J/A+A/426/399 HST photometry of brightest stars of NGC 588 (Jamet+, 2004)
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.,
Vilchez J.M.
<Astron. Astrophys., 426, 399-413 (2004)>
=2004A&A...426..399J 2004A&A...426..399J (SIMBAD/NED BibCode)
ADC_Keywords: H II regions ; Photometry, HST
Keywords: 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
Abstract:
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 5600M☉, as predicted by Cervino et al.
(2002A&A...381...51C 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.
Description:
We retrieved five pairs of WFPC2 images from the HST archive, taken
through the filters F547M, F439W, F336W, F170W and F469N. The images
were calibrated with the on-the-fly calibration system. Each pair of
exposures within a filter was combined with crrej in order to perform
cosmic ray rejection.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 97 56 Positions, reddened absolute magnitudes, E(B-V)
coefficients, and initial masses of the
brightest stars of NGC 588
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq Sequential number
4- 5 I2 h RAh Right ascension (J2000)
7- 8 I2 min RAm Right ascension (J2000)
10- 14 F5.2 s RAs Right ascension (J2000)
16 A1 --- DE- Declination sign (J2000)
17- 18 I2 deg DEd Declination (J2000)
20- 21 I2 arcmin DEm Declination (J2000)
23- 26 F4.1 arcsec DEs Declination (J2000)
28- 32 F5.2 mag F547M HST/WFPC2 F547M absolute magnitude
34- 37 F4.2 mag e_F547M rms uncertainty on F547M
39- 43 F5.2 mag F439W HST/WFPC2 F439W absolute magnitude
45- 48 F4.2 mag e_F439W rms uncertainty on F439W
50- 54 F5.2 mag F336W HST/WFPC2 F336W absolute magnitude
56- 59 F4.2 mag e_F336W rms uncertainty on F336W
61- 65 F5.2 mag F170W HST/WFPC2 F170W absolute magnitude
67- 70 F4.2 mag e_F170W rms uncertainty on F170W
72- 76 F5.2 mag F469N ?=- HST/WFPC2 F469N absolute magnitude
78- 81 F4.2 mag e_F469N ? rms uncertainty on F469N
83- 86 F4.2 mag E(B-V) Redenning
88- 91 F4.2 mag e_E(B-V) rms uncertainty on E(B-V)
92 A1 --- n_E(B-V) [a] a for E(B-V) values eventually set to 0.11
94- 97 F4.1 Msun Mini Initial mass
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 20-Sep-2016