The SALVATION Project: Characterizing the Properties of Previously Unclassified Variables

The Spectroscopic Analysis of Luminous Variables and Transients in our Neighbor (SALVATION) project is a spectroscopic monitoring program, following stars exhibiting photometric variability and exotic transients. Targets are selected using the community alert broker ANTARES to filter through real-time Zwicky Transient Facility (ZTF) data focused on luminous variable stars and transients in the line of sight of M31, our neighboring galaxy. Since the public portion of ZTF is only in two filters, follow-up spectroscopy is required to uniquely identify objects of interest and to gain physical insights into their observed photometric variability. The team selects stars with the most interesting light curves to follow up with Lick Observatories Shane 3m telescope, taking spectra with the Kast Dual Channel Spectrograph within the visible range (~4000-9000 Å) to classify these sources variability.

This poster presents a subset of the observed variables that are unclassified and uses the collected spectra to classify them and identify the atmospheric parameters; stellar effective temperature (T_eff), surface gravity (log(g)), and metallicity (Fe/H). The spectral continuum shape is used for a zeroth-order estimate of T_eff via a blackbody curve comparison, which is then improved with template fitting using popular empirical spectral libraries such as MILES. By obtaining spectra of these variable stars on different days, we can observe how their spectroscopic features and atmospheric conditions vary at different points along their light curve as the star evolves in time. This process has been used to classify 12 new variable stars in M31 from spectra taken in 2019, and has helped trace and identify atmospheric parameter changes with spectral and photometric changes over time. As this work continues, we are moving towards synthetic spectra to test a wider and more densely sampled grid of stellar atmospheric parameters to more robustly identify these and future unclassified variables.