The massive star population of the Virgo Cluster galaxy NGC 4535

We analyzed the massive star population of the Virgo Cluster galaxy NGC 4535 using archival Hubble Space Telescope Wide Field Planetary Camera 2 images in filters F555W and F814W, equivalent to Johnson V and Kron-Cousins I. We performed high precision point spread function fitting photometry of 24353 sources including 3762 candidate blue supergiants, 841 candidate yellow supergiants and 370 candidate red supergiants. We estimated the ratio of blue to red supergiants as a decreasing function of galactocentric radius. Using Modules for Experiments in Stellar Astrophysics isochrones at solar metallicity, we defined the luminosity function and estimated the star formation history of the galaxy over the last 60 Myrs. We conducted a variability search in the V and I filters using three variability indexes: the median absolute deviation, the interquartile range and the inverse von-Neumann ratio. This analysis yielded 120 new variable candidates with absolute magnitudes ranging from M$_{V}$ = $-$4 to $-$11 mag. We used the MESA evolutionary tracks at solar metallicity, to classify the variables based on their absolute magnitude and their position on the color-magnitude diagram. Among the new candidate variable sources are eight candidate variable red supergiants, three candidate variable yellow supergiants and one candidate luminous blue variable, which we suggest for follow-up observations.Comment: Accepted by A&A, 7 pages, 7 Tables, 53 figure

Deep optical study of the mixed-morphology supernova remnant G 132.7+1.3 (HB3)

We present optical CCD images of the large supernova remnant (SNR) G 132.7+1.3 (HB3) covering its full extent for the first time, in the emission lines of Hα +[N II], [S II], and [O III], where new and known filamentary and diffuse structures are detected. These observations are supplemented by new low-resolution long-slit spectra and higher resolution images in the same emission lines. Both the flux-calibrated images and spectra confirm that the optical emission originates from shock-heated gas since the [S II]/Hα > 0.4. Our findings are also consistent with the recently developed emission-line ratio diagnostics for distinguishing SNRs from H II regions. A multiwavelength comparison among our optical data and relevant observations in radio, X-rays, gamma-rays and CO bands, provided additional evidence on the interaction of HB3 with the surrounding clouds and clarified the borders of the SNR and the adjacent cloud. We discuss the supernova (SN) properties and evolution that led to the current observables of HB3 and we show that the remnant has most likely passed at the pressure driven snowplow phase. The estimated SN energy was found to be (3.7 ± 1.5) × 1051 erg and the current SNR age (5.1 ± 2.1) × 104 yr. We present an alternative scenario according to which the SNR evolved in the wind bubble cavity excavated by the progenitor star and currently is interacting with its density walls. We show that the overall mixed morphology properties of HB3 can be explained if the SN resulted by a Wolf−Rayet progenitor star with mass ∼34 M⊙⁠

AT2022aedm and a new class of luminous, fast-cooling transients in elliptical galaxies

We present the discovery and extensive follow-up of a remarkable fast-evolving optical transient, AT2022aedm, detected by the Asteroid Terrestrial impact Last Alert Survey (ATLAS). AT2022aedm exhibited a rise time of $9\pm1$ days in the ATLAS $o$-band, reaching a luminous peak with $M_g\approx-22$ mag. It faded by 2 magnitudes in $g$-band during the next 15 days. These timescales are consistent with other rapidly evolving transients, though the luminosity is extreme. Most surprisingly, the host galaxy is a massive elliptical with negligible current star formation. X-ray and radio observations rule out a relativistic AT2018cow-like explosion. A spectrum in the first few days after explosion showed short-lived He II emission resembling young core-collapse supernovae, but obvious broad supernova features never developed; later spectra showed only a fast-cooling continuum and narrow, blue-shifted absorption lines, possibly arising in a wind with $v\approx2700$ km s$^{-1}$. We identify two further transients in the literature (Dougie in particular, as well as AT2020bot) that share similarities in their luminosities, timescales, colour evolution and largely featureless spectra, and propose that these may constitute a new class of transients: luminous fast-coolers (LFCs). All three events occurred in passive galaxies at offsets of $\sim4-10$ kpc from the nucleus, posing a challenge for progenitor models involving massive stars or massive black holes. The light curves and spectra appear to be consistent with shock breakout emission, though usually this mechanism is associated with core-collapse supernovae. The encounter of a star with a stellar mass black hole may provide a promising alternative explanation.Comment: Accepted in ApJ

Optical emission-line Luminosity Function models for populations of Supernova Remnants

We present a basic model for the calculation of the luminosity distribution of supernova remnant populations. We construct theoretical Ha and joint [S II] - Ha luminosity functions for supernova remnants by combining prescriptions from a basic evolution model that provides the shock velocity and radius for SNRs of different age and pre-shock density, with shock excitation models that give the gas emissivity for shocks of different physical parameters. We assume a flat age distribution, and we explore the effect of different pre-shock density distributions or different magnetic parameters. We find very good agreement between the shape of the model Ha and the joint [S II] - Ha luminosity functions and those measured from SNR surveys in nearby galaxies.Comment: 11 pages, Accepted for publication in MNRA

AT 2022aedm and a new class of luminous, fast-cooling transients in elliptical galaxies

M. Nicholl et al.Nicholl, M.; Srivastav, S.; Fulton, M.D.; Gomez, S.; Huber, M.E.; Oates, S.R.; Ramsden, P.; Rhodes, L.; Smartt, S.J.; Smith, K.W.; Aamer, A.; Anderson, J.P.; Bauer, F.E.; Berger, E.; de Boer, T.; Chambers, K.C.; Charalampopoulos, P.; Chen, T.W.; Fender, R.P.; Fraser, M.; Gao, H.; Green, D.A.; Galbany, L.; Gompertz, B.P.; Gromadzki, M.; Gutiérrez, C.P.; Howell, D.A.; Inserra, C.; Jonker, P.G.; Kopsacheili, M.; Lowe, T.B.; Magnier, E.A.; McCully, C.; McGee, S.L.; Moore, T.; Müller-Bravo, T.E.; Newsome, M.; Gonzalez, E.P.; Pellegrino, C.; Pessi, T.; Pursiainen, M.; Rest, A.; Ridley, E.J.; Shappee, B.J.; Sheng, X.; Smith, G.P.; Terreran, G.; Tucker, M.A.; Vinkó, J.We present the discovery and extensive follow-up of a remarkable fast-evolving optical transient, AT 2022aedm, detected by the Asteroid Terrestrial impact Last Alert Survey (ATLAS). In the ATLAS o band, AT 2022aedm exhibited a rise time of 9 ± 1 days, reaching a luminous peak with Mg ≈ −22 mag. It faded by 2 mag in the g band during the next 15 days. These timescales are consistent with other rapidly evolving transients, though the luminosity is extreme. Most surprisingly, the host galaxy is a massive elliptical with negligible current star formation. Radio and X-ray observations rule out a relativistic AT 2018cow–like explosion. A spectrum in the first few days after explosion showed short-lived He ii emission resembling young core-collapse supernovae, but obvious broad supernova features never developed; later spectra showed only a fast-cooling continuum and narrow, blueshifted absorption lines, possibly arising in a wind with v ≈ 2700 km s−1. We identify two further transients in the literature (Dougie in particular, as well as AT 2020bot) that share similarities in their luminosities, timescales, color evolution, and largely featureless spectra and propose that these may constitute a new class of transients: luminous fast coolers. All three events occurred in passive galaxies at offsets of ∼4–10 kpc from the nucleus, posing a challenge for progenitor models involving massive stars or black holes. The light curves and spectra appear to be consistent with shock breakout emission, though this mechanism is usually associated with core-collapse supernovae. The encounter of a star with a stellar-mass black hole may provide a promising alternative explanation.M.N., A.A., and X.S. are supported by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No. 948381) and by UK Space Agency grant No. ST/Y000692/1. P.R. is supported by STFC grant 2742655. S.J.S. acknowledges funding from STFC grants ST/X006506/1 and ST/T000198/1. T.P. acknowledges the support by ANID through the Beca Doctorado Nacional 202221222222. J.V. is supported by NKFIH-OTKA grant K-142534 from the National Research, Development and Innovation Office, Hungary. T.-W.C. thanks the Max Planck Institute for Astrophysics for hosting her as a guest researcher. M.P. is supported by a research grant (19054) from VILLUM FONDEN. P.C. acknowledges support via an Academy of Finland grant (340613; PI: R. Kotak). P.W. acknowledges support from Science and Technology Facilities Council (STFC) grant ST/R000506/1. M.F. is supported by a Royal Society—Science Foundation Ireland University Research Fellowship. M.K. is partially supported by the program Unidad de Excelencia María de Maeztu CEX2020-001058-M. L.G., C.P.G., M.K., and T.E.M.B. acknowledge support from Unidad de Excelencia María de Maeztu CEX2020-001058-M, Centro Superior de Investigaciones Científicas (CSIC) under PIE project 20215AT016, and the Spanish Ministerio de Ciencia e Innovación (MCIN) and the Agencia Estatal de Investigación (AEI) 10.13039/501100011033 under the PID2020-115253GA-I00 HOSTFLOWS project. L.G. also acknowledges support from the European Social Fund (ESF) "Investing in your future" under the 2019 Ramón y Cajal program RYC2019-027683-I. C.P.G. also acknowledges financial support from the Secretary of Universities and Research (Government of Catalonia) and by the Horizon 2020 Research and Innovation Programme of the European Union under the Marie Sklodowska-Curie and the Beatriu de Pinós 2021 BP 00168 program. T.E.M.B. also acknowledges financial support from the 2021 Juan de la Cierva program FJC2021-047124-I. G.P.S. acknowledges support from the Royal Society, the Leverhulme Trust, and the Science and Technology Facilities Council (grant Nos. ST/N021702/1 and ST/S006141/1). F.E.B. acknowledges support from ANID-Chile BASAL CATA ACE210002 and FB210003, FONDECYT Regular 1200495, and Millennium Science Initiative Program —ICN12_009.With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2020-001058-M).Peer reviewe

Massive star population of the Virgo Cluster galaxy NGC4535: Discovery of new massive variable candidates with the Hubble Space Telescope ?

We analyzed the massive star population of the Virgo Cluster galaxy NGC 4535 using archival Hubble Space Telescope Wide Field Planetary Camera 2 images in filters F555W and F814W, equivalent to Johnson V and Kron-Cousins I. We performed high precision point spread function fitting photometry of 24353 sources including 3762 candidate blue supergiants, 841 candidate yellow supergiants, and 370 candidate red supergiants. We estimated the ratio of blue to red supergiants as a decreasing function of galactocentric radius. Using Modules for Experiments in Stellar Astrophysics (MESA) isochrones at solar metallicity, we defined the luminosity function and estimated the star formation history of the galaxy over the last 60 Myr. We conducted a variability search in the V and I filters using three variability indexes: the median absolute deviation, the interquartile range, and the inverse von-Neumann ratio. This analysis yielded 120 new variable candidates with absolute magnitudes ranging from MV = -4 to -11 mag. We used the MESA evolutionary tracks at solar metallicity to classify the variables based on their absolute magnitude and their position on the color-magnitude diagram. Among the new candidate variable sources are eight candidate variable red supergiants, three candidate variable yellow supergiants and one candidate luminous blue variable, which we suggest for follow-up observations. © ESO 2018

Deep optical study of the mixed-morphology supernova remnant G 132.7+1.3 (HB3)

We present optical CCD images of the large supernova remnant (SNR) G 132.7+1.3 (HB3) covering its full extent for the first time, in the emission lines of Hα +[N ii], [S ii], and [O iii], where new and known filamentary and diffuse structures are detected. These observations are supplemented by new low-resolution long-slit spectra and higher resolution images in the same emission lines. Both the flux-calibrated images and spectra confirm that the optical emission originates from shock-heated gas since the [S ii]/Hα > 0.4. Our findings are also consistent with the recently developed emission-line ratio diagnostics for distinguishing SNRs from H ii regions. A multiwavelength comparison among our optical data and relevant observations in radio, X-rays, gamma-rays and CO bands, provided additional evidence on the interaction of HB3 with the surrounding clouds and clarified the borders of the SNR and the adjacent cloud. We discuss the supernova (SN) properties and evolution that led to the current observables of HB3 and we show that the remnant has most likely passed at the pressure driven snowplow phase. The estimated SN energy was found to be (3.7 ± 1.5) × 1051 erg and the current SNR age (5.1 ± 2.1) × 104 yr. We present an alternative scenario according to which the SNR evolved in the wind bubble cavity excavated by the progenitor star and currently is interacting with its density walls. We show that the overall mixed morphology properties of HB3 can be explained if the SN resulted by a Wolf-Rayet progenitor star with mass ∼34\rm ∼M. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society

AT 2022aedm and a new class of luminous, fast-cooling transients in elliptical galaxies

We present the discovery and extensive follow-up of a remarkable fast-evolving optical transient, AT 2022aedm, detected by the Asteroid Terrestrial impact Last Alert Survey (ATLAS). In the ATLAS o band, AT 2022aedm exhibited a rise time of 9 ± 1 days, reaching a luminous peak with M g ≈ −22 mag. It faded by 2 mag in the g band during the next 15 days. These timescales are consistent with other rapidly evolving transients, though the luminosity is extreme. Most surprisingly, the host galaxy is a massive elliptical with negligible current star formation. Radio and X-ray observations rule out a relativistic AT 2018cow–like explosion. A spectrum in the first few days after explosion showed short-lived He ii emission resembling young core-collapse supernovae, but obvious broad supernova features never developed; later spectra showed only a fast-cooling continuum and narrow, blueshifted absorption lines, possibly arising in a wind with v ≈ 2700 km s−1. We identify two further transients in the literature (Dougie in particular, as well as AT 2020bot) that share similarities in their luminosities, timescales, color evolution, and largely featureless spectra and propose that these may constitute a new class of transients: luminous fast coolers. All three events occurred in passive galaxies at offsets of ∼4–10 kpc from the nucleus, posing a challenge for progenitor models involving massive stars or black holes. The light curves and spectra appear to be consistent with shock breakout emission, though this mechanism is usually associated with core-collapse supernovae. The encounter of a star with a stellar-mass black hole may provide a promising alternative explanation