Discovery of New, Dust-Poor B[e] Supergiants in the Small Magellanic Cloud

TL;DR

This paper reports the discovery of three new dust-poor B[e] supergiants in the Small Magellanic Cloud, expanding the known diversity of sgB[e] stars and suggesting a new subclass with less circumstellar dust.

Contribution

It identifies a new subclass of dust-poor sgB[e] stars in the SMC, based on spectroscopic and infrared observations, highlighting their distinct properties.

Findings

Stars show typical B[e] spectral features with lower infrared excess.

Stars have luminosities > 10^4 L_sun, confirming supergiant status.

Stars likely have less circumstellar dust or material than typical sgB[e] stars.

Abstract

We present the discovery of three new B[e] supergiants (sgB[e] stars) in the Small Magellanic Cloud (SMC). All three stars (R15, R38, and R48) were identified in the course of our Runaways and Isolated O Type Star Spectroscopic Survey of the SMC (RIOTS4). The stars show optical spectra that closely resemble those of previously known B[e] stars, presenting numerous low-ionization forbidden and permitted emission lines such as [Fe II] and Fe II. Furthermore, our stars have luminosities of log(L/L_sun) > 4, demonstrating that they are supergiants. However, we find lower infrared excesses and weaker forbidden emission lines than for previously identified B[e] supergiants. Thus our stars appear to either have less material in their circumstellar disks than other sgB[e] stars, or the circumstellar material has lower dust content. We suggest that these may constitute a new subclass of dust-poor sgB[e] stars.