共查询到20条相似文献，搜索用时 437 毫秒
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Ismanuel Rabadán Baljit K. Sarpal & Jonathan Tennyson 《Monthly notices of the Royal Astronomical Society》1998,299(1):171-175
Molecular R-matrix calculations are performed at a range of energies to give rotational and vibrational excitation and de-excitation cross-sections and, hence, rates for electron collisions with HeH+ up to electron temperatures of 20 000 K. Critical electron densities are also given. The rotational calculations include the Coulomb–Born completion of the cross-sections for high l values. Rates for the transition j = 0 → 2, which have previously been assumed to be negligible, are found to be up to half those for j = 0 → 1, raising the prospect of observing the HeH+ j = 2 → 1 emission line at 74.8 μm. 相似文献
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从在CepheusE中C18O（J＝1－0）的谱线频谱图发现,相对于峰速度的蓝移成分的积分流量密度明显大于相对于红移成分的积分流量密度．从在它的强度分布图也可以发现强度分布轮廓向西北和向东延伸．为此,研究了在CepheusE中C18O（J＝1－0）的速度分段积分等高图,发现相对于峰速度的蓝移速度分段积分等高图中的C18O（J＝1－0）的积分强度,要大于相对于红移速度分段积分等高图中的C18O（J＝1－0）的积分强度,同时强度分布图中的分子外流的不准直分布是由相对于峰速度的蓝移成分的分布的不准直性所引起的． 相似文献
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S. Maret A. Faure E. Scifoni L. Wiesenfeld 《Monthly notices of the Royal Astronomical Society》2009,399(1):425-431
Ammonia inversion lines are often used as probes of the physical conditions in the dense interstellar medium. The excitation temperature between the first two para-metastable (rotational) levels is an excellent probe of the gas kinetic temperature. However, the calibration of this ammonia thermometer depends on the accuracy of the collisional rates with H2 . Here, we present new collisional rates for ortho- and para-NH3 colliding with para-H2 ( J = 0) , and investigate the effects of these new rates on the excitation of ammonia. Scattering calculations employ a new, high-accuracy, potential energy surface computed at the coupled-cluster CCSD(T) level with a basis set extrapolation procedure. Rates are obtained for all transitions involving ammonia levels with J ≤ 3 and for kinetic temperatures in the range 5–100 K. We find that the calibration curve of the ammonia thermometer – which relates the observed excitation temperature between the first two para-metastable levels to the gas kinetic temperature – does not change significantly when these new rates are used. Thus, the calibration of ammonia thermometer appears to be robust. Effects of the new rates on the excitation temperature of inversion and rotation–inversion transitions are also found to be small. 相似文献
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Alexandre Faure Jonathan Tennyson 《Monthly notices of the Royal Astronomical Society》2001,325(1):443-448
Molecular R -matrix calculations are performed to give rotational excitation rates for electron collisions with linear molecular ions. Results are presented for CO+ , HCO+ , NO+ and H2 + up to electron temperatures of 10 000 K. De-excitation rates and critical electron densities are also given. It is shown that the widely used Coulomb–Born approximation is valid for Δ j =1 transitions when the molecular ion has a dipole greater than about 2D, but otherwise is not reliable for studying electron-impact rotational excitation. In particular, transitions with Δ j >1 are found to have appreciable rates and are found to be entirely dominated by short-range effects. 相似文献
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俞志尧 《中国天文和天体物理学报》1996,(4)
根据文[1]中图1（a）和图1（b），分别对CepB和CepF进行成图处理，得到了它们的强度分布图和速度分段积分等高图，通过对这些强度分布图和速度分段积分等高图的分析和研究，也得到了CegheusOB3巨分子云复合体是成块的，并且这些块是没有被自引力束缚的，同时还得到了CepB和CepF的外流的动力学时标。 相似文献
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俞志尧 《中国天文和天体物理学报》1999,(1)
分析ＣｅｐｈｅｕｓＥ中Ｃ１８Ｏ（Ｊ＝１－０）的速度位置图,发现相对于峰速度的红移速度成分主要分布在中心位置附近的核区,而相对于峰速度的蓝移速度成分除了分布在中心位置附近的核区外,还可以在向东和向西北方向的外流中找到。这说明强度分布图中的分子外流的不准直分布是由相对于峰速度的蓝移速度成分的不准直分布所引起的。 相似文献
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Yu. A. Shchekinov 《Astrophysics》2004,47(2):205-212
Observed correlations between linewidths and the characteristic size of the radiating region of molecular clouds, as well as the extremely weak dependence of their surface density on the cloud size, are usually interpreted as evidence that the molecular clouds in the galaxy are in a virial state. In this paper it is argued that no more than 30% of the molecular gas in the galaxy can be in a virial equilibrium. Possible alternative reasons for the observed correlations are discussed. It is argued that the mass of molecular gas which is not in virial equilibrium may be greatly underestimated because of its low surface density and a reduced concentration of CO molecules. 相似文献
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We discuss the propagation of spectral line and continuum radiation in a clumpy medium and give general expressions for the observed absorption or emission from a cloud population. We show that the affect of the medium clumpiness can usually be characterised by a single number multiplying the mean column opacity. Our result provides a simpler proof and generalization of the result of Martin et al. (1984). The formalism provides a simple way to understand the effects of clumping on molecular line profiles and ratios; for example, how clumping effects the interpretation of 13CO(1–0) to 12CO(1–0) line ratios. It also can be used as a propagation operator in physical models of clumpy media where the incident radiation effects the spectral line emissivity. We are working to extend the formalism to the propagation of masers in a clumpy medium, but in this case, there are special difficulties because formal expectation values are not characteristic of observations because they are biased by rare events. 相似文献
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D. R. Flower J. Le Bourlot G. Pineau des Forêts E. Roueff 《Monthly notices of the Royal Astronomical Society》2000,314(4):753-758
The results of recent quantum mechanical calculations of cross-sections for rotational transitions within the vibrational ground state of HD are used to evaluate the rate of radiative energy loss from gas containing HD, in addition to H, He and H2 . The cooling function for HD (i.e. the rate of cooling per HD molecule) is evaluated in steady state on a grid of values of the relevant parameters of the gas, namely the gas density and temperature, the atomic to molecular hydrogen abundance ratio and the ortho:para-H2 density ratio. The corresponding cooling function for H2 , previously computed by Le Bourlot et al., is slightly revised to take account of transitions induced by collisions with ground-state ortho-H2 ( J =1). The cooling functions and the data required for their calculation are available from http://ccp7.dur.ac.uk/. We then make a study of the rate of cooling of the primordial gas through collisions with H2 and HD molecules. In this case, radiative transitions induced by the cosmic background radiation field and, in the case of H2 , collisional transitions induced by H+ ions should additionally be included. 相似文献
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Recent studies of the star formation region BBW 36 and associated molecular clouds are presented. The 12CO (1-0) observations, carried out with the 15-m SEST (Swedish-ESO) telescope (Cerro La Silla, Chile), revealed the existence
of cloud a, connected with BBW 36 and of cloud b, having elongation in SE-NW direction. A red-shifted molecular outflow with
velocity ∼+5 km/s (with respect to cloud a), having a direction parallel to the line of sight, was also observed. VLA observations
showed the presence of a source VLA 2 at 3.6 cm with an elongation in the N-S direction. It is suggested that the VLA 2 source
coincides with a dust disc (surrounding the object BBW 36). The star 3, which is one of the YSOs in the star-forming region
BBW 36 and is connected with a bright comma-like nebula, can be the source of the molecular outflow. The star 3 has very high
IR colors and is associated with an IRAS point source IRAS 07280-1829, which has IR colors, typical for an IRAS point source,
connected with a water maser. On the 2MASS K image of BBW 36 we can see the existence of a bright nebula; a group of stars
is embedded in that nebula, and among these stars there are stars with dust discs (or envelopes). On the 2MASS K image several
spiral jets are also present, some of them with a condensation at the end.
Published in Astrofizika, Vol. 51, No. 3, pp. 469–477 (August 2008). 相似文献
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利用日本名古屋大学天体物理系的毫米波射电望远镜对CepheusC的C18O（J＝1－0）分子辐射首次进行了观测，得到了强度分布图．从强度分布图上，我们发现C18O（J＝1－0）分子的分布呈现三个核．通过计算得到了三个核的物理参数． 相似文献