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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>
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>
THE EXTENDED ENVIRONMENT OF M17: A STAR FORMATION HISTORY
Povich, Matthew S.,Churchwell, Ed,Bieging, John H.,Kang, Miju,Whitney, Barbara A.,Brogan, Crystal L.,Kulesa, Craig A.,Cohen, Martin,Babler, Brian L.,Indebetouw, Ré,my,Meade, Marilyn R.,Robitaill IOP Publishing 2009 The Astrophysical journal Vol.696 No.2
<i>SPITZER</i>AND HEINRICH HERTZ TELESCOPE OBSERVATIONS OF STARLESS CORES: MASSES AND ENVIRONMENTS
Stutz, Amelia M.,Rieke, George H.,Bieging, John H.,Balog, Zoltan,Heitsch, Fabian,Kang, Miju,Peters, William L.,Shirley, Yancy L.,Werner, Michael W. IOP Publishing 2009 The Astrophysical journal Vol.707 No.1
<P>We present Spitzer observations of a sample of 12 starless cores selected to have prominent 24 mu m shadows. The Spitzer images show 8 mu m and 24 mu m shadows and in some cases 70 mu m shadows; these spatially resolved absorption features trace the densest regions of the cores. We have carried out a (CO)-C-12 (2-1) and (CO)-C-13 (2-1) mapping survey of these cores with the Heinrich Hertz Telescope (HHT). We use the shadow features to derive optical depth maps. We derive molecular masses for the cores and the surrounding environment; we find that the 24 mu m shadow masses are always greater than or equal to the molecular masses derived in the same region, a discrepancy likely caused by CO freezeout onto dust grains. We combine this sample with two additional cores that we studied previously to bring the total sample to 14 cores. Using a simple Jeans mass criterion, we find that similar to 2/3 of the cores selected to have prominent 24 mu m shadows are collapsing or near collapse, a result that is supported by millimeter line observations. Of this subset at least half have indications of 70 mu m shadows. All cores observed to produce absorption features at 70 mu m are close to collapse. We conclude that 24 mu m shadows, and even more so the 70 mu m ones, are useful markers of cloud cores that are approaching collapse.</P>