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Observations of the luminous red nova AT 2021biy in the nearby galaxy NGC 4631: Forbidden hugs in pandemic times - III

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arXiv 2022年

作者： Cai, Yong Zhi Pastorello, A. Fraser, M. Wang, X.-F. Filippenko, A.V. Reguitti, A. Patra, K.C. Goranskij, V.P. Barsukova, E.A. Brink, T.G. Elias-Rosa, N. Stevance, H.F. Zheng, W. Yang, Y. Atapin, K.E. Benetti, S. De Boer, T.J.L. Bose, S. Burke, J. Byrne, R. Cappellaro, E. Chambers, K.C. Chen, W.-L. Emami, N. Gao, H. Hiramatsu, D. Howell, D.A. Huber, M.E. Kankare, E. Kelly, P.L. Kotak, R. Kravtsov, T. Lander, V.Yu. Li, Z.-T. Lin, C.-C. Lundqvist, P. Magnier, E.A. Malygin, E.A. Maslennikova, N.A. Matilainen, K. Mazzali, P.A. McCully, C. Mo, J. Moran, S. Newsome, M. Oparin, D.V. Padilla Gonzalez, E. Reynolds, T.M. Shatsky, N.I. Smartt, S.J. Smith, K.W. Stritzinger, M.D. Tatarnikov, A.M. Terreran, G. Uklein, R.I. Valerin, G. Vallely, P.J. Vozyakova, O.V. Wainscoat, R. Yan, S.-Y. Zhang, J.-J. Zhang, T.-M. Zheltoukhov, S.G. Dastidar, R. Fulton, M. Galbany, L. Gangopadhyay, A. Ge, H.-W. Gutiérrez, C.P. Lin, H. Misra, K. Ou, Z.-W. Salmaso, I. Tartaglia, L. Xiao, L. Zhang, X.-H. Tsinghua University Beijing100084 China Inaf - Osservatorio Astronomico di Padova Vicolo dell'Osservatorio 5 Padova35122 Italy School of Physics O'Brien Centre for Science North University College Dublin Dublin 4 Belfield Ireland Beijing Planetarium Beijing Academy of Science and Technology Beijing100044 China Department of Astronomy University of California BerkeleyCA94720-3411 United States Departamento de Ciencias Fisicas Universidad Andres Bello Fernandez Concha 700 Santiago Las Condes Chile Nuncio Monsenor Sòtero Sanz 100 Santiago Providencia8320000 Chile Nagaraj-Noll-Otelline Sternberg Astronomical Institute of the Moscow State University Moscow119234 Russia Special Astrophysical Observatory Russian Academy of Sciences Nizhnij Arkhyz 369167 Russia Campus UAB Carrer de Can Magrans s/n BarcelonaE-08193 Spain The Department of Physics The University of Auckland Private Bag 92019 Auckland New Zealand Astrophysics Research Centre School of Mathematics and Physics Queen's University Belfast Northern Ireland BelfastBT7 1NN United Kingdom Institute for Astronomy University of Hawaii 2680 Woodlawn Drive HonoluluHI96822 United States Department of Astronomy The Ohio State University 140 W. 18th Avenue ColumbusOH43210 United States The Ohio State University 191 W.Woodruff Avenue ColumbusOH43210 United States Las Cumbres Observatory 6740 Cortona Dr. Suite 102 GoletaCA93117 United States Department of Physics University of California Santa Barbara Santa BarbaraCA93106 United States Center for Astrophysics Harvard & Smithsonian 60 Garden Street CambridgeMA02138-1516 United States The Nsf Ai Institute for Artificial Intelligence and Fundamental Interactions United States School of Physics and Astronomy University of Minnesota 116 Church Street SE MinneapolisMN55455 United States Department of Physics and Astronomy University of Turku TurkuFI-20014 Finland Turku Collegium for Science Medicine and Technology University

We present an observational study of the luminous red nova (LRN) AT 2021biy in the nearby galaxy NGC 4631. The field of the object was routinely imaged during the pre-eruptive stage by synoptic surveys, but the transient was detected only at a few epochs from ∼ 231 days before maximum brightness. The LRN outburst was monitored with unprecedented cadence both photometrically and spectroscopically. AT 2021biy shows a short-duration blue peak, with a bolometric luminosity of ∼ 1.6×1041erg s-1, followed by the longest plateau among LRNe to date, with a duration of 210 days. A late-time hump in the light curve was also observed, possibly produced by a shell-shell collision. AT 2021biy exhibits the typical spectral evolution of LRNe. Early-time spectra are characterised by a blue continuum and prominent H emission lines. Then, the continuum becomes redder, resembling that of a K-type star with a forest of metal absorption lines during the plateau phase. Finally, late-time spectra show a very red continuum (TBB≈ 2050 K) with molecular features (e.g. TiO) resembling those of M-type stars. Spectropolarimetric analysis indicates that AT 2021biy has local dust properties similar to those of V838 Mon in the Milky Way Galaxy. Inspection of archival Hubble Space Telescope data taken on 2003 August 3 reveals a ∼ 20 Moprogenitor candidate with log (L/Lo) = 5.0 dex and Teff= 5900 K at solar metallicity. The above luminosity and colour match those of a luminous yellow supergiant. Most likely, this source is a close binary, with a 17-24 Moprimary component. Copyright © 2022, The Authors. All rights reserved.

关键词： Luminance

A mixture evolution scenario of the agn radio luminosity function. II. Do low- and high-power radio-loud agns evolve differently

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arXiv 2017年

作者： Yuan, Zunli Wang, Jiancheng Zhou, Ming Qin, Longhua Mao, Jirong Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing100012 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China University of Chinese Academy of Sciences Beijing100049 China

Following previous work, we further confirm that the cosmic evolution of steep-spectrum radio-loud AGNs (active galactic nuclei) can be reproduced by a simple combination of density evolution (DE) and luminosity evolution (LE). This mixture evolution scenario can naturally explain the luminosity-dependent evolution of radio-loud AGNs. Our models successfully fitted a large amount of data on radio luminosity functions (RLFs) of steep-spectrum sources and multi-frequency source counts. The modeling indicates that the DE slowly increase as (1 + z)0.3∼1.3 out to z ∼ 0.8, and then rapidly decreases as (1 + z)−6.8∼−5.7, while the LE rapidly increase as (1 + z)4.8 out to a higher redshift (at least z > 3.5). We find a high-redshift decline (i.e. redshift cutoff) in the number density of steep-spectrum radio sources, but we cannot conclude whether such decline is sharp or shallow. We believe that whether a redshift cutoff occurs or not depends mainly on DE, while its steepness is decided by LE, which, however, cannot be well constrained due to the lack of high-redshift samples. Most intriguingly, according to our mixture evolution scenario, there appears to be no need for different evolution for the low- and high-power radio-loud AGNs. Both types of sources experience the same combined evolution of DE and LE. Copyright © 2017, The Authors. All rights reserved.

关键词： Luminance

Merging of a CO WD and a He-rich white dwarf to produce a type Ia supernovae

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arXiv 2017年

作者： Liu, D. Wang, B. Wu, C. Han, Z. Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China University of Chinese Academy of Sciences Beijing100049 China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing100012 China

Context. Although type Ia supernovae (SNe Ia) play a key role in astrophysics, the companions of the exploding carbon-oxygen white dwarfs (CO WDs) are still not completely identified. It has been suggested recently that a He-rich WD (a He WD or a hybrid HeCO WD) that merges with a CO WD may produce an SN Ia. This theory was based on the double-detonation model, in which the shock compression in the CO core caused by the surface explosion of the He-rich shell might lead to the explosion of the whole CO WD. However, so far, very few binary population synthesis (BPS) studies have been made on the merger scenario of a CO WD and a He-rich WD in the context of SNe Ia. Aims. We aim to systematically study the Galactic birthrates and delay-time distributions of SNe Ia based on the merger scenario of a CO WD and a He-rich WD. Methods. We performed a series of Monte Carlo BPS simulations to investigate the properties of SNe Ia from the merging of a CO WD and a He-rich WD based on the Hurley rapid binary evolution code. We also considered the influence of different metallicities on the final results. Results. From our simulations, we found that no more than 15% of all SNe Ia stem from the merger scenario of a CO WD and a He-rich WD, and their delay times range from ∼110 Myr to the Hubble time. This scenario mainly contributes to SN Ia explosions with intermediate and long delay times. The present work indicates that the merger scenario of a CO WD and a He-rich WD can roughly reproduce the birthrates of SN 1991bg-like events, and cover the range of their delay times. We also found that SN Ia birthrates from this scenario would be higher for the cases with low metallicities. Copyright © 2017, The Authors. All rights reserved.

关键词： White dwarfs

Populations of accreting white dwarfs

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arXiv 2018年

作者： Chen, Hai-Liang Woods, Tyrone E. Yungelson, Lev Gilfanov, Marat Han, Zhanwen Yunnan Observatories CAS Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650011 China Center for Astronomical Mega-Science Chinese Academy of Science Beijing100012 China Institute of Gravitational Wave Astronomy School of Physics and Astronomy University of Birmingham BirminghamB15 2TT United Kingdom Institute of Astronomy RAS 48 Pyatnitskaya Str. Moscow119017 Russia Max Planck Institute for Astrophysics Karl-Schwarzschild-Str. 1 Garching b. München85741 Germany Space Research Institute of Russian Academy of Sciences Profsoyuznaya 84/32 Moscow117997 Russia

Using a hybrid binary population synthesis approach, we modelled the formation and evolution of populations of accreting WDs for differing star formation histories. We found that the delay time distribution of SNe Ia in the single degenerate scenario is inconsistent with observations. Additionally, we found that our predicted X-ray and UV emission of populations of accreting WDs are consistent with the X-ray luminosities of early-type galaxies observed by Chandra and the HeII 4686Å/Hβ line ratio measured in stacked SDSS spectra of passively evolving galaxies. Moreover, we found that the majority of current novae in elliptical-like galaxies have low-mass WDs, long decay times, long recurrence periods and are relatively faint. In contrast, the majority of current novae in spiral-like galaxies have massive WDs, short decay times, short recurrence periods and are relatively bright. Our predicted distribution of mass-loss timescales in an M31-like galaxy is consistent with observations for Andromeda. Copyright © 2018, The Authors. All rights reserved.

关键词： Galaxies

Photometric Analysis of the eclipsing Polar MN Hya

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arXiv 2018年

作者： Wang, Qi-Shan Qian, Sheng-Bang Han, Zhong-Tao Zejda, Miloslav Fernández-Lajus, Eduardo Zhu, Li-Ying P. O. Box 110 Kunming650216 China Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences P. O. Box 110 Kunming650216 China University of Chinese Academy of Sciences Yuquan Road 19# Sijingshang Block Beijing100049 China Department of Theoretical Physics and Astrophysics Masaryk University Kotlár ská 2 Brno611 37 Czech Republic Facultad de Ciencias Astronómicas y Geofísicas Universidad Nacional de La Plata Paseo del Bosque s/n La Plata Pcia. Bs. As1900 Argentina Argentina

As an eclipsing polar with 3.39 hrs orbital period, MN Hya was going through state change when we observed it during 2009-2016. 10 new mid-eclipse times, along with others obtained from literature, allow us to give a new ephemeris. The residuals of linear fit show that period decreased during the phase of state change. It means angular momentum was lost during this phase. The X-ray observation indicates the mass accretion rate as about 3.6 × 10−9M☉yr−1. The period decrease gives that at least 60 percent of mass being transfered from secondary was lost, maybe in form of the spherically symmetric stellar wind. In high state, the data shows the intensity of the flickering reduced when system had higher accretion rate, and that flickering sticks out with primary timescale about 2 minutes, which implies the position of the threading point as about 30 radius of the white dwarf above the surface of it. The trend of light curves of the system in high state follows that of low state for a large fraction of phase interval from phase 0 to phase 0.4 since which the cyclotron feature is visible, and the primary intensity hump of light curves near phase 0.7 when the system is in high state did not appear on the curve when it is in low state. Those facts contradict the predictions of the two-pole model. Copyright © 2018, The Authors. All rights reserved.

关键词： Flickering

Kinematic properties of the dual AGN system J0038+4128 based on long-slit spectroscopy

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Research in Astronomy and Astrophysics 2016年第3期16卷 43-50页

作者： Yang-Wei Zhang Yang Huang Jin-Ming Bai Xiao-Wei Liu Jian-Guo Wang Yunnan Observatories Chinese Academy of SciencesKunming 650011China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650011China Department of Astronomy Peking UniversityBeijing 100871China Kavli Institute for Astronomy and Astrophysics Peking UniversityBeijing 100871China University of Chinese Academy of Sciences Beijing 100049China

The study ofkiloparsec-scale dual active galactic nuclei （AGN） provides important clues for understanding the co-evolution between host galaxies and their central supermassive black holes undergoing a merging process. We present long-slit spectroscopy of J0038 ＋4128, a kiloparsec-scale dual AGN candidate, discovered recently by Huang et al., using the Yunnan Faint Object Spectrograph and Camera （YFOSC） mounted on the Lijiang 2.4-m telescope administered by Yunnan Observatories. From the long-slit spectra, we find that the average relative line-of-sight （LOS） velocity between the two nuclei （J0038＋4128N and J0038＋4128S） is about 150 km s-1. The LOS velocities of the emission lines from the gas ionized by the nuclei activities and of the absorption lines from stars governed by the host galaxies for different regions of J0038＋4128 exhibit the same trend. The same trend in velocities indicates that the gaseous disks are co-rotating with the stellar disks in this ongoing merging system. We also find several knots/giant H II regions scattered around the two nuclei with strong star formation revealed by the observed line ratios from the spectra. Those regions are also clearly detected in images from HST F336W/U-band and HST F555W/V-band.

关键词： techniques： spectroscopic -- galaxies： kinematics and dynamics -- galaxies： active -- galax- ies： interactions -- galaxies： nuclei -- galaxies： individual （J0038＋4128）

Small fire smoke region location and recognition in satellite image 9

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Small fire smoke region location and recognition in satellit...

9th International Congress on Image and Signal Processing, BioMedical Engineering and Informatics, CISP-BMEI 2016

作者： Miao, Sheng Hu, Kunrong Gao, Hao Wang, Xiaorui Southwest Forestry University Kunming China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming China Radio Astronomy Research Group Yunnan Observatory of Chinese Academy of Science Kunming China

ISBN: (纸本)9781509037100

Since ancient times, forest fires are an important threat to human beings, with the development of satellite technology, forest fires can be constantly monitored by satellite. But face to number of satellite pictures, its hard to detect fire location, especially the fire initial stage. An sub-region detection method has been proposed, this method supply fast partition domain detection method using information entropy, fast detect each sub-region whether there is smoke feature or not. Due to the satellite image has large region, our method first segment the image and then detect the smoke feature in each sub-region using information entropy. More than 50 pictures has been used to test this methods, shows this algorithm the effectiveness of small range fire detection. © 2016 IEEE.

关键词： Smoke

The broad-lined Type-Ic supernova SN 2022xxf with extraordinary two-humped light curves

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arXiv 2023年

作者： Kuncarayakti, H. Sollerman, J. Izzo, L. Maeda, K. Yang, S. Schulze, S. Angus, C.R. Aubert, M. Auchettl, K. Della Valle, M. Dessart, L. Hinds, K. Kankare, E. Kawabata, M. Lundqvist, P. Nakaoka, T. Perley, D. Raimundo, S.I. Strotjohann, N.L. Taguchi, K. Cai, Y.-Z. Charalampopoulos, P. Fang, Q. Fraser, M. Gutiérrez, C.P. Imazawa, R. Kangas, T. Kawabata, K.S. Kotak, R. Kravtsov, T. Matilainen, K. Mattila, S. Moran, S. Murata, I. Salmaso, I. Anderson, J.P. Ashall, C. Bellm, E.C. Benetti, S. Chambers, K.C. Chen, T.-W. Coughlin, M. De Colle, F. Fremling, C. Galbany, L. Gal-Yam, A. Gromadzki, M. Groom, S.L. Hajela, A. Inserra, C. Kasliwal, M.M. Mahabal, A.A. Martin-Carrillo, A. Moore, T. Müller-Bravo, T.E. Nicholl, M. Ragosta, F. Riddle, R.L. Sharma, Y. Srivastav, S. Stritzinger, M.D. Wold, A. Young, D.R. Tuorla Observatory Department of Physics and Astronomy University of Turku FI-20014 Finland University of Turku FI-20014 Finland Department of Astronomy Oskar Klein Centre AlbaNova Stockholm10691 Sweden DARK Niels Bohr Institute University of Copenhagen Copenhagen Denmark Department of Astronomy Kyoto University Kitashirakawa-Oiwake-cho Sakyo-ku Kyoto606-8502 Japan Henan Academy of Sciences Henan Zhengzhou450046 China The Oskar Klein Centre Department of Physics Stockholm University AlbaNova University Center StockholmSE 106 91 Sweden Université Clermont Auvergne CNRS IN2P3 LPC Clermont-Ferrand France School of Physics The University of Melbourne ParkvilleVIC3010 Australia Sydney2006 Australia Department of Astronomy and Astrophysics University of California Santa CruzCA95064 United States Capodimonte Astronomical Observatory INAF-Napoli Salita Moiariello 16 NapoliI-80131 Italy Institut d’Astrophysique de Paris CNRS-Sorbonne Université 98 bis boulevard Arago ParisF-75014 France Astrophysics Research Institute Liverpool John Moores University IC2 Liverpool Science Park 146 Brownlow Hill LiverpoolL3 5RF United Kingdom Turku Collegium for Science Medicine and Technology University of Turku TurkuFI-20014 Finland Hiroshima Astrophysical Science Center Hiroshima University 1-3-1 Kagamiyama Higashi-Hiroshima Hiroshima739-8526 Japan Department of Physics and Astronomy University of California Los AngelesCA United States Department of Physics & Astronomy University of Southampton Southampton United Kingdom Benoziyo Center for Astrophysics The Weizmann Institute of Science Rehovot76100 Israel Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China School of Physics O’Brien Centre for Science North University College Dublin Belfield Dublin 4 Dublin Ireland Department of Physics Graduate School

We report on our study of supernova (SN) 2022xxf based on observations obtained during the first four months of its evolution. The light curves (LCs) display two humps of similar maximum brightness separated by 75 days, unprecedented for a broad-lined (BL) Type Ic supernova (SN IcBL). SN 2022xxf is the most nearby SN IcBL to date (in NGC 3705, z = 0.0037, at a distance of about 20 Mpc). Optical and near-infrared photometry and spectroscopy are used to identify the energy source powering the LC. Nearly 50 epochs of high signal-to-noise-ratio spectroscopy were obtained within 130 days, comprising an unparalleled dataset for a SN IcBL, and one of the best-sampled SN datasets to date. The global spectral appearance and evolution of SN 2022xxf points to typical SN Ic/IcBL, with broad features (up to ∼ 14000 km s−1) and a gradual transition from the photospheric to the nebular phase. However, narrow emission lines (corresponding to ∼ 1000−2500 km s−1) are present in the spectra from the time of the second rise, suggesting slower-moving circumstellar material (CSM). These lines are subtle, in comparison to the typical strong narrow lines of CSM-interacting SNe, for example, Type IIn, Ibn, and Icn, but some are readily noticeable at late times such as in Mg I λ5170 and [O I] λ5577. Unusually, the near-infrared spectra show narrow line peaks in a number of features formed by ions of O and Mg. We infer the presence of CSM that is free of H and He. We propose that the radiative energy from the ejecta-CSM interaction is a plausible explanation for the second LC hump. This interaction scenario is supported by the color evolution, which progresses to the blue as the light curve evolves along the second hump, and the slow second rise and subsequent rapid LC drop. SN 2022xxf may be related to an emerging number of CSM-interacting SNe Ic, which show slow, peculiar LCs, blue colors, and subtle CSM interaction lines. The progenitor stars of these SNe likely experienced an episode of m

关键词： Supernovae

Forbidden hugs in pandemic times: IV. Panchromatic evolution of three luminous red novae

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Astronomy and Astrophysics 2023年 671卷

作者： Pastorello, A. Valerin, G. Fraser, M. Reguitti, A. Elias-Rosa, N. Filippenko, A.V. Rojas-Bravo, C. Tartaglia, L. Reynolds, T.M. Valenti, S. Andrews, J.E. Ashall, C. Bostroem, K.A. Brink, T.G. Burke, J. Cai, Y.-Z. Cappellaro, E. Coulter, D.A. Dastidar, R. Davis, K.W. Dimitriadis, G. Fiore, A. Foley, R.J. Fugazza, D. Galbany, L. Gangopadhyay, A. Geier, S. Gutiérrez, C.P. Haislip, J. Hiramatsu, D. Holmbo, S. Howell, D.A. Hsiao, E.Y. Hung, T. Jha, S.W. Kankare, E. Karamehmetoglu, E. Kilpatrick, C.D. Kotak, R. Kouprianov, V. Kravtsov, T. Kumar, S. Li, Z.-T. Lundquist, M.J. Lundqvist, P. Matilainen, K. Mazzali, P.A. McCully, C. Misra, K. Morales-Garoffolo, A. Moran, S. Morrell, N. Newsome, M. Padilla Gonzalez, E. Pan, Y.-C. Pellegrino, C. Phillips, M.M. Pignata, G. Piro, A.L. Reichart, D.E. Rest, A. Salmaso, I. Sand, D.J. Siebert, M.R. Smartt, S.J. Smith, K.W. Srivastav, S. Stritzinger, M.D. Taggart, K. Tinyanont, S. Yan, S.-Y. Wang, L. Wang, X.-F. Williams, S.C. Wyatt, S. Zhang, T.-M. De Boer, T. Chambers, K. Gao, H. Magnier, E. INAF Osservatorio Astronomico di Padova Vicolo dell Osservatorio 5 Padova35122 Italy Universitá Degli Studi di Padova Dipartimento di Fisica e Astronomia Vicolo dell Osservatorio 2 Padova35122 Italy School of Physics O Brien Centre for Science North University College Dublin Dublin 4 Belfield Ireland Instituto de Astrofísica Facultad de Ciencias Exactas Universidad Andres Bello Fernández Concha 700 Las Condes Santiago Chile Nuncio Monsenor Sótero Sanz 100 Santiago Providencia8320000 Chile CSIC Campus UAB Carrer de Can Magrans s/n Barcelona08193 Spain Department of Astronomy University of California BerkeleyCA94720-3411 United States Miller Institute for Basic Research in Science University of California BerkeleyCA94720 United States Department of Astronomy and Astrophysics University of California Santa CruzCA95064 United States Tuorla Observatory Department of Physics and Astronomy University of Turku Turku20014 Finland Niels Bohr Institute University of Copenhagen Jagtvej 128 København N2200 Denmark Department of Physics and Astronomy University of California Davis 1 Shields Avenue DavisCA95616-5270 United States Gemini Observatory 670 North A ohoku Place HiloHI96720-2700 United States Department of Physics Virginia Tech 850 West Campus Drive BlacksburgVA24061 United States DIRAC Institute Department of Astronomy University of Washington 3910 15th Avenue NE SeattleWA98195-0002 United States Las Cumbres Observatory 6740 Cortona Dr. Suite 102 GoletaCA93117 United States Department of Physics University of California Santa BarbaraCA93106 United States Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China Tsinghua University Beijing100084 China School of Physics Trinity College Dublin University of Dublin Dublin Ireland Fondazione Bruno Kessler Trento38123 Italy INFN-TI

We present photometric and spectroscopic data on three extragalactic luminous red novae (LRNe): AT 2018bwo, AT 2021afy, and AT 2021blu. AT 2018bwo was discovered in NGC 45 (at about 6.8 Mpc) a few weeks after the outburst onset. During the monitoring period, the transient reached a peak luminosity of 1040 erg s1. AT 2021afy, hosted by UGC 10043 (49.2 Mpc), showed a double-peaked light curve, with the two peaks reaching a similar luminosity of 2.1(±0.6) - 1041 erg s1. Finally, for AT 2021blu in UGC 5829 (∼8.6 Mpc), the pre-outburst phase was well-monitored by several photometric surveys, and the object showed a slow luminosity rise before the outburst. The light curve of AT 2021blu was sampled with an unprecedented cadence until the object disappeared behind the Sun, and it was then recovered at late phases. The light curve of LRN AT 2021blu shows a double peak, with a prominent early maximum reaching a luminosity of 6.5 - 1040 erg s1, which is half of that of AT 2021afy. The spectra of AT 2021afy and AT 2021blu display the expected evolution for LRNe: a blue continuum dominated by prominent Balmer lines in emission during the first peak, and a redder continuum consistent with that of a K-type star with narrow absorption metal lines during the second, broad maximum. The spectra of AT 2018bwo are markedly different, with a very red continuum dominated by broad molecular features in absorption. As these spectra closely resemble those of LRNe after the second peak, AT 2018bwo was probably discovered at the very late evolutionary stages. This would explain its fast evolution and the spectral properties compatible with that of an M-type star. From the analysis of deep frames of the LRN sites years before the outburst, and considerations of the light curves, the quiescent progenitor systems of the three LRNe were likely massive, with primaries ranging from about 13 M for AT 2018bwo, to 141+4 Mo for AT 2021blu, and over 40 M for AT 2021afy. © 2023 The Authors.

关键词： Luminance