• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.2
• /
• pp.143.1-143.1
• /
• 2012

We attempt to investigate the main reason of the asymmetrical light curves of contact and near-contact eclipsing binary base on the hypothesis that cool spot was produced on late type star while hot spot was produced from transferred material from their companion star hitting surface. We select 7 eclipsing binary systems which showed asymmetric light curves and mass transfer. Period variation and mass transfer rate were obtained from O-C diagram. Radial velocity curves and light curves of those 7 eclipsing binary system were adopted from available literature in order to obtain the absolute dimension. For four contact eclipsing binary system (AD Phe, EZ Hya, AG Vir and VW Boo), their component stars belonged to spectral type G to K was fitted by cool spot model. While the other two near-contact systems (RT Scl and V1010 Oph) and one contact system (SV Cen) was fitted by cool spot model. The densities of the materials are adopted from stellar model which calculate by stellar structure code. The calculated spot temperature turns out to agree with the photometric solution but there are no correlate between period variation rate and type of spot.

• Journal of Astronomy and Space Sciences
• /
• v.29 no.1
• /
• pp.69-77
• /
• 2012

This report describes the inception, development and extensive use over 30 years of elliptical polarimeters at the University of Pennsylvania. The initial Mark I polarimeter design utilized oriented retarder plates and a calcite Foster-Clarke prism as the analyzer. The Mark I polarimeter was used on the Kitt Peak 0.9 m in 1969-70 to accomplish a survey of approximately 70 objects before the device was relocated to the 0.72 m reflector at the Flower and Cook Observatory. Successive generations of automation and improvements included the early-80's optical redesign to utilize a photoelastic modulated wave plate and an Ithaco lock-in amplifier-the photoelastic modulating polarimeter. The final design in 2000 concluded with a fully remote operable device. The legacy of the polarimetric programs includes studies of close binaries, pulsating hot stars, and luminous late-type variables.

• The Bulletin of The Korean Astronomical Society
• /
• v.36 no.1
• /
• pp.69.2-69.2
• /
• 2011

We present medium resolution spectra in the near-infrared (IR) band 1.4-1.8 microns at a resolving power of R = 5000-10000 of template stars in G, K, and M types with luminosity classes of III observed by the echelle spectrometer, IRCS, at the SUBARU 8.2 m telescope. Identification of lines in the template star spectra has been completed base on the reference of Arcturus spectrum. We measured equivalent width (EW) of the lines, and analyze the trends of EW through the stellar spectral types.

• Publications of The Korean Astronomical Society
• /
• v.22 no.4
• /
• pp.89-95
• /
• 2007

The warm ionized medium (WIM) outside classical H II regions is a fundamental gas-phase constituent of the Milky Way and other late-type spiral galaxies, and is traced by faint emission lines at optical wavelengths. We calculate the photoionization models of the WIM in the Galaxy by a stellar UV radiation with the effective temperature 35,000 K assuming not only spherical geometry but also plane parallel geometry, and compare the results with the observed emission line ratios. We also show the dependence of the emission line ratios on various gas-phase abundances. The emergent emission-line ratios are in agreement with the average-values of observed ratios of [S II] ${\lambda}6716/H{\alpha}$, [N II] ${\lambda}6583/H{\alpha}$, [O I] ${\lambda}6300/H{\alpha}$, [O III] ${\lambda}5007/H{\alpha}$, He I ${\lambda}5876/H{\alpha}$. However, their extreme values could not be explained with the photoionization models. It is also shown that the addition of all stellar radiation from the OB stars in the Hipparcos stellar catalog resembles that of an O7-O8 type star.

• The Bulletin of The Korean Astronomical Society
• /
• v.38 no.2
• /
• pp.71.1-71.1
• /
• 2013

Among quadruples or higher multiplicity stars, only a few binary systems have been discovered. They are important targets to understand the formation and evolution of multiple stellar systems because we can obtain accurate stellar parameters from photometric and spectroscopic studies. We present the observational results of this kind of rare object 1SWASP J093010.78+533859.5, for which the doubly eclipsing feature had been detected previously from the SuperWASP photometric archive. Individual PSF photometry for two objects with a separation of about 1.9 arcsec was performed for the first time in this study. Our time-series photometric data show that the brighter object A is an Algol-type detached eclipsing binary with an orbital period of 1.3 days and the fainter B is a W UMa-type contact eclipsing binary with a period of 0.23 days. Using the high-resolution optical spectra, we obtained well-defined radial velocity variations of the system A. Furthermore, stationary spectral lines were detected and should have originated from the other stellar component, which was confirmed by the third object contribution from the light curve analysis. No spectral feature of the system B was detected, probably due to its faintness. We obtained the binary parameters and the absolute dimensions from each light curve synthesis. The primary and secondary components of the system A have a spectral type of K1 and K5 main sequences, respectively. Two components of system B have nearly the same type of K3 main sequence. Light variations at out of eclipses were appeared in both systems, interpreting as the effect of stellar spots on these late spectral type stars. We estimated the distances to the systems A and B individually. They may have similar distances of about 70 pc and seem to be gravitationally bound with a separation of about 130 AU. In conclusion, we suggest that 1SWASP J093010.78+533859.5 is a quintuple stellar system with a hierarchical structure of a triple system A(ab)c and a binary system B(ab).

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.1
• /
• pp.74.1-74.1
• /
• 2012

It is known that the diffuse H${\alpha}$ halos around bright H II regions are more extended than the dust-scattered halos around point sources and the line ratios [S II] ${\lambda}$6716/H${\alpha}$ and [N II] ${\lambda}$6583/H${\alpha}$ observed outside of bright H II regions are generally higher than those in H II regions. These observational facts have been regarded as evidence against the dust-scattering origin of the diffuse H${\alpha}$ emission and the effect of dust-scattering has been neglected in studying the diffuse H${\alpha}$ emission. In this paper, we find, however, that dust-scattered halos of H II regions should be more extended than those of point sources and is in good agreement with the observed H${\alpha}$ profiles around H II regions. We also found that the observed line ratios [S II]/H${\alpha}$, [N II]/H${\alpha}$, and He I ${\lambda}$5876/H${\alpha}$ in the diffuse regions can be well reproduced with the dust-scattered halos around H II regions which are photoionized by late O- and/or early B-type stars in the interstellar medium with the abundances close to those of the warm neutral medium. Therefore, we conclude that the diffuse H${\alpha}$ emission may originate mostly from the dust-scattering.

• The Bulletin of The Korean Astronomical Society
• /
• v.35 no.2
• /
• pp.59.1-59.1
• /
• 2010

We have carried out VLBI test observations of the Korean VLBI Network (KVN) at 22/43-GHz in collaboration with Japanese VLBI Exploration of Radio Astrometry (VERA). In order to evaluate the VLBI system of KVN, we have observed several sources using KVN+VERA. They consist of Active Galactic Nuclei (AGNs), which are expected to be compact and to have very well-known structures at spatial resolutions of 50-250 Mega-wavelengths, and Galactic star-forming regions and late-type stars, which have bright H2O and SiO maser emission regions. We have investigated baseline and imaging sensitivities of KVN+VERA. In this talk we report the preliminary results.

• The Bulletin of The Korean Astronomical Society
• /
• v.35 no.2
• /
• pp.59.2-59.2
• /
• 2010

We have carried out VLBI test observations of the Korean VLBI Network (KVN) at 22/43-GHz in collaboration with Japanese VLBI Exploration of Radio Astrometry (VERA). In order to evaluate the VLBI system of KVN, we have observed several sources using KVN+VERA. They consist of Active Galactic Nuclei (AGNs), which are expected to be compact and to have very well-known structures at spatial resolutions of 50-250 Mega-wavelengths, and Galactic star-forming regions and late-type stars, which have bright H2O and SiO maser emission regions. We have investigated baseline and imaging sensitivities of KVN+VERA. In this talk we report the preliminary results.

• Journal of The Korean Astronomical Society
• /
• v.37 no.4
• /
• pp.193-197
• /
• 2004

Anomalies in the far-infrared [C II] 158 ${\mu}m$ line emission observed in the central one-kiloparsec regions of spiral galaxies are reviewed. Low far-infrared intensity ratios of the [C II] line to the continuum were observed in the center of the Milky Way, because the heating ratio of the gas to the dust is reduced by the soft interstellar radiation field due to late-type stars in the Galactic bulge. In contrast, such low line-to-continuum ratios were not obtained in the center of the nearby spiral M31, in spite of its bright bulge. A comparison with numerical simulations showed that a typical column density of the neutral interstellar medium between illuminating sources at $hv {\~} 1 eV $ is $N_H {\le}10^{21}\;cm^{-2}$ in the region; the medium is translucent for photons sufficiently energetic to heat the grains but not sufficiently energetic to heat the gas. This interpretation is consistent with the combination of the extremely high [C Il]/CO J = 1-0 line intensity ratios and the low recent star-forming activity in the region; the neutral interstellar medium is not sufficiently opaque to protect the species even against the moderately intense incident UV radiation. The above results were unexpected from classical views of the [C II] emission, which was generally considered to trace intense interstellar UV radiation enhanced by active star formation.

• Journal of The Korean Astronomical Society
• /
• v.55 no.4
• /
• pp.131-138
• /
• 2022

We report the discovery of four quasars with M₁₄₅₀ ≳ -25.0 mag at z ~ 5 and supermassive black hole mass measurement for one of the quasars. They were selected as promising high-redshift quasar candidates via deep learning and Bayesian information criterion, which are expected to be effective in discriminating quasars from the late-type stars and high-redshift galaxies. The candidates were observed by the Double Spectrograph on the Palomar 200-inch Hale Telescope. They show clear Lyα breaks at about 7000-8000 Å, indicating they are quasars at 4.7 < z < 5.6. For HSC J233107-001014, we measure the mass of its supermassive black hole (SMBH) using its C _IV λ1549 emission line. The SMBH mass and Eddington ratio of the quasar are found to be ~10⁸ M_⊙ and ~0.6, respectively. This suggests that this quasar possibly harbors a fast growing SMBH near the Eddington limit despite its faintness (L_Bol < 10⁴⁶ erg s^-1). Our 100% quasar identification rate supports high efficiency of our deep learning and Bayesian information criterion selection method, which can be applied to future surveys to increase high-redshift quasar sample.