HS 0705+6700: A new eclipsing sdB binary

H. Drechsel; U. Heber; R. Napiwotzki; R. Østensen; J.-E. Solheim; F. Johannessen; S. L. Schuh; J. Deetjen; S. Zola

doi:10.1051/0004-6361:20011376

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Volume 379 / No 3 (December I 2001)

A&A, 379 3 (2001) 893-904

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Issue		A&A Volume 379, Number 3, December I 2001


Page(s)		893 - 904
Section		Interstellar and circumstellar matter
DOI		https://doi.org/10.1051/0004-6361:20011376
Published online		15 December 2001

A&A 379, 893-904 (2001)

HS 0705+6700: A new eclipsing sdB binary ^*,^**

H. Drechsel¹, U. Heber¹, R. Napiwotzki¹, R. Østensen²^,3, J.-E. Solheim³, F. Johannessen³, S. L. Schuh⁴, J. Deetjen⁴ and S. Zola⁵

¹ Dr. Remeis-Sternwarte Bamberg, Astronomisches Institut der Universität Erlangen-Nürnberg, Sternwartstraße 7, 96049 Bamberg, Germany
² Isaac Newton Group of Telescopes, 37800 Santa Cruz de La Palma, Canary Islands, Spain e-mail: roy@ing.iac.es
³ University of Tromsø, Department of Physics, 9037 Tromsø, Norway e-mail: janerik@phys.uit.no
⁴ Institut für Astronomie und Astrophysik, Universität Tübingen, Waldhäuser Straße 64, 72076 Tübingen, Germany e-mail: schuh@astro.uni-tuebingen.de
⁵ Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30-244 Cracow, Poland e-mail: sfzola@cyf-kr.edu.pl

Corresponding author: H. Drechsel, drechsel@sternwarte.uni-erlangen.de

Received: 14 August 2001
Accepted: 26 September 2001

Abstract

We report the discovery of an eclipsing binary -HS 0705+6700 -being an sdB star with a faint companion. From its light curve the orbital period of 8263.87 s, the mass ratio of the system $q = 0.28$ , the inclination of 84 $\fdg4$ and other system parameters are derived. The companion does not contribute to the optical light of the system except through a strong reflection effect. The semi-amplitude of the radial velocity curve $K_1 = 85.8$ km s^-1 and a mass function of $f(m) = 0.00626$ $M_{\odot}$ are determined. A spectroscopic analysis of the blue spectra results in $T_{\rm eff} = 28 800$ K, $\log g = 5.40$ , and $\log (n_{\rm He}/n_{\rm H}) = -2.68$ . These characteristics are typical for sdB stars, as is its mass of 0.48 $M_{\odot}$ . According to its mass (0.13 $M_{\odot}$ ) and radius (0.19 $R_{\odot}$ ), the companion is an M dwarf. The primary is in a core helium burning phase of evolution, and the system must have gone through a common envelope stage when the primary was near the tip of the red giant branch.

Key words: stars: subdwarfs / binaries: eclipsing / binaries: spectroscopic / stars: early-type / stars: fundamental parameters / stars: individual: HS 0705+6700

^*

Based on observations collected at the German-Spanish Astronomical Center (DSAZ), Calar Alto, operated by the Max-Planck-Institut für Astronomie Heidelberg jointly with the Spanish National Commission for Astronomy.

^**

Based on observations obtained at the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.

© ESO, 2001

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HS 0705+6700: A new eclipsing sdB binary *,**

HS 0705+6700: A new eclipsing sdB binary ^*,^**