VLT multi-object spectroscopy of 33 eclipsing binaries in the Small Magellanic Cloud

Abstract

Aims. Our purpose is to provide reliable stellar parameters for a significant sample of eclipsing binaries, which are representative of a whole dwarf and metal-poor galaxy. We also aim at providing a new estimate of the mean distance to the SMC and of its depth along the line of sight for the observed field of view. Methods. We use radial velocity curves obtained with the ESO FLAMES facility at the VLT and light curves from the OGLE-II photometric survey. The radial velocities were obtained by least-squares fits of the observed spectra to synthetic ones, excluding the hydrogen Balmer lines. Results. Our sample contains 23 detached, 9 semi-detached and 1 overcontact systems. Most detached systems have properties consistent with stellar evolution calculations from single-star models at the standard SMC metalicity Z = 0.004, though they tend to be slightly overluminous. The few exceptions are probably due to third-light contribution or insufficient signal-to-noise ratio. The mass ratios are consistent with a flat distribution, both for detached and semi-detached/contact binaries. A mass-luminosity relation valid from ∼4 to ∼18 M is derived. The uncertainties are in the ±2 to ±11% range for the masses, in the ±2 to ±5% range for the radii and in the ±1 to ±6% range for the effective temperatures. The average distance modulus is 19.11 ± 0.03 (66.4 ± 0.9 kpc). The moduli derived from the V and from the I data are consistent within 0.01 mag. The 2σ depth of the SMC is, for our field, of 0.25 mag or 7.6 kpc under the assumption of a Gaussian distribution of stars along the line of sight. Three systems show significant apsidal motion, one of them with an apsidal period of 7.6 years, the shortest known to date for a detached system with main sequence stars.

Tracing the structure of the Milky Way with detached eclipsing binaries from the VVV survey – I. The method and initial results★

“…Ribas 2004;Pietrzyński et al 2013) and SMC (e.g. Hilditch et al 2005;North et al 2010). Finally, spectroscopy and radial velocities of several EBs in the Andromeda Galaxy (Ribas et al 2005;Vilardell et al 2010a,b) and M33 (Bonanos et al 2006) were obtained, indicating the distance modulus fully compatible with other findings.…”

Light curve solutions of the eccentric Kepler binaries KIC 4281895 and KIC 5115178 with tidally-induced humps

“…North et al (2010) obtain that q for detached systems is within 0.8-1.1 and for semidetached and contact binaries within 0.4-0.7. Lucy (2006) found an excess of binary systems with q ≥ 0.95 in our Galaxy.…”

“…Information for the apsidal motions of 128 targets in our Galaxy can be found in the catalog of Petrova & Orlov (1999). The study of EEBs in close galaxies SMC and LMC began in the new millenium (Graczyk 2003;Michalska & Pigulski 2005;Michalska 2007;Bulut & Demircan 2007;North et al 2010;Zasche et al 2014).…”

Redshift-Independent Distances in the Nasa/Ipac Extragalactic Database: Methodology, Content, and Use of Ned-D

“…Such distances are available for Local Group galaxies, and most abundantly available for the LMC and SMC. These include individual distances to 136 Cepheids (Pejcha & Kochanek 2012), 56 planetary nebulae (Ortiz 2013), and 50 RR Lyrae stars (Borissova et al 2009) in the LMC and 53 Cepheids (Pejcha & Kochanek 2012) and 32 eclipsing binaries (North et al 2010) in the SMC. Recently published distances for 8876 Cepheids, including 4222 in the LMC and 4654 in the SMC (Jacyszyn- Dobrzeniecka et al 2016) are in the process of being included.…”