The triple system HIP 96515: a low-mass eclipsing binary with a DB white dwarf companion^*

¹ LAEX-CAB (INTA-CSIC); Postal address: LAEFF, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain e-mail: nhuelamo@laeff.inta.es
² Depto. de Física, Universidade Federal de Minas Gerais, C.P.702, 30161-970 – Belo Horizonte, MG, Brazil
³ Laboratório Nacional de Astrofísica/MCT, Rua Estados Unidos 154, 37504-364 Itajubá, Brazil
⁴ Département de Physique, Université de Montréal, C.P. 6128, Succ. Centre-Ville, Montréal, Québec H3C 3J7, Canada
⁵ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei Muenchen, Germany
⁶ European Southern Observatory, Alonso de Cordova 3107, Casilla 19, Santiago, Chile
⁷ Laboratoire d'Astrophysique, Observatoire de Grenoble, BP 53, 38041 Grenoble, Cedex 9, France
⁸ Instituto de Astrofísica de Canarias, C Vía Láctea, s/n, E38205 - La Laguna (Tenerife), Spain

Received: 11 December 2008
Accepted: 27 January 2009

Abstract

Context. HIP 96515 A is a double-lined spectroscopic binary included in the SACY catalog as a potential young star. It has a visual companion (CCDM 19371-5134 B, HIP 96515 B) at 86. If bound to the primary, the optical and infrared colors of this wide companion are consistent with those of a white dwarf.

Aims. We attempt to characterize the system HIP 96515 A&B by studying each of its components.

Methods. We analyzed spectroscopic and photometric observations of HIP 96515 A and its visual companion, HIP 96515 B. To confirm the system as a common proper-motion pair, we analyzed the astrometry of the components using high-angular resolution infrared observations obtained within a time span of two years, and archival astrometry.

Results. The high-resolution optical spectrum of HIP 96515 A was used to derive a mass ratio, , close to 0.9. The optical lightcurve of HIP 96515 A shows periodic variations with P_orbital = 2.3456 days, revealing that HIP 96515 A is an eclipsing binary with preliminary orbital parameters of i =  ± , and M₁ = 0.59 ± 0.03  and M₂ = 0.54 ± 0.03 , for the primary and secondary, respectively, at an estimated distance of 42 ± 3 pc. This is a new eclipsing binary with component masses below 0.6 . Multi-epoch observations of HIP 96515 A&B show that the system is a common proper-motion pair. The optical spectrum of HIP 96515 B is consistent with a pure helium atmosphere (DB) white dwarf. The comparison with evolutionary cooling sequence models provides  = 19 126 ± 195 K,  = 8.08,  = 0.6, and a distance of ~46 pc. The estimated WD cooling age is ~100 Myr and the total age of the object (including the main-sequence phase) is ~400 Myr. Finally, if HIP 96515 A&B are coeval, and assuming a common age of ~400 Myr, the comparison of the masses of the eclipsing binary members with evolutionary tracks shows that they are underestimated by ~15% and 10%, for the primary and secondary, respectively.