In-Soo Yuk

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.

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.

MULTICOLOR NEAR-INFRARED INTRA-DAY AND SHORT-TERM VARIABILITY OF THE BLAZAR S5 0716+714

In this paper, we report results of our near-infrared (NIR) photometric variability studies of the BL Lacertae (BL Lac) object S5 0716+714. NIR photometric observations were spread over seven nights during our observing run on 2007 April 2-9 at the 1.8 m telescope equipped with the Korea Astronomy and Space Science Institute Near-Infrared Camera System and J, H, and Ks filters at Bohyunsan Optical Astronomy Observatory, South Korea. We searched for intra-day variability (IDV), short-term variability, and color variability in the BL Lac object. We have not detected any genuine IDV in any of the J, H, and Ks passbands in our observing run. Significant short-term variabilities ~32.6%, 20.5% and 18.2% have been detected in the J, H, and Ks passbands, respectively, and ~11.9% in (J – H) color.

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.

Technical specifications of the KMTNet observation system

Korea Astronomy and Space Science Institute (KASI) has officially started a project to construct an astronomical widefield survey system, namely KMTNet (Korea Micro-lensing Telescope Network), from January 2009. Its primary scientific goal is to discover numerous extra-solar planets, especially earth-mass planets, using the gravitational microlensing technique. This goal requires continuous photometric observations with high cadence of about 10 minutes for tens of millions of stars in dense fields toward the Galactic bulge. KMTNet will comprise three identical systems at southern observatories with different time zones. Each observing system consists of a 1.6 m wide-field optical telescope and a 20k by 20k mosaic CCD camera, which covers a 2 by 2 degrees square field of view. In this proceeding, we present technical specifications, designs and fabrication schedule of the KMTNet system.

FAR-ULTRAVIOLET OBSERVATIONS OF THE OPHIUCHUS REGION WITH SPEAR

We present the first far-ultraviolet (FUV; 1370-1670 A) image of the Ophiuchus molecular cloud region, observed with the SPEAR imaging spectrograph. The flux levels of the diffuse FUV continuum are in reasonable agreement with those of the Voyager observations in the shorter FUV wavelengths (912-1216 A), provided that the diffuse FUV emission is dominated by the spectra from late O- and early B-type stars. The observed region of the present study was divided into five subregions according to their FUV intensities, and the spectrum was obtained for each subregion with prominent H_2 fluorescent emission lines. A synthetic model of the H_2 fluorescent emission indicates that the molecular cloud has more or less uniform physical parameters over the Ophiuchus region, with a hydrogen density n_H of 500 cm^−3 and a H2 column density N(H_2) of 2 × 10^(20) cm^−2. It is notable that the observed diffuse FUV continuum is well reproduced by a single-scattering model with scattered starlight from the dust cloud located at ~120-130 pc, except at a couple of regions with high optical depth. The model also gives reasonable properties of the dust grains of the cloud with an albedo a of 0.36 ± 0.20 and a phase function asymmetry factor g of 0.52 ± 0.22.

Diffuse Far-Ultraviolet Observations of the Taurus Region

Diffuse far-ultraviolet (FUV; 1370-1670 A) flux from the Taurus molecular cloud region has been observed with the SPEAR/FIMS imaging spectrograph. An FUV continuum map of the Taurus region, similar to the visual extinction maps, shows a distinct cloud core and halo region. The dense cloud core, where the visual extinction Av > 1.5, obscures the background diffuse FUV radiation, while scattered FUV radiation is seen in and beyond the halo region, where Av < 1.5. The total intensity of H2 fluorescence in the cloud halo is I = 6.5 × 104 photons cm-2 s-1 sr-1 in the 1370-1670 A wavelength band. A synthetic model of the H2 fluorescent emission fits the present observation best with a hydrogen density nH = 50 cm-3, H2 column density N(H2) = 0.8 × 1020 cm-2, and incident FUV intensity IUV = 0.2. H2 fluorescence is not seen in the core, presumably because the required radiation flux to induce fluorescence is unable to penetrate the core region.

Modeling Star Formation History and Chemical Evolution of Resolved Galaxies

We present a new numerical model (SMART) for deriving the star formation history and chemical evolution from the color-magnitude diagrams of resolved stars in galaxies. Our model differs from previous models in that it generates simulated color-magnitude diagrams with the metal enrichment law calculated from the galactic chemical evolution model. Hence, our model is free from the problem of age-metallicity degeneracy and provides us with information on the chemical enrichment history as well as the star formation history of galaxies. We have tested our model on artificial galaxies having different star formation histories and on the Local Group dwarf irregular galaxy IC 1613. Our model successfully reproduces the star formation history and chemical evolution of the artificial galaxies. The star formation and metal enrichment histories of IC 1613 derived in this study are consistent with those in previous studies. We also present the elemental abundance ratios for IC 1613 predicted by our model. Our model is expected to be useful for understanding not only the star formation history but also the chemical evolution of nearby galaxies.

SPEAR far UV spectral imaging of highly ionized emission from the North Galactic Pole Region

Aims. We present far ultraviolet (FUV: 912–1750 A) spectral imaging observations recorded with the SPEAR satellite of the interstellar OVI (1032 A), CIV (1550 A), SiIV (1394 A), SiII* (1533 A) and AlII (1671 A) emission lines originating in a 60 ◦ × 30 ◦ rectangular region lying close to the North Galactic Pole. These data represent the first large area, moderate spatial resolution maps of the distribution of UV spectral-line emission originating the both the highly ionized medium (HIM) and the warm ionized medium (WIM) recorded at high galactic latitudes. Methods. By assessing and removing a local continuum level that underlies these emission line spectra, we have obtained interstellar emission intensity maps for the aforementioned lines constructed in 8 ◦ × 8 ◦ spatial bins on the sky. Results. Our maps of OVI, CIV, SiIV and SiII* line emission show the highest intensity levels being spatially coincident with similarly high levels of soft X-ray emission originating in the edge of the Northern Polar Spur feature. However, the distribution of the low ionization AlII emission does not show this spatial correlation, and suggests that warm-neutral and/or partially ionized gas with a temperature <20 000 K may be quite pervasive at high galactic latitudes. The variation of the emission line intensity ratios as a function of sky position is contrasted with theoretical predictions concerning the physical state of interstellar gas in the galactic halo. The observed line ratios alone unfortunately do not provide us with a clear diagnostic tool to distinguish between the various physical production mechanisms responsible for both high and low ion states. However, our results do favor the hybrid model of Shull & Slavin (1994, ApJ, 427, 784) which incorporates the combined effects of turbulent mixing layers and isobarically cooling supernova remnant gas. For this highly ionized gas, our results are best explained assuming that the observed OVI halo emission is somewhat clumpy in nature, consistent with its production at interfaces between warm (T = 10 3 −10 4 K) and hotter (T = 10 6 K) soft X-ray emitting gas. CIV emission at these interfaces occurs in the intermediate temperature (T = 10 5 K) gas, which seems always present whenever OVI is strongly detected. Alternately, the data are also consistent with CIV emission being ubiquitous throughout the halo with a fairly constant level of emission line intensity (of ∼4000 LU), and our observations mostly reflect the superposition of spatially separate OVI emission originating at the cloud interfaces of random clumps of high latitude gas.