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THE INITIAL MASS FUNCTION AND YOUNG BROWN DWARF CANDIDATES IN NGC 2264. III. PHOTOMETRIC DATA
Sung, Hwankyung,Bessell, Michael S.,Chun, Moo-Young,Karimov, Rivkat,Ibrahimov, Mansur American Institute of Physics 2008 The Astronomical journal Vol.135 No.2
<P>We have performed deep wide-field CCD photometry of the young open cluster NGC 2264 to study the extent of star-forming regions (SFRs) and the shape of the initial mass function. In this paper, we present VRI and Hα photometry for more than 67,000 stars. From the spatial distribution of the selected Hα emission stars, we identify two active SFRs and a less active halo region surrounding these two SFRs. There are several Hα emission stars in the field region outside the halo region, and these may be newly formed stars in the Mon OB1 association surrounding the cluster. The locus of pre-main-sequence (PMS) stars in the I<SUB>C</SUB> versus V − I<SUB>C</SUB> diagram is revised from the distribution of Hα and X-ray emission stars in the diagram. The mean reddening of late-type PMS stars is estimated to be E(B − V) <img entity='thkap' SRC='http://ej.iop.org/icons/Entities/ap.gif' ALT='≈' ALIGN='ABSMIDDLE' /> 0.2 mag using the distribution of X-ray emission stars in the 2MASS color-color diagram. We can confirm that the Hα emission stars below the PMS locus (so-called BMS stars) are bona-fide members of NGC 2264 from their spatial distribution as well as from their near-IR excess in the 2MASS color-color diagram. In addition, four objects around IRS-2 detected with the Spitzer IRAC are also classified as BMS stars.</P>
A SPITZER VIEW OF THE YOUNG OPEN CLUSTER NGC 2264
Sung, Hwankyung,Stauffer, John R.,Bessell, Michael S. American Institute of Physics 2009 The Astronomical journal Vol.138 No.4
<P>We have performed mid-IR photometry of the young open cluster NGC 2264 using the images obtained with the Spitzer Space Telescope Infrared Array Camera and Multiband Imaging Photometer for Spitzer instruments and presented a normalized classification scheme of young stellar objects in various color-color diagrams to make full use of the information from multicolor photometry. These results are compared with the classification scheme based on the slope of the spectral energy distribution (SED). From the spatial distributions of Class I and II stars, we have identified two subclusterings of Class I objects in the CONE region of Sung et al. The disked stars in the other star-forming region S Mon are mostly Class II objects. These three regions show a distinct difference in the fractional distribution of SED slopes as well as the mean value of SED slopes. The fraction of stars with primordial disks is nearly flat between log m = 0.2 and –0.5 and that of transition disks is very high for solar mass stars. In addition, we have derived a somewhat higher value of the primordial disk fraction for NGC 2264 members located below the main pre-main-sequence locus (so-called BMS stars). This result supports the idea that BMS stars are young stars with nearly edge-on disks. We have also found that the fraction of primordial disks is very low near the most massive star S Mon and increases with distance from S Mon.</P>
UBVI CCD PHOTOMETRY OF YOUNG OPEN CLUSTERS. II. BOCHUM 7
SUNG HWANKYUNG,BESSELL M. S.,PARK B.-G.,KANG Y. H. The Korean Astronomical Society 1999 Journal of The Korean Astronomical Society Vol.32 No.2
UBVI CCD photometry has been obtained for a region around the Wolf-Rayet star WR 12. We found two young stellar associations in the observed field: the nearer one comprises the field members of Vela OBI association at d = 1.8kpc, while the farther one is the young open cluster Bochum 7 (Bo 7) at d = 4.8kpc. The stars associated with Bo 7 showed no central concentration which suggests that Bo 7 is not a young open cluster but simply a local concentration in the density of young stars belonging to the OB association (Vel OB3). These two associations have similar ages but remarkably different mass function slopes ($\Gamma$ = -2.1 $\pm$ 0.3 for Vel OBI and -1.0 $\pm$ 0.3 for Bo 7). The stars in Vel OBI shows an evident age spread (${\Delta}T\~ 9Myr$). We also found two strong H$\alpha$ emission stars - WR 12 and $\sharp$1066 - from narrow band H$\alpha$ photometry.
SEJONG OPEN CLUSTER SURVEY (SOS). 0. TARGET SELECTION AND DATA ANALYSIS
Sung, Hwankyung,Lim, Beomdu,Bessell, Michael S.,Kim, Jinyoung S.,Hur, Hyeonoh,Chun, Moo-Young,Park, Byeong-Gon The Korean Astronomical Society 2013 Journal of The Korean Astronomical Society Vol.46 No.3
Star clusters are superb astrophysical laboratories containing cospatial and coeval samples of stars with similar chemical composition. We initiate the Sejong Open cluster Survey (SOS) - a project dedicated to providing homogeneous photometry of a large number of open clusters in the SAAO Johnson-Cousins' UBV I system. To achieve our main goal, we pay much attention to the observation of standard stars in order to reproduce the SAAO standard system. Many of our targets are relatively small sparse clusters that escaped previous observations. As clusters are considered building blocks of the Galactic disk, their physical properties such as the initial mass function, the pattern of mass segregation, etc. give valuable information on the formation and evolution of the Galactic disk. The spatial distribution of young open clusters will be used to revise the local spiral arm structure of the Galaxy. In addition, the homogeneous data can also be used to test stellar evolutionary theory, especially concerning rare massive stars. In this paper we present the target selection criteria, the observational strategy for accurate photometry, and the adopted calibrations for data analysis such as color-color relations, zero-age main sequence relations, Sp - MV relations, Sp - $T_{eff}$ relations, Sp - color relations, and $T_{eff}$ - BC relations. Finally we provide some data analysis such as the determination of the reddening law, the membership selection criteria, and distance determination.
Sung, Hwankyung,Bessell, Michael S.,Chun, Moo-Young,Yi, Jonghyuk,Nazé,, Y.,Lim, Beomdu,Karimov, R.,Rauw, G.,Park, Byeong-Gon,Hur, Hyeonoh American Astronomical Society 2017 The Astrophysical journal Supplement series Vol.230 No.1
<P>We present deep wide-field optical CCD photometry and mid-infrared Spitzer/IRAC and MIPS 24 mu m data for about 100,000 stars in the young open cluster IC 1805. The members of IC 1805 were selected from their location in the various color-color and color-magnitude diagrams, and the presence of H alpha emission, mid-infrared excess emission, and X-ray emission. The reddening law toward IC 1805 is nearly normal (R-V = 3.05 +/- 0.06). However, the distance modulus of the cluster is estimated to be 11.9 +/- 0.2 mag (d = 2.4 +/- 0.2 kpc) from the reddening-free color-magnitude diagrams, which is larger than the distance to the nearby massive star-forming region W3(OH) measured from the radio VLBA astrometry. We also determined the age of IC 1805 (tau(MSTO) = 3.5 Myr). In addition, we critically compared the age and mass scale from two pre-main-sequence evolution models. The initial mass function with a Salpeter-type slope of Gamma = -1.3 +/- 0.2 was obtained and the total mass of IC 1805 was estimated to be about 2700 +/- 200 M-circle dot. Finally, we found our distance determination to be statistically consistent with the Tycho-Gaia Astrometric Solution Data Release 1, within the errors. The proper motion of the B-type stars shows an elongated distribution along the Galactic plane, which could be explained by some of the B-type stars being formed in small clouds dispersed by previous episodes of star formation or supernova explosions.</P>