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Search for companions around Sirius

Jean-Marc Bonnet-Bidaud·Francois Colas·Jean Lecacheux
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Abstract

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 of 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 $\sim$13 yr ago and using the Sirius proper motion, we are able to eliminate the most obvious companion candidates down to a magnitude m$_v$$\sim$17 in a field from 30 arcsec to 2.5 arcmin of the central star. None of the visible stars appears consistent in magnitude and colours with what expected from current theoretical models and observations of low-mass stars. From the study of the same field, it is also shown that the Sirius companion, consistently reported by observers during the years 1920-1930, is most probably an unrelated m$_g$$\simeq$12 background star, now $\sim$ 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 than 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.

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Jean-Marc Bonnet-Bidaud, Francois Colas, Jean Lecacheux. 2000-10-02. Search for companions around Sirius. https://arxiv.org/abs/astro-ph/0010032

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