Search for companions around Sirius *
J.M. Bonnet-Bidaud 1,
F. Colas 2 and
J. Lecacheux 3
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 13 yr ago and using the Sirius proper motion, we are able to eliminate the most obvious companion candidates down to a magnitude mv17 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 mg12 background star, now 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
Send offprint requests to: J.M. Bonnet-Bidaud
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© European Southern Observatory (ESO) 2000
Online publication: August 23, 2000