The First Radial Velocity measurements
of B[e] Supergiant LHA 115-S 18

The LHA 115-S 18 system (hereafter S18) has been the subject of studies for several decades and is still not well understood. It is a peculiar system which has led many studies to controversy. S18 has been suspected to be a binary system, but no classification for the companion has been discovered. Some works suggest a compact object, while others believe it houses a whole other star. In this paper I discuss the S18 system and present 75 new high resolution spectra as well as the analysis and initial findings from these spectra.


For a long time S18 has been noted as a strange source, with the first studies taking place in the 1950s (Henize 1956). It is a supergiant B[e] star in the Small Magellanic Cloud (SMC) that doubles as an X-ray source and a variable star. In addition, the star has in few cases exhibited an extreme and unexplained He II emission (Lepo 2015). My collaborators and I utilize the Southern Observatory for Astronomical Research (SOAR) telescope to produce high resolution spectra of S18. In the proceeding we examine spectra of this system and attempt the first period determination by measuring radial velocities from these spectra. Such a measurement would put a constraint on the nature of the companion.

Currently the proposed secondary star is unclassified. A white dwarf is however favored because of observed X-ray, visual, and UV luminosity (citation not found: 1987A&A...176...59S). This system is of interest to us because of the debate surrounding the classification of the system. Confirmation of a secondary object will help indicate the sources of many of the mysterious properties of the system. We are also interested in the classification of the companion object seeing as how both of these companion types have interesting implications for a B[e] system with such a range of physical parameters. Together this information will allow for better categorization of the central star and the system as a whole.