排序方式: 共有49条查询结果,搜索用时 15 毫秒
31.
Ye Xu Xing-Wu Zheng Dong-Rong JiangNational Astronomical Observatories Chinese Academy of Sciences Urumqi xuye@nju.edu.cnShanghai Astronomical Observatory Chinese Academy of Sciences Shanghai Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2003,3(1):49-68
We present a statistical analysis of 482 6.7 GHz methanol maser sources from the available literature, on their maser emission and the characteristics of their associated infrared sources. On the color-color diagram, more than 70% of the objects fall within a very small region (0.57 ≤ [25 - 12] ≤ 1.30 and 1.30 ≤[60 - 12] ≤ 2.50). This suggests that 6.7 GHz methanol maser emission occurs only within a very short evolutionary phase during the earliest stage of star formation. The velocity ranges of the masers belong to two main groups: one from 1 to 10 km s^-1, and one from about 11 to 20 km s^-1. These velocity ranges indicate that the masers are probably associated with both disks and outflows. The correlations between the maser and infrared flux densities, and between the maser and infrared luminosities, suggest that far-infrared radiation is a possible pumping mechanism for the masers which most probably originate from some outer molecular envelopes or disks. 相似文献
32.
We report narrowband (Δλ ≤ 10Å) imaging data obtained for the planetary nebula A 19 (PN G200.7+0.84) in continuing our programme of morphological study of planetary nebulae (PNe). Our deep survey through the Hα filter reveals a new nebula – probably a huge HII region –centred at R.A.(2000) = 6h59mn, DEC.(2000) = +14°40′. 相似文献
33.
M. J. Gaylard G. C. MacLeod D. P. Smits M. E. West D. J. van der Walt 《Astrophysics and Space Science》1995,230(1-2):341-350
Research into star-forming regions, evolved HII regions, late-type stars with circumstellar dust shells and comet Halley using spectroscopic observations made with the Hartebeesthoek radio telescope is reviewed. 相似文献
34.
The hydrogen Balmer‐α emission line spectrum of ten diffuse ionization sources in the Milk Way – NGC 40 (WC8), NGC 2022, NGC 6210, NGC 6618 (M17, Sh2‐45), NGC 6720 (M57), NGC 6781, NGC 6888 (Sh2‐105), NGC 6992 (Sh2‐103), NGC 7635 (Sh2‐162,) and IC 1848 (Sh2‐199) – has been investigated using a dual etalon Fabry‐Pérot optical spectrometer (DEFPOS) aatached to the 150 cm RTT150 telescope at TUBITAK National Observatory (TUG, Antalya, Turkey: 36° 51′ N; 30° 20′ E; elevation: 2547 m). All of our galactic Hα observations discussed in this paper were carried out during the nights of 2013 June 21–24 with exposure time of 3600 s. As main results the intensity, the full width at half maximum, and the radial velocity with respect to the LSR have been determined for each data set. The intensities, the radial velocities, and the line widths of the Hα emission line vary from 59.15 to 8923.44 R, –46.72 to +54.07 km s–1, and 31.4 to 48.01 km s–1, respectively. The radial velocities and the half‐widths of the Hii regions and planetary nebulae determined from our measurements are found tobe consistent with values given in literature, especially with those in Schneider et al. (1983) and Fich et al. (1990). (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
35.
罗绍光 《中国天文和天体物理学报》1995,(2)
对恒星形成区CepOB4的IRAS观测结果的详细分析和研究表明,与年轻星团Be59相联系的分子云物质的原始分布是高度成块的。Be59诞生于一个平均密度为100─200cm(-3)云的背向太阳一侧。强烈的电离辐射以及星风已经在其诞生地产生了一个半径大约为5pc的"水泡型(Blister)"电离氢区及与之相关的红外源。电离辐射也穿过云际介质到达与母云分离的另两个云的表面,形成了从侧面看到的电离波前及被压缩和加热的中性物质壳。在这个恒星形成区中,虽然有大量年轻恒星存在,但大质量恒星的形成已经停止。红外发射主要起源于标准尘埃粒子的热平衡发射。但在主激发星团Be59附近的HII区中25μm发射的显著增强可能与某种与电离气体相混合的新型尘埃粒子有关。 相似文献
36.
We report new echelle observations of the kinematics of 30 HII regions in the LMC, including the 30 Doradus giant HII region. All of the HII regions possess supersonic velocity dispersions, which can be attributed to a combination of turbulent motions and discrete velocity splitting produced by stellar winds and/or embedded supernova remnants (SNRs). The core of 30 Dor is unique, with a complex velocity structure that parallels its chaotic optical morphology. We use our calibrated echelle data to measure the physical properties and energetic requirements of these velocity structures. The most spectacular structures in 30 Dor are several fast expanding shells, which appear to be produced at least partially by SNRs. 相似文献
37.
A dual étalon Fabry‐Pérot spectrometer called DEFPOS has been used for observing physical properties of HII regions and planetary nebulae since May 2007 (Aksaker et al. 2009, 2011; Şahan et al. 2009; Şahan 2011). In this study, the Hα measurements of the HII region NGC 1499 (California Nebula) have been investigated with a 4′ circular field of view over a 200 km s–1 (4.4 Å) spectral window. These measurements provide information about the densities, line widths, and radial velocities of the surrounding NGC 1499 nebula. The intensities, the radial velocities and the line widths of the Hα emission line vary from 397.75 R to 1044.14 R, –4.88 km s–1 to –1.02 km s–1, and 36.72 km s–1 to 42.81 km s–1, respectively (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
38.
From an analysis of VLBI observations of H2CO and OH maser emission in the direction of the ultra-conpact HII region NGC 7538-IRS 1, the following model is proposed: The HII region is surrounded by a thick dusty shell which breaks open at the two poles and there is a bipolar outflow. Around it is a rotating gas/dust ring and matter falls from the ring onto the surface of the HII region. The whole system, HII region and the ring, moves with a sight line velocity of −61.0 km/s inside a large cloud which moves with a sight line velocity of −57 km/s. The H2CO and OH masers occur near the poles of the HII region and within 0.2 RHII of the surface. The positions of the H2O maser and other line sources are discussed in term of this model. 相似文献
39.
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
40.
A new scheme of radiation transfer for understanding the infrared spectra of HII regions, has been developed. This scheme
considers non-equilibrium processes (e.g. transient heating of the very small grains, VSG; and the polycyclic aromatic hydrocarbon,
PAH) also, in addition to the equilibrium thermal emission from normal dust grains (BG). The spherically symmetric interstellar
dust cloud is segmented into a large number of “onion skin” shells in order to implement the non-equilibrium processes. The
scheme attempts to fit the observed SED originating from the dust component, by exploring the following parameters: (i) geometrical
details of the dust cloud, (ii) PAH size and abundance, (iii) composition of normal grains (BG), (iv) radial distribution
of all dust (BG, VSG & PAH).
The scheme has been applied to a set of five compact H II regions (IRAS 18116 − 1646, 18162 − 2048, 19442 + 2427, 22308 +
5812, and 18434 - 0242) whose spectra are available with adequate spectral resolution. The best fit models and inferences
about the parameters for these sources are presented. 相似文献