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1.
Interstellar H2O and OH masers associated with massive star-forming regions can be classified into three morphological types: isolated H2O masers; isolated OH masers; and spatially overlapping OH/H2O maser groups. In a large sample of star-forming regions the total number of maser groups of each type is approximately equal. In order to account for these statistics we propose a pumping scheme based on a broadband radiative pump which produces inverted populations of both OH and H2O masers by a process involving predissociation and dissociation of H2O. This scheme overcomes some drawbacks of earlier radiative pumping models, and may account for the association of OH and H2O masers in massive star forming regions.  相似文献   

2.
We searched for the CSJ = 2 – 1 emission towards 29 southern H2O and H2O/OH masers and 1 OH maser with the SEST radio telescope. We detected and mapped 24 CS emitting regions probably associated with 27 H2O masers. The C34SJ = 2 – 1 and COJ = 1 – 0 lines were also observed at the grid positions closest to the CS peaks. Four cores were mapped in the CSJ = 5 – 4 and C34SJ = 2 – 1 lines.  相似文献   

3.
The data compiled for 34 very young massive compact infrared source (Becklin-Neugebauer objects) in a separately published catalogue serve as the basis for an investigation of their general properties. First, the correlations of the strength of the ice and silicate bands at 3.1 μm and 10 μm, resp., with each other and with other parameters of the sources are investigated. In accordance with theoretical expectations the strengths of both bands are not well correlated with each other. The ratio τ10/τ3 of their optical depths veries from 0.85 to 8 (and possibly up to 22). That implies for the number densities of the grains that (naked) silicate grains always are considerably more abundant than ice grains (grains with ice mantles). It follows from the discussion of the relationships between τ10, the temperature parameter of the sources, and their luminosity that relations between τ10 and temperature and possibly between τ10 and the luminosity exist. Stellar wind models for the ionized region around the embedded star are favoured after the analysis of the intensities of the hydrogen infrred emission lines and the radio continuum. The limited observational data do not yet allow a decision on a correlation between the silicate band depth and energy content and/or the velocity of the bipolar outflow detected in a number of sources. The BN objects are clearly more frequently associated with H2O masers than OH masers. The linear separations of the infrared peaks from the masers are compatible with models where the H2O masers are situated near the edges the gas-dust shells of the BN objects.  相似文献   

4.
We present MERLIN observations of OH and H2O masers in the circumstellar envelope of S Per. The results are consistent with a model of a thick shell of H2O masers in a region which is still accelerating.  相似文献   

5.
The pumping of 22.2-GHz H2O masers in the circumstellar envelopes of asymptotic giant branch stars has been simulated numerically. The physical parameters adopted in the calculations correspond to those of the circumstellar envelope around IK Tau. The one-dimensional plane-parallel structure of the gas-dust cloud is considered. The statistical equilibrium equations for the H2O level populations and the thermal balance equations for the gas-dust cloud are solved self-consistently. The calculations take into account 410 rotational levels belonging to the five lowest vibrational levels of H2O. The stellar radiation field is shown to play an important role in the thermal balance of the gas-dust cloud due to the absorption of emission in rotational-vibrational H2O lines. The dependence of the gain in the 22.2-GHz maser line on the gas density and H2O number density in the gas-dust cloud is investigated. Gas densities close to the mean density of the stellar wind, 107?108 cm?3, and a high relative H2O abundance, more than 10?4, have been found to be the most likely physical conditions in maser sources.  相似文献   

6.
The collisional pumping of H216O and H218O masers in hot dense gas-dust clouds has been simulated numerically. New data on the rate coefficients for collisional transitions from Faure et al. (2007) were used in the calculations. The possibility of detecting H218O emission in 22.2-GHz H216O maser sources is investigated. The medium is shown to become optically thick in the H218O lines for which an inverted level population is observed at H2O column densities of ∼1019–1020 cm−2. A simultaneous observation of H218O emission and H216O maser emission in the same source will allow the physical conditions in the gas-dust cloud to be refined.  相似文献   

7.
Altitude profiles for the number densities of NO, NO2, NO3, N2O5, HNO2, CH3O, CH3O2, H2CO, OH, and HO2 are calculated as a function of time of day with a steady-state photochemical model in which the altitude profiles for the number densities of H2O, CH4, H2, CO, O3, and the sum of NO and NO2 are fixed at values appropriate to a summer latitude of 34°. Average daily profiles are calculated for the long-lived species, HNO3, H2O2, and CH3O2H.The major nitrogen compound HNO3 may have a number density approaching 5 × 1011 molecules cm?3 at the surface, although an effective loss path due to collisions with particulates could greatly reduce this value.The number density of OH remains relatively unchanged in the first 6 km and reaches 1 × 107 molecules cm?3 at noon, while the number density of HO2 decreases throughout the lower troposphere from its noontime value of 8 × 108 molecules cm?3 at the surface.H2O2 and H2CO both have number densities in the ppb range in the lower troposphere.Owing to decreasing temperature and water concentration, the production of radicals and their steady-state number densities decrease with altitude, reaching a noontime minimum of 1 × 108 molecules cm?3 for OH and 3 × 107 molecules cm?3 for HO2 at the tropopause. The related minor species show even sharper decreases with increasing altitude.The primary path for interconverting OH and HO2 serves as the major sink for CO and leads to a tropospheric lifetime for CO of ~0.1 yr.Another reaction cycle, the oxidation of CH4, is quite important in the lower troposphere and leads to the production of H2CO along with the destruction of CH4 for which a tropospheric lifetime of ~2 yr is estimated.The destruction of H2CO that was produced in the CH4 oxidation cycle provides the major source of CO and H2 in the atmosphere.  相似文献   

8.
The large-scale distribution of interstellar H2O masers is given in this paper. Present results show that H2O masers can trace galactic spiral structure, and we also briefly discuss how to obtain a more accurate distribution of H2O masers from future observations.  相似文献   

9.
The interstellar UV field at 1565 Å is calculated around nearby OH/IR sources. The front-back asymmetry observed in the 1612 MHz maser line profile is well correlated with anisotropy of the interstellar UV flux. For some sources the spatial positions of the 1612 MHz masers are confined to the position angles for which stronger UV radiation occurs. These facts strongly support the theory of the photoproduction of OH from H2O induced by ambient interstellar UV photons penetrating the circumstellar shell. A simple model of the 1612 MHz maser with OH photoproduction suggests that the influence of the UV field on the observed maser profiles is governed by the mass loss rate and the relative abundances of OH and H2O molecules.  相似文献   

10.
The University of Wisconsin–Madison and NASA–Goddard conducted acomprehensive multi-wavelength observing campaign of coma emissionsfrom comet Hale–Bopp, including OH 3080 Å, [O I] 6300 Å H2O+ 6158 Å, H Balmer-α 6563 Å, NH2 6330 Å, [C I] 9850 ÅCN 3879 Å, C2 5141 Å, C3 4062 Å,C I 1657 Å, and the UV and optical continua. In thiswork, we concentrate on the results of the H2O daughter studies.Our wide-field OH 3080 Å measured flux agrees with other, similarobservations and the expected value calculated from published waterproduction rates using standard H2O and OH photochemistry.However, the total [O I] 6300 Å flux determined spectroscopically overa similar field-of-view was a factor of 3-4 higher than expected.Narrow-band [O I] images show this excess came from beyond theH2O scale length, suggesting either a previously unknown source of[O I] or an error in the standard OH + ν→ O(1 D) + H branching ratio. The Hale–Bopp OH and[O I] distributions, both of which were imaged tocometocentric distances >1 × 106 km, were more spatiallyextended than those of comet Halley (after correcting for brightnessdifferences), suggesting a higher bulk outflow velocity. Evidence ofthe driving mechanism for this outflow is found in the Hα lineprofile, which was narrower than in comet Halley (though likelybecause of opacity effects, not as narrow as predicted by Monte-Carlomodels). This is consistent with greater collisional coupling betweenthe suprathermal H photodissociation products and Hale–Bopp's densecoma. Presumably because of mass loading of the solar wind by ionsand ions by the neutrals, the measured acceleration of H2O+ downthe ion tail was much smaller than in comet Halley. Tailwardextensions in the azimuthal distributions of OH 3080 Å,[O I], and [C I] , as well as a Doppler asymmetry in the[O I] line profile, suggest ion-neutral coupling. While thetailward extension in the OH can be explained by increased neutralacceleration, the [O I] 6300 Å and [C I] 9850 Å emissions show 13%and >200% excesses in this direction (respectively), suggesting anon-negligible contribution from dissociative recombination of CO+and/or electron collisional excitation. Thus, models including theeffects of photo- and collisional chemistry are necessary for the fullinterpretation of these data.  相似文献   

11.
One-dimensional radial models of the chemistry in cometary comae have been constructed for heliocentric distances ranging from 2 to 0.125 AU. The coma's opacity to solar radiation is included and photolytic reaction rates are calculated. A parent volatile mixture similar to that found in interstellar molecular clouds is assumed. Profiles through the coma of number density and column density are presented for H2O, OH, O, CN, C2, C3, CH, and NH2. Whole-coma abundances are presented for NH2, CH, C2, C3, CN, OH, CO+, H2O+, CH+, N2+, and CO2+.  相似文献   

12.
In this paper we study the effect of shock waves on the chemical structure of the interstellar clouds. A model of molecular cloud has been assumed. The chemistry is investigated in a time dependent model. Our chemical network contains 56 species in 251 reactions to including molecules of the elements H, O, C, N, S, and Si.The results indicate that the calculated fractional abundance of the molecules NS, H2O, CN, NH, CO, and SO agrees well with the observations. The molecules OH, H2S, CS, H2CS, HS, NO, SiO, CH, CH2, CH3, HCO, C2, and HCN reach high post-shock abundances.  相似文献   

13.
A two-dimensional kinetic model calculation for the water group species (H2O, H2, O2, OH, O, H) in Europa's atmosphere is undertaken to determine its basic compositional structure, gas escape rates, and velocity distribution information to initialize neutral cloud model calculations for the most important gas tori. The dominant atmospheric species is O2 at low altitudes and H2 at higher altitudes with average day-night column densities of 4.5×1014 and 7.7×1013 cm−2, respectively. H2 forms the most important gas torus with an escape rate of ∼2×1027 s−1 followed by O with an escape rate of ∼5×1026 s−1, created primarily as exothermic O products from O2 dissociation by magnetospheric electrons. The circumplanetary distributions of H2 and O are highly peaked about the satellite location and asymmetrically distributed near Europa's orbit about Jupiter, have substantial forward clouds extending radially inward to Io's orbit, and have spatially integrated cloud populations of 4.2×1033 molecules for H2 and 4.0×1032 atoms for O that are larger than their corresponding populations in Europa's local atmosphere by a factor of ∼200 and ∼1000, respectively. The cloud population for H2 is a factor of ∼3 times larger than that for the combined cloud population of Io's O and S neutral clouds and provides the dominant neutral population beyond the so-called ramp region at 7.4-7.8 RJ in the plasma torus. The calculated brightness of Europa's O cloud on the sky plane is very dim at the sub-Rayleigh level. The H2 and O tori provide a new source of europagenic molecular and atomic pickup ions for the thermal plasma and introduce a neutral barrier in which new plasma sinks are created for the cooler iogenic plasma as it is transported radially outward and in which new sinks are created to alter the population and pitch angle distribution of the energetic plasma as it is transported radially inward. The europagenic instantaneous pickup ion rates are peaked at Europa's orbit, dominate the iogenic pickup ion rates beyond the ramp region, and introduce new secondary plasma source peaks in the solution of the plasma transport problem. The H2 torus is identified as the unknown Europa gas torus that creates both the observed loss of energetic H+ ions at Europa's orbit and the corresponding measured ENA production rate for H.  相似文献   

14.
C/2006 P1 McNaught is a dynamically new comet from the Oort cloud that passed very close to the Sun, driving overall volatile production rates up to about 1031 molecules s−1. Post-perihelion observations were obtained in a target-of-opportunity campaign using the CSHELL instrument at the NASA Infrared Telescope Facility atop Mauna Kea, Hawaii, on UT 2007 January 27 and 28. Eight parent volatiles (H2O, CH4, C2H2, C2H6, HCN, CO, NH3, H2CO) and two daughter fragments (OH and NH2) were detected, enabling the determination of a rotational temperature and production rate for H2O on UT January 27 and absolute and relative production rates for all the detected parent species on UT January 28. The chemical composition measured in the coma suggests that this close perihelion passage stripped off processed outer surface layers, likely exposing relatively fresh primordial material during these observations. The post-perihelion abundances we measure for CO and CH4 (relative to H2O) are slightly depleted while C2H2, NH2 and possibly NH3 are enhanced when compared to the overall comet population. Measured abundances for other detected molecular species were within the range typically observed in comets.  相似文献   

15.
A thermodynamical analysis of the multicomponent system SiTiAlFeMnMgCaNaKPCHO open with respect to CO2, CO, H2O was carried out. Hydration and carbonatization processes are proposed to be geochemical consequences of the hypothesis of quasi-equilibrium conditions between the troposphere and crustal surface rocks. The probable rock-forming hydrated mineral phases are represented by epidote, glaucophane, tremolite, phlogopite, and annite; the carbonatization results in existence of calcite and dolomite as rock-forming minerals of weathered alkaline lavas. The surface rocks are assumed to have high ferric/ferrous iron ratios. The wollastonite equilibrium is rejected as a buffering chemical reaction. Hydrated minerals could be stable at least up to 5-km depths and contribute about 0.1 × 1024 g of H2O whereas about (0.7–0.8) × 1024 g of H2O would be consumed in ferrous iron oxidation with concomitant hydrogen dissipation. The distribution of H2O in the outer planetary shells is possibly a function of their temperatures.  相似文献   

16.
SiS has been conclusively detected toward Orion-KL via its J = 6-5 and J = 5-4 rotational transitions at 91 and 109 GHz. Line profiles indicate that the species is present at an LSR velocity of 7.5 km s-1 with a half-width at zero power of 36 km s-1. Such characteristics associate SiS with the moderate velocity outflow (V approximately 18 km s-1) centered on IRc2 and observed in thermal SiO, the NH3 "plateau," and OH, H2O, and SiO masers. The column density estimated for SiS in this region is Ntot = 4 x 10(15) cm-2, corresponding to a fractional abundance of f approximately 4 x 10(-9). Such an abundance implies an SiO/SiS ratio of approximately 60 in the outflow material, remarkably close to the cosmic O/S ratio of approximately 40 and contrasting with the SiO/SiS value of > approximately 10(3) predicted by ion-molecule models. This difference is probably a result of the high temperatures and densities present in the outflow, which favor thermal equilibrium abundances similar to those observed in the circumstellar shells of late-type stars rather than "ion-molecule"-type concentrations. In addition to SiS, some twenty new unidentified lines near 91 and 109 GHz were detected toward KL, as well as transitions arising from HC5N, HC13CCN, HCC13CN, O13CS, and, possibly, CH3CH2OH, CH3CHO, and CH3OD.  相似文献   

17.
We measured the chemical composition of Comet C/2007 W1 (Boattini) using the long-slit echelle grating spectrograph at Keck-2 (NIRSPEC) on 2008 July 9 and 10. We sampled 11 volatile species (H2O, OH∗, C2H6, CH3OH, H2CO, CH4, HCN, C2H2, NH3, NH2, and CO), and retrieved three important cosmogonic indicators: the ortho-para ratios of H2O and CH4, and an upper-limit for the D/H ratio in water. The abundance ratios of almost all trace volatiles (relative to water) are among the highest ever observed in a comet. The comet also revealed a complex outgassing pattern, with some volatiles (the polar species H2O and CH3OH) presenting very asymmetric spatial profiles (extended in the anti-sunward hemisphere), while others (e.g., C2H6 and HCN) showed particularly symmetric profiles. We present emission profiles measured along the Sun-comet line for all observed volatiles, and discuss different production scenarios needed to explain them. We interpret the emission profiles in terms of release from two distinct moieties of ice, the first being clumps of mixed ice and dust released from the nucleus into the sunward hemisphere. The second moiety considered is very small grains of nearly pure polar ice (water and methanol, without dark material or apolar volatiles). Such grains would sublimate only very slowly, and could be swept into the anti-sunward hemisphere by radiation pressure and solar-actuated non-gravitational jet forces, thus providing an extended source in the anti-sunward hemisphere.  相似文献   

18.
The evolution and variability of atmospheric ozone over geological time   总被引：1，自引：0，他引：1  
The rise of atmospheric O3 as a function of the evolution of O2 has been investigated using a one-dimensional steady-state photochemical model based on the chemistry and photochemistry of Ox(O3, O, O(1D)), N2O, NOx(NO, NO2, HNO3), H2O, and HOx(H, OH, HO2, H2O2) including the effect of vertical eddy transport on the species distribution. The total O3 column density was found to maximize for an O2 level of 10?1 present atmospheric level (PAL) and exceeded the present total O3 column by about 40%. For that level of O2, surface and tropospheric O3 densities exceeded those of the present atmosphere by about an order of magnitude. Surface and tropospheric OH densities of the paleoatmosphere exceeded those of the present atmosphere by orders of magnitude. We also found that in the O2-deficient paleoatmosphere, N2O (even at present atmospheric levels) produces much less NOx than it does in the present atmosphere.  相似文献   

19.
The solar and galactic cosmic rays interact directly with lunar surface materials, and the dominant nature of interactions is essentially the complete absorption of corpuscles. These corpuscles damage the lattice structure, and induce a complex set of reactions in the materials producing various species. The cosmic ray damage of the lattice would not produce an amorphous layer, similar to that produced by the solar wind, because the solar wind erosion rate is faster than the cosmic ray-induced amorphous layer formation rate. The species formation rate considered in this paper are those produced by protons, the dominant component of cosmic rays. Protons produce H, H2, OH, H2O, and hydrogenated species of carbon, nitrogen, sulfur, etc. These species, while migrating in the material, encounter oncoming cosmic ray corpuscles, and undergo a complex set of reactions. Although a variety of species are produced by protons, the dominant contributor to the atmosphere is H2. The H2 flux (molecules cm–2 sec–1) is about 1.5 × 105 as compared to the H flux of 8.4 × 101 and the H2O flux of 4.6 × 10–2. These fluxes are about 10–3 smaller than the fluxes of the same species produced by the solar wind protons. Thus the contributions of the cosmic ray-induced species to the atmosphere is very small compared to the solar wind-induced species. Although simulated experiments showed high concentractions of OH and H2O in the terrestrial materials of lunar type, these species concentrations in the lunar materials under the lunar environment is much smaller than those observed in the simulated experiments.  相似文献   

20.
Experimental results on the spectral identification of new infrared absorption features and the changes of their absorbances produced through vacuum ultraviolet-extreme ultraviolet (VUV-EUV) photon-induced chemical reactions in the C2H2-H2O mixed ices at 10 K are obtained. To the best of our knowledge, this is the first time that EUV photons have been employed in the study of the photolysis of ice analogues. Two different compositions, i.e., C2H2:H2O=1:4 and 1:1, were investigated in this work. A tunable intense synchrotron radiation light source available at the Synchrotron Radiation Research Center, Hsinchu, Taiwan, was employed to provide the required VUV-EUV photons. In this study, the photon wavelengths selected to irradiate the icy samples corresponded to the prominent solar hydrogen, helium, and helium ion lines at 121.6 nm, 58.4 nm, and 30.4 nm, respectively. The photon dosages used were typically in the range of 1×1015 to 2×1017 photons. Molecular species produced and identified in the ice samples at 10 K resulting from VUV-EUV photon irradiation are mainly CO, CO2, CH4, C2H6, CH3OH, and H2CO. In addition to several unidentified features, we have tentatively assigned several absorption features to HCO, C3H8, and C2H5OH. While new molecular species were formed, the original reactants, i.e., H2O and C2H2, were detectably depleted due to their conversion to other species. The new chemical species produced by irradiation of photons at 30.4 nm and 58.4 nm can be different from those produced by the 121.6-nm photolysis. In general, the product column density of CO reaches saturation at a lower photon dosage than that of CO2. Furthermore, the production yield of CO is higher than that of CO2 in the photon irradiation. In the present study, we also observe that the photon-induced chemical reaction yields are high using photons at 30.4 and 58.4 nm. The results presented in this work are essential to our understanding of chemical synthesis in ice analogues, e.g., the cometary-type ices and icy satellites of planetary systems.  相似文献   

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