The pre-main-sequence binary HK Ori: spectro-astrometry and EXPORT data

Abstract

In this paper we present multi-epoch observations of the pre-main-sequence binary HK Ori. These data have been drawn from the EXPORT data base and are complemented by high-quality spectro-astrometric data of the system. The spectroscopic data appear to be very well represented by a combination of an A dwarf star spectrum superposed on a (sub)giant G-type spectrum. The radial velocity of the system is consistent with previous determinations, and does not reveal binary motion, as expected for a wide binary. The spectral, photometric and polarimetric properties and variability of the system indicate that the active object in the system is a T Tauri star with UX Ori characteristics. The spectro-astrometry of HK Ori is sensitive down to milliarcsecond scales and confirms the speckle interferometric results from Leinert et al. The spectro-astrometry allows the identification, with fair certainty, of the active star within the binary, which we suggest to be a G-type T Tauri star based on its spectral characteristics.