High-degree gravity modes in the single sdB star HD 4539
Silvotti R, Uzundag M, Baran AS, Ostensen RH, Telting JH, Heber U, Reed MD, Vuckovic M (2019)
Publication Type: Journal article
Publication year: 2019
Journal
Book Volume: 489
Pages Range: 4791-4801
Journal Issue: 4
Abstract
HD4539 (alias PG0044 + 097 or EPIC 220641886) is a bright (V = 10.2) long-period V1093 Her-type subdwarf B (sdB) pulsating star that was observed by the Kepler spacecraft in its secondary (K2) mission. We use the K2 light curve (78.7 d) to extract 169 pulsation frequencies, 124 with a robust detection. Most of these frequencies are found in the low-frequency region typical of gravity (g-)modes, but some higher frequencies corresponding to pressure (p-)modes are also detected. Therefore HD4539 is a hybrid pulsator and both the deep and surface layers of the star can potentially be probed through asteroseismology. The lack of any frequency splitting in its amplitude spectrum suggests that HD 4539 has a rotation period longer than the K2 run and/or that it is seen pole-on. From asymptotic period spacing we see many high-degree modes, up to l = 12, in the spectrum of HD 4539, with amplitudes as low as a few ppm. A large fraction of these modes can be identified and for similar to 29 per cent of them we obtain a unique and robust identification corresponding to l <= 8. Our study includes also a new determination of the atmospheric parameters of the star. From low-resolution spectroscopy we obtain T-eff = 22 800 +/- 160 K, log g = 5.20 +/- 0.02, and log(N(He)/N(H)) = -2.34 +/- 0.05. By fitting the SED we obtain T-eff = 23 470(-210)(+650) K, R-star = 0.26 +/- 0.01 R-circle dot, and M-star = 0.40 +/- 0.08 M-circle dot. Moreover, from 11 high-resolution spectra we see the radial velocity variations caused by the stellar pulsations, with amplitudes of approximate to 150 m s(-1) for the main modes, and we can exclude the presence of a companion with a minimum mass higher than a few Jupiter masses for orbital periods below similar to 300 d.
Authors with CRIS profile
Involved external institutions
National Institute for Astrophysics / Istituto Nazionale Astrofisica (INAF)
Italy (IT)
Uniwersytet Pedagogiczny im. Komisji Edukacji Narodowej w Krakowie
Poland (PL)
Missouri State University
United States (USA) (US)
Roque de los Muchachos Observatory / Observatorio del Roque de los Muchachos (ORM)
Spain (ES)
University of Valparaíso (UV) / Universidad de Valparaiso
Chile (CL)
Italy (IT)
Uniwersytet Pedagogiczny im. Komisji Edukacji Narodowej w Krakowie
Poland (PL)
Missouri State University
United States (USA) (US)
Roque de los Muchachos Observatory / Observatorio del Roque de los Muchachos (ORM)
Spain (ES)
University of Valparaíso (UV) / Universidad de Valparaiso
Chile (CL)
How to cite
APA:
Silvotti, R., Uzundag, M., Baran, A.S., Ostensen, R.H., Telting, J.H., Heber, U.,... Vuckovic, M. (2019). High-degree gravity modes in the single sdB star HD 4539. Monthly Notices of the Royal Astronomical Society, 489(4), 4791-4801. https://doi.org/10.1093/mnras/stz2244
MLA:
Silvotti, R., et al. "High-degree gravity modes in the single sdB star HD 4539." Monthly Notices of the Royal Astronomical Society 489.4 (2019): 4791-4801.
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