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Sooyoung Kim. Achievements. American Astronomical Society Meeting (2007. 1.4-1.10 Seattle, USA)   Poster presentation on “ Are There Two Distinct Globular Cluster Sub-systems in Elliptical Galaxies ?” Korean Astronomical Society Meeting (2007 . 4. 11-4.13, Jeju -do, Korea)

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  • American Astronomical Society Meeting (2007. 1.4-1.10 Seattle, USA)  

Poster presentation on “Are There Two Distinct Globular Cluster Sub-systems in Elliptical Galaxies?”

  • Korean Astronomical Society Meeting (2007. 4. 11-4.13, Jeju-do, Korea)


  • The First Subaru Conference (2007.12.10-12.16, Hayama, Japan)

Poster presentation on “SUBARU/FOCAS Multi-Object Spectroscopy of M87 Globular Clusters : How is Globular Cluster Colour Bimodality Interpreted?”

  • Korea-Japan Workshop (2008.01.21-01.23, Seoul, Korea)

Oral presentation on “SUBARU/FOCAS Multi-Object Spectroscopic study of M87 Globular Cluster System”

research in progress
Research in Progress


We are investigating the spectra of more than 130 GCs associated with the Virgo giant elliptical galaxy M87, obtained using the Subaru/FOCAS MOS mode. The spectroscopic data on the GCs carefully selected to represent the galaxy’s GC system enable us to derive the metallicity-colour relations, the most popular tools to extracting GC metallicity distribution functions (MDFs). The data are critical for testing the recent theoretical prediction of a significant inflection along the relations. If confirmed, the non-linearity of the relations would have far-reaching implications as this could cause GCs with a unimodal MDF to exhibit a bimodal colour distribution as found in M87. Furthermore, with the large sample acquired from the observation, we analysing abundance ratios and age structure of the M87 GCs. A thorough analysis of the data is underway towards the goal of obtaining more accurate information on the properties of M87 GC system, through which we expect to place a robust constraint on the formation theory of GCs and the host galaxy.

[MgFe] and Mgb indices are a good metallicity indicators and are plotted as a function of V-I colour. Overlaid blue dotted lines are predictions from YEPS SSP for 12Gyr, [α/Fe]=0.3 (Chung et al. in prep).

Balmer line indices are known to be good stellar age indicators, while [MgFe] traces metallicity. The plots compare the index measurements for M87 GCs with model grids from YEPS to disentangle the age-metallicity degeneracy. The models are shown for ages of 1,3,5,8,11 and 13 Gyr (Top to bottom) and metallicities [Fe/H]=-2.2, -1.3, -0.3, 0.0, 0.3 and 0.7 (left to right) for [α /Fe]=0.3. The heavier lines represent 13Gyr.

masters thesis
Masters Thesis
  • in Astrophysics by Univ. of Manchester, Jodrell Bank Observatory, 2004, on “Investigating Blending Problems in Galactic Microlensing”
  • Supervisor : Dr. Shude Mao
  • Abstract

The blending of source stars in Galactic microlensing is one of the largest uncertainties in analysing microlensing data. The flux contamination by other stars which are not associated with lensing is an important issue, since microlensing searches are conducted towards dense stellar fields (e.g. Galactic Bulge). In this thesis, we analyse the blending of bright source stars such as Red Clump Giants (RCGs), as they are thought to be less vulnerable to the blending problem. We produced colour-magnitude diagrams (CMDs) of the 49 OGLE II Galactic bulge fields. By plotting the microlensing events on these CMDs we found that ~20% of the visually selected RCG events exhibit a substantial amount of source star blending.

Another way of investigating blending is through the analysis of causitc crossing binary microlensing events. Using these events, we probe the distribution of the blending parameter (i.e. the ratio of the source flux to the blended flux). We show that in comparison with the single lens distributions, the binary lens distribution has far fewer weakly blended events. However, both single and binary distributions exhibit a large fraction of severely blended events.

Finally, we analyse two heavily blended, long duration events utilising the high resolution of the Hubble Space Telescope (HST) data. These events are of particular importance, since hey are likely to be caused by stellar mass black holes. The blending parameters from this analysis are found to be roughly consistent with the expected values.

papers in preparation
Papers in Preparation
  • “SUBARU/FOCAS Multi-Object Spectroscopic Study of M87 Globular Cluster System. II”
  • “SUBARU/NIR Study of Elliptical Galaxies and their Globular Clusters”

Subaru Telescope, NAOJ

The MultimissionArchive at STScI