Abundances in the planetary nebula NGC 6210

Autor: Stuart Pottasch, T. L. Roellig, Jeronimo Bernard-Salas
Přispěvatelé: Kapteyn Astronomical Institute
Jazyk: angličtina
Rok vydání: 2009
Předmět:
Zdroj: Astronomy & astrophysics, 499(1), 249-256. EDP Sciences
ISSN: 0004-6361
1432-0746
Popis: The spectra of the planetary nebula NGC 6210 is reanalysed using spectral measurements made in the mid-infrared with the Spitzer Space Telescope and the Infrared Space Observatory. The aim is to determine the chemical composition of this object. We also make use of IUE and ground based spectra. Abundances determined from the mid-infrared lines, which are insensitive to electron temperature, are used as the basis for the determination of the composition, which is found to differ somewhat from earlier results. The abundances found, especially the low value of helium and oxygen, indicate that the central star was originally of rather low mass, probably ≤1 M� . Abundances of phosphorus, iron, silicon, sodium, potassium and chlorine have been determined, some for the first time in this nebula. The electron temperature in this nebula is constant. The temperature, radius and luminosity of the central star is also discussed. It is shown that the luminosity is consistent with that predicted for a star of 0.9 M� . But the predicted nebular age is inconsistent with the observed kinetic age. NGC 6210 (PN G043.1+37.7) is a rather bright planetary nebula located at an unusually high galactic latitude and has only a small extinction. The nebula has an unusual morphology. It is usually classified as ellipsoidal, although Hajian et al. (1995) refer to it as “very amorphous and irregular”. An HST photograph of the nebula is shown in Fig. 1. This is the brightest part of the nebula. The central star is clearly seen in the photograph; while the brightest part of the nebula lies to the north of the central star. Various small scale structures are also present. Most of the emission is present within a region of about 12 �� × 8 �� . This region is surrounded by a halo-like structure with a diameter about twice as large and of much lower surface brightness, less than 1% of the brighter parts of the nebula. A long exposure photograph of the nebula is shown in Fig. 2 where it can be seen that there are four arm-like extensions in the halo. Phillips & Cuesta (1996) have shown that these features have a somewhat different spectrum than that of the main nebula. The integrated spectrum which is studied in this paper is essentially from the main part of the nebula, both because the halo emission is relatively small and because the size of the diaphragm limits the measurement to the central region. Because the nebula is found 38 degrees above the galactic plane it has only a small extinction. It is probably a nearby nebula since most PNe are located close to the galactic plane. An expansion distance has been measured by Hajian et al. (1995 )t o be 1.57 kpc. Although this is an uncertain distance it is not an unreasonable one since it agrees with the distance found from
Databáze: OpenAIRE
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