Radio recombination line observations at 1.0-1.5 GHz with FAST

H Ⅱ regions made of gas ionized by radiations from young massive stars,are widely distributed in the Milky Way.They are tracers for star formation,and their distributions are correlated with the Galactic spiral structure.Radio recombination lines(RRLs) of hydrogen and other atoms allow for the most precise determination of physical parameters such as temperature and density.However,RRLs at around 1.4 GHz from HⅡ regions are weak and their detections are difficult.As a result,only a limited number of detections have been obtained yet.The 19-beam receiver on board of the Five-hundred-meter Aperture Spherical radio Telescope(FAST) can simultaneously cover 23 RRLs for Hnα,Henα,and Cnα(n=164-186),respectively.This,combined with its unparalleled collecting area,makes FAST the most powerful telescope to detect weak RRLs.In this pilot survey,we use FAST to observe nine HⅡ regions at L band.We allocate20 minutes pointing time for each source to achieve a sensitivity of around 9 mK in a velocity resolution of2.0 km s^(-1).In total,21 RRLs for Hnα and Cnα at 1.0-1.5 GHz have been simultaneously detected with strong emission signals.Overall,the detection rates for the H167α and C167α RRLs are 100%,while that for the He167α RRL is 33.3%.Using hydrogen and helium RRLs,we measure the electron density,electron temperature,and pressure for three HⅡ regions.This pilot survey demonstrates the capability of FAST in RRL measurements,and a statistically meaningful sample with RRL detection,through which knowledge about Galactic spiral structure and evolution can be obtained,is expected in the future.

Evolutions of CHCN abundance in molecular clumps

To investigate the effects of massive star evolution on surrounding molecules,we select nine massive clumps previously observed with the Atacama Pathfinder Experiment(APEX) telescope and the Submillimeter Array(SMA) telescope.Based on the observations of APEX,we obtain luminosity to mass ratios Lclump/Mclump that range from 10 to 154 L_(⊙)/M_(⊙),where some of them embedded ultra compact(UC) H Ⅱ region.Using the SMA,CH3CN(12K-11K) transitions were observed toward nine massive starforming regions.We derive the CH3CN rotational temperature and column density using the XCLASS program,and calculate its fractional abundance.We find that CH3CN temperature seems to increase with the increase of Lclump/Mclump when the ratio is between 10 to 40 L_(⊙)/M_(⊙),then decrease when L_(clump)/M_(clump)≥ 40 L_(⊙)/M_(⊙).Assuming that the CH3CN gas is heated by radiation from the central star,the effective distance of CH3CN relative to the central star is estimated.The distance ranges from - 0.003 to - 0.083 pc,which accounts for - 1/100 to - 1/1000 of clump size.The effective distance increases slightly as Lclump/Mclump increases(Reff-(L_(clump)/M_(clump))0.5±0.2).Overall,the CH3 CN abundance is found to decrease as the clumps evolve,e.g.,XCH3CN -(L_(clump)/M_(clump))-1.0±0.7.The steady decline of CH3CN abundance as the clumps evolution can be interpreted as a result of photodissociation.

Quantifying the anisotropic density structure of the Central Molecular Zone–a 2D correlation function approach

The Central Molecular Zone(CMZ) is a ring-like structure sitting at the center of the Milky Way.Using the 870 μm continuum map from the APEX Telescope Large Area Survey of the Galaxy(ATLASGAL),we study anisotropy in the density structure of gas in the CMZ utilizing the 2 D correlation function.To quantify the spatial anisotropy,we define the critical angle θhalf,as well as the anisotropy parameter A≡(π/4θ_(half))-1.We find that the density structure is strongly anisotropic at a large scale(-100 pc),and the degree of spatial anisotropy decreases with decreasing scale.At the scale of - 10 pc,the structure is still mildly anisotropic.In our analyses,we provide a quantitative description of the anisotropic density structure of gas in the CMZ,and the formalism can be applied to different regions to study their differences.

Seroprevalence of Toxoplasma gondii infection in arthritis patients in eastern China

Background:There is accumulating evidence for an increased susceptibility to infection in patients with arthritis.We sought to understand the epidemiology of Toxoplasma gondii infection in arthritis patients in eastern China,given the paucity of data on the magnitude of T.gondii infection in these patients.Methods:Seroprevalence of T.gondii infection was assessed by enzyme-linked immunosorbent assay using a crude antigen of the parasite in 820 arthritic patients,and an equal number of healthy controls,from Qingdao and Weihai cities,eastern China.Sociodemographic,clinical and lifestyle information on the study participants were also obtained.Results:The prevalence of anti-T.gondii IgG was significantly higher in arthritic patients(18.8%)compared with 12%in healthy controls(P<0.001).Twelve patients with arthritis had anti-T.gondii IgM antibodies-comparable with 10 control patients(1.5%vs 1.2%).Demographic factors did not significantly influence these seroprevalence frequencies.The highest T.gondii infection seropositivity rate was detected in patients with rheumatoid arthritis(24.8%),followed by reactive arthritis(23.8%),osteoarthritis(19%),infectious arthritis(18.4%)and gouty arthritis(14.8%).Seroprevalence rates of rheumatoid arthritis and reactive arthritis were significantly higher when compared with controls(P<0.001 and P=0.002,respectively).A significant association was detected between T.gondii infection and cats being present in the home in arthritic patients(odds ratio[OR],1.68;95%confidence interval[CI]:1.24-2.28;P=0.001).Conclusions:These findings are consistent with and extend previous results,providing further evidence to support a link between contact with cats and an increased risk of T.gondii infection.Our study is also the first to confirm an association between T.gondii infection and arthritis patients in China.Implications for better prevention and control of T.gondii infection in arthritis patients are discussed.Trial registration:This is an epidemiological survey,therefore trial registration was not required.