• 천문학논총
• /
• 제27권4호
• /
• pp.117-122
• /
• 2012

The interstellar dust grains are formed and supplied to interstellar space from asymptotic giant branch (AGB) stars or supernova remnants, and become constituents of the star- and planet-formation processes that lead to the next generation of stars. Both a qualitative, and a compositional study of this cycle are essential to understanding the origin of the pre-solar grains, the missing sources of the interstellar material, and the chemical evolution of our Galaxy. The AKARI/MIR all-sky survey was performed with two mid-infrared photometric bands centered at 9 and $18{\mu}m$. These data have advantages in detecting carbonaceous and silicate circumstellar dust of AGB stars, and the interstellar polycyclic aromatic hydrocarbons separately from large grains of amorphous silicate. By using the AKARI/MIR All-Sky point source catalogue, we surveyed C-rich and O-rich AGB stars in our Galaxy, which are the dominant suppliers of carbonaceous and silicate grains, respectively. The C-rich stars are uniformly distributed across the Galactic disk, whereas O-rich stars are concentrated toward the Galactic center, following the metallicity gradient of the interstellar medium, and are presumably affected by the environment of their birth place. We will compare the distributions of the dust suppliers with the distributions of the interstellar grains themselves by using the AKARI/MIR All-Sky diffuse maps. To enable discussions on the faint diffuse interstellar radiation, we are developing an accurate AKARI/MIR All-Sky diffuse map by correcting artifacts such as the ionising radiation effects, scattered light from the moon, and stray light from bright sources.

• 천문학회보
• /
• 제38권2호
• /
• pp.36-36
• /
• 2013

Globular clusters (GCs) are among the oldest stellar objects in the universe and provide valuable constraints on many aspects of galaxy evolution. GC systems typically exhibit bimodal color distributions the phenomenon of which has been a major topic in the area of GC research. GC color bimodality established a paradigm where scenarios to explain its origin require two GC groups with different formation origins. The GC division, asserted mainly by photometric color bimodality so far, has been viewed as the presence of two distinct metallicity subgroups within individual galaxies. In this study, we make use of spectroscopy of GC systems associated with two giant galaxies, M31 (the Andromeda) and M87 (NGC 4486), to investigate the GC bimodality and the underlying metallicity distributions. Recent spectroscopy on the globular cluster (GC) system of M31 with unprecedented precision witnessed a clear bimodality in absorption-line index distributions of old GCs. Given that spectroscopy is a more detailed probe into stellar population than photometry; the discovery of index bimodality may point to the very existence of dual GC populations. However, here we show that the observed spectroscopic dichotomy of M31 GCs emerges due to the nonlinear nature of metallicity-to-index conversion and thus one does not necessarily have to invoke two separate GC subsystems. We present spectra of 130 old globular clusters (GCs) associated with the Virgo giant elliptical galaxy M87, obtained using the Multi-Object Spectrography (MOS) mode of Faint Object Camera and Spectrograph (FOCAS) on the Subaru telescope. M87 GCs with reliable metallicity measurements exhibit significant inflection along the color-metallicity relations, through which observed color bimodality is reproduced from a broad, unimodal metallicity distribution. Our findings lend further support to this new interpretation of the GC color bimodality, which could change much of the current thought on the formation of GC systems and their host galaxies.

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

• 천문학회지
• /
• 제39권2호
• /
• pp.41-50
• /
• 2006

We present the results of new multi-color CCD photometry for the contact binary XZ Leo, together with reasonable explanations for the period and light variations. Six new times of minimum light have been determined. A period study with all available timings confirms Qian's (2001) finding that the O-C residuals have varied secularly according to $dP/dt\;=\;+8.20{\times}10^{-8}\;d\;yr^{-l}$. This trend could be interpreted as a conservative mass transfer from the less massive cool secondary to the more massive hot primary in the system with a mass flow rate of about $5.37{\times}10^{-8}\;M_{\odot}\;yr^{-l}$. By simultaneous analysis of our light curves and the previously published radial-velocity data, a consistent set of light and velocity parameters for XZ Leo is obtained. The small differences between the observed and theoretical light curves are modelled by a blue third light and by a hot spot near the neck of the primary component. Our period study does not support the tertiary light but the hot region which may be formed by gas streams from the cool secondary. The solution indicates that XZ Leo is a deep contact binary with the values of q=0.343, $i=78^{\circ}.8$, ${\Delta}(T_1-T_2)=126\;K$, and f=33.6 %, differing much from those of Niarchos et al. (1994). Absolute parameters of XZ Leo are determined as follows: $M_1=1.84\;M_{\odot},\;M_2=0.63\;M_{\odot},\;R_1=1.75\;R_{\odot},\;R_2=1.10\;R_{\odot},\;L_1=7.19\;L_{\odot},\;and\;L_2=2.66\;L_{\odot}$.

• Journal of Astronomy and Space Sciences
• /
• 제25권2호
• /
• pp.77-86
• /
• 2008

EROS, MACHO, OGLE 등 대규모 탐사관측으로 외부은하에서 식쌍성의 발견은 물론 식쌍성의 광도곡선이 대량으로 발표되고 있다. 식쌍성의 광도곡선은 별의 물리양에 대한 정보를 제공하므로 대량으로 발표된 식쌍성의 광도곡선은 항상천문학 연구에 매우 유용한 자료가 될 것이다. 그러나 식쌍성의 광도 곡선을 분석하는 작업은 많은 시간을 요한다. 이에 시간을 단축하여 광도곡선을 분석하는 방법을 제시하고, 소마젤란 은하에 있는 식쌍성중에서 측광학적으로 질량비를 유일하게 결정할 수 있는 20개의 식쌍성을 표본으로 선정하여 측광학적인 해를 구하였다.

• 천문학회보
• /
• 제40권1호
• /
• pp.84.1-84.1
• /
• 2015

The Baptistina family is one of the typical young asteroid families with an age estimated to be about 140-320 Myrs old (Masiero et al. 2012); considered to have not enough time to experience a significant collisional and dynamical evolution since it was formed. Therefore, it may offer a unique insight into spin rate distribution of relatively fresh fragments and physical mechanism of a family break-up event. Observations of the Baptistina family asteroids were conducted during 111 nights from 2013 Oct. to 2015 Feb., using 0.5 m- to 2 m- class telescopes at 6 observatories in the northern hemisphere. We used CCD cameras on the Sobaeksan Optical Astronomy Observatory (SOAO) 0.6 m telescope on Mt. Sobaek, Korea, the Lemmonsan Optical Astronomy Observatory (LOAO) 1.0 m telescope on Mt. Lemmon, USA, the Tubitak Ulusal Gozlemevi (TUG) 1.0 m telescope in Bakirlitepe, Turkey, the Bohyunsan Optical Astronomy Observatory (BOAO) 1.8 m telescope on Mt. Bohyun, Korea, the McDonald Observatory 2.1 m Otto Struve Telescope on Mt. Locke, USA, and the National Astronomical Research Institute of Thailand (NARIT) Observatory 2.4 m telescope on Mt. Doi Inthanon, Thailand. Here, we will present our preliminary results for lightcurve analyses of Baptistina family members.

• 천문학회보
• /
• 제39권2호
• /
• pp.111-111
• /
• 2014

Intensity interferometry, based on the Hanbury Brown--Twiss effect, is a simple and inexpensive method for optical interferometry at microarcsecond angular resolutions. Motivated by recent technical developments, we argue that the sensitivity of large modern intensity interferometers can be improved by factors up to approximately 25,000, corresponding to 11 photometric magnitudes, compared to the pioneering Narrabri Stellar Interferometer of the 1970s when resolving. Our approach, based on spectrally resolved light, permits the construction of large optical interferometers at the cost of (very) long-baseline radio interferometers. Realistic intensity interferometers are able to spatially resolve main-sequence O-type stars in the Magellanic Clouds. Multi-channel intensity interferometers can address a wide variety of science cases: (i) linear radii, effective temperatures, and luminosities of stars; (ii) mass-radius relationships of compact stellar remnants; (iii) stellar rotation; (iv) stellar convection and the interaction of stellar photospheres and magnetic fields; (v) the structure and evolution of multiple stars; (vi) direct measurements of interstellar distances; (vii) the physics of gas accretion onto supermassive black holes; and (viii) calibration of amplitude interferometers by providing a sample of calibrator stars.

• 천문학회보
• /
• 제42권2호
• /
• pp.54.3-55
• /
• 2017

The Deep Lens Survey (DLS), a precursor to the Large Synoptic Survey Telescope (LSST), is a 20 deg2 survey carried out with NOAO's Blanco and Mayalltelescopes. DLS is unique in its depth reaching down to ~27th mags in BVRz bands. This enables a broad redshift baseline and is optimal for investigating cosmological evolution of the large scale structure. Galaxy-galaxylensing is a powerful tool to estimate averaged matter distribution around lensgalaxies by measuring shape distortions of background galaxies. The signal from galaxy-galaxy lensing is sensitive not only to galaxy halo properties, but also to cosmological environment at large scales. In this study, we measure galaxy-galaxy lensing and galaxy clustering, which together put strong constraints on the cosmological parameters. We obtain significant galaxy-galaxy lensing signals out to ~20 Mpc while tightly controlling systematics. The B-mode signals are consistent with zero. Our lens-source flip test indicates that minimal systematic errors are present in DLS photometric redshifts. Shear calibration is performed using high-fidelity galaxy image simulations. We demonstrate that the overall shape of the galaxy-galaxy lensing signal is well described by the halo model comprised of central and non-central halo contributions. Finally, we present our preliminary constraints on the matter density and the normalization parameters.

• 천문학회보
• /
• 제42권2호
• /
• pp.47.1-47.1
• /
• 2017

We study the alignment of kinematic position angles (PAkin) of early-type galaxies in the Virgo cluster using Atlas3D data. The PAkin represent the direction of the angular momentum of the galaxies better than the photometric position angles. Therefore, the alignment of their PA$_{kin}$ is a useful tool to trace the momentum direction. The early-type galaxies in the Virgo cluster have been known to be distributed as filamentary structures inside the cluster. We found that their PAkin are aligned to two directions of 20degree and -80degree. This fact is confirmed using the bootstrap test, and that is, the two alignment angles are statistically significant. Besides, these two angles are surprisingly aligned parallel to the filamentary structures inside the cluster. These results suggest that early-type galaxies were formed by major merging in the filament structures and then fall into the Virgo cluster while maintaining their position angles.

• 천문학회지
• /
• 제41권5호
• /
• pp.109-119
• /
• 2008

We present an optical-infrared photometric study of galaxies in six nearby clusters of galaxies at $z=0.041{\sim}0.098$ (A1436, A1773, A1809, A2048, A2142, and A2152). Using BV I photometry obtained at the Bohyunsan Optical Astronomical observatory and $JHK_S$ photometry extracted from the 2-Micron All-Sky Survey catalog, we investigate the colors of galaxies in the clusters. Using the (B - V) versus ($I\;-\;K_S$) color-color diagrams in comparison with the simple stellar population model, we estimate the ages and metallicities of bright early-type member galaxies. Early-type galaxies in each cluster show the color-magnitude relation. Ages and metallicities of early-type members show little dependence on their velocity dispersions. Mean ages of early-types in the clusters range from 3 Gyr to 20 Gyr, showing a large dispersion, and mean metallicities range from Z = 0.03 to 0.05 above the solar value, showing a negligible dispersion.