• Journal of Astronomy and Space Sciences
• /
• v.29 no.2
• /
• pp.123-129
• /
• 2012

The BINSYN program package, recently expanded to calculate synthetic spectra of cataclysmic variables, is being further extended to include synthetic photometry of ordinary binary stars in addition to binary stars with optically thick accretion disks. The package includes a capability for differentials correction optimization of eclipsing binary systems using synthetic photometry.

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.179-182
• /
• 2015

Dust has recently been found to be prevalent in compact binaries such as non-magnetic Cataclysmic Variable systems. As a possible source of this dust is from solid bodies, we explore impacts to non-magnetic Cataclysmic Variable disks. We use three-dimensional Smoothed Particle Hydrodynamic simulations to search for impact signatures. From injections of whole bodies to these disks, we find pulse shapes in simulated bolometric light curves that resemble impact flashes in the light curves of the Shoemaker-Levy 9 event. As a result, we tentatively identify these light curve shapes as signatures of impacts.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.2
• /
• pp.60.3-60.3
• /
• 2019

Binary systems of a white dwarf showing mass transfer activities are classified into cataclysmic variables and symbiotic stars. In the case of cataclysmic variables, the companion is usually a late type main sequence star filling its Roche lobe, where material is transferred through the inner Lagrangian point to form an accretion disk around the white dwarf. The disk becomes unstable and highly viscous when the surface density exceeds the critical density, leading to dwarf nova outbursts. In contrast, symbiotic stars are wide binary systems having a giant as the mass donor. Some fraction of giant stellar wind is accreted to the white dwarf giving rise to various symbiotic activities. In particular, half of symbiotics show Raman O VI at 6830 and 7088, which are important spectroscopic probe of mass transfer process. Monitoring observations using 1 m class telescopes will produce valuable information regarding the mass loss and mass transfer to white dwarf stars, shedding much light on the last stage of stellar evolution of low and intermediate mass stars.

• Journal of The Korean Astronomical Society
• /
• v.25 no.1
• /
• pp.47-64
• /
• 1992

Cores of globular clusters are an ideal place for close encounters between stars. The outcome of tidal capture can be stellar mergers, close binaries between normal stars (W UMa type), cataclysmic variables composed of white dwarf and normal star pairs, or low-mass X-ray binaries consisting of a neutron star and a normal star pairs. Stellar mergers can be the origin of blue stragglers in dense globular clusters although they are hard to observe. Low mass X-ray binaries would eventually become binary pulsars with short pulse periods after the neutron stars accrete sufficient amount of matter from the companion. However, large number of recently discovered, isolated millisecond pulsars (as opposed to binary pulsars) in globular clusters may imply that they do not have to gain angular speeds during the X-ray binary phase. We propose that these isolated millisecond pulsars may have formed through the disruptive encounters, which lead to the formation of accretion disk without Roche lobe filling companion, between a neutron star and a main-sequence star. Based on recently developed multicomponent models for the dynamical evolution of globular clusters, we compute the expected numbers of various systems formed by tidal capture as a function of time.

• Journal of Astronomy and Space Sciences
• /
• v.29 no.2
• /
• pp.169-173
• /
• 2012

A summary is presented of what is currently known about the surface temperatures of accreting white dwarfs (WDs) detected in non-magnetic and magnetic cataclysmic variables (CVs) based upon synthetic spectral analyses of far ultraviolet data. A special focus is placed on WD temperatures above and below the CV period gap as a function of the orbital period, $P_{orb}$. The principal uncertainty of the temperatures for the CV WDs in the $T_{eff}-P_{orb}$ distribution, besides the distance to the CV, is the mass of the WD. Only in eclipsing CV systems, an area of eclipsing binary studies, which was so central to Robert H. Koch's career, is it possible to know CV WD masses with high precision.

• Journal of Astronomy and Space Sciences
• /
• v.21 no.3
• /
• pp.191-200
• /
• 2004

The accuracy of CCD observations obtained at the Korean 1.8m telescope has been studied. Seventeen comparison stars in the vicinity of the cataclysmic variable BG CMi have been measured. The 'artificial' star has been used instead of the 'control' star, what made possible to increase accuracy estimates by a factor of 1.3-2.1 times for 'good' and 'cloudy' nights, respectively. The algorithm of iterative determination of accuracy and weights of few comparison stars contributing to the artificial star, has been presented. The accuracy estimates for 13-mag stars are around $0.^m002$ mag for exposure times of 30 sec.

• The Bulletin of The Korean Astronomical Society
• /
• v.35 no.1
• /
• pp.52.1-52.1
• /
• 2010

The relationship between orbital periods of cataclysmic variables (CV) and mass-loss rates of their donor stars is an important subject of theoretical researches. The observed donor's radii are oversized in comparison with those of isolated unperturbed stars of the same mass, which is thought to be a consequence of the mass-loss. Using the empirical mass-radius relation of CVs and the Hayashi theory for changes in effective temperature, orbital period, and luminosity of the donor with the stellar radius, we find the mass-loss rate of CVs as a function of the orbital period P. The derived mass-loss rate is more or less constant at 10-9.6-10-10M$\odot$ yr-1 with P above 90 minutes and declines very rapidly with P below 90 minutes, reaching 10-10.3-10-11.7M$\odot$ yr-1 when P is close to the minimum period. The turnaround behavior of the mass-loss rate shape with P near the minimal period is much less pronounced than suggested by earlier numerical models, making observational detection of the turnaround highly unlikely. When applied to our new results, SDSS 1035, 1507, 1501 and 1433 systems, previously known as post-bounce CVs, are more likely to be systems that have yet to reach the minimal period.

• Journal of Astronomy and Space Sciences
• /
• v.36 no.4
• /
• pp.283-292
• /
• 2019

The purpose of this study was to develop a period analysis algorithm for detecting new variable stars in the time-series data observed by charge coupled device (CCD). We used the data from a variable star monitoring program of the CBNUO. The R filter data of some magnetic cataclysmic variables observed for more than 20 days were chosen to achieve good statistical results. World Coordinate System (WCS) Tools was used to correct the rotation of the observed images and assign the same IDs to the stars included in the analyzed areas. The developed algorithm was applied to the data of DO Dra, TT Ari, RXSJ1803, and MU Cam. In these fields, we found 13 variable stars, five of which were new variable stars not previously reported. Our period analysis algorithm were tested in the case of observation data mixed with various fields of view because the observations were carried with 2K CCD as well as 4K CCD at the CBNUO. Our results show that variable stars can be detected using our algorithm even with observational data for which the field of view has changed. Our algorithm is useful to detect new variable stars and analyze them based on existing time-series data. The developed algorithm can play an important role as a recycling technique for used data

• Publications of The Korean Astronomical Society
• /
• v.15 no.spc1
• /
• pp.147-151
• /
• 2000

Symbiotic stars, believed to be binary systems of a mass-losing giant and a white dwarf with an emission nebula, are known to exhibit very broad wings around Hex that extend to $\~10^3km\;s^{-1}$. The wing formation mechanism is not a settled matter and recently Lee (2000) proposed that Raman scattering of Ly$\beta$ by neutral hydrogen is responsible for the broad H$\alpha$ wings. In this model, it is predicted that. the Hex wings will be polarized depending on the geometric and kinematic distribution of the scatterers relative to the UV emission region. In this paper, we investigate the polarization of Hex wings in symbiotic stars. Noting that many symbiotic stars possess bipolar nebular morphology, we assume that the distribution of neutral scatterers follows the similar pattern with a receding velocity of several tens of km $s^{-1}$ that mimics the expansion of the neutral envelope of the nebula. It is found that the red wing is more strongly polarized than the blue and main part and that the polarization direction is along the equatorial plane. We obtain a typical degree of polarization $\~10$ percent, however, it varies depending on the detailed distribution of H I scatterers We conclude that spectropolarimetry will provide very important information on the origin of the Hex wings.

• Journal of The Korean Astronomical Society
• /
• v.44 no.3
• /
• pp.89-96
• /
• 2011

We present results of two-color VR photometry of the intermediate polar RXS J1803. The data were aquired using the Korean 1-m telescope located at Mt. Lemmon, USA. Different "high" and "low" luminosity states, similar to other intermediate polars, were discovered. No statistically significant variability of the color index with varying luminosity was detected. The orbital variability was found to be not statistically significant. Spin maxima timings were determined, as well as the photometric ephemeris for the time interval of our observations. The spin period variations, caused by interaction of the accretion structure with the rotating magnetic white dwarf, were also detected. These variations are of complicated character, and their study requires further observations. We determine the color transformation coefficients for our photometric systems, and improve on the secondary photometric standards.