J/AJ/106/1906ivo://CDS.VizieR/J/AJ/106/1906doi:10.26093/cds/vizier.51061906CDSHillenbrand L.A.Massey P.Strom S.E.Merrill K.M.2023-04-06T16:50:04Z2005-10-06T14:58:18ZCDS support team

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

cds-question@unistra.fropen-star-clustersinfrared-photometryvisible-astronomybroad-band-photometrymorgan-keenan-classificationWe have combined optical CCD photometry and spectroscopy with infrared imaging photometry to study the young cluster NGC 6611. We use these data to derive improved values for the reddening law (R=3.75) and the distance modulus (m-M=11.5), and to construct a physical H-R diagram from which we can probe the ages, masses, and evolutionary states of this stellar ensemble. The H-R diagram shows a strong population of high-mass stars, the most massive of which has a mass of roughly 80 solar masses, similar to what we find in other Galactic and Magellanic Cloud clusters and associations. The age of the massive stellar population in NGC 6611 is approximately 2 million years, with an age spread of, perhaps, a million years, although the data are also consistent with there being no discernible age spread among the most massive stars. However, the H-R diagram does reveal that one star of somewhat lower mass (30 solar masses) must have formed approximately 6 million years ago. The upper end of the mass function of NGC 6611 is found to have a slope of Gamma=-1.1+/-0.3, indistinguishable from a Salpeter slope, and similar to what we have found in other Galactic associations, but shallower than what we have found in the Magellanic Clouds. Our most significant result, however, is that we catch this cluster in the act of forming intermediate mass (3-8 Solar masses) stars. This is the first well-established case where large numbers of intermediate-mass stars have been seen on their way to the zero-age main sequence. That intermediate mass pre-main sequence stars are indeed present is evidenced both by their location above the zero-age main sequence in the H-R diagram, and in some cases by their spectroscopic and infrared signatures of (possibly remnant protostellar) circumstellar material. The pre-main sequence population ranges from as young as 0.25 million years to at least 1 million years of age. We find an highly unusual number (27) of emission-line stars, which appear quite similar in their optical and infrared continuum and optical spectroscopic properties to "classical Be/Ae" stars (as opposed to Herbig Be/Ae stars). Our data are inconsistent with the traditional interpretation that these "classical Be/Ae" stars are slightly evolved stars undergoing mass loss. Instead, we offer the conjecture that these may be young stars whose circumstellar disks have become optically thin, and produce Balmer emission lines. The infrared data do indicate a number of stars, particularly amongst the embedded sample, whose colors are consistent with those of stars thought to be surrounded by optically thick circumstellar accretion disks. The identification of such disks around young massive stars continues to be rare, and implies that the disk survival times around intermediate and high mass stars are much shorter (< 0.5Myr) than those of disks surrounding lower mass stars.1993AJ....106.1906Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/106/1906CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/106/1906https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/106/1906http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/106/1906https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/106/1906https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/106/1906http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/106/1906GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/AJ/106/1906/table1 (NGC 6611 Optical and Near-IR Photometry Data)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/106/1906/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/106/1906/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/106/1906/table1?GETtext/xml+votable180.050000true274.2958333-13.69386110.005555555555555556Cone search capability for table J/AJ/106/1906/posmk (MK classification, with accurate position)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/106/1906/posmk?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/106/1906/posmk?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/106/1906/posmk?GETtext/xml+votable180.050000true274.5386667-13.78183330.0055555555555555566/29461 29463 29504 29506https://cdsarc.cds.unistra.fr/viz-bin/moc/J/AJ/106/1906?format=asciiOpticalInfrareddefaultJ/AJ/106/1906/table1NGC 6611 Optical and Near-IR Photometry DatarecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintn_ID[ *]? emission line object flagcharID? Previous identification number (G1)intnullableprimaryRAJ2000[18/18]! hours of right ascension (J2000) (G2)pos.eq.ra;meta.mainDEJ2000[13/14]! degrees of declination (J2000) (G2)pos.eq.dec;meta.mainVmagV magnitudemagfloatu_Vmag[ :] uncertainty flag in VcharB-VB-V colormagfloatu_B-V[ :] uncertainty flag in B-VcharU-B?U-B colormagfloatnullableu_U-B[ :] uncertainty flag in U-BcharKmag?K magnitude (2.2um)magfloatnullableu_Kmag[ :] uncertainty flag in KcharH-K?H-K colormagfloatnullableu_H-K[ :] uncertainty flag in H-KcharJ-H?J-H colormagfloatnullableu_J-H[ :] uncertainty flag in J-KcharV-K?V-K colormagfloatnullableMKSimbad column added by the CDScharJ/AJ/106/1906/posmkMK classification, with accurate positionrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintID? Identification number, as in table1 (G1)intnullableRAJ2000Right Ascension J2000 (G2)pos.eq.ra;meta.mainDEJ2000Declination J2000 (G2)pos.eq.dec;meta.mainrPos[MTUs] Reference of position (G2)charVmagV mag, as in table1magfloatu_Vmag[:?] Uncertainty flag on VmagcharSpTypeMK spectral typecharNotesRemarks by B. Skiff (G1)char