A study of the neglected Galactic H II region NGC 2579 and its companion ESO 370-9

Abstract

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 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. Key words. ISM: H ii regions -ISM: planetary nebulae: general IntroductionDue to observational difficulties, the knowledge acquisition in many research areas of astrophysics has still relied largely on data obtained from a small group of characteristic objects. This is certainly the case of the optical studies of Galactic H ii regions. In this field, the Orion Nebula is by far the most studied object. In fact, the number of papers on this object is comparable to the total number of optical studies of all other Galactic H ii regions. Even the standard procedure of measuring the electron temperature in Galactic H ii regions from optical emission line ratios, such as [O iii] (λ4959 + λ5007)/λ4363 and [N ii] (λ6548 + λ6584)/λ5755, until now could only be accomplished in a small sample of a dozen or so objects. So, the addition of new members to the selected list of well studied (or easy to observe) objects is welcome, especially becaus...

Radio-continuum detections of Galactic Planetary Nebulae - I. MASH PNe detected in large-scale radio surveys

“… References: 1: F08; 2: Copetti et al (2007); 3: Kohoutek (2001); 4: Frew et al (2010); 5: Frew & Parker (2010); 6: Cohen et al (2010); 7: Kastner et al (2003); 8: Parker et al (in preparation). …”

Spectral classification and distance determination of stars in nine southern Galactic $\ion{H}{ii}$ regions

“…Even the nature of some of these emission nebulae remain unclear or unconfirmed. Some of these objects have even been reclassified (Frew et al 2006;Copetti et al 2007;Stupar et al 2008), but there are several objects with unverified, uncertain or even with no distance determination or classification. In this paper, we present a study of stars in nine southern Galactic H ii regions with discrepant or unknown distance estimates.…”

The spiral structure of our Milky Way Galaxy

“…Column 19 to 21 are the same as Column 13-15 but with constants R 0 = 8.4 kpc and Θ 0 = 254 km s −1 for kinematic distances. References: ab09: Anderson & Bania (2009); ahck02: Araya et al (2002); bdc01: Blum et al (2001);brm+08: Brunthaler et al (2008);ccg+98: Condon et al (1998);cf08: Crowther & Furness (2008); cor+07: Copetti et al (2007); ch87 : Caswell & Haynes (1987);gg76: Georgelin & Georgelin (1976); GB6: Gregory et al (1996); hh09: This work; kjb+03: Kolpak et al (2003); kb94: Kuchar & Bania (1994); lt08: ; mrm+08: Moscadelli et al (2008);pbd+03: Paladini et al (2003); pdd04: Paladini et al (2004); pmg08: Pandian et al (2008);rus03: Russeil (2003); rag07: Russeil et al (2007); rmb+08 swa+04: Sewilo et al (2004); tlhj08: ; was+03: Watson et al (2003); PMN: Wright et al (1994Wright et al ( , 1996; Griffith et al (1994Griffith et al ( , 1995; xrm+08: Xu et al (2008); zzr+08: Zhang et al (2008) GMCs as tracers of spiral arms. Columns 1 and 2 are the Galactic longitude and latitude; Column 3 to 6 list velocity, the luminosity of CO emission line (in unit of 10 3 K km s −1 pc 2 ), distance and mass of molecular cloud, which were all taken from the reference given in Column 8; Column 7 is the note for distance ambiguity given in this reference, used as the same convention as in Table A1; Columns 9 and 10 list the distances to the Sun and to the Galactic center, which are estimated by the velocity and the rotation curve with R 0 = 8.5 kpc and Θ 0 = 220 km s −1 when the stellar distance is unavailable; Column 11 gives the mass of molecular clouds re-scaled by the newly estimated distance; Columns 12, 13 and 14 are the same as Columns 9-11 but with R 0 = 8.0 kpc and Θ 0 = 220 km s…”