Maíz Apellániz, J.
Astronomy and Astrophysics, Volume 518, id.A1, 12 pp.
Context. Massive stars have high-multiplicity fractions, and many of them have still undetected components, thus hampering the study of their properties.
Aims: I study a sample of massive stars with high angular resolution to better characterize their multiplicity.
Methods: I observed 138 fields that include at least one massive star with AstraLux, a lucky imaging camera at the 2.2 m Calar Alto telescope. I also used observations of 3 of those fields with ACS/HRC on HST to obtain complementary information and to calibrate the AstraLux data. The results were compared with existing information from the Washington Double Star Catalog, Tycho-2, 2MASS, and other literature results.
Results: I discover 16 new optical companions of massive stars, the majority of which are likely to be physically bound to their primaries. I also improve the accuracy for the separation and magnitude difference of many previously known systems. In a few cases the orbital motion is detected when comparing the new data with existing ones and constraints on the orbits are provided.
Conclusions: The analysis indicate that the majority of the AstraLux detections are bound pairs. For a range of separations of 0.1 arcsec-14'' and magnitude differences lower than 8, I find that the multiplicity fraction for massive stars is close to 50%. When objects outside those ranges are included, the multiplicity fraction should be considerably higher.
Table 3 is also available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/518/A1