Metallicity and the spectral energy distribution and spectral types of dwarf O-stars

Mokiem, M.R.; Martín-Hernández, N. L.; Lenorzer, A.; Koter, A. de; Tielens, A. G. G. M.

doi:10.1051/0004-6361:20040074

Cited by 41 publications

(48 citation statements)

References 62 publications

(121 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Martin-Hernandez et al (2002) attributed the decrease in the degree of ionization of neon with metallicity, observed in Galactic and extragalactic H ii regions and in starbursts with the ISO satellite, to a metallicity effect on the spectral energy distribution of the ionizing stars. A similar conclusion has been drawn by Morisset et al (2004) and Mokiem et al (2004). Rubin et al (2007) have published one of the first tests between theoretical expectations and mid-IR observations obtained with the IRS spectrograph aboard the Spitzer space telescope.…”

Section: Radiation Fieldsupporting

confidence: 76%

Massive Stars in the Nuclei and Arms of Spirals

Bresolin

2007

Proc. IAU

View full text Add to dashboard Cite

Abstract. Many of the properties of massive stars in external galaxies, such as chemical compositions, mass functions, and ionizing fluxes, can be derived from the study of the associated clouds of ionized gas. Moreover, the signatures of Wolf-Rayet stars are often detected in the spectra of extragalactic H ii regions. This paper reviews some aspects of the recent work on the massive star content of nearby spiral galaxies, as inferred from the analysis of giant H ii regions. Particular attention is given to regions of high metallicity, including nuclear hot spots, and to the chemical abundance comparison between supergiant stars and ionized gas.

show abstract

Section: Radiation Fieldsupporting

confidence: 76%

Massive Stars in the Nuclei and Arms of Spirals

Bresolin

2007

Proc. IAU

View full text Add to dashboard Cite

show abstract

“…Studies like those performed by Kudritzki (2002), Evans & Howarth (2003), Mokiem et al (2004Mokiem et al ( , 2006, Massey et al (2005), Trundle et al (2007), Tramper et al (2011Tramper et al ( , 2014, Garcia & Herrero (2013;hereafter GH13), and Garcia et al (2014) analyzed the dependence of effective temperature, wind properties, or ionizing flux on metallicity.…”

Section: Introductionmentioning

confidence: 99%

OB stars at the lowest Local Group metallicity

Camacho

García

Herrero

2015

A&A

View full text Add to dashboard Cite

Context. Massive stars play an important role in the chemical and dynamical evolution of the Universe. The first metal-poor stars may have started the reionization of the Universe. To understand these early epochs it is necessary to know the behavior and the physical properties of massive stars in very metal-poor environments. We focus on the massive stellar content of the metal-poor irregular galaxy Sextans A. Aims. Our aim is to find and classify OB stars in Sextans A, so as to later determine accurate stellar parameters of these blue massive stars in this low-metallicity region (Z ∼ 0.1 Z ). Methods. Using UBV photometry, the reddening-free index Q and GALEX imaging, we built a list of blue massive star candidates in Sextans A. We obtained low-resolution (R ∼ 1000) GTC-OSIRIS spectra for a fraction of them and carried out spectral classification. For the confirmed O-stars, we derived preliminary stellar parameters. Results. The target selection criteria and observations were successful and have produced the first spectroscopic atlas of OB-type stars in Sextans A. From the whole sample of 18 observed stars, 12 were classified as early OB-types, including 5 O-stars. The radial velocities of all target stars are in agreement with their Sextans A membership, although three of them show significant deviations. We determined the stellar parameters of the O-type stars using the stellar atmosphere code FASTWIND and revisited the sub-SMC temperature scale. Two of the O-stars are consistent with relatively strong winds and enhanced helium abundances, although results are not conclusive. We discuss the position of the OB stars in the HRD. Initial stellar masses run from slightly below 20 up to 40 solar masses. Conclusions. The target selection method worked well for Sextans A. The stellar temperatures are consistent with findings in other galaxies. Some of the targets deserve follow-up spectroscopy because of indications of a runaway nature, an enhanced helium abundance, or a relatively strong wind. We observe a correlation between HI and OB associations similar to the irregular galaxy IC 1613, confirming the previous result that the most recent star formation of Sextans A is currently ongoing near the rim of the H i cavity.

show abstract

“…3 is the increase in the excitation of the nebular models that accompanies the decrease in the abundances in the ionizing SEDs. Such an effect was suggested earlier by Mokiem et al (2004), who computed stellar atmosphere models for main sequence O-stars using the cmfgen code (Hillier & Miller 1998) with varying abundances. They found that a higher metallicity causes more opacity and softens the SED, and a lower metallicity does the opposite.…”

Section: Constraints On the Ionizing Sed For The Stars Exciting The Hmentioning

confidence: 69%

Spitzerobservations of extragalactic H ii regions – III. NGC 6822 and the hot star, H ii region connection

Rubin

Simpson

Colgan

et al. 2016

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

Using the short-high module of the Infrared Spectrograph on the Spitzer Space Telescope, we have measured the [S iv] , thereby allowing an analysis of the neon to sulphur abundance ratio as well as the ionic abundance ratios Ne + /Ne ++ and S 3+ /S ++ . By extending our studies of H ii regions in M83 and M33 to the lower metallicity NGC 6822, we increase the reliability of the estimated Ne/S ratio. We find that the Ne/S ratio appears to be fairly universal, with not much variation about the ratio found for NGC 6822: the median (average) Ne/S ratio equals 11.6 (12.2±0.8). This value is in contrast to Asplund et al.'s currently best estimated value for the Sun: Ne/S = 6.5. In addition, we continue to test the predicted ionizing spectral energy distributions (SEDs) from various stellar atmosphere models by comparing model nebulae computed with these SEDs as inputs to our observational data, changing just the stellar atmosphere model abundances. Here we employ a new grid of SEDs computed with different metallicities: Solar, 0.4 Solar, and 0.1 Solar. As expected, these changes to the SED show similar trends to those seen upon changing just the nebular gas metallicities in our plasma simulations: lower metallicity results in higher ionization. This trend agrees with the observations.

show abstract

Metallicity and the spectral energy distribution and spectral types of dwarf O-stars

Cited by 41 publications

References 62 publications

Massive Stars in the Nuclei and Arms of Spirals

Massive Stars in the Nuclei and Arms of Spirals

OB stars at the lowest Local Group metallicity

Spitzerobservations of extragalactic H ii regions – III. NGC 6822 and the hot star, H ii region connection

Contact Info

Product

Resources

About