Ton S 415: a close binary containing an intermediate helium subdwarf discovered with SALT and TESS

Snowdon EJ, Jeffery CS, Schlagenhauf S, Dorsch M, Monageng IM (2023)

Publication Type: Journal article

Publication year: 2023

Journal

Monthly Notices of the Royal Astronomical Society Oxford University Press

Book Volume: 525

Pages Range: 183-189

Journal Issue: 1

DOI: 10.1093/mnras/stad2303

Abstract

Hot subdwarfs are early-type low-mass stars lying between the main sequence and the white dwarf sequence. The majority have helium-burning cores and helium-poor surfaces. A minority have helium-rich surfaces. A few, including Ton S 415, have surfaces with between 10 per cent and 90 per cent helium (by number). Their properties are diverse and their origins mostly unknown. Ton S 415 was identified as a suspected binary in a Southern African Large Telescope (SALT) survey of hot subdwarfs from its large radial velocity. Using SALT spectroscopy and Transiting Exoplanet Survey Satellite light curves, we confirm that Ton S 415 is a close binary with an orbital period and velocity semi-amplitude. Analysis of the SALT spectrum and broad-band spectral energy distribution shows the visible star to have an effective temperature, surface gravity, surface helium-to-hydrogen ratio log y = -0.62 ± 0.10, radius, and mass. By modelling the light curve, we estimate the binary mass ratio to be q = 0.7 ± 0.3 and infer an unseen white dwarf companion with a mass of. The results are consistent with a post-common-envelope binary that lost its hydrogen envelope before reaching the peak of the red giant branch, becoming a hot subdwarf with a non-canonical mass. We predict that the system will evolve into a double white dwarf binary before eventually either forming a stably accreting AM CVn system, or merging to form an R CrB star.

Involved external institutions

Armagh Observatory GB United Kingdom (GB) Universität Potsdam DE Germany (DE) South African Astronomical Observatory (SAAO) ZA South Africa (ZA)

How to cite

APA:

Snowdon, E.J., Jeffery, C.S., Schlagenhauf, S., Dorsch, M., & Monageng, I.M. (2023). Ton S 415: a close binary containing an intermediate helium subdwarf discovered with SALT and TESS. Monthly Notices of the Royal Astronomical Society, 525(1), 183-189. https://dx.doi.org/10.1093/mnras/stad2303

MLA:

Snowdon, E. J., et al. "Ton S 415: a close binary containing an intermediate helium subdwarf discovered with SALT and TESS." Monthly Notices of the Royal Astronomical Society 525.1 (2023): 183-189.

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