The radio structure of BL Lac object S5 2007+777

BL Lac object S5 2007+777 has been classified as a HYMOR (Hybrid Morphology radio source) for its hybrid FR I and FR II radio morphology. It is one of four BL Lac objects with a kpc scale extended X-ray jet. In this paper, we searched the unpublished European VLBI Network (EVN) archived high resolution data for this source, and present the high resolution radio structure. The EVN images all show a core-jet structure in 1.6, 5 and 8 GHz. In combination with the VLA data in the literature, we found position angle differences (ΔPA) of about 10°–20° between pc and kpc scale jet structures. The brightness temperature estimated from multi-band EVN images are around 10^11.2–10^11.8 K, from which the Doppler factor ranges from 3.2 to 12.0. We found significant flux variations of the radio core in 1.6 and 5 GHz, from which we derived the variability in brightness temperature T _var to be 10^13.6 K and 10^14.0 K, corresponding to the Doppler factors of 9.3 and 12.4, respectively.

     

350 μm map of the Ophiuchus molecular cloud: core mass function

Stars are born in dense cores of molecular clouds. The core mass function(CMF), which is the mass distribution of dense cores, is important for understanding the stellar initial mass function(IMF). We obtained 350 μm dust continuum data using the SHARC-II camera at the Caltech Submillimeter Observatory(CSO) telescope. A 350 μm map covering 0.25 deg2 of the Ophiuchus molecular cloud was created by mosaicing 56 separate scans. The CSO telescope had an angular resolution of 9′′, corresponding to 1.2×103AU at the distance of the Ophiuchus molecular cloud(131 pc). The data was reduced using the Comprehensive Reduction Utility for SHARC-II(CRUSH). The flux density map was analyzed using the Gauss Clumps algorithm, within which 75 cores has been identified. We used the Spitzer c2 d catalogs to separate the cores into 63 starless cores and 12 protostellar cores. By locating Jeans instabilities, 55 prestellar cores(a subcategory of starless cores) were also identified. The excitation temperatures, which were derived from FCRAO12 CO data, help to improve the accuracy of the masses of the cores. We adopted a Monte Carlo approach to analyze the CMF with two types of functional forms; power law and log-normal. The whole and prestellar CMF are both well fitted by a log-normal distribution, with μ =-1.18±0.10, σ = 0.58±0.05 and μ = 1.40±0.10, σ = 0.50±0.05 respectively. This finding suggests that turbulence influences the evolution of the Ophiuchus molecular cloud.