The luminous red nova AT 2018bwo in NGC 45 and its binary yellow supergiant progenitor

Abstract

Luminous Red Novae (LRNe) are astrophysical transients associated with the partial ejection of a binary system's common envelope (CE) shortly before its merger. Here we present the results of our photometric and spectroscopic follow-up campaign of AT2018bwo (DLT18x), a LRN discovered in NGC45, and investigate its progenitor system using binary stellar-evolution models. The transient reached a peak magnitude of $M_r=-10.97\pm 0.11$ and maintained this brightness during its optical plateau of $t_p=41\pm 5$days. During this phase, it showed a rather stable photospheric temperature of ~3300K and a luminosity of ~$10^{40}$erg/s. The photosphere of AT2018bwo at early times appeared larger and cooler than other similar LRNe, likely due to an extended mass-loss episode before the merger. Towards the end of the plateau, optical spectra showed a reddened continuum with strong molecular absorption bands. The reprocessed emission by the cooling dust was also detected in the mid-infrared bands ~1.5 years after the outburst. Archival Spitzer and Hubble Space Telescope data taken 10-14 years before the transient event suggest a progenitor star with $T_{prog}\sim 6500$K, $R_{prog}\sim 100R_{\odot }$ and $L_{prog}\sim 2\times 10^4{L}_{\odot }$, and an upper limit for optically thin warm (1000 K) dust mass of $M_d<10^{-6}{M}_{\odot }$. Using stellar binary-evolution models, we determined the properties of binary systems consistent with the progenitor parameter space. For AT2018bwo, we infer a primary mass of 12-16 $M_{\odot }$, which is 9-45% larger than the ~11$M_{\odot }$ obtained using single-star evolution models. The system, consistent with a yellow-supergiant primary, was likely in a stable mass-transfer regime with -2.4<log ($\dot{M}/M_{\odot }$/yr)<-1.2 a decade before the main instability occurred. During the dynamical merger, the system would have ejected 0.15-0.5$M_{\odot }$ with a velocity of ~500 km/s.

21 pages, 16 figures, accepted version for A&A

References in corpus (33)

• Modules for Experiments in Stellar Astrophysics (MESA)
• Binary interaction dominates the evolution of massive stars
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• Initial Performance of the NEOWISE Reactivation Mission
• PESSTO : survey description and products from the first data release by the Public ESO Spectroscopic Survey of Transient Objects
• How mergers magnetise massive stars
• Efficiency of mass transfer in massive close binaries, Tests from double-lined eclipsing binaries in the SMC
• The 2008 Luminous Optical Transient in the Nearby Galaxy NGC 300
• Stellar Mergers Are Common
• The Triple-Ring Nebula around SN1987A: Fingerprint of a binary merger
• Mass Transfer from Giant Donors
• Gaia Photometric Science Alerts
• Shock-powered light curves of luminous red novae as signatures of pre-dynamical mass loss in stellar mergers
• Evolution of Mass Functions of Coeval Stars through Wind Mass Loss and Binary Interactions
• Massive donors in interacting binaries: effect of metallicity
• The X-Shooter Spectral Library (XSL): Data Release 2
• A Spitzer/IRS Spectrum of the 2008 Luminous Transient in NGC 300: Connection to Proto-Planetary Nebulae
• Luminous Red Novae: population models and future prospects
• A Luminous Red Nova in M31 and its Progenitor System
• A new survey of cool supergiants in the Magellanic Clouds
• The transitional gap transient AT 2018hso: new insights on the luminous red nova phenomenon
• The thermal equilibrium mass loss model and its applications in binary evolution
• The VLT-FLAMES Tarantula Survey. XXX. Red stragglers in the clusters Hodge 301 and SL 639
• A Young Stellar Cluster Surrounding the Peculiar Eruptive Variable V838 Monocerotis
• Evolution of the stellar-merger red nova V1309 Scorpii: SED analysis
• The Value of Progenitor Radius Measurements for Explosion Modeling of Type II-Plateau Supernovae
• SN Hunt 248: a super-Eddington outburst from a massive cool hypergiant
• Luminous Red Nova AT 2019zhd, a new merger in M 31
• The January 2015 outburst of a red nova in M31
• The Evolution of Luminous Red Nova AT 2017jfs in NGC 4470
• The luminous red nova variety: AT 2020hat and AT 2020kog
• The Carnegie Supernova Project II. Observations of the luminous red nova AT 2014ej
• SiO maser astrometry of the red transient V838 Monocerotis

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