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SUBMILLIMETER OBSERVATIONS OF DENSE CLUMPS IN THE INFRARED DARK CLOUD G049.40-00.01
Kang, Miju,Choi, Minho,Bieging, John H.,Rho, Jeonghee,Lee, Jeong-Eun,Tsai, Chao-Wei IOP Publishing 2011 The Astrophysical journal Vol.743 No.2
<P>We obtained 350 and 850 mu m continuum maps of the infrared dark cloud G049.40-00.01. Twenty-one dense clumps were identified within G049.40-00.01 based on the 350 mu m continuum map with an angular resolution of about 9 ''.6. We present submillimeter continuum maps and report physical properties of the clumps. The masses of clumps range from 50 to 600 M-circle dot. About 70% of the clumps are associated with bright 24 mu m emission sources, and they may contain protostars. The two most massive clumps show extended, enhanced 4.5 mu m emission indicating vigorous star-forming activity. The clump-size-mass distribution suggests that many of them are forming high-mass stars. G049.40-00.01 contains numerous objects in various evolutionary stages of star formation, from pre-protostellar clumps to H II regions.</P>
Kang, Miju,Bieging, John H.,Povich, Matthew S.,Lee, Youngung IOP Publishing 2009 The Astrophysical journal Vol.706 No.1
<P>We present 737 candidate young stellar objects (YSOs) near the W51 giant molecular cloud over an area of 1 degrees.25 x 1 degrees.00 selected from Spitzer Space Telescope data. We use spectral energy distribution fits to identify YSOs and distinguish them from main-sequence (MS) or red giant stars, asymptotic giant branch stars, and background galaxies. Based on extinction of each YSO, we separate a total of 437 YSOs associated with the W51 region from the possible foreground sources. We identify 69 highly embedded Stage 0/I candidate YSOs in our field with masses >5 M-circle dot (corresponding to mid- to early-B MS spectral types), 46 of which are located in the central active star-forming regions of W51A and W51B. From the YSOs associated with W51, we find evidence for mass segregation showing that the most massive YSOs are concentrated on the W51 H II region complex. We find a variation in the spatial distribution of the mass function (MF) of YSOs in the mass range between 5 M-circle dot and 18 M-circle dot. The derived slopes of the MF are -1.26 and -2.36 in the active star-forming region and the outer region, respectively. The variation of the MF for YSOs embedded in the molecular cloud implies that the distribution of stellar masses in clusters depends on the local conditions in the parent molecular cloud.</P>
MEASUREMENT OF HDCO/H<sub>2</sub>CO RATIOS IN THE ENVELOPES OF EXTREMELY COLD PROTOSTARS IN ORION
Kang, Miju,Choi, Minho,Stutz, Amelia M.,Tatematsu, Ken’ichi IOP Publishing 2015 The Astrophysical journal Vol.814 No.1
<P>We present observations of HDCO and H2CO emission toward a sample of 15 Class 0 protostars in the Orion A and B clouds. Of these, 11 protostars are Herschel-identified PACS Bright Red Sources (PBRSs) and 4 are previously identified protostars. Our observations revealed the chemical properties of the PBRS envelope for the first time. The column densities of HDCO and H2CO are derived from single-dish observations at an angular resolution of similar to 20 '' (similar to 8400 AU). The degree of deuteration in H2CO ([HDCO]/[H2CO]) was estimated to range from 0.03 to 0.31. The deuterium fractionation of most PBRSs (70%) is similar to that of the non-PBRS sources. Three PBRSs (30%) exhibit high deuterium fractionation, larger than 0.15. The large variation of the deuterium fractionation of H2CO in the whole PBRS sample may reflect the diversity in the initial conditions of star-forming cores. There is no clear correlation between the [HDCO]/[H2CO] ratio and the evolutionary sequence of protostars.</P>
A Comparative Observational Study of YSO Classification in Four Small Star-forming H ii Regions
Kang, Sung-Ju,Kerton, C. R.,Choi, Minho,Kang, Miju American Astronomical Society 2017 The Astrophysical journal Vol.845 No.1
<P>We have developed a new young stellar object (YSO) identification and classification technique using mid-infrared Wide-field Infrared Survey Explorer (WISE) data. We compare this new technique with previous WISE. YSO detection and classification methods that used either infrared colors or spectral energy distribution slopes. In this study, we also use the new technique to detect and examine the YSO population associated with four small H II. regions: KR 7, KR 81, KR 120, and KR 140. The relatively simple structure of these regions allows us to effectively use both spatial and temporal constraints to identify YSOs that are potential products of triggered star formation. We are also able to identify regions of active star formation around these H II. regions that are clearly not influenced by the H II. region expansion, and thus demonstrate that star formation is on-going on megayear timescales in some of these molecular clouds.</P>