Directional radiation and photodissociation regions in molecular hydrogen clouds     

S. A. Balashev  D. A. Varshalovich  A. V. Ivanchik 《Astronomy Letters》2009,35(3):150-166

Some astrophysical observations of molecular hydrogen point to a broadening of the velocity distribution for molecules at excited rotational levels. This effect is observed in both Galactic and high-redshift clouds. Analysis of H₂, HD, and CI absorption lines has revealed the broadening effect in the absorption system of QSO 1232+082 (z _abs = 2.33771). We analyze line broadening mechanisms by considering in detail the transfer of ultraviolet radiation (in the resonance lines of the Lyman and Werner H₂ molecular bands) for various velocity distributions at excited rotational levels. The mechanism we suggest includes the saturation of the lines that populate excited rotational levels (radiative pumping) and manifests itself most clearly in the case of directional radiation in the medium. Based on the calculated structure of a molecular hydrogen cloud in rotational level populations, we have considered an additional mechanism that takes into account the presence of a photodissociation region. Note that disregarding the broadening effects we investigated can lead to a significant systematic error when the data are processed.  相似文献   

类星体3C345的光变周期特性研究     

张雄  谢光中  白金明 《天文学报》1998,39(3):256-264

从大量文献资料中,收集了类星体3C345光学B波段的有效观测数据点共1642个,获得了从1896年至1993年的历史光变曲线．用Jurkevich方法计算分析3C345的光变周期,结果表明3C345的长光变周期为10．1±0．8年（或21．8±1．5年）,预期2002年1月应该为再次爆发期．  相似文献   

Magnetic fields in Quasar 3C147 on milliarcsecond scales     

H.Y. Zhang  R.D. Nan 《Astrophysics and Space Science》2001,275(1-2):143-146

The R Coronae Borealis (RCB) stars represent a rare, or short-lived stage of low and intermediate mass stellar evolution. They are important in the context of mass-loss anddust formation on the Asymptotic Giant Branch.These stars are defined by their large declines in brightness at irregular intervals caused by dust formation.There are two major evolutionary models for the origin of RCB stars, the Double Degenerate and the Final Helium Shell Flash.In the final flash model, RCB stars lie at the centers of old Planetary Nebulae (PN). Here I discuss possible relationships with the [WC] stars.  相似文献   

Quasars in the field of 88 Leonis     

L. Erculiani-Abati  V. L. Afanasjev  O. Spiridonova  H. Lorenz 《Astronomische Nachrichten》1989,310(2):97-102

We present spectroscopically confirmed quasars in the 25 sq. degrees A1-field to a limiting magnitude of m_B = 18.0. Our estimate of the quasar density of 0.28 ± 0.11 objects per sq. degree based on the “complete” sample of A1-qusars is in agreement with the observed integral number-magnitude relation. However, we consider this value as still a lower limit of the quasar density in the A1-field due to the uncertainties during the colour based selection of objects, especially their brightness dependence, resulting in serious selection effects. Thus, the quasar density of the A1 survey may be underestimated up to 30% and does not contradict the recently estimated incompletness of the BQS survey.  相似文献