Statistics of wide pre-main sequence binaries in the Orion OB1 association

TL;DR

This study analyzes the statistics of wide pre-main sequence binaries in the Orion OB1 association, revealing their frequency, distribution, and differences between subgroups using Gaia and VISTA data.

Contribution

It provides the first comprehensive statistical analysis of wide binaries in Orion OB1, highlighting differences between subgroups and their relation to stellar density.

Findings

Average companion fraction is 0.09+-0.01.

Ori OB1b has 1.6 times more binaries than OB1a.

No overall dependence of binary frequency on stellar density.

Abstract

Statistics of low-mass pre-main sequence binaries in the Orion OB1 association with separations ranging from 0.6" to 20" (220 to 7400 au at 370 pc) are studied using images from the VISTA Orion mini-survey and astrometry from Gaia. The input sample based on the CVSO catalog contains 1137 stars of K and M spectral types (masses between 0.3 and 0.9 Msun), 1021 of which are considered to be association members. There are 135 physical binary companions to these stars with mass ratios above ~0.13. The average companion fraction is 0.09+-0.01 over 1.2 decades in separation, slightly less than, but still consistent with, the field. We found a difference between the Ori OB1a and OB1b groups, the latter being richer in binaries by a factor 1.6+-0.3. No overall dependence of the wide-binary frequency on the observed underlying stellar density is found, although in the Ori OB1a off-cloud population these binaries seem to avoid dense clusters. The multiplicity rates in Ori OB1 and in sparse regions like Taurus differ significantly, hinting that binaries in the field may originate from a mixture of diverse populations.