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Visiting Astronomer, German-Spanish Astronomical Centre, Calar Alto

By M. Mugrauer, R. Neuhäuser, E. W. Guenther, A. P. Hatzes, N. Huélamo, M. Fernández, M. Ammler, J. Retzlaff, B. König, D. Charbonneau, W. Br and Thüringer Landessternwarte Tautenburg

Abstract

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 HD77407 and one close to GJ577. For the companion candidate near GJ577, we obtained an optical spectrum showing spectral type M4.5; 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 0.5 M ⊙ and ∼ 0.16 to 0.2 M⊙, respectively. Compared to Siess al. (2000) models, each of the two pairs appears co-eval with HD77407 A,B being 10 to 40Myrs and GJ 577 A,B being ≥ 100 Myrs old. We also took multi-epoch high-resolution spectra of HD77407 to search for sub-stellar companions, but did not find any with 3 MJup as upper mass (msin i) limit (for up to 4 year orbits); however, we detected a long-term radial velocity trend in HD77407 A, consistent with a ∼ 0.3 M ⊙ companion at ∼ 50AU separation, i.e. the one detecte

Year: 2003
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