Luminous Red Novae: Stellar Mergers or Giant Eruptions?
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Author/sPastorello, A.; Mason, E.; Taubenberger, S.; Fraser, M.; Cortini, G.; Tomasella, L.; Botticella, M.T.; Elias-Rosa, N.; Kotak, R.; Smartt, S.J.; Benetti, S.; Cappellaro, E.; Turatto, M.; Tartaglia, L.; Djorgovski, S.G.; Drake, A.J.; Berton, M.; Briganti, F.; Brimacombe, J.; Bufano, F.; Cai, Y.-Z.; Chen, S.; Christensen, E.J.; Ciabattari, F.; Congiu, E.; Dimai, A.; Inserra, C.; Kankare, E.; Magill, L.; Maguire, K.; Martinelli, F.; Morales-Garoffolo, A.; Ochner, P.; Pignata, G.; Reguitti, A.; Sollerman, J.; Spiro, S.; Terreran, G.; Wright, D.E.
SourceAstronomy & Astrophysics (A&A) Volume 630, October 2019 A75
We present extensive datasets for a class of intermediate-luminosity optical transients known as luminous red novae. They show double-peaked light curves, with an initial rapid luminosity rise to a blue peak (at -13 to -15 mag), which is followed by a longer-duration red peak that sometimes is attenuated, resembling a plateau. The progenitors of three of them (NGC 4490-2011OT1, M 101-2015OT1, and SNhunt248), likely relatively massive blue to yellow stars, were also observed in a pre-eruptive stage when their luminosity was slowly increasing. Early spectra obtained during the first peak show a blue continuum with superposed prominent narrow Balmer lines, with P Cygni profiles. Lines of Fe II are also clearly observed, mostly in emission. During the second peak, the spectral continuum becomes much redder, H alpha is barely detected, and a forest of narrow metal lines is observed in absorption. Very late-time spectra (similar to 6 months after blue peak) show an extremely red spectral continuum, peaking in the infrared (IR) domain. H alpha is detected in pure emission at such late phases, along with broad absorption bands due to molecular overtones (such as TiO, VO). We discuss a few alternative scenarios for luminous red novae. Although major instabilities of single massive stars cannot be definitely ruled out, we favour a common envelope ejection in a close binary system, with possibly a final coalescence of the two stars. The similarity between luminous red novae and the outburst observed a few months before the explosion of the Type IIn SN 2011ht is also discussed.