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1.
本项研究给出了１７个个有Ⅱ类星陆甲醇分子脉泽源的致密氢Ⅱ区的轫致辐射、尘埃红外辐射和中心年轻恒星Ｌａｙｍａｎ辐射的特性。以脉泽的光子发射率和辐射亮温度作为两个主要的辐射抽运约束条件，讨论了Ⅱ类星陆甲醇分子脉泽的几种可能的激发机制。 相似文献
2.
利用甚长基线干涉仪，在１６６５ＭＨｚ频率上，观测超致密氢ＩＩ区Ｇ４５．０７＋０．１３的左右圆偏振羟基（ＯＨ）分子脉泽辐射．利用多条纹率成图方法，获得了这个区域２０ｍａｓ相对位置精度的脉泽结构图．除两个弱子源以外，所有脉泽子源都位于彗状结构氢ＩＩ区“彗头”的前沿．脉泽团离致密氢ＩＩ区中心投影距离为０＂．４．在完全饱和辐射的假设下，估计脉泽活动区具有氢分子数密度约为４．５×１０８（Ｈ２）ｃｍ－３．在脉泽源中，发现一对Ｚｅｅｍａｎ对，从它们的ＬＳＲ速度差，导出脉泽区的磁场约为３ｍＧ，方向为远离地球方向．在致密氢ＩＩ区Ｇ４５．０７＋０．１３彗头附近的脉泽团的直径为６×１０１６ｃｍ．这与Ｇ３４．０３＋０．２的观测结果很类似．这给解释彗状结构的氢ＩＩ区的各种模型提供了一个可靠的观测约束条件． 相似文献
3.
天文中醇脉泽源可分为两类．第一类脉泽源在6．7GHz及12．2GHz上有强的吸收特征，而第二类脉泽源则在6.7GHz和12.2GHz上有强的脉泽发射．注意到甲醇的第二类源总是6．7GHz和12．2GHz脉泽同时存在，并与超致密HII区成协，本文对此提出一种新的激发机制，即无粒子数反转的甲醇6．7GHz脉泽激发机制．本文论证了这一机制与天文条件相符，与其它机制工不排斥，互相补充，是一种有前途的模型． 相似文献
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5.
用中科院射电联合实验室上海天台２５米望远镜,对１９个已知水脉泽源和２０个ＨＩＩ区候选源进行了水脉泽观测和搜寻,共测到水脉泽辐射２１个,包括２个首次测到Ｓ／Ｎ≥３σ的源。结合已知脉泽资料求出了脉泽时变,发现峰值流量的变化比较普遍,包括同一峰强度变化及不同成分置换引起的变化两种情况,峰值速度变化多数由不同成分置换所造成。证认了对应的ＩＲＡＳ源并探讨了脉泽辐射与红外参量的关系,表明红外辐射的强度对脉泽 相似文献
6.
本文对猎户座ＩＲｃ２的正、仲水脉泽区的物理条件作初步研究。结果表明在动能温度６００Ｋ左右，尘埃温度低于３５０Ｋ，密度约１０~（８±０．５）ｃｍ~（－３）和水对氢分子相对丰度与速度梯度比为４×１０~（－９）ｐｃｓｋｍ~（－１）的条件下，仲水３_（１３）—２_（２０），５_（１５）—４_（２２）及正水６_（１６）—５_（２３），４_（１４）—３_（２１）脉泽可能同时呈现。这个区域的水丰度约为４×１０~（－６）。热尘埃并不使脉泽加强，碰撞抽运是激发星际水脉泽的一个可能机制。高密度下，准共振碰撞效应的计入可以解释６_（１６）—５_（２３）脉泽的高亮温度。 相似文献
7.
本文提出OH超脉泽源的一个具体模型,在该模型中OH超脉泽源由非饱和的球型子源组成.在此估算出超脉泽星系致密射电核的尺度和连续谱亮温度,以及OH源距星系核的最小非饱和距离.计算表明,OH超脉泽源所包含的子源数目可能相当大.R_H～log ρ_(25μm)/ρ_(60μm)图、log L_(OH)/L_(IR)～log ρ_(25μm)/ρ_(60μm)图和其它结果显示,有一部分OH超脉泽源很可能是弱饱和的,本文对此作了解释. 相似文献
8.
介绍了近年来河外H2O超脉泽的主要观测结果。H2O超脉泽通常起源于活动星系核中央的拱核盘。它们主要寄生在Serfert2星系或低电离核区。至今为止，已有20个星系探测到H2O超脉泽。脉泽辐射的各向同性光度为10－6000L。所有超脉泽星系显示出核的活动，显然，脉泽是由核活动所产生的射电和X射线光子或激波来抽运的。H2O超脉泽倾向存在于高倾斜度的星系，这使得沿视线上的分子柱密度增高，产生足够大的放大光深。最有可能产生H2O超脉泽辐射的星系应有一个包含着射电源的侧向的分子盘以及一个适当的抽运机制。 相似文献
9.
介绍了近年来河外Ｈ２Ｏ超脉泽的主要观测结果。Ｈ２Ｏ超脉泽通常起源于活动星系核中央的拱核盘。它们主要寄生在 Ｓｅｒｆｅｒｔ ２星系或低电离核区。至今为止，已有２０个星系探测到Ｈ２Ｏ超脉泽。脉泽辐射的各向同性光度为１０～６０００Ｌ⊙。所有超脉泽星系显示出核的活动，显然，脉泽是由核活动所产生的射电和Ｘ射线光子或激波来抽运的。Ｈ２Ｏ超脉泽倾向存在于高倾斜度的星系，这使得沿视线上的分子柱密度增高，产生足够大的放大光深。最有可能产生Ｈ２Ｏ超脉泽辐射的星系应有一个包含着射电源的侧向的分子盘以及一个适当的抽运机制。 相似文献
10.
《天文学进展》2021,(3)
利用VLBI档案数据研究了5个在40%阿雷西博河外HI巡天天区(α.40天区)发现的具有本征HI吸收线的星系,分析了它们在毫角秒尺度下的射电结构及亮温度TB,并计算了星系的q值(远红外流量与射电流量密度之比)以及利用WISE (wide-field infrared survey explorer)数据对星系进行了分类。研究发现5个源中的NGC 315,NGC 5363存在明显的射电喷流结构,IC 860和CGCG 049-057在pc尺度下存在致密的核,但流量小于NVSS流量的20%,以上4个源的核区的亮温度均超过106K,UGC 6081在毫角秒尺度下没有致密的射电结构,几乎完全分解。通过射电结构、亮温度以及q值得出这5个源的射电连续谱辐射可能来自射电喷流、星暴活动与射电喷流共存,及纯星暴活动等3种情况,说明HI吸收线的探测可能不依赖于中央核区连续谱辐射的类型。利用WISE数据分类显示5个源可以分为2类,3个为4.6μm亮星系,2个为12μm亮星系。没有贫尘埃星系,说明这类星系在α.40天区的数量较少或HI吸收线探测率较低。 相似文献
11.
Han－PingLiu JinSun 《中国天文和天体物理学报》2002,2(1):51-58
It is recognized that the interstellar methanol-107 GHz masers and OH-4.765 GHz masers towards Class Ⅱ sources are associated with each other and coexist towards ultracompact HⅡ regions. Therefore we suggest a new pumping mechanism-methanol masers without population inversion. It can explain the formation of 107GHz methanol masers, with the 4.765GHz OH masers acting as a driving coherent microwave field. It is argued that this mechanism is compatible with the astronomical conditions. 相似文献
12.
All interstellar methanol maser sources can be divided into two classes. Their spectra are distinctive. In particular, the
prominent Class II maser transitions, 6.7GHz and 12.2GHz lines show enhanced absorption toward Class I sources. We notice
that the 6.7 and 12.2GHz methanol masers toward Class II sources are associated with each other and coexist toward ultracompact
HII regions. Therefore we suggest a new pumping mechanism – methanol masers without population inversion. It can be used to
explain the formation of 6.7GHz methanol masers while the 12.2GHz methanol masers are regarded as driving coherent microwave
field. In this paper, we demonstrate that the new mechanism is associated with astronomical conditions and does not contradict
with other mechanisms.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
From the observed data of 17 Class-II methanol masers and their asociated HII regions and infrared sources and using the maser photon emission rate and the brightness temperature as two constraints on the pump, we conclude that infrared sources with a brightness temperature of about 100 K and a photon rate of about 1053s−1, associated with compact HII regions are the most probable pumping source 相似文献
14.
S. P. Ellingsen 《Monthly notices of the Royal Astronomical Society》2005,359(4):1498-1516
The Australia Telescope National Facility Mopra millimetre telescope has been used to search for 95.1-GHz class I methanol masers towards 62 6.6-GHz class II methanol masers. A total of 26 95.1-GHz masers were detected, 18 of these being new discoveries. Combining the results of this search with observations reported in the literature, a near complete sample of 66 6.6-GHz class II methanol masers has been searched in the 95.1-GHz transition, with detections towards 38 per cent (25 detections; not all of the sources studied in this paper qualify for the complete sample, and some of the sources in the sample were not observed in the present observations).
There is no evidence of an anticorrelation between either the velocity range, or peak flux density of the class I and II transitions, contrary to suggestions from previous studies. The majority of class I methanol maser sources have a velocity range that partly overlaps with the class II maser transitions. The presence of a class I methanol maser associated with a class II maser source is not correlated with the presence (or absence) of main-line OH or water masers. Investigations of the properties of the infrared emission associated with the maser sources shows no significant difference between those class II methanol masers with an associated class I maser and those without. This may be consistent with the hypothesis that the objects responsible for driving class I methanol masers are generally not those that produce main-line OH, water or class II methanol masers. 相似文献
There is no evidence of an anticorrelation between either the velocity range, or peak flux density of the class I and II transitions, contrary to suggestions from previous studies. The majority of class I methanol maser sources have a velocity range that partly overlaps with the class II maser transitions. The presence of a class I methanol maser associated with a class II maser source is not correlated with the presence (or absence) of main-line OH or water masers. Investigations of the properties of the infrared emission associated with the maser sources shows no significant difference between those class II methanol masers with an associated class I maser and those without. This may be consistent with the hypothesis that the objects responsible for driving class I methanol masers are generally not those that produce main-line OH, water or class II methanol masers. 相似文献
15.
Methanol masers are known to be associated with regions of massive star formation. By studying the distribution of these masers
with respect to unidentified EGRET sources, one may be able to identify regions of enhanced star formation leading to either
supernova remnants and/or pulsars. In this study, we test for positional coincidences between class II methanol masers and
EGRET sources and determine the statistical significance of these coincidences. 相似文献
16.
K. P. Johns D. M. Cragg P. D. Godfrey & A. M. Sobolev 《Monthly notices of the Royal Astronomical Society》1998,300(4):999-1005
We investigate the possibility of interstellar masers in transitions of the methanol isotopomers CH3 OD, 13 CH3 OH and CH3 18 OH, and of CH3 SH. The model used, in which masers are pumped through the first and second torsionally excited states by IR radiation, has accounted successfully for the Class II masers in main species methanol, 12 CH3 16 OH. Several potential maser candidates are identified for CH3 OD, their detectability depending on the enrichment of this species in star-forming regions. In 13 CH3 OH and CH3 18 OH the best maser candidates are direct counterparts of the well-known 6.7- and 12.2-GHz methanol masers, but the lower interstellar abundance of these substituted species means that the expected brightness is greatly reduced. The maser candidates in CH3 SH are also weak. By comparing these species we find that the large b -component of the dipole moment in methanol plays a significant role in its propensity to form masers, as does the strong torsion–rotation interaction due to the light hydroxyl frame. Thus the exceptional brightness of interstellar methanol masers is due to a favourable combination of molecular properties as well as high interstellar abundance. 相似文献
17.
We report the astronomical detections of several ammonia inversion transitions involving nonmetastable levels with energies as high s 1090 K above the ground state. The (J, K) = (9, 6) inversion transition shows maser-like emission in the directions of W51, NGC 7538, W49, and DR 21(OH). The NH3 (6, 3) line exhibits similar characteristics in W51 but is seen in absorption in NGC 7538. These are the first definite detections of ammonia masers in space. The intensities and narrow line widths (0.5-1.5 km s-1) for the emission features are in contrast to the previously detected broad, weak, nonmetastable lines attributed to thermal emission in these sources. Temporal variability appears to be evident in the (9, 6) emission in W49 over a 4 month period. The highly excited (J, K) = (9, 6) and (6, 3) ammonia lines are found in regions containing compact H II regions and strong infrared sources with associated H2O and OH masers; i.e., in regions of active star formation. 相似文献
18.
S. L. Breen S. P. Ellingsen M. Johnston-Hollitt S. Wotherspoon I. Bains M. G. Burton M. Cunningham N. Lo C. E. Senkbeil T. Wong 《Monthly notices of the Royal Astronomical Society》2007,377(2):491-506
We report the results of a blind search for 22-GHz water masers in two regions, covering approximately half a square degree, within the giant molecular cloud associated with RCW 106. The complete search of the two regions was carried out with the 26-m Mount Pleasant radio telescope and resulted in the detection of nine water masers, five of which are new detections. Australia Telescope Compact Array (ATCA) observations of these detections have allowed us to obtain positions with arcsecond accuracy, allowing meaningful comparison with infrared and molecular data for the region. We find that for the regions surveyed there are more water masers than either 6.7-GHz methanol, or main-line OH masers. The water masers are concentrated towards the central axis of the star formation region, in contrast to the 6.7-GHz methanol masers which tend to be located near the periphery. The colours of the GLIMPSE point sources associated with the water masers are similar to those of 6.7-GHz methanol masers, but slightly less red. We have made a statistical investigation of the properties of the 13 CO and 1.2-mm dust clumps with and without associated water masers. We find that the water masers are associated with the more massive, denser and brighter 13 CO and 1.2-mm dust clumps. We present statistical models that are able to predict those 13 CO and 1.2-mm dust clumps that are likely to have associated water masers, with a low misclassification rate. 相似文献
19.
S. P. Ellingsen 《Monthly notices of the Royal Astronomical Society》2007,377(2):571-583
The University of Tasmania Mt Pleasant 26-m and Ceduna 30-m radio telescopes have been used to search for 6.7-GHz class II methanol masers towards 200 GLIMPSE ( The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire ) sources. The target regions were selected on the basis of their mid-infrared colours as being likely to be young high-mass star formation regions and are either bright at 8.0 μm, or have extreme [3.6]–[4.5] colour. Methanol masers were detected towards 38 sites, nine of these being new detections. The prediction was that approximately 20 new 6.7-GHz methanol masers would be detected within 3.5 arcmin of the target GLIMPSE sources, but this is the case for only six of the new detections. A number of possible reasons for the discrepancy between the predicted and actual number of new detections have been investigated. It was not possible to draw any firm conclusions as to the cause, but it may be because many of the target sources are at an evolutionary phase prior to that associated with 6.7-GHz methanol masers. Through comparison of the spectra collected as part of this search with those in the literature, the average lifetime of individual 6.7-GHz methanol maser spectral features is estimated to be around 150 yr, much longer than is observed for 22-GHz water masers. 相似文献
20.
D. J. van der Walt E. Churchwell M. J. Gaylard S. Goedhart 《Monthly notices of the Royal Astronomical Society》2003,341(1):270-276
Class II methanol masers are believed to be associated with high-mass star formation. Recent observations by Walsh et al. and Phillips et al. reported a very low detection rate of radio continuum emission toward a large sample of 6.7-GHz methanol masers. These results raise questions about the evolutionary phase and/or the mass range of the exciting stars of the masers. Here we report the results of a VLA search for 8.4-GHz continuum emission from the area around five Class II methanol masers, four of which were not detected by Walsh et al. at 8.6 GHz. Radio continuum emission was detected in all five fields although only two of the nine maser spot groups in the five fields were found to be superimposed on radio continuum sources that appear to be ultra-compact H ii (UCH ii ) regions. This suggests that continuum counterparts for some masers might be found in further surveys for which the sensitivity level is lower than 1 mJy beam−1 . Considering our results as well as observations from other studies of methanol masers we conclude that masers without radio continuum counterparts are most likely associated with high-mass stars in a very early evolutionary stage, either prior to the formation of a UCH ii region or when the H ii region is still optically thick at centimetre wavelengths. With one exception all maser spot groups in the five fields were found to be associated with mid-infrared objects detected in the Midcourse Space Experiment survey. 相似文献