Beomdu Lim

SEJONG OPEN CLUSTER SURVEY (SOS). 0. TARGET SELECTION AND DATA ANALYSIS

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-Cousin’ UBVI 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.

CCD PHOTOMETRY OF STANDARD STARS AT MAIDANAK ASTRONOMICAL OBSERVATORY IN UZBEKSTAN: TRANSFORMATIONS AND COMPARISONS

Observation of standard stars is of crucial importance in stellar photometry. We have studied the standard transformation relations of the UBV RI CCD photometric system at the Maidanak Astronomical Observatory in Uzbekistan. All observations were made with the AZT-22 1.5m telescope, SITe 2k CCD or Fairchild 486 CCD, and standard Bessell UBV RI filters from 2003 August to 2007 September. We observed many standard stars around the celestial equator observed by SAAO astronomers. The atmospheric extinction coecients, photometric zero points, and time variation of photometric zero points of each night were determined. Secondary extinction coecients and photometric zero points were very stable, while primary extinction coecients showed a distinct seasonal variation. We also determined the transformation coecients for each filter. For B, V , R, and I filters, the transformation to the SAAO standard system could be achieved with a straight line or a combination of two straight lines. However, in the case of the U filter and Fairchild 486 CCD combination, a significant non-linear correction term - related to the size of Balmer jump or the strength of the Balmer lines - of up to 0:08 mags was required. We found that our data matched well the SAAO photometry in V , B i V , V i I, and R i I. But in U i B, the dierence in zero point was about 3 :6 mmag and the scatter was about 0:02 mag. We attribute the relatively large scatter in U iB to the larger error in U of the SAAO photometry. We confirm the mostly small dierences between the SAAO standard UBV RI system and the Landolt standard system. We also attempted to interpret the seasonal variation of the atmospheric extinction coecients in the context of scattering sources in the earth’s atmosphere.

Reddening, distance, and stellar content of the young open cluster Westerlund 2

We present deep

Sejong open cluster survey (SOS) - III. The young open cluster NGC 1893 in the H II region W8

UBVI_C

The Sejong Open Cluster Survey (SOS). IV. the Young Open Clusters NGC 1624 and NGC 1931

photometric data of the young open cluster Westerlund 2. An abnormal reddening law of

A CONSTRAINT ON THE FORMATION TIMESCALE OF THE YOUNG OPEN CLUSTER NGC 2264: LITHIUM ABUNDANCE OF PRE-MAIN SEQUENCE STARS

R_{V,cl}=4.14\pm0.08

CHARACTERISTICS OF THE FAIRCHILD 486 CCD AT MAIDANAK ASTRONOMICAL OBSERVATORY IN UZBEKISTAN

was found for the highly reddened early-type members (

SEJONG OPEN CLUSTER SURVEY (SOS) - V. THE ACTIVE STAR FORMING REGION SH 2-255 - 257

E(B-V)\geq 1.45

An Optical and Infrared Photometric Study of the Young Open Cluster IC 1805 in the Giant H ii Region W4

), whereas a fairly normal reddening law of

TIME-SERIES PHOTOMETRY OF VARIABLE STARS IN THE GLOBULAR CLUSTER NGC 288

R_{V,fg}=3.33\pm0.03