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1.
We develop a semiempirical grey radiative model to quantify Titan’s surface temperature as a function of pressure and composition of a nitrogen-methane-hydrogen atmosphere, solar flux and atmospheric haze. We then use this model, together with non-ideal gas-liquid equilibrium theory to investigate the behavior of the coupled surface-atmosphere system on Titan. We find that a volatile-rich Titan is unstable with respect to a runaway greenhouse—small increases in solar luminosity from the present value can lead to massive increases in surface temperature. If methane has been photolyzed throughout Titan’s history, then this runaway can only be avoided if the photolytic ethane is removed from the surface-atmosphere system.  相似文献   

2.
In the forthcoming months, the KamLAND experiment will probe the parameter space of the solar large mixing angle MSW solution as the origin of the solar neutrino deficit with ’s from distant nuclear reactors. If however the solution realized in nature is such that Δm2sol2×10−4 eV2 (thereafter named the HLMA region), KamLAND will only observe a rate suppression but no spectral distortion and hence it will not have the optimal sensitivity to measure the mixing parameters. In this case, we propose a new medium baseline reactor experiment located at Heilbronn (Germany) to pin down the precise value of the solar mixing parameters. In this paper, we present the Heilbronn detector site, we calculate the interaction rate and the positron spectrum expected from the surrounding nuclear power plants. We also discuss the sensitivity of such an experiment to |Ue3| in both normal and inverted neutrino mass hierarchy scenarios. We then outline the detector design, estimate background signals induced by natural radioactivity as well as by in situ cosmic ray muon interaction, and discuss a strategy to detect the anti-neutrino signal ‘free of background’.  相似文献   

3.
Tau neutrinos interacting inside the Earth produce τ leptons which thereafter can decay inside the atmosphere. The propagation of extremely energetic ντ’s and τ’s through the Earth is studied by means of a detailed Monte Carlo simulation, taking into account all major mechanisms of ντ interactions and τ energy loss as well as decay modes. The rates of τ’s emerging from the Earth are determined as a function of τ’s energy for several cosmic neutrino models.  相似文献   

4.
The neighbouring lines a 6D5/2– x 6Po3/2 (1272.617 Å) and a 6D5/2– w 2Po3/2 (1272.657 Å) have been observed in the UV spectrum of χ Lupi to be of comparable intensity. The latter, Δ S  = 2, transition would be expected to be very weak. The two upper states should display negligible mixing. We give a detailed, quantitative discussion of how the two upper states are in fact strongly mixed through their mixing with 3d6(3D)4p 4Po3/2, and hence we explain the relative strengths of the two UV lines.  相似文献   

5.
Two photographs of Comet Halley in CN were obtained in 1986 April 8 and 12, and two in C3, on March 21 and May 5. Photometry led to mean brightness profiles of the CN and C3 comae on these days. Using Haser's coma model, the scale-heights of these two molecules and of the parent molecules were derived.  相似文献   

6.
Inspection of recent spectra presented by Sivjee (1983) show evidence of the 0–4 and 0–5 bands of the N2(c′41Σu+ → a1Πg) Gaydon-Herman system. In conjunction with earlier spectra, it is now possible that this band system is a significant auroral component, with an intensity approx. 7% that of the N2 2P system. The absence in aurorae of the potentially far stronger N2(c′41Σu+ → X1Πg) system is discussed. It is that the O2(A3Σu+ → X3Σg−) band system is indiscernible in Sivjee's auroral spectra, under conditio the foreground nightglow is expected to be clearly visible. On the other hand, at least one relatively strong O2(A′3Δu → a1Δg) band appears to be present in these spectra.  相似文献   

7.
Minor planet 1997 CU26 is a Centaur, and is probably undergoing dynamical evolution inwards from the Kuiper Belt. We present optical and infrared ( VRIJHK ) photometry which gives mean colours of V − R =0.46±0.02, V − I =1.02±0.02, V − J =1.74±0.02, V − H =2.15±0.02 and V − K =2.25±0.02. The resulting relative reflectance spectrum lies between those of Chiron and Pholus (although closer to that of Chiron). A 1.6–2.6 μm spectrum confirms the broad absorption feature at 2.05 μm associated with water ice reported by Brown et al. 1997 CU26 displays no significant light curve variation and (unlike Chiron) has no observable coma. We place an upper limit to the dust production rate of 1.5 kg s−1. J -band data taken at phase angles of 1.°7 to 4.°0 give a phase parameter of G J =0.36±0.1, and are consistent with a phase parameter of G =0.15 in the V band (a value often assigned to low-albedo objects when no other information is available) if we assume a phase reddening of 0.017 mag deg−1 in the J band. We find V (1, α =4.°1) =7.022±0.02, from which we deduce, by assuming G =0.15±0.1, an absolute visual magnitude of H V =6.64±0.04.  相似文献   

8.
Recent rocket observations of the N2 V-K (Vegard-Kaplan) system in the aurora have been reinterpreted using an atmospheric model based on mass spectrometer measurements in an aurora of similar intensity at the same time of year. In contrast to the original interpretation, we find that population by cascade from the C3Πu and B3Πg states in the A3Σu+v=0,1 levels, as calculated using recently measured electron excitation cross sections, accurately accounts for the observed relative emission rates (IV-K/12PG0.0). In addition there is no need to change the production rate of A 3 Σ u+ molecules relative to that of C3Πuv=0 as a function of altitude in order to fit the profile of the deactivation probability to the atmospheric model. Quenching of A 3 Σ u+ molecules at high altitudes is dominated by atomic oxygen. The rate constants for the v=0 and v=1 levels are 8 × 10−11 cm3 sec−1 and 1.7 × 10−10 cm3 sec−1 respectively, as determined using the model atmosphere mentioned above. Recent observations with a helium cooled mass spectrometer suggest that conventional mass spectrometer measurements tend to underestimate the atomic oxygen relative concentration. The rate coefficients may therefore be too large by as much as a factor of 3. Below 130 Km we find that it is possible to account for the deactivation in bright auroras by invoking large nitric oxide concentrations, similar to those recently observed mass spectrometrically and using a rate constant of 8 × 10−11 cm3 sec−1 for both the v=1 levels. This rate constant is very nearly the same as that measured in the laboratory (7 × 10−11 cm3 sec−1). Molecular oxygen appears not to play a significant role in deactivating the lower A 3 Σ u+ levels.  相似文献   

9.
In the superluminal source quasar 3C 345, five VLBI knots have been observed to have superluminal motion and, in particular, the two knots C4 and C5 move along different curved orbits. This paper examines the possibility that this pair of orbits are due to the motion of the radio core. Using the available data, the motions of C4 and C5 are resolved as a superposition of a motion of the core and a motion along a common orbit. The results show that such a resolution can fit well the observations. A brief discussion is made on further test of the model and its physical implications.  相似文献   

10.
Pectroscopic data on the shifts and widths of the energy levels of molecular oxygen have been used in the empirical construction of a diabatic potential matrix that characterizes the interactions of the B3∑−u state with the 5Πu, 23∑+u, 3Πu and 1Πu states. The diabatic potential matrix is u theory formulation to calculate the cross-sections for the excitation of O(1D) atoms in collisions of two O(3P) atoms. Total cross-sections are obtained by adding the excitation from the 3Πg, channel. The rate coefficient for quenching of O(1D) by O(3P) is evaluated as a function of temperature. The values conflict with a recent analysis of the emission of the oxygen red line in the upper atmosphere.  相似文献   

11.
The formation of CO2 in the gas phase and on a polyaromatic hydrocarbon surface (coronene) via three possible pathways is investigated with density functional theory. Calculations show that the coronene surface catalyses the formation of CO2 on model grain surfaces. The addition of 3O to CO is activated by 2530 K in the gas phase. This barrier is lowered by 253 K for the Eley–Rideal mechanism and 952 K for the hot-atom mechanism on the surface of coronene. Alternative pathways for the formation of CO2 are the addition of 3O to the HCO radical, followed by dissociation of the HCO2 intermediate. The O + HCO addition is barrierless in the gas phase and on the surface and is more than sufficiently exothermic to subsequently cleave the H–C bond. The third mechanism, OH + CO addition followed by H removal from the energized HOCO intermediate, has a gas-phase exit barrier that is 1160 K lower than the entrance barrier. On the coronene surface, however, both barriers are almost equal. Because the HOCO intermediate can also be stabilized by energy dissipation to the surface, it is anticipated that for the surface reaction the adsorbed HOCO could be a long-lived intermediate. In this case, the stabilized HOCO intermediate could react, in a barrierless manner, with a hydrogen atom to form H2+ CO2, HCO2H, or H2O + CO.  相似文献   

12.
《Planetary and Space Science》1999,47(10-11):1331-1340
The discovery that Titan, the largest satellite of Saturn, has an atmosphere and that methane is a significant constituent of it, was the starting point for a systematic study of Titan’s atmospheric organic chemistry. Since then, the results from numerous ground-based observations and two flybys of Titan, by Voyager I and II, have led to experimental laboratory simulation studies and photochemical and physical modeling. All these works have provided a more detailed picture of Titan. We report here a continuation of such a study performing an experimental laboratory simulation of Titan’s atmospheric chemistry, and considering the two physical phases involved: gases and aerosols. Concerning the gaseous phase, we report the first detection of C4N2 and we propose possible atmospheric abundances for 70 organic compounds on Titan’s upper atmosphere. Concerning the solid phase, we have characterized aerosol analogues synthesized in conditions close to those of Titan’s environment, using elemental analysis, pyrolysis, solubility studies and infrared spectroscopy.  相似文献   

13.
Measurements of the O2(A3Σ − X3Σ) Herzberg system in the night airglow have been made with the ESRO TD-1 satellite in the wavelength range 2400–3100 A. The slant emission rate varies from 3.5 to 15 kR, indicating an irregular structure of the atomic oxygen near the turbopause. A statistical maximum intensity is found near the tropic in the winter hemisphere. The intensity profile is consistent with excitation by three-body recombination of oxygen atoms. The observed total emission rate can be accounted for by reasonable atomic oxygen densities and an O2(A3Σ) production efficiency of about 20% if quenching by N2 occurs at the rate deduced from laboratory and other airglow measurements.  相似文献   

14.
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15.
We have used the Ultra-High-Resolution Facility (UHRF) at the AAT, operating at a resolution of 0.35 km s−1 (FWHM), to observe K  i and C2 absorption lines arising in the circumstellar environment of the post-AGB star HD 56126. We find three narrow circumstellar absorption components in K  i , two of which are also present in C2. We attribute this velocity structure to discrete shells resulting from multiple mass-loss events from the star. The very high spectral resolution has enabled us to resolve the intrinsic linewidths of these narrow lines for the first time, and we obtain velocity dispersions ( b -values) of 0.2–0.3 km s−1 for the K  i components, and 0.54±0.03 km s−1 for the strongest (and best defined) C2 component. These correspond to rigorous kinetic temperature upper limits of 211 K for K  i and 420 K for C2, although the b -value ratio implies that these two species do not co-exist spatially. The observed degree of rotational excitation of C2 implies low kinetic temperatures ( T k≈10 K) and high densities ( n ≈106 to 107 cm−3) within the shell responsible for the main C2 component. Given this low temperature, the line profiles then imply either mildly supersonic turbulence or an unresolved velocity gradient through the shell.  相似文献   

16.
We have obtained an H2 v =1–0 S(1) image of a merging galaxy system, NGC 6090, by using a Fabry–Perot imager. The H2 emission originates between the double nuclei of pre-merger galaxies, and exhibits an arc-like or ring-like structure almost connecting the double nuclei. This structure is similar to that suggested for Arp 220 from the velocity field measured by CO radio emission. The separation of the double nuclei in NGC 6090 is 5–6 arcsec, corresponding to a projected distance of 3–4 kpc. This is much larger than that of Arp 220 and suggests that the molecular gas distribution can form an organized shape between the nuclei, such as a ring, in a rather early phase of merging.  相似文献   

17.
We present a quantitative analysis of CO thermal emissions discovered on the nightside of Titan by Baines et al. [2005. The atmospheres of Saturn and Titan in the near-infrared: First results of Cassini/VIMS. Earth, Moon, and Planets, 96, 119–147]. in Cassini/VIMS spectral imagery. We identify these emission features as the P and R branches of the 1-0 vibrational band of carbon monoxide (CO) near 4.65 μm. For CH3D, the prominent Q branch of the ν2 fundamental band of CH3D near 4.55 μm is apparent. CO2 emissions from the strong v3 vibrational band are virtually absent, indicating a CO2 abundance several orders of magnitude less than CO, in agreement with previous investigations. Analysis of CO emission spectra obtained over a variety of altitudes on Titan's nightside limb indicates that the stratospheric abundance of CO is 32±15 ppm, and together with other recent determinations, suggests a vertical distribution of CO nearly constant at this value from the surface throughout the troposphere to at least the stratopause near 300 km altitude. The corresponding total atmospheric content of CO in Titan is 2.9±1.5×1014 kg. Given the long lifetime of CO in the oxygen-poor Titan atmosphere (0.5–1.0 Gyr), we find a mean CO atmospheric production rate of 6±3×105 kg yr−1. Given the lack of primordial heavy noble gases observed by Huygens [Niemann et al., 2005. The abundances of constituents of Titan's atmosphere from the GCMS on the Huygens probe. Nature, 438, 779–784], the primary source of atmospheric CO is likely surface emissions. The implied CO/CH4 mixing ratio of near-surface material is 1.8±0.9×10−4, based on an average methane surface emission rate over the past 0.5 Gyr of 1.3×10−13 gm cm−2 s−1 as required to balance hydrocarbon haze production via methane photolysis [Wilson and Atreya, 2004. Current state of modeling the photochemistry of Titan's mutually dependent atmosphere and ionosphere. J. Geophys. Res. 109, E06002 Doi:10.1029/2003JE002181]. This low CO/CH4 ratio is much lower than expected for the sub-nebular formation region of Titan and supports the hypothesis [e.g., Atreya et al., 2005. Methane on Titan: photochemical-meteorological-hydrogeochemical cycle. Bull. Am. Astron. Soc. 37, 735] that the conversion of primordial CO and other carbon-bearing materials into CH4-enriched clathrate-hydrates occurs within the deep interior of Titan via the release of hydrogen through the serpentinization process followed by Fischer–Tropsch catalysis. The time-averaged predicted emission rate of methane-rich surface materials is 0.02 km3 yr−1, a value significantly lower than the rate of silicate lava production for the Earth and Venus, but nonetheless indicative of significant active geological processes reshaping the surface of Titan.  相似文献   

18.
Co-ordinated rocket measurements of the O2(a1Δg−X3Σg−) Infrared Atmospheric (0-0) band emission profile and the atomic oxygen densities in an undisturbed night-time atmosphere are used to investigate the processes responsible for the excitation of O2(a1Δg) in the terrestrial nightglow. It is shown that three-body recombination of atomic oxygen, and subsequent energy transfer processes, can explain only part of the observed emission profile and that at least two other sources of O2(a1Δg) emission must exist. One of these additional sources, responsible for most of the emission observed below 90km, is identified as arising from the night-time residual of the very large dayglow 1Δg population. The other additional source is required to explain most of the emission observed above 95km. The processes responsible for this high altitude component cannot be identified but the vertical distribution of the required source function strongly resembles the profile of the atomic oxygen density squared and suggests that a two-body radiative recombination process may be involved. However, the measured zenith emission rates can also be explained without the high altitude source of O2(a1Δg) if optical emission at 1.27 μm was induced by the rocket as it penetrated the nightglow layer.  相似文献   

19.
We suggest a new way to establish the relation between the electron temperature t 3 within the [O  iii ] zone and the electron temperature t 2 within the [O  ii ] zone in high-metallicity  (12 + log(O/H) > 8.25)  H  ii regions. The   t 2– t 3  diagram is constructed by applying our method to a sample of 372 H  ii regions. We find that the correlation between t 2 and t 3 is tight and can be approximated by a linear expression. The new   t 2– t 3  relation can be used to determine t 2 and accurate abundances in high-metallicity H  ii regions with a measured t 3. It can also be used in conjunction with the ff relation for the determination of t 3 and t 2 and oxygen abundances in high-metallicity H  ii regions, where the [O  iii ]λ4363 auroral line is not detected. The derived   t 2– t 3  relation is independent of photoionization models of H  ii regions.  相似文献   

20.
We have observed the Sunyaev–Zel'dovich (SZ) effect in a sample of five moderate-redshift clusters with the Ryle Telescope, and used them in conjunction with X-ray imaging and spectral data from ROSAT and ASCA to measure the Hubble constant. This sample was chosen with a strict X-ray flux limit using both the Bright Cluster Sample and the Northern ROSAT All-Sky Survey (RASS) cluster catalogues to be well above the surface brightness limit of the RASS, and hence to be unbiased with respect to the orientation of the cluster. This controls a major potential systematic effect in the SZ/X-ray method of measuring H 0. Taking the weighted geometric mean of the results and including the main sources of error, namely the noise in the SZ measurement, the uncertainty in the X-ray temperatures and the unknown ellipticity and substructure of the clusters, we find   H 0= 59+10−9 (random)+8−7(systematic) km s−1 Mpc−1  assuming a standard cold dark matter model with  ΩM= 1.0, ΩΛ= 0.0  or   H 0= 66+11−10 +9−8 km  s−1 Mpc−1  if  ΩM= 0.3, ΩΛ= 0.7  .  相似文献   

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