Browsing by Author "Schaffenroth, V"

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    EPIC 216747137: a new HW Vir eclipsing binary with a massive sdOB primary and a low-mass M-dwarf companion
    (Ithaca, 2020) Silvotti, R; Schaffenroth, V; Heber, U; Drechsel, H
    EPIC 216747137 is a new HW Virginis system discovered by the Kepler spacecraft during its K2 ‘second life’. Like the other HW Vir systems, EPIC 216747137 is a post-common-envelope eclipsing binary consisting of a hot subluminous star and a cool low-mass companion. The short orbital period of 3.87 h produces a strong reflection effect from the secondary (∼9 per cent in the R band). Together with AA Dor and V1828 Aql, EPIC 216747137 belongs to a small subgroup of HW Vir systems with a hot evolved sdOB primary. We find the following atmospheric parameters for the hot component: Teff = 40400 ± 1000 K, log g = 5.56 ± 0.06, and log(N(He)/N(H)) = −2.59 ± 0.05. The sdOB rotational velocity v sin  i = 51 ± 10 km s−1 implies that the stellar rotation is slower than the orbital revolution and the system is not synchronized. When we combine photometric and spectroscopic results with the Gaia parallax, the best solution for the system corresponds to a primary with a mass of about 0.62 M⊙ close to, and likely beyond, the central helium exhaustion, while the cool M-dwarf companion has a mass of about 0.11 M⊙.
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    A quantitative in-depth analysis of the prototype sdB+BD system SDSS J08205+0008 revisited in the Gaia era
    (Oxford University Press, 2021) Kilkenny, D; Schaffenroth, V; Casewell, S.L
    Subdwarf B stars are core-helium-burning stars located on the extreme horizontal branch (EHB). Extensive mass loss on the red giant branch is necessary to form them. It has been proposed that substellar companions could lead to the required mass loss when they are engulfed in the envelope of the red giant star. J08205+0008 was the first example of a hot subdwarf star with a close, substellar companion candidate to be found. Here, we perform an in-depth re-analysis of this important system with much higher quality data allowing additional analysis methods. From the higher resolution spectra obtained with ESOVLT/ XSHOOTER, we derive the chemical abundances of the hot subdwarf as well as its rotational velocity. Using the Gaia parallax and a fit to the spectral energy distribution in the secondary eclipse, tight constraints to the radius of the hot subdwarf are derived. From a long-term photometric campaign, we detected a significant period decrease of -3.2(8) × 10-12 dd-1.