• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.42.4-43
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• 2017

We investigate the long-period radial velocity (RV) variations for M giant HD 18438 and K giant HD 158996 using the high-resolution Bohyunsan Observatory Echelle Spectrograph at the 1.8m telescope of Bohyunsan Optical Astronomy Observatory in Korea. These two target stars are important because HD 18438 is the largest star and HD 158996 is the brightest star for exoplantary system candidate so we can understarnd how evolved stars affect planets by researching these stars. We calculated precise RV measurements of 38 and 24 spectra from November 2010 to January 2017 and June 2010 to January 2017, respectively. We dreived the RV variation period for 719.0 days of HD 18438, 775.6 days for HD 158996. We conclude that the RV variation of HD 158996 is caused by planetary companion which has the mass of 14.7 MJup, semi-major axis of 2.2 AU, and eccentricity of 0.27 assuming the stellar mass of $2.34M{\odot}$. On the other hand, the origin of RV variation of HD 18438 with period of 719.0 days is still uncertain. It might be caused by stellar chromospheric activity or planetary companion, so more observations and tests are required.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.51.3-51.3
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• 2017

To investigate the connection between radio activity and AGN outflows, we present a study of ionized gas kinematics by using [O III] ${\lambda}5007$ emission line along the radio jet for six radio AGNs. These AGNs are selected based on the radioactivity (L1.4GHz ${\geq}$ 1039.8 erg s-1) as well as optical properties as type 2 AGNs. By using the high spatial resolution of the Red Channel Cross Dispersed Echellette Spectrograph at the Multiple Mirror Telescope, we investigate in detail the [O III] and stellar kinematics. We spatially resolve and probe the central AGN-photoionization sizes, which is important in understanding the structures and evolutions of galaxies. We find that the typical central AGN-photoionization sizes of our targets are in range of 1.8-3.8 kpc. We study the [O III] kinematics along the radio jets to test whether there is a link between gas outflows in the narrow-line region and radio jet emissions. Contrary to our expectation, we find no evidence that the gas outflows are directly connected to radio jet emission.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.140.2-140.2
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• 2011

We present high-resolution radial velocity (RV) measurements of K2 giant HD 66141 from December 2003 to January 2011 using the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) at Bohyunsan Optical Astronomy Observatory (BOAO). We find that the RV measurements for HD 66141 exhibit a periodic variation of 480 days with a semi-amplitude of 146 m/s. We do not find the correlation between RV variations and a chromospheric activity indicator (H line). The Hipparcos photometry as well as bisector velocity span (BVS) also do not show any obvious correlations with RV variations. Thus, Keplerian motion is the most likely explanation, which suggests that the RV variations arise from an orbital motion. Assuming a possible stellar mass of 1.5 $M{\odot}$, for HD 66141, we obtain a minimum mass for the planetary companion of 7.4 MJup with an orbital semi-major axis of 1.4 AU, and an eccentricity of 0.07. We support that planet occurrence rate around evolved stars is more than 10 % (Dollinger et al. 2009) as well as more massive stars do form significantly more massive planetary companions (Johnson et al. 2007; Lovis & Mayor 2007; Dollinger et al. 2009).

• Journal of The Korean Astronomical Society
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• v.41 no.3
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• pp.59-64
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• 2008

To detect exoplanets and study pulsation of K giant stars, we have observed precise RV (radial velocity) of about 55 early K giant (K0 - K4) stars brighter than V = 5 magnitude since 2003 by using BOES, a high resolution Echelle spectrograph attached to the 1.8 m telescope at BOAO (Bohyunsan Optical Astronomy Observatory). We detected periodic RV variation of KO III star $\beta$ Gem (HD 62509) with a period $P\;=\;596.6\;{\pm}\;2.3$ days and a semi-amplitude $K\;=\;44.8\;{\pm}\;0.7\;ms^{-1}$. If we adopt 1.7 $M_{\odot}$ for the mass of $\beta$ Gem, this yields the minimum mass of the companion m sin i = 2.64 $M_{Jupiter}$. Our results agree well with Hatzes et al. (2006) and Reffert et al. (2006), and confirm their discovery of a planetary object around $\beta$ Gem. We also confirmed about 192 minutes short period stellar oscillation found by Hatzes and Zechmeister (2007). This is the first report of exoplanet detection using BOES and demonstrates that the RV observation using BOES is accurate and stable enough to detect exoplanets around bright K giant stars.

• Journal of Astronomy and Space Sciences
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• v.35 no.1
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• pp.7-18
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• 2018

We have investigated the intensities and full width at half maximum (FWHM) of the high dispersion spectroscopic N III emission lines of AG Peg, observed with the Hamilton Echelle Spectrograph (HES) in three different epochs at Mt. Hamilton's Lick Observatory. The earlier theoretical Bowen line study assumed the continuum fluorescence effect, presenting a large discrepancy with the present data. Hence, we analyzed the observed N III lines assuming line fluorescence as the only suitable source: (1) The O III and N III resonance line profiles near ${\lambda}$ 374 were decomposed, using the Gaussian function, and the contributions from various O III line components were determined. (2) Based on the theoretical resonant N III intensities, the expected N III Bowen intensities were obtained to fit the observed values. Our study shows that the incoming line photon number ratio must be considered to balance at each N III Bowen line level in the ultraviolet radiation according to the observed lines in the optical zone. We also found that the average FWHM of the N III Bowen lines was about $5km{\cdot}s^{-1}$ greater than that of the O III Bowen lines, perhaps due to the inherently different kinematic characteristics of their emission zones.

• Journal of The Korean Astronomical Society
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• v.41 no.2
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• pp.23-37
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• 2008

The high-resolution optical region spectroscopic data of the symbiotic nova AG Peg secured with the Hamilton Echelle Spectrograph at the Lick Observatory, have been analyzed along with the International Ultraviolet Explorer UV archive data. We measure about 700 line intensities in the wavelengths of 3859 to $9230{\AA}$ and identify about 300 lines. We construct pure photoionization models that represent the observed lines and the physical condition for this symbiotic nova. The spectral energy distribution of the ionizing radiation is adopted from stellar model atmospheres. Based on photoionization models, we derive the elemental abundances; C & N appear to be similar to be smaller than the Galactic planetary nebular value while O is enhanced. Our result is compared with the Contini (1997, 2003) who analyzed the UV region spectral data with the shock + ionization model. The Fe abundance appears to be enhanced than that of normal planetary nebulae, which suggests that AG Peg may have formed in the Galactic disk. The models indicate that the temperature of the central star which excite the shell gas may have fluctuated to an unexpected extent during the years 1998 - 2002.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.59.2-59.2
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• 2013

Wilson and Bappu found a tight correlation between the stellar absolute visual magnitude (MV) and the width of the Ca II K emission line for late-type stars in 1957. Here, we revisit the Wilson-Bappu relationship (hereafter, WBR) to claim that WBR can be an excellent indicator of stellar surface gravity of late-type stars as well as a distance indicator. We have measured the width (W) of the Ca II K emission line in high resolution spectra of 125 late-type stars, which were obtained with Bohyunsan Optical Echelle Spectrograph (BOES) and adopted from the UVES archive. Based on our measurement of the emission line width (W), we have obtained a WBR of $M_V=33.76-18.00{\log}W$. In order to extend the WBR to be a surface gravity indicator, the stellar atmospheric parameters such as effective temperature ($T_{eff}$), surface gravity (logg), metallicity ([Fe/H]), and micro-turbulence (${\xi}_{tur}$) have been derived from the self-consistent detailed analysis using the Kurucz stellar atmospheric model and the abundance analysis code, MOOG. Using these stellar parameters and logW, we found that ${\log}g=-5.85\;{\log}W+9.97\;{\log}T_{eff}-23.48$ for late-type stars.

• Journal of The Korean Astronomical Society
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• v.47 no.2
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• pp.69-76
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• 2014

We report the detection of an exoplanet candidate in orbit around ${\sigma}$ Persei from a radial velocity (RV) survey. The system exhibits periodic RV variations of $579.8{\pm}2.4$ days. The purpose of the survey is to search for low-amplitude and long-period RV variations in giants and examine the origin of the variations using the fiber-fed Bohyunsan Observatory Echelle Spectrograph installed at the 1.8-m telescope of Bohyunsan Optical Astronomy Observatory in Korea. We present high-accuracy RV measurements of ${\sigma}$ Per made from December 2003 to January 2014. We argue that the RV variations are not related to the surface inhomogeneities but instead a Keplerian motion of the planetary companion is the most likely explanation. Assuming a stellar mass of $2.25{\pm}0.5$ $M_{\odot}$, we obtain a minimum planetary companion mass of $6.5{\pm}1.0$ $M_{Jup}$, with an orbital semi-major axis of $1.8{\pm}0.1$ AU, and an eccentricity of $0.3{\pm}0.1$ around ${\sigma}$ Per.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.251-254
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• 2015

Low resolution spectra of Nova Delphini 2013 (V339 Del) in the optical range have been obtained at Bosscha Observatory, Indonesia during its maximum light (V = 4.3). Spectra were observed from August 16 to 27, 2013. The GAO-ITB RTS 20.3 cm telescope, and SBIG DSS-7 spectrograph and SBIG ST-7 XE as the detector have been employed throughout the observations. The spectra show P-Cygni profiles in Balmer, NaI'D' and Fe II lines, from which we determined shell expansion velocities of $1421.66{\pm}39.18km/s$, $1227.54{\pm}21.57km/s$ and 1402.86 km/s, respectively. Our spectroscopic observations followed the spectral evolution of V339 Del from the pre-maximum phase to early Orion phase. The characteristics of the nova Delphini 2013 resembles those of Fe II-type novae.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.28.2-28.2
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• 2011

To search for and study the nature of the long-periodic variations of massive stars, we have been carrying out a precise radial velocity (RV) survey for supergiants. Here, we present high-resolution RV measurements of ${\alpha}$ Per which lies near the Cepheid instability strip from November 2005 to February 2011 using the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) at Bohyunsan Optical Astronomy Observatory (BOAO). The orbital solution yields a period of 129 days, a 2K amplitude of 80 m/s, and an eccentricity of 0.1. Assuming a possible stellar mass of 7.3 $M{\bigodot}$, we estimate the minimum mass for the planetary companion to be 7.5 MJup with the orbital semi-major axis of 0.97 AU. We do not find the correlation between RV variations and chromospheric activity indicator (Ca II H & K region). The Hipparcos photometry and bisector velocity span (BVS) do not show any obvious correlations with RV variations. These analyses suggest that ${\alpha}$ Per is a pulsating supergiant that hosts an exoplanet. If the 129 days variations of ${\alpha}$ Per do not come from an exoplanet but Cepheid-like pulsations, the theoretical boundary of the Cepheid instability strip may need to be extended to the bluer side.