Galactic H II Regions. I. Observations of Their Continuum Radiation at the Frequency 5 GHz

Mezger, P. G.; Henderson, Alex

doi:10.1086/149030

Cited by 551 publications

(470 citation statements)

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“…An approximation to the free-free optical depth is given by Altenhoff, Strittmatter, & Wendker (1981) or equation (A.1a) of Mezger & Henderson (1967),…”

Section: Radio Emission Of Optically Thick H II Regionsmentioning

confidence: 99%

The Formation of Massive Stars by Accretion through Trapped Hypercompact HiiRegions

Keto¹

2003

ApJ

197

189

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The formation of massive stars may take place at relatively low accretion rates over a long period of time if the accretion can continue past the onset of core hydrogen ignition. The accretion may continue despite the formation of an ionized H ii region around the star if the H ii region is small enough that the gravitational attraction of the star dominates the thermal pressure of the H ii region. The accretion may continue despite radiation pressure acting against dust grains in the molecular gas if the momentum of the accretion flow is sufficient to push the dust grains through a narrow zone of high dust opacity at the ionization boundary and into the H ii region where the dust is sublimated. This model of massive star formation by continuing accretion predicts a new class of gravitationally trapped, long-lived, hypercompact H ii regions. The observational characteristics of the trapped hypercompact H ii regions can be predicted for comparison with observations.

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“…An approximation to the free-free optical depth is given by Altenhoff, Strittmatter, & Wendker (1981) or equation (A.1a) of Mezger & Henderson (1967),…”

Section: Radio Emission Of Optically Thick H II Regionsmentioning

confidence: 99%

The Formation of Massive Stars by Accretion through Trapped Hypercompact HiiRegions

Keto¹

2003

ApJ

197

189

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“…At frequencies lower than the so-called turnover frequency ν 0 (around a few GHz), the cloud is optically thick and the flux is partially self-absorbed from the cloud itself. For frequencies between a few GHz to about one hundred GHz the spectrum shows the feature of the free-free emission, with a powerlaw of the form ν −0.15 (Mezger & Henderson 1967). At higher frequencies (ν ≥ 100 GHz) the spectrum is dominated by dust emission.…”

Section: Resultsmentioning

confidence: 95%

Millimetric observations of southern HII regions

Sabbatini¹,

Cavaliere

Dall'Oglio³

et al. 2005

A&A

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Abstract. We report on millimetric continuum observations of two bright compact H  regions, which have been observed for the first time in this frequency range. For the two observed regions (G291.6-0.5 and G291.3-0.7), we derive the flux densities at the two observed wavelengths (1.25 and 2 mm) as well as the spectral index and the temperature of the surrounding dust by fitting a modified blackbody curve to our results combined with IR values obtained from the literature. We also estimate the dust mass and the bolometric luminosity of the two regions.

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“…It is important to note that as MM1a is optically thick beyond 25 GHz, use of the 23 (or indeed 25) GHz will lead to an underestimate in N Lym for this source, meaning that our calculated value is a lower limit. As we indicated previously, we set T e = 10 000 K, giving α(ν, T e ) = 0.966 (Mezger & Henderson 1967). The N Lym values were then compared with the Lyman continuum values for ZAMS stars given in Davies et al (2011) and spectral types from Mottram et al (2011).…”

Section: Derived Propertiesmentioning

confidence: 99%

Tightening the belt: Constraining the mass and evolution in SDC335

Avison

Peretto

Fuller

et al. 2015

A&A

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Aims. Recent ALMA observations identified one of the most massive star-forming cores yet observed in the Milky Way: SDC335-MM1, within the infrared dark cloud SDC335.579-0.292. Along with an accompanying core MM2, SDC335 appears to be in the early stages of its star formation process. We aim to constrain the properties of the stars forming within these two massive millimetre sources. Methods. Observations of SDC335 at 6, 8, 23 and 25 GHz were made with the Australia Telescope Compact Array. We report the results of these continuum measurements, which combined with archival data, allow us to build and analyse the spectral energy distributions (SEDs) of the compact sources in SDC335. Results. Three hyper-compact H regions within SDC335 are identified, two of which are within the MM1 core. For each HCH region, we fit a free-free emission curve to the data, providing the derivation of the sources' emission measure, ionising photon flux, and electron density. Using these physical properties we assign each HCH region a zero-age main sequence (ZAMS) spectral type, finding two protostars with characteristics of spectral type B1.5 and one with a lower limit of B1-B1.5. Ancillary data from infrared to mm wavelength are used to construct free-free component subtracted SEDs for the mm-cores, which allows us to calculate the bolometric luminosities and revise the previous gas mass estimates. Conclusions. The measured luminosities for the two mm-cores are lower than expected from accreting sources displaying characteristics of the ZAMS spectral type assigned to them. The protostars are still actively accreting, suggesting that a mechanism is limiting the accretion luminosity. We present the case for two different mechanisms capable of causing lower than expected accretion luminosity. Finally, using the ZAMS mass values as lower limit constraints, a final stellar population for SDC335 was synthesised finding SDC335 is likely to be in the process of forming a stellar cluster comparable to the Trapezium cluster and NGC 6334 I(N).

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Galactic H II Regions. I. Observations of Their Continuum Radiation at the Frequency 5 GHz

Cited by 551 publications

References 0 publications

The Formation of Massive Stars by Accretion through Trapped Hypercompact HiiRegions

The Formation of Massive Stars by Accretion through Trapped Hypercompact HiiRegions

Millimetric observations of southern HII regions

Tightening the belt: Constraining the mass and evolution in SDC335

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