# Proper motion separation of Be star candidates in the Magellanic Clouds and the Milky Way

## TL;DR

This study uses proper motion data to distinguish between Be star candidates in the Magellanic Clouds and the Milky Way, revealing distinct populations and clarifying their galactic origins.

## Contribution

It introduces a method combining proper motions and infrared colors to separate Be star populations in the Magellanic Clouds and the Milky Way.

## Key findings

- Two populations in the LMC with different colors and kinematics identified.
- Redder Be candidates in the LMC are confirmed to be Milky Way disk stars.
- Similar but less clear separation observed in the SMC.

## Abstract

We present a proper motion investigation of a sample of Be star candidates towards the Magellanic Clouds, which has resulted in the identification of separate populations, in the Galactic foreground and in the Magellanic background. Be stars are broadly speaking B-type stars that have shown emission lines in their spectra. In this work, we studied a sample of 2446 and 1019 Be star candidates towards the LMC and SMC respectively, taken from the literature and proposed as possible Be stars due to their variability behaviour in the OGLE-II I band. JHKs magnitudes from the IRSF catalog and proper motions from the SPM4 catalog, were obtained for 1188 and 619 LMC and SMC Be stars candidates, respectively. Color-color and vector-point diagrams were used to identify different populations among the Be star candidates. In the LMC sample, two populations with distinctive infrared colours and kinematics were found, the bluer sample is consistent with being in the LMC and the redder one with belonging to the Milky Way disk. This settles the nature of the redder sample which had been described in previous publications as a possible unknown subclass of stars among the Be candidates in the LMC. In the SMC sample, a similar but less evident result was obtained, since this apparent unknown subclass was not seen in this galaxy. We confirm that in the selection of Be stars by their variability, although generally successful, there is a higher risk of contamination by Milky Way objects towards redder B$-$V and V$-$I colors.