The Lyman-Continuum Fluxes and Stellar Parameters of O and Early B-Type Stars

Vacca, William D.; Garmany, C. D.; Shull, J. M.

doi:10.1086/177020

Cited by 756 publications

(1,104 citation statements)

References 21 publications

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“…Doyon, Puxley, & Joseph (1992) derive a value of 4 ] 1052 s~1 from their measured Brc Ñux inside a 5@@ aperture, which compares well with the value of 3 ] 1052 s~1 estimated from the Brc Ñux density measured inside an aperture of (Kawara et al 1989). For an 7@@ ] 3A .5 of 4 ] 1052 s~1, the number of O stars required is N Lyc D2900 and the total stellar mass is D5.5 ] 105 (using M _ a Salpeter IMF with and m upper \ 80 M _ , m lower \ 1.0 M _ the results of Vacca et al 1996). As in the case of NGC 5253, the corresponding stellar density for a 3È10 pc region corresponds to an SSC, if we assume that the ionized gas is physically conÐned to this D5 pc region (see°5.2 for more details).…”

Section: He 2-10supporting

confidence: 79%

Very Large Array Observations of the H92α Line from NGC 5253 and Henize 2‐10: Ionized Gas around Super Star Clusters

Mohan

Anantharamaiah

Goss

2001

ApJ

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We have detected the H92a radio recombination line from two dwarf starburst galaxies, NGC 5253 and He 2-10, using the Very Large Array. Both the line data as well as the radio continuum data are used to model the properties of the ionized gas in the centers of these galaxies. We consider a multidensity model for radio recombination lines and show why previous models, which were based on the assumption of gas at a single density, are valid in many situations. The models show that the ionized gas has a density of D104 cm~3 in both galaxies, with an e †ective size of 2È10 pc and a total mass of D104The derived production rate of Lyman continuum photons is D2.5 ] 1052 s~1 in both the galaxies, M _ . and the corresponding mass of stars (assuming a Salpeter initial mass function) is D105 The M _ . implied stellar density shows that the observed radio recombination lines arise from ionized gas around super star clusters (SSCs) in both galaxies (these SSCs have been recently detected through their radio continuum emission). The existence of D104 of ionized gas within a few parsecs of an SSC places M _ strict constraints on dynamical models. Using simple arguments, the parameter space for a few possible models are derived. The well-known radioÈfar-infrared correlation also holds for NGC 5253, although the radio emission from this galaxy is almost completely thermal. It is shown that NGC 5253 is strong evidence that the component of far-infrared emission from warm dust is correlated separately with the component of radio emission from thermal bremsstrahlung.

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Section: He 2-10supporting

confidence: 79%

Very Large Array Observations of the H92α Line from NGC 5253 and Henize 2‐10: Ionized Gas around Super Star Clusters

Mohan

Anantharamaiah

Goss

2001

ApJ

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“…At this point they would likely have spectral types B0 IV and B0 III respectively. The B0-1 III range is therefore populated by stars of ZAMS mass in the 20 − 25M ⊙ range on their way to the end of their H core-burning phase, in good agreement with the mass calibration of Vacca et al (1996).…”

Section: The Oe Starssupporting

confidence: 78%

On the class of Oe stars'

2004

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Abstract. We present high-quality spectra of the majority of stars that have been classified as Oe and find that their published spectral types are generally too early, most likely due to infilling of He I lines. As a matter of fact, all stars classified as Oe actually fall inside the range O9-B0 with the important exception of HD 155806 (O7.5 III) and perhaps HD 39680 (difficult to classify, but likely O8.5 V). Observations of a sample of objects with published spectral types in the O9-B0 range previously classified as peculiar or emission-line stars fail to reveal any new Oe star with spectral type earlier than O9.5. Most objects classified as peculiar in "classical" literature show signs of binarity in our spectra, but no spectral anomalies. We conclude that there is likely a real decline in the fraction of Be stars for spectral types earlier than B0, not due to observational bias. The few Oe stars with spectral types earlier than O9.5 deserve detailed investigation in order to provide constraints on the physical reasons of the Be phenomenon.

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“…Since we are unable to resolve an ionised skin of this thickness in the large-scale simulation presented in section 2, we explore scattering on smaller scales with a model of a single cloud. The total Lyman continuum flux in the Galaxy is 3.74 × 10 7 cm −2 s −1 (Vacca, Garmany & Shull 1996). We assume that half of this flux travels upwards from the midplane of the Galaxy, towards the cirrus cloud, while the other half travels downwards, away from the cloud.…”

Section: Galactic Cirrusmentioning

confidence: 99%

Models of diffuse Hα in the interstellar medium: the relative contributions from in situ ionization and dust scattering

Barnes

Wood

Hill

et al. 2014

Monthly Notices of the Royal Astronomical Society

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Using three dimensional Monte Carlo radiation transfer models of photoionisation and dust scattering, we explore different components of the widespread diffuse Hα emission observed in the interstellar medium of the Milky Way and other galaxies. We investigate the relative contributions of Hα from recombination emission in ionised gas and Hα that originates in Hii regions near the Galactic midplane and scatters off high altitude dust in the diffuse interstellar medium. For the radiation transfer simulations we consider two geometries for the interstellar medium: a three dimensional fractal geometry that reproduces the average density structure inferred for hydrogen in the Milky Way, and a density structure from a magneto hydrodynamic simulation of a supernovae driven turbulent interstellar medium. Although some sight lines that are close to Hii regions can be dominated by scattered light, overall we find that less than ∼ 20% of the total Hα intensity in our simulations can be attributed to dust scattering. Our findings on the relative contribution of scattered Hα are consistent with previous observational and theoretical analyses. We also investigate the relative contributions of dust scattering and in situ ionisation of high density dust clouds in the diffuse gas. Dust scattering in these partially ionised clouds contribute ∼ 40% to the total intensity of Hα.

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The Lyman-Continuum Fluxes and Stellar Parameters of O and Early B-Type Stars

Abstract: B-TYPE STARS _'_ _'5'._" / ?" '-' WILLIAM D. VACCA 1'2 Astronomy Department, 601 Campbe[l Hall,

Cited by 756 publications

References 21 publications

Very Large Array Observations of the H92α Line from NGC 5253 and Henize 2‐10: Ionized Gas around Super Star Clusters

Very Large Array Observations of the H92α Line from NGC 5253 and Henize 2‐10: Ionized Gas around Super Star Clusters

On the class of Oe stars'

Models of diffuse Hα in the interstellar medium: the relative contributions from in situ ionization and dust scattering

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