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Li J, Bergin EA, Blake GA, Ciesla FJ, Hirschmann MM. Earth's carbon deficit caused by early loss through irreversible sublimation. Sci Adv 2021; 7:eabd3632. [PMID: 33811069 PMCID: PMC11059936 DOI: 10.1126/sciadv.abd3632] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Accepted: 02/16/2021] [Indexed: 06/12/2023]
Abstract
Carbon is an essential element for life, but its behavior during Earth's accretion is not well understood. Carbonaceous grains in meteoritic and cometary materials suggest that irreversible sublimation, and not condensation, governs carbon acquisition by terrestrial worlds. Through astronomical observations and modeling, we show that the sublimation front of carbon carriers in the solar nebula, or the soot line, moved inward quickly so that carbon-rich ingredients would be available for accretion at 1 astronomical unit after the first million years. On the other hand, geological constraints firmly establish a severe carbon deficit in Earth, requiring the destruction of inherited carbonaceous organics in the majority of its building blocks. The carbon-poor nature of Earth thus implies carbon loss in its precursor material through sublimation within the first million years.
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Affiliation(s)
- J Li
- Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109, USA.
| | - E A Bergin
- Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA
| | - G A Blake
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
| | - F J Ciesla
- Department of Geophysical Sciences and Chicago Center for Cosmochemistry, University of Chicago, Chicago, IL 60637, USA
| | - M M Hirschmann
- Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN 55455, USA
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Joblin C, Bron E, Pinto C, Pilleri P, Le Petit F, Gerin M, Le Bourlot J, Fuente A, Berne O, Goicoechea JR, Habart E, Köhler M, Teyssier D, Nagy Z, Montillaud J, Vastel C, Cernicharo J, Röllig M, Ossenkopf-Okada V, Bergin EA. Structure of photodissociation fronts in star-forming regions revealed by observations of high-J CO emission lines with Herschel. Astron Astrophys 2018; 615:A129. [PMID: 30185990 PMCID: PMC6120684 DOI: 10.1051/0004-6361/201832611] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
CONTEXT In bright photodissociation regions (PDRs) associated to massive star formation, the presence of dense "clumps" that are immersed in a less dense interclump medium is often proposed to explain the difficulty of models to account for the observed gas emission in high-excitation lines. AIMS We aim at presenting a comprehensive view of the modeling of the CO rotational ladder in PDRs, including the high-J lines that trace warm molecular gas at PDR interfaces. METHODS We observed the 12CO and 13CO ladders in two prototypical PDRs, the Orion Bar and NGC 7023 NW using the instruments onboard Herschel. We also considered line emission from key species in the gas cooling of PDRs (C+, O, H2) and other tracers of PDR edges such as OH and CH+. All the intensities are collected from Herschel observations, the literature and the Spitzer archive and are analyzed using the Meudon PDR code. RESULTS A grid of models was run to explore the parameter space of only two parameters: thermal gas pressure and a global scaling factor that corrects for approximations in the assumed geometry. We conclude that the emission in the high-J CO lines, which were observed up to J up =23 in the Orion Bar (J up =19 in NGC 7023), can only originate from small structures of typical thickness of a few 10-3 pc and at high thermal pressures (Pth ~ 108 K cm-3). CONCLUSIONS Compiling data from the literature, we found that the gas thermal pressure increases with the intensity of the UV radiation field given by G0, following a trend in line with recent simulations of the photoevaporation of illuminated edges of molecular clouds. This relation can help rationalising the analysis of high-J CO emission in massive star formation and provides an observational constraint for models that study stellar feedback on molecular clouds.
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Affiliation(s)
- C Joblin
- IRAP, Université de Toulouse, CNRS, UPS, CNES, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
| | - E Bron
- Instituto de Fisica Fundamental (CSIC), Calle Serrano 121-123, 28006, Madrid, Spain
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-92190, Meudon, France
| | - C Pinto
- Aix-Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
| | - P Pilleri
- IRAP, Université de Toulouse, CNRS, UPS, CNES, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
| | - F Le Petit
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-92190, Meudon, France
| | - M Gerin
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-92190, Meudon, France
| | - J Le Bourlot
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-92190, Meudon, France
- Université Paris-Diderot, Paris, France
| | - A Fuente
- Observatorio Astronómico Nacional, Apdo. 112, 28803 Alcalá de Henares, Madrid, Spain
| | - O Berne
- IRAP, Université de Toulouse, CNRS, UPS, CNES, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
| | - J R Goicoechea
- Instituto de Fisica Fundamental (CSIC), Calle Serrano 121-123, 28006, Madrid, Spain
| | - E Habart
- Institut d'Astrophysique Spatiale (IAS), Université Paris Sud & CNRS, 91405 Orsay, France
| | - M Köhler
- Institut d'Astrophysique Spatiale (IAS), Université Paris Sud & CNRS, 91405 Orsay, France
| | - D Teyssier
- European Space Astronomy Centre, ESA, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
| | - Z Nagy
- I. Physikalisches Institut der Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
| | - J Montillaud
- Institut Utinam, CNRS UMR 6213, OSU THETA, Université de Franche-Comté, 41bis avenue de l'Observatoire, 25000 Besançon, France
| | - C Vastel
- IRAP, Université de Toulouse, CNRS, UPS, CNES, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
| | - J Cernicharo
- Instituto de Fisica Fundamental (CSIC), Calle Serrano 121-123, 28006, Madrid, Spain
| | - M Röllig
- I. Physikalisches Institut der Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
| | - V Ossenkopf-Okada
- I. Physikalisches Institut der Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
| | - E A Bergin
- Department of Astronomy, University of Michigan, 311 West Hall, 1085 S. University Avenue, Ann Arbor, MI 48109, USA
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Goicoechea JR, Teyssier D, Etxaluze M, Goldsmith PF, Ossenkopf V, Gerin M, Bergin EA, Black JH, Cernicharo J, Cuadrado S, Encrenaz P, Falgarone E, Fuente A, Hacar A, Lis DC, Marcelino N, Melnick GJ, Müller HSP, Persson C, Pety J, Röllig M, Schilke P, Simon R, Snell RL, Stutzki J. VELOCITY-RESOLVED [C ii] EMISSION AND [C ii]/FIR MAPPING ALONG ORION WITH HERSCHEL.. ACTA ACUST UNITED AC 2015; 812. [PMID: 26568638 DOI: 10.1088/0004-637x/812/1/75] [Citation(s) in RCA: 79] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
We present the first ~7.5'×11.5' velocity-resolved (~0.2 km s-1) map of the [C ii] 158 μm line toward the Orion molecular cloud 1 (OMC 1) taken with the Herschel/HIFI instrument. In combination with far-infrared (FIR) photometric images and velocity-resolved maps of the H41α hydrogen recombination and CO J=2-1 lines, this data set provides an unprecedented view of the intricate small-scale kinematics of the ionized/PDR/molecular gas interfaces and of the radiative feedback from massive stars. The main contribution to the [C ii] luminosity (~85 %) is from the extended, FUV-illuminated face of the cloud (G0>500, nH>5×103 cm-3) and from dense PDRs (G≳104, nH≳105 cm-3) at the interface between OMC 1 and the H ii region surrounding the Trapezium cluster. Around ~15 % of the [C ii] emission arises from a different gas component without CO counterpart. The [C ii] excitation, PDR gas turbulence, line opacity (from [13C ii]) and role of the geometry of the illuminating stars with respect to the cloud are investigated. We construct maps of the L[C ii]/LFIR and LFIR/MGas ratios and show that L[C ii]/LFIR decreases from the extended cloud component (~10-2-10-3) to the more opaque star-forming cores (~10-3-10-4). The lowest values are reminiscent of the "[C ii] deficit" seen in local ultra-luminous IR galaxies hosting vigorous star formation. Spatial correlation analysis shows that the decreasing L[C ii]/LFIR ratio correlates better with the column density of dust through the molecular cloud than with LFIR/MGas. We conclude that the [C ii] emitting column relative to the total dust column along each line of sight is responsible for the observed L[C ii]/LFIR variations through the cloud.
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Affiliation(s)
- Javier R Goicoechea
- Instituto de Ciencia de Materiales de Madrid (CSIC). Calle Sor Juana Ines de la Cruz 3, E-28049 Cantoblanco, Madrid, Spain
| | - D Teyssier
- Herschel Science Centre, ESA/ESAC, P.O. Box 78, Villanueva de la Cañada, E-28691 Madrid, Spain
| | - M Etxaluze
- Instituto de Ciencia de Materiales de Madrid (CSIC). Calle Sor Juana Ines de la Cruz 3, E-28049 Cantoblanco, Madrid, Spain ; RAL Space, Rutherford Appleton Laboratory, Didcot OX11 0QX, UK
| | - P F Goldsmith
- Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099, USA
| | - V Ossenkopf
- I. Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
| | - M Gerin
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-75014, Paris, France ; École Normale Supérieure, 24 rue Lhomond, F-75005, Paris, France
| | - E A Bergin
- Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109, USA
| | - J H Black
- Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-43992 Onsala, Sweden
| | - J Cernicharo
- Instituto de Ciencia de Materiales de Madrid (CSIC). Calle Sor Juana Ines de la Cruz 3, E-28049 Cantoblanco, Madrid, Spain
| | - S Cuadrado
- Instituto de Ciencia de Materiales de Madrid (CSIC). Calle Sor Juana Ines de la Cruz 3, E-28049 Cantoblanco, Madrid, Spain
| | - P Encrenaz
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-75014, Paris, France
| | - E Falgarone
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-75014, Paris, France ; École Normale Supérieure, 24 rue Lhomond, F-75005, Paris, France
| | - A Fuente
- Observatorio Astronómico Nacional (OAN IGN), Apdo. 112, 28803, Alcalá de Henares, Spain
| | - A Hacar
- Institute for Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180, Vienna, Austria
| | - D C Lis
- LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-75014, Paris, France
| | - N Marcelino
- INAF, Istituto di Radioastronomia, via P. Gobetti 101, 40129, Bologna, Italy
| | - G J Melnick
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 66, Cambridge, MA 02138, USA
| | - H S P Müller
- I. Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
| | - C Persson
- Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-43992 Onsala, Sweden
| | - J Pety
- Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Saint-Martin d'Héeres, France
| | - M Röllig
- I. Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
| | - P Schilke
- I. Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
| | - R Simon
- I. Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
| | - R L Snell
- Department of Astronomy, University of Massachusetts, LGRT-B 619E, 710 North Pleasant Street, Amherst, MA 01003, USA
| | - J Stutzki
- I. Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
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Cleeves LI, Bergin EA, Alexander CMO, Du F, Graninger D, Oberg KI, Harries TJ. The ancient heritage of water ice in the solar system. Science 2014; 345:1590-3. [DOI: 10.1126/science.1258055] [Citation(s) in RCA: 195] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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Abstract
Nitrogen is the fifth most abundant element in the Universe. In the interstellar medium, it has been thought to be mostly molecular (N2). However, N2 has no observable rotational or vibrational transitions, so its abundance in the interstellar medium remains poorly known. In comets, the N2 abundance is very low, while the elemental nitrogen abundance is deficient with respect to the solar value. Moreover, large nitrogen isotopic anomalies are observed in meteorites and interstellar dust particles. Here we report the N2H+ (and by inference the N2) abundance inside a cold dark molecular cloud. We find that only a small fraction of nitrogen in the gas phase is molecular, with most of it being atomic. Because the compositions of comets probably reflect those of dark clouds, this result explains the low N2 abundance in comets. We argue that the elemental nitrogen abundance deficiency in comets can be understood if the atomic oxygen abundance is lower than predicted by present chemical models. Furthermore, the lack of molecular nitrogen in molecular clouds explains the nitrogen anomalies in meteorites and interstellar dust particles, as nitrogen fractionation is enhanced if gaseous nitrogen is atomic.
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Affiliation(s)
- S Maret
- Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, Michigan 48109-1042, USA.
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6
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Abstract
Maps of comet C/1995 O1 (Hale-Bopp) in the millimeter-wave emission of the ion HCO+ revealed a local minimum near the nucleus position, with a maximum about 100,000 km in the antisolar direction. These observed features of the HCO+ emission require a low abundance of HCO+ due to enhanced destruction in the inner coma of the comet, within a region of low electron temperature (Te). To set constraints on the formation of HCO+ in the coma, as well as the location and magnitude of the transition to higher Te, the data are compared with the results of ion-molecule chemistry models.
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Affiliation(s)
- A J Lovell
- Five College Radio Astronomy Observatory, University of Massachusetts, Amherst 01003, USA
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7
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Abstract
Significant gas-phase chemistry occurs in the comae of bright comets, as is demonstrated here for the case of Comet Hale-Bopp. The abundance ratio of the two isomers, hydrogen cyanide and hydrogen isocyanide, is shown to vary with heliocentric distance in a way that is consistent with production of HNC by ion-molecule chemistry initiated by the photoionization of water. Likewise, the first maps of emission from HCO+ show an abundance and an extended distribution that are consistent with the same chemical model.
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Affiliation(s)
- W M Irvine
- Five College Radio Astronomy Observatory, University of Massachusetts, Amherst 01003, USA
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Irvine WM, Bergin EA, Dickens JE, Jewitt D, Lovell AJ, Matthews HE, Schloerb FP, Senay M. Chemical processing in the coma as the source of cometary HNC. Nature 1998; 393:547-50. [PMID: 9634231 DOI: 10.1038/31171] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The discovery of hydrogen isocyanide (HNC) in comet Hyakutake with an abundance (relative to hydrogen cyanide, HCN) similar to that seen in dense interstellar clouds raised the possibility that these molecules might be surviving interstellar material. The preservation of material from the Sun's parent molecular cloud would provide important constraints on the processes that took place in the protostellar nebula. But another possibility is that HNC is produced by photochemical processes in the coma, which means that its abundance could not be used as a direct constraint on conditions in the early Solar System. Here we show that the HNC/HCN ratio determined for comet Hale-Bopp varied with heliocentric distance in a way that matches the predictions of models of gas-phase chemical production of HNC in the coma, but cannot be explained if the HNC molecules were coming from the comet's nucleus. We conclude that HNC forms mainly by chemical reactions in the coma, and that such reactions need to be considered when attempting to deduce the composition of the nucleus from observations of the coma.
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Affiliation(s)
- W M Irvine
- Five College Radio Astronomy Observatory, University of Massachusetts, Amherst 01003, USA.
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Abstract
We present a comprehensive study of the physical and chemical conditions along the TMC-1 ridge. Temperatures were estimated from observations of CH3CCH, NH3, and CO. Densities were obtained from a multitransition study of HC3N. The values of the density and temperature allow column densities for 13 molecular species to be estimated from statistical equilibrium calculations, using observations of rarer isotopomers where possible, to minimize opacity effects. The most striking abundance variations relative to HCO+ along the ridge were seen for HC3N, CH3CCH, and SO, while smaller variations were seen in CS, C2H, and HCN. On the other hand, the NH3, HNC, and N2H+ abundances relative to HCO+ were determined to be constant, indicating that the so-called NH3 peak in TMC-1 is probably a peak in the ammonia column density rather than a relative abundance peak. In contrast, the well-studied cyanopolyyne peak is most likely due to an enhancement in the abundance of long-chain carbon species. Comparisons of the derived abundances to the results of time-dependent chemical models show good overall agreement for chemical timescales around 10(5) yr. We find that the observed abundance gradients can be explained either by a small variation in the chemical timescale from 1.2 x 10(5) to 1.8 x 10(5) yr or by a factor of 2 change in the density along the ridge. Alternatively, a variation in the C/O ratio from 0.4 to 0.5 along the ridge produces an abundance gradient similar to that observed.
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Affiliation(s)
- P Pratap
- Five College Radio Astronomy Observatory, University of Massachusetts, Amherst 01003, USA
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Bergin EA, Ungerechts H, Goldsmith PF, Snell RL, Irvine WM, Schloerb FP. A survey of the chemical properties of the M17 and Cepheus A cloud cores. Astrophys J 1997; 482:267-284. [PMID: 11541432 DOI: 10.1086/304106] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We present the results of a systematic survey of the chemical properties of two giant molecular cloud (GMC) cores in M17 and Cepheus A. In all, we have mapped the emission from 32 molecular transitions of 13 molecules and seven isotopic variants over a 4' x 5' region in each core. Each map includes known sites of massive star formation, as well as the more extended quiescent material. In M17 most molecules have emission peaks away from the H II region/molecular cloud interface, while two species, HC3N and CH3C2H, deviate from this structure with sharp maxima closer to this interface. In Cepheus A the core is influenced by a compact high-velocity molecular outflow and a more extended low-velocity flow. The molecular emission distributions in this source are generally quite similar, with most molecules peaking near the center of the core to the east of the compact H II region HW 2. A few molecules, SO, CH3OH, H13CN, and C18O, have more extended emission. Only two molecules, CO and HCO+, appear to trace the high- and low-velocity outflows; all other species are tracing the quiescent core. We have used the results of previous studies of the density and temperature of the dense gas in the same cloud cores to derive accurate abundances relative to CO for several positions in each core. The principal result is that the chemical composition of all the cores we have surveyed (which include OMC-1 as well as M17 and Cepheus A) show remarkable similarity, both within a given core and among the cores. This suggests that the chemical processes are similar in quiescent GMC core material. In M17 the lack of variation of molecular abundances is remarkable because the radiation field and the gas temperature are known to vary appreciably throughout the surveyed region, suggesting that the bulk of the emission arises from gas that is well shielded from radiation.
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Affiliation(s)
- E A Bergin
- Department of Physics and Astronomy, University of Massachusetts, Amherst 01003, USA
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Ungerechts H, Bergin EA, Goldsmith PF, Irvine WM, Schloerb FP, Snell RL. Chemical and physical gradients along the OMC-1 ridge. Astrophys J 1997; 482:245-266. [PMID: 11541431 DOI: 10.1086/304110] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We present a survey of the distribution of 20 chemical and isotopic molecular species along the central ridge of the Orion molecular cloud from 6' north to 6' south of BN-KL observed with the QUARRY focal plane array on the FCRAO 14 m telescope, which provides an angular resolution of approximately 50" in the 3 mm wavelength region. We use standard tools of multivariate analysis for a systematic investigation of the similarities and differences among the maps of integrated intensities of the 32 lines observed. The maps fall in three broad classes: first, those strongly peaked toward BN-KL; second, those having rather flat distributions along the ridge; and third, those with a clear north-south gradient or contrast. We identify six positions or regions where we calculate relative abundances. Line velocities and line widths indicate that the optically thin lines generally trace the same volume of dense gas, except in the molecular bar, where C18O, C34S, H13CO+, CN, C2H, SO, and C3H2 have velocities characteristic of the bar itself, whereas the emission from other detected species is dominated by the background cloud. The strongest abundance variations in our data are the well-known enhancements seen in HCN, CH3OH, HC3N, and SO toward BN-KL and, less strongly, toward the Orion-South outflow 1'.3S. The principal result of this study is that along the extended quiescent ridge the chemical abundances, within factors of 3-4, exhibit an impressive degree of uniformity. The northern part of the ridge has a chemistry closest to that found in quiescent dense clouds. While temperature and density are similar around the northern radical-ion peak near 3'.5N and in the southern core near 4'.2S, some abundances, in particular, those of the ions HCO+ and N2H+, are significantly lower toward 4'.2S. The areas near 4.'2S and the molecular bar itself around (1'.7E, 2'.4S) stand out with peculiar and similar properties probably caused by stronger UV fields penetrating deeper into the clumpy molecular gas. This leads to higher electron abundances and thereby reduced abundances of the ions, as well as a lack of complex molecules.
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Affiliation(s)
- H Ungerechts
- Department of Physics and Astronomy, University of Massachusetts, Amherst 01003, USA
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Abstract
The abundance ratio of the isomers HCN and HNC has been investigated in comet Hale-Bopp (C/1995 O1) through observations of the J = 4-3 rotational transitions of both species for heliocentric distances 0.93 < r < 3 AU, both pre- and post-perihelion. After correcting for the optical depth of the stronger HCN line, we find that the column density ratio of HNC/HCN in our telescope beam increases significantly as the comet approaches the Sun. We compare this behavior to that predicted from an ion-molecule chemical model and conclude that the HNC is produced in significant measure by chemical processes in the coma; i.e., for comet Hale-Bopp, HNC is not a parent molecule sublimating from the nucleus.
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Affiliation(s)
- W M Irvine
- Five College Radio Astronomy Observatory, University of Massachusetts, Amherst 01003, USA
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