In:
Astronomy & Astrophysics, EDP Sciences, Vol. 653 ( 2021-09), p. A134-
Abstract:
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 ∼10 40 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 × 10 4 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 .
Type of Medium:
Online Resource
ISSN:
0004-6361
,
1432-0746
DOI:
10.1051/0004-6361/202140525
Language:
English
Publisher:
EDP Sciences
Publication Date:
2021
detail.hit.zdb_id:
1458466-9
SSG:
16,12
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