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A. Ali 《Journal of Astrophysics and Astronomy》2006,27(4):399-409
We have constructed two gas-phase models to study the chemistry of circumstellar envelope surrounding the carbon-rich variable
star IRAS 15194-5115. The network used consists of 3893 reactions involving 397 gas-phase species. The derived fractional
abundances for many molecules are in excellent agreement with values obtained from observations. The predicted column densities
from the two models go well with the observed values of carbon star IRC + 10216. The dominant formation routes for three groups
of species are discussed through the inner and outer envelopes. 相似文献
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I. S. Glass 《Astrophysics and Space Science》1995,230(1-2):215-223
The term Active Galactic Nuclei includes QSOs (Quasi-Stellar Objects), Seyfert galaxies, BL Lac objects and nuclei showing unusual amounts of star formation. South African work has centred on the photometric properties of these objects, both in the optical(UBVRI) and the infrared(JHKL). Photometry has been used to investigate the nature of the relevant emission mechanisms by studying both the colours of the nuclear components and their variations. In particular, it has been demonstrated convincingly that circumnuclear dust shells are present in several Seyfert 1 galaxies at temperatures of around 1500 K.It has also been shown that the variable component in many Seyfert 1 galaxies retains a constant spectral shape independent of its actual flux at a given time. Further, there is evidence that this shape is largely the same in all Seyfert 1 galaxies. Other studies have concentrated on surveys of morphological, spectroscopic and photometric characteristics of certain classes of galaxies such as those found by the IRAS satellite and those listed in the Arp-Madore catalogue of interacting galaxies. 相似文献
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12CO J=2-1 maps of L379 IRS1 show a molecular outflow seen almost end-on while C18O J=2-1 emission covers a smaller central region, tracing virially bound material deeper within the cloud. Continuum maps at 450, 800 and 1100µm all trace an identical double peaked arc west of IRS1 and VLA NH3 (1,1) & (2,2) integrated intensity maps reveal the same double-peaked structure. An identical velocity gradient is seen in12CO,13CO, C18O and NH3 (1,1) & (2,2) following the arc-like structure of the continuum emission. 相似文献
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R. J. Wilman A. C. Fabian R. M. Cutri C. S. Crawford & W. N. Brandt 《Monthly notices of the Royal Astronomical Society》1998,300(1):L7-L10
We report long, pointed ROSAT HRI observations of the hyperluminous galaxies IRAS F00235+1024, F12514+1027, F14481+4454 and F14537+1950. Two of them are optically classified as Seyfert-like. No X-ray sources are detected at the positions of any of the objects, with a mean upper limit L X / L Bol ≃ 2.3 × 10−4 . This indicates that any active nuclei are either atypically weak at X-ray wavelengths or obscured by column densities N H > 1023 cm−2 . They differ markedly from 'ordinary' Seyfert 2 galaxies, bearing a closer resemblance in the soft X-ray band to composite Seyfert 2 galaxies or to some types of starburst. 相似文献
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星系间的相互作用和合并是一个非常普遍的现象,在星系的形成和演化过程中扮演了一个重要角色。理论和实测都有表明星系并合是椭圆星系形成的重要途径。极亮红外星系（ＵＬＩＲＧｓ）与星系间的相互作用和并合密切相关,是研究星系并合现象的理想实验室,对它们的测光研究将有助于理解星系的并合过程。哈勃望远镜（ＨＳＴ）的高分辨率观测为这方面的研究提供了条件。我们利用哈勃望远镜（ＨＳＴ）的宽场行星照相机（ＷＦＰＣ２）对极亮红外星短曝光巡天的Ｉ波段数据,选出了一个子样本。该子样本由２１个以单核为主的极亮红外星系组成,这些星系一般处于星系并合的晚期。我们对这些星系进行了面源测光研究,并根据面亮度轮廓与Ｒ１／４律的差别利用χ＾２判据律将它们分成了两大类：第一类八个星系的面亮度轮廓可以用Ｒ１／４律很好地拟合;而第二类星系在面亮度轮廓与Ｒ１／４ 相似文献
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Embedded Young Stellar Objects (YSO) in dense interstellar clouds are treated self-consistently to understand their spectral
energy distributions (SED). Radiative transfer calculations in spherical geometry involving the dust as well as the gas component,
have been carried out to explain observations covering a wide spectral range encompassing near-infrared to radio continuum
wavelengths. Various geometric and physical details of the YSOs are determined from this modelling scheme.
In order to assess the effectiveness of this self-consistent scheme, three young Galactic star forming regions associated
with IRAS 18314-0720, 18355-0532 and 18316-0602 have been modelled as test cases. They cover a large range of luminosity (≈
40). The modelling of their SEDs has led to information about various details of these sources, e.g. embedded energy source,
cloud structure and size, density distribution, composition and abundance of dust grains etc. In all three cases, the best
fit model corresponds to the uniform density distribution. Two types of dust have been considered, viz., Draine & Lee (DL)
and the Mezger, Mathis & Panagia (MMP). Models with MMP type dust explain the dust continuum and radio continuum emission
from IRAS 18314-0720 and 18355-0532 self-consistently. These models predict much lower intensities for the fine structure
lines of ionized heavy elements, than those observed for IRAS 18314-0720 and 18355-0532. This discrepancy has been resolved
by invoking clumpiness in the interstellar medium. For IRAS 18316-0602, the model with DL type dust grains is preferred. 相似文献