• 천문학회보
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• 제44권1호
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• pp.48.1-48.1
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• 2019

Mass and radius of a neutron star in low-mass X-ray binary (LMXB) can be estimated simultaneously when the observed light curve and spectrum show the photospheric radius expansion feature. This method has been applied to 4U 1746-37 and the mass and radius were found to be unusually small in comparison with typical neutron stars. We re-estimate the mass and radius of this target by considering that the observed light curve and spectrum can be affected by other X-ray sources because this LMXB belongs to a very crowded globular cluster NGC 6441. The new estimation increases the mass and radius but they do not reach the typical values yet.

• 천문학회보
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• 제45권1호
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• pp.51.3-52
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• 2020

We present the status of the development of a Markov Chain Monte Carlo (MCMC) parameter estimation (PE) pipeline for compact binary coalescences (CBCs) with the Japanese KAGRA gravitational-wave (GW) detector. The pipeline is included in the KAGRA Algorithm Library (KAGALI). Basic functionalities are benchmarked from the LIGO Algorithm Library (LALSuite) but the KAGRA MCMC PE pipeline will provide a simpler, memory-efficient pipeline to estimate physical parameters from gravitational waves emitted from compact binaries consisting of black holes or neutron stars. Applying inspiral-merge-ringdown and inspiral waveforms, we performed simulations of various black hole binaries, we performed the code sanity check and performance test. In this talk, we present the situation of GW observation with the Covid-19 pandemic. In addition to preliminary PE results with the KAGALI MCMC PE pipeline, we discuss how we can optimize a CBC PE pipeline toward the next observation run.

• 천문학논총
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• 제8권1호
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• pp.169-177
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• 1993

Observed spectra of supernovae allow the empirical classification of supernovae into two basic categories, Type I with little or no evidence of hydrogen, and Type II with obvious evidence for hydrogen. The broad class of Type I can be subdivided depending on whether helium or silicon and other intermediate mass elements is observed. Understanding the physical processes that underlie these classifications---the progenitor evolution. the explosion mechanism, and end products---requires calculation of radiative transfer and model spectra. While most Type II occur in evolved massive stars that undergo core collapse. some may span the dividing line between degenerate and non-degenerate carbon burning and involve both core collapse and thermonuclear explosion. Type Ia are still most plausibly explained as thermonuclear explosions in carbon/oxygen white dwarfs in binary systems. Type Ib reveal helium atmospheres and are probably the result of core collapse in the helium core of a massive star that has lost its hydrogen envelope to a binary companion or to a wind. Type Ic supernovae are probably related to Type Ib but have also lost their helium envelope to reveal a mantle rich in oxygen.

• Journal of Astronomy and Space Sciences
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• 제15권1호
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• pp.65-68
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• 1998

We construct the X-ray light curves of the W UMa type contact binary SS Arietis(HD12929) from the EXOSAT data in HEASARC data archive. The phase dependent X-ray light curves obtained by using the ephimeris of Kaluzny & Pojmanski of SS Ari is modulated on the orbital phase as in the case of other W UMa type binaries. Although a detailed analysis of these data is impossible because of the very low X-ray light curves in the context of the radiation in the corona region of W UMa type stars.

• 천문학회지
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• 제29권spc1호
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• pp.277-278
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• 1996

In attempts to detect gravitational waves, the response of some celestial systems such as the earth[l] or binary systems[2] to such waves have been investigated. Following this line of thought, here we study the possibility of excitation of the oscillation modes of a polytropic star by gravitational radiation and calculate the relevant absorption cross sections.

• 천문학회보
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• 제39권1호
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• pp.77.1-77.1
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• 2014

Gravitational waves predicted by the general relativity almost 100 years ago have been implicated indirectly only by astrophysical observations such as the orbital evolution of binary pulsars. The advanced detectors of gravitational waves will become operational in a few years and they are expected to make direct detection of gravitational wave signal coming from merging of binaries composed of neutron stars or stellar mass black holes from external galaxies. Korean Gravitational Wave Group (KGWG) is contributing to the possible detection through the data analysis of LIGO and Virgo. We summarize the perspectives of the gravitational wave research and the impacts of the detection in the near future in astronomy and astrophysics.

• 천문학회보
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• 제44권2호
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• pp.54.2-54.2
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• 2019

Mass and radius of a neutron star in low-mass X-ray binary (LMXB) can be estimated simultaneously when the observed light curve and spectrum show the photospheric radius expansion feature. This method has been applied to 4U 1746-37 and the mass and radius were found to be unusually small in comparison with typical neutron stars. We re-estimate the mass and radius of this target by considering that the observed light curve and spectrum can be affected by other X-ray sources because this LMXB belongs to a very crowded globular cluster NGC 6441. The new estimation increases the mass and radius but they do not reach the typical values yet.

• 천문학회지
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• 제38권2호
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• pp.237-240
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• 2005

We present images of L1551 IRS5 at angular resolutions as high as ${\~}$30 mas, corresponding to a spatial resolution of ${\~}$5 AU, made at 7 mm with the VLA. Previously known to be a binary protostellar system, we show that L1551 IRS5 is likely a triple protostellar system. The primary and secondary components have a projected separation of ${\~}$46 AU, whereas the tertiary component has a projected separation of ${\~}$11 AU from the primary component. The circumstellar dust disks of the primary and secondary components have dimensions of ${\~}$15 AU, whereas that of the tertiary component has a dimension of ${\~}$10 AU. Their major axes are closely, but not perfectly, aligned with each other, as well as the major axis of the surrounding flattened, rotating, and contracting molecular condensation (pseudodisk). Furthermore, the orbital motion of the primary and secondary components is in the same direction as the rotational motion of this pseudodisk. We suggest that all three protostellar components formed as a result of the fragmentation of the central region of the molecular pseudo disk. The primary and secondary components, but apparently not the tertiary component, each exhibits a bipolar ionized jet that is centered on and which emergers perpendicular to its associated dust disk. Neither jets are resolved along their base, implying that they are driven within a radial distance of ${\~}$2.5 AU from their central protostars. Finally, we show evidence for what may be dusty matter streams feeding the two main protostellar components.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 1992년도 한국우주과학회보 제1권1호
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• pp.15-15
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• 1992

AQ Cassiopeiae (BD+61`0242, uv=10, Sp=B3+Bg) is a totally eclipsing binary system with the obital period of about 12 days. 71 was observed for 15 nights in 1985 with the1.8-m telescope at the DAO, employing a Reticon and a three-stage image tube attached to the spectrograph. And also, photometric observations of AQ Cas had been made inUBv for six years from 1982 to 1988 at Yonsei University Observatory(YUO). This work includes UBV observations obtained at YUO as a part of The Ten-Year Observing Program(1982-1992). Double lined radial, velocity curves and Ufv light curves of AQC as are constructed. The light curves and radial velocity curves show a strong evidence of circumstellar matter or mass stream. It is clear at the phases of just outside externaleclipse contacts, particularly at phase 0.8-0.9, shown in Figures 1 and 2. A solution by combining the radial velocity and photometric curves of the binary was obtained with the Wilson-Devinney Code. We found that the system is semi-detached with the coolcomponent filling its Roche lobe. The absolute dimensions of AQ Cas are calculated. The result shows that this system consists of two massive and subgiant stars.

• 천문학회보
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• 제38권1호
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• pp.57.2-57.2
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• 2013

Based on N-body simulations, we find out that significant fraction of dynamically formed BH-BH (10 $M_{\odot}$ and NS-NS (1.4 $M_{\odot$ ecah) binaries are ejected from globular clusters. About 30 percent of compact stars are ejected in the form of binary. The merging time of ejected binary depends on the velocity dispersion of globular cluster. Some of ejected binaries have merging time-scales shorter than Hubble time and are expected to produce gravitational waves that can be detectable by the advanced ground-based interferometers. The merger rates of ejected BH-BH and NS-NS binaries per globular cluster are estimated to be 3.5 and 17 per Gyr, respectively. Assuming the spatial density of globular clusters as 8.4 $h^3$ clusters $Mpc^{-3}$ and extrapolating to the horizon distance of the advanced LIGO-Virgo network, we expect the detection rates solely attributed to BH-BH and NS-NS with cluster origin are to be 42 and 1.7 $yr^{-1}$, respectively. Besides, we find out that BH-NS binary ejection hardly occurs in globular clusters and dynamically formed compact binaries may possibly be the source of short GRBs whose locations are far from host galaxies.