Observations of interplanetary scintillation with a single-station mode at Urumqi

The Sun affects physical phenomena on Earth in multiple ways. In particular, the material in interplanetary space comes from coronal expansion in the form of inhomogeneous plasma flow （solar wind）, which is the primary source of the interplanetary medium. Ground-based Interplanetary Scintillation （IPS） observations are an important and effective method for measuring solar wind speed and the structures of small diameter radio sources. We discuss one mode of ground-based single-station observations： Single-Station Single-Frequency （SSSF） mode. To study the SSSF mode, a new system has been established at Urumqi Astronomical Observatory （UAO）, China, and a series of experimental observations were successfully carried out from May to December, 2008.

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.

A Monte Carlo Study of the Evolution of the Scale Height of Normal Pulsars in the Galaxy

Based on the undisturbed, finite thickness disk gravitational potential, we carried out 3-D Monte Carlo simulations of normal pulsars. We find that their scale height evolves in a similar way for different velocity dispersions （δv）： it first increases linearly with time, reaches a peak, then gradually decreases, and finally approaches a stable asymptotic value. The initial velocity dispersion has a very large influence on the scale height. The time evolution of the scale height is studied. When the magnetic decay age is used as the time variable, the observed scale height has a similar trend as the simulated results in the linear stage, from which we derive velocity dispersions in the range 70 - 178km s^-1, which are near the statistical result of 90 - 270km s^-1 for 92 pulsars with known transverse velocities. If the characteristic age is used as the time variable, then the observed and theoretical curves roughly agree for t 〉 10^8 yr only if av 〈 25km s^-1.

CO Clouds around SNR G21.8-0.6 and G32.8-0.1

We made the first CO（1-0） mapping to SNR G21.8-0.6 and SNR G32.8-0.1, both associated with OH 1720MHz maser. Based on the morphological correspondence and velocity and position agreement between the radio remnant and the CO clouds, we tentatively identify the clouds that are respectively interacting with the two SNRs.

The ROSAT bright source 1RXS J201607.0+251645:an active Algol-type binary

1RXS J201607.0＋251645 is identified as an eclipsing binary. We present preliminary observations in the V band with the 0.6-m telescope for three years and extensive observations in the V and R bands with the 0.8-m telescope for six nights, respectively. The light curve of the system is E13 type. Five light minimum times were obtained and the orbital period of 0.388058^d（±0.00044d） is determined. The photometric solution given by the 2003-version of the Wilson-Devinney program suggests that the binary is a semidetached system with photometric mass ratio 0.895（±0.006）, which is probably comprised of a G5 primary and an oversized K5 secondary. The tess massive component has completely filled its Roche lobe, while the other one almost fills its Roche lobe with a filling factor of 93.4%. The system shows a varying O＇Connell effect in its phase folded diagrams from 2005 to 2007, and is X-ray luminous with log Lx/Lbol - -3.27. Possible mechanisms to account for these two phenomena are discussed. Finally, we infer that the binary may be in thermal oscillation or may evolve into a contact binary.

Seven-frequency VLBI Observations of the GHz-Peaked-Spectrum Source OQ 208

We present quasi-simultaneous VLBI images of the GHz-Peaked-Spectrum radio source OQ 208 obtained with the Very Long Baseline Array at 1.4, 1.7, 2.3, 5.0, 8.4, 15.4 GHz and the European VLBI Network at 6.7 GHz. The low frequency （1.4, 1.7 and 2.3 GHz） observations reveal a weak and extended steep-spectrum component at about 30 mas away at position angle - 110°, which may be a remnant emission. The radio structure of OQ 208 consists of two mini-lobes at 5.0, 6.7, 8.4 and 15.4 GHz. Our spectral analysis further confirms that the southwest lobe undergoes free-free absorption and finds that the free-free absorption is stronger in the inner region. By fitting the 8.4 GHz images from 1994 to 2005, we obtain a separation speed of 0.0314-0.006 mas yr^-1 between the two mini-lobes. This indicates a jet proper motion of 0.1054-0.020 c and a kinematic age of 219±42 yr for the radio source.

1_(10)-1_(11) H_2CO and H_(110α) observations towards the giant HII region in cloud complex W43

The 110-111 formaldehyde （H2CO） absorption line and H110α radio recombination line （H RRL） are observed towards the giant HII region in cloud complex W43. The observations are obtained using the Nanshan 25 m single dish operated by Urumqi Observatory, National Astronomical Observatories of China. A region about 30 × 30 is observed, which covers the whole HII region in W43. Except for the central 10 region, all the other seven points are first observed with the H2CO 110-111 absorption. The column density of the H2CO is calculated, and the H2CO density contours show some differences with the infrared image. Multiple features appear in the H2CO and H RRL which indicate complex structure. The intensities of the H2CO and the velocities of the H110α seem to present a linear correlation, which illustrates that the sphere of influence of the central WR/OB cluster may be much more extended than presently known, since the size is nearly 50 pc.

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.

Population synthesis of high mass X-ray binaries

By simulating the evolution of spin periods of magnetized neutron stars which interact with their environment in binary systems,we investigate the Galactic population of high mass X-ray binaries（HMXBs） .The number of HMXBs in the Galaxy is between 190 and 240,and their birthrate is from 5.9×10-5 yr-1 to 6.3× 10-5 yr-1.Comparing the Corbet diagram（the positions of the spin periods vs.the orbital periods of HMXBs） in our model with the associated observations,we find that the stellar wind structure and the process of matter transfer are very important for understanding HMXBs.

Measurements for the Performance of the Digital Autocorrelation Spectrometer

Injecting phase calibration （PCAL） signals to the feed horn of the observation system and analyzing the output response signals of the spectrometer, we measured the working performance of a 4096-channel digital autocalibration spectrometer. The results demonstrate that the spectrometer has a fine working performance： （1） the channels are distributed uniformly in the spectrometer; （2） line drift produces little effect on the observation results; （3） spectral resolution shows little changes with observation time. The distribution of the frequency resolution in an 80 MHz bandwidth was measured. A trial observation on the two molecular spectral lines of H2CO and H110α taken with this spectrometer is described.

A Composite Model for GHz Peaked Spectra of Radio Sources

GHz-Peaked Spectrum （GPS） radio sources are powerful and compact sources with convex spectra. With increasing observational findings, it has been realized that either Synchrotron Self-Absorption （SSA） alone or Free-Free Absorption （FFA） alone is not enough to account for all the spectral features. We present a model consisting of an SSA region partially covered by FFA plasma, and derive a composite spectral formula. By applying the model to a sample of 19 GPS sources having strong absorption, it is found that the external FFA process makes the SSA peak frequency linearly shift to a higher （observed） peak frequency. The shift indicates that the FFA does play a role at the frequency close to the observed peak frequency.

Evidence of Evolution in the Dense Cores in Massive Star Forming Regions

The excitation of H2O masers usually needs very high density gas,hence it can serve as a marker of dense gas in HⅡ region. We selected a sample of H2O maser sources from Plume et al. （four with, and four without detected CS（J = 7 - 6） emission）, and observed them in ^13CO（J=1-0） and C^18O （J=1-0）. C^18O （J=1-0） emission was detected only in three of the sources with detected CS（J=7-6） emission. An analysis combined with some data in the literature suggests that these dense cores may be located at different evolutionary stages. Multi-line observation study may provide us clues on the evolution of massive star forming regions and the massive stars themselves.

The spatial distribution of old neutron stars in the Galaxy

The spatial distributions of old neutron stars (NSs) with ages 109 to 1010 yr in our Galaxy are investigated by Monte Carlo simulation under two different initial random velocity models.It is found that the scale heights of the distribution increase with the Galactic radial distance.The location of the peak of the NS distribution is closer to the Galactic center than that of their progenitors.The results from our detailed numerical analysis reveal that there is resemblance between the simulated old NS distribution and the structure of the observed HI disk.