Close binary companions of the HAeBe stars LkHα 198, Elias 1, HK Ori and V380 Ori^*

¹ Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany e-mail: kester@mpifr-bonn.mpg.de
² Special Astrophysical Observatory, Nizhnij Arkhyz, Zelenchuk region, Karachai-Cherkesia 357147, Russia
³ Institut für Theoretische Astrophysik, Tiergartenstrasse 15, 69121 Heidelberg, Germany

Received: 21 April 2004
Accepted: 19 October 2004

Abstract

We present diffraction-limited bispectrum speckle interferometry observations of four well-known Herbig Ae/Be (HAeBe) stars, LkHα 198, Elias 1, HK Ori and V380 Ori. For two of these, LkHα 198 and Elias 1, we present the first unambiguous detection of close companions. The plane of the orbit of the new LkHα 198 companion appears to be significantly inclined to the plane of the circumprimary disk, as inferred from the orientation of the outflow. We show that the Elias 1 companion may be a convective star, and suggest that it could therefore be the true origin of the X-ray emission from this object. In the cases of HK Ori and V380 Ori, we present new measurements of the relative positions of already-known companions, indicating orbital motion. For HK Ori, photometric measurements of the brightness of the individual components in four bands allowed us to decompose the system spectral energy distribution (SED) into the two separate component SEDs. The primary exhibits a strong infrared excess which suggests the presence of circumstellar material, whereas the companion can be modelled as a naked photosphere. The infrared excess of HK Ori A was found to contribute around two thirds of the total emission from this component, suggesting that accretion power contributes significantly to the flux. Submillimetre constraints mean that the circumstellar disk cannot be particularly massive, whilst the near-infrared data indicates a high accretion rate. Either the disk lifetime is very short, or the disk must be seen in an outburst phase.