Luminous Red Nova AT 2019zhd, a new merger in M 31
A. Pastorello, M. Fraser, G. Valerin, A. Reguitti, K. Itagaki, P., Ochner, S. C. Williams, D. Jones, J. Munday, S. J. Smartt, K. W. Smith, S., Srivastav, N. Elias-Rosa, E. Kankare, E. Karamehmetoglu, P. Lundqvist, P. A., Mazzali, U. Munari, M. D. Stritzinger, L. Tomasella

TL;DR
This paper reports on the detailed observation and analysis of the luminous red nova AT 2019zhd in M 31, revealing its light curve, spectral evolution, and likely binary merger origin, contributing to understanding stellar mergers.
Contribution
It provides the first detailed follow-up of AT 2019zhd, including light curves, spectra, and archival data, establishing it as a stellar merger event similar to other LRNe.
Findings
Peak luminosity of M_r=-9.61 mag
Spectral evolution from blue continuum to M-type star features
Archival data suggest a binary system with an M5-type star
Abstract
We present the follow-up campaign of the luminous red nova (LRN) AT~2019zhd, the third event of this class observed in M 31. The object was followed by several sky surveys for about five months before the outburst, during which it showed a slow luminosity rise. In this phase, the absolute magnitude ranged from M_r=-2.8+-0.2 mag to M_r=-5.6+-0.1 mag. Then, over a four-five day period, AT 2019zhd experienced a major brightening, reaching at peak M_r=-9.61+-0.08 mag, and an optical luminosity of 1.4x10^39 erg/s. After a fast decline, the light curve settled onto a short-duration plateau in the red bands. Although less pronounced, this feature is reminiscent of the second red maximum observed in other LRNe. This phase was followed by a rapid linear decline in all bands. At maximum, the spectra show a blue continuum with prominent Balmer emission lines. The post-maximum spectra show a much…
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Taxonomy
TopicsAstrophysical Phenomena and Observations · Gamma-ray bursts and supernovae · Pulsars and Gravitational Waves Research
