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The SALVATION Project: A Red Nova in M31 and Other Highlights

Presentation #204.16 in the session Pulsating Variable Stars — iPoster Session.

Published onJun 29, 2022
The SALVATION Project: A Red Nova in M31 and Other Highlights

The SALVATION (Spectroscopic Analysis of Luminous Variables and Transients in our Neighbor) project, which started in the fall of 2019, uses Lick Observatory’s Shane 3-m telescope and Kast double spectrograph in cadence and target-of-opportunity modes to carry out visible (~4000–9000 Angstrom) spectroscopic follow up of variable stars and transients identified by the ANTARES community alert broker from the real-time data stream of the Zwicky Transient Factory. Most of these sources are in the Andromeda galaxy (M31) or along the line-of-sight to it; during times of the night when M31 is inaccessible, we obtain spectra of transients along other lines of sight. We are carrying out routine spectroscopic monitoring of ~50 luminous variable stars, and have obtained spectra of several tens of transients to date, many of which have been reported in rapid response via Astronomer’s Telegrams.

In fall of 2021, we spectroscopically classified a transient, ZTF21abihsto, identified from the community alert broker ANTARES as a red nova in M31. Red novae and their luminous counterparts are thought to be the result of stellar mergers and occupy a particularly sparse portion of the transient gap (the gap between classical novae and supernovae) with only a few published examples, three of which are recorded in M31, making this the discovery of a rare object. We have also identified two additional RNe candidates in M31, ZTF18acsxqmp and ZTF21abkgfgc. Interestingly, ZTF18acsxqmp was identified by Barsukova et al. (2008) to have a RN-like spectrum on Oct 2, 2008. If the August 2021 outburst of ZTF18acsxqmp were indeed a RN, this will be the first time a RN would be documented to recur on a timescale such as this, fundamentally challenging present ideas of the mechanisms that govern RNe and their progenitors. Currently, we are finding future RN targets from ongoing surveys to possibly reveal peculiar activity in RN systems not yet observed.

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