A spectroscopic study of the DR 21 outflow source. III - The CO line emission

Garden, Rognvald P.; Hayashi, Masahiko; Gatley, I.; Hasegawa, Tetsuo; Kaifu, Norio

doi:10.1086/170143

Cited by 202 publications

(240 citation statements)

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“…Usually this will affect the derived masses by a factor of less than 2 (Ridge & Moore 2001). Occasionally it could be larger, from 2.5 × 10 −5 to 10 −4 (Garden et al 1991). We accept a factor of 4 as the abundance error.…”

Section: Physical Parametersmentioning

confidence: 97%

“…The outflow emission at line wings is often accepted as being optically thin. Nevertheless, some authors deal with it using a derived or assumed optical depth, which may bring a factor of about 5 to the final value of outflow mass, momentum, kinetic energy and so on Goldsmith et al 1984;Shepherd & Churchwell 1996a;Garden et al 1991;Yu et al 1999). Different authors used different [CO]/[H 2 ] abundance ratios.…”

Section: Physical Parametersmentioning

confidence: 99%

“…We accept a factor of 4 as the abundance error. Some authors use 1.36 as the mean atomic weight of the mixture of hydrogen and helium (see Garden et al 1991), while others only consider pure hydrogen molecular gas (see Snell et al 1984). Therefore an uncertainty of 0.36 is introduced.…”

Section: Physical Parametersmentioning

confidence: 99%

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A study of high velocity molecular outflows with an up-to-date sample

Wu¹,

Wei²,

Zhao³

et al. 2004

A&A

294

291

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Abstract.A statistical study of the properties of molecular outflows is performed based on an up-to-date sample. 391 outflows were identified in published articles or preprints before February 28, 2003. The parameters of position, morphology, mass, energy, outflow dynamics and central source luminosity are presented for each outflow source. Outflow lobe polarity is known for all the sources, and 84% are found to be bipolar. The sources are divided into low mass and high mass groups according to either the available bolometric luminosity of the central source or the outflow mass. The pace of discovery of outflows over the past seven years has increased much more rapidly than in previous periods. Surveys for outflows are still continuing. The number of high-mass outflows detected (139) has considerably increased, showing that they are commonly associated with massive as well as low mass stars. Energetic mass ejection may be a common aspect of the formation of high mass as well as low mass stars. Outflow masses are correlated strongly with bolometric luminosity of the center sources, which was obtained for the first time. There are also correlations between the central source luminosity and the parameters of mechanical luminosity and the thrust or force necessary to drive the outflow. The results show that flow mass, momentum and energy depend on the nature of the central source. Despite their similarity, there are differences between the high mass and low mass outflows. Low mass outflows are more collimated than high mass outflows. On average, the mass of high mass sources can be more than two orders of magnitude larger than those of low mass outflows. The relation between flow mass and dynamical time appears to differ for the two types of outflows. Low mass sources make up 90% of outflows associated with HH objects while high mass outflows make up 61% of the sources associated with H 2 O masers. Sources with characteristics of collapse or infall comprise 12% of the entire outflow sample. The spatial distribution of the outflow sources in the Galaxy is presented and the local occurrence rate is compared with the stellar birth rate.

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Section: Physical Parametersmentioning

confidence: 97%

Section: Physical Parametersmentioning

confidence: 99%

See 1 more Smart Citation

A study of high velocity molecular outflows with an up-to-date sample

Wu¹,

Wei²,

Zhao³

et al. 2004

A&A

294

291

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show abstract

“…In this case, η bf 1 should be a reasonable assumption. The 13 CO optical depth is derived using (Garden et al 1991) …”

Section: Calculation Of the Physical Parametersmentioning

confidence: 99%

A CO observation of the Galactic methanol masers

Ren

et al. 2014

A&A

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Context. We investigated the molecular gas associated with 6.7 GHz methanol masers throughout the Galaxy using a J = 1−0 transition of the CO isotopologues. Aims. The methanol maser at 6.7 GHz is an ideal tracer for young high-mass star-forming cores. Based on molecular line emissions in the maser sources throughout the Galaxy, we can estimate their physical parameters and, thereby, investigate the forming conditions of the high-mass stars. Methods. Using the 13.7-m telescope at the Purple Mountain Observatory (PMO), we have obtained 12 CO and 13 CO (1−0) lines for 160 methanol masers sources from the first to the third Galactic quadrants. We made efforts to resolve the distance ambiguity by careful comparison with the radio continuum and HI 21 cm observations. We examined the statistical properties in three aspects: first, the variation throughout the Galaxy; second, the correlation between the different parameters; third, the difference between the maser sources and the infrared dark clouds. In addition, we have also carried out 13 CO mapping for 33 sources in our sample. Results. First, the maser sources show increased 13 CO line widths toward the Galactic center, suggesting that the molecular gas are more turbulent toward the Galactic center. This trend can be noticeably traced by the 13 CO line width. In comparison, the Galactic variation for the H 2 column density and the 12 CO excitation temperature are less significant. Second, the 12 CO excitation temperature shows a noticeable correlation with the H 2 column density. A possible explanation consistent with the collapse model is that the higher surface-density gas is more efficient to the stellar heating and/or has a higher formation rate of high-mass stars. Third, comparing the infrared dark clouds, the maser sources on average have significantly lower H 2 column densities, moderately higher temperatures, and similar line widths. Fourth, In the mapped regions around 33 masers, 51 13 CO cores have been revealed. Among them, only 17 coincide with the radio continuum emission (F cm > 6 mJy), while a larger fraction (30 cores) coincide with the infrared emissions. Only one maser source has no significant IR emission. The IR-bright and radio-bright sources exhibit significantly higher 12 CO excitation temperatures than the IR-faint and radio-faint sources, respectively. Conclusions. The 6.7 GHz masers show a moderately low ionization rate but have a common-existing stellar heating that generates the IR emissions. The relevant properties can be characterized by the 12 CO and 13 CO (1−0) emissions in several aspects as described above.

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“…Column densities were calculated following Garden et al (1991): (3.10) where N is the column density of the species in question, B and µ d are the rotational constant and permanent dipole moment of the molecule respectively, and J is the lower rotational level of the transition. This equation, and the analysis that follows, assumes that the species under consideration is in local thermodynamic equilibrium (LTE) -i.e.…”

Section: )mentioning

confidence: 99%

Submillimetre Studies of Prestellar and Starless Cores in the Ophiuchus, Taurus and Cepheus Molecular Clouds

Pattle¹

2017

Springer Theses

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A spectroscopic study of the DR 21 outflow source. III - The CO line emission

Cited by 202 publications

References 0 publications

A study of high velocity molecular outflows with an up-to-date sample

A study of high velocity molecular outflows with an up-to-date sample

A CO observation of the Galactic methanol masers

Submillimetre Studies of Prestellar and Starless Cores in the Ophiuchus, Taurus and Cepheus Molecular Clouds

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