水脉泽辐射的探测和时变考察

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     

水脉泽寄主星系的倾角分析

迄今已经在104个河外星系中检测到水脉泽辐射.同其它没有检测到水脉泽的星系相比,水脉泽星系可能隐含着某种或某些特殊性质.收集了到当前为止(截止2008.09)发表的所有水脉泽星系以及相关的观测资料.计算得到了这些源的星系盘的倾角,并分析讨论了这些水脉泽源星系盘和脉泽盘的倾角可能存在的相关.统计发现只有大约10%的盘脉泽源的星系盘侧面对着我们的视线.然而VLBI对6个盘脉泽源高空间分辨率的成图观测显示那些旋转脉泽盘都是近似侧向的,脉泽盘的倾角都大于80°.对大多数水盘脉泽星系而言,他们的星系盘和脉泽盘方向不一致,这可能间接支持盘脉泽仅仅同星系核相关.为了探讨遮蔽物质的由来和水脉泽辐射的放大机制,对整个水脉泽样本的脉泽光度,X射线吸收气体柱密度和寄主星系倾角的可能相关进行了分析.结果显示高密度的遮蔽物质主要来自于星系核区,而水脉泽辐射的放大更可能发生在围绕核的尘埃盘(～100Pc)或更小尺度的核盘上.     

分子区域水脉泽的搜寻

本文描述了1993年使用13.7m射电望远镜对一些水脉泽的观测搜寻，而这些脉泽源是根据北京天文台兴隆观测站对一批恒星脉泽源进行的红外观测而挑选出来的。     

水脉泽寄主活动星系核的吸积率(英文)

水超脉泽辐射( 各向同性光度超过 10 个太阳光度) 通常在星系中心最内部的核区( 小于几个秒差距) 被发现,因而活动星系核被认为是其唯一的能量源。同其它没有检测到水脉泽辐射的活动星系核相比,水脉泽寄主活动星系核可能隐含着某种或某些特殊性质。基于此我们调研了已经公开发表的所有水脉泽源的 X 射线观测情况,得到了一个有 X 射线观测研究结果的子样本( 39 个源) 。由它们的 X 射线光度以及估算的黑洞质量,导出了它们的无量纲吸积率( logL2-10keV /LEdd,其中 L2-10keV和 LEdd分别是 2 - 10keV 的固有光度和爱丁顿光度) ; 与距离范围相当的、没有检测到水脉泽的活动星系核样本相比,发现脉泽寄主活动星系核有较高的吸积率。进一步分析比较这两个活动星系核样本的质量吸积率,也发现类似的趋势。此外,为了探索吸积率和水脉泽辐射间可能的内在联系,我们对它们的脉泽光度和吸积率进行了统计分析,然而结果显示二者之间没有明显的相关性。     

星际水脉泽源中高速气体的CO巡测

用射电天文联合实验室紫金山天文台青海站１３．７米望远镜，于１９９７年４月对９７个水脉泽源做了ＣＯ（Ｊ＝１－０）的巡测及部分成图观测，结果表明８１个源的谱线适于作成协星体活动分析．经初步证认有外向流候选者３３个，全部为首次给出高速范围．对其轮廓特点及与Ｈ２Ｏ脉泽辐射的关系作了简要讨论．ＣＯ高速气体和Ｈ２Ｏ脉泽的速度范围和峰值速度在多数情况下分别相符，这说明两者的激发可能相关．     

星际水脉泽源中高速气体的CO巡测

用射电天联合实验紫金山天台青海站１３．７米望远镜,于１９９７年４月对９７个水脉泽源做了ＣＯ（Ｊ＝１－０）的巡测及部分成图观测。结果表明８１个源的谱线适于作成协星体活动分析。经初步认证认有外向流候选３３个,全部为首次给出高速范围,对其轮廓特点及与Ｈ２Ｏ脉泽辐射的关系作了简要讨论,ＣＯ高速气体和Ｈ２Ｏ脉泽的速度范围和峰值速度在多数情况下的分别相符,这说明两的激发可能相关。     

河外水脉泽的研究进展

人们对河外水脉泽的观测与研究已经30年了。目前已经在约70个河外星系中检测到水脉泽辐射（已公开发表64个）。近年来，河外水脉泽的观测及理论研究十分活跃。重点介绍了目前河外水脉泽的检测及研究进展，包括水脉泽源的分类、水脉泽对研究活动星系核的重要科学价值、水脉泽源的X射线观测研究及其各物理量之间的统计分析结果等。     

SiO脉泽星的近红外测光与分析

本文给出３５个不同类型含ＳｉＯ（ｖ＝１,Ｊ＝１－０）脉泽发射的ＡＧＢ星的近红外观测结果（其中包括６个Ⅰ型ＯＨ星,１３个Ⅱ型ＯＨ星,９个仅有ＳｉＯ脉泽的星以及７个无ＯＨ脉泽但有ＳｉＯ和Ｈ２Ｏ脉泽的星）．得出了它们的ＪＨＫ星等和流量．同时经认证找出了它们对应的ＩＲＡＳ观测数据．通过对它们的近红外、中远红外以及ＯＨ射电资料的同时分析,得出了不同类型ＳｉＯ脉泽星的色指数、谱斜率以及在近红外波段上拟合的等效黑体温度Ｔｅｑ．由红外及ＯＨ射电资料导出了其中心星的质量损失率Ｍ,并在此基础上结合已知的ＳｉＯ脉泽源资料,找出了不同类型ＳｉＯ脉泽星各量之间的关系．计算结果表明,ＳｉＯ脉泽具有普遍性,在各类脉泽星中都可出现．ＳｉＯ脉泽的光度与质量损失率弱相关,并且从（Ｍｉｒａ）ＳｉＯ到（ＯＨ／ＩＲ）ＳｉＯ逐渐增加．ＳｉＯ脉泽的流量与近红外“色”以及等效黑体温度Ｔｅｑ的关系较为密切．ＳｉＯ脉泽积分流量的上限与ＩＲＡＳ在１２μｍ和２５μｍ上流量分别都相关．本文对ＳｉＯ脉泽在ＡＧＢ演化中的地位和特殊性进行了简单讨论．     

星际甲醇分子脉泽的辐射抽运研究

本项研究给出了17个具有Ⅱ类星际甲醇分子脉泽源的致密氢11区的轫致辐射、尘埃红外辐射和中心年轻恒星Layman辐射的特征．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类星际甲醇分子脉泽的几种可能的激发机制．我们认为热辐射亮温度为100K与致密氢Ⅱ区成协的红外辐射体很可能是Ⅱ类甲醇脉泽的抽运源．     

青海13.7米射电望远镜水脉泽谱线观测

本文报导了1990年6月-8月青海13.7米射电望远镜首轮水脉泽谱线观测结果,在检测到的47个水脉泽源中,包括与HⅡ区,HH天体、红外点源和恒星成协的各类源,并发现了一个新水脉泽源,1654-1604,最强的源是Orion-KL,46700Jy;最弱的源是0536 3529,70Jy。观测结果与最新发表的国外观测结果进行了统计分析,证实了本观测结果的可靠性,并可开展有关课题的观测研究。     

Observation of water masers and a study of their time variation

Using the 25-m telescope of Shanghai Observatory, Joint Radio Astronomy Laboratory, 19 known maser sources and 20 candidates in H II regions were surveyed for water vapour maser emission at 22.2 GHz. 21 sources were detected, of which two are for the first time. Combining with some previous data, the time variations in the flux and velocity are obtained and discussed. Time variation in the peak flux density is common and is of two types, a change in the intensity of the same peak, and a swapping-over of two peaks. The corresponding IRAS sources were identified and the relation between the maser emission and the infrared parameters discussed. It is shown that maser production rate is more sensitive to the infrared flux intensity than the infrared colour distribution.     

Statistical Properties of 6.7 GHz Methanol Maser Sources

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.     

The relationship between class I and class II methanol masers

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.     

The brightest OH maser in the sky: A flare of emission in W75 N

A flare of maser radio emission in the 1665-MHz OH line with a flux density of about 1000 Jy was discovered in the star-forming region W75 N in 2003. At the time of its observations, it was the strongest OH maser in the entire history of research since the discovery of cosmic OH masers in 1965. The linear polarization of the flare emission reached 100%. A weaker flare with a flux density of 145 Jy was observed in this source in 2000–2001; this was probably a precursor of the intense flare. The intensity of two other spectral features decreased when the flare emerged. This change in the intensity of the emission from maser condensations (a brightening of some of them and a weakening of others) can be explained by the passage of a magnetohydrodynamic shock through regions of enhanced gas concentration.     

Studies of ultracompact H II regions – III. Near-infrared survey of selected regions

A survey towards a selection of 35 methanol maser and/or ultracompact (UC) H  ii regions, reported in Papers I and II and by Norris et al., has been conducted in the near-infrared (NIR). Out of 25 methanol maser sites surveyed, 12 are associated with a NIR counterpart. Out of 18 UC H  ii regions (8 of which overlap with maser emission), 12 are associated with a NIR counterpart. Counterparts can be confidently identified not only by the positional agreements, but also by their unusually red colours. Spectral types for the embedded stars can be unambiguously determined for six sources, all of which imply massive, ionizing stars. One of these infrared sources has methanol maser emission, but no UC H  ii region. It is possible that the maser emission associated with this source arises from a pre-UC H  ii phase of massive stellar evolution or it could be that nearly all the ultraviolet photons are absorbed by dust within the UC H  ii region. We have modelled the spectral energy distributions (SEDs) for some sources and find that a single blackbody can be used to estimate the stellar luminosity, but cannot represent the whole infrared SED. A two-component blackbody model and a radiative transfer model were also used to derive essential parameters of the infrared sources. The radiative transfer model also indicates which infrared sources are relatively young and which are older. Both models show that silicate absorption at 9.7 μm must be a dominant feature of these SEDs.     

Spatial distribution and luminosity function of OH/IR maser sources

In this paper, we study the galactic distribution and luminosity function of OH/IR maser sources. All the selected OH/IR sources have optical or infrared identification. Most of them are associated with late-type (>M5) Mira variables. Their derived density distribution shows a steep peak at a galactocentric distance of r₀-7.5 kpc and decreases rapidly at smaller and larger R₀. The FWHM of the distribution curve is 2.1 kpc. This is similar to the galactic distribution of Mira variables investigated by Glass et al.

We also derive the luminosity function of the identified OH/IR maser sources from their distances, their detection probabilities, and their corrected OH radio peak flux densities. The luminosity function ρ(L) varies as L_OH^−1.79. This is similar to that of unidentified maser sources. The range of luminosity of identified OH/IR sources is approximately from 0.16 Jy · kpc² to 1000 Jy · kpc². It is quite different from that of unidentified OH sources.

Finally, we discuss some differences and relations between identified and unidentified OH/IR maser sources.     

Hydrodynamic Instability of Ionization Front in HII Regions: From Linear to Nonlinear Evolution

A sample of 54 6.7-GHz methanol maser sources was monitored at HartRAO for 4 years, and 11 12.2-GHz methanol masers for 3 years. The majority of the maser features display a significant degree of variability but with a wide range of timescales and behaviors. Some maser features remained unvarying throughout the monitoring programme, while others showed sporadic flares or sudden drops in flux density. Yet another group show quasi-periodic and periodic variations. In some cases the maser features dropped below the detection limit for a significant length of time before increasing in intensity and reappearing.     

Discovery of molecular hydrogen line emission associated with methanol maser emission

We report the discovery of H₂ line emission associated with 6.67-GHz methanol maser emission in massive star-forming regions. In our UNSWIRF/AAT observations, H₂ 1–0 S(1) line emission was found associated with an ultracompact H  ii region IRAS 14567–5846 and isolated methanol maser sites in G318.95–0.20 , IRAS 15278–5620 and IRAS 16076–5134 . Owing to the lack of radio continuum in the latter three sources, we argue that their H₂ emission is shock excited, while it is UV-fluorescently excited in IRAS 14567–5846 . Within the positional uncertainties of 3 arcsec, the maser sites correspond to the location of infrared sources. We suggest that 6.67-GHz methanol maser emission is associated with hot molecular cores, and propose an evolutionary sequence of events for the process of massive star formation.     

Resolved OH megamaser emission in the nuclear region of the ultraluminous infrared galaxy Markarian 273

We present high angular resolution MERLIN observations of the 18-cm OH maser and continuum emission associated with the active core of the ultraluminous infrared galaxy Markarian 273. The continuum emission comes from three distinct regions in the central arcsecond of the galaxy. The brightest region of emission has a double-peaked structure which is spatially coincident with similar structures observed at 6 cm and 2.2 μm. The peak of the OH maser emission is spatially coincident with the peak in the continuum. For the first time the maser emission is spatially resolved, allowing us to measure the gas motion within the central 100 pc of the galaxy. Maser emission is found in both the 1665- and 1667-MHz lines, with no systematic offset found in the spatial locations of the two lines. The brighter component of the maser emission shows ordered motion and is aligned along the axis of the double-peaked structure in the brightest continuum region. The gas motion enables us to estimate the central mass density to be 850±50 M_⊙ pc⁻³, which corresponds to a total mass of ≈1.5×10⁸ M_⊙.     

Extragalactic H<Subscript>2</Subscript>O maser sources and their properties

The properties of a sample of extragalactic H₂O maser sources over a wide spectral range are discussed. Based on a sample of 81 maser galaxies it is shown that mega- and kilomasers have completely different properties. In particular, for megamasers the strongest observed relationships are between the parameters of the H₂O line and the mass of the galactic nucleus, while the parameters of the line are uncorrelated with the x-ray, infrared, and radio emission. A weak correlation between megamaser emission and the surface (column) density of hydrogen is observed. As for kilomasers, their H₂O luminosity depends weakly on the x-ray emission, although in the case of soft x rays this dependence is significant. The H₂O luminosity of kilomasers is moderately correlated with the infrared and radio continuum luminosities, but the line parameters are independent of the mass of the nucleus and the surface density of hydrogen.