• Title/Summary/Keyword: globular

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COLOR GRADIENTS WITHIN GLOBULAR CLUSTERS: RESTRICED NUMERICAL SIMULATION

  • Sohn, Young-Jong;Chun, Mun-Suk
    • Journal of Astronomy and Space Sciences
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    • v.14 no.1
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    • pp.1-17
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    • 1997
  • The results of a restricted numerical simulation for the color gradients within globular clusters have been presented. The standard luminosity function of M3 and Salperter's initial mass functions were used to generate model clusters as a fundamental population. Color gradients with the sample clusters for both King and power law cusp models of surface brightness distributions are discussed in the case of using the standard luminosity function. The dependence of color gradients on several parameters for the simulations with Salpter's initial mass functions, such as slope of initial mass functions, cluster ages, metallicities, concentration parameters of King model, and slopes of power law, are also discussed. No significant radial color gradients are shown to the sample clusters which are regenerated by a random number generation technique with various parameters in both of King and power law cusp models of surface brightness distributions. Dynamical mass segregation and stellar evolution of horizontal branch stars and blue stragglers should be included for the general case of model simulations to show the observed radial color gradients within globular clusters.

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DISTANCES OF GLOBULAR CLUSTERS BASED ON HIPPARCOS PARALLAXES OF NEARBY SUBDWARFS

  • SAAD SOMAYA MOHAMED;LEE SANG-GAK
    • Journal of The Korean Astronomical Society
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    • v.34 no.2
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    • pp.99-109
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    • 2001
  • In the present study we have determined the distance moduli for seven globular clusters M2, M3, Ml0, M12, NGC 2808, NGC 6229, and NGC 6752, whose metallicities are in the range -1.54 < [Fe/H] < -1.10. We have derived distances for them by the main-sequence fitting method using a sample of local subdwarfs, whose accurate parallaxes are taken from the Hipparcos Catalog. The derived distance moduli are 15.52 for M2, 14.98 for M3, 14.23 for Ml0, 14.03 for M12, 15.56 for NGC 2808, 17.34 for NGC 6229, and 13.29 for NGC 6752.

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Monte-Carlo Simulation to the Color Distribution within Galactic Globular Clusters

  • Sohn, Young-Jong;Chun, Mun-Suk
    • Bulletin of the Korean Space Science Society
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    • 1993.10a
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    • pp.18-18
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    • 1993
  • According to the CCD photometric studies, the color distributions of globular clusters with collapsed cores, which are characterized by a power law cusp in thier surface brighness pronto, become bluer toward their centers, but this is not the case in the flat core clusters which are fit by the King model. To test the statistical implication of the color distribution within globular clusters, we built the sample dusters which follows the surface brightness pofile of the King model and power law cusp profile with the Sandage's standao luminosity function for M3 and the Salpter's initial mass functions. On the results from simulations based on the uniform random number generation the color gadients within globualr dusters mar be not likely to come from the statistical random distributions of stars but from the dynamical process on the cluster evolution.

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A fundamental study on semi-solid forging with light and hardly formable materials (난가공성 경량소재의 반용융 단조에 관한 기초 연구)

  • Choi, J.C.;Cho, H.Y.;Min, G.S.;Park, H.J.;Choi, J.U.
    • Journal of the Korean Society for Precision Engineering
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    • v.13 no.7
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    • pp.29-35
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    • 1996
  • For semi-solid forging with aluminuim alloys, it is required to develope the globular grain structure. It was studide that cold upsetting ration in SIMA process has effect on the globularization of grain structure. Globular microstructure was generated without cold upsettings for commercial aluminium alloys. In the case of A12024, the range of grain size was 40 .approx. 50 .mu. m. The grain growth in growth in globular microstructure depend on heating time. Spur gear was forged in semi-solid state to investigate the forging condition for A12024 with hydraulic press.

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RADIAL ABUNDANCE GRADIENT IN GLOBULAR CLUSTERS

  • Chun, M.S.
    • Journal of The Korean Astronomical Society
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    • v.14 no.1
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    • pp.13-17
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    • 1981
  • The observed radial UBV colour variations (both B-V and U-B) of some globular clusters are examined for correlations with radial variations in the integrated spectra. The results show that the presence of a radial colour gradient is correlated with the presence of a gradient of the CN (and possibly the G-band) line strength, in the sense that the CN (and possibly the G-band) is stronger in the centre (where the cluster is redder) and becomes weaker in the outer region of the cluster (where the cluster is bluer). This may suggest that a primordial abundance, possibly nitrogen and carbon gradient was set up in the early stage of cluster formation.

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BV STELLAR PHOTOMETRY OF 23 GALACTIC GLOBULAR CLUSTERS

  • 손영종;천문석;변용익
    • Journal of Astronomy and Space Sciences
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    • v.15 no.2
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    • pp.277-289
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    • 1998
  • We report V-(B - V) CCD Color Magnitude Diagrams (CMDs) for 23 southern Galactic globular clusters. Limiting magnitudes for each cluster are between 18 and 20 magnitudes in V. Most CMDs show subgiant starts, red giant stars, and horizontal branch stars. From the CMDs, we have determined the horizontal branch magnitudes, V(HB), reddenings, E(B - V), and distances of each cluster.

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METALLICITIES OF GLOBULAR CLUSTRES M3 AND M5 FROM VI CCD PHOTOMETRY

  • Sohn, Young-Jong;Lee, Hyun-Chul
    • Journal of Astronomy and Space Sciences
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    • v.17 no.1
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    • pp.1-10
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    • 2000
  • To derive the metallicities of M3 and M5, we used the shape of red giant branch, horizontal branch magnitude, and red giant branch bump on the (V-I)-V color magnitude diagrams. [Fe/H] values ranging -1.46 ∼ -1.69 for M3, and -1.00 ∼ -1.49 for M5 are estimated. These values are in good agreements with the previously determined ones. This result leads the morphologies of red giant and horizontal branches on the (V-I)-V color magnitude diagrams can be good indirect metallicity indicators of galactic globular clusters.

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CN BAND DISTRIBUTIONS OF THE STARSON THE RED GIANT BRANCH IN THE GLOBULAR CLUSTERS M3 AND M13

  • LEE SANG-GAK
    • Publications of The Korean Astronomical Society
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    • v.13 no.1 s.14
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    • pp.111-122
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    • 1998
  • Among the sample of red giant stars in the globular clusters M3 and M13 whose CN bands $(3883{\AA})$ have been measured by various authors, the stars on the red giant evolutionary state are selected to have their CN band distributions. It is found that all stars brighter than Mv = 0, are CN-strong in M3, while all stars except IV-29 are CN-strong in M13. It hints that the onset of meridional mixing is related with the RGB bumps of the clusters.

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OBSERVATIONAL EVIDENCE OF MULTIPLE STELLAR POPULATIONS IN STAR CLUSTERS

  • Piotto, Giampaolo
    • Publications of The Korean Astronomical Society
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    • v.25 no.3
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    • pp.91-99
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    • 2010
  • An increasing number of observations have confirmed the presence of multiple stellar populations in Galactic globular clusters. Multiple populations evidence come from the complex chemical pattern of stars hosted in GCs and from the split or broadening of different evolutionary sequences in the color-magnitude diagrams. Multiple stellar populations have been identified in Galactic and Magellanic Cloud clusters, as well as in external galaxies. In this paper I will summarize the observational facts.

High resolution spectroscopic study of the peculiar globular cluster M22 (NGC 6656)

  • Kim, Hyeong-Jun;Lee, Jae-Woo
    • The Bulletin of The Korean Astronomical Society
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    • v.42 no.2
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    • pp.65.1-65.1
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    • 2017
  • We present the high-resolution spectroscopic study of the red-giant branch (RGB) stars in the peculiar globular cluster M22 (NGC 6656). We obtained high-resolution spectra of 55 RGB stars using the CTIO 4-m telescope and the HYDRA multi-object spectrograph. By employing an improved LTE analysis method, we measured accurate elemental abundances. In this talk, we will discuss the differences in the chemical composition between the two stellar populations in the context of the formation of M22.

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