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 11, 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 8μm 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.

The potential of FAST in detecting celestial hydroxyl masers and related science topics

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) will make contributions to studies of Galactic and extragalactic masers. This telescope, with construction finished and now undergoing commissioning, has an innovative design that leads to the highest sensitivity of any single dish radio telescope in the world. FAST's potential for OH megamaser research is discussed, including the sky density of masers detectable in surveys. The scientific impact expected from FAST maser studies is also discussed.

Observational characteristics of SiO masers around VX Sgr

SiO maser VLBA observations toward VX Sgr are performed at five epochs, and lots of maser spots are obtained. We make a statistical analysis on these spots. It is shown that the apparent sizes and the fluxes of maser spots decrease with increasing the distance from the central star. In addition, the similarity between the v = 1,2(J =1–0) spectrums increases with epochs, consistent with the full width at half maximum(FWHM), while the total fluxes increase. The results may be related to the changeable pumping mechanisms.

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.

Characteristics of infrared point sources associated with OH masers

We collect 3249 OH maser sources from the literature published up to April 2007, and compile a new catalog of OH masers. We look for the exciting sources of these masers and their infrared properties from IRAS and MSX data, and make a sta- tistical study. MSX sources associated with stellar 1612 MHz OH masers are located mainly above the blackbody line; this is caused by the dust absorption of stellar en- velopes, especially in the MSX_A band. The mid-IR sources associated with stellar OH masers are concentrated in a small region in an [A]-[D] vs.[A]-[E] diagram with a small fraction of contamination; this gives us a new criterion to search for new stellar OH masers and distinguish stellar masers from unknown types of OH masers. IR sources associated with 1612 MHz stellar OH masers show an expected result： the average flux of sources with F60 〉 F25 increases with increasing wavelength, while those with F60 〈 F25 vary little with wavelength, because the sources with F60 〈 F25 are much hotter than those with F60 〉 F25.

Multiwavelength study of low-luminosity 6.7-GHz methanol masers

We present results of 13CO（1-0）,C18O（1-0）,and HCO＋（1-0） map observations and N2H＋（1-0） single point observations directed towards a sample of nine low-luminosity 6.7-GHz masers.N2H ＋ line emission has been detected from six out of nine sources,C18O line emission has been detected from eight out of nine sources,and HCO ＋ and 13CO emission has been detected in all sources.In particular,a ＂blue profile＂ of the HCO ＋ spectrum,a signature of inflow,is found towards one source.From integrated intensity emission maps,we identified 17 cores in the sample.Among them,nine cores are closely associated with low-luminosity methanol masers.For these cores,we derive the column densities,core sizes,masses and molecular abundances.Comparison of our results with similar molecular line surveys towards the southern sky methanol masers indicates that linewidths of our sample,including only the low-luminosity masers,are smaller than the sample that includes both lowand high-luminosity masers.For the maser associated cores,their gas masses have the same order of magnitude as their virial masses,indicating that these cores are gravitationally bound systems.In addition,we have found from our observations that the low-luminosity methanol masers tend to coexist with H2O masers and outflows rather than with OH masers.

A Search for High-velocity Gas Associated H_2O Masers and Ultracompact HII Regions

With the objective of studying the relationships between high-velocity gas and water maser emissions the results of a search from 95 IRAS sources for high-velocity gas associated with star forming molecular clouds are reported. 21 sources have been identified as molecular outflow candidates.

A Possible Pumping Mechanism for Interstellar Class Ⅱ107 GHz Methanol Masers

It is recognized that the interstellar methanol-107GHz 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 4.765 GHz OH masers acting as a driving coherent microwave field. It is argued that this mechanism is compatible with the astronomical conditions.

Analysis and design of the taper in metal-grating periodic slow-wave structures for rectangular Cerenkov masers

The hybrid-mode dispersion equation of the metal-grating periodic slow-wave structure for a rectangular Cerenkov maser is derived by using the Borgnis function and field-matching methods.An equivalent-circuit model for the taper of the groove depth that matches the smooth waveguide to the metal-grating structure is proposed.By using the equivalentcircuit method,as well as the Ansoft high frequency structure simulator（HFSS） code,an appropriate electromagnetic mode for beam-wave interaction is selected and the equivalent-circuit analysis on the taper is given.The calculated results show that a cumulative reflection coefficient of 0.025 for the beam-wave interaction structure at a working frequency of 78.1 GHz can be reached by designing the exponential taper with a TE z10 rectangular waveguide mode as the input and the desired TE x10 mode as the output.It is worth pointing out that by using the equivalent-circuit method,the complex field-matching problems from the traditional field-theory method for taper design can be avoided,so the taper analysis process is markedly simplified.

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.

First observations of the water masers with the Urumqi 25m radio telescope

A new radio spectral receiving system has been installed on the 25 m radio telescope of the Urumqi Astronomical Observatory. The back end is a surface acoustic wave chirp transform spectrometer (SAW CZT), used for the first time in radio astronomy. The calibration of the line observations has carefully been investigated for the new-type spectrometer. In order to test the feasibility of the prototype spectrometer, we observed water maser emission from a number of known Galactic sources. We describe the observed spectra of W49N, W3(OH), 2248+600 and 1909+090. We found that W49N spectrum showed high-velocity features ranging from -330 to 146 km s-1. In comparison with the spectra observed by Medicina, the feature at the LSR velocity -52 km s-1 in the W3(OH) presented the rapid variation in flux density.

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.

A UNIFIED DESCRIPTION OF FREE-ELECTRON MASERS——GYROKINETICS

The instabilities of gyrotron, gyro-peniotron and cyclotron auto-resonance masers(CARM) and their relationship are analysed in detail. By introducing gyrokinetic variablesin the Vlasov equation, a unified description, i.e. the gyrokinetics, of these free-electronmasersisgiven.

NEW METHOD OF EFFICIENCY ENHANCEMENT IN FREE-ELECTRON MASERS

A new method is proposed to enhance the efficiency of free-electron maser (EM). Aradial electrostatic field is introduced to assist the axial magnetic field to focus a large-orbitclectron beam. A new kind of azimuthal bunching mechanism. caused by the angular-momentum effect, is demonstrated. Nonlinear simulation of the interaction between a rela-tivistic electron beam and TE_(5,1,1) mode or TE_(10,1,1) mode shows that, as long as the initialparameters are properly chosen, the method is valid.

The spiral structure of the Milky Way

The morphology and kinematics of the spiral structure of the Milky Way are long-standing problems in astrophysics.In this review we firstly summarize various methods with different tracers used to solve this puzzle.The astrometry of Galactic sources is gradually alleviating this difficult situation caused mainly by large distance uncertainties, as we can currently obtain accurate parallaxes(a few μas) and proper motions(≈1 km s-1) by using Very Long Baseline Interferometry(VLBI).On the other hand, the Gaia mission is providing the largest, uniform sample of parallaxes for O-type stars in the entire Milky Way.Based upon the VLBI maser and Gaia O-star parallax measurements, nearby spiral structures of the Perseus, Local, Sagittarius and Scutum Arms are determined in unprecedented detail.Meanwhile, we estimate fundamental Galactic parameters of the distance to the Galactic center,R0, to be 8.35 ± 0.18 kpc, and circular rotation speed at the Sun, Θ0, to be 240±10 km s-1.We found kinematic differences between O stars and interstellar masers: the O stars, on average, rotate faster,>8 km s-1than maser-traced high-mass star forming regions.

激光之父:1964年诺贝尔物理学奖得主汤斯博士——深切缅怀汤斯教授逝世1周年(四)

美国实验和理论物理学家、发明家和教育家查尔斯·汤斯是微波激射器(Maser)的主要发明者和激光器(Laser)的先驱者之一,与前苏联(现俄罗斯)物理学家和微波波谱学家巴索夫以及普罗霍罗夫分享1964年诺贝尔物理学奖,还与多人共享"激光之父"之美誉。激光技术是20世纪人类的重大技术发明之一,为了纪念汤斯教授逝世1周年并寄托笔者的深情哀思,特撰写出此长文。笔者在此全面介绍了汤斯教授的生平与家庭成员;主要学术成就与贡献;与中国的渊源以及所获雅称、奖项与荣衔,重点梳理出激光技术波澜壮阔发展历程的整个脉络和概貌,还顺便简介了并非激光器的半导体发光二极管(LED)的发展概况,简明扼要地阐述了诺贝尔自然科学奖中与激光技术密切相关的有关情况。

激光之父:1964年诺贝尔物理学奖得主汤斯博士——深切缅怀汤斯教授逝世1周年(三)

美国实验和理论物理学家、发明家和教育家查尔斯·汤斯是微波激射器(Maser)的主要发明者和激光器(Laser)的先驱者之一,与前苏联(现俄罗斯)物理学家和微波波谱学家巴索夫以及普罗霍罗夫分享1964年诺贝尔物理学奖,还与多人共享"激光之父"之美誉。激光技术是20世纪人类的重大技术发明之一,为了纪念汤斯教授逝世1周年并寄托笔者的深情哀思,特撰写出此长文。笔者在此全面介绍了汤斯教授的生平与家庭成员;主要学术成就与贡献;与中国的渊源以及所获雅称、奖项与荣衔,重点梳理出激光技术波澜壮阔发展历程的整个脉络和概貌,还顺便简介了并非激光器的半导体发光二极管(LED)的发展概况,简明扼要地阐述了诺贝尔自然科学奖中与激光技术密切相关的有关情况。

激光之父:1964年诺贝尔物理学奖得主汤斯博士——深切缅怀汤斯教授逝世1周年(一)

美国实验和理论物理学家、发明家和教育家查尔斯·汤斯是微波激射器(Maser)的主要发明者和激光器(Laser)的先驱者之一,与前苏联(现俄罗斯)物理学家和微波波谱学家巴索夫以及普罗霍罗夫分享1964年诺贝尔物理学奖,还与多人共享"激光之父"之美誉。激光技术是20世纪人类的重大技术发明之一,为了纪念汤斯教授逝世1周年并寄托笔者的深情哀思,特撰写出此长文。笔者在此全面介绍了汤斯教授的生平与家庭成员;主要学术成就与贡献;与中国的渊源以及所获雅称、奖项与荣衔,重点梳理出激光技术波澜壮阔发展历程的整个脉络和概貌,还顺便简介了并非激光器的半导体发光二极管(LED)的发展概况,简明扼要地阐述了诺贝尔自然科学奖中与激光技术密切相关的有关情况。

激光之父:1964年诺贝尔物理学奖得主汤斯博士——深切缅怀汤斯教授逝世1周年(五)

美国实验和理论物理学家、发明家和教育家查尔斯·汤斯是微波激射器(Maser)的主要发明者和激光器(Laser)的先驱者之一,与前苏联(现俄罗斯)物理学家和微波波谱学家巴索夫以及普罗霍罗夫分享1964年诺贝尔物理学奖,还与多人共享"激光之父"之美誉。激光技术是20世纪人类的重大技术发明之一,为了纪念汤斯教授逝世1周年并寄托笔者的深情哀思,特撰写出此长文。笔者在此全面介绍了汤斯教授的生平与家庭成员;主要学术成就与贡献;与中国的渊源以及所获雅称、奖项与荣衔,重点梳理出激光技术波澜壮阔发展历程的整个脉络和概貌,还顺便简介了并非激光器的半导体发光二极管(LED)的发展概况,简明扼要地阐述了诺贝尔自然科学奖中与激光技术密切相关的有关情况。

激光之父:1964年诺贝尔物理学奖得主汤斯博士——深切缅怀汤斯教授逝世1周年(二)

美国实验和理论物理学家、发明家和教育家查尔斯·汤斯是微波激射器(Maser)的主要发明者和激光器(Laser)的先驱者之一,与前苏联(现俄罗斯)物理学家和微波波谱学家巴索夫以及普罗霍罗夫分享1964年诺贝尔物理学奖,还与多人共享"激光之父"之美誉。激光技术是20世纪人类的重大技术发明之一,为了纪念汤斯教授逝世1周年并寄托笔者的深情哀思,特撰写出此长文。笔者在此全面介绍了汤斯教授的生平与家庭成员;主要学术成就与贡献;与中国的渊源以及所获雅称、奖项与荣衔,重点梳理出激光技术波澜壮阔发展历程的整个脉络和概貌,还顺便简介了并非激光器的半导体发光二极管(LED)的发展概况,简明扼要地阐述了诺贝尔自然科学奖中与激光技术密切相关的有关情况。