Twenty-Five Sub-Arcsecond Binaries Discovered By Lunar Occultations

TL;DR

This study reports the discovery of 25 sub-arcsecond binary star systems using lunar occultations in the near-infrared, revealing new companions and analyzing their properties and frequency among field stars.

Contribution

First-time detection of 25 binaries via lunar occultations, including a pre-main sequence star and a Mira-like variable, with detailed analysis of their characteristics and binary frequency.

Findings

Median binary separation of 18 milliarcseconds

Binary frequency among field stars ~10%

Detected binaries include a pre-main sequence star and a Mira-like variable

Abstract

We report on 25 sub-arcsecond binaries, detected for the first time by means of lunar occultations in the near-infrared as part of a long-term program using the ISAAC instrument at the ESO Very Large Telescope. The primaries have magnitudes in the range K=3.8 to 10.4, and the companions in the range K=6.4 to 12.1. The magnitude differences have a median value of 2.8, with the largest being 5.4. The projected separations are in the range 6 to 748 milliarcseconds and with a median of 18 milliarcseconds, or about 3 times less than the diffraction limit of the telescope. Among our binary detections are a pre-main sequence star and an enigmatic Mira-like variable previously suspected to have a companion. Additionally, we quote an accurate first-time near-IR detection of a previously known wider binary. We discuss our findings on an individual basis as far as made possible by the available literature, and we examine them from a statistical point of view. We derive a typical frequency of binarity among field stars of ~10%, in the resolution and sensitivity range afforded by the technique (~0.003" to ~0.5", and K~12mag, respectively). This is in line with previous results by the same technique but we point out interesting differences that we can trace up to sensitivity, time sampling, and average distance of the targets. Finally, we discuss the prospects for further follow-up studies.