J/A+A/632/L6ivo://CDS.VizieR/J/A+A/632/L6doi:10.26093/cds/vizier.36329006CDSCai Y-Z.A. PastorelloM. FraserPrentice S.J.Reynolds T.M.,Cappellaro E.Benetti S.Morales-Garoolo A.Reguitti A.Elias-Rosa N.,Brennan S.Callis E.Cannizzaro G.Fiore A.Gromadzki M.,Galindo-Guil F.J.Gall C.Heikkilae T.Mason E.Moran S.Onori F.,Sagues Carracedo A.Valerin G.2020-08-07T08:22:44Z2019-12-03T08:31:26ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frsupernovaevariable-starsvisible-astronomysloan-photometryinfrared-photometrybroad-band-photometryspectroscopyThe absolute magnitudes of luminous red novae (LRNe) are intermediate between those of novae and supernovae (SNe), and show a relatively homogeneous spectro-photometric evolution. Although they were thought to derive from core instabilities in single stars, there is growing support for the idea that they are triggered by binary interaction that possibly ends with the merging of the two stars. AT 2018hso is a new transient showing transitional properties between those of LRNe and the class of intermediate-luminosity red transients (ILRTs) similar to SN 2008S. Through the detailed analysis of the observed parameters, our study support that it actually belongs to the LRN class and was likely produced by the coalescence of two massive stars. We obtained ten months of optical and near-infrared photometric monitoring, and 11 epochs of low-resolution optical spectroscopy of AT 2018hso. We compared its observed properties with those of other ILRTs and LRNe. We also inspected the archival Hubble Space Telescope (HST) images obtained about 15 years ago to constrain the progenitor properties. The light curves of AT 2018hso show a first sharp peak (reddening-corrected M_r_=13.93mag), followed by a broader and shallower second peak that resembles a plateau in the optical bands. The spectra dramatically change with time. Early-time spectra show prominent Balmer emission lines and a weak [CaII] doublet, which is usually observed in ILRTs. However, the strong decrease in the continuum temperature, the appearance of narrow metal absorption lines, the great change in the H{alpha} strength and profile, and the emergence of molecular bands support an LRN classification. The possible detection of a M_I_~8mag source at the position of AT 2018hso in HST archive images is consistent with expectations for a pre-merger massive binary, similar to the precursor of the 2015 LRN in M101. We provide reasonable arguments to support an LRN classification for AT 2018hso. This study reveals growing heterogeneity in the observables of LRNe than has been thought previously, which is a challenge for distinguishing between LRNe and ILRTs. This suggests that the entire evolution of gap transients needs to be monitored to avoid misclassifications.2019A&A...632L...6Chttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/632/L6CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/632/L6https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/632/L6http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/632/L6https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/632/L6https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/632/L6http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/632/L6GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tap7.952274030004205e-20 5.042107639525881e-19OpticalInfrareddefaultJ/A+A/632/L6/tablea1Optical (BVugriz) light curves of AT 2018hsol_BmagLimit flag on Bmagmeta.code.errorchare_zmag? Sloan z band magnitude errormagstat.error;phot.magfloatnullableTel[1/4] Telescope numerical code (1)meta.codeintMJDModified Julian Datedtime.epochdoublerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintDateDate of observation (yyyy/mm/dd)time.epochnullableBmag? Johnson-Cousins B band magnitudemagphot.mag;em.opt.Bfloatnullablee_Bmag? Johnson-Cousins B band magnitude errormagstat.error;phot.magfloatnullablel_VmagLimit flag on Vmagmeta.code.errorcharVmag? Johnson-Cousins V band magnitudemagphot.mag;em.opt.Vfloatnullablee_Vmag? Johnson-Cousins V band magnitude errormagstat.error;phot.magfloatnullablel_umagLimit flag on umagmeta.code.errorcharumag? Sloan u band magnitudemagphot.mag;em.opt.Ufloatnullablee_umag? Sloan u band magnitude errormagstat.error;phot.magfloatnullablel_gmagLimit flag on gmagmeta.code.errorchargmag? Sloan g band magnitudemagphot.mag;em.opt.Bfloatnullablee_gmag? Sloan g band magnitude errormagstat.error;phot.magfloatnullablel_rmagLimit flag on rmagmeta.code.errorcharrmag? Sloan r band magnitudemagphot.mag;em.opt.Rfloatnullablee_rmag? Sloan r band magnitude errormagstat.error;phot.magfloatnullablel_imagLimit flag on imagmeta.code.errorcharimag? Sloan i band magnitudemagphot.mag;em.opt.Ifloatnullablee_imag? Sloan i band magnitude errormagstat.error;phot.magfloatnullablezmag? Sloan z band magnitudemagphot.mag;em.opt.IfloatnullableJ/A+A/632/L6/tablea2Near-infrared (NIR) JHK light curves of AT 2018hsorecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintDateDate of observation (yyyy/mm/dd)time.epochnullableMJDModified Julian Datedtime.epochdoubleJmagNIR J band magnitudemagphot.mag;em.IR.Jfloate_JmagNIR J band magnitude errormagstat.error;phot.magfloatHmag? NIR H band magnitudemagphot.mag;em.IR.Hfloatnullablee_Hmag? NIR H band magnitude errormagstat.error;phot.magfloatnullableKmag? NIR K band magnitudemagphot.mag;em.IR.Kfloatnullablee_Kmag? NIR K band magnitude errormagstat.error;phot.magfloatnullableTel[1] Telescope numerical code (1)meta.codeintJ/A+A/632/L6/listList of fits filesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNxNumber of pixels along X-axismeta.numberintNy? Number of slices, for the multi-spectrameta.numberintnullableObs.dateObservation datestime.epoch;obsnullableblambdaLower value of wavelength interval0.1nmem.wlfloatBlambdaUpper value of wavelength interval0.1nmem.wldoubledlambdaWavelength resolution0.1nmspect.resolutiondoublesizeSize of FITS fileKibytephys.size;meta.fitsintspShow the Radial Velocity curvesmeta.ref.urlcharFileNameName of FITS file, in subdirectory fitsmeta.id;meta.fitscharTitleTitle of the FITS filemeta.title;meta.fitschar