Rotational excitation of formaldehyde by hydrogen molecules: ortho-H<sub>2</sub>CO at low temperature

Troscompt, N.; Fauré, Alexandre; Wiesenfeld, Laurent; Ceccarelli, C.; Valiron, P.

doi:10.1051/0004-6361:200810712

Cited by 64 publications

(69 citation statements)

References 44 publications

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“…These discrepancies are expected because the rates were computed by Green within the IOS scattering approach based on a coarse electron-gas approximation used for the PES. However, we point out that similar trends for He/H 2 have been found for other systems such as SO (Lique et al 2007), SiS (Lique et al 2008), HC 3 N (Wernli et al 2007a,b), and H 2 CO (Troscompt et al 2009), even though the PES's and the cross sections were computed with the same accuracy. For all these systems, the potential well for interaction with H 2 is deeper by a factor of about two than the one found for interaction with He, leading to larger cross sections and rates for collisions with H 2 .…”

Section: Para and Ortho H 2 Ratessupporting

confidence: 81%

Collisional excitation of sulfur dioxide in cold molecular clouds

Cernicharo

Spielfiedel

Balança

et al. 2011

A&A

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We present collisional rate coefficients for SO 2 with ortho and para molecular hydrogen for the physical conditions prevailing in dark molecular clouds. Rate coefficients for the first 31 rotational levels of this species (energies up to 55 K) and for temperatures between 5 and 30 K are provided. We have found that these rate coefficients are about ten times more than those previously computed for SO 2 with helium. We calculated the expected emission of the centimeter wavelength lines of SO 2 . We find that the transition connecting the metastable 2 02 level with the 1 11 one is in absorption against the cosmic background for a wide range of densities. The 4 04 −3 13 line is found to be inverted for densities below a few 10 4 cm −3 . We observed the 1 11 −2 02 transition with the 100 m Green Bank Telescope towards some dark clouds. The line is observed, as expected, in absorption and provides an abundance of SO 2 in these objects of a few 10 −10 . The potential use of millimeter lines of SO 2 as tracers of the physical conditions of dark clouds is discussed.

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Section: Para and Ortho H 2 Ratessupporting

confidence: 81%

Collisional excitation of sulfur dioxide in cold molecular clouds

Cernicharo

Spielfiedel

Balança

et al. 2011

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“…The recent analysis of H 2 CO observations towards a cold molecular cloud by Troscompt et al (2009) confirms theoretical estimates (e.g. Flower et al 2006) that in molecular clouds the H 2 OPR is lower than 1.…”

Section: Continuum Emission: Modellingsupporting

confidence: 78%

Physical structure of the envelopes of intermediate-mass protostars

Ceccarelli¹,

Alonso-Albi

Fuente

et al. 2010

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Context. Intermediate mass protostars provide a bridge between low-and high-mass protostars. Furthermore, they are an important component of the UV interstellar radiation field. Despite their relevance, little is known about their formation process. Aims. We present a systematic study of the physical structure of five intermediate mass, candidate Class 0 protostars. Our two goals are to shed light on the first phase of intermediate mass star formation and to compare these protostars with low-and high-mass sources. Methods. We derived the dust and gas temperature and density profiles of the sample. We analysed all existing continuum data on each source and modelled the resulting SED with the 1D radiative transfer code DUSTY. The gas temperature was then predicted by means of a modified version of the code CHT96. Results. We found that the density profiles of five out of six studied intermediate mass envelopes are consistent with the predictions of the "inside-out" collapse theory. We compared several physical parameters, like the power law index of the density profile, the size, the mass, the average density, the density at 1000 AU and the density at 10 K of the envelopes of low-, intermediate, and high-mass protostars. When considering these various physical parameters, the transition between the three groups appears smooth, suggesting that the formation processes and triggers do not substantially differ.

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“…This can be explained by excitation considerations, because of the smaller critical densities of the observed transitions of H 2 CO compared to CN N = 2−1. These transitions have similar Einstein coefficients, but the collisional rates of H 2 CO with para-H 2 (Troscompt et al 2009) are typically 5 to 10 times larger than those of CN with para-H 2 at 10 K (Kalugina et al 2012). On average, CN is brighter than H 2 CO (see Fig.…”

Section: So and H 2 Co As Outflow Or Envelope Tracersmentioning

confidence: 99%

A sensitive survey for¹³CO, CN, H₂CO, and SO in the disks of T Tauri and Herbig Ae stars

Guilloteau¹,

Folco²,

Dutrey³

et al. 2013

A&A

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Aims. We investigate the suitability of several molecular tracers, in particular CN N = 2−1 line emission, as a confusion-free probe of the kinematics of circumstellar disks. Methods. We use the IRAM 30-m telescope to perform a sensitive search for CN N = 2−1 in 42 T Tauri or Herbig Ae systems located principally in the Taurus-Auriga region. 13 CO J = 2−1 is observed simultaneously to provide an indication of the level of confusion with the surrounding molecular cloud. The bandpass also contains two transitions of ortho-H 2 CO, one of SO and the C 17 O J = 2−1 line which provide complementary information on the nature of the emission. Results. While 13 CO is in general dominated by residual emission from the cloud, CN exhibits a high disk detection rate >50% in our sample. We even report CN detection in stars for which interferometric searches failed to detect 12 CO, presumably because of obscuration by a foreground, optically thick, cloud. Comparison between CN and o-H 2 CO or SO line profiles and intensities divide the sample in two main categories. Sources with SO emission are bright and have strong H 2 CO emission, leading in general to [H 2 CO/CN] > 0.5. Furthermore, their line profiles, combined with a priori information on the objects, suggest that the emission is coming from outflows or envelopes rather than from a circumstellar disk. On the other hand, most sources have [H 2 CO/CN] < 0.3, no SO emission, and some of them exhibit clear double-peaked profiles characteristics of rotating disks. In this second category, CN is likely tracing the proto-planetary disks. From the line flux and opacity derived from the hyperfine ratios, we constrain the outer radii of the disks, which range from 300 to 600 AU. The overall gas disk detection rate (including all molecular tracers) is ∼68%, and decreases for fainter continuum sources. Conclusions. The current study demonstrates that gas disks, like dust disks, are ubiquitous around young PMS stars in regions of isolated star formation, and that a large fraction of them have R out > ∼ 300 AU. It also shows the potential of the CN N = 2−1 transition to probe the kinematics of these disks, thereby measuring the stellar mass, using high resolution observations with ALMA.

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Rotational excitation of formaldehyde by hydrogen molecules: ortho-H₂CO at low temperature

Cited by 64 publications

References 44 publications

Collisional excitation of sulfur dioxide in cold molecular clouds

Collisional excitation of sulfur dioxide in cold molecular clouds

Physical structure of the envelopes of intermediate-mass protostars

A sensitive survey for¹³CO, CN, H₂CO, and SO in the disks of T Tauri and Herbig Ae stars

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Rotational excitation of formaldehyde by hydrogen molecules: ortho-H2CO at low temperature

Cited by 64 publications

References 44 publications

Collisional excitation of sulfur dioxide in cold molecular clouds

Collisional excitation of sulfur dioxide in cold molecular clouds

Physical structure of the envelopes of intermediate-mass protostars

A sensitive survey for13CO, CN, H2CO, and SO in the disks of T Tauri and Herbig Ae stars

Contact Info

Product

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Rotational excitation of formaldehyde by hydrogen molecules: ortho-H₂CO at low temperature

A sensitive survey for¹³CO, CN, H₂CO, and SO in the disks of T Tauri and Herbig Ae stars