• 천문학회보
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• 제37권1호
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• pp.80.1-80.1
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• 2012

NGC 6803 is an elliptical ring shape planetary nebula. We analyzed the high dispersion spectra which had been observed with the Hamilton Echelle Spectrograph attached to the 3-m Shane telescope of Lick Observatory. We also investigated the low dispersion UV spectral data obtained with the 60-cm interstellar ultraviolet explorer. Diverse excitation lines were found from neutral to quadruply ionized ions. The temperature diagnostic lines indicate relatively low electron temperatures, i.e., $T_{\epsilon}{\leq}9500$ K for most lines except for [ClIV] - 11,500 K. In spite of its simplistic bi-laterally symmetrical elliptical shape, the nebula appears to be very complex of a hugh density range from 1300 to 80,000 $cm^3$. A comparison of the two epoch data suggests that the density increase occurred in the high excitation line zone near the inner boundary. We derived the chemical abundances of He, C, N, O, Ne, S, Ar, Cl, and K. The chemical abundances of NGC 6803 are enhanced compared with the average Galactic planetary nebula. Our self-consistent photo-ionization model study implies that the effective temperature of the central star is 90,000 K and its luminosity is 2400 $L_{\odot}$. The evolutionary track suggests that the progenitor of NGC 6803 was about 0.9 -- 1.0 $M_{\odot}$ star, which might be born from a metal-rich zone near the galactic disk, but now relocated into the present high Galactic latitude.

• 천문학회보
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• 제42권2호
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• pp.56.4-57
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• 2017

The GMT-Consortium Large Earth Finder (G-CLEF) is the very first light instrument of the Giant Magellan Telescope (GMT) to be commissioned in 2022. The instrument is a fiber feed, optical band echelle spectrograph that is capable of extremely precise radial velocity measurement. Korea Astronomy and Space Science Institute (KASI) has been involved in the development of the G-CLEF as one member of the international consortium consisted of five astronomical institutes including Smithsonian Astrophysical Observatory (SAO), Observatories of the Carnegie Institution of Washington (OCIW). It is scheduled to have KASI side Critical Design Review in December 2017. In this presentation we will report the recent progress on the critical design activities for the G-CLEF Flexure Control Camera (FCC).

• 천문학회보
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• 제42권2호
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• pp.61.2-61.2
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• 2017

We report a fine scale transient brightening event near a pore boundary with the Fast Imaging Solar Spectrograph (FISS) of the 1.6m Goode Solar Telescope (GST), the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO), and Helioseismic and Magnetic Imager (HMI) aboard SDO. The event appears in all AIA extreme ultraviolet bands, also in the two FISS lines, $H{\alpha}$ and Ca II $8542{\AA}$, and lasted for a minute. The brightening occurred at a footpoint of a loop. The conjugate brightening occurred at the other foot point outside the FISS field of view. The brightening near the pore exhibit a redshift of 4.3 km s-1 in the $H{\alpha}$ and about 2.3 km s-1 in Ca II line. Differential emission measure derived from 6 AIA EUV passbands and cloud model fitting of the two FISS lines indicate the temperature increase of between 10,000 and 20 MK at the main event. After the brightening, the upward mass motion appears in the AIA images. We discuss the physical implication of this brightening in the context of magnetic reconnection and coronal heating.

• 천문학회지
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• 제53권1호
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• pp.27-34
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• 2020

We report the detection of exoplanet candidates in orbits around HD 60292 and HD 112640 from a radial velocity (RV) survey. The stars exhibit RV variations with periods of 495 ±3 days and 613±6 days, respectively. These detections are part of the Search for Exoplanets around Northern Circumpolar Stars (SENS) survey using the fiber-fed Bohyunsan Observatory Echelle Spectrograph installed at the 1.8-m telescope of the Bohyunsan Optical Astronomy Observatory in Korea. The aim of the survey is to search for planetary or substellar companions. We argue that the periodic RV variations are not related to surface inhomogeneities; rather, Keplerian motions of planetary companions are the most likely interpretation. Assuming stellar masses of 1.7 ± 0.2M_⊙ (HD 60292) and 1.8 ± 0.2M_⊙ (HD 112640), we obtain minimum planetary companion masses of 6.5 ± 1.0M_Jup and 5.0 ± 1.0M_Jup, and periods of 495.4 ± 3.0 days and 613.2 ± 5.8 days, respectively.

• 천문학회보
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• 제35권1호
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• pp.68.2-68.2
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• 2010

We present near-infrared (NIR) spectra of 6 young stellar objects (YSOs) around the supernova remnant G54.1+0.3 obtained with TripleSpec, a slit-based NIR cross-dispersion echelle spectrograph on th 5-m Palomar Hale telescope covering the entire NIR atmospheric window of 1-2.4 micron. These YSOs, whose formation was possibly triggered by the progenitor of G54.1+0.3, show significant mid-infrared (MIR) excess and have been proposed to be late O- and early B-type YSOs based on their spectral energy distribution. Our TripleSpec observations reveal the existence of strong H and He I lines, consistent with the previous interpretation of their spectral types, while the absence of Br-gamma emission line indicates that the YSOs do not have a nearby circumstellar disk. We discuss the relation between these YSOs and G54.1+0.3 based on the TripleSpec data and previous photometric data as well.

• 천문학회보
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• 제35권2호
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• pp.73.1-73.1
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• 2010

Using the spectroscopic data secured with the Hamilton Echelle Spectrograph attached to a 3-m telescope at the Lick Observatory, we derived the expansion velocities from various line profiles in the 3600 $\AA$ to 10,000 $\AA$ based on the full width at half maximum and double peak of the high dispersion line profiles. The symmetrical shapes of the permitted line profiles indicate that the permitted line zone is symmetrical e.g., a spherical shell or bipolar + torus structures, which might be evidence of relatively recent ejection from the central star. Most other stronger forbidden lines might be coming from a main shell which appears as a bilateral symmetrical morphology, seen in HST and other ground-based telescopic images. The overall expansion velocities of this main shell structure that are responsible for most lines, seem to show the Hubble type expansion, i.e., accelerating shell. The faster expansion velocities of the permitted OII, NII, NIII and perhaps CII lines that do not suit to the Hubble type expansion, imply the existence of a somewhat smaller inner shell inside the outer main shell. We conclude that the nebular shell consists of a swiftly expanding inner shell and an outer normal shell excited by a central star of about 55,000K. The former compact zone appears to be responsible for the permitted C, N, and O lines while the latter extended shell appears to be responsible for H, He, and forbidden lines. We present some evidence that NGC 6833 be a member of the Galactic halo.

• 천문학회보
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• 제35권1호
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• pp.32.1-32.1
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• 2010

KASI's Solar and Space Weather Research Group (SSWRG) is actively involved in solar and space weather research. Since its inception, the SSWRG has been utilizing ground-based assets for its research, such as the Solar Flare Telescope, Solar Imaging Spectrograph, and Sunspot Telescope. In 2007 SSWRG initiated the Korean Space Weather Prediction Center (KSWPC). The goal of KSWPC is to extend the current ground observation capabilities, construct space weather database and networking, develop prediction models, and expand space weather research. Beginning in 2010, SSWRG plans to expand its research activities by collaborating with new international partners, continuing the development of space weather prediction models and forecast system, and phasing into developing and launching space-based assets. In this talk, we will report on KASI's recent activities of international collaborations with NASA for STEREO (Solar Terrestrial Relations Observatory), SDO (Solar Dynamic Observatory), and Radiation Belt Storm Probe (RBSP).

• 천문학회보
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• 제35권1호
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• pp.32.2-32.2
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• 2010

The Korean Solar Radio Burst Locator (KSRBL) is a single dish radio spectrograph, which is designed to record the spectra of microwave (0.5 - 18 GHz) bursts with 1 MHz spectral resolution and 1 s time cadence, and locate their positions on the solar disk within 2 arcmin. It was installed at KASI in 2009 August, and operational thereafter. The antenna pointing coefficients were initially determined during the installation and refined later using a series of antenna pointing calibrations. The filter to prevent the radio frequency interference around 2 GHz was designed and is to be installed. After the installation, the full frequency coverage will be recovered from the temporarily restricted frequency coverage (5 - 14 GHz). Also an effort to solve a couple of minor problems for the full performance of the system is in progress.

• 천문학회보
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• 제35권2호
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• pp.68.1-68.1
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• 2010

Cassiopeia A supernova remnant is a young (~330 yr) remnant of Type IIb SN explosion with a massive progenitor. It shows two distinct optical knots; fast moving ejecta knots (FMKs) and quasi stationary circumstellar knots (QSFs). These knots offer an unique opportunity to explore the details of the explosion and also the end state evolution of the Type IIb SN progenitor. We have obtained NIR long-slit (30") spectra of 7 positions around the bright rim of Cas A in [Fe II] 1.644 micron using Triplespec which is a cross-dispersed near-infrared spectrograph that provides continuous wavelength coverage from 0.95-2.46um at intermediate resolution of 2700. Most of the FMKs show strong sulfur, silicon, and iron forbidden lines but no hydrogen or helium lines. The QSFs, on the other hand, show a much richer spectrum with strong hydrogen, helium, and iron lines, but no sulfur and silicon lines. We measure their fluxes and radial velocities, and derive their physical parameters such as electron density and temperature. We also measure the proper motion of these knots from two [Fe II] 1.644 micron images obtained at 3-year interval. We analyze the physical properties of these knots and discuss the evolution and explosion of the progenitor of Cas A.

• 천문학회보
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• 제35권1호
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• pp.55.2-55.2
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• 2010

We present a photometric and spectroscopic study of the globular clusters (GCs) in the giant elliptical galaxy NGC 4636 in the Virgo cluster. The photometry of the GCs is based on HST/WFPC2 images for the inner region and deep, wide field Washington $CT_1$ CCD images for the outer region. We investigated the color distribution, the radial number density profile, the spatial distribution, and the mean color of the bright blue GCs about the GCs in NGC 4636. We obtained spectra of the GC candidates in NGC 4636 using the Multi-Object Spectroscopy (MOS) mode of Faint Object Camera and Spectrograph (FOCAS) on the SUBARU 8.2m Telescope. We measured the velocities for 105 GCs in NGC 4636. Using the 238 GCs obtained from combining our results with data in the literature, we investigated the kinematics of the GC system of NGC 4636: the rotation, the velocity dispersion, the radial variation, and the orbit. We also investigated the distribution and the radial variation of the metallicities, ages, and alpha-elements of the GCs in NGC 4636 derived using the absorption lines. We compared the GC kinematics of NGC 4636 with those of other six gEs, finding that the kinematic properties of the GCs are diverse among gEs. We found several correlations between the kinematics of the GCs and the global parameters of their host galaxies. Finally we discuss the implication of the results for the formation models of the GC system in gEs, and suggest a mixture scenario for the origin of the GCs in gEs.