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

Blagorodnova, Nadejda and Klencki, Jakub and Pejcha, Ondrej and Vreeswijk, Paul M. and Bond, Howard E. and Burdge, Kevin B. and De, Kishalay and Fremling, Christoffer and Gehrz, Robert D. and Jencson, Jacob E. and Kasliwal, Mansi M. and Kupfer, Thomas and Lau, Ryan M. and Masci, Frank J. and Rich, Michael R. (2021) The luminous red nova AT 2018bwo in NGC 45 and its binary yellow supergiant progenitor. . (Unpublished)

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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 ± 0.11 and maintained this brightness during its optical plateau of t_p = 41 ± 5days. During this phase, it showed a rather stable photospheric temperature of ~3300K and a luminosity of ~10⁴⁰ erg s⁻¹. 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) ∼ 6500K, R_(prog) ∼ 100 R_⊙ and L_(prog) ∼ 2 × 10⁴ L_⊙, and an upper limit for optically thin warm (1000 K) dust mass of M_d < 10⁻⁶ M_⊙. 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_⊙, which is 9-45% larger than the ~11M⊙ 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 (Ṁ/M_⊙ yr⁻¹) < -1.2 a decade before the main instability occurred. During the dynamical merger, the system would have ejected 0.15-0.5M⊙ with a velocity of ~500 km s⁻¹.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
Blagorodnova, Nadejda0000-0003-0901-1606
Vreeswijk, Paul M.0000-0002-7572-9088
Bond, Howard E.0000-0003-1377-7145
Burdge, Kevin B.0000-0002-7226-836X
De, Kishalay0000-0002-8989-0542
Fremling, Christoffer0000-0002-4223-103X
Gehrz, Robert D.0000-0003-1319-4089
Jencson, Jacob E.0000-0001-5754-4007
Kasliwal, Mansi M.0000-0002-5619-4938
Kupfer, Thomas0000-0002-6540-1484
Masci, Frank J.0000-0002-8532-9395
Additional Information:The authors would like to thank the members of the Stellar Evolution group at Radboud University, Tomasz Kamiński and Morgan MacLeod for useful discussions; to Søren Larsen and Esteban Silva-Villa for sharing their photometric catalogues. This work is part of the research programme VENI, with project number 016.192.277, which is (partly) financed by the Netherlands Organisation for Scientific Research (NWO). This work was supported by the GROWTH project funded by the National Science Foundation (NSF) under grant AST-1545949. The research of OP has been supported by Horizon 2020 ERC Starting Grant ‘Cat-In-hAT’ (grant agreement no. 803158). RDG was supported, in part, by the United States Air Force. J.K. acknowledges support from the Netherlands Organisation for Scientific Research (NWO). Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration (NASA); the observatory was made possible by the generous financial support of the W. M. Keck Foundation. We acknowledge ESA Gaia, DPAC and the Photometric Science Alerts Team ( This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project. ATLAS is primarily funded to search for near earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen’s University Belfast, the Space Telescope Science Institute, and the South African Astronomical Observatory. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by NASA and the NSF. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by NASA. This work makes use of observations from the Las Cumbres Observatory global telescope network. Based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESAC/ESA) and the Canadian Astronomy Data Centre (CADC/NRC/CSA).
Subject Keywords:binaries: general – novae, cataclysmic variables – Stars: flare – Stars: individual: AT 2018bwo– Stars: winds, outflows – Stars: evolution
Record Number:CaltechAUTHORS:20210520-145947094
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109211
Deposited By: George Porter
Deposited On:24 May 2021 19:23
Last Modified:24 May 2021 19:23

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