Bibcode
Copetti, M. V. F.; Oliveira, V. A.; Riffel, R.; Castañeda, H. O.; Sanmartim, D.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 472, Issue 3, September IV 2007, pp.847-854
Fecha de publicación:
9
2007
Revista
Número de citas
16
Número de citas referidas
15
Descripción
Context: The Galactic H ii region NGC 2579 has stayed undeservedly
unexplored due to identification problems which persisted until
recently. Both NGC 2579 and its companion ESO 370-9 have been
misclassified as planetary or reflection nebula, confused with each
other and with other objects. Due to its high surface brightness, high
excitation, angular size of few arcminutes and relatively low
interstellar extinction, NGC 2579 is an ideal object for investigations
in the optical range. Located in the outer Galaxy, NGC 2579 is an
excellent object for studying the Galactic chemical abundance gradients.
Aims: To present the first comprehensive observational study on
the nebular and stellar properties of NGC 2579 and ESO 370-9, including
the determination of electron temperature, density structure, chemical
composition, kinematics, distance, and the identification and spectral
classification of the ionizing stars, and to discuss the nature of ESO
370-9. Methods: Long slit spectrophotometric data in the optical
range were used to derive the nebular electron temperature, density and
chemical abundances and for the spectral classification of the ionizing
star candidates. Hα and UBV CCD photometry was carried out to
derive stellar distances from spectroscopic parallax and to measure the
ionizing photon flux. Results: The chemical abundances of He, N,
O, Ne, S, Cl, and Ar were obtained. Maps of electron density and radial
velocity with a spatial resolution of 5" × 5" were composed from
long slit spectra taken at different declinations. Three O stars
classified as O5 V, O6.5 V, and O8 V were found responsible for the
ionization of NGC 2579, while ESO 370-9 is ionized by a single O8.5 V
star. The estimated mass of ionized gas of ≈25 M_&sun; indicates that
ESO 370-9 is not a planetary nebula, but a small H ii region. A
photometric distance of 7.6 ± 0.9 kpc and a kinematic distance of
7.4 ± 1.4 kpc were obtained for both objects. At the
galactocentric distance of 12.8 ± 0.7 kpc, NGC 2579 is one of the
most distant Galactic H ii regions for which direct abundance
determinations have been accomplished.