High-resolution imaging of Galactic massive stars with AstraLux. I. 138 fields with delta > -25 degrees

TL;DR

This study uses high-resolution AstraLux imaging to identify and characterize companions of massive stars, revealing a high multiplicity fraction and discovering new bound systems, thus enhancing understanding of massive star properties.

Contribution

The paper presents new high-resolution imaging data that significantly increases the known multiplicity and improves orbital parameter estimates for massive stars.

Findings

Discovered 16 new optical companions to massive stars.

Most AstraLux detections are likely physically bound pairs.

Multiplicity fraction for massive stars is close to 50% within certain separation and magnitude difference ranges.

Abstract

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"-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.