Embedded clusters are ideal laboratories for understanding the early phase of the dynamical evolution of clusters as well as massive star formation. An interesting observational phenomenon is that some of the embedded clusters show mass segregation, i.e., the most massive stars are preferentially found near the cluster center. We develop a new approach to describe mass segregation. Using this approach and the Two Micron All Sky Survey Point Source Catalog （2MASS PSC）, we analyze 18 embedded clusters in the Galaxy. We find that 11 of them are mass-segregated and that the others are not mass-segregated. No inversely mass-segregated cluster is found.
Gravitational accretion accumulates the original mass.This process is crucial for us to understand the initial phases of star formation.Using the specific infall profiles in optically thick and thin lines,we searched the clumps with infall motion from the Milky Way Imaging Scroll Painting(MWISP)CO data in previous work.In this study,we selected 133 sources as a sub-sample for further research and identification.The excitation temperatures of these sources are between 7.0 and 38.5 K,while the H2 column densities are between 10^21 and 10^23 cm^-2.We have observed optically thick lines HCO+(1-0)and HCN(1-0)using the DLH 13.7-m telescope,and found 56 sources with a blue profile and no red profile in these two lines,which are likely to have infall motions,with a detection rate of 42%.This suggests that using CO data to restrict the sample can effectively improve the infall detection rate.Among these confirmed infall sources are 43 associated with Class O/I young stellar objects(YSOs),and 13 which are not.These 13 sources are probably associated with the sources in the earlier evolutionary stage.In comparison,the confirmed sources that are associated with Class O/I YSOs have higher excitation temperatures and column densities,while the other sources are colder and have lower column densities.Most infall velocities of the sources that we confirmed are between 10^-1 to 10^0 km s^-1,which is consistent with previous studies.
Yang YangZhi-Bo JiangZhi-Wei ChenShao-Bo ZhangShu-Ling YuYi-Ping Ao
We present a study of the Galactic bubble N4 using the 13.7 m millimeterwave telescope, which is managed by Purple Mountain Observatory at Qinghai Station. N4 is one of the science demonstration regions where simultaneous observations of ^12CO （J = 1 - 0）, ^13CO （J = 1 - 0） and C^18O （J = 1 - 0） line emission towards N4 were carried out under the project Milky Way Imaging Scroll Painting （MWISP）. We analyze the spectral profile and the distribution of the molecular gas. Morphologically, the CO emissions correlate well with Spitzer IRAC 8.0 p-m emission. The channel map and velocity-position diagram show that N4 is more likely to be an inclined expanding ring rather than a spherical bubble. We calculated the physical parameters of N4 including mass, size, column density and optical depth. Some massive star candidates were discovered in the region of N4 using the （J, J-H） colormagnitude diagram. We found a candidate for the energy source driving the expansion of N4, a massive star with a mass of -15 M⊙ and an age of - 1Myr. There is the signature of infall motion in N4, which can be a good candidate for the infall area. Combining millimeter and infrared data, we suggest that triggered star formation can exist in N4.
