Abstract
We explored the regions within a radius of 25473 nearby, low-metallicity G- to M-type stars using (VR)I optical filters and small-aperture telescopes. About 10%the sample was searched up to angular separations of 90. Target stars with metallicities in the interval -3.5[Fe/H]0.0 were selected from the surveys by Carney-Latham. We applied photometric and astrometric techniques to detect true physical companions to these stars. We identified 13 new proper motion stellar companions and retrieved 29 previously known companions that are up to 8 magnitudes fainter than their primary stars in the I-band. The masses of these companions are estimated to be between 0.5 M[] and 0.1 M[], i.e., close to the substellar borderline for low metallicities. Projected orbital separations are between ~ 32 and ~ 57000 AU. Our results indicate that about 15%the metal-poor stars have stellar companions in wide orbits, which is in agreement with the binary fraction observed among main sequence G- to M-type stars and T Tauri stars. Similar searches conducted with 4-m class telescopes will lead to the discovery of low-metallicity brown dwarfs around stars. Their spectroscopic follow-up requires 10-m class telescopes and instrumentation like that of the GTC.
