ROTATIONAL QUENCHING OF CO DUE TO H<sub>2</sub>COLLISIONS

Yang, Benhui; Stancil, P. C.; Balakrishnan, N.; Forrey, Robert C.

doi:10.1088/0004-637x/718/2/1062

Cited by 348 publications

(311 citation statements)

References 68 publications

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“…The molecular data were retrieved from the LAMDA data base 4 . The collisional rate coefficients were adopted from Yang et al (2010), who calculated the collisional rates between CO and H 2 , incorporating energy levels up to J = 40 for kinetic temperatures of up to 3000 K. For the purposes of our study of the physical conditions as a function of velocity, we use the integrated intensities in the EHV, IHV, and SHV ranges ( Table 2). The value that we adopt for the linewidth, Δ , is directly inferred from the definition of our different velocity ranges (40, 50, and 30 km s −1 , for EHV, IHV and SHV, respectively).…”

Section: Discussion: Physical Conditionsmentioning

confidence: 99%

High-JCO emission in the Cepheus E protostellar outflow observed with SOFIA/GREAT

Gómez-Ruiz¹,

Leurini²,

Codella³

et al. 2012

A&A

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Context. Owing to the high energy required for their excitation, high-J CO transitions are a valuable tool for the study of protostellar jets and outflows. However, high spectral resolution observations of high-J CO lines, which are essential to distinguish the different components in the line profiles, were impossible until the start of operations of the Herschel Space Observatory and the Stratospheric Observatory For Infrared Astronomy (SOFIA).Aims. We present and analyze two spectrally resolved high-J CO lines toward a protostellar outflow. We study the physical conditions, as a function of velocity, traced by such high-energy transitions in bipolar outflows. Methods. We selected the molecular outflow Cep E, driven by an intermediate-mass class 0 protostar. Using the German REceiver for Astronomy at Terahertz frequencies (GREAT) onboard SOFIA, we observed the CO (12-11) and (13-12) transitions (E u ∼ 430 and 500 K, respectively) toward one position in the blue lobe of this outflow, that had been known to display high-velocity molecular emission. Results. We detect the outflow emission in both transitions, up to extremely high velocities (∼100 km s −1 with respect to the systemic velocity). We divide the line profiles into three velocity ranges that each have interesting spectral features: standard, intermediate, and extremely high-velocity. One distinct bullet is detected in each of the last two. A large velocity gradient analysis for these three velocity ranges provides constraints on the kinetic temperature and volume density of the emitting gas, 100 K and 10 4 cm −3 , respectively. These results are in agreement with previous ISO observations and are comparable with results obtained by Herschel for similar objects. Conclusions. High-J CO lines are a good tracer of molecular bullets in protostellar outflows. Our analysis suggests that different physical conditions are at work in the intermediate velocity range compared with the standard and extremely high-velocity gas.

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Section: Discussion: Physical Conditionsmentioning

confidence: 99%

High-JCO emission in the Cepheus E protostellar outflow observed with SOFIA/GREAT

Gómez-Ruiz¹,

Leurini²,

Codella³

et al. 2012

A&A

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“…LIME performs non-LTE (Local Thermodynamic Equilibrium) line radiative transfer modeling, where the rotational level populations are found iteratively. The CO isotopologue data files containing collisional rate coefficients (Yang et al 2010) were downloaded from the LAMDA 2 database (Schöier et al 2005). The collisional rate coefficients of the CO isotopologues with H 2 in these files include collisions with both ortho-and para-H 2 .…”

Section: Gas Line Emission Modelingmentioning

confidence: 99%

The ALMA-PILS survey: 3D modeling of the envelope, disks and dust filament of IRAS 16293–2422

Jacobsen

Jørgensen

Wiel

et al. 2018

A&A

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Context. The Class 0 protostellar binary IRAS 16293-2422 is an interesting target for (sub)millimeter observations due to, both, the rich chemistry toward the two main components of the binary and its complex morphology. Its proximity to Earth allows the study of its physical and chemical structure on solar system scales using high angular resolution observations. Such data reveal a complex morphology that cannot be accounted for in traditional, spherical 1D models of the envelope. Aims. The purpose of this paper is to study the environment of the two components of the binary through 3D radiative transfer modeling and to compare with data from the Atacama Large Millimeter/submillimeter Array. Such comparisons can be used to constrain the protoplanetary disk structures, the luminosities of the two components of the binary and the chemistry of simple species. Methods. We present 13 CO, C 17 O and C 18 O J=3-2 observations from the ALMA Protostellar Interferometric Line Survey (PILS), together with a qualitative study of the dust and gas density distribution of IRAS 16293-2422. A 3D dust and gas model including disks and a dust filament between the two protostars is constructed which qualitatively reproduces the dust continuum and gas line emission.Results. Radiative transfer modeling in our sampled parameter space suggests that, while the disk around source A could not be constrained, the disk around source B has to be vertically extended. This puffed-up structure can be obtained with both a protoplanetary disk model with an unexpectedly high scale-height and with the density solution from an infalling, rotating collapse. Combined constraints on our 3D model, from observed dust continuum and CO isotopologue emission between the sources, corroborate that source A should be at least six times more luminous than source B. We also demonstrate that the volume of high-temperature regions where complex organic molecules arise is sensitive to whether or not the total luminosity is in a single radiation source or distributed into two sources, affecting the interpretation of earlier chemical modeling efforts of the IRAS 16293-2422 hot corino which used a single-source approximation. Conclusions. Radiative transfer modeling of source A and B, with the density solution of an infalling, rotating collapse or a protoplanetary disk model, can match the constraints for the disk-like emission around source A and B from the observed dust continuum and CO isotopologue gas emission. If a protoplanetary disk model is used around source B, it has to have an unusually high scale-height in order to reach the dust continuum peak emission value, while fulfilling the other observational constraints. Our 3D model requires source A to be much more luminous than source B; L A ∼ 18 L and L B ∼ 3 L .

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“…The second step is the ray tracing, i.e., calculating the emergent spectrum at a given distance and inclination. The collisional rate coefficients required for the first step are collected from the Leiden Atomic and Molecular Database 1 (LAMDA; Schöier et al 2005), where the most recent data files for CO and H 2 O are from Yang et al (2010) and Faure et al (2007), respectively. The ortho-to-para ratio for H 2 is taken to be thermalised, with a maximum value of 3.…”

Section: Radiative Transfermentioning

confidence: 99%

ModellingHerschelobservations of hot molecular gas emission from embedded low-mass protostars

Visser

Kristensen

Bruderer

et al. 2012

A&A

119

185

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Aims. Young stars interact vigorously with their surroundings, as evident from the highly rotationally excited CO (up to E u /k = 4000 K) and H 2 O emission (up to 600 K) detected by the Herschel Space Observatory in embedded low-mass protostars. Our aim is to construct a model that reproduces the observations quantitatively, to investigate the origin of the emission, and to use the lines as probes of the various heating mechanisms. Methods. The model consists of a spherical envelope with a power-law density structure and a bipolar outflow cavity. Three heating mechanisms are considered: passive heating by the protostellar luminosity, ultraviolet irradiation of the outflow cavity walls, and small-scale C-type shocks along the cavity walls. Most of the model parameters are constrained from independent observations; the two remaining free parameters considered here are the protostellar UV luminosity and the shock velocity. Line fluxes are calculated for CO and H 2 O and compared to Herschel data and complementary ground-based data for the protostars NGC 1333 IRAS2A, HH 46 and DK Cha. The three sources are selected to span a range of evolutionary phases (early Stage 0 to late Stage I) and physical characteristics such as luminosity and envelope mass. Results. The bulk of the gas in the envelope, heated by the protostellar luminosity, accounts for 3-10% of the CO luminosity summed over all rotational lines up to J = 40-39; it is best probed by low-J CO isotopologue lines such as C 18 O 2-1 and 3-2. The UV-heated gas and the C-type shocks, probed by 12 CO 10-9 and higher-J lines, contribute 20-80% each. The model fits show a tentative evolutionary trend: the CO emission is dominated by shocks in the youngest source and by UV-heated gas in the oldest one. This trend is mainly driven by the lower envelope density in more evolved sources. The total H 2 O line luminosity in all cases is dominated by shocks (>99%). The exact percentages for both species are uncertain by at least a factor of 2 due to uncertainties in the gas temperature as function of the incident UV flux. However, on a qualitative level and within the context of our model, both UV-heated gas and C-type shocks are needed to reproduce the emission in far-infrared rotational lines of CO and H 2 O.

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ROTATIONAL QUENCHING OF CO DUE TO H₂COLLISIONS

Cited by 348 publications

References 68 publications

High-JCO emission in the Cepheus E protostellar outflow observed with SOFIA/GREAT

High-JCO emission in the Cepheus E protostellar outflow observed with SOFIA/GREAT

The ALMA-PILS survey: 3D modeling of the envelope, disks and dust filament of IRAS 16293–2422

ModellingHerschelobservations of hot molecular gas emission from embedded low-mass protostars

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ROTATIONAL QUENCHING OF CO DUE TO H2COLLISIONS

Cited by 348 publications

References 68 publications

High-JCO emission in the Cepheus E protostellar outflow observed with SOFIA/GREAT

High-JCO emission in the Cepheus E protostellar outflow observed with SOFIA/GREAT

The ALMA-PILS survey: 3D modeling of the envelope, disks and dust filament of IRAS 16293–2422

ModellingHerschelobservations of hot molecular gas emission from embedded low-mass protostars

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ROTATIONAL QUENCHING OF CO DUE TO H₂COLLISIONS