• Journal of Astronomy and Space Sciences
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• 제29권1호
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• pp.47-49
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• 2012

Massive binary stars lose mass by two mechanisms: jet-driven mass loss during periods of active mass transfer and by wind-driven mass loss. Beta Lyrae is an eclipsing, semi-detached binary whose state of active mass transfer provides a unique opportunity to study how the evolution of binary systems is affected by jet-driven mass loss. Roche lobe overflow from the primary star feeds the thick accretion disk which almost completely obscures the mass-gaining star. A hot spot predicted to be on the edge of the accretion disk may be the source of beta Lyrae's bipolar outflows. I present results from spectropolarimetric data taken with the University of Wisconsin's Half-Wave Spectropolarimeter and the Flower and Cook Observatory's photoelastic modulating polarimeter instrument which have implications for our current understanding of the system's disk geometry. Using broadband polarimetric analysis, I derive new information about the structure of the disk and the presence and location of a hot spot. These results place constraints on the geometrical distribution of material in beta Lyrae and can help quantify the amount of mass lost from massive interacting binary systems during phases of mass transfer and jet-driven mass loss.

• 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.

• 천문학회지
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• 제56권2호
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• pp.149-157
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• 2023

The propagation speed of a circumstellar pattern revealed in the plane of the sky is often assumed to represent the expansion speed of the wind matter ejected from a post-main-sequence star at the center. We point out that the often-adopted isotropic wind assumption and the binary hypothesis as the underlying origin for the circumstellar pattern in the shape of multilayered shells are, however, mutually incompatible. We revisit the hydrodynamic models for spiral-shell patterns induced by the orbital motion of a hypothesized binary, of which one star is losing mass at a high rate. The distributions of transverse wind velocities as a function of position angle in the plane of the sky are explored along viewing directions. The variation of the transverse wind velocity is as large as half the average wind velocity over the entire three dimensional domain in the simulated models investigated in this work. The directional dependence of the wind velocity is indicative of the overall morphology of the circumstellar material, implying that kinematic information is an important ingredient in modeling the snapshot monitoring (often in the optical and near-infrared) or the spectral imaging observations for molecular line emissions.

• 천문학회보
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• 제12권
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• pp.10.2-10.2
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• 1987

• Journal of Astronomy and Space Sciences
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• 제10권1호
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• pp.25-35
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• 1993

Stars lose their masses constantly after their birth, but the stellar mass loss is especially prominent in the last stages of their lives. It has been believed that red superginats are losing their masses at rates of 10-8∼10-4M/yr. They are known to be asymptotic giant branch stars that are at the end stages of the evolution for the stars with zero age main sequence masses of 1∼10M. Red supergiants are often characterized by the thick dust envelopes and large amplitude pulsations. According to their energy spectra, chemical composition, they are divided into three main group; M-type Miras, C-type carbon stars, and OH/IR stars. The purpose of this work is to clarify the evolutionary aspects in the physical parameters of the red supergiants mainly from the direct interpretation of their infrared spectra.

• 천문학회지
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• 제53권6호
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• pp.117-123
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• 2020

We investigate the plausibility of mass return, from stellar mass loss processes within the central ~100 pc region of the Milky Way (the inner nuclear bulge), as a mass supply mechanism for the Circumnuclear Disk (CND). Gas in the Galactic disk migrates inward to the Galactic centre due to the asymmetric potential caused by the Galactic bar. The inward migration of gas stops and accumulates to form the central molecular zone (CMZ), at 100-200 pc from the Galactic center. It is commonly assumed that stars have formed in the CMZ throughout the lifetime of the Galaxy and have diffused inward to form a 'r-2 stellar cusp' within the inner nuclear bulge. We propose that the stars migrating inward from the CMZ supply gas to the inner nuclear bulge via stellar mass loss, resulting in the formation of a gas disk along the Galactic plane and subsequent inward migration down to the central 10 pc region (CND). We simulate the evolution of a gas distribution that initially follows the stellar distribution of the aforementioned stellar cusp, and illustrate the potential gas supply toward the CND.

• 천문학회보
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• 제43권2호
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• pp.51.4-51.4
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• 2018

Luminous blue variables (LBVs) are luminous evolved massive stars (thus with very large initial masses) typified by their irregular variabilities, which are sometimes associated with eruptive mass loss. G026.47+0.02 is one of the known Galactic LBV surrounded by large circumstellar shell (r~1') detected in far IR. In this presentation, we report the identification of another shell of smaller radii (r~20") indicating that the central star experienced multiple episodes of eruptions. We present detailed multi-wavelength study of the inner shell in near IR and sub-mm, with which we reconstruct its mass-loss history.

• 천문학회보
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• 제41권1호
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• pp.43.2-43.2
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• 2016

We present results of a calibrator search near twenty evolved stars using the Korean VLBI Network (KVN). Our evolved star targets include candidate sources for a Key Science Project (KSP) of the KVN. The KSP plans to investigate the spatial structure and dynamical effects between SiO and H2O maser regions including mass-loss process and development of asymmetry in circumstellar envelopes of evolved stars. For these purposes, we need compact and strong extragalactic sources close to the evolved stars. We carried out 5 observations in order to detect radio continuum sources that can be used for source frequency phase-referencing (SFPR) -based analysis. We observed 153 sources, out of which we detected 29 at 22 GHz and 20 at 43 GHz at signal-to-noise ratios higher than 50 at all baselines. Therefore, we successfully found target and calibrator pairs for the KVN KSP.

• Journal of Astronomy and Space Sciences
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• 제23권3호
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• pp.189-198
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• 2006

BVRI CCD 측광 관측에 의하여 질량비가 작은 접촉쌍성 HN UMa와 II UMa의 새로운 광도곡선을 얻었다. 새로운 광도곡선과 이미 발표된 분광관측으로부터 Wilson-Devinney 프로그램을 이용하여 이 두 별의 궤도요소와 절대 물리량을 얻었다. HN UMa와 II UMa를 포함한 절대물리량이 잘 알려진 21개의 질량비가 작은 접촉쌍성들의 진화 상태를 조사하였다. 그 결과 질랑비가 작은 접촉쌍성의 반성은 영년주계열 아래 놓이며, 이러한 현상은 질량이 작은 접촉쌍성의 반성에서의 질량손실을 가정할 경우, 비록 작의 양의 질량이지만 반성에서의 질량 감소는 상대적으로 광도의 감소가 현저히 작아지기 때문일 것으로 예상된다.

• 천문학논총
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• 제22권1호
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• pp.21-33
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• 2007

Ever since the identification of 6830 and 7088 features as the Raman scattered O VI 1032, 1038 resonance doublets in symbiotic stars by Schmid (1989), Raman scattering by atomic hydrogen has been a very unique tool to investigate the mass transfer processes in symbiotic stars. Discovery of Raman scattered He II in young planetary nebulae (NGC 7027, NGC 6302, IC 5117) allow one to expect that Raman scattering can be an extremely useful tool to look into the mass loss processes in these objects. Because hydrogen is a single electron atom, their wavefunctions are known in closed form, so that exact calculations of cross sections are feasible. In this paper, I review some basic properties of Raman scattered features and present detailed and explicit matrix elements for computation of the scattering cross section of radiation with atomic hydrogen. Some astrophysical objects for which Raman scattering may be observationally pertinent are briefly mentioned.