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A study of the neglected Galactic H ii region NGC 2579 and its companion ESO 370-9
Context: The Galactic H ii region NGC 2579 has stayed undeservedlyunexplored due to identification problems which persisted untilrecently. Both NGC 2579 and its companion ESO 370-9 have beenmisclassified as planetary or reflection nebula, confused with eachother and with other objects. Due to its high surface brightness, highexcitation, angular size of few arcminutes and relatively lowinterstellar extinction, NGC 2579 is an ideal object for investigationsin the optical range. Located in the outer Galaxy, NGC 2579 is anexcellent object for studying the Galactic chemical abundance gradients. Aims: To present the first comprehensive observational study on thenebular and stellar properties of NGC 2579 and ESO 370-9, including thedetermination of electron temperature, density structure, chemicalcomposition, kinematics, distance, and the identification and spectralclassification of the ionizing stars, and to discuss the nature of ESO370-9. Methods: Long slit spectrophotometric data in the optical rangewere used to derive the nebular electron temperature, density andchemical abundances and for the spectral classification of the ionizingstar candidates. Hα and UBV CCD photometry was carried out toderive stellar distances from spectroscopic parallax and to measure theionizing photon flux. Results: The chemical abundances of He, N, O, Ne,S, Cl, and Ar were obtained. Maps of electron density and radialvelocity with a spatial resolution of 5" × 5" were composed fromlong slit spectra taken at different declinations. Three O starsclassified as O5 V, O6.5 V, and O8 V were found responsible for theionization of NGC 2579, while ESO 370-9 is ionized by a single O8.5 Vstar. The estimated mass of ionized gas of ≈25 M_ȯ indicatesthat ESO 370-9 is not a planetary nebula, but a small H ii region. Aphotometric distance of 7.6 ± 0.9 kpc and a kinematic distance of7.4 ± 1.4 kpc were obtained for both objects. At thegalactocentric distance of 12.8 ± 0.7 kpc, NGC 2579 is one of themost distant Galactic H ii regions for which direct abundancedeterminations have been accomplished.
| Open clusters in the Third Galactic Quadrant. II. The intermediate age open clusters NGC 2425 and NGC 2635
We analyse CCD broad band (UBV(RI)_C) photometric data obtained in thefields of the poorly studied open clusters NGC 2425and NGC 2635. Both clusters are found to be ofintermediate age thus increasing the population of open clusters knownto be of the age of, or older than, the Hyades. More explicitly, we findthat NGC 2425 is a 2.2 Gyr old cluster, probably ofsolar metallicity, located at 3.5 kpc from the Sun. NGC2635 is a Hyades age (600 Myr) cluster located at a distanceof 4.0 kpc from the Sun. Its Colour Magnitude Diagram reveals that it isextremely metal poor for its age and position, thus making it a veryinteresting object in the context of Galactic Disk chemical evolutionmodels.
| The Vela-Puppis open clusters Pismis 8 and Pismis 13
CCD UBVI imaging photometry was carried out in the fields of the openclusters Pismis 8 and Pismis 13, located in the Vela-Puppis region inour Galaxy. MK spectral types have also been determined for a number ofstars located in the fields of these two clusters which were used tosecure membership among the brightest stars. Since our photometry goesto a fainter limit than previous studies we could provide betterreddening, distance and age determinations. Both clusters are locatedclose to the edge of the local arm in the third quadrant. Pismis 8 is acluster about 5-7 My old located at 2000 pc from the Sun, while Pismis13 was found at 2750 pc with a probable age of about 100 My. Theestimate of the slopes of the mass functions in both cases yielded x≈1.7 and x≈ 2.1 for Pismis 8 and 13 respectively.Based on observations collected at the University of Toronto SouthernObservatory, Las Campanas, Chile, and the Complejo Astronómico ElLeoncito, San Juan, Argentina. Table 3 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/432/491
| NGC 2580 and NGC 2588. Two open clusters in the Third Galactic Quadrant
We present CCD broad band photometric observations in the fields of theThird Galactic Quadrant open clusters NGC 2580 and NGC 2588(V(I)C and UBV(RI)C respectively). From theanalysis of our data we found that NGC 2580 is located at a distance ofabout 4 kpc and its age is close to 160 Myr. As for NGC 2588, it isplaced at about 5 kpc from the Sun and is 450 Myr old. This means thatNGC 2588 belongs to the extension of the Perseus arm, whereas NGC 2580is closer to the local arm structure. The luminosity functions (LFs)have been constructed for both clusters down to V ˜ 20 togetherwith their initial mass functions (IMFs) for stars with masses above M˜ 1-1.5 Mȯ. The IMF slopes for the most massivebins yielded values of x ≈ 1.3 for NGC 2580 and x ≈ 2 for NGC2588. In the case of this latter cluster we found evidence of acore-corona structure produced probably by dynamical effect. In the mainsequences of both clusters we detected gaps, which we suggest could bereal features.Based on observations c ollected at ESO, CASLEO and CTIO.Table 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/417/961
| R associations. I - UBV photometry and MK spectroscopy of stars in southern reflection nebulae
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975AJ.....80..212H&db_key=AST
| Catalogue of southern stars embedded in nebulosity.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975AJ.....80..208V&db_key=AST
| Uniform survey of clusters in the southern Milky Way.
Abstract image available at:http://adsabs.harvard.edu/abs/1975AJ.....80...11V
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