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.
A theoretical model of a circular flexure-mode piezoelectric bimorph ac- tuator is established. The circular bimorph structure, consisting of two flexible layers of piezoelectric material and a layer of metallic material in the middle, is powered to the flexural deformation. The analytical solutions including the statics solution and the dynamics solution are derived from the 3D equations of the linear theory of piezoelectric- ity. Numerical results are included to show the circular bimorph piezoelectric actuator （CBPA） performance, depending on the physical parameters.
We present the analysis of Spitzer/IRAC and near infrared imaging obser- vation of AFGL 5157, an active star forming region. In the IRAC images, this region shows strong emissions of polycyclic aromatic hydrocarbons in channel 4 and emis- sions of H2 in channel 2. Many of the H2 features are aligned to form jet-like struc- tures. Three bipolar jets in the NHa core region and a couple of jets northwest of the core have been identified. We identify the possible driving agents of the bipolar jets and show them to be very young. An embedded cluster has been detected in the NH3 core; many members in the cluster have spectral energy distributions that increase from JHK bands toward longer wavelengths, indicative of their early evolutionary stages. Millimeter and submillimeter continuum emissions in the NH3 core and the northwest subregion are found to coincide spatially with these presumable Class0/I sources. The existence of H2 bipolar jets and very young stellar objects suggests that star formation is continuing at the present epoch in these subregions. Combining in- formation from previous studies, we propose a sequential star formation scenario in the whole AFGL 5157 region.
We present a detailed comparison of two approaches, the use of a precalculated database and simulated annealing （SA）, for fitting the continuum spectral energy distribution （SED） of astrophysical objects whose appearance is dominated by surrounding dust. While pre-calculated databases are commonly used to model SED data, only a few studies to date employed SA due to its unclear accuracy and convergence time for this specific problem. From a methodological point of view, different approaches lead to different fitting quality, demand on computational resources and calculation time. We compare the fitting quality and computational costs of these two approaches for the task of SED fitting to provide a guide to the practitioner to find a compromise between desired accuracy and available resources. To reduce uncertainties inherent to real datasets, we introduce a reference model resembling a typical circumstellar system with 10 free parameters. We derive the SED of the reference model with our code MC3 D at 78 logarithmically distributed wavelengths in the range [0.3 μm, 1.3 mini and use this setup to simulate SEDs for the database and SA. Our result directly demonstrates the applicability of SA in the field of SED modeling, since the algorithm regularly finds better solutions to the optimization problem than a precalculated database. As both methods have advantages and shortcomings, a hybrid approach is preferable. While the database provides an approximate fit and overall probability distributions for all parameters deduced using Bayesian analysis, SA can be used to improve upon the results returned by the model grid.
We present modeling work on three young stellar objects that are promis-ing targets for future high-resolution observations to investigate circumstellar disk evolution. The currently available data comprise the spectral energy distribution from optical to millimeter wavelengths which allow constraining the structure of the cir-cumstellar disk using self-consistent radiative transfer models. The results suggest that the assumption of well-mixed dust and gas leads to overestimation of flux in the far-infrared. Observational and theoretical arguments suggest that an overall decrease in far-infrared excess can be explained by dust settling towards the midplane. A new disk model is hence employed to take the effect of dust sedimentation into account. The extended model satisfactorily reproduces all existing observations. The three tar-gets studied here therefore deserve follow-up observations to reveal the evolutionary state of their protoplanetary disks.
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.
