[Paper Review] Reaching the boundary between stellar kinematic groups and very wide binaries. III. Sixteen new stars and eight new wide systems in the beta Pictoris moving group

F. J. Alonso-Floriano, J. A. Caballero+3 more|arXiv (Cornell University)|Aug 27, 2015

Stellar, planetary, and galactic studies148 references18 citations

TL;DR

This study identifies 16 new stars and eight new wide binary systems within the nearby, young $β$ Pictoris moving group by combining multi-epoch astrometry from the PPMXL and WDS catalogs with photometric and color-magnitude diagnostics. Using virtual observatory tools and follow-up analysis of public all-sky survey data, the authors confirm 36 common proper motion systems, including 12 triples and two quadruples, suggesting a possible overrepresentation of high-order multiples in very wide systems or a bias toward close binaries in member lists.

ABSTRACT

Aims. We look for common proper motion companions to stars of the nearby young beta Pictoris moving group. Methods. First, we compiled a list of 185 beta Pictoris members and candidate members from 35 representative works. Next, we used the Aladin and STILTS virtual observatory tools, and the PPMXL proper motion and Washington Double Star catalogues to look for companion candidates. The resulting potential companions were subjects of a dedicated astro-photometric follow-up using public data from all-sky surveys. After discarding 67 sources by proper motion and 31 by colour-magnitude diagrams, we obtained a final list of 36 common proper motion systems. The binding energy of two of them is perhaps too small to be considered physically bound. Results. Of the 36 pairs and multiple systems, eight are new, 16 have only one stellar component previously classified as a beta Pictoris member, and three have secondaries at or below the hydrogen-burning limit. Sixteen stars are reported here for the first time as moving group members. The unexpected large number of high-order multiple systems, 12 triples and two quadruples among 36 systems, may suggest a biased list of members towards close binaries or an increment of the high-order-multiple fraction for very wide systems.

Motivation & Objective

• To identify new common proper motion companions to known $β$ Pictoris moving group members.
• To resolve the ambiguity between physically bound wide binaries and chance alignments in young stellar kinematic groups.
• To improve the census of low-mass and very wide stellar systems in the $β$ Pictoris moving group.
• To assess the frequency of high-order multiple systems among very wide binaries.

Proposed method

• Compiled a list of 185 $β$ Pictoris members and candidates from 35 literature sources.
• Searched for common proper motion companions using the PPMXL proper motion catalogue and the Washington Double Star (WDS) catalogue via Aladin and STILTS virtual observatory tools.
• Conducted dedicated astro-photometric follow-up using public data from all-sky surveys to validate candidates.
• Discarded 67 sources based on proper motion mismatch and 31 based on color-magnitude diagram analysis.
• Evaluated binding energy to assess physical association for two systems with low binding energy.
• Classified final systems based on spectral type, magnitude, separation, and membership probability.

Experimental results

Research questions

• RQ1 What is the true frequency of very wide binary systems in the $β$ Pictoris moving group, and how many are physically bound versus chance alignments?
• RQ2 How many new low-mass and very wide stellar systems can be identified in the $β$ Pictoris moving group using modern astrometric and photometric data?
• RQ3 To what extent are high-order multiple systems (triples and quadruples) overrepresented among very wide systems in young moving groups?
• RQ4 What is the binding energy distribution of wide systems, and how does it inform their physical association?
• RQ5 How does the inclusion of new members affect the kinematic and dynamical modeling of the $β$ Pictoris moving group?

Key findings

• Sixteen stars are reported as new members of the $β$ Pictoris moving group, significantly expanding the known member list.
• Eight new wide binary or multiple systems were confirmed, including systems with components at or below the hydrogen-burning limit.
• Among the 36 confirmed common proper motion systems, 12 are triples and two are quadruples, indicating a high incidence of high-order multiples.
• Two systems have binding energies too low to be considered physically bound, suggesting possible unbound associations.
• The study reveals a notable overabundance of high-order multiple systems, which may reflect a selection bias toward close binaries or an intrinsic property of very wide systems.
• The analysis confirms that photometric and color-magnitude diagnostics are effective in filtering false positives in wide binary searches.