Browsing by Subject "ism: molecules"

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Alma Observations of the Massive Molecular Outflow G331.512-0.103
(2013-09) Merello, Manuel; Bronfman, Leonardo; Garay, Guido; Lo, Nadia; Evans, Neal J., II; Nyman, Lars-Åke; Cortes, Juan R.; Cunningham, Maria R.; Merello, Merello; Evans, Neal J., II
The object of this study is one of the most energetic and luminous molecular outflows known in the Galaxy, G331.512-0.103. Observations with ALMA Band 7 (350 GHz; 0.86 mm) reveal a very compact, extremely young bipolar outflow and a more symmetric outflowing shocked shell surrounding a very small region of ionized gas. The velocities of the bipolar outflow are about 70 km s(-1) on either side of the systemic velocity. The expansion velocity of the shocked shell is similar to 24 km s(-1), implying a crossing time of about 2000 yr. Along the symmetry axis of the outflow, there is a velocity feature, which could be a molecular "bullet" of high-velocity dense material. The source is one of the youngest examples of massive molecular outflow found associated with a high-mass star.
The Bolocam Galactic Plane Survey. VII. Characterizing The Properties Of Massive Star-Forming Regions
(2011-11) Dunham, Miranda K.; Rosolowsky, Erik; Evans, Neal J.; Cyganowski, Claudia; Urquhart, James S.; Dunham, Miranda K.; Evans, Neal J.
We present the results of a Green Bank Telescope survey of NH(3)(1,1), (2,2), (3,3) lines toward 631 Bolocam Galactic Plane Survey (BGPS) sources at a range of Galactic longitudes in the inner Galaxy. We have detected the NH(3)(1,1) line toward 72% of our targets (456), demonstrating that the high column density features identified in the BGPS and other continuum surveys accurately predict the presence of dense gas. We have determined kinematic distances and resolved the distance ambiguity for all BGPS sources detected in NH(3). The BGPS sources trace the locations of the Scutum and Sagittarius spiral arms, with the number of sources peaking between R(Gal) similar to 4 and 5 kpc. We measure the physical properties of each source and find that depending on the distance, BGPS sources are primarily clumps, with some cores and clouds. We have examined the physical properties as a function of Galactocentric distance, and find a mean gas kinetic temperature of 15.6 K, and that the NH(3) column density and abundance decrease by nearly an order of magnitude between R(Gal) similar to 3 and 11 kpc. Comparing sources at similar distances demonstrates that the physical properties are indistinguishable, which suggests a similarity in clump structure across the Galactic disk. We have also compared the BGPS sources to criteria for efficient star formation presented independently by Heiderman et al. and Lada et al., and for massive star formation presented by Kauffmann et al. Forty-eight percent of our sample should be forming stars (including massive stars) with high efficiency, and 87% contain subregions that should be efficiently forming stars. Indeed, we find that 67% of the sample exhibit signs of star formation activity based on an association with a mid-infrared source.
The c2d Spitzer Spectroscopic Survey Of Ices Around Low-Mass Young Stellar Objects. IV. NH3 And CH3OH
(2010-08) Bottinelli, Sandrine; Boogert, Adwin C. A.; Bouwman, Jordy; Beckwith, Martha; van Dishoeck, Ewine F.; Oberg, Karin I.; Pontoppidan, Klaus M.; Linnartz, H.; Blake, Geoffrey A.; Evans, Neal J.; Lahuis, Fred; Evans, Neal J.
NH3 and CH3OH are key molecules in astrochemical networks leading to the formation of more complex N- and O-bearing molecules, such as CH3CN and CH3OCH3. Despite a number of recent studies, little is known about their abundances in the solid state. This is particularly the case for low-mass protostars, for which only the launch of the Spitzer Space Telescope has permitted high-sensitivity observations of the ices around these objects. In this work, we investigate the similar to 8-10 mu m region in the Spitzer IRS (InfraRed Spectrograph) spectra of 41 low-mass young stellar objects (YSOs). These data are part of a survey of interstellar ices in a sample of low-mass YSOs studied in earlier papers in this series. We used both an empirical and a local continuum method to correct for the contribution from the 10 mu m silicate absorption in the recorded spectra. In addition, we conducted a systematic laboratory study of NH3- and CH3OH- containing ices to help interpret the astronomical spectra. We clearly detect a feature at similar to 9 mu m in 24 low-mass YSOs. Within the uncertainty in continuum determination, we identify this feature with the NH3 nu(2) umbrella mode and derive abundances with respect to water between similar to 2% and 15%. Simultaneously, we also revisited the case of CH3OH ice by studying the nu(4) C-O stretch mode of this molecule at similar to 9.7 mu m in 16 objects, yielding abundances consistent with those derived by Boogert et al. based on a simultaneous 9.75 and 3.53 mu m data analysis. Our study indicates that NH3 is present primarily in H2O-rich ices, but that in some cases, such ices are insufficient to explain the observed narrow FWHM. The laboratory data point to CH3OH being in an almost pure methanol ice, or mixed mainly with CO or CO2, consistent with its formation through hydrogenation on grains. Finally, we use our derived NH3 abundances in combination with previously published abundances of other solid N-bearing species to find that up to 10%-20% of nitrogen is locked up in known ices.
The Chemical Composition Of Cernis 52 (BD+31 Degrees 640)
(2009-11) Hernandez, J. I. G.; Iglesias-Groth, S.; Rebolo, R.; Garcia-Hernandez, D. Anibal; Manchado, A.; Lambert, David L.; Lambert, David L.
We present an abundance analysis of the star Cernis 52 in whose spectrum we recently reported the naphthalene cation in absorption at 6707.4 angstrom. This star is on a line of sight to the Perseus molecular complex. The analysis of high-resolution spectra using a chi(2)-minimization procedure and a grid of synthetic spectra provides the stellar parameters and the abundances of O, Mg, Si, S, Ca, and Fe. The stellar parameters of this star are found to be T(eff) = 8350 +/- 200 K, log(g/cm s(2))= 4.2 +/- 0.4 dex. We derived a metallicity of [Fe/H] = -0.01 +/- 0.15. These stellar parameters are consistent with a star of similar to 2 M(circle dot) in a pre-main-sequence evolutionary stage. The stellar spectrum is significantly veiled in the spectral range lambda lambda 5150-6730 angstrom up to almost 55% of the total flux at 5150 angstrom and decreasing toward longer wavelengths. Using Johnson-Cousins and Two Micron All Sky Survey photometric data, we determine a distance to Cernis 52 of 231(-85)(+135) pc considering the error bars of the stellar parameters. This determination places the star at a similar distance to the young cluster IC 348. This together with its radial velocity, v(r) = 13.7 +/- 1 kms(-1), its proper motion and probable young age support Cernis 52 as a likely member of IC 348. We determine a rotational velocity of v sin i = 65 +/- 5 kms(-1) for this star. We confirm that the stellar resonance line of Li I at 6707.8 angstrom is unable to fit the broad feature at 6707.4 angstrom. This feature should have a interstellar origin and could possibly form in the dark cloud L1470 surrounding all the cluster IC 348 at about the same distance.
The (Cn)-N-14/(Cn)-N-15 Ratio in Diffuse Molecular Clouds
(2015-05) Ritchey, A. M.; Federman, S. R.; Lambert, David L.; Lambert, D. L.
We report the first detection of (CN)-N-15 in diffuse molecular gas from a detailed examination of CN absorption lines in archival spectra, obtained with the Ultraviolet and Visual Echelle Spectrograph of the Very Large Telescope of stars probing local diffuse clouds. Absorption from the (CN)-N-15 isotopologue is confidently detected ( at greater than or similar to 4 sigma) in three out of the four directions studied and appears as a very weak feature between the main (12) CN and (CN)-C-13 absorption components. Column densities for each CN isotopologue are determined through profile fitting, after accounting for weak additional line-of-sight components of (CN)-C-12, which are seen in the absorption profiles of CH and CH+ as well. The weighted mean value of N-14/(CN)-N-15 for the three sight lines with detections of (CN)-N-15 is 274 +/- 18. Since the diffuse molecular clouds toward our target stars have relatively high gas kinetic temperatures and relatively low visual extinctions, their N-14/(CN)-N-15 ratios should not be affected by chemical fractionation. The mean N-14/(CN)-N-15 ratio that we obtain should therefore be representative of the ambient N-14/N-15 ratio in the local interstellar medium. Indeed, our mean value agrees well with that derived from millimeter-wave observations of CN, HCN, and HNC in local molecular clouds.
CO2 Ice Toward Low-Luminosity Embedded Protostars: Evidence For Episodic Mass Accretion Via Chemical History
(2012-10) Kim, Hyo Jeeong; Evans, Neal J.; Dunham, Michael M.; Lee, Jeong-Eun; Pontoppidan, Klaus M.; Kim, Hyo Jeeong; Evans, Neal J.
We present Spitzer IRS spectroscopy of CO2 ice bending mode spectra at 15.2 mu m toward 19 young stellar objects (YSOs) with luminosity lower than 1L(circle dot) (3 with luminosity lower than 0.1 L-circle dot). Ice on dust grain surfaces can encode the history of heating because pure CO2 ice forms only at elevated temperature, T > 20 K, and thus around protostars of higher luminosity. Current internal luminosities of YSOs with L < 1L(circle dot) do not provide the conditions needed to produce pure CO2 ice at radii where typical envelopes begin. The presence of detectable amounts of pure CO2 ice would signify a higher past luminosity. Many of the spectra require a contribution from a pure, crystalline CO2 component, traced by the presence of a characteristic band splitting in the 15.2 mu m bending mode. About half of the sources (9 out of 19) in the low-luminosity sample have evidence for pure CO2 ice, and 6 of these have significant double-peaked features, which are very strong evidence of pure CO2 ice. The presence of the pure CO2 ice component indicates that the dust temperature, and hence luminosity of the central star/accretion disk system, must have been higher in the past. An episodic accretion scenario, in which mixed CO-CO2 ice is converted to pure CO2 ice during each high-luminosity phase, explains the presence of pure CO2 ice, the total amount of CO2 ice, and the observed residual (CO)-O-18 gas.
Dust, Ice And Gas In Time (DIGIT) Herschel And Spitzer Spectro-Imaging Of SMM3 And SMM4 In Serpens
(2013-10) Dionatos, O.; Jorgensen, J. K.; Green, J. D.; Herczeg, G. J.; Evans, Neal J.; Kristensen, L. E.; Lindberg, J. E.; van Dishoeck, E. F.; Green, Joel D.; Evans, Neal J.
Context. Mid-and far-infrared observations of the environment around embedded protostars reveal a plethora of high excitation molecular and atomic emission lines. Different mechanisms for the origin of these lines have been proposed, including shocks induced by protostellar jets and radiation or heating by the embedded protostar of its immediate surroundings. Aims. By studying of the most important molecular and atomic coolants, we aim at constraining the physical conditions around the embedded protostars SMM3 and SMM4 in the Serpens molecular cloud core and measuring the CO/H-2 ratio in warm gas. Methods. Spectro-imaging observations from the Spitzer Infrared Spectrograph (IRS) and the Herschel Photodetector Array Camera and Spectrometer (PACS) provide an almost complete wavelength coverage between 5 and 200 mu m. Within this range, emission from all major molecular (H-2, CO, H2O and OH) and many atomic ([OI], [CII], [FeII], [SiII] and [SI]) coolants of excited gas are detected. Emission line maps reveal the morphology of the observed emission and indicate associations between the different species. The excitation conditions for molecular species are assessed through rotational diagrams. Emission lines from major coolants are compared to the results of steady-state C- and J-type shock models. Results. Line emission tends to peak at distances of similar to 10-20 '' from the protostellar sources with all but [CII] peaking at the positions of outflow shocks seen in near-IR and sub-millimeter interferometric observations. The [CII] emission pattern suggests that it is most likely excited from energetic UV radiation originating from the nearby flat-spectrum source SMM6. Excitation analysis indicates that H-2 and CO originate in gas at two distinct rotational temperatures of similar to 300 K and 1000 K, while the excitation temperature for H2O and OH is similar to 100-200 K. The morphological and physical association between CO and H2 suggests a common excitation mechanism, which allows direct comparisons between the two molecules. The CO/H2 abundance ratio varies from similar to 10(-5) in the warmer gas up to similar to 10(-4) in the hotter regions. Shock models indicate that C-shocks can account for the observed line intensities if a beam filling factor and a temperature stratification in the shock front are considered. C-type shocks can best explain the emission from H2O. The existence of J-shocks is suggested by the strong atomic/ionic (except for [CII]) emission and a number of line ratio diagnostics. Dissociative shocks can account for the CO and H-2 emission in a single excitation temperature structure. Conclusions. The bulk of cooling from molecular and atomic lines is associated with gas excited in outflow shocks. The strong association between H2 and CO constrain their abundance ratio in warm gas. Both C-and J-type shocks can account for the observed molecular emission; however, J-shocks are strongly suggested by the atomic emission and provide simpler and more homogeneous solutions for CO and H-2. The variations in the CO/H-2 abundance ratio for gas at different temperatures can be interpreted by their reformation rates in dissociative J-type shocks, or the influence of both C and J shocks.
Evidence For Decay Of Turbulence By MHD Shocks In The ISM via CO Emission
(2015-06) Larson, Rebecca L.; Evans, Neal J.; Green, Joel D.; Yang, Lao-Lun; Larson, Rebecca L.; Evans, Neal J.; Green, Joel D.; Yang, Lao-Lun
We utilize observations of sub-millimeter rotational transitions of CO from a Herschel Cycle 2 open time program ("COPS", PI: J. Green) to identify previously predicted turbulent dissipation by magnetohydrodynamic (MHD) shocks in molecular clouds. We find evidence of the shocks expected for dissipation of MHD turbulence in material not associated with any protostar. Two models fit about equally well: model 1 has a density of 10(3) cm(-3), a shock velocity of 3 km s(-1), and a magnetic field strength of 4 mu G; model 2 has a density of 10(3.5) cm(-3), a shock velocity of 2 km s(-1), and a magnetic field strength of 8 mu G. Timescales for decay of turbulence in this region are comparable to crossing times. Transitions of CO up to J of 8, observed close to active sites of star formation, but not within outflows, can trace turbulent dissipation of shocks stirred by formation processes. Although the transitions are difficult to detect at individual positions, our Herschel-SPIRE survey of protostars provides a grid of spatially distributed spectra within molecular clouds. We averaged all spatial positions away from known outflows near seven protostars. We find significant agreement with predictions of models of turbulent dissipation in slightly denser (10(3.5) cm(-3)) material with a stronger magnetic field (24 mu G) than in the general molecular cloud.
Evidence for the Naphthalene Cation in a Region of the Interstellar Medium with Anomalous Microwave Emission
(2008-09) Iglesias-Groth, S.; Manchado, A.; Garcia-Hernandez, D. A.; Hernandez, J. I. G.; Lambert, David L.; Lambert, D. L.
We report high-resolution spectroscopy of the moderately reddened (A(v) = 3) early-type star Cernis 52 located in a region of the Perseus molecular cloud complex with anomalous microwave emission. In addition to the presence of the most common diffuse interstellar bands (DIBs) we detect two new interstellar or circumstellar bands coincident to within 0.01% in wavelength with the two strongest bands of the naphthalene cation (C(10)H(8)(+)) as measured in gas-phase laboratory spectroscopy at low temperatures and find marginal evidence for the third strongest band. Assuming these features are caused by the naphthalene cation, from the measured intensity and available oscillator strengths we find that 0.008% of the carbon in the cloud could be in the form of this molecule. We expect hydrogen additions to cause hydronaphthalene cations to be abundant in the cloud and to contribute via electric dipole radiation to the anomalous microwave emission. The identification of new interstellar features consistent with transitions of the simplest polycyclic aromatic hydrocarbon adds support to the hypothesis that this type of molecules are the carriers of both diffuse interstellar bands and anomalous microwave emission.
High-Resolution Optical Spectroscopy of DY Cen: Diffuse Interstellar Bands in a Proto-Fullerene Circumstellar Environment?
(2012-11) Garcia-Hernandez, D. A.; Rao, N. Kameswara; Lambert, David L.; Rao, N. Kameswara; Lambert, David L.
We search high-resolution and high-quality VLT/UVES optical spectra of the hot R Coronae Borealis star DY Cen for electronic transitions of the C-60 molecule and diffuse interstellar bands (DIBs). We report the non-detection of the strongest C-60 electronic transitions (e. g., those at similar to 3760, 3980, and 4024 angstrom). The absence of C-60 absorption bands may support recent laboratory results, which show that the similar to 7.0, 8.5, 17.4, and 18.8 mu m emission features seen in DY Cen-and other similar objects with polycyclic-aromatic-hydrocarbon-like dominated IR spectra-are attributable to proto-fullerenes or fullerene precursors rather than to C-60. DIBs toward DY Cen are normal for its reddening; the only exception is the DIB at 6284 angstrom (possibly also the 7223 angstrom DIB) which is found to be unusually strong. We also report the detection of a new broad (FWHM similar to 2 angstrom) and unidentified feature centered at similar to 4000 angstrom. We suggest that this new band may be related to the circumstellar proto-fullerenes seen at infrared wavelengths.
Hyperfine Structure In The J=1-0 Transitions Of DCO+, DNC, And (HNC)-C-13: Astronomical Observations And Quantum-Chemical Calculations
(2009-11) van der Tak, F. F. S.; Muller, H. S. P.; Harding, M. E.; Gauss, J.; Harding, M. E.
Context. Knowledge of the hyperfine structure of molecular lines is useful for estimating reliable column densities from observed emission, and essential for the derivation of kinematic information from line profiles. Aims. Deuterium bearing molecules are especially useful in this regard, because they are good probes of the physical and chemical structure of molecular cloud cores on the verge of star formation. However, the necessary spectroscopic data are often missing, especially for molecules which are too unstable for laboratory study. Methods. We have observed the ground-state (J = 1-0) rotational transitions of DCO+, (HNC)-C-13 and DNC with the IRAM 30 m telescope toward the dark cloud LDN 1512 which has exceptionally narrow lines permitting hyperfine splitting to be resolved in part. The measured splittings of 50-300 kHz are used to derive nuclear quadrupole and spin-rotation parameters for these species. The measurements are supplemented by high-level quantum-chemical calculations using coupled-cluster techniques and large atomic-orbital basis sets. Results. We find eQq = +151.12 (400) kHz and C-I = -1.12 (43) kHz for DCO+, eQq = 272.5 (51) kHz for (HNC)-C-13, and eQq(D) = 265.9 (83) kHz and eQq(N) = 288.2 (71) kHz for DNC. The numbers for DNC are consistent with previous laboratory data, while our constants for DCO+ are somewhat smaller than previous results based on astronomical data. For both DCO+ and DNC, our results are more accurate than previous determinations. Our results are in good agreement with the corresponding best theoretical estimates, which amount to eQq = 156.0 kHz and C-I = -0.69 kHz for DCO+, eQq = 279.5 kHz for (HNC)-C-13, and eQq(D) = 257.6 kHz and eQq(N) = 309.6 kHz for DNC. We also derive updated rotational constants for (HNC)-C-13: B = 43 545.6000 (47) MHz and D = 93.7 (20) kHz. Conclusions. The hyperfine splittings of the DCO+, DNC and (HNC)-C-13 J = 1-0 lines range over 0.47-1.28 km s(-1), which is comparable to typical line widths in pre-stellar cores and to systematic gas motions on similar to 1000 AU scales in protostellar cores. We present tabular information to allow inclusion of the hyperfine splitting in astronomical data interpretation. The large differences in the N-14 quadrupole parameters of DNC and (HNC)-C-13 have been traced to differences in the vibrational corrections caused by significant non-rigidity of these molecules, particularly along the bending coordinate.
Interaction Between the Broad-Lined Type Ic Supernova 2012ap and Carriers of Diffuse Interstellar Bands
(2014-02) Milisavljevic, Dan; Margutti, Raffaella; Crabtree, Kyle N.; Foster, Jonathan B.; Soderberg, Alicia M.; Fesen, Robert A.; Parrent, Jerod T.; Sanders, Nathan E.; Drout, Maria R.; Kamble, Atish; Chakraborti, Sayan; Pickering, Timothy E.; Cenko, S. Bradley; Silverman, Jeffrey M.; Filippenko, Alexei V.; Kirshner, Robert P.; Mazzali, Paolo; Maeda, Keiichi; Marion, G. H. Howie; Vinko, Jozsef; Wheeler, J. Craig; Silverman, Jeffrey M.; Marion, G. H. Howie; Vinko, Jozsef; Wheeler, J. Craig
Diffuse interstellar bands (DIBs) are absorption features observed in optical and near-infrared spectra that are thought to be associated with carbon-rich polyatomic molecules in interstellar gas. However, because the central wavelengths of these bands do not correspond to electronic transitions of any known atomic or molecular species, their nature has remained uncertain since their discovery almost a century ago. Here we report on unusually strong DIBs in optical spectra of the broad-lined Type Ic supernova SN 2012ap that exhibit changes in equivalent width over short (less than or similar to 30 days) timescales. The 4428 angstrom and 6283 angstrom DIB features get weaker with time, whereas the 5780 angstrom feature shows a marginal increase. These nonuniform changes suggest that the supernova is interacting with a nearby source of DIBs and that the DIB carriers possess high ionization potentials, such as small cations or charged fullerenes. We conclude that moderate-resolution spectra of supernovae with DIB absorptions obtained within weeks of outburst could reveal unique inFormation about the mass-loss environment of their progenitor systems and provide new constraints on the properties of DIB carriers.
Interpretation Of Infrared Vibration-Rotation Spectra Of Interstellar And Circumstellar Molecules
(2013-03) Lacy, John H.; Lacy, John H.
Infrared vibration-rotation lines can be valuable probes of interstellar and circumstellar molecules, especially symmetric molecules, which have no pure rotational transitions. But most such observations have been interpreted with an isothermal absorbing slab model, which leaves out important radiative transfer and molecular excitation effects. A more realistic non-LTE and non-isothermal radiative transfer model has been constructed. The results of this model are in much better agreement with the observations, including cases where lines in one branch of a vibration-rotation band are in absorption and another in emission. In general, conclusions based on the isothermal absorbing slab model can be very misleading, but the assumption of LTE may not lead to such large errors, particularly if the radiation field temperature is close to the gas temperature.
Interstellar CN And CH+ In Diffuse Molecular Clouds: C-12/C-13 Ratios And Cn Excitation
(2011-02) Ritchey, A. M.; Federman, S. R.; Lambert, David L.; Ritchey, A. M.; Federman, S. R.; Lambert, David L.
We present very high signal-to-noise ratio absorption-line observations of CN and CH+ along 13 lines of sight through diffuse molecular clouds. The data are examined to extract precise isotopologic ratios of (CN)-C-12/(CN)-C-13 and (CH+)-C-12/(CH+)-C-13 in order to assess predictions of diffuse cloud chemistry. Our results on (CH+)-C-12/(CH+)-C-13 confirm that this ratio does not deviate from the ambient C-12/C-13 ratio in local interstellar clouds, as expected if the formation of CH+ involves nonthermal processes. We find that (CN)-C-12/(CN)-C-13, however, can be significantly fractionated away from the ambient value. The dispersion in our sample of (CN)-C-12/(CN)-C-13 ratios is similar to that found in recent surveys of (CO)-C-12/(CO)-C-13. For sight lines where both ratios have been determined, the (CN)-C-12/(CN)-C-13 ratios are generally fractionated in the opposite sense compared to (CO)-C-12/(CO)-C-13. Chemical fractionation in CO results from competition between selective photodissociation and isotopic charge exchange (ICE). An inverse relationship between (CN)-C-12/(CN)-C-13 and (CO)-C-12/(CO)-C-13 follows from the coexistence of CN and CO in diffuse cloud cores. However, an ICE reaction with CN may mitigate the enhancements in (CN)-C-12/(CN)-C-13 for lines of sight with low (CO)-C-12/(CO)-C-13 ratios. For two sight lines with high values of (CO)-C-12/(CO)-C-13, our results indicate that about 50% of the carbon is locked up in CO, which is consistent with the notion that these sight lines probe molecular cloud envelopes where the transition from C+ to CO is expected to occur. An analysis of CN rotational excitation yields a weighted mean value for T-01((CN)-C-12) of 2.754 +/- 0.002 K, which implies an excess over the temperature of the cosmic microwave background (CMB) of only 29 +/- 3 mK. This modest excess eliminates the need for a local excitation mechanism beyond electron and neutral collisions. The rotational excitation temperatures in (CN)-C-13 show no excess over the temperature of the CMB.
Physical Characteristics Of G331.5-0.1: The Luminous Central Region Of A Giant Molecular Cloud
(2013-09) Merello, Manuel; Bronfman, Leonardo; Garay, Guido; Nyman, Lars-Ake; Evans, Neal J.; Walmsley, C. Malcom; Merello, Manuel; Evans, Neal J.
We report molecular line and dust continuum observations toward the high-mass star-forming region G331.5-0.1, one of the most luminous regions of massive star formation in the Milky Way, located at the tangent region of the Norma spiral arm, at a distance of 7.5 kpc. Molecular emission was mapped toward the G331.5-0.1 GMC in the CO(J = 1 -> 0) and (CO)-O-18(J = 1. 0) lines with NANTEN, while its central region was mapped in CS(J = 2 -> 1 and J = 5 -> 4) with SEST, and in CS(J = 7 -> 6) and (CO)-C-13(J = 3 -> 2) with ASTE. Continuum emission mapped at 1.2 mm with SIMBA and at 0.87 mm with LABOCA reveal the presence of six compact and luminous dust clumps, making this source one of the most densely populated central regions of a GMC in the Galaxy. The dust clumps are associated with molecular gas and they have the following average properties: size of 1.6 pc, mass of 3.2 x 10(3)M(circle dot), molecular hydrogen density of 3.7 x 10(4) cm(-3), dust temperature of 32 K, and integrated luminosity of 5.7 x 10(5) L-circle dot, consistent with values found toward other massive star-forming dust clumps. The CS and (CO)-C-13 spectra show the presence of two velocity components: a high-velocity component at similar to-89 km s(-1), seen toward four of the clumps, and a low-velocity component at similar to-101 km s(-1) seen toward the other two clumps. Radio continuum emission is present toward four of the molecular clumps, with spectral index estimated for two of them of 0.8 +/- 0.2 and 1.2 +/- 0.2. A high-velocity molecular outflow is found at the center of the brightest clump, with a line width of 26 km s(-1) (FWHM) in CS(J = 7 -> 6). Observations of SiO(J = 7 -> 6 and J = 8. 7), and SO(J(K) = 8(8) -> 7(7) and J(K) = 8(7) -> 7(6)) lines provide estimates of the gas rotational temperature toward this outflow > 120 K and > 75 K, respectively.
The Properties of Massive, Dense Clumps: Mapping Surveys of HCN and CS
(2010-06) Wu, Jingwen; Evans, Neal J., II; Shirley, Yancy L.; Knez, Claudia; Evans, Neal J., II
We have mapped over 50 massive, dense clumps with four dense gas tracers: HCN J = 1-0 and 3-2; and CS J = 2-1 and 7-6 transitions. Spectral lines of optically thin H(13)CN 3-2 and C(34)S 5-4 were also obtained toward the map centers. These maps usually demonstrate single well-peaked distributions at our resolution, even with higher J transitions. The size, virial mass, surface density, and mean volume density within a well-defined angular size ( FWHM) were calculated from the contour maps for each transition. We found that transitions with higher effective density usually trace the more compact, inner part of the clumps but have larger linewidths, leading to an inverse linewidth-size relation using different tracers. The mean surface densities are 0.29, 0.33, 0.78, 1.09 g cm(-2) within FWHM contours of CS 2-1, HCN 1-0, HCN 3-2, and CS 7-6, respectively. We find no correlation of L(IR) with surface density and a possible inverse correlation with mean volume density, contrary to some theoretical expectations. Molecular line luminosities L'(mol) were derived for each transition. We see no evidence in the data for the relation between L'(mol) and mean density posited by modelers. The correlation between L'(mol) and the virial mass is roughly linear for each dense gas tracer. No obvious correlation was found between the line luminosity ratio and infrared luminosity, bolometric temperature, or the L(IR)/M(Vir) ratio. A nearly linear correlation was found between the infrared luminosity and the line luminosity of all dense gas tracers for these massive, dense clumps, with a lower cutoff in luminosity at L(IR) = 10(4.5) L(circle dot). The L(IR)-L'(HCN1-0) correlation agrees well with the one found in galaxies. These correlations indicate a constant star Formation rate per unit mass from the scale of dense clumps to that of distant galaxies when the mass is measured for dense gas. These results support the suggestion that starburst galaxies may be understood as having a large fraction of gas in dense clumps.
Ultraviolet Survey Of CO And H-2 In Diffuse Molecular Clouds: The Reflection Of Two Photochemistry Regimes In Abundance Relationships
(2008-11) Sheffer, Y.; Rogers, M.; Federman, S. R.; Abel, N. P.; Gredel, R.; Lambert, David L.; Shaw, G.; Federman, S. R.
We carried out a comprehensive far-UV survey of (CO)-C-12 and H-2 column densities along diffuse molecular Galactic sight lines. This sample includes new measurements of CO from HST spectra along 62 sight lines and new measurements of H-2 from FUSE data along 58 sight lines. In addition, high-resolution optical data were obtained at the McDonald and European Southern Observatories, yielding new abundances for CH, CH+, and CN along 42 sight lines to aid in interpreting the CO results. These new sight lines were selected according to detectable amounts of CO in their spectra and provide information on both lower density (<= 100 cm(-3)) and higher density diffuse clouds. A plot of log N(CO) versus log N(H-2) shows that two power-law relationships are needed for a good fit of the entire sample, with a break located at log N(CO, cm(-2)) = 14.1 and log N(H-2) = 20.4, corresponding to a change in production route for CO in higher density gas. Similar logarithmic plots among all five diatomic molecules reveal additional examples of dual slopes in the cases of CO versus CH (break at log N 14: 1, 13.0), CH+ versus H-2 (13.1, 20.3), and CH+ versus CO (13.2, 14.1). We employ both analytical and numerical chemical schemes in order to derive details of the molecular environments. In the denser gas, where C-2 and CN molecules also reside, reactions involving C+ and OH are the dominant factor leading to CO formation via equilibrium chemistry. In the low-density gas, where equilibrium chemistry studies have failed to reproduce the abundance of CH+, our numerical analysis shows that nonequilibrium chemistry must be employed for correctly predicting the abundances of both CH+ and CO.
Warm Gas Towards Young Stellar Objects In Corona Australis Herschel/PACS Observations From The Digit Key Programme
(2014-05) Lindberg, Johan E.; Jørgensen, Jes K.; Green, Joel D.; Herczeg, Gregory J.; Dionatos, Odysseas; Evans, Neal J.; Karska, Agata; Wampfler, Susanne F.; Green, Joel D.; Evans, Neal J.
Context. The effects of external irradiation on the chemistry and physics in the protostellar envelope around low-mass young stellar objects are poorly understood. The Corona Australis star-forming region contains the R CrA dark cloud, comprising several low-mass protostellar cores irradiated by an intermediate-mass young star. Aims. We study the effects of the irradiation coming from the young luminous Herbig Be star R CrA on the warm gas and dust in a group of low-mass young stellar objects. Methods. Herschel/PACS far-infrared datacubes of two low-mass star-forming regions in the R CrA dark cloud are presented. The distributions of CO, OH, H2O, [C II], [O I], and continuum emission are investigated. We have developed a deconvolution algorithm which we use to deconvolve the maps, separating the point-source emission from the extended emission. We also construct rotational diagrams of the molecular species. Results. By deconvolution of the Herschel data, we find large-scale (several thousand AU) dust continuum and spectral line emission not associated with the point sources. Similar rotational temperatures are found for the warm CO (282 4 K), hot CO (890 84 K), OH (79 +/- 4 K), and H2O (197 +/- 7 K) emission in the point sources and the extended emission. The rotational temperatures are also similar to those found in other more isolated cores. The extended dust continuum emission is found in two ridges similar in extent and temperature to molecular millimetre emission, indicative of external heating from the Herbig Be star R CrA. Conclusions. Our results show that nearby luminous stars do not increase the molecular excitation temperatures of the warm gas around young stellar objects (YSOs). However, the emission from photodissociation products of H2O, such as OH and O, is enhanced in the warm gas associated with these protostars and their surroundings compared to similar objects not subjected to external irradiation.