N(CO)/N(H2)-ratio in the local interstellar medium

Harjunpaa, P.; Mattila, K.

doi:10.1007/3-540-58196-0_46

Cited by 18 publications

(29 citation statements)

References 6 publications

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“…3, independent of the different assumptions used in the modeling (see Table C.1). Harjunpää & Mattila (1996) and Anderson et al (1999) have also found similar abundance ratios in dark clouds and cores. …”

Section: Modelingmentioning

confidence: 57%

The physical state of selected cold clumps

Parikka

Juvela

Pelkonen

et al. 2015

A&A

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Context. The study of prestellar cores is essential to understanding the initial stages of star formation. With Herschel more cold clumps have been detected than ever before. For this study we have selected 21 cold clumps from 20 Herschel fields observed as a follow-up on original Planck detections. We have observed these clumps in 13 CO (1−0), C 18 O (1−0), and N 2 H + (1−0) lines. Aims. Our aim is to find out if these cold clumps are prestellar. We have examined to what extent independent analysis of the dust and the molecular lines lead to similar conclusions about the masses of these objects. Methods. We calculate the clump masses and densities from the dust continuum and molecular line observations and compare these to each other and to the virial and Bonnor-Ebert masses calculated for each clump. Finally we examine two of the fields with radiative transfer models to estimate CO abundances. Results. When excitation temperatures could be estimated, the column densities derived from molecular line observations were comparable to those from dust continuum data. The median column density estimates are 4.2 × 10 21 cm −2 and 5.5 × 10 21 cm −2 for the line and dust emission data, respectively. The calculated abundances, column densities, volume densities, and masses all have large uncertainties and one must be careful when drawing conclusions. Abundance of 13 CO was found in modeling the two clumps in the field G131.65+9.75 to be close to the usual value of 10 −6 . The abundance ratio of 13 CO and C 18 O was ∼10. Molecular abundances could only be estimated with modeling, relying on dust column density data. Conclusions. The results indicate that most cold clumps, even those with dust color temperatures close to 11 K, are not necessarily prestellar.

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Section: Modelingmentioning

confidence: 57%

The physical state of selected cold clumps

Parikka

Juvela

Pelkonen

et al. 2015

A&A

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“…The observed temperature gradients are nevertheless quite small, and even going from, say, T ex = 8 K to T ex = 15 K does not produce a large enough difference to explain the observed N(C 18 O) variations in clumps (see the discussion e.g. in Harjunpää & Mattila 1996). Furthermore, the neglection of the temperature gradient should lead to similar variations in clumps with equal maximum extinction.…”

Section: Discussionmentioning

confidence: 91%

“…Hayakawa et al (2001) studied the ratio also in different parts within Cha I. Harjunpää and Mattila (1996) derived the N(C 18 O)/A V ratio for about 20 individual lines of sight across Cha I using the SEST telescope and near-IR extinction values from literature. The results of the present study are compared with these results in Sect.…”

Section: Chamaeleon Cloud Complexmentioning

confidence: 99%

“…Since then, the ratio has been examined by Frerking et al (1982) in Taurus and ρ Ophiuchi, Harjunpää et al (1996) in Chamaeleon I, R Corona Australis and Coalsack, Hayakawa et al (1999Hayakawa et al ( , 2001 in the Chamaeleon complex, and by Lada et al (1994), Alves et al (1999), Juvela et al (1997Juvela et al ( , 2002 and Harjunpää et al (2004) in several small globules. These data, reviewed and compared in more detail by Harjunpää et al (2004), show some evidence supporting the correlation of N(C 18 O)/A V with star forming activity.…”

Section: Introductionmentioning

confidence: 99%

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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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“…relation from Harjunpää & Mattila (1996) and Cardelli et al (1989), it would normally be possible to get column densities for molecular hydrogen from the extinction data alone. However, as the dense cores along the filament have high extinction values, acquiring reliable values for A V around them by using the NICER-method alone is unreliable due to very low star densities close to and inside the cores.…”

Section: H 2 Column Densitiesmentioning

confidence: 99%

CH abundance gradient in TMC-1

Suutarinen

Geppert

Harju

et al. 2011

A&A

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Aims. The aim of this study is to examine if the well-known chemical gradient in TMC-1 is reflected in the amount of rudimentary forms of carbon available in the gas-phase. As a tracer we use the CH radical which is supposed to be well correlated with carbon atoms and simple hydrocarbon ions. Methods. We observed the 9-cm Λ-doubling lines of CH along the dense filament of TMC-1. The CH column densities were compared with the total H 2 column densities derived using the 2MASS NIR data and previously published SCUBA maps and with OH column densities derived using previous observations with Effelsberg. We also modelled the chemical evolution of TMC-1 adopting physical conditions typical of dark clouds using the UMIST Database for Astrochemistry gas-phase reaction network to aid the interpretation of the observed OH/CH abundance ratios. Results. The CH column density has a clear peak in the vicinity of the cyanopolyyne maximum of TMC-1. The fractional CH abundance relative to H 2 increases steadily from the northwestern end of the filament where it lies around 1.0 × 10 −8 , to the southeast where it reaches a value of 2.0 × 10 −8 . The OH and CH column densities are well correlated, and we obtained OH/CH abundance ratios of ∼16-20. These values are clearly larger than what has been measured recently in diffuse interstellar gas and is likely to be related to C to CO conversion at higher densities. The good correlation between CH and OH can be explained by similar production and destruction pathways. We suggest that the observed CH and OH abundance gradients are mainly due to enhanced abundances in a low-density envelope which becomes more prominent in the southeastern part and seems to continue beyond the dense filament.Conclusions. An extensive envelope probably signifies an early stage of dynamical evolution, and conforms with the detection of a large CH abundance in the southeastern part of the cloud. The implied presence of other simple forms of carbon in the gas phase provides a natural explanation for the observation of "early-type" molecules in this region.

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N(CO)/N(H2)-ratio in the local interstellar medium

Cited by 18 publications

References 6 publications

The physical state of selected cold clumps

The physical state of selected cold clumps

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

CH abundance gradient in TMC-1

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