The Carnegie-Chicago Hubble Program: Discovery of the Most Distant Ultra-faint Dwarf Galaxy in the Local Universe

Lee, Myung Gyoon,Jang, In Sung,Beaton, Rachael,Seibert, Mark,Bono, Giuseppe,Madore, Barry American Astronomical Society 2017 ASTROPHYSICAL JOURNAL LETTERS - Vol.835 No.2

<P>Ultra-faint dwarf galaxies (UFDs) are the faintest known galaxies, and due to their incredibly low surface brightness, it is difficult to find them beyond the Local Group. We report a serendipitous discovery of a UFD, Fornax UFD1, in the outskirts of NGC 1316, a giant galaxy in the Fornax cluster. The new galaxy is located at a projected radius of 55 kpc in the south-east of NGC 1316. This UFD is found as a small group of resolved stars in the Hubble Space Telescope images of a halo field of NGC 1316, obtained as part of the Carnegie-Chicago Hubble Program. Resolved stars in this galaxy are consistent with being mostly metal-poor red giant branch (RGB) stars. Applying the tip of the RGB method to the mean magnitude of the two brightest RGB stars, we estimate the distance to this galaxy, 19.0. +/-. 1.3 Mpc. Fornax UFD1 is probably a member of the Fornax cluster. The color-magnitude diagram of these stars is matched by a 12 Gyr isochrone with low metallicity ([Fe/H]approximate to-2.4). Total magnitude and effective radius of Fornax UFD1 are M-V approximate to -7.6 +/- 0.2 mag and r(eff) = 146 +/- 9 pc, which are similar to those of Virgo UFD1 that was discovered recently in the intracluster field of Virgo by Jang & Lee. Fornax UFD1 is the most distant known UFD that is confirmed by resolved stars. This indicates that UFDs are ubiquitous and that more UFDs remain to be discovered in the Fornax cluster.</P>

장기간의 걷기 트레이닝이 중년 여성의 체력과 혈액성분에 미치는 영향

유명근,이만균,문황운 경희대학교 체육대학 한국체육과학연구소 2004 體育學論文集 Vol.32 No.-

This study was designed to investigate the effects of a 12-week walking training on body composition, physical fitness, and blood variables in obese middle age women. Fourteen subjects who had percent of body fat over 30% were selected from the members of diet class of K pubic health center. Then they participated in the twelve weeks of walking training program. Before and after the training program, percent body fat, five items of physical fitness, and blood variables regarding to metabolism were measured and compared between pre and post test. Paired t-test was utilized to detect the mean difference between the pre and post test. The results of this study were as follows: First, after twelve weeks of training, PBF and weight of subjects significantly decreased(P<.05). Second, after twelve weeks of training, left grip strength of subjects did not change significantly, but right grip strength, back strength sit-and-reach, sit-up, and sargent jump increased significantly(P<.05). Finally, after twelve weeks of training, blood glucose and triglyceride of subjects did not change significantly, whereas total cholesterol decreased significantly. There was a significant increase in forced vital capacity(P<.05). According to these findings, it was concluded that walking training was effective on the decrease of percent body fat, enhancement of physical fitness, partial improvement of metabolism and pulmonary function in obese middle age women if the training was conducted for long period despite the intensity fo the walking was relatively low.

UBV CCD PHOTOMETRY OF THE LMC DOUBLE CLUSTER NGC 1850

Lee, Myung-Gyoon The Korean Astronomical Society 1995 Journal of The Korean Astronomical Society Vol.28 No.2

We present UBV CCD photometry of the double cluster NGC 1850 located at the NW edge of the bar of the Large Magellanic Cloud. The color-magnitude diagram shows that NGC 1850 has a prominent population of massive core-He burning stars which is incomparably richer than any other known star clusters. The reddening is estimated from the (U-B) - (B-V) diagram to be E(B - V) = $0.15{\pm}0.05$. We have estimated the ages of NGC 1850 and a very compact blue star cluster (NGC 1850A) located at ${\sim}30''$ west of NGC 1850 using isochrones based on the convective overshooting models: $80{\sim}10$ Myrs and $5{\sim}2$ Myra, respectively. Several evidence suggest that it is probably the compact cluster NGC 1850A that is responsible for the arc-shaped nebulosity (Henize N 103B) surrounding the east side of NGC 1850.

DUAL STELLAR HALOS IN THE STANDARD ELLIPTICAL GALAXY M105 AND FORMATION OF MASSIVE EARLY-TYPE GALAXIES

Lee, Myung Gyoon,Jang, In Sung American Astronomical Society 2016 The Astrophysical journal Vol.822 No.2

<P>M105 is a standard elliptical galaxy, located in the Leo I Group. We present photometry of the resolved stars in its inner region at R approximate to 4' approximate to 4R(eff), obtained from F606W and F814W images in the Hubble Space Telescope archive. We combine this with photometry of the outer region at R approximate to 12' approximate to 12R(eff) from archival imaging data. Color-magnitude diagrams of the resolved stars in the inner region show a prominent red giant branch (RGB) with a large color range, while those for the outer region show better a narrow blue RGB. The metallicity distribution function (MDF) of the RGB stars shows the existence of two distinct subpopulations: a dominant metal-rich population (with a peak at [M/H] approximate to 0.0) and a much weaker metal-poor population (with a peak at [M/H] approximate to -1.1). The radial number density profiles of the metal-rich and metal-poor RGB stars are fit well by a Sersic law with n = 2.75 +/- 0.10 and n = 6.89 +/- 0.94, and by a single power law (sigma proportional to R-3.8 and sigma proportional to R-2.6), respectively. The MDFs of the inner and outer regions can be described well by accretion gas models of chemical evolution with two components. These provide strong evidence that there are two distinct stellar halos in this galaxy, blue metal-poor and red metal-rich halos, consistent with the results based on globular cluster systems in bright early-type galaxies (ETGs). We discuss the implications of these results with regard to the formation of massive ETGs in the dual halo mode formation scenario.</P>

UBVRI CCD PHOTOMETRY OF THE TYPE Ic SUPERNOVA SN 1994I IN M51: THE FIRST TWO MONTHS

LEE MYUNG GYOON,KIM EUNHYEUK,KIM SANG CHUL,KIM SEUNG LEE,PARK WON KEE,PYO TAE SOO The Korean Astronomical Society 1995 Journal of The Korean Astronomical Society Vol.28 No.1

We present UBVRI CCD photometry of the Type Ie supernova SN 19941 in M51 which was discovered on April 2, 1994 (UT). UBVRI CCD photometry of SN 1994 I were obtained for the period of the first two months from April 4, 1994, using the Seoul National University Observatory 60 cm telescope. The light curves of SN 19941 show several interesting features: (a) SN 19941 reaches the maximum brightness at B-band on April 8.23 (B = 13.68 mag), at V-band on April 9.10 (V = 12.89 mag), and at I-band on April 10.32 (I = 12.48 mag); (b) The light curves around the maximum brightness are much narrower than those of other types of supernovae; (c) The light curves after the peak decline more steeply than those of other types of supernovae; and (d) The colors get redder from $(V-R){\approx}0.2 mag ((V - I){\approx} 0.3 mag, (B - V){\approx}0.7 mag)$ on April 4 to $(V-R){\approx}0.6 mag ((V-1){\approx}0.9 mag, (B-V){\approx}1.3 mag)$ on April 18. Afterwards (V - R) colors get bluer slightly $(by\~0.005 mag/day)$, while (V-I) colors stay almost constant around $(V-1){\approx}1.0 mag$. The color at the maximum brightness is (B-V)=0.9 mag, which is $\~1$mag redder than the mean color of typical Type la supernovae at the maximum brightness. The light curves of SN 1994I are similar to those of the Type Ie supernova SN 1962L in NGC 1073. Adopting the distance modulus of $(m-M)_0 = 29.2 mag$ and the reddening of E(B - V) = 0.45 mag [Iwamoto et al. 1994, preprint for ApJ], we derive absolute magnitudes at the maximum brightness of SN 1994I, Mv(max) = -17.7 mag and MB(max) = -17.4 mag. This result shows that SN 1994I was $\~2$mag fainter at the maximum brightness compared with typical Type Ia supernovae. A narrower peak and faster decline after the maximum in the light curve of SN 1994I compared with other types of supernovae indicate that the progenitor of SN 1994I might be a lower mass star compared with those of other types of supernovae.

BOAO 1.8m CCD PHOTOMETRY OF OLD OPEN CLUSTERS: PROGRESS REPORT

Myung Gyoon Lee,Won-Kee Park,Sang Chul Kim 한국천문학회 1997 天文學會報 Vol.22 No.-

A TEST OF THE INTRACLUSTER GLOBULAR CLUSTER MODEL

Myung Gyoon Lee,Doug Geisler 한국천문학회 1997 天文學會報 Vol.22 No.-

HEATING OF SUNSPOT CHROMOSPHERES BY SLOW-MODE ACOUSTIC SHOCK WAVES

Lee, Myung-Gyoon,Yun, Hong-Sik The Korean Astronomical Society 1985 Journal of The Korean Astronomical Society Vol.18 No.1

Making use of the arbitrary shock theory developed by Ulmschneider (1967, 1971) and Ulmschneider and Kalkofen (1978), we have calculated the dissipation rates of upward-travelling slow-mode acoustic shock waves in umbral chromospheres for two umbral chromosphere models, a plateau model by Avrett (1981) and a gradient model by Yun and Beebe (1984). The computed shock dissipation rates are compared with the radiative cooling rate given by Avrett (1981). The results show that the slow-mode acoustic shock waves with a period of about 20 second can heat the low umbral chromospheres travelling with a mechanical energy flux of $2.6{\times}10^6\;erg/cm^2s$ at a height of $300{\sim}400km$ above the temperature minimum region.

A Globular Cluster Luminosity Function Distance to NGC 4993 Hosting a Binary Neutron Star Merger GW170817/GRB 170817A

Lee, Myung Gyoon,Kang, Jisu,Im, Myungshin American Astronomical Society 2018 ASTROPHYSICAL JOURNAL LETTERS - Vol.859 No.1

GLOBULAR CLUSTERS, ULTRACOMPACT DWARFS, AND DWARF GALAXIES IN ABELL 2744 AT A REDSHIFT OF 0.308

Lee, Myung Gyoon,Jang, In Sung American Astronomical Society 2016 The Astrophysical journal Vol.831 No.1

<P>We report a photometric study of globular clusters (GCs), ultracompact dwarfs (UCDs), and dwarf galaxies in the giant merging galaxy cluster Abell 2744 at z = 0.308. Color-magnitude diagrams of the point sources derived from deep F814W (rest frame r') and F105W (rest frame I) images of Abell 2744 in the Hubble Space Telescope Frontier Field show a rich population of point sources, which have colors that are similar to those of typical GCs. These sources are as bright as -14.9< M-r' <= -11.4 (26.0 < F814W(Vega) <= 29.5) mag, being mostly UCDs and bright GCs in Abell 2744. The luminosity function (LF) of these sources shows a break at M-r' approximate to -12.9 (F814W approximate to 28.0) mag, indicating a boundary between UCDs and bright GCs. The numbers of GCs and UCDs are estimated to be 1,711,640(-430,500)(+589,760) and 147 +/- 26, respectively. The clustercentric radial number density profiles of the UCDs and bright GCs show similar slopes, but these profiles are much steeper than those. of the dwarf galaxies and the mass density profile based on gravitational lensing analysis. We derive an LF of the red sequence galaxies for -22.9< M-r' <= -13.9 mag. The faint end of this LF is fit well by a flat power law with alpha = -1.14 +/- 0.08, showing no faint upturn. These results support the galaxy-origin scenario for bright UCDs: they are the nuclei of dwarf galaxies that are stripped when they pass. close to the center of massive galaxies or a galaxy cluster, while some of the faint UCDs are at. the bright end of the GCs.</P>