HD 77407 and GJ 577: Two new young stellar binaries

Detected with the Calar Alto Adaptive Optics system ALFA

¹ Astrophysikalisches Institut, Universität Jena, Schillergäßchen 2-3, 07745 Jena, Germany
² MPI für extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany
³ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
⁴ European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago, Chile
⁵ Instituto de Astrofísica de Andalucía, CSIC, Apdo. Correos 3004, 18080 Granada, Spain
⁶ California Institute of Technology, mail stop 105-24, 1200 E. California Blvd., Pasadena CA 91125, USA
⁷ Department of Astronomy, University of Michigan, Ann Arbor MI 48109, USA
⁸ MPI für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany

Corresponding author: M. Mugrauer, markus@astro.uni-jena.de

Received: 16 May 2003
Accepted: 8 December 2003

Abstract

We present the first results from our search for close stellar and sub-stellar companions to young nearby stars on the northern sky. Our infrared imaging observations are obtained with the 3.5 m Calar Alto telescope and the AO system ALFA. With two epoch observations which were separated by about one year, we found two co-moving companion candidates, one close to HD 77407 and one close to GJ 577. For the companion candidate near GJ 577, we obtained an optical spectrum showing spectral type M 4.5; this candidate is a bound low-mass stellar companion confirmed by both proper motion and spectroscopy. We estimate the masses for HD 77407 B and GJ 577 B to be ~0.3 to  and ~0.16 to , respectively. Compared to Siess et al. ([CITE]) models, each of the two pairs appears co-eval with HD 77407 A, B being 10 to 40 Myrs and GJ 577 A, B being ≥100 Myrs old. We also took multi-epoch high-resolution spectra of HD 77407 to search for sub-stellar companions, but did not find any with as upper mass () limit (for up to 4 year orbits); however, we detected a long-term radial velocity trend in HD 77407 A, consistent with a ~0.3  companion at ~50 AU separation, i.e. the one detected by the imaging. Hence, HD 77407 B is confirmed to be a bound companion to HD 77407 A. We also present limits for undetected, but detectable companions using a deep image of HD 77407 A and B, also observed with the Keck NIRC2 AO system; any brown dwarfs were detectable outside of 0.5 arcsec (17 AU at HD 77407), giant planets with masses from ~6.5 to 12  were detectable at ≥1.5 arcsec.