Orbital and physical parameters of eclipsing binaries from the All-Sky Automated Survey catalogue

II. Two spotted M  < 1 M_⊙ systems at different evolutionary stages^⋆

¹ Nicolaus Copernicus Astronomical Center, Department of Astrophysics, ul. Rabiańska 8, 87-100 Toruń, Poland
e-mail: xysiek@ncac.torun.pl; maciej@ncac.torun.pl
² Astronomical Observatory, Adam Mickiewicz University, ul. Słoneczna 36, 60-286 Poznań, Poland

Received: 22 September 2009
Accepted: 19 September 2010

Abstract

Aims. We present the results of our detailed spectroscopic and photometric analysis of two previously unknown  <1   M_⊙ detached eclipsing binaries: ASAS J045304-0700.4 and ASAS J082552-1622.8.

Methods. With the HIgh Resolution Echelle Spectrometer (HIRES) on the Keck-I telescope, we obtained spectra of both objects covering large fractions of orbits of the systems. We also obtained V and I band photometry with the 1.0-m Elizabeth telescope of the South African Astronomical Observatory (SAAO). The orbital and physical parameters of the systems were derived with the PHOEBE and JKTEBOP codes. We investigated the evolutionary status of both binaries with several sets of widely-used isochrones.

Results. Our modelling indicates that (1) ASAS J045304-0700.4 is an old, metal-poor, active systemwith component masses of M₁ = 0.8338  ±  0.0036   M_⊙, M₂ = 0.8280  ±  0.0040   M_⊙ and radii of R₁ = 0.848  ±  0.005   R_⊙ and R₂ = 0.833  ±  0.005   R_⊙, which places it at the end of the Main Sequence evolution – a stage rarely observed for this type of stars. (2) ASAS J082552-1622.8 is a metal-rich, active binary with component masses of M₁ = 0.7029  ±  0.0045   M_⊙, M₂ = 0.6872  ±  0.0049   M_⊙ and radii of ${\mathit{R}}_{\mathrm{1}}\mathrm{=}\mathrm{0.69}{\mathrm{4}}_{-0.011}^{\mathrm{+}\mathrm{0.007}} {\mathit{R}}_{\mathrm{\odot }}$ and ${\mathit{R}}_{\mathrm{2}}\mathrm{=}\mathrm{0.69}{\mathrm{9}}_{-0.014}^{\mathrm{+}\mathrm{0.011}} {\mathit{R}}_{\mathrm{\odot }}$. Both systems show significant out-of-eclipse variations, probably owing to large, cold spots.We also investigated the influence of a third light in the second system.