Eunhyeuk Kim - Academia.edu (original) (raw)

Papers by Eunhyeuk Kim

We have studied the dynamical evolution of rotating star clusters with mass spectrum using a Fokk... more We have studied the dynamical evolution of rotating star clusters with mass spectrum using a Fokker-Planck code. As a simplest multi-mass model, we first investigated the two-component clusters. Rotation is found to accelerate the dynamical evolution through the transfer of angular momentum outward, as well as from the high masses to the low masses. However, the degree of acceleration depends sensitively on the assumed initial mass function since dynamical friction, which generates mass segregation, also tends to accelerate the evolution, and the combined effect of both is not linear or multiplicative. As long as dynamical friction dominates in the competition with angular momentum exchange the heavy masses lose random energy and angular momentum, sink towards the centre, but their remaining angular momentum is sufficient to speed them up rotationally. This is gravo-gyro instability. As a consequence, we find that the high mass stars in the central parts rotate faster than low mass ...

We present the first post core collapse models of initially rotating star clusters, using the num... more We present the first post core collapse models of initially rotating star clusters, using the numerical solution of an orbit-averaged 2D Fokker-Planck equation. Based on the code developed by Einsel & Spurzem (1999), we have improved the speed and the stability and included the steady three-body binary heating source. We have confirmed that rotating clusters, whether they are in a tidal field or not, evolve significantly faster than non-rotating ones. Consequences for observed shapes, density distribution, and kinematic properties of young and old star clusters are discussed. The results are compared with gaseous and 1D Fokker-Planck models in the non-rotating case.

We present wide-field multiband photometry of globular cluster (GC) systems in NGC 1399, NGC 1404... more We present wide-field multiband photometry of globular cluster (GC) systems in NGC 1399, NGC 1404, and NGC 1387 located at the central region of the Fornax galaxy cluster. Observation was carried out through U, B, V, and I bands, which marks one of the widest and deepest U-band studies on extragalactic GC systems. The present U-band photometry enables us to significantly reduce the contamination by a factor of two for faint sources (Vo~23.5). The main results based on some 2000 GC candidates around NGC 1399, NGC 1404, and NGC 1387 are as follows: (1) the GC system in each galaxy exhibits bimodal color distributions in all colors examined, but the shape of color histograms varies systematically depending on colors; (2) NGC 1399 shows that the mean colors of both blue and red GCs become bluer with increasing galactocentric radius; (3) NGC 1399 shows overabundance of GCs in the directions of NGC 1404 and NGC 1387, indicating their ongoing interactions; and (4) NGC 1399 also exhibits a ...

Abstract. We present a preliminary analysis of HST-WFPC2 observations of globular cluster systems... more Abstract. We present a preliminary analysis of HST-WFPC2 observations of globular cluster systems in the two brightest galaxies, UGC 9799 (cD) and NGC 1129 (non-cD), located in the center of rich clusters. UGC 9799 is a cD galaxy located in the center of the massive Abell 2052 cluster at z=0.035, and is known to have the largest number of the globular clusters (N(total) ≈ 46,000) and the highest specific frequency of globular clusters from the ground-based observations (SN = 20 ± 6, Harris, Pritchet, & McClure 1995). On the other hand, NGC 1129 is a giant, but not cD galaxy, located in the center of a rich cluster AWM7 at z=0.018. Its globular cluster system has not yet been studied. The foreground reddenings are known to be E(V −I) = 0.051 for UGC 9799 and E(V − I) = 0.159 for NGC 1129. We adopt the redshift distance modulus (m − M)0 = 36.0 for UGC 9799 and (m − M)0 = 34.5 for NGC 1129 based on the Hubble constant of H0 = 65 km/s/Mpc. Deep images of these galaxies were obtained usi...

Fokker-Planck simulations for rotating star clusters: I. Equal-mass system

We have carried out comparative study between direct N-body technique and Fokker-Planck approach ... more We have carried out comparative study between direct N-body technique and Fokker-Planck approach for the dynamical evolution of rotating stellar systems. Because of limitations of computing resources, we have restricted to relatively small N (» 10,000) systems compared to realistic star clusters. We found that these two difierent approached generally give very similar results. Some minor difierences are found to exist, but they can be understood because Fokker-Planck approach has to make some simplifying assumptions.

Symposium - International Astronomical Union

We present a preliminary analysis of HST-WFPC2 observations of globular cluster systems in the tw... more We present a preliminary analysis of HST-WFPC2 observations of globular cluster systems in the two brightest galaxies, UGC 9799 (cD) and NGC 1129 (non-cD), located in the center of rich clusters.

Symposium - International Astronomical Union

A two color CCD survey for globular clusters in the galactocentric range from 2 to 7 arcmin from ... more A two color CCD survey for globular clusters in the galactocentric range from 2 to 7 arcmin from the galaxy centers is presented for NGC 1399 and NGC 4486 (M87), two systems that, for a long time, have been considered as class archetypes of the so called “high specific frequency phenomenon”. The new results, combined with previously published HST data for the inner 2 arcmin, and with a re-discussion of the surface brightness profiles, allow a new estimate of the globular cluster specific frequencies. The resulting SN values cannot be considered as anomalously large and, rather, they are consistent with values obtained for other galaxies with similar morphologies.

Symposium - International Astronomical Union, 2003

The impact of rotation on the relaxational dynamics of dense stellar systems is reviewed; while i... more The impact of rotation on the relaxational dynamics of dense stellar systems is reviewed; while in the past linear stability analysis and a few N-body models existed only, we report recent advances in the technique of 2D Fokker-Planck models for axisymmetric rotating star cluster, now extending into the post-core collapse phase. It is confirmed that rotating clusters, whether they are in a tidal field or not, evolve significantly faster in pre-collapse than non-rotating ones, while in post-collapse only those in a tidal field keep their larger speed of evolution. Consequences for observed shapes, density distribution, and kinematic properties of young and old star clusters are discussed.

Symposium - International Astronomical Union, 1996

NGC 4472 (M49) is a giant elliptical galaxy in the Virgo cluster, and has a rich GCS. Radial surf... more NGC 4472 (M49) is a giant elliptical galaxy in the Virgo cluster, and has a rich GCS. Radial surface density profiles of the GCS in this galaxy are well-known (Cohen 1988, Harris 1986). However, little information is available for the ellipticity (e) and position angles of the GCS in NGC 4472. In this study we have investigated in detail the spatial structures of the GCS in NGC 4472 (the surface density, the ellipticity, the color, and the position angle) in comparison with those of the halo, using a large sample of the globular clusters located in a wide field (16′ × 16′) of NGC 4472.

Symposium - International Astronomical Union, 1996

NGC 4472, the brightest elliptical galaxy in the Virgo cluster, has a rich globular cluster syste... more NGC 4472, the brightest elliptical galaxy in the Virgo cluster, has a rich globular cluster system. We present a study of the metallicity and luminosity functions of a large number of globular clusters in NGC 4472. Deep Washington CT1 photometry of a wide (16′ × 16′) field of NGC 4472 was obtained using Tek 2048 × 2048 CCD at the KPNO 4m telescope.

Journal of the Korean Astronomical Society, Sep 29, 1994

We have detected a SiO maser line(v = 1, J = 2-1) for 15 stars out of about 80 long period variab... more We have detected a SiO maser line(v = 1, J = 2-1) for 15 stars out of about 80 long period variables in the wide range of period. No new sources are detected; all detected sources are variables with period longer than 300 days; no evidence is found that the dust grains in the outer envelope have influenced on this

Astronomische Gesellschaft Abstract Series, 1999

We have studied the dynamical evolution of rotating star clusters with mass spectrum using a Fokk... more We have studied the dynamical evolution of rotating star clusters with mass spectrum using a Fokker-Planck code. As a simplest multi-mass model, we first investigated the two-component clusters. Rotation is found to accelerate the dynamical evolution through the transfer of angular momentum outward, as well as from the high masses to the low masses. However, the degree of acceleration depends sensitively on the assumed initial mass function since dynamical friction, which generates mass segregation, also tends to accelerate the evolution, and the combined effect of both is not linear or multiplicative. As long as dynamical friction dominates in the competition with angular momentum exchange the heavy masses lose random energy and angular momentum, sink towards the centre, but their remaining angular momentum is sufficient to speed them up rotationally. This is gravo-gyro instability. As a consequence, we find that the high mass stars in the central parts rotate faster than low mass ...

We present the first post core collapse models of initially rotating star clusters, using the num... more We present the first post core collapse models of initially rotating star clusters, using the numerical solution of an orbit-averaged 2D Fokker-Planck equation. Based on the code developed by Einsel & Spurzem (1999), we have improved the speed and the stability and included the steady three-body binary heating source. We have confirmed that rotating clusters, whether they are in a tidal field or not, evolve significantly faster than non-rotating ones. Consequences for observed shapes, density distribution, and kinematic properties of young and old star clusters are discussed. The results are compared with gaseous and 1D Fokker-Planck models in the non-rotating case.

We present wide-field multiband photometry of globular cluster (GC) systems in NGC 1399, NGC 1404... more We present wide-field multiband photometry of globular cluster (GC) systems in NGC 1399, NGC 1404, and NGC 1387 located at the central region of the Fornax galaxy cluster. Observation was carried out through U, B, V, and I bands, which marks one of the widest and deepest U-band studies on extragalactic GC systems. The present U-band photometry enables us to significantly reduce the contamination by a factor of two for faint sources (Vo~23.5). The main results based on some 2000 GC candidates around NGC 1399, NGC 1404, and NGC 1387 are as follows: (1) the GC system in each galaxy exhibits bimodal color distributions in all colors examined, but the shape of color histograms varies systematically depending on colors; (2) NGC 1399 shows that the mean colors of both blue and red GCs become bluer with increasing galactocentric radius; (3) NGC 1399 shows overabundance of GCs in the directions of NGC 1404 and NGC 1387, indicating their ongoing interactions; and (4) NGC 1399 also exhibits a ...

Abstract. We present a preliminary analysis of HST-WFPC2 observations of globular cluster systems... more Abstract. We present a preliminary analysis of HST-WFPC2 observations of globular cluster systems in the two brightest galaxies, UGC 9799 (cD) and NGC 1129 (non-cD), located in the center of rich clusters. UGC 9799 is a cD galaxy located in the center of the massive Abell 2052 cluster at z=0.035, and is known to have the largest number of the globular clusters (N(total) ≈ 46,000) and the highest specific frequency of globular clusters from the ground-based observations (SN = 20 ± 6, Harris, Pritchet, & McClure 1995). On the other hand, NGC 1129 is a giant, but not cD galaxy, located in the center of a rich cluster AWM7 at z=0.018. Its globular cluster system has not yet been studied. The foreground reddenings are known to be E(V −I) = 0.051 for UGC 9799 and E(V − I) = 0.159 for NGC 1129. We adopt the redshift distance modulus (m − M)0 = 36.0 for UGC 9799 and (m − M)0 = 34.5 for NGC 1129 based on the Hubble constant of H0 = 65 km/s/Mpc. Deep images of these galaxies were obtained usi...

Fokker-Planck simulations for rotating star clusters: I. Equal-mass system

We have carried out comparative study between direct N-body technique and Fokker-Planck approach ... more We have carried out comparative study between direct N-body technique and Fokker-Planck approach for the dynamical evolution of rotating stellar systems. Because of limitations of computing resources, we have restricted to relatively small N (» 10,000) systems compared to realistic star clusters. We found that these two difierent approached generally give very similar results. Some minor difierences are found to exist, but they can be understood because Fokker-Planck approach has to make some simplifying assumptions.

Symposium - International Astronomical Union

We present a preliminary analysis of HST-WFPC2 observations of globular cluster systems in the tw... more We present a preliminary analysis of HST-WFPC2 observations of globular cluster systems in the two brightest galaxies, UGC 9799 (cD) and NGC 1129 (non-cD), located in the center of rich clusters.

Symposium - International Astronomical Union

A two color CCD survey for globular clusters in the galactocentric range from 2 to 7 arcmin from ... more A two color CCD survey for globular clusters in the galactocentric range from 2 to 7 arcmin from the galaxy centers is presented for NGC 1399 and NGC 4486 (M87), two systems that, for a long time, have been considered as class archetypes of the so called “high specific frequency phenomenon”. The new results, combined with previously published HST data for the inner 2 arcmin, and with a re-discussion of the surface brightness profiles, allow a new estimate of the globular cluster specific frequencies. The resulting SN values cannot be considered as anomalously large and, rather, they are consistent with values obtained for other galaxies with similar morphologies.

Symposium - International Astronomical Union, 2003

The impact of rotation on the relaxational dynamics of dense stellar systems is reviewed; while i... more The impact of rotation on the relaxational dynamics of dense stellar systems is reviewed; while in the past linear stability analysis and a few N-body models existed only, we report recent advances in the technique of 2D Fokker-Planck models for axisymmetric rotating star cluster, now extending into the post-core collapse phase. It is confirmed that rotating clusters, whether they are in a tidal field or not, evolve significantly faster in pre-collapse than non-rotating ones, while in post-collapse only those in a tidal field keep their larger speed of evolution. Consequences for observed shapes, density distribution, and kinematic properties of young and old star clusters are discussed.

Symposium - International Astronomical Union, 1996

NGC 4472 (M49) is a giant elliptical galaxy in the Virgo cluster, and has a rich GCS. Radial surf... more NGC 4472 (M49) is a giant elliptical galaxy in the Virgo cluster, and has a rich GCS. Radial surface density profiles of the GCS in this galaxy are well-known (Cohen 1988, Harris 1986). However, little information is available for the ellipticity (e) and position angles of the GCS in NGC 4472. In this study we have investigated in detail the spatial structures of the GCS in NGC 4472 (the surface density, the ellipticity, the color, and the position angle) in comparison with those of the halo, using a large sample of the globular clusters located in a wide field (16′ × 16′) of NGC 4472.

Symposium - International Astronomical Union, 1996

NGC 4472, the brightest elliptical galaxy in the Virgo cluster, has a rich globular cluster syste... more NGC 4472, the brightest elliptical galaxy in the Virgo cluster, has a rich globular cluster system. We present a study of the metallicity and luminosity functions of a large number of globular clusters in NGC 4472. Deep Washington CT1 photometry of a wide (16′ × 16′) field of NGC 4472 was obtained using Tek 2048 × 2048 CCD at the KPNO 4m telescope.

Journal of the Korean Astronomical Society, Sep 29, 1994

We have detected a SiO maser line(v = 1, J = 2-1) for 15 stars out of about 80 long period variab... more We have detected a SiO maser line(v = 1, J = 2-1) for 15 stars out of about 80 long period variables in the wide range of period. No new sources are detected; all detected sources are variables with period longer than 300 days; no evidence is found that the dust grains in the outer envelope have influenced on this

Astronomische Gesellschaft Abstract Series, 1999