A low-mass stellar companion of the planet host star HD 75289^*

¹ Astrophysikalisches Institut, Universität Jena, Schillergäßchen 2-3, 07745 Jena, Germany e-mail: markus@astro.uni-jena.de
² Tel Aviv University, Tel Aviv 69978, Israel
³ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
⁴ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany

Received: 2 April 2004
Accepted: 3 June 2004

Abstract

We report on the detection of a new low-mass stellar companion of HD 75289, a G0V star that harbors one known radial-velocity planet (Udry et al. [CITE], A&A, 356, 590). Comparing an image from 2MASS with an image we obtained with SofI at the ESO 3.58 m NTT three years later, we detected a co-moving companion located  arcsec ( AU at 29 pc) east of HD 75289. A second SofI image taken 10 months later confirmed the common proper motion of HD 75289 B with its host star. The infrared spectrum and colors of the companion are consistent with an M 2 to M 5 main-sequence star at the distance of HD 75289. No further (sub)stellar companion down to  mag could be detected. With the SofI detection limit we can rule out additional stellar companions beyond 140 AU and substellar companions with masses from 400 AU up to 2000 AU.