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Titolo:
Luminosity functions for globular clusters
Autore:
Silvestri, F; Ventura, P; DAntona, F; Mazzitelli, I;
Indirizzi:
Osservatorio Astron Roma, I-00040 Monte Porzio Catone, Italy Osservatorio Astron Roma Monte Porzio Catone Italy I-00040 Catone, Italy Ist Astrofis Spaziale, I-00044 Frascati, Italy Ist Astrofis Spaziale Frascati Italy I-00044 le, I-00044 Frascati, Italy
Titolo Testata:
ASTROPHYSICAL JOURNAL
fascicolo: 1, volume: 509, anno: 1998,
parte:, 1
pagine: 192 - 202
SICI:
0004-637X(199812)509:1<192:LFFGC>2.0.ZU;2-#
Fonte:
ISI
Lingua:
ENG
Soggetto:
LOW-MASS STARS; RR LYRAE STARS; MAIN-SEQUENCE; STELLAR EVOLUTION; HST OBSERVATIONS; HALO FIELD; 47 TUCANAE; STATE; MODELS; EQUATION;
Keywords:
globular clusters : general; stars : low-mass, brown dwarfs; stars : luminosity function, mass function; subdwarfs;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
60
Recensione:
Indirizzi per estratti:
Indirizzo: Silvestri, F Osservatorio Astron Roma, I-00040 Monte Porzio Catone, Italy Osservatorio Astron Roma Monte Porzio Catone Italy I-00040
Citazione:
F. Silvestri et al., "Luminosity functions for globular clusters", ASTROPHYS J, 509(1), 1998, pp. 192-202

Abstract

We present theoretical mass-luminosity relations and luminosity functions (LFs) for globular cluster stars, from luminosities above the horizontal branch down to the minimum luminosity of hydrogen-burning stars. The LFs are available for metal mass fraction Z from Z = 10(-4) to Z = 4 x 10(-3), in the Johnson V band and in the Bessell-Cousins I band, and are based on tracks especially computed for this program, with the input physics of the models developed recently by D'Antona et al., Mazzitelli et al., and D'Antona & Mazzitelli. Two typical comparisons with observations are presented and discussed: (1) comparisons and statistical analysis with the LFs of the lower giant branch, turnoff region, and upper main sequence of several globular clusters from low to high metallicity, (2) derivation of the initial mass function (IMF) for the stars below the turnoff for several globular clusters for which Hubble Space Telescope data are available. In the first analysis we find that, for relatively large metallicities (Z greater than or equal to 10(-3)) a good fit between theoretical and observed LFs can be found, although a simple chi(2) statistical analysis shows that it is not possible to derive a strongly preferred age (or, equivalently, distance modulus) from the LF comparison. The fit with lower metallicity [Z- (1-2) x 10(-4)] LFs is less good but statistically acceptable. The main result-is that the difference between observed and theoretical LFs of low-metallicity clusters reported by VandenBerg, Bolte, & Stetson appears to be much reduced in present models, and we give the possible reason why this happens and its consequences for the important parameter of the helium core mass at the flash. in the second application, we explore the effect of varying age and distance modulus on the mass function derived for a globular cluster. Distance moduli corresponding to the "long" distance scale (and relatively low ages) seem to be preferred based on these comparisons. The resulting index of the IMF: is smaller than with a lower distance modulus, and generally an insignificant amount of mass in brown dwarfs is predicted if theIMF is extrapolated below the hydrogen-burning limit.

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Documento generato il 05/12/20 alle ore 08:09:01