• The Bulletin of The Korean Astronomical Society
• /
• v.38 no.2
• /
• pp.74.2-74.2
• /
• 2013

Recent spectroscopic observations have provided evidences for the multiple stellar populations having different abundances in some massive globular clusters (GCs). In particular, some of these GCs show clear separations of red giant-branches (RGBs) in calcium narrow band photometry. In order to confirm the differences in heavy element abundances and radial velocities among multiple RGBs, we have performed the low-resolution spectroscopy for the RGB stars in these GCs. The spectral data were taken from the multi-object spectroscopic mode with WFCCD mounted on the du Pont 2.5m telescope in Las Campanas Observatory. In this talk, we will present our progress in the spectroscopic analysis of the RGB stars in these GCs.

• The Bulletin of The Korean Astronomical Society
• /
• v.38 no.2
• /
• pp.74.1-74.1
• /
• 2013

We have performed new narrow-band calcium photometry for Milky Way globular clusters (GCs) and detected multiple red giant branches (RGBs) in some massive GCs. Our new calcium filter was designed to avoid the CN contamination below $3883{\AA}$ and to measure only Ca II H&K lines. The fact that we are detecting multiple RGBs from the new filter is suggesting that they are indeed different in calcium abundance, which can only be produced by supernovae (SNe). Therefore, the presence of the multiple RGBs for the peculiar GCs in the calcium photometry is best understood if the later generation of stars are enhanced in some SNe products. In this talk, we will present our progress in the calcium photometry for the peculiar GCs showing the multiple RGBs.

• The Bulletin of The Korean Astronomical Society
• /
• v.38 no.2
• /
• pp.63.2-63.2
• /
• 2013

Unlike the conventional wisdom, observations made during the past decade have revealed that many globular clusters possess more than one stellar population. Here, we have discovered evidence for multiple red giant branches (RGBs) in the globular cluster NGC 6388 from the narrow-band Calcium and Str$\ddot{o}$mgren b & y (Caby) photometry. In order to confirm the difference in Calcium abundance, we have acquired the low resolution spectroscopy for these RGB stars. In this paper, we will present results of our photometry and hand in the preliminary results of spectroscopic observations.

• The Bulletin of The Korean Astronomical Society
• /
• v.36 no.2
• /
• pp.75.2-75.2
• /
• 2011

We present a new, year 2011 version of the Yonsei Evolutionary Population Synthesis (YEPS 2011) model for simple stellar populations. The standard YEPS employs the most up-to-date Yonsei-Yale stellar evolutionary tracks and the BaSeL flux libraries. The spectro-photometric model data of the entire parameter space are available at http://web.yonsei.ac.kr/cosmic/data/YESP.htm.

• The Bulletin of The Korean Astronomical Society
• /
• v.41 no.1
• /
• pp.32.3-32.3
• /
• 2016

The presence of multiple stellar populations is now well established in most globular clusters in the Milky Way. Here we show that two populations of RR Lyrae stars and the double red clump observed in the Milky Way bulge are another manifestations of the same multiple population phenomenon observed in halo globular clusters. We will discuss the implications of this result on the stellar populations and formation of early-type galaxies.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.2
• /
• pp.144.1-144.1
• /
• 2012

A number of recent observations have established that many globular clusters have double or multiple stellar populations. In particular, recent Calcium and Stromgren b & photometry shows a split in the RGB of some of these globular clusters, including M22, NGC 1851, and NGC 288. However, the origin of this split in the RGB is still controversial. In order to confirm the real difference in Calcium abundance between the two RGBs, we have performed low resolution spectroscopy for RGB stars in these globular clusters. The spectral data were obtained from WFCCD/duPont 2.5m telescope in Las Campanas Observatory. We found a significant bimodality of both Calcium and CN abundances in M22 and NGC 1851. NGC 288, however, shows a clear bimodality only in CN abundance.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.1
• /
• pp.70.1-70.1
• /
• 2019

Recent investigation of the APOGEE bulge stars by Zasowski et al. (2018) shows a fraction of stars enhanced in O, Ca, and Mg abundances. It is not clear, however, that this apparent ${\alpha}$-bimodality is reflecting a real feature or an artifact from spectral fitting. We will report our progress in understanding the nature and reality of this phenomenon. We will also discuss the spread in Na abundance among the inner bulge stars with respect to that observed among disk sample.

• The Bulletin of The Korean Astronomical Society
• /
• v.46 no.1
• /
• pp.29.2-29.2
• /
• 2021

Intracluster light (ICL) is composed of the stars diffused throughout the galaxy cluster but does not bound to any galaxy. The ICL is a ubiquitous feature of galaxy clusters and occupies a significant fraction of the total stellar mass in the cluster. Therefore, the ICL components are believed to help understand the formation and evolution of the clusters. However, in the numerical study, one needs to perform the high-resolution cosmological hydrodynamic simulations, which require an expensive calculation, to trace these low-surface brightness structures (LSB). Here, we introduce the Galaxy Replacement Technique (GRT) that focuses on implementing the gravitational evolution of the diffused ICL structures without the expensive baryonic physics. The GRT reproduces the ICL structures by a multi-resolution cosmological N-body re-simulation using a full merger tree of the cluster from a low-resolution DM-only cosmological simulation and an abundance matching model. Using the GRT, we show the preliminary results about the evolution of the ICL in the on-going simulations for the various clusters.

• The Bulletin of The Korean Astronomical Society
• /
• v.43 no.1
• /
• pp.31.1-31.1
• /
• 2018

While astronomers are working hard to detect the earliest galaxies and to follow their evolution to redshift z~0, they remain baffled by the present-day dichotomy between disky, star forming (aka late-type) galaxies and quiescent, spheroidal (aka early-type) galaxies. The key is to find galaxies in transition from one class to the other, whose spectra indicate intense recent star formation that has now ended. We have identified thousands of such "post-starburst galaxies" and discovered that they are often the products of late-type galaxy-galaxy mergers. Their current kinematics, stellar populations, and morphologies are consistent with late- to early-type galaxy evolution. I will discuss recent work that suggests new connections between this violent history and the central supermassive black hole. In particular, the molecular gas reservoir of a post-starburst galaxy declines rapidly after the starburst ends and in a manner consistent with feedback from an active nucleus. Furthermore, a star is ~300x more likely to be tidally disrupted by the nucleus of a post-starburst galaxy than in other galaxies. Like the well-known black hole-bulge mass correlation, these surprising links between the properties of a galaxy on kpc scales and its supermassive black hole on pc scales require explanation.

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.469-471
• /
• 2015

How galaxies are affected by their neighboring galaxies during galaxy-galaxy interactions is a long-standing question. We investigate the role of neighbors in galaxy pairs based on the SDSS data release 7 and the KIAS value-added galaxy catalog. Three groups of galaxies are identified: (a) galaxies with an early-type neighbor, (b) with a late-type neighbor, and (c) isolated ones with no neighbor. We compare their UV + optical colors and $H{\alpha}$ emission as indicators of the recent star-formation rate (SFR). Given that galaxies show systematic differences in SFR as functions of morphology, luminosity, and large-scale environments, we construct a control sample in which the galaxies have the same conditions (in terms of morphology, luminosity, and large-scale environment) except for the neighbor's properties (i.e., morphology, mass, and distance). The results are as follows. (1) Galaxies with a late-type companion demonstrate more enhanced SFR than those with an early-type companion. (2) Galaxies with an early-type neighbor show NUV- and u-band derived SFRs that are even lower than that of isolated galaxies, while they have similar or slightly higher $H{\alpha}$-based SFR compared to isolated ones.