The Araucaria project. Precise physical parameters of the eclipsing binary IO Aquarii

¹ Millenium Institute of Astrophysics, Santiago 22, Chile
e-mail: darek@astro-udec.cl
² Universidad de Concepción, Departamento de Astronomía, Casilla 160-C, Concepción, Chile
³ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
⁴ Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warsaw, Poland
⁵ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁶ Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
⁷ Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
⁸ Department of Physics, University of Warwick, Coventry CV4 7AL, UK

Received: 29 March 2015
Accepted: 18 June 2015

Abstract

Aims. Our aim is to precisely measure the physical parameters of the eclipsing binary IO Aqr and derive a distance to this system by applying a surface brightness – colour relation. Our motivation is to combine these parameters with future precise distance determinations from the Gaia space mission to derive precise surface brightness – colour relations for stars.

Methods. We extensively used photometry from the Super-WASP and ASAS projects and precise radial velocities obtained from HARPS and CORALIE high-resolution spectra. We analysed light curves with the code JKTEBOP and radial velocity curves with the Wilson-Devinney program.

Results. We found that IO Aqr is a hierarchical triple system consisting of a double-lined short-period (P = 2.37 d) spectroscopic binary and a low-luminosity and low-mass companion star orbiting the binary with a period of ≳25 000 d (≳70 yr) on a very eccentric orbit. We derive high-precision (better than 1%) physical parameters of the inner binary, which is composed of two slightly evolved main-sequence stars (F5 V-IV + F6 V-IV) with masses of M₁ = 1.569 ± 0.004 and M₂ = 1.655 ± 0.004 M_⊙ and radii R₁ = 2.19 ± 0.02 and R₂ = 2.49 ± 0.02 R_⊙. The companion is most probably a late K-type dwarf with mass ≈0.6 M_⊙. The distance to the system resulting from applying a () surface brightness – colour relation is 255 ± 6 (stat.) ± 6 (sys.) pc, which agrees well with the Hipparcos value of 270⁺⁹¹_-55 pc, but is more precise by a factor of eight.