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Forbidden hugs in pandemic times I. Luminous red nova AT 2019zhd, a new merger in M 31

Pastorello, A. (author)
Fraser, M. (author)
Valerin, G. (author)
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Reguitti, A. (author)
Itagaki, K. (author)
Ochner, P. (author)
Williams, S. C. (author)
Jones, D. (author)
Munday, J. (author)
Smartt, S. J. (author)
Smith, K. W. (author)
Srivastav, S. (author)
Elias-Rosa, N. (author)
Kankare, E. (author)
Karamehmetoglu, E. (author)
Lundqvist, Peter (author)
Stockholms universitet,Institutionen för astronomi,Oskar Klein-centrum för kosmopartikelfysik (OKC)
Mazzali, P. A. (author)
Munari, U. (author)
Stritzinger, M. D. (author)
Tomasella, L. (author)
Anderson, J. P. (author)
Chambers, K. C. (author)
Rest, A. (author)
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 (creator_code:org_t)
2021-02-17
2021
English.
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 646
Related links:
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  • Journal article (peer-reviewed)
Abstract Subject headings
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  • 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 to five day period, AT 2019zhd experienced a major brightening, reaching a peak of M-r=-9.61 +/- 0.08 mag and an optical luminosity of 1.4x10(39) erg s(-1). 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 redder continuum, resembling that of an intermediate-type star. In this phase, H alpha becomes very weak, H beta is no longer detectable, and a forest of narrow absorption metal lines now dominate the spectrum. The latest spectra, obtained during the post-plateau decline, show a very red continuum (T-eff approximate to 3000 K) with broad molecular bands of TiO, similar to those of M-type stars. The long-lasting, slow photometric rise observed before the peak resembles that of LRN V1309 Sco, which was interpreted as the signature of the common-envelope ejection. The subsequent outburst is likely due to the gas outflow following a stellar merging event. The inspection of archival HST images taken 22 years before the LRN discovery reveals a faint red source (M-F555W=0.21 +/- 0.14 mag, with F555W-F814W=2.96 +/- 0.12 mag) at the position of AT 2019zhd, which is the most likely quiescent precursor. The source is consistent with expectations for a binary system including a predominant M5-type star.

Subject headings

NATURVETENSKAP  -- Fysik (hsv//swe)
NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

Keyword

binaries: close
stars: winds
outflows
stars: individual: AT 2019zhd
stars: individual: M31-LRN2015
stars: individual: M31-RV
stars: individual: V838 Mon

Publication and Content Type

ref (subject category)
art (subject category)

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