J/ApJ/836/15ivo://CDS.VizieR/J/ApJ/836/15doi:10.26093/cds/vizier.18360015CDSKamath D.Van Winckel H.Wood P.R.Asplund M.Karakas A.I.,Lattanzio J.C.2017-11-06T14:05:39Z2017-10-06T12:43:28ZCDS support team

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

cds-question@unistra.frgiant-starsspectroscopychemical-abundancesline-intensitiesPost-asymptotic giant branch (post-AGB) stars are known to be chemically diverse. In this paper we present the first observational evidence of a star that has failed the third dredge-up (TDU). J005252.87-722842.9 is an A-type (T_eff_=8250+/-250K) luminous (8200+/-700L_{sun}_) metal-poor ([Fe/H]=-1.18+/-0.10) low-mass (M_initial_~1.5-2.0M_{sun}_) post-AGB star in the Small Magellanic Cloud. Through a systematic abundance study, using high-resolution optical spectra from UVES, we found that this likely post-AGB object shows an intriguing photospheric composition with no confirmed carbon-enhancement (upper limit of [C/Fe]<0.50) nor enrichment of s-process elements. We derived an oxygen abundance of [O/Fe]=0.29+/-0.1. For Fe and O, we took the effects of nonlocal thermodynamic equilibrium into account. We could not derive an upper limit for the nitrogen abundance as there are no useful nitrogen lines within our spectral coverage. The chemical pattern displayed by this object has not been observed in single or binary post-AGBs. Based on its derived stellar parameters and inferred evolutionary state, single-star nucleosynthesis models predict that this star should have undergone TDU episodes while on the AGB, and it should be carbon enriched. However, our observations are in contrast with these predictions. We identify two possible Galactic analogs that are likely to be post-AGB stars, but the lack of accurate distances (hence luminosities) to these objects does not allow us to confirm their post-AGB status. If they have low luminosities, then they are likely to be dusty post-RGB stars. The discovery of J005252.87-722842.9 reveals a new stellar evolutionary channel whereby a star evolves without any TDU episodes.2017ApJ...836...15Khttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/836/15CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/ApJS/92/125 : Post-AGB evolution (Vassiliadis+, 1994)J/A+A/425/595 : OGLE+2MASS+DENIS LPV in Magellanic Clouds (Groenewegen, 2004)J/ApJS/155/651 : Evolution of extremely metal-poor stars (Herwig+, 2004)J/AJ/132/2268 : SAGE calibration stars (Meixner+, 2006)J/ApJ/655/212 : S3MC IRAC and MIPS photometry (Bolatto+, 2007)J/A+A/484/815 : Scaled solar tracks and isochrones (Bertelli+, 2008)J/MNRAS/403/1413 : Updated stellar yields from AGB models (Karakas, 2010)J/A+A/533/A109 : Pisa pre-main sequence tracks and isochrones (Tognelli+, 2011)J/A+A/530/A90 : Optically bright post-AGB population of LMC (van Aarle+, 2011)J/A+A/557/A104 : CO observations of post-AGB stars (Bujarrabal+, 2013)J/A+A/554/A106 : Abundance study of LMC post-AGB stars (van Aarle+, 2013)J/A+A/560/A44 : Abundances of LMC bar and disk stars (Van der Swaelmen+, 2013)J/MNRAS/439/2211 : Post-AGB/RGB and YSOs in SMC (Kamath+, 2014)J/A+A/568/A25 : C and O abundances in stellar populations (Nissen+, 2014)J/A+A/583/A56 : Abundance study of two LMC post-AGB stars (De Smedt+, 2015)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/836/15https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/836/15http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/836/15https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/836/15https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/836/15http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/836/15GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapAssociated datahttps://cdsarc.cds.unistra.fr/assocdata/?obs_collection=J/ApJ/836/15OpticaldefaultJ/ApJ/836/15/table3The linelist of J005252.87-722842.9recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintIon[8/28.1] Atomic number+0.1*ionisation stagephys.atmol.ionStagefloatlambda[3408.7/6456.4] Wavelength in rest frame; in Angstroms0.1nmem.wldoublechi[0/10.8] Excitation potentialeVphys.atmol.excitationfloatloggf[-4.1/0.4] Log Oscillator strengthphys.atmol.oscStrengthfloatEW[3.8/124] Equivalenth width; in milli-Angstroms1e-13mspect.line.widthfloatAbd[2.1/8.3] Obtained abundancephys.abundfloat