[ Korean ]
[ Curriculum Vitae | Research Interests | Current Projects | Recent Publications ]
- Associate Professor, Chungbuk National University.
- Sr. Research Astronomer in KAO, 2000.- 2002.2
- BrainPool Scientist in KASI & KOSEF, 1997-1999.
- PostDoc and Research Astronomer in Phys. & Astronomy, UCLA, 1992 -1996
- Ph.D. in Astronomy, University of California, Los Angeles, 1992.3
- (M.S. in Astronomy, Yonsei University, 1985)
- B.S. in Astronomy, Yonsei University, 1983
- Galactic Planetary Nebulae
- Symbiotic Stars
- Emission Line Galaxies (HII regions, AGNs) (Korean)
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Our objective is to investigate the gaseous state of the PNs, galaxies and AGNs, utilizing the spectrographic and narrow filter imaging techniques. Many strategically important diagnostic lines of these celestial objects, e.g. [OIII]4959/5007,4363, [OII]3727, [SII]6717/31, obtainable with the medium to high dispersion spectrometer, would provide an useful information on the physical states. Planetary nebulae, symbiotic stars, and super nova remnants could be studied with relatively small aperture telescopes such as BOAO 1.8m telescope, while AGNs, such as those of Seyferts and Quasars, may require a relatively large aperture telescope. To achieve our goal, we plan to obtain the observing time of the large optical telescopes. The other approach is to study the narrow band images using the computer simulation technique of hydrodynamic codes.
We have carried out the research program on PNe and symbiotics, mainly collaborating with Lawrence H. Aller (UCLA) and Walter A. Feibelman (NASA) using the Lick 3-m telescope. Our study on the galaxies began with the nearby Seyfert galaxies from Malkan et al.'s recent HST survey list (1998). According to the unified hypothesis, the viewing direction causes the difference between Seyfert 1s and Seyfert 2s, while the statistical result contradicts this popular scheme. The other possibility would be that the excess galactic dust may absorb the BLR emission of Seyfert 2s. With a number of HST archive images of nearby Seyfert galaxies, we try to find the nature and location of the absorbers in Seyfert 2s. We also try to find the connection between the morphologies of circumnuclear region and host galaxy. We investigated the HST WFPC2 (gaseous) and NICMOS (dust) imagings of nuclear regions to see whether the strong barred potentials exist, whose presence might indicate a primary mechanism of driving gas into the nuclear region. Since the gas easily transfers angular momentum to stars in strong bars, inner bars are likely candidates. We also investigate whether spiral arms which can be traced to the nucleus up to the limit of a few 10 pc (<0.1") can be a possible fueling mechanism. The velocity field of the ionized gas, secured with the adoptive optic imaging spectrograph, e.g. CFHT/OASIS, may provide a clue on the accretion flows or outflows of Seyfert AGNs.
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Specific goals are :
1) to study the formation and chemical evolution history of the Galactic PNe, constructing photo-ionization and gas-dynamic models;
2) to investigate chemical enrichments (by spectroscopically observing PNe, HII regions, SNRs) in nearby galaxies (such as M31 and M32)
3) to investigate the formation and evolution of distant galaxies and active galactic nuclei, utilizing the spectroscopic observational results.
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Members
Name
Title
Field (e-mail)
Current Affiliation
Hyung, Siek
Research Astronomer
Son, Dong-Hoon
Ph.D. candidate
KyungHee U./Astronomy
Kim, Yeo-Jeong
M.S. graduate
Chungnam Natl U./Astronomy
Kim, Hyouk
Ph.D. candidate
HanKuk Ed. U./Astronomy
Han, Soo Ryeon
M.S. graduate
HII region galaxies (spectra)
HanKuk Ed. U./Astronomy
Spectroscopy of Planetary Nebulae (PNe) (w/ Lawrence H. Aller(UCLA), Walter A. Feibelman(NASA))
- During the asymptotic giant branch (AGB) phase, 1 - 8 M stars eject large amounts of matter. Nuclear burning takes place in shells near the abundance discontinuities. Quiescent hydrogen shell burning is interrupted by helium shell flashes and leave the AGB during a helium shell flash. Wolf-Rayet (WR), especially WC type spectra are shown by a number of central stars (CSPNs), lthough these stars obviously belong to an older population and are less massive and less luminous than their Pop. I relatives. The idea that WR-type CSPNs come directly from the AGB stars which form their planetary nebulae, has been accepted as a most likely evolutionary scenario. The difference between an AGB star and a CSPN is that the hydrogen envelope in the CSPN is much less massive ( <10^{-3} M). A kinematic study suggests peculiar motions in the central part of WR type PNs, e.g. being the expansion velocity larger in [OIII] than in HI. High resolution IUE spectra of these CSPNs exhibit changes in the shape of their P Cygni profiles up to levels of 10% -- 50% in time scales of years, analogous to similar time scale variations exhibited by hot stars of Pop. I. At first sight, the PNs surrounding the WR-type CSPNs do not seem to differ significantly from the rest of PN population. However, since the CSPN creates the PN and it governs its subsequent evolution, one can expect the chemical abundance anomaly in these objects, different from the rest of PNs. Detailed Hamilton echelle spectroscopy secured on a few bright spot(s) indicates point to point changes of the excitation and chemical abundances. [ Top ]
Hydrodynamic Simulation of PNe and AGNs (w/ SeongJae Lee, Dongsu Ryu)
- Some PNe show a faint giant halo. For example,a mutiple shell PN, NGC 6543, of which the faint outer halo is thought to be the remnants of the original red giant wind. The HST/WFPC2 [OIII] narrow band filter images indicate much higher temperatures in the outer halo region than in the inner bright core, i.e. 15000 K vs. 8500 K (Kim et al 1999). Using ISA-Wind non-LTE unified model atmospheres, we have determined the basic parameters of the central star and the bright H II region core of NGC 6543. The temperature of the filamentaries in the halo region might become higher when the hot fast wind flows past them (BOW-SHOCK HEATING). The origin of filamentary structures, however, was not known. Using both SPH and TVD code simulations, we investigate whether the filamentary blobs can be formed due to a pulsation of the central star in its evolutionary phase, RGB stage. The shock heating temperatures in the halo are also derived from our simulation.
- If AGNs in Seyferts are powered by the accretion of matter onto massive black holes, how does the gas in the host galaxy approach the black hole? Since gas easily transfers angular momentum to stars in strong bars, inner bars are likely candidates. The episodic and self-regulating process of cutting off (turning off) the AGN and re-developing short-lived (~10^7 yrs) runaway bar instabilities may exist. The NICMOS imaging of nuclear dust morphology suggests that the strong barred potentials cannot be a primary mechanism of driving gas into the nuclear region (Regan & Mulchaey 1999), though. Alternatively, spiral arms which can be traced to the nucleus up to the limit of a few 10 pc (<0.1'') may be a possible fueling mechanism. What is the role of hydro-magnetic winds which originate from an accretion disk or the black hole (Blanford 1993)? Are there radiation-driven winds from evaporating molecular clouds at the inner edge of the torus (Balsara & Krolik 1993)? Can the photo-ionizing shocks in the BLR power the extended narrow emission zone? We may be able to get some of hints by studying the circumnulcear structures, e.g. disk or ring; it rotation or interaction, shock, photo-ionization, etc. [ Top ]
Active Galactic Nuclei (AGNs) (w/ Eon.C. Sung, SeongJae Lee, J. Rhee, Heewon Lee)
- In order to constraint the different models for accretions and outflows (along with excitation characteristics) of Seyfert galactic nuclei, we propose to map the velocity fields and diagnostic structures of the circumnuclear region. According to a popular unified hypothesis, the viewing direction causes the difference between Seyfert 1s and Seyfert 2s, while the statistical result contradicts this popular scheme. Alternatively, the excess galactic dust may be responsible for absorbing the BLR emission of Seyfert 2s. We have selected 5 Seyfert galaxies (unaffected by dust patches) to find the nature and location of the absorbers (other than the galactic dust). The OASIS/PUEO will be useful to find nebular diagnostic line ratios at 0.11 arcsec (~ a few 100 pc) spatial resolution over the narrow emission line region (NLR) clouds. We will try to separate the core regions that might contain the broad line region (BLR), hidden in the case of Seyfert 2 galaxies, from the NLR. The chemical abundance gradient within the OASIS field (~ 3" or a few kpc) will be also investigated. [ Top ]
Evolutionary connection between Planetary-Formation and Interstellar Matter (collaboration with S.J. Kim,, Y.H., Kim, Y.H. Kim)
- The major goal is: to derive abundances of neutrals and ions in comets, giant planets, local interstellar media, and planetary nebulae; to study chemical connections among these celestial objects; and to eventually clarify the evolutional processes of matter from planetary nebula mass loss through local interstellar media and proto-solar nebula to the formations of comets and planets. In order to unambiguously explain this evolutional path, we will conduct spectroscopic observations to identify new matter, derive abundances of neutrals and ions in these celestial objects, study chemical reactions among neutrals and ions in these celestial objects, and perform spectroscopic observations from ultraviolet through visible and infrared to radio spectral ranges. We will utilize cutting-edge instrument available in modern western observatories in addition to domestic astronomical instrument, and therefore, the outputs from the proposed research are anticipated to be scientifically excellent. Successful results from the proposed research will establish a realistic theory of the formation of the solar system compared with existing formation scenarios. Furthermore, our interdisciplinary research will greatly contribute in an effort to bridge the existing academic gap between planetary science and interstellar medium astronomy. Our scientific results in the spectroscopic areas will stimulate chemists who are conducting researches in spectroscopic and chemical reaction areas. Our spectroscopic observations from ultraviolet to radio regions will also contribute greatly in the advancement of spectroscopic instrument. [ Top ]
Symbiotic Stars (w/ YeoJeong Kim)
- Symbiotic stars known as binary systems with both cool and hot components with enshrounding nebulous gas. The cool component, M-type giant, is presumably loosing its mass into a hot white or main sequence companion star through the inner Lagrangian point, The lines emit from the ionized nebulous region around the hot star while the mass loss or accretion activity is believed to be the main cause of sudden variation of the continuum and line fluxes. With the IUE archival data and the ground based telescopic optical data, we tried to investigate the physical condition of the emission line region.
Supernova Remnants (w/ Hyouk Kim)
H II regions/Planetary Nebulae in Nearby Galaxies (w/ SooRyeon Han, YoungKwang Kim)
- Utilizing the spectum published in the literatures, e.g. CFHT/MOS by by Richer et al (1994), we are modeling the M 31 and M 32 bulge planetary nebulae. Most of planetary nebulae in M 31 and M32 showed the [{O {\sc III}}] $\lambda$ 4363/5007. With these line ratios and the [OII]3727/3729, we determined the electron temperatures and number densities. With the Nebula code (Hyung, 1994), we construct a simple model for each object which can fit the line intensities and diagnotic temperatures. The derived chemical abundances are compared with those of the
well-known Galactic planetary nebulae, such as NGC 7027, NGC 7009, and NGC 7662.[ Top ]
Recent Publications (selected from Hyung et al.)
2003
- Pottasch, S. R.; S. Hyung; Aller, L. H.; Beintema, D. A.; Bernard-Salas, J.; Feibelman, W. A.; Kloumlckner, H.-R. Abundances of the planetary nebula Hu 1-2 2003A&A.401.205
- Keenan, F. P.; Aller, L. H.; Exter, K. M.; S. Hyung; Pollacco, D. L. Emission Lines of [Cl II] in the Optical Spectra of Gaseous Nebulae, 2003ApJ.584.385
2002
- S. Hyung. Lee, Seong-Jae , Halo Emission of the Cat's Eye Nebula, NGC 6543 Shock Excitation by Fast Stellar Winds, 2002JASS.19.173
- S. Hyung, Aller, L. H.; Kim, S. Ionization Models for Axi-symmetrical Objects or Jets, 2002RMxAC.12.82
- Aller, Lawrence H.; L. H. S. Hyung High Dispersion Spectra for Planetary Nebula Studies,2002RMxAC.12.95
2001
- S. Hyung, Aller, Lawrence H.; Feibelman, Walter A.; Lee, Seong-Jae, Optical Spectrum of the Compact Planetary Nebula IC 5117, 2001ApJ.563.889
- S. Hyung, Aller, Lawrence H.; Lee, Woo-baik, Spectroscopic Observation of the Planetary Nebula IC 4846, 2001PASP.113.1559
- S. Hyung. Aller, Lawrence H.; Feibelman, Walter A.; Lee, Woo-Baik, Abundances in the Planetary Nebula IC 5217, 2001AJ.122.954.
- S. Hyung, Mellema, G.; Lee, S.-J.; Kim, H., The electron temperature of the inner halo of the Planetary Nebula NGC 6543, 2001A&A.378.587
2000
- S. Hyung, L.H. Aller, W.A. Feibelman, W.B. Lee, A. de Koter, The Optical Spectrum of the Planetary Nebula NGC 6543, MNRAS, in press (ngc6543.tar.gz) (mns, fig1a, fig1b)
- S.J. Kim, Y.C. Minh, S. Hyung, Y.H. Kim, High Resolution Optical and Infrared Observations of Molecules in Commets, 2000, eds. Y.C. Minh \& E. F. van Dishoeck (ASP), IAU Symposia p. 471
- H.W. Lee, S. Hyung. Broad H alpha Wing formation in the Planetary Nebula IC 4997, 2000, ApJL, 530, 49
- F. P. Keenan, C. A. Ramsbottom, . H. Aller, K. L. Bell, F. L. Crawford, S. Hyung, Nebular and auroral emission lines of [Cl III] in the optical spectra of planetary nebulae, 2000, Proc. Natioanl Academy of Sci, USA. 97, 4551.
1999
- S. Hyung, L. H. Aller, W. A. Feibelman, Chemical Abundances of the Planetary Nebula IC 4634, 1999, Astrophysical Journal, 525, 294
- S. Hyung, L. H. Aller, W. A. Feibelman, Spectroscopic Observations of the Planetary nebula NGC 6818, 1999, Astrophysical Journal, 514, 878 )
- L. H. Aller, S. Hyung, W. A. Feibelman, A remarkable High Excitation Planetary Nebula NGC 6537, 1999, Proc. of National Academy of Science, USA. 96, 5366 (1999).
1998
- F.P. Keenan, L.H. Aller, K.L. Bell, B.R. Espey, W.A. Feibelman, S. Hyung, F.C. McKenna, C.A. Ramsbottom, Forbidden emission lines of [Ne IV] in the optical and ultraviolet spectra of gaseous nebulae, 1998, Monthly Notice of Royal Astronomical Soc., 295, 683.
- S. Hyung, and L.H. Aller, The Optical Spectrum of the Planetary Nebula NGC 2440, 1998, Pub. Astron. Soc. of Pacific, 110, 466.
1997
- S. Hyung, and L.H. Aller, The High Excitation Planetary Nebula, NGC 6741, 1997, Monthly Notice of Royal Astronomical Soc., 292, 71.
- S. Hyung, L.H. Aller, and W.A. Feibelman, The spectrum of the Planetary nebula NGC 6884, 1997, Astrophysical J. Suppl., 108, 503.
- F.P. Keenan, F.C. McKenna, K.L. Bell, C.A. Ramsbottom, A.W. Wickstead, L.H. Aller, S. Hyung, A. Hibbert, Nebular and Auroral Emission Lines of [Ar IV] in The Optical Spectra of Planetary Nebulae, 1997, Astrophysical J., 487, 457.
- S. Hyung, and L.H. Aller, The High Excitation Planetary Nebula, NGC 7662, 1997, Astrophysical J., 491, 242.
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Prof. Hyung, Siek
Science of Education (Astronomy, Education Building 82-114)
ChungBuk National University
48 Gaeshin-dong Heungduk-gu, CheongJu
ChungBuk 361-763
S. KOREA
- (e-mail) hyung@chungbuk.ac.kr/ (phone) 82-43-261-2726 / (fax) 82-43-271-0526
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[ Curriculum Vitae | Research Interests | Current Projects | Recent Publications ]