• 천문학회지
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• 제38권2호
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• pp.267-270
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• 2005

We investigate the spectral energy distributions (SEDs) of low mass-loss rate O-rich asymptotic giant branch (AGB) stars using the infrared observational data including the Infrared Space Observatory (ISO) data. Comparing the results of detailed radiative transfer model calculations with observations, we find that the dust formation temperature is much lower than 1000 K for standard dust shell models. We find that the superwind model with a density-enhanced region can be a possible alternative dust shell model for LMOA stars.

• 천문학회보
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• 제35권2호
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• pp.80.2-80.2
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• 2010

We have made an improved catalog of O-rich AGB stars in our Galaxy from the sources listed in the Infrared Astronomical Satellite (IRAS) point source catalog (PSC). We compile the lists of previous works with various verifying processes. We have removed 115 stars from the previous catalog of Suh & Kwon (2009) and added 958 more stars. The improved catalog contains 3036 O-rich AGB stars. The content of the revised catalog can be divided into 3 groups based on the verifying processes: OH/IR stars, SiO maser stars, and other detecting methods. We compare the new catalog with the previous catalog on the infrared two-color diagrams for the large sample of O-rich AGB stars. And we discuss differences among the 3 groups of the improved catalog and identification processes of some stars in exceptive cases.

• 천문학회지
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• 제49권4호
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• pp.127-136
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• 2016

We investigate optical properties of amorphous alumina (Al2O3) dust grains in the envelopes around O-rich asymptotic giant branch (AGB) stars using laboratory measured optical data. We derive the optical constants of amorphous alumina over a wide wavelength range that satisfy the Kramers-Kronig relation and reproduce the laboratory data. Using the amorphous alumina and silicate dust, we compare the radiative transfer model results with the observed spectral energy distributions. Comparing the theoretical models with observations on various IR two-color diagrams for a large sample of O-rich AGB stars, we find that the amorphous alumina dust (about 10-40%) mixed with amorphous silicate better models the observed points for the O-rich AGB stars with thin dust envelopes.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2009년도 한국우주과학회보 제18권2호
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• pp.35.3-36
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• 2009

To investigate properties of the stellar contents of the resolved asymptotic giant branch stars in the nearby dwarf galaxies, we obtained wide-field JHKs images of the dwarf irregular galaxies NGC 6822, IC 1613 and the dwarf elliptical galaxy NGC 205, using the WIRCam near-infrared imager of the CFHT. The obtained (J-Ks, Ks) and (H-Ks, Ks) color-magnitude diagrams for the resolved stars in the galaxies contain populations of foreground stars, super giant stars, red giant stars and the asymptotic giant branch (AGB) stars. Using corollary photometric data in the visible bands, AGB stars were selected in the color-magnitude diagrams with a wide wavelength baseline in color indices. In color-color diagrams of the resolved AGB stars, we identified C stars from M giant stars for each galaxies, i.e., 726 C stars in NGC 6822, 126 C stars in IC 1613 and 593 C stars in NGC 205. The number ratios of C stars to M-giants were estimated to be $0.59\pm0.03$ in NGC 6822, $0.30\pm0.03$ in IC 1613 and $0.14\pm0.01$ in NGC 205. From analyses of the correlations of the spatial distribution of the C/M ratios with the HI properties and dynamical structures of the target galaxies, we discuss environmental effects of the star formation in the galaxies. We also discuss the epochs of the AGB star formation in the galaxies by comparing theoretical isochrones with the color distributions and luminosity functions of the AGB stars.

• 천문학회지
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• 제45권6호
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• pp.139-146
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• 2012

We investigate the properties of OH, SiO, and $H_2O$ maser emission in O-rich AGB stars. We use a sample of 3373 objects, which is an updated version of the list of O-rich AGB stars presented in Suh & Kwon (2011). We divide the 3373 O-rich AGB stars into four different groups based on the maser emission: OH maser sources (1533), SiO sources (1627), $H_2O$ sources (452), and sources with no maser (610). To understand the nature of the maser sources, we present various infrared two-color diagrams (2CDs) using IRAS, 2MASS, and AKARI data. For each group, we compare the positions on various infrared 2CDs with theoretical models. We find that the OH maser sources generally show larger color indices and larger dust optical depths than SiO or $H_2O$ sources. We suggest that the differences of the color indices for different maser sources are due to different mass-loss rates and dust formation processes.

• 천문학논총
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• 제15권spc1호
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• pp.85-91
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• 2000

Infrared spectroscopic observations and their analysis revealed many physical and chemical characteristics of the various stars with dust envelopes. Especially, AGB stars and young stellar objects are believed to be major contributors of infrared radiation from galaxies. The wavelength of the peak spectral energy for typical galaxies is about $100{\mu}m$. Therefore, infrared spectral observations of galaxies provide important information for their overall properties. The qualitative analysis of the infrared spectra which are made of various stars and interstellar matter will be possible through a new population synthesis.

• 천문학회보
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• 제35권2호
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• pp.80.1-80.1
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• 2010

From the Akari observational data, we have cross-identified a major portion of AGB stars listed in the catalog of AGB stars presented by Suh & Kwon (2009). We have used the Akari-IRC (Infrared Camera) PSC (Point Source Catalogue; about 850,000 sources at 9 and $18\;{\mu}m$) and Akari-FIS (Far-infrared Surveyer) BSC (Bright Source Catalogue; about 440,000 sources at 65, 90, 140 and $160\;{\mu}m$) as well as the IRAS and NIR observational data to make various meaningful two-color diagrams for AGB stars. We compare them with the theoretical models with various dust shell model parameters and chemical compositions.

• 천문학회보
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• 제36권1호
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• pp.30.2-30.2
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• 2011

Dust species in the envelopes around AGB stars would have multiple components rather than a single component. Each dust species may have its own temperature and density structure. We use the radiative transfer code RADMC-3D developed by Dullemond et al. 2011 to model the multi-component dust envelopes around O-rich AGB stars. For reasonable combinations of physical and chemical parameters of the dust envelopes, we use multi-component dust species of silicate, corundum, and water ice. We find that the new model results can explain the observations of O-rich AGB stars better than conventional models.

• Journal of Astronomy and Space Sciences
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• 제26권3호
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• pp.279-286
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• 2009

To study properties of the variation of the infrared emission of OH/IR stars, we collect and analyze the infrared observational data in K band for nine OH/IR stars. We use the observational data obtained for about three decades including recent data from the two micron all sky survey (2MASS) and the deep near infrared survey of the southern sky (DENIS). We use Marquardt-Levenberg algorithm to determine the pulsation period and amplitude for each star and compare them with previous results of infrared and radio investigations.

• 천문학논총
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• 제30권2호
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• pp.355-358
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• 2015

We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group galaxy M33. The main aim was to identify stars in the very final stage of their evolution, and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity. The pulsating giant stars (AGB and red supergiants) are identified and their distributions are used to derive the star formation rate as a function of age. These stars are also important dust factories; we measure their dust production rates from a combination of our data with Spitzer Space Telescope mid-IR photometry. The mass-loss rates are seen to increase with increasing strength of pulsation and with increasing bolometric luminosity. Low-mass stars lose most of their mass through stellar winds, but even super-AGB stars and red superginats lose ~40% of their mass via a dusty stellar wind. We construct a 2-D map of the mass-return rate, showing a radial decline but also local enhancements due to agglomerations of massive stars. By comparing the current star formation rate with total mass input to the ISM, we conclude that the star formation in the central regions of M33 can only be sustained if gas is accreted from further out in the disc or from circum-galactic regions.