• Journal of Astronomy and Space Sciences
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• v.1 no.1
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• pp.67-74
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• 1984

Photoelectric UBV light curves of AR lacertae made in one season during 1981-82 are presented. Although the shape of the light curves in the outside eclipses shows a strong distortion, the scatter of observations as well as phase coverage are better than those previously available. Fourier coefficients are derived from the V-light curve and the observed curve successfully rectified to the Russell model. Light curve solutions are computed and the geometrical and physical parameters of AR Lac are derived as $a_s$=0.182, $a_g$=0.341, j=$86^{circ}$3, $L_s$=0.372, $L_g$=0.628, k=0.53, $X_s$=0.85, $X_g$=0.4.

• Journal of Astronomy and Space Sciences
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• v.13 no.1
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• pp.19-31
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• 1996

We have analyzed collected photoelectric light curves for light variations of SW Lac. The method of Fourier analysis was adopted to quantify the light variation from season to season. We found the linear relation between the Fourier coefficient, B1 and the magnitude difference between two maxima. The total light of the system has been decreased as much as 0m.04 during approxiamately 20 years time interval. Photoelectric parameters including spot parameters for all light curves were obtained by the method of the Wilson and Devinney differential correction in order to secure the variations of parameters from season to season. SW Lac, not like RS CVn type stars, required to adjust all parameters as well as spot parameters for a reasonable fit to the observations of each epoch. A surface temperature of cooler star is one of the most sensitive parameters to affect a shape of light curve of SW Lac. We conclude that the shape of light curve of SW Lac varies even during one season as well as season to season. The light curve is mainly caused by inhomogeneous surface temperature due to strong chromospheric activity of the system.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.53.1-53.1
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• 2017

The YONSEI (YOnsei Nearby Supernova Evolution Investigation) project is to investigate the luminosity evolution of Type Ia supernovae (SNe Ia) by using their early-type host galaxies. As a part of this project, we have constructed our own SN catalogue. SALT2 and MLCS2k2 light-curve fitters implemented in SNANA package are employed to analyze the light-curve data. The catalogue provides a rest-frame peak magnitude in B-band or distance modulus, a light-curve shape parameter, and a color or an extinction value of each SN in the redshift range from 0.01 to 1.4. In this poster, we will present our progress in the detailed systematic tests for this catalogue.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.225-227
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• 2015

We introduce a code called tlc_s05, to fit sparsely sampled JHK band Cepheid light curve data with template light curves to derive the mean magnitude. A brief description of the code is provided here. We tested the performance of the code in deriving the mean JHK band magnitudes using simulations, and we found that it is better to observe more than four evenly spaced data points per light curve, which permits tlc_s05 to derive accurate mean magnitudes for Cepheid JHK band light curves.

• Journal of Astronomy and Space Sciences
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• v.11 no.2
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• pp.196-207
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• 1994

Data on 27 W UMa systems having a asymmetric light curve so called O'Conell effect have been collected. Investigated 27 W UMa systems were classified into 12 positive and 15 negative type according to the shape of its asymmetric light curve. A list of members of the group, their current observational statue, and their physical and evolutional relationship to asymmetric W UMa type binaries are discussed.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.54.1-54.1
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• 2019

We use iterative smoothing reconstruction method along with exploring in the parameter space of the light curves of the JLA supernova compilation (Joint Light-curve Analysis) to simultaneously reconstruct the expansion history of the universe as well as putting constrains on the light curve parameters without assuming any cosmological model. Our constraints on the light curve parameters of the JLA from our model-independent analysis seems to be closely in agreement with results assuming ΛCDM cosmology or using Chevallier-Polarski-Linder (CPL) parametrization for the equation of state of dark energy. This implies that there is no hidden significant feature in the data that could be neglected by cosmology model assumption. The reconstructed expansion history of the universe and properties of dark energy seems to be in good agreement with expectations of the standard ΛCDM model. Our results also indicate that the data allows a considerable flexibility for expansion history of the universe.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.48.4-49
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• 2020

We reconstruct the expansion history of the universe using type Ia supernovae (SN Ia) in a manner independent of any cosmological model assumptions. To do so, we implement a nonparametric iterative smoothing method on the Joint Light-curve Analysis (JLA) data while exploring the SN Ia light-curve hyperparameter space by Markov Chain Monte Carlo (MCMC) sampling. We test to see how the posteriors of these hyperparameters depend on cosmology, whether using different dark energy models or reconstructions shift these posteriors. Our constraints on the SN Ia light-curve hyperparameters from our model-independent analysis are very consistent with the constraints from using different parameterizations of the equation of state of dark energy, namely the flat ΛCDM cosmology, the Chevallier-Polarski-Linder model, and the Phenomenologically Emergent Dark Energy (PEDE) model. This implies that the distance moduli constructed from the JLA data are mostly independent of the cosmological models. We also studied that the possibility the light-curve parameters evolve with redshift and our results show consistency with no evolution. The reconstructed expansion history of the universe and dark energy properties also seem to be in good agreement with the expectations of the standard ΛCDM model. However, our results also indicate that the data still allow for considerable flexibility in the expansion history of the universe. This work is published in ApJ.

• Journal of Korea Multimedia Society
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• v.25 no.8
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• pp.991-998
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• 2022

Recently, object recognition using image/video signals is rapidly spreading on autonomous driving and mobile phones. However, the actual input image/video signals are easily exposed to a poor illuminance environment. A recent researches for improving illumination enable to estimate and compensate the illumination parameters. In this study, we propose VE-DCE (video enhancement zero-reference deep curve estimation) to improve the illumination of low-light images. The proposed VE-DCE uses unsupervised learning-based zero-reference deep curve, which is one of the latest among learning based estimation techniques. Experimental results show that the proposed method can achieve the quality of low-light video as well as images compared to the previous method. In addition, it can reduce the computational complexity with respect to the existing method.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.55.2-56
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• 2021

The progenitor of Type Ia supernovae (SNe Ia) is mainly believed to be a close binary system of acarbon-oxygen white dwarf (CO WD) and non-degenerate companion (single degenerate) or another WD (double degenerate). However, it is unclear which system is more prevalent. Here, we present a high cadence optical/Near-IR light curve of normal but slightly faint type Ia SN 2019ein from IMSNG project. We fit the early light curve (t <+8.3 days from the first detection) with various models to find the shock-heated cooling emission from SN ejecta-companion interaction. No significant shock-heated cooling emission is found, from which we constrain the progenitor star size as the following. The upper limit (R_upper,*) of the companion size in R-band is ~0.2R_⊙ when forcing the first light time (t_fl) to have one value and ~0.9R_⊙ when using the mean value of tfl from the fitting in each band. Assuming the source of the I-band curve is almost powered from the radioactive decay, we obtained R_upper,*~1.2R_⊙. The early B-V color curve is in agreement with the model color curve of the 2M_⊙ main sequence companion. These results allow us to at least rule out large stars like red giants as a companion star of the binary progenitor system of this supernova. B-R and V-R color do not show any significant signs of a red bump, which shows a thin helium shell (MHe<0.1M_⊙) for the sub-Mch WD (double detonation model). In addition, we estimated the distance to NGC 5353 as 37.098±0.028Mpc.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.56.1-56.1
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• 2018

Tidal disruption events (TDEs) provide evidence for quiescent supermassive black holes (SMBHs) in the centers of inactive galaxies. TDEs occur when a star on a parabolic orbit approaches close enough to a SMBH to be disrupted by the tidal force of the SMBH. The subsequent super-Eddington accretion of stellar debris falling back to the SMBH produces a characteristic flare lasting several months. The theoretically expected bolometric light curve decays with time as proportional to $t^{-5/3}$. However, the light curves observed in most of the optical-UV TDEs deviate from the $t^{-5/3}$ decay rate especially at early time, while the light curves of some soft-X-ray TDEs are overall in good agreement with the $t^{-5/3}$ law. Therefore, it is required to construct the theoretical model for explaining these light curve variations consistently. In this paper, we revisit the mass fallback rates analytically and semi-analytically by taking account of the structure of the star, which is simply modeled by the polytrope. We find the relation between a polytropic index and the power law index of the mass fallback rate. We also discuss whether and how the decay curves, which we derived, fit the observed ones.