The Temperature Structure of Be Star Disks in the Small Magellanic Cloud

TL;DR

This study examines the temperature structure of Be star disks in the Small Magellanic Cloud, revealing they are hotter than Milky Way disks, which affects Be star detection rates and suggests differences in disk properties between galaxies.

Contribution

It provides the first detailed comparison of Be star disk temperatures at sub-solar metallicity, highlighting how metallicity influences disk temperature and observational detection.

Findings

SMC Be star disks are systematically hotter than Milky Way disks.

The hotter disks in SMC lead to 5-10% lower detection efficiency of Be stars.

Discrepancies in Hα equivalent width distributions suggest larger disks may be needed in SMC models.

Abstract

The temperature structure of Be star circumstellar disks at the sub-solar metallicity appropriate to the Small Magellanic Cloud (SMC) is investigated. It is found that for central stars of the same spectral type, Be star disks in the SMC are systematically hotter by several thousand degrees compared to Milky Way (MW) disks with the same density structure. For early spectral types (B0e - B3e), this results in systematically smaller H{\alpha} equivalent widths for Be stars in the SMC. The implication of this result on Be star frequency comparisons between MW and SMC clusters is shown to be a 5 - 10% lowering of the detection efficiency of Be stars in SMC clusters. These calculations are also compared to the known H{\alpha} equivalent width distributions in the MW and SMC. For the MW, reasonable agreement is found; however, for the SMC, the match is not as good and systematically larger Be star disks may be required.