Study of candidate Be stars in the Magellanic Clouds using NIR photometry and optical spectroscopy

Abstract

Mennickent et al.and Sabogal et al.identified a large number of Classical Be (CBe) candidates in the L&SMC based on their photometric variability using the OGLEII database. They classified these stars into four different groups based on the appearance of their variability. We studied the infrared properties of the sample as well as the spectroscopic properties of a subsample. We cross-correlated the optical sample with the IRSF catalog to obtain the J, H, Ks magnitudes of all the four types of stars in the L&SMC. Spectra of 120 stars belonging to the types 1, 2 and 3 were analysed to study their spectral properties. Among the four types, the type 4 stars is the dominant group. The NIR colour-colour diagrams suggest that the type 4 stars in the LMC have a subclass, which is not found in our Galaxy or in the SMC. The main type 4 sample which is \sim 49% of the total sample has NIR properties similar to the Galactic CBe stars and the SMC type 4 stars. Though the new subclass of type 4 stars have high E(B - V) \sim 0.75, they are not located close to regions with high reddening. The type 3 stars (\sim 6% & 7.3% in the L&SMC) are found to have large Hα EW in the SMC and some are found to have large NIR excess. This small fraction of stars are unlikely to be CBe stars. The type 2 stars are found in larger fraction in the SMC, when compared to the LMC. The spectroscopic and the NIR properties suggest that these could be CBe stars. The spectroscopic sample of type 1 stars which show Hα in emission and confirmed as CBe stars are more abundant in the SMC by a factor of 2.6. If the effect of metallicity is to cause more CBe stars in the SMC, when compared to the LMC, then type 1, type 2 and type 4 stars follow this rule, with an enhancement of 2.6, 2.4 and 1.3 respectively.

14 figures, 12 tables, Accepted for Publication in MNRAS

References in corpus (4)

• Spitzer SAGE-SMC Infrared Photometry of Massive Stars in the Small Magellanic Cloud
• Instability strips of SPB and beta Cephei stars: the effect of the updated OP opacities and of the metal mixture
• Be phenomenon in open clusters: Results from a survey of emission-line stars in young open clusters
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Cited by in corpus (12)

• Classical Be Stars: Rapidly Rotating B Stars with Viscous Keplerian Decretion Disks
• The life cycles of Be viscous decretion discs: fundamental disc parameters of 54 SMC Be stars
• Mapping atomic and diffuse interstellar band absorption across the Magellanic Clouds and the Milky Way
• A study of Be stars in the Magellanic Clouds
• Identification of new Classical Ae stars in the Galaxy using LAMOST DR5
• Optical spectroscopy of Galactic field Classical Be stars
• Discovery of a possibly single blue supergiant star in the intra-cluster region of Virgo cluster of galaxies
• Identification of emission-line stars in transition phase from pre-main sequence to main sequence
• Red Be stars in the Magellanic Clouds?
• Proper motion separation of Be star candidates in the Magellanic Clouds and the Milky Way
• Study of the transient nature of classical Be stars using multi-epoch optical spectroscopy
• Study of Classical Be stars in open clusters older than 100 Myr