EDP Sciences
Free Access
Volume 407, Number 1, August III 2003
Page(s) 91 - 104
Section Galactic structure and dynamics
DOI https://doi.org/10.1051/0004-6361:20030807

A&A 407, 91-104 (2003)
DOI: 10.1051/0004-6361:20030807

Spectroscopic and photometric studies of low-metallicity star-forming dwarf galaxies

II. HS 1442+4250
N. G. Guseva1, P. Papaderos2, Y. I. Izotov1, R. F. Green3, K. J. Fricke2, T. X. Thuan4 and K. G. Noeske2

1  Main Astronomical Observatory, Ukrainian National Academy of Sciences, Zabolotnoho 27, Kyiv 03680, Ukraine
2  Universitäts-Sternwarte, Geismarlandstraße 11, 37083 Göttingen, Germany
3  National Optical Astronomy Observatory, Tucson, AZ 85726, USA
4  Astronomy Department, University of Virginia, Charlottesville, VA 22903, USA

(Received 21 November 2002 / Accepted 16 May 2003 )

We present broad-band V and I imaging and long-slit spectroscopy in the optical range $\lambda$ $\lambda$3600-7500 Å of the dwarf irregular galaxy HS 1442+4250. The oxygen abundance $12 + \log{\rm (O/H)} =
7.63 \pm 0.02$ ( $Z = Z_\odot/19$) in the brightest H II region of HS 1442+4250 places the galaxy among the most metal-deficient emission-line galaxies. The low metallicity and blue colour ( $V-I) \sim 0.4$ mag of the low-surface-brightness (LSB) component make HS 1442+4250 a likely rare young dwarf galaxy candidate. We use four methods to estimate the stellar population age in the LSB component of HS 1442+4250. Different star formation histories are considered. The equivalent widths of hydrogen H $\alpha$ and H $\beta$ emission lines, and of hydrogen H $\gamma$ and H $\delta$ absorption lines, the spectral energy distribution and the observed ( V-I) colours of the LSB regions are reproduced quite well by models with only young and intermediate-age stellar populations. By contrast, the observational data cannot be reproduced by a stellar population formed continuously with a constant star formation rate in the age range from 0 to  $\ga$2 Gyr. While a faint old stellar population in HS 1442+4250 with an age  $\ga$2 Gyr is not excluded, we find no evidence for such a population from the present data.

Key words: galaxies: abundances -- galaxies: dwarf -- galaxies: evolution -- galaxies: starburst -- galaxies: stellar content

Offprint request: N. G. Guseva, guseva@mao.kiev.ua

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