J/A+A/601/A76ivo://CDS.VizieR/J/A+A/601/A76doi:10.26093/cds/vizier.36010076CDSKourniotis M.Bonanos A.Z.Yuan W.Macri L.M.Garcia-Alvarez D.,Lee C.-H.2018-12-03T13:06:25Z2017-05-09T06:11:09ZCDS support team

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

cds-question@unistra.frsupergiant-starsvariable-starsccd-photometryThe evolution of massive stars surviving the red supergiant (RSG) stage remains unexplored due to the rarity of such objects. The yellow hypergiants (YHGs) appear to be the warm counterparts of post-RSG classes located near the Humphreys-Davidson upper luminosity limit, which are characterized by atmospheric instability and high mass-loss rates. We aim to increase the number of YHGs in M33 and thus to contribute to a better understanding of the pre-supernova evolution of massive stars. Optical spectroscopy of five dust-enshrouded YSGs selected from mid-IR criteria was obtained with the goal of detecting evidence of extensive atmospheres. We also analyzed BVIc photometry for 21 of the most luminous YSGs in M33 to identify changes in the spectral type. To explore the properties of circumstellar dust, we performed SED-fitting of multi-band photometry of the 21 YSGs. We find three luminous YSGs in our sample to be YHG candidates, as they are surrounded by hot dust and are enshrouded within extended, cold dusty envelopes. Our spectroscopy of star 2 shows emission of more than one H{alpha} component, as well as emission of CaII, implying an extended atmospheric structure. In addition, the long-term monitoring of the star reveals a dimming in the visual light curve of amplitude larger than 0.5mag that caused an apparent drop in the temperature that exceeded 500K. We suggest the observed variability to be analogous to that of the Galactic YHG {rho} Cas. Five less luminous YSGs are suggested as post-RSG candidates showing evidence of hot or/and cool dust emission. We demonstrate that mid-IR photometry, combined with optical spectroscopy and time-series photometry, provide a robust method for identifying candidate YHGs. Future discovery of YHGs in Local Group galaxies is critical for the study of the late evolution of intermediate-mass massive stars.2017A&A...601A..76Khttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/601/A76CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/AJ/121/861 : BVI photometry of central part of M33 (Macri+, 2001)J/ApJS/193/26 : The M33 synoptic stellar survey. I. (Pellerin+, 2011)J/ApJ/750/97 : The yellow and red supergiants of M33 (Drout+, 2012)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/601/A76https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/601/A76http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/601/A76https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/601/A76https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/601/A76http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/601/A76GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/601/A76/stars (List of stars with photometry)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/601/A76/stars?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/601/A76/stars?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/601/A76/stars?GETtext/xml+votable180.050000true23.405291730.51969440.0055555555555555566/2155https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/601/A76?format=asciidefaultJ/A+A/601/A76/starsList of stars with photometryLCShow the light curvesmeta.ref.urlcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintLGGSLGGS designation of the star (JHHMMSS.ss+DDMMSS.s)meta.id;meta.maincharRAJ2000Simbad Right ascension (J2000.0)pos.eq.ra;meta.mainDEJ2000Simbad Declination (J2000.0)pos.eq.dec;meta.mainSimbadSimbad column added by the CDSmeta.ref.urlcharJ/A+A/601/A76/photomBVIc photometry of 21 luminous YSGs in M33 (table 1)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintLGGSLGGS designation of the star (JHHMMSS.ss+DDMMSS.s)meta.id;meta.maincharFilter[BVI] Filter passband (Johnson-Cousins)instr.bandpasscharJDObservation date (JD-2450000)dtime.epochdoublemagMagnitude in Filtermagphot.magfloate_magUncertainty in magnitudemagstat.error;phot.magfloat