An Updated Ephemeris for the Single-lined Orbit of the Supergiant μ Sagittarii

Abstract

μ Sagittarii (HD 166937, HR 6812) is a blue supergiant (B8Ia) in an eclipsing binary system. The stellar masses of evolved supergiants are ill-defined due, in part, to their rarity and long orbital periods when in binary systems. Most supergiants begin their lives as massive stars, which can typically be found in binary systems (Sana et al. 2012, 2014). Understanding the orbit and derived masses of these systems increases our understanding of their evolution, particularly with respect to both mass loss and transfer. In this research note, we present an updated orbit derived from 61 radial velocities collected between 1899 and 2017, including previous results from Campbell (1901), Frost & Adams (1904), Ichinohe (1907), Frost et al. (1926), and Buscombe (1963). We collected spectra with the University of Toledo's Ritter Observatory equipped with an echelle spectrograph, Clarkson University's Reynolds Observatory, and with personal telescopes equipped with amateur spectrographs such as the LHIRES III during 2016 and 2017. Data were reduced with standard techniques to subtract biases, darks, and remove pixel-to-pixel variations. The spectra were normalized individually and then stacked with respect to their instrument. This allowed them to be more easily compared to one another. Si IIλλ6347, 6371, Hα, and C IIλλ6578, 6582 lines were recorded for the measurement of radial velocities and stellar wind activity. Both Hα and C ii were contaminated with telluric lines, so we measured the Si ii doublet in this research note, resulting in 35 new measurements of the radial velocity. We present our new radial velocity measurements in conjunction with the values from the aforementioned papers in Figure 1.