J/A+A/638/A157ivo://CDS.VizieR/J/A+A/638/A157doi:10.26093/cds/vizier.36380157CDSHolgado G.Simon-Diaz S.Haemmerle L.Lennon D.J.Barba R.H.,Cervino M.Castro N.Herrero A.Meynet G.Arias J.I.2021-09-07T06:50:33Z2020-07-05T14:35:37ZCDS support team

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

cds-question@unistra.frearly-type-starso-starseffective-temperatureextinctionspectroscopyThe apparent lack of massive O-type stars near the Zero Age Main Sequence, or ZAMS, (at ages <2Myr) has been a topic widely discussed in the last 40 years. Different explanations for the elusive detection of these young massive stars have been proposed from both the observational and theoretical side, but no firm conclusions have been reached yet. The aim of this work is to perform a reassessment of this empirical result benefiting from the high quality spectroscopic observations of (more than 400) Galactic O-type stars gathered by the IACOB and OWN surveys. We use effective temperatures and surface gravities resulting from a homogeneous, semi-automatized, IACOB-GBAT/FASTWIND spectroscopic analysis to locate our sample of stars in the Kiel and spectroscopic Hertzsprung-Russell (HR) diagrams. We evaluate the completeness of our magnitude limited sample of stars - as well as the existence of potential observational biases affecting the compiled sample - using information from the Galactic O star catalog (GOSC). We discuss limitations and possible systematics of our analysis methodology, and compare our results with other recent studies using smaller samples of Galactic O-type stars. We mainly base our discussion on the distribution of stars in the spectroscopic HR diagram in order to avoid the use of still uncertain distances to most of the stars in our sample. However, we also perform a more detailed study of the young cluster Trumpler-14 as an illustrative example of how Gaia cluster distances can help to construct the associated classical HR diagram. We find that the apparent lack of massive O-type stars near the zero-age main sequence with initial evolutionary masses in the range between ~30 and 70M_{sun}_ still persist despite using spectroscopic results from a large, non-biased sample of stars. We do not find any correlations between the dearth of stars close to the ZAMS and obvious observational biases, limitations of our analysis methodology, and/or the use of one example spectroscopic HR diagram instead of the classical one. Finally, by investigating the impact of the efficiency of mass accretion during the formation process of massive stars, we conclude that an adjustment of the mass accretion rate towards lower values than canonically assumed could reconcile the hotter boundary of the empirical distribution of optically detected O-type stars in the spectroscopic HR diagram and the theoretical birthline for stars with masses above 30M_{sun}_. Last, we also discuss how the presence of a small sample of O2-O3.5 stars found much closer to the ZAMS than the main distribution of Galactic O-type star could be explained in the context of this scenario taking also into account the effect of non-standard star evolution (e.g. binary interaction, mergers, and/or homogeneous evolution).2020A&A...638A.157Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/638/A157CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/A+A/562/A135 : Northern Galactic OB stars vsini (Simon-Diaz+, 2014)J/A+A/597/A22 : Massive O- and B-type stars velocities (Simon-Diaz+, 2017)J/A+A/613/A65 : Spectroscopic parameters of O-type stars (Holgado+, 2018)J/A+A/613/A9 : Extinction towards Galactic O stars (Maiz Apellaniz+, 2018)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/638/A157https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/638/A157http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/638/A157https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/638/A157https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/638/A157http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/638/A157GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/638/A157/tablee1 (O-type stars considered in this work with spectroscopic parameters)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/638/A157/tablee1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/638/A157/tablee1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/638/A157/tablee1?GETtext/xml+votable180.050000true160.98941-59.54760970.0055555555555555565/3661 6/1287 1293 1299 1303 1332 1355 1558 1790 1946 2409 3011 3037 3051 3054 3231 3245 3247 3249 3256 3261 3263 3272 3301 3307 3315 3331 3337 3430 3585 3600 3622 3644 3649 3653 3724 5506 6891 12943 13255 13557 13999 14008 14179 14240 14253 14263 14283 14295 14311 14353 14359 14456 14624 14630 14633 14636 14643 14654 14658 14692-14693 14712 14740-14741 14743 14745 14793 14824 15369 15476 15577 15631 15656 15663 15670 15672 15682-15683 15745 20613 21432 21635 21638 21655-21656 22033 22088 22211 22216 22240 22243 22249 22253 22854 22884 23637 23717 23774 23962 23982 24179 24555 28687 28796 28809 28865 28890-28891 28900 28913 28915 29025 29036 29089 29091 29095 29098 29115 29158 29162 29463 29504 29513 29515 29517 29525 29530 29600 29866 30216 30818 31748 37245 37333-37334 37339 37750 37833 37861 37863 37870 37897 37899-37901 37907 37915 37923 37926 37930-37932 37934 37938 37948 38016 38020 38022 38024 38026 38074 39238 39248 39252 39264 39281 39374 39386 39804 39971 41103 41592 41610 41630 41653 41673 41675 41685-41686 41702 41715 41750 41769 41787 41813 41903 42206 42226 42228 42236 42283 42287 42303 42383 42390 42394 42398 42405 42416-42417 42456 42458 42470-42471 42483 42764 43034 43041 43062 43144https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/638/A157?format=asciidefaultJ/A+A/638/A157/tablee1O-type stars considered in this work with spectroscopic parametersSimbadNameSimbad column added by the CDSmeta.idcharTargetStar namemeta.id;meta.maincharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSpTypeSpectral typesrc.spTypecharLumClassLuminosity classsrc.class.luminositycharl_TeffLimit flag on Teffmeta.code.error;phys.temperature.effectivecharTeffEffective temperaturekKphys.temperature.effectivefloate_Teff? Effective temperature errorkKstat.error;phys.temperature.effectivefloatnullablel_loggtLimit flag on loggtmeta.code.errorcharloggtGravity corrected from rotational effectslog(cm.s**-2)phys.gravityfloate_loggt? Gravity corrected from rotational effects errorlog(cm.s**-2)stat.errorfloatnullablel_logLspLimit flag on logLsp-Lspometa.code.errorcharlogLspLsp parameter (1)log(solLum)phys.luminosityfloate_logLsp? Lsp parameter errorlog(solLum)stat.errorfloatnullableBmagB magnitudemagphot.mag;em.opt.BfloatE(4405-5495)? E(4405-5495) extinctionmagphys.absorptionfloatnullableNotesMulti-epoch notesmeta.notechar_RARight Ascension (J2000) from SIMBAD (not part of the original data)degpos.eq.ra;meta.main_DEDeclination (J2000) from SIMBAD (not part of the original data)degpos.eq.dec;meta.main