Abundances in planetary nebulae: NGC 6826

Roellig

2009

A&A

Self Cite

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.

Section: Discussion Of Stellar Evolutionsupporting

confidence: 64%

Abundances in the planetary nebula NGC 6210

Pottasch¹,

Roellig

2009

A&A

Self Cite

“…The luminosities, which are distance dependent, are considerably lower than given by the theories of Kudritzki et al (1997) or Pauldrach et al (2004). This has already been discussed by Napiwotzki (2006) in a general way and by Surendiranath & Pottasch (2008) for the case of NGC 6826. This is evidence that all of the nebulae listed in Table 15 have central stars of quite low luminosity, probably between 500 L and 2000 L .…”

Section: Discussionmentioning

confidence: 75%

Abundances of planetary nebulae NGC 3242 and NGC 6369

Pottasch¹,

2008

A&A

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The spectra of the planetary nebulae NGC 3242 and NGC 6369 are reanalysed using spectral measurements made in the mid-infrared with the Spitzer Space Telescope and the Infrared Space Observatory (ISO). The aim is to determine the chemical composition of these objects. We also make use of International Ultraviolet Explorer (IUE) and ground based spectra. These elliptical PNe are interesting because they are well-studied, nearby, bright objects and therefore allow a reasonably complete comparison of this type of nebulae. 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 are 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. The abundance of phosphorus has been determined for the first time in NGC 3242. The electron temperature in both of these nebulae is roughly constant unlike NGC 6302 and NGC 2392 where a strong temperature gradient is found. The temperature of the central star is discussed for both nebulae. Finally a comparison of the element abundances in these nebulae with the solar abundance is made. The low abundance of Fe and P is noted and it is suggested that these elements are an important constituent of the nebular dust.

“…Because the model is dependant on so many imperfectly known parameters it is difficult to make an accurate model. This can be seen in the models published by Surendiranath & Pottasch (2008) and Surendiranath et al (2004) where the best-fitting models do not accurately reproduce the above ratios. See also the discussion of this problem by Mokiem et al (2004) is less than 0.2, the stellar temperature is less than 35 000 K. To obtain more precise values of the temperature it is necessary to model the star-nebula combination which can be a difficult task.…”

Section: Radiation Fieldmentioning

confidence: 92%

Abundances of planetary nebulae in the Galactic bulge

Pottasch

2015

A&A

Self Cite

Context. Planetary nebulae (PNe) abundances are poorly known for those nebulae in the Galactic bulge. This is because of the high and uneven extinction in the bulge which makes visual spectral measurements difficult. In addition, the extinction corrections may be unreliable. Elements considered are O, N, Ne, S, Ar, and Cl. Aims. We determine the abundances in 19 PNe, 18 of which are located in the bulge. This doubles the number of PNe abundance determinations in the bulge. The Galactic abundance gradient is discussed for five elements. Methods. The mid-infrared spectra measured by the Spitzer Space Telescope are used to determine the abundances. This part of the spectrum is little affected by extinction for which an uncertain correction is no longer necessary. In addition the connection with the visible and ultraviolet spectrum becomes simpler because hydrogen lines are observed both in the infrared and in the visible spectra. In this way we more than double the number of PNe with reliable abundances. Results. Reliable abundances are obtained for O, N, Ne, S, and Ar for Galactic bulge PNe. Conclusions. The Galactic abundance gradient is less steep than previously thought. This is especially true for oxygen. The sulfur abundance is reliable because all stages of ionization expected have been measured. It is not systematically low compared to oxygen as has been found for some Galactic PNe.