The transitional gap transient AT 2018hso: new insights into the luminous red nova phenomenon
Pastorello; E.; Elias-Rosa; C.; Cannizzaro; S. J.; Cappellaro; F.; T. M.; Valerin; F. J.; Y. -Z.; Galindo-Guil; S. Onori; Callis; M.; Heikkilä; Reguitti; Benetti; N.; Sagués Carracedo; Gromadzki; Fraser; Cai; Reynolds; Prentice; T.; Mason; A.; Gall; S.; Fiore; G.; Morales-Garoffolo; Moran; Brennan
https://urn.fi/URN:NBN:fi-fe2021042824842
Tiivistelmä
Context. The absolute magnitudes of luminous red novae (LRNe) are
intermediate between those of novae and supernovae (SNe), and show a
relatively homogeneous spectro-photometric evolution. Although they were
thought to derive from core instabilities in single stars, there is
growing support for the idea that they are triggered by binary
interaction that possibly ends with the merging of the two stars.
Aims: AT 2018hso
is a new transient showing transitional properties between those of
LRNe and the class of intermediate-luminosity red transients (ILRTs)
similar to SN 2008S. Through the detailed analysis of
the observed parameters, our study supports that it actually belongs to
the LRN class and was likely produced by the coalescence of two massive
stars.
Methods: We obtained ten months of optical and
near-infrared photometric monitoring, and 11 epochs of low-resolution
optical spectroscopy of AT 2018hso. We compared its
observed properties with those of other ILRTs and LRNe. We also
inspected the archival Hubble Space Telescope (HST) images obtained
about 15 years ago to constrain the progenitor properties.
Results: The light curves of AT 2018hso show a first sharp peak (reddening-corrected Mr
= -13.93 mag), followed by a broader and shallower second peak that
resembles a plateau in the optical bands. The spectra dramatically
change with time. Early-time spectra show prominent Balmer emission
lines and a weak [Ca II] doublet, which is usually observed in ILRTs.
However, the strong decrease in the continuum temperature, the
appearance of narrow metal absorption lines, the great change in the Hα
strength and profile, and the emergence of molecular bands support an
LRN classification. The possible detection of a MI ̃ -8 mag source at the position of AT 2018hso
in HST archive images is consistent with expectations for a pre-merger
massive binary, similar to the precursor of the 2015 LRN in M101.
Conclusions: We provide reasonable arguments to support an LRN classification for AT 2018hso.
This study reveals growing heterogeneity in the observables of LRNe
than has been thought previously, which is a challenge for
distinguishing between LRNe and ILRTs. This suggests that the entire
evolution of gap transients needs to be monitored to avoid
misclassifications.
Kokoelmat
- Rinnakkaistallenteet [19207]