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제목 :  Study of sparse star clusters and metallicity distribution in the Large Magellanic Cloud

연사 :  Samyaday Choudhury 박사님 (연세대학교)

언어 :  English


요약

          The Large Magellanic Cloud (LMC), located in the southern sky, is by far the most liveliest and lustrous satellite of the Milky Way (d ~ 50 kpc)! I shall present our study of sparse star clusters and metallicity distribution in this nearby galaxy. The study of sparse star clusters in the LMC aims 
to increase our understanding of such objects, using deep Washington photometric data of 45 star clusters obtained from 4-m Blanco Telescope, CTIO. A systematic study was performed to estimate their parameters (radius, reddening, and age) using the main-sequence turn-off, as well as
the evolved portion of the color-magnitude diagram. We grouped the clusters into two categories based on their genuineness, namely true clusters and possible clusters/asterisms. The sizes (~2-10 pc) and masses (~a few 100 - 1000 M⊙) of these 45 inconspicuous clusters emphasizes that
the LMC has a significant population of clusters, which are similar to the open clusters in our Galaxy. To understand the metallicity distribution and
gradient of the LMC, we estimated a metallicity map using the red giant branch (RGB) stars, from the MCPS and OGLE III photometric data.
This is a first of its kind map of metallicity up to a radius of 4˚ - 5˚, with good sampling of the bar region. The slope of the RGB is used as an indicator of the average metallicity of a subregion, and it is calibrated to metallicity using spectroscopic data for field and cluster red giants in selected
subregions. We estimated the mean metallicities of different regions within the LMC using both data sets. The bar is found to have an uniform and higher metallicity compared to the disk, and is indicative of an active bar in the past. Both the data sets suggest a shallow radial metallicity gradient up to a radius of 4 kpc for the LMC disk (−0.049 ± 0.002 dex/kpc to −0.066 ± 0.006 dex/kpc ), which resembles the gradient seen in spiral galaxies, and is also similar to that found in our Galaxy.

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