On the determination of temperatures of ionizing stars in H II regions

1988 ◽  
Vol 231 (2) ◽  
pp. 257-267 ◽  
Author(s):  
J. M. Vilchez ◽  
B. E. J. Pagel
Keyword(s):  
H Ii Regions

scholarly journals Planetary Nebulae and the Pregalactic Helium Abundance

1989 ◽  
Vol 131 ◽  
pp. 213-213 ◽  
Author(s):  
Walter J. Maciel
Keyword(s):  
Chemical Composition ◽  
Recent Work ◽  
Planetary Nebulae ◽  
H Ii Regions ◽  
Helium Abundance

Recent work has emphasized the determination of the pregalactic helium abundance by mass Yp and the slope ΔY/ΔZ based on the chemical composition of both galactic and extragalactic H II regions (Pagel, 1987; Pagel et al., 1986).

scholarly journals Distribution of star-forming complexes and the structure of our Galaxy

2003 ◽  
Vol 212 ◽  
pp. 431-440 ◽  
Author(s):  
Delphine Russeil
Keyword(s):  
Large Scale ◽  
Stellar Population ◽  
Line Of Sight ◽  
H Ii Regions ◽  
Spiral Arms ◽  
Ob Stars ◽  
Star Forming ◽  
Optical Images ◽  
External Galaxies

The determination of the external galaxies morphology is generally based on their appearance on optical images. At these wavelengths young stellar population and their associated H ii regions, which can be grouped into star-forming complexes, appear preferentially located along spiral arms. Hence, it is naturally to use the same tracers to delineate the arms of our own Galaxy. But, where for external galaxies the distribution of star-forming complexes along the spiral arms is generally evident from direct imaging, for our Galaxy the spiral arms are strung out along the line of sight, leading to the superposition and mixing of information from the different complexes in the spiral arms making it difficult to distinguish them. Thus to access to the spatial distribution of young objects, hence to the large scale structure of our Galaxy, it is required first to identify and collect star-forming complexes (molecular clouds – H ii regions – OB stars) and then to determine their distance. In this framework I review the observational results and difficulties concerning the distribution of star-forming complexes and the determination of the structure of our Galaxy.

scholarly journals Determination of temperature of the ionizing stars of H II regions

2003 ◽  
Vol 404 (3) ◽  
pp. 969-974 ◽  
Author(s):  
O. L. Dors ◽  
M. V. F. Copetti
Keyword(s):  
H Ii Regions

scholarly journals The Magellanic Clouds and the Primordial Helium Abundance

2000 ◽  
Vol 198 ◽  
pp. 194-203 ◽  
Author(s):  
Manuel Peimbert ◽  
Antonio Peimbert
Keyword(s):  
Neutral Hydrogen ◽  
Magellanic Clouds ◽  
Heavy Elements ◽  
H Ii Regions ◽  
Helium Abundance ◽  
Temperature Variations ◽  
Systematic Effects ◽  
H Ii Region ◽  
Primordial Helium

A new determination of the pregalactic helium abundance based on the Magellanic Clouds H II regions is discussed. This determination amounts to Yp = 0.2345 ± 0.0030 and is compared with those derived from giant extragalactic H II regions in systems with extremely low heavy elements content. It is suggested that the higher primordial value derived by other authors from giant H II region complexes could be due to two systematic effects: the presence of neutral hydrogen inside the helium Strömgren sphere and the presence of temperature variations inside the observed volume.

scholarly journals Measurements of 4He in metal-poor extragalactic H ii regions: the primordial Helium abundance and the ΔY/ΔO ratio

2009 ◽  
Vol 5 (S268) ◽  
pp. 91-100 ◽  
Author(s):  
Manuel Peimbert ◽  
A. Peimbert ◽  
L. Carigi ◽  
V. Luridiana
Keyword(s):  
Chemical Evolution ◽  
H Ii Regions ◽  
Helium Abundance ◽  
Galactic Chemical Evolution ◽  
Primordial Helium

AbstractWe present a review on the determination of the primordial helium abundance Yp, based on the study of hydrogen and helium recombination lines in extragalactic H ii regions. We also discuss the observational determinations of the increase of helium to the increase of oxygen by mass ΔY/ΔO, and compare them with predictions based on models of galactic chemical evolution.

scholarly journals Stellar content of obscured compact H II regions

2003 ◽  
Vol 212 ◽  
pp. 467-473 ◽  
Author(s):  
Margaret M. Hanson ◽  
Lex Kaper ◽  
Arjan Bik ◽  
Fernando Comerón ◽  
Joachim Puls ◽  
...  
Keyword(s):  
Massive Star ◽  
Near Infrared ◽  
Massive Stars ◽  
Model Atmosphere ◽  
Spectroscopic Studies ◽  
H Ii Regions ◽  
Stellar Content ◽  
High Quality ◽  
Physical Conditions

Near-infrared, spectroscopic studies of central ionizing sources of very young H ii regions is presented in conjunction with a recently available, sophisticated atmospheric code to constrain the physical conditions and environment of very massive stars at very early stages of evolution. Combining high quality near-infrared spectroscopy of very young massive stars with model atmosphere calculations should allow for the most accurate quantitative determination of Teff, rotation, L, and log g, and to search for binaries and possible disk or in-fall signatures in forming or recently formed massive stars. These characteristics make up a vital boundary condition constraining theories on massive star formation.

scholarly journals Differential Abundances of B-type Supergiants in M33

1999 ◽  
Vol 192 ◽  
pp. 272-276
Author(s):  
M. I. Monteverde ◽  
A. Herrero
Keyword(s):  
H Ii Regions ◽  
Line Formation ◽  
Atmospheric Parameters ◽  
Oxygen Abundance ◽  
Abundance Gradient ◽  
Preliminary Results ◽  
Metal Abundances ◽  
Effective Temperatures ◽  
Abundance Determination

In previous papers we have published preliminary results on the stellar oxygen-abundance gradient in M33 by using B-type supergiants. In the following study, we include one new B-supergiant and derive effective temperatures and gravities for these stars. Determination of atmospheric parameters is based on analyses of silicon ionisation balance.Detailed non-LTE model atmospheres and non-LTE line formation calculations were used for the abundance determination of Si and O. Careful differential analyses are used to quantify the differences in metal abundances between M33 stars and MK spectral standards in our Galaxy.We compare our results with the abundances expected from studies of H II regions.

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