Galactic H II Regions. II. Observations of Their Hydrogen 109α Recombination-Line Radiation at the Frequency 5009 MHz

Mezger, P. G.; Höglund, B.

doi:10.1086/149031

Cited by 94 publications

(39 citation statements)

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“…This is in excellent agreement with the values of 5 SOOoK found by Mezger and Hoglund (1967) from 109", measurements and 5200 0 K by Dieter (1967) from 15S", results.…”

Section: (D) Excited H-line Halfwidthssupporting

confidence: 91%

“…The lO901: line was observed by Mezger and Hoglund (1967), the lO401: by Gudnov and Sorochenko (1966), the 15801: by Lilley et al (1966) and Dieter (1967), and the 16601: by Palmer and Zuckerman (1966) and McGee and Gardner (1967). In many cases the agreement in radial velocity is satisfactory but in M 8, W 49, and W 51 differences of lO km/sec and more are noted.…”

Section: (A) Oomparison With Other Resultsmentioning

confidence: 90%

“…regions, on the assumption that the radial velocities of the nebulae and the excited H lines must be reasonably close, could be attempted in the same way as was outlined for OH clouds by McGee, Gardner, and Robinson (1967). Dieter (1967) and Mezger and Hoglund (1967) have positioned about 30 of the northern sources by similar means. In the present survey the majority of the sources lie in the area of positional ambiguity and have no optical identifications.…”

Section: (B) Location Of Hii Regions Using the Excited H-line Radial mentioning

confidence: 99%

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The Excited Atomic Hydrogen Lines 126a and 127a in HII Regions

McGee¹,

Gardner²

1968

Aust. J. Phys.

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SummaryForty radio sources have been observed for the presence of the hydrogen recombination lines 126", at 3248·708 MHz and 127", at 3172·864 MHz with a 6' arc aerial beam and a receiver with 48 channels of 37 kHz bandwidth each. Detections were made in 34 sources, all of which were either HI! regions or optically unidentified thermal sources.The mean ratio of line intensity to thermal continuum intensity was 3·4% (± 1· 3 % s.d.); the mean halfwidth of the lines was 340 kHz (± 50 kHz s.d.), which is equivalent to 31·5 km/sec in radial velocity.It is suggested that many of the profiles are complex and contain two or more major components that represent large·scale motions in the HI! regions. The Orion and Omega nebulae are shown to have this type of profile and are discussed in some detail.

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“…This is in excellent agreement with the values of 5 SOOoK found by Mezger and Hoglund (1967) from 109", measurements and 5200 0 K by Dieter (1967) from 15S", results.…”

Section: (D) Excited H-line Halfwidthssupporting

confidence: 91%

Section: (A) Oomparison With Other Resultsmentioning

confidence: 90%

Section: (B) Location Of Hii Regions Using the Excited H-line Radial mentioning

confidence: 99%

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The Excited Atomic Hydrogen Lines 126a and 127a in HII Regions

McGee¹,

Gardner²

1968

Aust. J. Phys.

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“…The L/C expected for an optically thin plasma is in the range from 47.6 to 30.6 km s −1 for LTE electron temperatures, T * e , ranging from 7000 to 10 4 K. (Mezger & Höglund 1967). We note that we have neglected any ionized helium in this calculation in line with the low upper limit observed (Sect.…”

Section: Line-to-continuum Ratiosmentioning

confidence: 75%

LkHα 101 at millimeter wavelengths

Thum

Neri

Báez-Rubio

et al. 2013

A&A

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We present new millimeter observations made with the IRAM interferometer and 30 m telescope of the ionized wind from the massive young stellar object LkHα 101. Several recombination lines, including higher order transitions, were detected for the first time at radio wavelengths in this source. From three α-transitions, we derive an accurate value for the stellar velocity and for the first time, an unambiguous expansion velocity of the wind that is 55 km s −1 . This velocity is much slower than reported previously, and the resulting mass loss rate is 1.8 × 10 −6 M yr −1 . The wideband continuum spectra and the interferometer visibilities show that the density of the wind falls off more steeply than what is compatible with constant-velocity expansion. We argue that these properties indicate that the wind is launched from a radially narrow region of the circumstellar disk, and we propose that slow speed and a steep density gradient are characteristic properties of the evolutionary phase, where young stars of intermediate and high mass clear away the gaseous component of their accretion disks. The recombination lines are emitted close to local thermal equilibrium, but the higher order transitions appear systematically broader and weaker than expected, probably because of impact broadening. Finally, we show that LkHα 101 shares many properties with MWC 349, the only other stellar wind source where radio recombination lines have been detected, with some of them masing. We argue that LkHα 101 evades masing at millimeter wavelengths because of the disk's smaller size and unfavorable orientation. Some amplification may however be detectable at shorter wavelengths.

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“…Using this ratio and the parameters for the continuum and H54α line and assuming local thermodynamic equilibrium (LTE), we derive an electron temperature of 8200 ± 130 K (i.e. Mezger & Hoglund 1967). This value is in the range of electron temperatures derived from radio recombination line observations of other UC H ii regions (Afflerbach et al 1996).…”

Section: Detection Of the H54α And He54α Recombination Linesmentioning

confidence: 99%

High angular resolution 7 mm images toward the UC HII region W3(OH)

Dzib

Rodrı́guez

Medina

et al. 2014

A&A

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Context. Recent high angular resolution radio observations of the ultracompact H ii region W3(OH) confirm the presence of an extremely compact (0. 05), time-variable source near its center. Aims. We use new, sensitive high angular resolution observations of radio continuum and recombination lines to study the compact source in W3(OH) and the ultracompact H ii region itself.Methods. We reduced and analyzed extensive Jansky Very Large Array observations of W3(OH) in the continuum at 41.0 GHz and in the H54α and He54α lines. Results. Our images confirm there is the compact source and show that it is connected by a linear filament to the brightest part of W3(OH). We discuss several possible explanations for this structure and propose future observations that may clarify its nature.

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Galactic H II Regions. II. Observations of Their Hydrogen 109α Recombination-Line Radiation at the Frequency 5009 MHz

Cited by 94 publications

References 0 publications

The Excited Atomic Hydrogen Lines 126a and 127a in HII Regions

The Excited Atomic Hydrogen Lines 126a and 127a in HII Regions

LkHα 101 at millimeter wavelengths

High angular resolution 7 mm images toward the UC HII region W3(OH)

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