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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. Astronomy and Astrophysics, 653 . Art. No. A134. ISSN 0004-6361. doi:10.1051/0004-6361/202140525.

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Luminous red novae (LRNe) are astrophysical transients associated with the partial ejection of a binary system’s common envelope shortly before its merger. Here we present the results of our photometric and spectroscopic follow-up campaign of AT 2018bwo (DLT 18x), a LRN discovered in NGC 45, 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 ± 5 days. During this phase, it showed a rather stable photospheric temperature of ∼3300 K and a luminosity of ∼10⁴⁰ erg s⁻¹. Although the luminosity and duration of AT 2018bwo is comparable to the LRNe V838 Mon and M31-2015LRN, its photosphere at early times appears larger and cooler, likely due to an extended mass-loss episode before the merger. Toward the end of the plateau, optical spectra showed a reddened continuum with strong molecular absorption bands. The IR spectrum at +103 days after discovery was comparable to that of a M8.5 II type star, analogous to an extended AGB star. 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 yrs before the transient event suggest a progenitor star with T_(prog) ∼ 6500 K, 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 AT 2018bwo, we infer a primary mass of 12–16 M⊙, which is 9–45% larger than the ∼11 M⊙ 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 0.15–0.5 M⊙ with a velocity of ∼500 km s⁻¹.

Item Type:Article
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URLURL TypeDescription Paper
Blagorodnova, Nadejda0000-0003-0901-1606
Klencki, Jakub0000-0002-7527-5741
Pejcha, Ondrej0000-0003-2512-2170
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
Rich, Michael R.0000-0003-0427-8387
Additional Information:© ESO 2021. Article published by EDP Sciences. Received 10 February 2021; Accepted 16 June 2021; Published online 23 September 2021. 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 catalogs. 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).
Funding AgencyGrant Number
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)016.192.277
European Research Council (ERC)803158
United States Air ForceUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:binaries: general – novae, cataclysmic variables – stars: individual: AT 2018bwo – stars: winds, outflows – stars: evolution – stars: flare
Record Number:CaltechAUTHORS:20210520-145947094
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Official Citation:The luminous red nova AT 2018bwo in NGC 45 and its binary yellow supergiant progenitor. Nadejda Blagorodnova, Jakub Klencki, Ondřej Pejcha, Paul M. Vreeswijk, Howard E. Bond, Kevin B. Burdge, Kishalay De, Christoffer Fremling, Robert D. Gehrz, Jacob E. Jencson, Mansi M. Kasliwal, Thomas Kupfer, Ryan M. Lau, Frank J. Masci and Michael R. Rich. A&A, 653 (2021) A134; DOI:
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:28 Sep 2021 17:02

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