Calculating the Excitation Temperature for H_2CO Absorption Lines in Molecular Clouds

The excitation temperature T_(ex)for molecular emission and absorption lines is an essential parameter for interpreting the molecular environment.This temperature can be obtained by observing multiple molecular transitions or hyperfine structures of a single transition,but it remains unknown for a single transition without hyperfine structure lines.Earlier H_(2)CO absorption experiments for a single transition without hyperfine structures adopted a constant value of T_(ex),which is not correct for molecular regions with active star formation and H II regions.For H_(2)CO,two equations with two unknowns may be used to determine the excitation temperature T_(ex)and the optical depthτ,if other parameters can be determined from measurements.Published observational data of the4.83 GHz(λ=6 cm)H_(2)CO(1_(10)-1_(11))absorption line for three star formation regions,W40,M17 and DR17,have been used to verify this method.The distributions of T_(ex)in these sources are in good agreement with the contours of the H110αemission of the H II regions in M17 and DR17 and with the H_(2)CO(1_(10)-1_(11))absorption in W40.The distributions of T_(ex)in the three sources indicate that there can be significant variation in the excitation temperature across star formation and H II regions and that the use of a fixed(low)value results in misinterpretation.

Comparison of NH_(3) and ^(12)CO,^(13)CO,C^(18)O Molecular Lines in the Aquila Rift Cloud Complex

The observations of the Aquila Rift cloud complex at 23.708 and 115.271 GHz made using the Nanshan 26 m radio telescope and the 13.7 m millimeter-wavelength telescope are presented.We find that the CO(1-0)gas distribution is similar to the NH_(3)gas distribution in the Aquila Rift cloud complex.In some diffusion regions characterized by CO,we identified several dense clumps based on the distribution of detected ammonia molecular emission.Through the comparison of spectral line parameters for NH_(3),^(13)CO,and C^(18)O,our study reveals that the line center velocities of the NH_(3),^(13)CO,and C^(18)O lines are comparable and positively correlated,indicating that they originate from the same emission region.No significant correlation was identified for other parameters,including integrated intensity,line widths,main beam brightness temperature,as well as the column densities of NH_(3),^(13)CO,and C^(18)O.The absolute difference in line-center velocities between the^(13)CO and NH_(3)lines is less than both the average line width of NH_(3)and that of^(13)CO.This suggests that there are no significant movements of NH_(3)clumps in relation to their envelopes.The velocity deviation is likely due to turbulent activity within the clumps.

Investigating Sulfur Chemistry in the HD163296 Disk

Sulfur chemistry in the formation process of low-mass stars and planets remains poorly understood.The protoplanetary disks are the birthplace of planets and its distinctive environment provides an intriguing platform for investigating models of sulfur chemistry.We analyzed the Atacama Large Millimeter/submillimeter Array observations of CS 7-6 transitions in the HD 163296 disk and performed astrochemical modeling to explore its sulfur chemistry.We simulated the distribution of sulfur-containing molecules and compared it with observationally deduced fractional column densities.We have found that the simulated column density of CS is consistent with the observationally deduced fractional column densities,while the simulated column density of C_(2)S is lower than the observationally deduced upper limits on column densities.This results indicate that we have a good understanding of the chemical properties of CS and C_(2)S in the disk.We also investigated the influence of the C/O ratio on sulfur-containing molecules and found that the column densities of SO,SO_(2),and H_2S near the centra star are dependent on the C/O ratio.Additionally,we found that the N[CS]/N[SO]ratio can serve as a promising indicator of the disk’s C/O ratio in HD 163296.Overall,the disk of HD 163296 provides a favorable environmen for the detection of sulfur-containing molecules.

Gas-Grain Modeling of Interstellar O2

Molecular oxygen(O2)is essential to human beings on the earth.Although elemental oxygen is rather abundant,O2 is rare in the interstellar medium.It was only detected in two galactic and one extra-galactic region.The inconsistency between observations and theoretical studies is a big challenge for astrochemical models.Here we report a two-phase modeling research of molecular oxygen,using the Nautilus gas-grain code.We apply the isothermal cold dense models in the interstellar medium with two typical sets of initial elemental abundances,as well as the warm-up models with various physical conditions.Under cold dense conditions,we nd that the timescales for gas-phase CO,O2 and H2O to reach peak values are dependent on the hydrogen density and are shortened when hydrogen density increases.In warm-up models,O2 abundances are in good agreement with observations at temperatures rising after 10^5 yr.In both isothermal and warm-up models,the steady-state O2 fractional abundance is independent of the hydrogen density,as long as the temperature is high enough(>30 K),at which O2 is prevented from signi cant depleting onto grain surface.In addition,low density is preferable for the formation of O2,whether molecular oxygen is under cold conditions or in warm regions.

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 Environment and Star Formation around the Infrared Bubble N 13

Infrared bubbles provide a unique opportunity to study the interactions between massive stars and surrounding material.We conduct a multi-wavelength study on the environment and star formation around an infrared bubble N13.Three dust clumps and two molecular clumps are identified around N 13,which are all distributed on the layer.Young stellar objects(YSOs)are carefully searched using infrared colors and YSO candidates of WISE and Gaia DR2,and three Class I/II YSOs are found in N 13.In addition,four O-type stars identified in N 13 are probably the exciting stars.The dynamical and fragmentation ages of N 13 are 0.32-0.35 and 1.37-2.80 Myr respectively,which suggest that the radiation-driven implosion model may be dominant in N 13.By comparing the small-size bubble N 13(R~1.9 pc)and the larger-size bubble G15.684-0.29(R~15.7 pc)we found that star formation activity is more active in the large-size bubble.Brief comparisons of ten bubbles show that small-size bubbles have a small ratio of kinetic age versus the fragmentation time.Triggering star formation may be more active in bubbles with larger ratio between kinetic and fragmentation ages.Furthermore,the collect and collapse mechanism may play the dominant role in the large-size ones.

E ect of Optical Depth on Study of Chemical Properties of Massive Star Forming Clumps

Here we present the study on chemical properties of massive star forming clumps using N2H^+(1-0),H^13CO+(1-0),HCN(1-0)and HN^13C(1-0)data from the literature[Astron.Astrophys.563,A97(2014)].We found that abundances of H^13CO+ and HN^13C are a ected by H2 column densities.As the median values of these two abundances increase by nearly 10 times from stages A to B,H^13CO+and HN^13C are suitable for tracing the evolution of massive star forming clumps.The order of rapidity in growth of abundances of all the four studied molecules from stages A to B,is H^13CO^+,HCN,HN^13C,and N2H^+,from the highest to the lowest.Our results suggest that the observing optically thin molecular lines with high angular resolution are necessary to study the chemical evolution of massive star forming clumps.

The comparison of H_2CO(1_(10)–1_(11)),C^(18)O(1–0) and the continuum towards molecular clouds

We present large scale observations of C^18O （1-0） towards four massive star forming regions： MON R2, S156, DR17/L906 and M17/M18. The transitions of H2CO （110-111）, C^18O （1-0） and the 6cm continuum are compared in these four regions. Our analysis of the observations and the results of the Non-LTE model shows that the brightness temperature of the formaldehyde absorption line is strongest in a background continuum temperature range of about 3 - 8 K. The excitation of the H2CO absorption line is affected by strong background continuum emission. From a comparison of H2CO and C^18O maps, we found that the extent of H2CO absorption is broader than that of C^18O emission in the four regions. Except for the DR17 region, the maximum in H2CO absorption is located at the same position as the C^18O peak. A good correlation between intensities and widths of H2CO absorption and C^18O emission lines indicates that the H2CO absorption line can trace the dense, warm regions of a molecular cloud. We find that N（H2CO） is well correlated with N（ C^18O） in the four regions and that the average ratio of column densities is （N（H2CO）/N（ClSO）） ～0.03.

Does the Masing Gas Fall Inward VY CMa?

The water maser emission from the unusual supergiant,VY CMa,has been observed with the Urumqi 25 m radio telescope.A simple red-shifted maser spectrum was detected in the 1.6 Jy noise level during our monitoring observations.All of the H2O maser features are red-shifted with respect to the VY CMa stellar velocity of 17.6 km.s-1.The spectrum appears to be consisted of two striking like groups and each group has three features.The appearances and the ratio of these three features in the two maser groups are very similar.The H2O maser emission arises from a region close to the supergiant,about 10 stellar radii of the star.The simple red-shifted spectrum could be due to infall masing gas on the near side of the disk.Pulsation of the central star causes oscillations in this portion of the envelope,with shock wave propagating outward and with material falling inward.The masing gas motions are very complex,by which the dramatic changes or the quasi-sinusoidal fluctuation in flux may be explained.

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.

An H2O Maser survey towards BGPS sources in the Outer Galaxy

We performed an H20 maser survey towards 274 Bolocam Galactic Plane Survey （BGPS） sources with 85° 〈 1 〈 193° using the Nanshan 25 m radio telescope. We detected 25 H2O masers, and five of them are new detections. The detection rate of H2O masers in our sample is 9% which is very low. The detection rate of H2O masers increases as the 1.1 mm flux density of BGPS sources increases, and both the peak flux density and luminosity of H2O masers increase as the sources evolve. The detection rate of H2O masers toward BGPS sources without HCO＋ emission is low. The BGPS sources associated with both H2O and CH3OH masers seem to be more compact than those only associated with H2O masers. This indicates that the sources with both masers may be in a relatively later evolutionary stage. The strongest H2O maser source G133.715＋01.217, also well known as W3 IRS 5 which has a flux density of 2.9 × 103 Jy, was detected at eight different nearby positions. By measuring the correlation between the flux densities of these H2O masers and their angular distance from the true source location, we get the influence radius r = 1/0.8 1og（F0/3rms）. For our observations, strong sources can be detected anywhere within this radius. It is helpful to determine whether or not a weak maser nearby the strong maser is a true detection.

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.

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.

The OH Maser Line Receiving System for the Urumqi 25m Radio Telescope

A maser spectral line system is newly implemented on the Urumqi 25m Radio Telescope. The system consists mainly of a cooling receiver and a 4096 channels digital correlation spectrometer. The frequency resolution of the spectrometer at the maximum signal bandwidth of 80MHz is 19.5kHz. After careful calibrations observation at the 1665 MHz OH maser emission was made towards a number of sources, including W49N and W75N. The observed results demonstrate that the digital correlation spectrometer is suitable for astronomical spectral line observations.

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.