共查询到20条相似文献，搜索用时 31 毫秒
1.
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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本文使用红外天文卫星（IRAS）巡天数据的最新版本IRAS天空巡天图（ISSA），经过进一步处理，得到了S140S141和S142SharplessHII区－分子云复合体的红外发射强度、温度及其光深的分布．在此基础上对各HII区的一些物理参量进行了统计分析，得到了分子云复合体的红外发射总光度以及复合体中尘埃的分布情况，对小尺度尘埃（VSG）的丰度进行了分析．并对各恒星形成区中的致密团块进行了研究，揭示出其中一些可能的恒星形成区域．同时，对S140区中的有关红外点源作出了能谱分析，并对S141区的激发星进行了讨论． 相似文献
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Takashi Tsuji 《Journal of Astrophysics and Astronomy》1981,2(3):253-276
On the basis of the effective temperature scale proposed previously for cool carbon stars (Paper I), other intrinsic properties
of them are examined in detail. It is shown that the major spectroscopic properties of cool carbon stars, including those
of molecular bands due to polyatomic species (SiC2, HCN, C2H2
etc.), can most consistently be understood on the basis of our new effective temperature scale and the theoretical prediction of
chemical equilibrium. Various photometric indices of cool carbon stars also appear to be well correlated with the new effective
temperatures. Furthermore, as effective temperatures of some 30 carbon stars are now obtained, the calibration of any photometric
index is straightforward, and some examples of such a calibration are given. In general, colour index-effective temperature
calibrations for carbon stars are quite different from those for K-M giant stars. It is found that the intrinsic (R —I)0 colour is nearly the same for N-irregular variables in spite of a considerable spread in effective temperatures, and this
fact is used to estimate the interstellar reddening of carbon stars.
An observational HR diagram of red giant stars, including carbon stars as well as K-M giant stars, is obtained on the basis
of our colour index-effective temperature calibrations and the best estimations of luminosities. It is shown that carbon stars
and M giant stars are sharply divided in the HR diagram by a nearly vertical line at aboutT
eff = 3200 K (logT
eff = 3.50) and the carbon stars occupy the upper right region of M giant stars (except for some high luminosity, high temperature
J-type stars in the Magellanic Clouds; also Mira variables are not considered). Such an observational HR diagram of red giant
stars shows rather a poor agreement with the current stellar evolution models. Especially, a more efficient mixing process
in red giant stars, as compared with those ever proposed, is required to explain the formation of carbon stars. 相似文献
4.
E. Herbst R. Terzieva D. Talbi 《Monthly notices of the Royal Astronomical Society》2000,311(4):869-876
The attempt to understand the temperature dependence of the HNC/HCN abundance ratio in interstellar clouds has been long standing and indecisive. In this paper we report quantum chemical and dynamical studies of two neutral–neutral reactions thought to be important in the formation of HNC and HCN, respectively – C+NH2 →HNC+H, and N+CH2 →HCN+H. We find that although these reactions do lead initially to the products suggested by astronomers, there is so much excess energy available in both reactions that the HCN and HNC products are able to undergo efficient isomerization reactions after production. The isomerization leads to near equal production rates of the two isomers, with HNC slightly favoured if there is sufficient rotational excitation. This result has been incorporated into our latest chemical model network of dense interstellar clouds. 相似文献
5.
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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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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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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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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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
16.
G. J. Harris J. Tennyson B. M. Kaminsky Ya. V. Pavlenko H. R. A. Jones 《Monthly notices of the Royal Astronomical Society》2006,367(1):400-406
We build an accurate data base of 5200 HCN and HNC rotation–vibration energy levels, determined from existing laboratory data. 20 000 energy levels in the Harris et al. linelist are assigned approximate quantum numbers. These assignments, lab-determined energy levels and Harris et al. energy levels are incorporated in to a new energy level list. A new linelist is presented, in which frequencies are computed using the lab-determined energy levels where available, and the ab initio energy levels otherwise.
The new linelist is then used to compute new model atmospheres and synthetic spectra for the carbon star WZ Cas. This results in better fit to the spectrum of WZ Cas in which the absorption feature at 3.56 μm is reproduced to a higher degree of accuracy than has previously been possible. We improve the reproduction of HCN absorption features by reducing the abundance of Si to [Si/H]=−0.5 dex, however, the strengths of the Δ v = 2 CS band heads are overpredicted. 相似文献
The new linelist is then used to compute new model atmospheres and synthetic spectra for the carbon star WZ Cas. This results in better fit to the spectrum of WZ Cas in which the absorption feature at 3.56 μm is reproduced to a higher degree of accuracy than has previously been possible. We improve the reproduction of HCN absorption features by reducing the abundance of Si to [Si/H]=−0.5 dex, however, the strengths of the Δ v = 2 CS band heads are overpredicted. 相似文献
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星系中的巨分子云(GMCs)是恒星形成的主要区域,因此它的形成和演化对于星系的演化是至关重要的。本文中将介绍分子云的基本特性、分子云之间的碰撞和巨分子云的形成、碎裂和寿命以及其他环境因素,如旋臂扰动、较差自转等在巨分子云的形成和演化中的作用。同时也探讨在采用数值模拟研究巨分子云演化时所取分子云数目的影响。 相似文献
19.
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