Methyl acetylene as a temperature probe for dense interstellar clouds

Kuiper, T. B. H.; Kuiper, E. N. Rodriguez; Dickinson, D. F.; Turner, B. E.; Zuckerman, B.

doi:10.1086/161604

Cited by 42 publications

(25 citation statements)

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“…Our methyl acetylene abundances are in agreement with the abundances estimated for warm gas in Orion (Blake et al 1987;Kuiper et al 1984), Sgr B2 (Churchwell & Hollis 1983;Kuiper et al 1984), S 140 (Kuiper et al 1984), and with the abundance, which can be estimated for the cold cloud TMC-1 from the ob- Table 3. Rotational temperatures and column densities determined from the methyl acetylene observations.…”

Section: Source Parameters Derived From the Mapssupporting

confidence: 88%

Parameters of warm molecular clouds from methyl acetylene observations

et al. 2002

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Abstract. The results of a survey of 63 galactic star-forming regions in the 6K − 5K and 5K − 4K methyl acetylene lines at 102 and 85 GHz, respectively, are presented. Fourty-three sources were detected at 102 GHz, and twentyfive at 85 GHz. Emission was detected towards molecular clouds with kinetic temperatures 20-60 K (so-called "warm clouds"). The CH3CCH abundances in these clouds appeared to be about several units × 10 −9 . Five mapped sources were analyzed using the maximum entropy method. The sizes of the mapped clouds fall within the range between 0.1 and 1.7 pc, virial masses -between 90 -6200 M , and densities -between 6 × 10 4 and 6 × 10 5 cm −3 . The CH3CCH sources spatially coincide with the CO and CS sources. Chemical evolution simulations showed that the typical methyl acetylene abundance in the observed clouds corresponds to an age of ≈ 6 × 10 4 years.

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Section: Source Parameters Derived From the Mapssupporting

confidence: 88%

Parameters of warm molecular clouds from methyl acetylene observations

et al. 2002

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“…From weighted least-squares fits to the data points, temperature and column densities can be derived (see e.g. Kuiper et al 1984;Bergin et al 1994). The resulting rotational temperature T rot , asumed to be equal to the gas kinetic temperature T kin , and column densities, assuming optically thin emission, are collected in Cols.…”

Section: The Cmentioning

confidence: 99%

A molecular-line study of clumps with embedded high-mass protostar candidates

Brand

Cesaroni

Palla

et al. 2001

A&A

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Abstract. We present molecular line observations made with the IRAM 30-m telecopes of the immediate surroundings of a sample of 11 candidate high-mass protostars. These observations are part of an effort to clarify the evolutionary status of a set of objects which we consider to be precursors of UC Hii regions. In a preceding series of papers we have studied a sample of objects, which on the basis of their IR colours are likely to be associated with compact molecular clouds. The original sample of 260 objects was divided approximately evenly into a High group, with IR colour indices [25−12] ≥ 0.57 and [60−12] ≥ 1.3, and a Low group with complementary colours. The FIR luminosity of the Low sources, their distribution in the IR colour-colour diagram, and their lower detection rate in H2O maser emission compared to the High sources, led to the hypothesis that the majority of these objects represent an earlier stage in the evolution than the members of the High group, which are mostly identifiable with UC Hii regions. Subsequent observations led to the selection of 12 Low sources that have FIR luminosities indicating the presence of B2.5 to O8.5 V0 stars, are associated with dense gas and dust, have (sub-)mm continuum spectra indicating temperatures of ∼30 K, and have no detectable radio continuum emission. One of these sources has been proposed by us to be a good candidate for the high-mass equivalent of a Class 0 object. In the present paper we present observations of the molecular environment of 11 of these 12 objects, with the aim to derive the physical parameters of the gas in which they are embedded, and to find further evidence in support of our hypothesis that these sources are the precursors to UC Hii regions. We find that the data are consistent with such an interpretation. All observed sources are associated with well-defined molecular clumps. Masses, sizes, and other parameters depend on the tracer used, but typically the cores have average diameters of ∼0.5-1 pc (with a range of 0.2 to 2.2 pc), and masses of a few tens to a few thousand solar masses. Compared to a similar analysis of High sources, the present sample has molecular clumps that are more massive, larger, cooler, and less turbulent. They also tend to have a smaller ratio of virial-to-luminous mass, indicating they are less dynamically stable than their counterparts in which the High sources are embedded. The large sizes suggest these clumps should still undergo substantial contraction (their densities are ∼10 times smaller than those of the High sources). The lower temperatures and small linewidths are also expected in objects in an earlier evolutionary state. In various sources indications are found for outflowing gas, though its detection is hampered by the presence of multiple emission components in the line spectra. There are also signs of self-absorption, especially in the spectra of 13 CO and HCO + . We find that the masses of the molecular clumps associated with our objects increase with L fir (M clump ∝ L 1.17 fir ), and that there i...

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“…The rotational temperature, T rot , derived from a series of J K −(J −1) K rotational lines of CH 3 CCH is considered a good estimate of the gas kinetic temperature, T kin , in molecular clouds (e.g., Askne et al 1984;Bergin et al 1994). Since CH 3 CCH has a relatively low dipole moment (µ = 0.78 D, Bauer et al 1979;Burrell et al 1980), its rotational levels are thermalized at densities n(H 2 ) ∼ 10 4 cm −3 or higher (e.g., Kuiper et al 1984). This property together with the assumption that CH 3 CCH emission is optically thin (τ 1), allows us to assume local thermodynamic equilibrium (LTE), so that T kin may be derived.…”

Section: Introductionmentioning

confidence: 99%

SiO and CH₃CCH abundances and dust emission in high-mass star-forming cores

Miettinen

Harju

Haikala

et al. 2006

A&A

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Aims. We determine the fractional SiO abundance in high-mass star-forming cores, and investigate its dependence on physical conditions, to provide constraints on the chemistry models of the formation of SiO in the gas phase or via grain mantle evaporation. The work addresses also CH 3 CCH chemistry, as the kinetic temperature is determined using this molecule. Methods. We estimate the physical conditions of 15 high-mass star-forming cores and derive the fractional SiO and CH 3 CCH abundances using spectral line and dust continuum observations with the SEST. Results. The kinetic temperatures as derived from CH 3 CCH range from 25 to 39 K, the average being 33 K. The average gas density in the cores is 4.5 × 10 6 cm −3 . The SiO emission regions are extended and typically half of the integrated line emission comes from the velocity range traced out by CH 3 CCH emission. The upper limit of SiO abundance in this "quiescent" gas component is ∼10 −10 . The average CH 3 CCH abundance is about 7 × 10 −9 . It shows a shallow, positive correlation with the temperature, whereas SiO shows the opposite tendency. Conclusions. We suggest that the high CH 3 CCH abundance and its possible increase when the clouds become warmer is related to the intensified desorption of the chemical precursors of the molecule from grain surfaces. In contrast, the observed tendency of SiO does not support the idea that the evaporation of Si-containing species from the grain mantles would be important, and it contradicts models where neutral reactions with activation barriers dominate SiO production. A possible explanation for the decrease is that warmer cores represent more evolved stages of core evolution with fewer high-velocity shocks and thus less efficient SiO replenishment.

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Methyl acetylene as a temperature probe for dense interstellar clouds

Cited by 42 publications

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Parameters of warm molecular clouds from methyl acetylene observations

Parameters of warm molecular clouds from methyl acetylene observations

A molecular-line study of clumps with embedded high-mass protostar candidates

SiO and CH₃CCH abundances and dust emission in high-mass star-forming cores

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Methyl acetylene as a temperature probe for dense interstellar clouds

Cited by 42 publications

References 0 publications

Parameters of warm molecular clouds from methyl acetylene observations

Parameters of warm molecular clouds from methyl acetylene observations

A molecular-line study of clumps with embedded high-mass protostar candidates

SiO and CH3CCH abundances and dust emission in high-mass star-forming cores

Contact Info

Product

Resources

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SiO and CH₃CCH abundances and dust emission in high-mass star-forming cores