars and determine their orbital solutions. We used short cadence data from the Transiting Exoplanet Survey Satellite (TESS) to search for previously undiscovered companions to sdBs. In this paper, we focus on searching for companions with orbital periods shorter than 13.5$\,$d which are detectable within one sector of TESS data (about 27$\,d$). The timing method requires that we derive pulsation frequencies in subsets of data significantly shorter than the periods we are searching for, which we set at 0.5 to 1.5$\,$d. We investigated ten sdB stars with previously detected p-mode pulsations for which at least one p-mode pulsation remains detectable with a signal-to-noise ratio (S/N) $>$ 4 within data subsets of duration 0.5 - 1.5$\,$d. We find that two (TIC$\,$202354658 and TIC$\,$69298924) of these ten sdB stars likely have white dwarf companions and set limits on companion masses for the other eight sdB stars.

astro-ph.SR↗

arXiv2022

A Monte Carlo Method for Evaluating Empirical Gyrochronology Models and its Application to Wide Binary Benchmarks

Accurate stellar ages are essential for our understanding of the star formation history of the Milky Way, Galactic chemical evolution, and to constrain exoplanet formation models. Gyrochronology, a relationship between stellar rotation and age, appears to offer a reliable age indicator for main sequence (MS) stars over the mass range of approximately 0.6 to 1.3 $M_\odot$. Those stars lose their angular momentum due to magnetic braking and as a result, their rotation speeds decrease with age. Although current gyrochronology relations are fairly well tested for young MS stars with masses greater than 1 $M_\odot$, primarily in young open clusters, insufficient tests exist for older and lower mass MS stars. Binary stars offer the potential to expand and fill in the range of ages and metallicity over which gyrochronology can be empirically tested. In this paper, we demonstrate a Monte Carlo approach to evaluate gyrochronology models using binary stars. As examples, we used five previously published wide binary pairs. We also demonstrate a Monte Carlo approach to assess the precision and accuracy of ages derived from each gyrochronology model. For the traditional Skumanich models, the age uncertainties are $σ_{age}$/$age$ = 15-20\% for stars with $B-V$ = 0.65, and $σ_{age}$/$age$ = 5-10\% for stars with $B-V$ = 1.5 and rotation period P $\leq$ 20 days.

astro-ph.SR↗