共查询到20条相似文献,搜索用时 186 毫秒
1.
The neighbouring lines a 6 D5/2 – x 6 Po 3/2 (1272.617 Å) and a 6 D5/2 – w 2 Po 3/2 (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 (3 D)4p 4 Po 3/2 , and hence we explain the relative strengths of the two UV lines. 相似文献
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J. Fleming A. Hibbert K. L. Bell & N. Vaeck 《Monthly notices of the Royal Astronomical Society》1998,300(3):767-772
The superposition of configurations (SOC) method has been used to calculate f -values for the Mg ii doublet at 1240 Å, which has been observed in the interstellar medium near stars such as ζ Ophiuchi. Our best value for the multiplet oscillator strength is 0.00083. SOC calculations have also been undertaken for the stronger (3s−3p) doublet at 2800 Å giving a multiplet f -value of 0.92. 相似文献
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K. P. Johns D. M. Cragg P. D. Godfrey & A. M. Sobolev 《Monthly notices of the Royal Astronomical Society》1998,300(4):999-1005
We investigate the possibility of interstellar masers in transitions of the methanol isotopomers CH3 OD, 13 CH3 OH and CH3 18 OH, and of CH3 SH. The model used, in which masers are pumped through the first and second torsionally excited states by IR radiation, has accounted successfully for the Class II masers in main species methanol, 12 CH3 16 OH. Several potential maser candidates are identified for CH3 OD, their detectability depending on the enrichment of this species in star-forming regions. In 13 CH3 OH and CH3 18 OH the best maser candidates are direct counterparts of the well-known 6.7- and 12.2-GHz methanol masers, but the lower interstellar abundance of these substituted species means that the expected brightness is greatly reduced. The maser candidates in CH3 SH are also weak. By comparing these species we find that the large b -component of the dipole moment in methanol plays a significant role in its propensity to form masers, as does the strong torsion–rotation interaction due to the light hydroxyl frame. Thus the exceptional brightness of interstellar methanol masers is due to a favourable combination of molecular properties as well as high interstellar abundance. 相似文献
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Alan Hibbert Tomas Brage Janine Fleming 《Monthly notices of the Royal Astronomical Society》2002,333(4):885-893
We use both the civ3 and mchf codes to calculate oscillator strengths of allowed and intercombination lines in the 3s2 3p–3s3p2 multiplets. Valence, core–valence and some core–core correlation effects are included. The two approaches give results in excellent agreement. Core effects are particularly important for the intercombination lines, though relatively minor for allowed transitions.
We obtain a branching ratio of 1.42 with an estimated accuracy of 0.02 for the transitions, compared with an experimental value of 1.12±0.1 . The A -values of the intercombination lines are substantially different from those of previous calculations. 相似文献
We obtain a branching ratio of 1.42 with an estimated accuracy of 0.02 for the transitions, compared with an experimental value of 1.12±0.1 . The A -values of the intercombination lines are substantially different from those of previous calculations. 相似文献
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M. M. Maldoni † T. R. Ireland G. Robinson 《Monthly notices of the Royal Astronomical Society》2008,386(4):2290-2296
Radiative transfer modelling of the Infrared Space Observatory ( ISO ) spectrum of IRAS 22036+5306 has shown that its unusual 11-μm band can be suitably modelled with an alumina-olivine mixture substantially dominated by the former. The results of this work add further credence to recent findings that significant amounts of Al 2 O3 dust grains are present in the dust shells of stars near or beyond the tip of the asymptotic giant branch. Indeed, in the case of IRAS 22036+5306, Al 2 O3 dominates the dust composition to the extent that it shifts the 9.8-μm band due to amorphous silicates to 11 μm. IRAS 22036+5306 may be an unusual case in that the inner dust torus is maintained at a sufficiently high temperature for Al 2 O3 condensation, but not silicate. 相似文献
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J. E. Bowey A. Morlok † M. Köhler M. Grady 《Monthly notices of the Royal Astronomical Society》2007,376(3):1367-1374
We present mid-infrared spectra from individual enstatite silicate grains separated from primitive type 3 chondritic meteorites. The 2–16 μm transmission spectra were taken with microspectroscopic Fourier-transform infrared (FT-IR) techniques as part of a project to produce a data base of infrared spectra from minerals of primitive meteorites for comparison with astronomical spectra. In general, the wavelength of enstatite bands increases with the proportion of Fe. However, the wavelengths of the strong En100 bands at 10.67 and 11.67 decrease with increasing Fe content. The 11.67-μm band exhibits the largest compositional wavelength shift (twice as large as any other). Our fits of the linear dependence of the pyroxene peaks indicate that crystalline silicate peaks in the 10-μm spectra of Herbig AeBe stars, HD 179218 and 104237, are matched by pyroxenes of En90−92 and En78−80 , respectively. If these simplistic comparisons with the astronomical grains are correct, then the enstatite pyroxenes seen in these environments are more Fe-rich than are the forsterite (Fo100 ) grains identified in the far-infrared which are found to be Mg end-member grains. This differs from the general composition of type 3 chondritic meteoritic grains in which the pyroxenes are more Mg-rich than are the olivines from the same meteorite. 相似文献
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Cesare Cecchi-Pestellini Alexander Dalgarno 《Monthly notices of the Royal Astronomical Society》2000,313(1):L6-L8
A model is constructed of the material in front of the star Cygnus OB2 no. 12 in which dense cores are embedded in diffuse clumps of gas. The model reproduces the measured abundances of C2 and CO, and predicts a column density of 91010 cm2 for HCO+ . 相似文献
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Franco Cataldo Giovanni Strazzulla Susana Iglesias-Groth 《Monthly notices of the Royal Astronomical Society》2009,394(2):615-623
The stability of C60 and C70 fullerenes in the interstellar medium deposited on dust surface or embedded in meteorites and comets has been simulated with γ irradiation and with He+ ion bombardment. It is shown by vibrational spectroscopy that a γ radiation dose of 2.6 MGy (1 Gy = 1 joule absorbed energy per kilogram) causes partial oligomerization of both C60 and C70 fullerenes. Oligomers are made by fullerene cages chemically connected each other which can yield back free fullerenes by a thermal treatment. The amount of irreversibly polymerized fullerenes caused by 2.6 MGy as deduced as the toluene insoluble fraction has been determined as 1.7 and 15 per cent by weight, respectively, for C60 and C70 fullerene. The radiation dose generated by radionuclides decay and expected to be delivered to fullerenes buried at a depth of more than 20 m in comets and meteorites is about 3 MGy per 109 yr. Since fullerenes are by far resistant to such radiation dose they can survive for at least some billion years inside comets and meteorites and in fact have been detected inside certain carbonaceous chondrites. On the other hand, the direct exposure of fullerenes to cosmic rays for instance when they are adsorbed or deposited on the surface of carbon dust corresponds to the delivery of a radiation dose comprised between 30 and 65 MGy per 109 yr. Experimental bombardment of both C60 and C70 fullerenes for instance with He+ ions has shown that the complete amorphization occurs at about 250 MGy. Thus in ∼4 Gyr exposure to cosmic rays it is expected a complete amorphization. 相似文献
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Frans J. M. Rietmeijer Aurora Pun Joseph A. Nuth III 《Monthly notices of the Royal Astronomical Society》2009,396(1):402-408
Here, we report on a kinetically controlled vapour phase condensation experiment using a low-calcium Ca–Fe–SiO–H2 –O2 vapour. Under these conditions of extreme disequilibrium, the condensate properties become predictable. They are amorphous solids with (predictable) deep metastable eutectic compositions. This study also shows how chemical evolution of the condensate grains will lead to chemically complex amorphous solids. The highly disordered structure of the deep metastable eutectic condensates is the very key to this predictable chemical evolution to grains with a silicate mineral composition, yet being amorphous. We compare our results with astronomical observations of dust around young stellar objects. 相似文献
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Flower 《Monthly notices of the Royal Astronomical Society》1998,297(1):334-336
We present rate coefficients for rotational transitions induced in collisions between H2 molecules. Rotational levels J ≤ 8 and kinetic temperatures T ≤ 1000 K are considered. The interaction potential computed by Schwenke has been used, together with the quantal coupled channels method of calculating the cross-sections. Comparison is made with the more recent of previous results. 相似文献
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G. A. Galazutdinov J. Kreowski F. A. Musaev P. Ehrenfreund B. H. Foing 《Monthly notices of the Royal Astronomical Society》2000,317(4):750-758
The identity of the carriers of the diffuse interstellar bands (DIBs) is one of the most fascinating puzzles of modern spectroscopy. Over the last few years the number of known DIBs has grown substantially. In this paper we discuss the two recently discovered near-infrared weak interstellar features which have already been proposed as fingerprints of the buckminsterfullerene We present and discuss measurements of the two related DIBs within a larger sample of reddened targets, observed with different spectrometers, telescopes and site conditions. We provide additional arguments in favour of the interstellar origin of the two bands. We find evidence around the 9577-Å DIB of far-wing structures, which may affect broad-band measurements. We estimate corrections and errors for telluric and stellar blends, and show that the cores of the two DIBs are well correlated with a ratio near unity within 20 per cent. Finally, we discuss their relation to the laboratory spectra of and the search for two expected weaker transitions. 相似文献
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F. Rossi C. Guidorzi L. Amati F. Frontera P. Romano S. Campana G. Chincarini E. Montanari A. Moretti G. Tagliaferri 《Monthly notices of the Royal Astronomical Society》2008,388(3):1284-1292
Using a sample of 14 BeppoSAX and 74 Swift GRBs with measured redshift we tested the correlation between the intrinsic peak energy of the time-integrated spectrum, E p, i , the isotropic-equivalent peak luminosity, L p,iso , and the duration of the most intense parts of the GRB computed as T 0.45 ('Firmani correlation'). For 41 out of 88 GRBs we could estimate all of the three required properties. Apart from 980425, which appears to be a definite outlier and notoriously peculiar in many respects, we used 40 GRBs to fit the correlation with the maximum likelihood method discussed by D'Agostini, suitable to account for the extrinsic scatter in addition to the intrinsic uncertainties affecting every single GRB. We confirm the correlation. However, unlike the results by Firmani et al., we found that the correlation does have a logarithmic scatter comparable with that of the E p, i – E iso ('Amati') correlation. We also find that the slope of the product L p,iso T 0.45 is equal to ∼0.5, which is consistent with the hypothesis that the E p, i – L p,iso – T 0.45 correlation is equivalent to the E p, i – E iso correlation (slope ∼0.5). We conclude that, based on presently available data, there is no clear evidence that the E p, i – L p,iso – T 0.45 correlation is different (both in terms of slope and dispersion) from the E p, i – E iso correlation. 相似文献
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