• 천문학회지
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• 제32권1호
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• pp.7-16
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• 1999

Open clusters are useful tools to investigate the structure and evolution of the Galactic disk. We have started a long-term project to obtain UBVI CCD photometry of open clusters which were little studied before, using the Doyak 1.8 m telescope of Bohyunsan Optical Astronomy Observatory in Korea. The primary goals of this project are (1) to make a catalog of UBVI photometry of open clusters, (2) to make an atlas of open clusters, and (3) to survey and monitor variable stars in open clusters. Here we describe this project and report the first results based on preliminary analysis of the data on four open clusters in the survey sample: Be 14, Cr 74, Biu 9, and NGC 2355. Isochrone fitting of the color-magnitude diagrams of the clusters shows that all of them are intermediate age to old (0.3-1.6 Gyrs) open clusters with moderate metallicity.

• 천문학회지
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• 제52권5호
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• pp.145-158
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• 2019

We conducted a survey of open clusters within 1 kpc from the Sun using the astrometric and photometric data of the Gaia Data Release 2. We found 655 cluster candidates by visual inspection of the stellar distributions in proper motion space and spatial distributions in l - b space. All of the 655 cluster candidates have a well defined main-sequence except for two candidates if we consider that the main sequence of very young clusters is somewhat broad due to differential extinction. Cross-matching of our 653 open clusters with known open clusters in various catalogs resulted in 207 new open clusters. We present the physical properties of the newly discovered open clusters. The majority of the newly discovered open clusters are of young to intermediate age and have less than ~50 member stars.

• 천문학회지
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• 제34권3호
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• pp.137-141
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• 2001

We derive a new relationship between the giant branch slope as measured in the color-magnitude diagram (K, J - K) and [Fe/H] metallicity for old open clusters. Previously such relationships have been derived for globular clusters, while similar tendency has been expected for open clusters. New derived correlation, [Fe/H]=-17.2($\pm$0.23)GB slope - 1.95($\pm$0.02), is based on a collection of data for 10 old open clusters. Most clusters behave as expected from the theoretical predictions.

• 천문학회보
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• 제44권1호
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• pp.84.1-84.1
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• 2019

722 open clusters in the Sim open cluster catalogue show the outermost structure of open clusters. The catalogue is based on the proper motion and parallax of the stars. These results reveal the hidden structures of weak membership signals in the field star contamination. It contains the tidal tails, flattened structure along the galactic plane, interacting double clusters and very poor and spread clusters. We will show these interesting structures.

• 천문학회지
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• 제39권4호
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• pp.115-123
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• 2006

We present $JHK_S$ near-infrared CCD photometric study for the Galactic open clusters NGC 1641 and NGC 2394. These clusters have never been studied before, and we provide, for the first time the cluster parameters; reddening, distance, metallicity and age. NGC 1641 is an old open cluster with age $1.6{\pm}0.2$ Gyr, metallicity $[Fe/H]=0.0{\pm}0.2$ dex, distance modulus$(m-M)_0=10.4{\pm}0.3\;mag(d=1.2{\pm}02\;kpc)$, and reddening $E(B-V)=0.10{\pm}0.05$ mag. The parameters for the other old open cluster NGC 2394 are estimated to be $age=1.1{\pm}0.2$ Gyr, $[Fe/H]=0.0{\pm}0.2$ dex, $(m-M)_0=9.1{\pm}0.4\;mag(d=660{\pm}120\;pc)$, and $E(B-V)=0.05{\pm}0.10$ mag. The metallicities and distance values for these two old open clusters are consistent with the relation between the metallicities and the Galactocentric distances of other old open clusters. We find the metallicity gradient of 53 old open clusters including NGC 1641 and NGC 2394 to be ${\Delta}[Fe/H]/{\Delta}R_{gc}=-0.067{\pm}0.009\;dex\;kpc^{-1}$.

• 천문학회보
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• 제40권2호
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• pp.58.3-58.3
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• 2015

Blue Straggler Stars (BSSs), kind of unusual main sequence stars, are the brighter and bluer stars than the main sequence turn off (MSTS) stars in coeval clusters. Since the first detection in globular clusters (GCs), BSSs have been shown to reveal an anti-correlation between the luminosity of their host star cluster and the number of BSSs in the cluster. Further, conclusions based on this result can be expanded to the open clusters. BSSs seem to play an important role in GCs according to the relation between the dynamical time scale of GCs and the number of BSSs along the cluster radius. This relation, however, remains to be verified in open clusters, In this study, we divide open clusters by the existence of BSSs into two groups. Then we compare parameters between these groups to specify the role of BSSs in open clusters.

• 천문학회지
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• 제44권1호
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• pp.1-11
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• 2011

A sample of 145 JHK-2MASS observations of NGC open star clusters is studied, of which 132 have never been studied before. Twelve are classified as non-open clusters and 13 are re-estimated self-consistently, after applying the same methods in order to compare and calibrate our reduction procedures. The fundamental and structural parameters of the 120 new open clusters studied here are derived using color-magnitude diagrams of JHK Near-IR photometry with the fitting of solar metallicity isochrones. We provide here, for the first time, a catalog of the main parameters for these 120 open clusters, namely, diameter, distance, reddening and age.

• 천문학회지
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• 제50권3호
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• pp.51-59
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• 2017

The presence of blue stragglers pose challenges to standard stellar evolution theory, in the sense that explaining their presence demands a complex interplay between stellar evolution and cluster dynamics. In the meantime, mass transfer in binary systems and stellar collisions are widely studied as a blue straggler formation channel. We explore properties of the Galactic open clusters where blue stragglers are found, in attempting to estimate the relative importance of these two favored processes, by comparing them with those resulting from open clusters in which blue stragglers are absent as of now. Unlike previous studies which require a sophisticated process in understanding the implication of the results, this approach is straightforward and has resulted in a supplementary supporting evidence for the current view on the blue straggler formation mechanism. Our main findings are as follows: (1) Open clusters in which blue stragglers are present have a broader distribution with respect to the Z-axis pointing towards the North Galactic Pole than those in which blue stragglers are absent. The probability that two distributions with respect to the Z-axis are drawn from the same distribution is 0.2%. (2) Average values of $log_10(t)$ of the clusters with blue stragglers and those without blue stragglers are $8.58{\pm}0.232$ and $7.52{\pm}0.285$, respectively. (3) The clusters with blue stragglers tend to be relatively redder than the others, and are distributed broader in colors. (4) The clusters with blue stragglers are likely brighter than those without blue stragglers. (5) Finally, blue stragglers seem to form in condensed clusters rather than simply dense clusters. Hence, we conclude that mass transfer in binaries seems to be a relatively important physical mechanism of the generation of blue stragglers in open clusters, provided they are sufficiently old.

• 천문학회보
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• 제40권2호
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• pp.28.1-28.1
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• 2015

Open clusters are one of stellar systems consisting of a few hundreds to thousands of stars. The cluster members are, in general, believed to be a coeval stellar population at the same distance, and therefore they have almost the same properties in chemical composition and kinematics. Owing to these advantages, the clusters are utilized in many astronomy studies, such as the calibrations of distance and stellar age scales, assessments of stellar evolution theories, and the chemical evolution of the Galactic disk. Young open clusters are, inter alia, superb objects to study star formation process as most of stars are known to be formed in clusters. In this talk, I will review the uses of these young open clusters in star formation studies based on the ongoing work of our research group on the stellar initial mass function, an age spread problem, mass accretion rate of pre-main sequence stars, and a feedback of high-mass stars on surroundings.

• 천문학회지
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• 제44권5호
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• pp.177-193
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• 2011

We present a photometric study of five open clusters (Czernik 5, Alessi 53, Berkeley 49, Berkeley 84, and Pfleiderer 3) in the Sloan Digital Sky Survey. The position and size of these clusters are determined using the radial number density profiles of the stars, and the member stars of the clusters are selected using the proper motion data in the literature. We estimate the reddening, distance and age of the clusters based on the isochrone fitting in the color-magnitude diagram. The foreground reddenings for these clusters are estimated to be E(B - V ) = 0.71 - 1.55 mag. The distances to these clusters are derived to be 2.0 - 4.4 kpc, and their distances from the Galactic center range from 7.57 kpc to 12.35 kpc. Their ages are in the range from 250 Myr to 1 Gyr. Berkeley 49 and Berkeley 84 are located in the Orion spur, Czernik 5 is in the Perseus arm, and Pfleiderer 3 and Alessi 53 are located beyond the Perseus arm.