Generation of Interstellar Class Ⅱ 7_2-8_1A^+ and 7_2-8_1A^-Methanol Masers

New methanol maser lines at 72 → 63A^-（86.6 GHz） and 72 → 63A^＋（86.9 GHz） together with two candidate methanol maser lines at 72 → 81A-（80.99GHz） and 72→81A^＋（111.29GHz） have been detected in W3（OH）. We use a pumping mechanism, i.e., methanol masers without population inversion, to explain the formation of weak methanol masers of 72 → 81A^＋ and 72→ 81A^-. We explain well why the line-shape of the transition 72 → 81A^＋ is not typical. A similar argument can be applied to the A-type level system 72A^-, 63A^- and 81A^-, as well as to the 72 → 81A^- 80.99 GHz masers.

The interstellar methanol masers and their environments

To promote the understanding of massive star formation processes, we have studied the 6.6 GHz methanol (CH3OH) masers and their environments—the dense cores and the outer regions of the molecular cloud. The physics of the CH3OH maser or the thermal emission formation region is studied by fitting the observational data of the 6.6 GHz 51–60A+ and the 107 GHz 31–40A+CH3OH maser emission, using the radiative transfer calculations. The type II characteristics of the 6.6 GHz CH3OH maser are confirmed by the calculation results. A greater intensity of the radiation field leads to an increase in the peak intensity of the maser; however, high densities tend to turn off the maser. The calculation results show that to be a maser the 6.6 GHz CH3OH emission needs a radiation field of 150–300 K and a density not higher than 107cm?3, while the 107 GHz emission requires a radiation field of 210–300 K and a density not higher than 3×106 cm?3. The 6.6 GHz line is maser towards all six studied sources, while the 107 GHz line is maser towards Cep A only. Moreover, the former’s intensity is much stronger than the latter. The radiative transfer calculations also indicate that the 6.6 GHz maser emission is so strong that the requirements of its formation (e.g. the radiation field, the density and the kinetic parameters) can only be satisfied at a certain stage of the processes of the massive star formation. Therefore it is often used as one of the most prominent tracers for the massive star formation regions. The calculation results of the simutaneous observations of (1,1) through (4,4) inversion lines of the ammonia (NH3) indicate that both the temperature and the density in the 6.6 GHz CH3OH maser formation regions are higher than that of the NH3 line formation regions. Furthermore, the common fact of |Visr(CO)| > |Visr(NH3)|>|Visr(CH3OH 6.6GHz maser)| in all six sources implies the ongoing developing trends of those gas flows driven by the masers.

Review of galactic and extragalactic searches for class I methanol masers

Class I methanol masers are important tools for investigations of star formation throughout the Universe.Recently, a series of surveys for class I methanol masers at the 95 GHz transition toward samples of young stellar objects have been undertaken. These surveys have resulted in the detection of about 200 new class I methanol masers and combined with previous observations they have increased the number of known class I methanol masers in our Galaxy to *400. From analysis of the relationship between class I methanol maser emission and associated astrophysical objects, it has been shown that the intensity of the class I methanol maser emission is closely correlated with the properties of the 1.1 mm Bolocam Galactic Plane Survey(BGPS) dust continuum sources and outflow properties. This further supports the hypothesis that class Imethanol masers are collisionally pumped and excited in shocked regions. Based on these observations, it can be inferred that the BGPS catalog is likely to provide more reliable samples for targeting further class I methanol maser searches. A new survey for class I methanol masers toward a larger size sample of BGPS sources to test this is currently underway. The prospects for detecting class I methanol megamasers in extragalactic sources is discussed,and observations constituting the first sensitive search have been proposed.

Disk-Outflow Models as Applied to High Mass Star Forming Regions through Methanol and Water Maser Observations

As the recent publication by Breen et al. (2013) found, Class II methanol masers are exclusively associated with high mass star forming regions. Based on the positions of the Class I and II methanol and H2O masers, UC H II regions and 4.5 μm infrared sources, and the center velocities (vLSR) of the Class I methanol and H2O masers, compared to the vLSR of the Class II methanol masers, we propose three disk-outflow models that may be traced by methanol masers. In all three models, we have located the Class II methanol maser near the protostar, and the Class I methanol maser in the outflow, as is known from observations during the last twenty years. In our first model, the H2O masers trace the linear extent of the outflow. In our second model, the H2O masers are located in a circumstellar disk. In our third model, the H2O masers are located in one or more outflows near the terminating shock where the outflow impacts the ambient interstellar medium. Together, these models reiterate the utility of coordinated high angular resolution observations of high mass star forming regions in maser lines and associated star formation tracers.

A search for massive young stellar objects with 98 CH_3OH maser sources

Using the 13.7 m telescope of the Purple Mountain Observatory （PMO）, a survey of the 3 = 1 - 0 lines of CO and its isotopes was carried out on 98 methanol maser sources in January 2008. Eighty-five sources have infrared counterparts within one arcmin. In the survey, except for 43 sources showing complex or multiple-peak profiles, almost all the ^13CO line profiles of the other 55 sources have large line widths of 4.5km s^-1 on average and are usually asymmetric. Fifty corresponding Infrared Astronomical Satellite （IRAS） sources of these 55 sources have Lbdl larger than 10^3 L⊙, which can be identified as possible high-mass young stellar sources. Statistics show that the ^13CO line widths correlate with the bolometric luminosity of the associated IRAS sources. Here, we also report the mapping results of two sources; IRAS 06117＋1350 and IRAS 07299-1651. Two cores were found in IRAS 06117＋1350 and one core was detected in IRAS 07299-1651. The northwest core in IRAS 06117＋1350 and the core in IRAS 07299-1651 can be identified as precursors of UC HII regions or high-mass protostellar objects （HMPOs）. The southeast core of IRAS 06117＋1350 has no infrared counterpart, seeming to be at a younger stage than the pre-UC HII phase.

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．

第2类星际甲醇J_0→J_(-1)E型系列脉泽的一种新机制

The features of the interstellar classⅡ methanol source reg io ns are grasped. A new pumping mechanism is argued. It can explain the formation of a series of J 0→J -1 E methanol masers and the increase of the maser intensity with J, while the 2 1→3 0A-+ methanol masers are regard ed as driving coherent microwave field.

星际甲醇6.7GHz脉泽的激发机制

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．

星际甲醇107GHz脉泽的激发

It is recognized that the interstellar methanol 107 GHz and OH 4 765 GHz masers toward Class Ⅱ sources are associated with each other and coexist toward ultracompact HⅡ regions. A new excitation mechanism is suggested. It can explain the formation of methanol 107 GHz masers. And it is argued that this mechanism is associated with astronomical conditions.