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Astron. Astrophys. 360, 991-996 (2000)

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Research Note

Search for companions around Sirius *

J.M. Bonnet-Bidaud 1, F. Colas 2 and J. Lecacheux 3

1 Service d'Astrophysique, DSM/DAPNIA/SAp, CE Saclay, 91191 Gif sur Yvette Cedex, France
2 Institut de Mécanique Céleste, 77 Av. Denfert Rochereau, 75014 Paris, France
3 DESPA, Observatoire de Paris-Meudon, 5 Pl Jules Janssen, 92195 Meudon, France

Received 27 December 1999 / Accepted 30 May 2000


Since the discovery of Sirius-B about 130 yr ago, there have been several claims of a possible second companion around the brightest star Sirius-A. Such a companion could, in particular, be responsible for the suspected colour change of the star, now strongly suggested from two independent historical sources. We reported here on a new observation of the sky region around Sirius, to search for such a companion, using a coronographic device.

By comparison of the new stellar field with a similar image obtained by us [FORMULA]13 yr ago and using the Sirius proper motion, we are able to eliminate the most obvious companion candidates down to a magnitude mv[FORMULA]17 in a field from 30 arcsec to 2.5 arcmin of the central star. None of the visible stars appears consistent in magnitude and colours with what expected from current theoretical models and observations of low-mass stars.

From the study of the same field, it is also shown that the Sirius companion, consistently reported by observers during the years 1920-1930, is most probably an unrelated mg[FORMULA]12 background star, now [FORMULA] 1 arcmin away but located precisely on the Sirius proper motion trajectory. The closest apparent conjunction with Sirius was realized in 1937 with a minimum angular distance of 6.9 arcsec, of the same order as the Sirius A-B binary separation.

The reported observations do not eliminate the possibility of a second companion but now confined the search to the more central 30 arcsec region around Sirius. In particular, the existence of a long period companion cannot definitively be ruled out since the arbitrary orientation of the orbit can yield an observed projected position on sky inside this more central region.

Key words: stars: low-mass, brown dwarfs – astrometry – stars: binaries: visual – stars: individual: Sirius

* Based on data collected at the Pic du Midi-Toulouse Observatory (France)

Send offprint requests to: J.M. Bonnet-Bidaud

Correspondence to: bobi@discovery.saclay.cea.fr

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© European Southern Observatory (ESO) 2000

Online publication: August 23, 2000