Collisional Pumping of OH Masers near Supernova Remnants

Astronomy Letters - The collisional pumping of OH masers in non-dissociative C-type shocks near supernova remnants is considered. The emergence of maser emission in OH lines is investigated for...     

Excitation of Far-Infrared Lines of OH and Maser Pumping Efficiency in Circumstellar Envelopes

We present the results obtained with a radiative transfer model to investigate the excitation of OH molecules. Maser pumping efficiencies are estimated from the model and compared to the value calculated using recent OH far-infrared (FIR) observations with ISO and OH maser data. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Possible Pumping Mechanism for Interstellar Class Ⅱ 107 GHz Methanol Masers

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.     

A Radiative Pumping Scheme for OH and H<Subscript>2</Subscript>O Masers in Massive Star Forming Regions

Interstellar H₂O and OH masers associated with massive star-forming regions can be classified into three morphological types: isolated H₂O masers; isolated OH masers; and spatially overlapping OH/H₂O maser groups. In a large sample of star-forming regions the total number of maser groups of each type is approximately equal. In order to account for these statistics we propose a pumping scheme based on a broadband radiative pump which produces inverted populations of both OH and H₂O masers by a process involving predissociation and dissociation of H₂O. This scheme overcomes some drawbacks of earlier radiative pumping models, and may account for the association of OH and H₂O masers in massive star forming regions.     

Evidence for Co-Propagation of 4765- and 1720-MHz OH Masers in Star-Forming Regions

Two star-forming regions Cepheus A and W75N, were searched for the 4765-MHz OH maser emission using the multi-element radio linked interferometer network (MERLIN). The excited OH emission has an arc-like structure of 40 mas in Cep A and a linear structure of size 45 mas in W75N. We also found the 1720-MHz line in Cep A and Hutawarakorn [MNRAS 330 (2002) 349] reported the 1720-MHz emission in W75N. The 1720- and 4765-MHz OH spots coincided in space within 60 mas and in velocity within 0.3 km s^–1 in both targets implying that both maser transitions arise from the same region. According to the modelling by Gray [MNRAS 252 (1991) 30] the 1720/4765-MHz co-propagation requires a low density, warm environment. The masers lie at the edges of H II regions where such conditions are expected.     

A Survey and Statistics of Interstellar OH and H_2O Masers

We present a statistical analysis of a sky survey of interstellar H2O and OH masers. These masers can be classified into three categories: isolated H2O masers, isolated OH masers, and simple OH/H2O maser associations. The total number of sources in each category is of the same order of magnitude, and as an evolutionary phase they can maintain -105 yr. An improved radiative pumping mechanism is proposed. This model avoids some of the deficiencies of previous radiative models, such as shortage of exciting photons. The statistical results obtained from the survey can be interpreted by the new mechanism together with the evolutionary model in which the gravitational force of the central stellar objects is responsible for the HII region.     

ON2中部以西区域OH1665和1667MHz脉泽的观测和研究

利用法国巴黎天文台的南锡射电望远镜对ON2中部以西区域OH1665和1667MHz脉泽进行观测，结合模型对中部以西区域的OH1665和1667MHz脉泽谱线频谱图进行分析和研究、利用薄盘模型，得到相应于ON2中部以西区域的OH1665和1667MHz峰的脉泽斑的位置及其Keplerian运动速度。     

A New Pumping Mechanism for A Series of Class II Methanol Masers in the J 0 - J -1 E Transitions

A new pumping mechanism – methanol masers without population inversion is presented in this paper. It can be used to explain the formation of a series of J ₀ → J _-1 E methanol masers, while the 2₁ → 3₀ A ⁺ methanol masers are regarded as a driving coherent micrwave field. In the new mechanism, the intensities of J ₀ - J _-1 E methanol masers are increased with the decreasing transition frequencies (or with rotational number J, approximately). These results agree with Slysh et al. (1995) and Slysh et al. (1999) J ≤ 5 observations for G3345.01+1.79 and W48, in which both J ₀ → J _-1 E and 2₁ → 3₀ A ⁺ methanol masers are detected coincidentally. Other astronomical conditions, such as magnetic field, 2₁ → 3₀ A ⁺ coherent radition, incoherent pumping rate by thermal radition and so on are also discussed. The new mechanism can operate as a complement to other ordinary maser pumping mechanisms for some class II methonal maser sources. This revised version was published online in July 2006 with corrections to the Cover Date.     

Masers, Lasers and the Interstellar Medium

This paper discusses recent results obtained by myself and my colleagues in three domains of astrophysics: interstellar supersonic turbulence, circumstellar disks, and natural masers and lasers. S.A. Kaplan, S.B. Pikelner, and I.S. Shklovskii were among those who, 30-40 years ago, laid the foundation of these domains.H2O masers become an effective probe of supersonic turbulence associated with mass outflow from very young stars. They demonstrate a very low (1) fractal dimension of the spatial set on which turbulence dissipates its kinetic energy, and, thereby, a strong intermittency of the turbulence. They also indicate that supersonic turbulence, like incompressible turbulence, has an inner scale, on which the bulk of turbulent energy dissipates in low-Mach, random shocks. H2O masers themselves find thereby a new pumping source in these random shocks.Masers in hydrogen recombination lines, discovered 8 years ago, originate in a circumstellar disk surrounding a massive star MWC 349A. They give a possibility to investigate kinematics and structure of the disk. Far-infrared nydrogen recombination lines, recently detected in MWC349A from the Kuiper Airborn Observatory, proved to be amplified as well. They are the first known natural amplifiers of electromagnetic waves in the laser wavelength domain. Analysis of their radiation, along with the radiation in other recombination lines, gives a possible key to understanding the lack of optical lasers in the Universe.     

自动调谐器在氢脉泽上的应用结果

本文介绍上海天文台自行研制的氢脉泽调谐［１．２］在我台制造的氢脉泽Ｈ８、Ｈ９、Ｈ１０上的应用．结果表明：氢脉泽自动调谐器有效地改善了氢脉泽的长期稳定度．     

氢脉泽守时应用研究

对国产实验室型氢脉泽在守时中两方面的应用可能性进行了初步分析和实验研究：１．分析了影响长期稳定工作的可能因素并进行了控制，使氢脉泽可直接参加守时；２．氢脉泽作为实时主钟高稳源的可能性，取得了较为乐观的结果．ＨＺ在ＴＡＩ计算中权重最高已达到９．实验在继续进行中．     

ISO Far-IR spectroscopy of IR-bright galaxies and ULIRGs

Based on far-infrared spectroscopy of a small sample of nearbyinfrared-bright and ultraluminous infrared galaxies (ULIRGs) with theISO Long Wavelength Spectrometer we find adramatic progression in ionic/atomic fine-structure emission line andmolecular/atomic absorption line characteristics in these galaxiesextending from strong [O III]52,88 m and [N III]57 m lineemission to detection of only faint [C II]158 m line emissionfrom gas in photodissociation regions in the ULIRGs. The molecularabsorption spectra show varying excitation as well, extending fromgalaxies in which the molecular population mainly occupies the groundstate to galaxies in which there is significant population in higherlevels. In the case of the prototypical ULIRG, the merger galaxy Arp220, the spectrum is dominated by absorption lines of OH, H₂O, CH,and [O I]. Low [O III]88 m line flux relative to the integratedfar-infrared flux correlates with low excitation and does not appear tobe due to far-infrared extinction or to density effects. A progressiontoward soft radiation fields or very dusty H II regions may explainthese effects.     

A Radiation Mechanism for Interstellar Methanol 6.7GHz Masers

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.     

Methanol Masers as Precursors of Gamma-Ray Sources

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.     

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文台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产生率的影响比颜色分布的影响大．     

Infrared Characteristics of Associated Sources of Water Masers

We present an analysis of the infrared properties of 1417 water masers collected from the literature published by December 2004. The associated infrared sources of the water masers were identified with IRAS and MSX (Midcourse Space Experiment) catalogues. There are 1252 water masers associated with IRAS sources within 1', which include 700 interstellar and 552 stellar sources. For 382 sources, the IRAS counterpart identification and the maser classification are new. We found the colors of the interstellar maser sources are much redder than those of the stellar ones at IRAS wavelength bands; 99% of the interstellar maser sources are above black body line, while 95% of the stellar masers are below. The distribution difference of the two kinds of masers shown in the color-color diagram is due to their different optical depths and temperature distributions of dust regions. There are 743 water masers with MSX counterparts, of which 552 are interstellar masers and 191 are stellar masers. MSX colors of the associated sources of water masers are here analyzed for the first time. The color differences among the MSX bands are small and the interstellar masers are redder than the stellar masers. There is a correlation between the intensity of the stellar water maser emission and that of the 12μm and 25μm emissions, while there is no correlation between the water maser emission and the 8 μm emission. The infrared intensity increases with increasing wavelength for the interstellar masers, while it is the opposite for stellar masers. These results may provide clues for the pumping of water maser and for the properties of the two kinds of maser emission regions.