منابع مشابه
The Spatial Homogeneity of Nebular and Stellar Oxygen Abundances
To test the existence of a possible radial gradient in oxygen abundances within the Local Group dwarf irregular galaxy NGC 6822, we have obtained optical spectra of 19 nebulae with the EFOSC2 spectrograph on the 3.6-m telescope at ESO La Silla. The extent of the measured nebulae spans galactocentric radii in the range between 0.05 kpc and 2 kpc (over four exponential scale lengths). In five H I...
متن کاملStellar Abundances: Recent and Foreseeable Trends
The determination of chemical abundances from stellar spectra is considered a mature field of astrophysics. Digital spectra of stars are recorded and processed with standard techniques, much like samples in the biological sciences. Nevertheless, uncertainties typically exceed 20%, and are dominated by systematic errors. The first part of this paper addresses what is being done to reduce measure...
متن کاملPlanetary nebulae abundances and stellar evolution ⋆
A summary is given of planetary nebulae abundances from ISO measurements. It is shown that these nebulae show abundance gradients (with galactocentric distance), which in the case of neon, argon, sulfur and oxygen (with four exceptions) are the same as HII regions and early type star abundance gradients. The abundance of these elements predicted from these gradients at the distance of the Sun f...
متن کاملPlanetary nebulae abundances and stellar evolution II *
Context. In recent years midand far infrared spectra of planetary nebulae have been analysed and lead to more accurate abundances. It may be expected that these better abundances lead to a better understanding of the evolution of these objects. Aims. The observed abundances in planetary nebulae are compared to those predicted by the models of Karakas (2003, Thesis, Monash Univ. Melbourne) in or...
متن کاملInvestigating the Possible Anomaly between Nebular and Stellar Oxygen Abundances in the Dwarf Irregular Galaxy Wlm
We obtained new optical spectra of 13 H II regions in WLM with EFOSC2; oxygen abundances are derived for nine H II regions. The temperature-sensitive [O III]λ4363 emission line was measured in two bright H II regions HM 7 and HM 9. The direct oxygen abundances for HM 7 and HM 9 are 12+log(O/H) = 7.72±0.04 and 7.91±0.04, respectively. We adopt a mean oxygen abundance of 12+log(O/H) = 7.83±0.06. ...
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ژورنال
عنوان ژورنال: Publications of the Astronomical Society of the Pacific
سال: 1994
ISSN: 0004-6280,1538-3873
DOI: 10.1086/133395