Moo-Young Chun

[ITAL]UBVRI[/ITAL] and Hα Photometry of the Young Open Cluster NGC 6231

New UBVI and Hα photometry has been performed for the young open cluster NGC 2244. We classified 30 OB stars as being members of the cluster using proper-motion data and spectral types from previous investigators, along with photometric diagrams obtained in this study. We measured Hα emission strength of the stars by Hα photometry and set up a selection criterion to select pre–main-sequence (PMS) stars with Hα emission. Fourteen PMS stars and seven PMS candidates were found using the criterion. In addition, six stars found near the positions of ROSAT HRI X-ray sources were assumed to be PMS stars and the optical counterparts of these X-ray sources. We determined a reddening of E(B-V) = 0.47 ± 0.04 for the cluster and a total-to-selective extinction ratio of RV = 3.1 ± 0.2. The distance modulus derived was V0 - MV = 11.1. By comparing our photometric results with theoretical evolution models, we derived a main-sequence turnoff age of 1.9 Myr and a PMS age spread of about 6 Myr. The slope of the initial mass function, Γ, calculated in the mass range 0.5 ≤ log m ≤ 2.0 could be flat (Γ = -0.7 ± 0.1).

KMTNET: A NETWORK OF 1.6 M WIDE-FIELD OPTICAL TELESCOPES INSTALLED AT THREE SOUTHERN OBSERVATORIES

The Korea Microlensing Telescope Network (KMTNet) is a wide-field photometric system installed by the Korea Astronomy and Space Science Institute (KASI). Here, we present the overall technical specifications of the KMTNet observation system, test observation results, data transfer and image processing procedure, and finally, the KMTNet science programs. The system consists of three 1.6 m wide-field optical telescopes equipped with mosaic CCD cameras of 18k by 18k pixels. Each telescope provides a 2.0 by 2.0 square degree field of view. We have finished installing all three telescopes and cameras sequentially at the Cerro-Tololo Inter-American Observatory (CTIO) in Chile, the South African Astronomical Observatory (SAAO) in South Africa, and the Siding Spring Observatory (SSO) in Australia. This network of telescopes, which is spread over three different continents at a similar latitude of about -30 degrees, enables 24-hour continuous monitoring of targets observable in the Southern Hemisphere. The test observations showed good image quality that meets the seeing requirement of less than 1.0 arcsec in I-band. All of the observation data are transferred to the KMTNet data center at KASI via the international network communication and are processed with the KMTNet data pipeline. The primary scientific goal of the KMTNet is to discover numerous extrasolar planets toward the Galactic bulge by using the gravitational microlensing technique, especially earth-mass planets in the habitable zone. During the non-bulge season, the system is used for wide-field photometric survey science on supernovae, asteroids, and external galaxies.

The Initial Mass Function and Young Brown Dwarf Candidates in NGC 2264. I. The Initial Mass Function around S Monocerotis

The young open cluster NGC 2264 was observed on 2002 January 6?7 with the CFH12K mosaic CCD on the 3.6 m Canada-France-Hawaii Telescope to investigate the shape of the initial mass function (IMF). In order to select the pre?main-sequence (PMS) members more completely, Chandra X-Ray Observatory archival data were retrieved and used for the identification of X-ray?emitting weak-line T Tauri stars. In addition, the (R-I, V-I) diagram was used to exclude background late-type giants, and a statistical approach was applied to estimate the number of contaminating foreground main-sequence stars. The shape of the IMF of the Chandra field of view is flat between log m = -0.4 and ~-1.0 (m in solar mass units), with a weak signature of a dip near log m = -0.2. The overall shape of the IMF is very similar to those obtained for the Pleiades or the Trapezium. The fraction of disked PMS stars, as noted by Rebull and coworkers, does not show any signature of mass dependency. The age of PMS stars between log m = 0 and -1 is 3.1 ? 0.5 Myr.

The Initial Mass Function and Young Brown Dwarf Candidates in NGC 2264. III. Photometric Data

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 IC versus V − IC 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) 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.

Design and early performance of IGRINS (Immersion Grating Infrared Spectrometer)

The Immersion Grating Infrared Spectrometer (IGRINS) is a compact high-resolution near-infrared cross-dispersed spectrograph whose primary disperser is a silicon immersion grating. IGRINS covers the entire portion of the wavelength range between 1.45 and 2.45μm that is accessible from the ground and does so in a single exposure with a resolving power of 40,000. Individual volume phase holographic (VPH) gratings serve as cross-dispersing elements for separate spectrograph arms covering the H and K bands. On the 2.7m Harlan J. Smith telescope at the McDonald Observatory, the slit size is 1ʺ x 15ʺ and the plate scale is 0.27ʺ pixel. The spectrograph employs two 2048 x 2048 pixel Teledyne Scientific and Imaging HAWAII-2RG detectors with SIDECAR ASIC cryogenic controllers. The instrument includes four subsystems; a calibration unit, an input relay optics module, a slit-viewing camera, and nearly identical H and K spectrograph modules. The use of a silicon immersion grating and a compact white pupil design allows the spectrograph collimated beam size to be only 25mm, which permits a moderately sized (0.96m x 0.6m x 0.38m) rectangular cryostat to contain the entire spectrograph. The fabrication and assembly of the optical and mechanical components were completed in 2013. We describe the major design characteristics of the instrument including the system requirements and the technical strategy to meet them. We also present early performance test results obtained from the commissioning runs at the McDonald Observatory.

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.

BOAO Photometric Survey of Galactic Open Clusters. II. Physical Parameters of 12 Open Clusters

We have initiated a long-term project, the BOAO photometric survey of open clusters, to enlarge our understanding of Galactic structure using UBVI CCD photometry of open clusters, which have been little studied before. This is the second paper of the project, in which we present the photometry of 12 open clusters. We have determined the cluster parameters by fitting the Padua isochrones to the color-magnitude diagrams of the clusters. All the clusters except for Be 60 and NGC 1348 are found to be intermediate-age to old (0.2–4.0 Gyrs) open clusters with a mean metallicity of [Fe/H] ≈ 0.0.

Preliminary design of IGRINS (Immersion GRating INfrared Spectrograph)

The Korea Astronomy and Space Science Institute (KASI) and the Department of Astronomy at the University of Texas at Austin (UT) are developing a near infrared wide-band high resolution spectrograph, IGRINS. IGRINS can observe all of the H- and K-band atmospheric windows with a resolving power of 40,000 in a single exposure. The spectrograph uses a white pupil cross-dispersed layout and includes a dichroic to divide the light between separate H and K cameras, each provided with a 2kx2k HgCdTe detector. A silicon immersion grating serves as the primary disperser and a pair of volume phased holographic gratings serve as cross dispersers, allowing the high resolution echelle spectrograph to be very compact. IGRINS is designed to be compatible with telescopes ranging in diameter from 2.7m (the Harlan J. Smith telescope; HJST) to 4 - 8 m telescopes. Commissioning and initial operation will be on the 2.7m telescope at McDonald Observatory from 2013.

DESIGN AND MANUFACTURING OF THE CASSEGRAIN INTERFACE MODULE OF THE BOAO ECHELLE SPECTROGRAPH

Cassegrain interface module (CIM) of the fiber-fed high resolution echelle spectrograph has been designed and manufactured for the 1.8 m reflector at the Bohynsan Optical Astronomy Observatory. We also constructed a long slit spectrograph attached to this CIM, which would replace the earlier rather inefficient medium dispersion spectrometer. We present detailed description for design and manufacturing concepts of the CIM which consists of a slit assembly, slit monitoring system, calibration lamp system and a long slit spectrograph, in order to provide how the overall system and each part. are constructed. The preliminary performance test carried out so far seems to indicate a successful result.

A deep survey of the AKARI north ecliptic pole field . I. WSRT 20 cm radio survey description, observations and data reduction

Aims. The Westerbork Radio Synthesis Telescope, WSRT, has been used to make a deep radio survey of an ∼1.7 degree 2 field coinciding with the AKARI north ecliptic pole deep field. The observations, data reduction and source count analysis are presented, along with a description of the overall scientific objectives. Methods. The survey consisted of 10 pointings, mosaiced with enough overlap to maintain a similar sensitivity across the central region that reached as low as 21 μJy beam −1 at 1.4 GHz. Results. A catalogue containing 462 sources detected with a resolution of 17.0 �� × 15.5 �� is presented. The differential source counts calculated from the WSRT data have been compared with those from the shallow VLA − NEP survey of Kollgaard et al. 1994, and show a pronounced excess for sources fainter than ∼1 mJy, consistent with the presence of a population of star forming galaxies at sub-mJy flux levels. Conclusions. The AKARI north ecliptic pole deep field is the focus of a major observing campaign conducted across the entire spectral region. The combination of these data sets, along with the deep nature of the radio observations will allow unique studies of a large range of topics including the redshift evolution of the luminosity function of radio sources, the clustering environment of radio galaxies, the nature of obscured radio-loud active galactic nuclei, and the radio/far-infrared correlation for distant galaxies. This catalogue provides the basic data set for a future series of paper dealing with source identifications, morphologies, and the associated properties of the identified radio sources.