Astronomy & Astrophysics

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Issue		A&A Volume 437, Number 2, July II 2005
Page(s)		L31 - L34
Section		Letters
DOI		10.1051/0004-6361:200500133

A&A 437, L31-L34 (2005)
DOI: 10.1051/0004-6361:200500133

Letter

A substellar companion around the intermediate-mass giant star HD 11977

J. Setiawan¹, J. Rodmann¹, L. da Silva², A. P. Hatzes³, L. Pasquini⁴, O. von der Lühe⁵, J. R. de Medeiros⁶, M. P. Döllinger⁴ and L. Girardi⁷

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: setiawan@mpia.de
² Observatório Nacional, R. Gal. José Cristino 77, 20921-400 São Cristóvão, Rio de Janeiro, Brazil
³ Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
⁴ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
⁵ Kiepenheuer-Institut für Sonnenphysik, Schöneck-Str. 6, 79104 Freiburg, Germany
⁶ Departamento de Física, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, Brazil
⁷ Osservatorio Astronomico di Trieste, via Tiepolo 11, 34131 Trieste, Italy

(Received 2 February 2005 / Accepted 25 May 2005 )

Abstract
We report the discovery of a substellar companion to the intermediate-mass star HD 11977 (G5 III). Radial velocities of this star have been monitored for five years with FEROS at the 1.52-m ESO and later at the 2.2-m MPG/ESO telescope in La Silla, Chile. Based on the collected data we calculated an orbital solution with a period of $P=711~{\rm days}$ , a semi-amplitude of $K_{1}=105~{\rm m\,s}^$ , and an eccentricity of e=0.4. The period of the radial-velocity variation is longer than that of the estimated stellar rotation, rendering it unlikely that rotational modulation is the source of the variation in the radial velocity. This hypothesis is supported by the absence of a correlation between stellar activity indicators and radial-velocity variation. By determining a primary stellar mass of $M_{\star}=1.91~M_{\odot}$ , the best-fit minimum mass of the companion and semi-major axis of the orbit are $m_{2}\sin{i}=6.54~M_{{\rm Jup}}$ and $a_{2}=1.93~{\rm AU}$ , respectively. An upper limit for the mass of the companion of $m_{2} \la 65.5~M_{{\rm Jup}}$ has been calculated from HIPPARCOS astrometric measurements. Although the possibility of a brown-dwarf companion cannot be excluded, HD 11977 B is one of the few planet candidates detected around an intermediate-mass star. The progenitor main-sequence star of HD 11977 is probably an A-type star. This discovery gives an indirect evidence for planetary companions around early type main-sequence stars.

Key words: stars: general -- stars: planetary system -- stars: individual: HD 11977 -- technique: radial velocity

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