MOBSTER -- V: Discovery of a magnetic companion star to the magnetic $\beta$ Cep pulsator HD 156424
Autor: | Shultz, M. E., Rivinius, Th., Wade, G. A., Kochukhov, O., Alecian, E., David-Uraz, A., Sikora, J., Collaboration, the MiMeS |
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Rok vydání: | 2020 |
Předmět: | |
Druh dokumentu: | Working Paper |
DOI: | 10.1093/mnras/staa3158 |
Popis: | HD 156424 (B2 V) is a little-studied magnetic hot star in the Sco OB4 association, previously noted to display both high-frequency radial velocity (RV) variability and magnetospheric H$\alpha$ emission. We have analysed the TESS light curve, and find that it is a $\beta$ Cep pulsator with 11 detectable frequencies, 4 of which are independent $p$-modes. The strongest frequency is also detectable in RVs from ground-based high-resolution spectroscopy. RVs also show a long-term variation, suggestive of orbital motion with a period of $\sim$years; significant differences in the frequencies determined from TESS and RV datasets are consistent with a light-time effect from orbital motion. Close examination of the star's spectrum reveals the presence of a spectroscopic companion, however as its RV is not variable it cannot be responsible for the orbital motion and we therefore infer that the system is a hierarchical triple with a so-far undetected third star. Reanalysis of LSD profiles from ESPaDOnS and HARPSpol spectropolarimetry reveals the surprising presence of a strong magnetic field in the companion star, with $\langle B_z \rangle$ about $+1.5$ kG as compared to $\langle B_z \rangle \sim -0.8$ kG for the primary. HD 156424 is thus the second hot binary with two magnetic stars. We are unable to identify a rotational period for HD 156424A. The magnetospheric H$\alpha$ emission appears to originate around HD 156424B. Using H$\alpha$, as well as other variable spectral lines, we determine a period of about 0.52 d, making HD 156424B one of the most rapidly rotating magnetic hot stars. Comment: 16 pages, 13 figures, 4 tables, accepted for publication in MNRAS |
Databáze: | arXiv |
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