Program: GS-2021A-Q-415

We propose to secure homogeneous, low resolution, high SNR spectra with GMOS-S, for a sample of single-line spectroscopic binaries (SB1) that have been resolved by our on-going Speckle program with HRCam@SOAR. For these systems, the Speckle observations lead directly only to the mass sums, which demands and independent procedure to estimate the mass of the primary, and thus the masses of the individual components. From the spectra we will assign spectral types and luminosity classes, and from them we will estimate the masses of the primaries. However, rather than using the mass of the primary in a deterministic way, we will apply a new Bayesan method (Videla, 2020) which better considers the interdependence of prior data to jointly derive the system’s orbital parameters and the individual component masses, and gives a measure of the uncertainties. This method can also detect and prioritize the best source of prior information available, which reduces the errors of the estimates. The proposed observations are part of a large astrometric + spectroscopic survey to characterize binary systems within 250pc form the sun. Along with parallaxes from Gaia, we are obtaining high precision orbital parameters and mass sums, that will result in the first all-sky, volume-limited, study of binary systems. When complete, our survey will provide sensitive tests to stellar evolution theory and add a significant number of new points on the mass-luminosity relation. An increase of the number of well-studied binary stars will also contribute to other astrophysical areas, such as star formation and comprehensive studies of the solar neighborhood, which require precise knowledge of the multiplicity fraction. In this proposal we concentrate on the brighter subset of our SB1 sample (V ~ 6 – 8), which can be observed in poor weather conditions (B4)