• 천문학회지
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• 제26권2호
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• pp.141-152
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• 1993

The sample of sub dwarfs are selected from LHS catalogue on the bases of the reduced proper motion diagram utilizing Chui criteria, and confirmed with the available photometric and/or kinematic data. Among them, 20 sub dwarfs have trigonometric parallaxes with accuracy better than $20\%$. The color­absolute magnitude relation is derived with them. By adopting this color-magnitude relation and $V/V_m$ method, we have derived the sub dwarf luminosity function over the absolute magnitude range of $M_v$= 4.5 and 9.5. This halo luminosity function is consistent with that of Eggen(1987). By adopting the available mass-luminosity relations for halo stars, we have found that the halo IMF is steeper than disk IMFs of Scalo(1986) and Salpter(1955) in this small mass region.

• 천문학회보
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• 제45권1호
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• pp.57.3-57.3
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• 2020

The chemical and kinematic properties of stars in the Galactic halo provide crucial information on the origin of the Galactic halo as well as the assembly history of the Milky Way. In this study, we present metallicity distribution functions (MDFs) in different regions of the Galactic halo as well as the kinematic characteristics in each region. The different MDFs and kinematic properties of stars in investigated regions allow us to associate them with the possible progenitor dwarf galaxies discovered to date; hence the assembly history of the Galactic halo.

• 천문학회보
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• 제46권2호
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• pp.81.1-81.1
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• 2021

Stellar kinematics is a useful tool to understand the formation and evolution of young stellar systems. Here, we present a kinematic study of the HII region, NGC 821, using the Gaia Early Data Release 3. NGC 281 contains the open cluster IC 1590. This cluster has a core and a low-stellar density halo. We detect a pattern of cluster expansion from the Gaia proper motion vectors. Most stars radially escaping from the cluster are distributed in the halo. We measure the 1-dimensional velocity dispersion of stars in the core. The velocity dispersion (1 km/s) is comparable to the expected virial velocity dispersion of this cluster, and therefore the core is at a virial state. The core has an initial mass function shallower than that of the halo, which is indicative of mass segregation. However, there is no significant correlation between stellar masses and tangential velocities. This result suggests that the mass segregation has a primordial origin. On the other hand, it has been believed that the formation of young stars in NGC 281 West was triggered by feedback from massive stars in IC 1590. We investigate the ages of stars in the two regions, but the age difference between the two regions is not comparable to the timescale of the passage of an ionization front. Also, the proper motion vectors of the NGC 281 West stars relative to IC 1590 do not show any systematic receding motion from the cluster. Our results suggest that stars in NGC 281 West might have been formed spontaneously. In conclusion, the formation of NGC 281 can be understood in the context of hierarchical star formation model.

• Journal of Astronomy and Space Sciences
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• 제39권4호
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• pp.169-180
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• 2022

We investigated the chemical composition of the planetary host halo star HD47536 via high-resolution spectral observations recorded using a 1.5 meter Cerro Tololo Inter-American Observatory (CTIO) telescope (Chile). Furthermore, we determined the abundances of 38 chemical elements. Both light and heavy elements were overabundant compared to the iron group elements. The abundance pattern of HD47536 was similar to that of halo-type stars, with an enrichment of heavy elements. We analyzed the relationships between the relative abundances of chemical elements and their second ionization potentials and condensation temperatures. We demonstrated that the interplay of charge-exchange reactions owing to the accretion of interstellar matter and the gas-dust separation mechanism can influence the initial abundances and can be used to qualitatively explain the abundance patterns in the atmosphere of HD47536.

• 천문학회보
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• 제42권2호
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• pp.51.1-51.1
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• 2017

We present the dependence of halo properties on two different Galactic potentials: the $St{\ddot{a}}ckel$ potential and the Milky Way-like potential known as "Galpy". Making use of the Sloan Digital Sky Survey Data Release 12 (SDSS DR12), we find that the shape of the metallicity distribution and rotation velocity distribution abruptly changes at 15 kpc of $Z_{max}$ (the maximum distance of stellar orbit above or below the Galactic plane) and 32 kpc of $r_{max}$ (the maximum distance of an orbit from the Galactic center) in the $St{\ddot{a}}ckel$, which indicates that the transition from the inner to outer halo occurs at those distances. When adopting the $St{\ddot{a}}ckel$ potential, stars with $Z_{max}$ > 15 kpc show a retrograde motion of $V_{\phi}=-60km\;s^{-1}$, while stars with $r_{max}$ > 32 kpc show $V_{\phi}=-150km\;s^{-1}$. If we impose $V_{\phi}$ < $-150km\;s^{-1}$ to the stars with $Z_{max}$> 15 kpc or $r_{max}$> 32, we obtain the peak of the metallicity distribution at [Fe/H] = -1.9 and -1.7 respectively. However, there is the transition of the metallicity distribution at $Z_{max}=25kpc$, whereas there is no noticeable retrograde motion in the Galpy. The reason for this is that stars with high retrograde motion in the $St{\ddot{a}}ckel$ potential are unbound and stars with low rotation velocity reach to larger region of $Z_{max}$ and $r_{max}$ due to shallower potential in the Galpy. These results prove that as the adopted Galactic potential can affect the interpretation of the halo properties, it is required to have a more realistic Galactic potential for the thorough understanding of the dichotomy of the Galactic halo.

• 천문학회지
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• 제31권1호
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• pp.19-26
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• 1998

The wide field $(\~20'\times20')$ CCD photometry has been performed for more than 4,000 stars over a whole region of NGC 362 which is located inside the SMC halo. The Color-Magnitude diagram (CMD) and luminosit function (LF) for red giant branch (RGB) stars are presented, discussing a distinct bump along the RGB and some blue stars appearing in the blue horizontal branch (BHB) and above BHB. The anomalous globular cluster NGC 362 with highly populated red horizontal branch (RHB) stars is compared with the another anomalous globular cluster NGC 288 with highly populated BHB stars. A metal-rich, young blue component and metal-'poor, old red component of the SMC halo stars are examined.

• 천문학회보
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• 제36권2호
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• pp.144.1-144.1
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• 2011

We explore the metallicity distribution of the Galactic halo based on the SDSS ugriz photometry. We use empirically calibrated sets of stellar isochrones to determine distances and metallicities of individual main-sequence stars in the halo. At heliocentric distances greater than 5 kpc, we find that the in situ photometric metallicity distribution reveals chemically divided dual halo components, which supports arguments from earlier studies based on the medium resolution spectroscopy. Our finding provides an unbiased estimate of relative fractions of each of these stellar components in the Galactic halo.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2008년도 한국우주과학회보 제17권2호
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• pp.38.1-38.1
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• 2008

Tides caused by the Galactic gravitational field affect the current dynamical structure of globular clusters in the Galaxy. Indeed, the observed feature of tidal tails stretching beyond globular clusters' tidal radii provides a key information of interaction with the gravitational field of the Galaxy and kinematical orbit of the clusters, which can be an evidence of the merging scenario of the Galaxy formation and evolution. To find such a tidal feature, we have studied spatial density distribution of stars around five globular clusters in the Galactic halo and one cluster in the Galactic bulge, for which we have used wide-field deep photometric data of gri and JHK bands obtained from the MegaCam and WIRCam of the CFHT. Applying the statistical contrast filtering of field stars in the color-magnitude plane of detected stars around five halo clusters, we have found features of tidal tails for four clusters M53, M15, NGC 5053, and NGC 5466. The detected over-density tidal features are well aligned with the cluster's orbits and stretched into the direction of the Galactic center. Statistical analysis indicate that these tidal tails are believed to be cluster stars that have escaped due to the tidal effects to the clusters. A similar tidal feature to that of halo clusters is also detected for the bulge cluster NGC 6626, while the over-density feature seems to be extended into the Galactic plane rather than into the orbital direction and the Galactic center. Conclusively, our result adds further observational evidence of the merging scenario of the Galaxy formation and evolution.

• 천문학회보
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• 제46권1호
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• pp.52.2-52.2
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• 2021

The Black Eye Galaxy M64 is an intriguing spiral galaxy with a Type III disk break. To trace the origin of its Type III component, we present HST/ACS F606W/F814W photometry of resolved stars in the outer disk of M64 (2.5' < R < 6.5'). First, we discover a bright extended globular cluster (GC) M64-GC1 at R ~ 5.5', and find that it is an old metal-poor halo GC ([Fe/H] = -1.5 +/- 0.2). Second, we find that there are two distinct subpopulations of red giant branch stars (RGBs). One is an old metal-rich ([Fe/H] ~ -0.4) disk population, and the other is an old metal-poor halo population similar to the resolved stars in M64-GC1. The radial number density profile of the metal-rich RGB follows an exponential disk law, while that of the metal-poor RGB follows a de Vaucouleurs's low. From these results, we conclude that the origin of the Type III component in M64 is a halo, not a disk or a bulge. We will further discuss the results in regards to the formation and evolution of M64.

• 천문학회보
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• 제44권1호
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• pp.68.4-68.4
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• 2019

It is inferred that many stars in the Galactic halo or bulge were once members of globular clusters (GCs), which are now dissolved. To distinguish the GC-originated stars, which can provide valuable information on the origin of the bulge and halo, from the in situ field stars, the Na abundance plays an important role. However, the interstellar Na in certain directions can unnecessarily enhance the estimate of the Na abundance from stellar spectra due to blended Na D lines unless the spectral resolution is very high, which allows to resolve the lines from the interstellar Na. In this study, we present a means of correcting the Na abundance affected by the interstellar Na in the low-resolution of the Sloan Digital Sky Survey stellar spectra.