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

• Published in: Astronomy and astrophysics (Berlin) Vol. 503; no. 3; pp. 873 - 881
• Main Authors: Huélamo, N., Vaz, L. P. R., Torres, C. A. O., Bergeron, P., Melo, C. H. F., Quast, G. R., Barrado y Navascués, D., Sterzik, M. F., Chauvin, G., Bouy, H., Landin, N. R.
• Format: Journal Article
• Language: English
• Published: Les Ulis EDP Sciences 01.09.2009
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; stars: binaries: eclipsing; stars: individual: HIP 96515; stars: white dwarfs; Eclipsing binary stars; Photometric observation; White dwarf stars; Color; Light curves; Infrared observation; Periodic variations; stars: white dwarfs; Astrometry; Young stars; stars: individual: HIP 96515; Mass ratio; Astronomical catalogues; Models; Dwarf stars; stars: binaries: eclipsing; Spectroscopical observation; Age; Spectroscopic binary stars; Proper motion; Optical spectrum
• ISSN: 0004-6361; 1432-0746; 1432-0756
• DOI: 10.1051/0004-6361/200811514

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 8$\farcs$6. 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, $M_2/M_1$, close to 0.9. The optical lightcurve of HIP 96515 A shows periodic variations with Porbital = 2.3456 days, revealing that HIP 96515 A is an eclipsing binary with preliminary orbital parameters of i = $89\fdg 0$ ± $0\fdg 2$, and M1 = 0.59 ± 0.03 $M_{\odot}$ and M2 = 0.54 ± 0.03 $M_{\odot}$, 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 $M_{\odot}$. 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 $T_{{\rm eff,WD}}$ = 19 126 ± 195 K, $\log g_{{\rm WD}}$ = 8.08, $M_{{\rm WD}}/M_{\odot}$ = 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.