Transitions Of HCO Research Articles

Circum-Protostellar Environments. III. Gas Densities and Kinetic Temperatures

view Abstract Citations (33) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Circum-Protostellar Environments. III. Gas Densities and Kinetic Temperatures Moriarty-Schieven, G. H. ; Wannier, P. G. ; Mangum, J. G. ; Tamura, M. ; Olmsted, V. K. Abstract We have surveyed a complete, flux-limited, IRAS-selected sample of protostars in Taurus whose infrared through millimeter-wave properties indicate them to be younger than T Tauri stars. We have observed CS J = 3-2, 5-4, and 7-6, and H2CO JK-1K+1 = 303-202 and 322-221, toward the central positions of all 25 objects. CS traces the dense gas in the circumstellar envelope, while H2CO probes the kinetic temperature of the dense gas. Only three of the sources were detected in both transitions of H2CO, making it of limited use as a temperature probe of these objects. Combining the CS- and H2CO-derived properties with those previously derived from dust continuum emission, we have placed limits on the temperatures of the envelopes, typically 20 K ≃ TK ≃ 50 K. Derived envelope gas densities and CS column densities were typically a few × 106 cm-3 and a few × 1012 cm-2, respectively. Where CS 5-4 was detected (roughly half of the observed sources), the derived envelope masses were consistent with those derived from dust emission (assuming a CS/H2 abundance of 10-8). Since most of the embedded (i.e., not optically visible) sources were detected in CS 5-4, and most of the visible sources were not, this may mean either that the CS-emitting envelope has dissipated in the more evolved objects (confirming Ohashi et al. 1991), or CS has become depleted. L1551NE may have an asymmetric, double-peaked line profile like that of B335, suggestive of a collapsing envelope. L1551NE may be in transition from the much younger "class 0" protostar stage to the somewhat more evolved "class I" protostar stage. Several of the sources have broad CS line wings probably originating from dense gas in a molecular outflow. In at least one case, the kinetic temperature of the outflowing gas may be greater than that in the envelope. Publication: The Astrophysical Journal Pub Date: December 1995 DOI: 10.1086/176567 Bibcode: 1995ApJ...455..190M Keywords: STARS: CIRCUMSTELLAR MATTER; ISM: JETS AND OUTFLOWS; ISM: KINEMATICS AND DYNAMICS; ISM: MOLECULES; STARS: PRE-MAIN-SEQUENCE full text sources ADS | data products SIMBAD (27) Related Materials (2) Part 1: 1992ApJ...400..260M Part 2: 1994ApJ...436..800M

Modeling Line Profiles of Protostellar Collapse in B335 with the Monte Carlo Method

view Abstract Citations (141) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Modeling Line Profiles of Protostellar Collapse in B335 with the Monte Carlo Method Choi, Minho ; Evans, Neal J., II ; Gregersen, Erik M. ; Wang, Yangsheng Abstract A collapsing dark cloud core, B335, is modeled as an inside-out collapse. The radiative transfer code uses the Monte Carlo method and new collision rates for CS. Line profiles for several observed transitions of CS and H2CO are computed. We confirm that a double-peaked spectrum with a stronger blue peak is a good qualitative signature of infall. Compared to the models using the large velocity gradient method by Zhou et al., our best-fit model using the Monte Carlo method has 20% smaller infall radius, 70% larger CS abundance, and 30% larger H2CO abundance. Also, infall radii found from CS and H2CO agree better than they did in the modeling by Zhou et al. Our model also produces off-center spectra close to the observations. Publication: The Astrophysical Journal Pub Date: August 1995 DOI: 10.1086/176002 Bibcode: 1995ApJ...448..742C Keywords: HYDRODYNAMICS; ISM: GLOBULES; ISM: INDIVIDUAL ALPHANUMERIC: B335; ISM: MOLECULES; METHODS: NUMERICAL; STARS: FORMATION full text sources ADS | data products SIMBAD (1)

The densest prestellar condensations: H2CO Studies of? Oph B1

The ρ Oph B1 cloud core region is unique in that it exhibits 2-cm H2CO line emission over a substantial area (indicating gas densities ≥ 106 cm-3), while lacking any known embedded infrared sources. Subsequent H2CO studies at the VLA and the JCMT have not provided a consistent model of the gas structure and kinematics. Here, we present the first high-velocity resolution maps in the 218 GHz and 352 GHz transitions of H2CO. Our multi-transition study, at velocity and spatial resolutions comparable to existing VLA data, has proven crucial to forming a coherent picture of the gas kinematics.

Formaldehyde as a probe of physical conditions in dense molecular clouds

view Abstract Citations (191) References (112) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Formaldehyde as a Probe of Physical Conditions in Dense Molecular Clouds Mangum, Jeffrey G. ; Wootten, Alwyn Abstract We present a detailed analysis describing the utility of the formaldehyde (H2CO) molecule in the derivation of the kinetic temperature and spatial density within molecular clouds. Measurements of 13 transitions from both the ortho and para species of H2CO have been made toward a sample of 11 active star formation regions. These H2CO transitions range in frequency from 211 to 365 GHz and in upper-state energy from 21 to 241 K. This range in excitation has allowed us to analyze H2CO sensitivity to both cool (TK less than or approximately equal to 50 K) and warm (TK greater than 50 K) molecular material. Using a spherical large velocity gradient (LVG) model to solve for the excitation of H2CO, we analyze the sensitivity of several ortho- and para-H2CO transition intensity ratios to the kinetic temperature and spatial density within molecular clouds. Using our measured H2CO radiation temperatures, we have constrained LVG model solutions for the kinetic temperature, spatial density, and H2CO species column density in each of the sources in our sample. In all of the regions in our sample, though, we measure kinetic temperatures greater than 50 K, significantly higher than previous estimates for many of these sources. Using our ortho- and para-H2CO measurements we have calculated the N(ortho-H2CO)/N(para-H2CO) ratio in several of the sources in our sample. Our measurements indicate that N(ortho-H2CO)/N(para-H2CO) less than 3 for most of our sources. When combined with the relatively high kinetic temperature in these objects, this N(ortho-H2CO)/N(para-H2CO) ratio suggests that dust grains might play an active role in H2CO chemistry. Publication: The Astrophysical Journal Supplement Series Pub Date: November 1993 DOI: 10.1086/191841 Bibcode: 1993ApJS...89..123M Keywords: Energy Levels; H Ii Regions; Interstellar Gas; Molecular Clouds; Molecular Spectra; Radiative Transfer; Star Formation; Velocity Distribution; Molecular Spectroscopy; Space Density; Spatial Resolution; Temperature; Astrophysics; ISM: MOLECULES; ISM: H II REGIONS; ISM: CLOUDS; MOLECULAR PROCESSES full text sources ADS | data products SIMBAD (14)

On the nature of the molecular cores in high-latitude cirrus clouds. V - NH3 and its chemistry

view Abstract Citations (25) References (45) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Nature of the Molecular Cores in High-Latitude Cirrus Clouds. V. NH 3 and Its Chemistry Turner, B. E. Abstract The paper presents the first report on the (1, 1) and (2, 2) transitions of NH3 in a subset of 11 cirrus clouds observed mainly in January 1989 at the 43 m telescope equipped with dual maser receivers, each of which could be tuned to wide enough bandwidth to include both lines simultaneously. The transitions are analyzed using methodology applied by Turner (1993) to analyze the 2 and 6 cm H2CO transitions. It was found that the radial distributiom of NH3 within the cirrus cores followes that of (C-18)O (Turner at al, 1992; Turner, 1993), in contrast to H2CO, which was found to have a flat or rising distribution with increasing radius. The ratio of (1, 1) to (2, 2) intensities was found to depend only on the temperature of all values of density of astrophysical interest. Publication: The Astrophysical Journal Pub Date: July 1993 DOI: 10.1086/172821 Bibcode: 1993ApJ...411..219T Keywords: Ammonia; Cirrus Clouds; Interstellar Chemistry; Interstellar Matter; Molecular Clouds; Star Formation; Carbon Monoxide; Far Infrared Radiation; Formaldehyde; Gravitational Collapse; Molecular Excitation; Astrophysics; ISM: CLOUDS; ISM: MOLECULES; MOLECULAR PROCESSES full text sources ADS | data products SIMBAD (12) Related Materials (4) Part 1: 1989ApJ...344..292T Part 2: 1992ApJ...391..158T Part 3: 1993ApJ...405..229T Part 4: 1993ApJ...410..140T

HCO+ emission in the HH7–11 region: the slowest component of the outflow?

The region of the high-velocity outflow in HH7–11 has been mapped in the J = 4–3 transition of HCO+. The results are compared with published optical, CO and J = 1–0 HCO+ maps. Unlike the latter interferometric data, we see a bright compact source associated with the exciting star, plus weaker emission throughout the region. Extended emission surrounds the line of HH objects, and has a structure very similar to that of the blueshifted CO outflow. Spectra of the J = 4–3 and 3–2 lines in selected positions within the flow region indicate two physical components: (i) cool gas at a density of a few × 106 cm–3 at the velocity of SSV13 and the ambient cloud; and (ii) warm (35 K) gas at a few × 105 cm–3 blueshifted by ≈ 1 km s– 1. The close agreement between the HCO+ and higher velocity CO suggests that the former arises from the densest, slowest component of the molecular flow. The structure appears to favour a confined jet rather than a shocked cloudlet model

The physical structure of Orion-KL on 2500 AU scales using the K-doublet transitions of formaldehyde

view Abstract Citations (44) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Physical Structure of Orion-KL on 2500 AU Scales Using the K-Doublet Transitions of Formaldehyde Mangum, Jeffrey G. ; Wootten, Alwyn ; Plambeck, Richard L. Abstract Synthesized beamwidths of 5.1 arcsec for 2400 AU and 7.6 arcsec for 3500 AU are used, in the present study of interferometric observations of the 110 to 111 and 514 to 515 transitions of H2CO toward the molecular cloud Orion-KL, to identify emission from the hot core, compact ridge, and northern cloud regions. A discussion of H2CO as a spatial density probe indicates that the K-doublet transitions are ideal for this role, since they achieve appreciable optical depths only at the highest column densities. Publication: The Astrophysical Journal Pub Date: May 1993 DOI: 10.1086/172663 Bibcode: 1993ApJ...409..282M Keywords: Electron Transitions; Formaldehyde; Interstellar Matter; Molecular Clouds; Orion Nebula; Physical Properties; Interferometry; Star Formation; Stellar Mass; Astrophysics; ISM: INDIVIDUAL NAME: ORION NEBULA; ISM: MOLECULES full text sources ADS | data products SIMBAD (2)

Molecular observations of HH34: does NH3 accurately trace dense molecular gas near young stars?

We discuss single-dish NH 3 , observations of the molecular environment around HH34 and its exciting star. NH 3 (1, 1) integrated intensity contours reveal two peaks, though neither is coincident with the HH34S bow shock, nor with the exciting source of the system. Instead, the northern peak is offset ∼40 arcsec east of the source HH34IRS, while a ridge of emission follows the outflow direction. Towards HH34IRS, the NH 3 column density is lower by a factor of ∼10 than towards NH 3 , peaks elsewhere in the HH34 system. Observations of the J = 4-3 transition of HCO + , however, show a clear peak around the central star, which we associate with a density and temperature peak

Evidence for protostellar collapse in B335

We have observed five rotational transitions of H2CO and CS toward the Bok globule, B335, with high spatial and spectral resolution. The characteristic shape of the observed profiles provides direct, kinematic evidence of collapse. In addition, we have modeled line profiles of collapsing dense cores with density and velocity structures taken from the theory of Shu and coworkers. Using the age of collapse as the only free parameter, we found that the strengths and profiles of the observed lines can be well fitted by the theoretical model. Our best-fit model gives an age of 1.5 x 10 exp 5 yr, corresponding to an infall radius of 0.04 pc and a total mass of 0.4 solar mass for the central star and disk. Outside the infall radius, there is a static envelope with a r exp -2 density distribution, an average temperature of 13 K, and a turbulent velocity (1/e width) of 0.12 km/s. The CS abundance is 3.6 x 10 exp -9 with about 30 percent uncertainty.

The molecular core in G34.3 + 0.2 - Millimeter interferometric observations of HCO(+), H(C-13)N, H(C-15)N, and SO

This study presents high-resolution observations of the molecular core in the star-forming region G34.3 + 0.2. Maps at 6-arcsec resolution of emission and absorption of the J = 1 - 0 transitions of HCO(+), H (C-13)N, H(C-15)N, and of the 2(2) - 1(1) transition of SO were obtained in addition to a map of the 3.4-mm continuum emission from the compact H II component. The HCL(+) emission toward G34.3 + 0.2 traces a warm molecular core about 0.9 pc in size. Emission from H (C-13)N is detected over about 0.3 pc. The cometary H II region lies near the edge of the molecular core. The blueshift of the radio recombination lines with respect to the molecular emission suggests that gas from the H II region is accelerated in a champagne flow caused by a steep gradient in the ambient gas density.

Protostellar condensations in the core of NGC 2024

The J = 4-3 transition of HCO(+) was observed in the core of NGC 2024. The findings indicate a possibly expanding torus centered around the FIR 6 continuum source and an E-W ridge below the ionization front. The presence of HCO(+) J = 4-3 emission from the torus and E-W ridge suggests relatively high gas densities in these regions. The relatively strong intensity of the observed HCO(+) J = 4-3 emission toward the FIR source suggests that the emission originates from relatively warm and dense gas. Continuum radiation transport modeling of the core shows that submillimeter and millimeter continuum observations of the cores can be reproduced under the assumption that the cores are externally heated objects without internal heating sources. This requires a factor of about 250 enhancement of the external radiation field intensity compared to the standard Galactic radiation field. This enhancement is consistent with the stellar luminosities required to explain the observed FIR continuum emission from the region.

Observations of an expanding molecular ring in S106

The 3 mm rotational transition of HCO(+) toward S106 has been mapped with the Berkeley-Illinois-Maryland Array and the NRAO 12 m telescope. The maps show evidence for an expanding molecular ring around IRS 4, the exciting star in S106. The radius of the ring is about 2 x 10 to the 17th cm, and its mass is 10 solar masses or less. The ring is expanding with a velocity of about 2 km/s. The ring cannot be supported by rotation; magnetic fields and gas pressure may be important in determining the kinematics of the region. Clumps of high-velocity material are observed which may have been ablated from the ring and entrained in the ionized bipolar outflow. 13 refs.

High-resolution molecular observations of NGC 7538 IRS 1

This paper presents results of high-resolution (about 3 arcsec) observations of HCN and HCO(+) toward NGC 7538 IRS 1, carried out with the Berkeley-Illinois-Maryland Array and the NRAO 12-m telescope. The J = 1-0 transition of HCO(+) shows an elongated structure extending from the northeast to the southwest. The wings of the HCO(+) line show the blue lobe of an outflow which is in the same direction as the CO outflow in the source. A detailed comparison between individual HCN and HCO(+) emission peaks shows a definite anticorrelation, which is an indication of different mechanisms which excite the two molecules. 22 refs.

Observations of the formaldehyde emission in Orion-KL - Abundances, distribution, and kinematics of the dense gas in the Orion molecular ridge

view Abstract Citations (49) References (48) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of the Formaldehyde Emission in Orion-KL: Abundances, Distribution, and Kinematics of the Dense Gas in the Orion Molecular Ridge Mangum, Jeffrey G. ; Wootten, Alwyn ; Loren, Robert B. ; Wadiak, E. James Abstract The "hot core," "plateau," and "ridge" features in the Orion-KL molecular cloud have been mapped in 2 cm H2CO emission with a 6" synthesized beam. We have also observed all ΔJ = 1 millimeter wave transitions of H2CO and several of the H213CO and H2C18O transitions in the 211 to 363 GHz window toward Orion-KL with a single antenna. The H2CO hot core emission has been identified for the first time both in high- excitation line profiles and in the 2 cm maps. We identify a velocity shift in the 2 cm H2CO emission which we attribute to the plateau or bipolar flow. This velocity shift lies at a position angle of 120° ± 30°, which is parallel to the bipolar flows seen in SiO, HCO+, H2, SO2, CO, and SO emission. The large primary beam available for these observations has provided a particularly sensitive map of the rather extended "ridge" structure in Orion-KL. The "ridge" component in our 2 cm H2CO emission maps can be decomposed into two clumps, called the "compact ridge" and "10 km s-1 feature." The compact ridge dominates the observed emission. Comparison with aperture synthesis maps in other molecules demonstrates that the 2 cm H2CO compact ridge defines an extensive high-density (≳106 cm-3) region at the southern edge of the bipolar flow near IRc2. With this multitransition, multi-isotopomer^{5 }data set, we have modeled the spatial density in the compact ridge component. We find that n(H2) = 5.0 × 106-1.0 × 107 cm-3 in the H2CO compact ridge. These models also reveal that there is no evidence for substantial variation in the H2CO abundances among the hot core, compact ridge, and 10 km s-1 feature. However, H2CO is 3-25 times more abundant in these Orion-KL components than it is in other molecular clouds (Mundy et al.; Wootten et al.). This abundance enhancement may be due to the epidemic of massive star formation in the region. Observers have noted in the past that 2 cm H2CO emission occurs only rarely in interstellar clouds, though density sufficient to cause the emission is found in many cloud cores. We suggest that the reason the emission is notably intense in Orion-KL lies in the enhancement of the H2CO abundance, as well as in the high density. Publication: The Astrophysical Journal Pub Date: January 1990 DOI: 10.1086/168262 Bibcode: 1990ApJ...348..542M Keywords: Abundance; Formaldehyde; Kinematics; Molecular Clouds; Orion Nebula; Antennas; Astronomical Models; Emission Spectra; Gas Density; Interstellar Matter; Star Formation; interstellar: molecules; nebulae: abundances; nebulae: individual (Orion Nebula); Astrophysics; INTERSTELLAR: MOLECULES; NEBULAE: ABUNDANCES; NEBULAE: ORION NEBULA full text sources ADS | data products SIMBAD (2)

Shock chemistry in the molecular clouds associated with SNR IC 443.

Several interstellar molecules have been detected toward the highly perturbed B and G clouds associated with the supernova remnant IC 443 via their 3 mm transitions, including N2H+, SiO, SO, CN, HNC, and H13CO+. The (J, K) = (1, 1) and (2, 2) inversion lines of metastable ammonia have also been observed, as well as the J = 3-2 transition of HCO+ at 1.2 mm. Analysis of the (1, 1) and (2, 2) inversion lines of NH3 indicates minimum gas kinetic temperatures of TK = 70 K toward cloud B, and TK = 33 K in cloud G. Modeling of the J = 1-0 and J = 3-2 transitions of HCO+ implies densities greater than 10(5) cm-3 toward both positions. These data clearly show that hot and dense material is present in IC 443, and they suggest the presence of shocks in both regions. A careful analysis of the HCO+ lines indicates that the HCO+ abundance is at most enhanced by factors of a few over that found in cold, quiescent gas. This conclusion contradicts past claims of HCO+ abundance enhancements of several orders of magnitude in the perturbed regions. The N2H+ abundance was also found to be similar to that in cold gas, suggesting that there is no increase in ionization in the clouds. The abundances of SO and CS, as well as CN and NH3, do not appear to differ significantly from those found in cold dark clouds, although chemistry models predict sulfur-containing species to undergo high-temperature enhancements. SiO, however, is found to have an abundance in the perturbed gas 100 times larger than the upper limits observed in the dark cloud TMC 1, a result in agreement with high temperature chemistry models. In addition, the HNC/HCN ratio in both IC 443 B and G was found to be approximately 0.1--far from the ratio of 1 predicted by low-temperature ion-molecule chemistry, but similar to the values observed in clouds where elevated temperatures are present.

Vector and product quantum-state correlations for photofragmentation of formaldehyde

The vector correlations of para-H2(ν= 1, J= 0–8) produced form H2CO photolysis on the rR0(0)e line of the 21 41 S1â†� S0 transition have been measured by analysing Doppler-resolved laser-induced fluorescence line-shapes. The correlations of the H2CO transition dipole moment µ with the H2 recoil velocity v and µ with the angular momentum J are small, probably because H2CO rotates many times between excitation and fragmentation. The correlation of v with J has been found to be between the limiting cases of v∥J and v⊥J. In addition, the H2(ν, J) linewidths have been used to measure the product state correlation. H2 fragments in high vibrational states correlate with CO fragments in low rotational states.

Interferometric observations of the 1-0 transition of HCO(+) toward NGC 7538 IRS 1

Interferometric observations of the molecular cloud toward the compact H II region IRS 1 in NGC 7538 in the 1-0 line of HCO(+) are reported. Employing a resolution of 8.5 arcsec, a highly elongated molecular cloud oriented at position angle 52 deg is found, perpendicular to the axis of the bipolar CO outflow. In perfect alignment with the blueshifted lobe in CO, strong blueshifted line wings are detected in HCO(+). The origin of the flow is at the center of the HCO(+) cloud, 15 arcsec to the south of IRS 1, which is clearly not the source that powers this outflow. So far no other indication of star formation has been detected at this position. 8 references.

Microwave spectroscopy of HCO + and DCO + in excited vibrational states

The J = 3-2, 4-3, and 5-4 transitions of DCO + and the J = 3-2 and 4-3 transitions of HCO +, both in the ν 2, 2 ν 2, ν 1, and ν 3 states, were observed to derive the rotational, centrifugal distortion, and l-type doubling constants. The Fermi resonance between the ν 1 and 4 ν 2 0 states of DCO + was analyzed using the observed molecular constants of the ν 1, ν 2, and 2 ν 2 states. The effect of the discharge electric field was noticed on the ν 2 and 2 ν 2 spectra.

VLA observations of the 4.8-GHz H2CO transition in L1551

Les cartes revelent une configuration symetrique de l'absorption H 2 CO centree sur IRS 5. En continu, on a detecte IRS 5 et deux autres sources

The Submillimetre Wavelength Spectrum of Orion A

We report on the first submillimetre wavelength spectral scan of the Orion A molecular cloud in the frequency range 342-463 GHz (0.88-0.65 mm) using the Queen Mary College Submillimetre Heterodyne Receiver at UKIRT. Twenty-eight molecular transitions were detected, the majority of these for the first time. The lines include transitions of CO, CS, HCN, HCO+, H2CO, H2CS, SO, SO2, CCH, SiO and CH3OH. Upper limits are reported for a number of lines including CO+ and the ground state transition of NH2. A number of the lines are surprisingly intense, and we will present maps of the relative distributions of HCO+, HCN, H2CO and CCH, which show striking differences in their spatial structures. We will present details of the excitation of a number of the lines based on the results from this survey.