Shakespeare in Washington, D.C.

Williams, Gary Jay

doi:10.2307/2870312

Cited by 4 publications

(4 citation statements)

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“…Such enhanced abundances may result from the destruction of ice mantles on dust grains and the release of previously depleted CO molecules. Williams (1985) summarizes several mechanisms including the evaporation of the mantles from the energy released in radical reactions on the dust grains, photodesorption by UV radiation triggered by cosmic ray interactions with H2 molecules in the interior of the cloud, and shocks generated from the interaction between dense clumps and stellar winds from young stellar objects. The transition of 13 CO abundances from the UVilluminated envelope to the self-shielded interior are dependent on the physical conditions.…”

Section: Co Abundance Variations Frommentioning

confidence: 99%

CO abundance variations in the Orion Molecular Cloud

Ripple

Heyer

Gutermuth

et al. 2013

Monthly Notices of the Royal Astronomical Society

102

116

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Infrared stellar photometry from the Two Micron All Sky Survey (2MASS) and spectral line imaging observations of 12 CO and 13 CO J = 1-0 line emission from the Five College Radio Astronomy Observatory (FCRAO) 14m telescope are analysed to assess the variation of the CO abundance with physical conditions throughout the Orion A and Orion B molecular clouds. Three distinct A v regimes are identified in which the ratio between the 13 CO column density and visual extinction changes corresponding to the photon dominated envelope, the strongly self-shielded interior, and the cold, dense volumes of the clouds. Within the strongly self-shielded interior of the Orion A cloud, the 13 CO abundance varies by 100% with a peak value located near regions of enhanced star formation activity. The effect of CO depletion onto the ice mantles of dust grains is limited to regions with A v > 10 mag and gas temperatures less than ∼20 K as predicted by chemical models that consider thermal-evaporation to desorb molecules from grain surfaces.Values of the molecular mass of each cloud are independently derived from the distributions of A v and 13 CO column densities with a constant 13 CO-to-H 2 abundance over various extinction ranges. Within the strongly self-shielded interior of the cloud (A v > 3 mag), 13 CO provides a reliable tracer of H 2 mass with the exception of the cold, dense volumes where depletion is important. However, owing to its reduced abundance, 13 CO does not trace the H 2 mass that resides in the extended cloud envelope, which comprises 40-50% of the molecular mass of each cloud. The implied CO luminosity to mass ratios, M/L CO , are 3.2 and 2.9 for Orion A and Orion B respectively, which are comparable to the value (2.9), derived from γ-ray observations of the Orion region. Our results emphasize the need to consider local conditions when applying CO observations to derive H 2 column densities.

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Section: Co Abundance Variations Frommentioning

confidence: 99%

CO abundance variations in the Orion Molecular Cloud

Ripple

Heyer

Gutermuth

et al. 2013

Monthly Notices of the Royal Astronomical Society

102

116

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“…This is because they chose to estimate the upper limit of N(C 18 O) by assuming that T ex (C 18 O) = 0.5 × T ex ( 12 CO). On the basis of the theoretical predictions by Williams (1985) and Charnley et al (1988) (see Sect. 1), these empirical results can be interpreted as a consequence of differing CO-to-H 2 abundance ratios in the star forming and in the quiescent clouds.…”

Section: N(co)/a J Vs Star Formation Activity As Derived From the Samentioning

confidence: 99%

“…It is usual to measure the distribution and mass of H 2 in molecular clouds using one canonical N(H 2 ) to N(CO) ratio (see e.g., Sanders et al 1984), where CO here stands for the different isotopes of CO, such as 13 CO and/or C 18 O. However, there is no theoretical reason why there should be one universal N(H 2 )/N(CO) ratio for molecular clouds, even though in most chemical schemes the presence of H 2 is important for effective production of CO (Williams 1985). Instead, according to Williams, the ratio may vary from cloud to cloud and even within a cloud.…”

Section: Introductionmentioning

confidence: 99%

The relationship of CO abundance to extinction andN(H$\mathsf{_{2}}$):

Harjunpaa

Lehtinen

Haikala

2004

A&A

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Abstract.We have studied the ratio of 13 are given. These ratios were found to vary from cloud to cloud so that they are larger in B 335 than in B 133 and L 466. These variations are thought to primarily arise from variations of the column density ratio of CO and its isotopes to H 2 . The alternative explanation in terms of the N(H 2 )/A J ratio being larger in starforming regions (B 335) than in more quiescent regions lacking star formation (B 133 and L 466) appears less likely. We also discuss the evidence for N(CO)/A J variations on the basis of previous observations in star forming and non-star forming dark clouds.

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“…Especially, heating due to radiation and schocks in the vicinity of vigorous star formation should alter the level of depletion (e.g. Williams 1985;Charnley et al 1988). Williams (1985) concludes that variations can occur from cloud to cloud, and even within the different regions of the same cloud reflecting the local star formation activity.…”

Section: Introductionmentioning

confidence: 99%

The ratio ofN(C$\mathsf{^{18}}$O) andA$\mathsf{_{V}}$ in Chamaeleon I and III-B

Kainulainen¹,

Lehtinen²,

Harju³

2006

A&A

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The shallow proportionality suggests that C 18 O is heavily depleted in these regions. As the degree of depletion is proportional to the gas density, these regions probably contain very dense, cold cores, which do not stand out in CO mappings. A comparison with the dust temperature map derived from the ISO data shows that the most prominent of the potentially depleted cores indeed coincides with a dust temperature minimum. It seems therefore feasible to use N(C 18 O) and A V data together for identifying cold, dense cores in large scale mappings.

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Shakespeare in Washington, D.C.

Cited by 4 publications

References 0 publications

CO abundance variations in the Orion Molecular Cloud

CO abundance variations in the Orion Molecular Cloud

The relationship of CO abundance to extinction andN(H$\mathsf{_{2}}$):

The ratio ofN(C$\mathsf{^{18}}$O) andA$\mathsf{_{V}}$ in Chamaeleon I and III-B

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