2004A&A...426..399J


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.13CEST03:07:50

2004A&A...426..399J - Astronomy and Astrophysics, volume 426, 399-413 (2004/11-1)

On the importance of the few most massive stars: The ionizing cluster of NGC 588.

JAMET L., PEREZ E., CERVINO M., STASINSKA G., GONZALEZ-DELGADO R.M. and VILCHEZ J.M.

Abstract (from CDS):

We present the results of a double analysis of the ionizing cluster in NGC 588, a giant Hii region (GHR) in the outskirts of the nearby galaxy M33. For this purpose, we obtained ground based long-slit spectroscopy and combined it with archival ground based and space borne imaging and spectroscopy, in the wavelength range 1100-9800Å. A first modeling of the cluster was performed using integrated properties, such as the spectral energy distribution (SED), broad band colors, nebular emission Hβ equivalent width, the main ultraviolet resonance lines, and the presence of Wolf-Rayet star features. By applying standard assumptions about the initial mass function (IMF), we were unable to fit satisfactorily these observational data. This contradictory result led us to carry out a second modeling, based on a resolved photometric analysis of individual stars in Hubble Space Telescope (HST) images, by means of finding the best fit isochrone in color-magnitude diagrams (CMD), and assigning a theoretical SED to each individual star. The overall SED of the cluster, obtained by integrating the individual stellar SEDs, is found to fit better the observed SED than the best solution found through the integrated first analysis, but at a significantly later stage of evolution of the cluster of 4.2Myr, as obtained from the best fit to the CMD. A comparative analysis of both methods traces the different results to the effects of statistical fluctuations in the upper end of the IMF, which are significant in NGC 588, with a computed cluster mass of 5600 M, as predicted by Cervino et al. (2002A&A...381...51C). We discuss the results in terms of the strong influence of the few most massive stars, six in the case of NGC 588, that dominate the overall SED and, in particular, the ionizing far ultraviolet range beyond the Lyman limit.

Abstract Copyright:

Journal keyword(s): stars: evolution - stars: luminosity function, mass function - stars: Hertzsprung-Russell (HR) and C-M diagrams - stars: Wolf-Rayet - ISM: individual objects: NGC 588 - galaxies: individual: M 33

VizieR on-line data: <Available at CDS (J/A+A/426/399): table4.dat>

Nomenclature: Table 4: [JPC2004] NN (Nos 1-56).

Simbad objects: 8

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Number of rows : 8

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NGC 588 HII 01 32 45.2 +30 38 54 14.59 14.40 14.44 14.89 15.16 ~ 116 1
2 [JPC2004] 1 * 01 32 45.23 +30 38 58.4           ~ 2 0
3 [JPC2004] 2 * 01 32 45.56 +30 38 54.4           ~ 2 0
4 M 33 GiG 01 33 50.904 +30 39 35.79 6.17 6.27 5.72     ~ 5135 1
5 NGC 604 HII 01 34 32.1 +30 47 01           ~ 544 0
6 BD+52 913 WD* 05 05 30.6182785658 +52 49 51.920797126 10.25 11.44 11.69 11.93 12.108 DA.8 983 0
7 GD 71 WD* 05 52 27.6197286025 +15 53 13.228639956 11.675 12.783 13.032 13.169 13.337 DA1.5 334 0
8 BD+28 4211 HS* 21 51 11.0220905905 +28 51 50.366090892 8.922 10.25 10.58 10.656 10.831 sdO2VIIIHe5 735 0

    Equat.    Gal    SGal    Ecl

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2020.07.13-03:07:50

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