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Titolo:
The CFHT Open Star Cluster Survey. II. Deep CCD photometry of the old openstar cluster NGC 6819
Autore:
Kalirai, JS; Richer, HB; Fahlman, GG; Cuillandre, JC; Ventura, P; DAntona, F; Bertin, E; Marconi, G; Durrell, PR;
Indirizzi:
Univ British Columbia, Dept Phys & Astron, Vancouver, BC V6T 1Z1, Canada Univ British Columbia Vancouver BC Canada V6T 1Z1 ver, BC V6T 1Z1, Canada Canada France Hawaii Telescope Corp, Kamuela, HI 96743 USA Canada France Hawaii Telescope Corp Kamuela HI USA 96743 la, HI 96743 USA Osservatorio Astron Roma, I-00136 Rome, Italy Osservatorio Astron Roma Rome Italy I-00136 on Roma, I-00136 Rome, Italy Inst Astrophys Paris, Paris, France Inst Astrophys Paris Paris FranceInst Astrophys Paris, Paris, France European So Observ, D-8046 Garching, Germany European So Observ GarchingGermany D-8046 erv, D-8046 Garching, Germany Penn State Univ, University Pk, PA 16802 USA Penn State Univ University Pk PA USA 16802 v, University Pk, PA 16802 USA
Titolo Testata:
ASTRONOMICAL JOURNAL
fascicolo: 1, volume: 122, anno: 2001,
pagine: 266 - 282
SICI:
0004-6256(200107)122:1<266:TCOSCS>2.0.ZU;2-5
Fonte:
ISI
Lingua:
ENG
Soggetto:
INITIAL MASS FUNCTION; WHITE-DWARFS; TURBULENT CONVECTION; PRIMORDIAL BINARIES; DYNAMICAL EVOLUTION; MAIN-SEQUENCE; MODELS; TAURI; RICH;
Keywords:
color-magnitude diagrams; open clusters and associations : individual (NGC 6819); stars : luminosity function, mass function; white dwarfs;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
54
Recensione:
Indirizzi per estratti:
Indirizzo: Kalirai, JS Univ British Columbia, Dept Phys & Astron, 6224 Agr Rd, Vancouver, BC V6T 1Z1, Canada Univ British Columbia 6224 Agr Rd Vancouver BC Canada V6T 1Z1
Citazione:
J.S. Kalirai et al., "The CFHT Open Star Cluster Survey. II. Deep CCD photometry of the old openstar cluster NGC 6819", ASTRONOM J, 122(1), 2001, pp. 266-282

Abstract

We present analysis of deep CCD photometry for the very rich, old open star cluster NGC 6819. The science goals are to catalog the white dwarfs in the cluster and measure the cluster luminosity and mass functions. These CFH12K data results represent the first of nineteen open star clusters which were imaged as a part of the CFHT Open Star Cluster Survey. We find a tight, very rich, main-sequence and turnoff consisting of over 2900 cluster stars in the V, B-V color-magnitude diagram (CMD). Main-sequence fitting of the unevolved cluster stars with the Hyades star cluster yields a distance modulus of (m-M)(V) = 12.30 +/- 0.12, for a reddening of E(B-V) = 0.10. These values are consistent with a newly calculated theoretical stellar isochrone of age 2.5 Gyr, which we take to be the age of the cluster. Both the depth gained in the photometry and the increased projected area of the CFH12K Mosaic CCD allow for detailed star counts in concentric annuli out to large angular radii. These indicate a much larger cluster extent (R = 9'.5 +/- 1'.0), by a factor of similar to2 over some previous estimates. Incompleteness tests confirm a slightly negatively sloped luminosity function extending to faint (V similar to 23) magnitudes which is indicative of a dynamically evolved cluster. Further luminosity function and mass segregation tests indicate that low-mass objects (M less than or equal to 0.65 M-circle dot) predominate in the outer regions of the cluster, 3'.5 less than or equal to R less than or equal to 9'.5. The estimation of the number of white dwarfs in NGC 6819, based on stellar evolution models, white dwarf cooling timescales, and conservation of star number arguments applied to the red giant stars ofthe cluster are in good agreement with the observed number. For those white dwarf candidates which pass both a statistical subtraction that removes background galaxies and field stars and a high star/galaxy confidence by using image classification, we show comparisons with white dwarf isochrones and cooling models which suggest the need for spectroscopy to confirm the white dwarf nature of the brighter objects. This is entirely feasible for all objects, before a statistical subtraction cut, with the current generation of 8 m-class telescopes and multiobject spectrometers.

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Documento generato il 29/11/20 alle ore 16:00:01