Search for companions around Sirius

Since the discovery of Sirius-B about 130yr ago, there have been several cl aims of a possible second companion around the brightest star Sirius-A. Suc h 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 Si rius, to search for such a companion, using a coronographic device. By comparison of the new stellar field with a similar image obtained by us similar to 13 yr ago and using the Sirius proper motion, we are able to eli minate the most obvious companion candidates down to a magnitude m(nu)simil ar to 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 companio n, consistently reported by observers during the years 1920-1930, is most p robably an unrelated m(g)similar or equal to 12 back ground star, now simil ar to 1 arcmin away but located precisely on the Sirius proper motion traje ctory. The closest apparent conjunction with Sirius was realized in 1937 wi th a minimum angular distance of 6.9 arcsec, of the same order as the Siriu s A-B binary separation. The reported observations do not eliminate the possibility of a second comp anion but now confined the search to the more central 30 arcsec region arou nd Sirius. In particular, the existence of a long period companion cannot d efinitively be ruled out since the arbitrary orientation of the orbit can y ield an observed projected position on sky inside this more central region.