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Do Hertzsprung‐gap stars show any chemical anomaly?
Takeda, Yoichi,Jeong, Gwanghui,Han, Inwoo WILEY‐VCH Verlag GmbH Co. KGaA 2019 Astronomische Nachrichten Vol.340 No.5
<P><B>Abstract</B></P><P>With the aim of investigating how the surface abundances of intermediate‐mass stars off the main sequence (evolving toward the red‐giant stage) are affected by the evolution‐induced envelope mixing, we spectroscopically determined the abundances of Li, C, N, O, and Na for selected 62 late A through G subgiants, giants, and supergiants, which are often called “Hertzsprung‐gap stars,” by applying the synthetic spectrum‐fitting technique to Li <SMALL>i</SMALL> 6708, C <SMALL>i</SMALL> 5380, N <SMALL>i</SMALL> 7460, O <SMALL>i</SMALL> 6156–8, and Na <SMALL>i</SMALL> 6161 lines. A substantially large star‐to‐star dispersion (≳2 dex) was confirmed for the Li abundances, indicating that this vulnerable element can either suffer significant depletion before the red‐giant stage or almost retain the primordial composition. Regarding C, N, O, and Na possibly altered by dredge‐up of nuclear‐processed products, their abundances turned out to show considerable scatter. This suggests that these abundance results are likely to suffer appreciable uncertainties, the reason for which is not clear but might be due to some kind of inadequate modeling for the atmospheric structure. Yet, paying attention to the fact that the relative abundance ratios between C, N, and O should be more reliable (because systematic errors may be canceled as lines of similar properties are used for these species), we could confirm a positive correlation between [O/C] (ranging from ∼0 to ∼+0.5 dex) and [N/C] (showing a larger spread from ∼0 to ∼+1 dex), which is reasonably consistent with the theoretical prediction. This observational detection of C deficiency as well as N enrichment in our program stars manifestly indicates that the dredge‐up of H‐burning product can take place before entering the red‐giant stage, with its extent differing from star to star.</P>
Lee, Byeong-Cheol,Jeong, Gwanghui,Park, Myeong-Gu,Han, Inwoo,Mkrtichian, David E.,Hatzes, Artie P.,Gu, Shenghong,Bai, Jinming,Lee, Sang-Min,Oh, Hyeong-Il,Kim, Kang-Min American Astronomical Society 2017 The Astrophysical journal Vol.844 No.1
<P>We present the detection of long-period RV variations in HD. 36384, HD. 52030, and HD. 208742 by using the high-resolution, fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) for the precise radial velocity (RV) survey of about 200 northern circumpolar stars. Analyses of RV data, chromospheric activity indicators, and bisector variations spanning about five years suggest that the RV variations are compatible with planet or brown dwarf companions in Keplerian motion. However, HD. 36384 shows photometric variations with a period very close to that of RV variations as well as amplitude variations in the weighted wavelet Z-transform (WWZ) analysis, which argues that the RV variations in HD. 36384 are from the stellar pulsations. Assuming that the companion hypothesis is correct, HD. 52030 hosts a companion with minimum mass 13.3 M-Jup orbiting in 484 days at a distance of 1.2 au. HD. 208742 hosts a companion of 14.0 M-Jup at 1.5 au with a period of 602 days. All stars are located at the asymptotic giant branch (AGB) stage on the H-R diagram after undergoing. the helium flash and leaving. the giant clump. With stellar radii of 53.0 R-circle dot and 57.2 R-circle dot for HD. 52030 and HD. 208742, respectively, these stars may be the largest yet, in terms of stellar radius, found to host substellar companions. However, given possible RV amplitude variations and the fact that these are highly evolved stars, the planet hypothesis is not yet certain.</P>
정광희,한인우,이병철,Jeong, Gwanghui,Han, Inwoo,Lee, Byeong-Cheol 한국천문학회 2014 天文學論叢 Vol.29 No.3
In ground-based astronomical spectroscopic observations, there are many telluric absorption lines that are laid on the spectra of celestial objects. To study the physical properties of the celestial objects with these contaminated spectra, the telluric lines should be removed. A conventional method for removing the telluric lines is using the standard stellar spectrum as telluric line. In this paper, we introduce a technique to calculate synthetic telluric spectra and use them to remove telluric lines from a spectrum of a celestial object. We used Line-by-Line Radiative Transfer Model (LBLRTM) for calculating a synthetic spectrum and selected Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) model as atmospheric model. We apply our method to some spectra obtained by Bohyunsan Observatory Echelle Spectrograph (BOES) to show that the telluric lines are well removed from the observed spectra by our model within an accuracy of 2% which is close to the 1-sigma rms of the original spectra.
Diagnostic accuracy of fine needle aspiration cytology for high-grade salivary gland tumors.
Kim, Bo Young,Hyeon, Jiyeon,Ryu, Gwanghui,Choi, Nayeon,Baek, Chung-Hwan,Ko, Young-Hyeh,Jeong, Han-Sin Raven Press 2013 Annals of surgical oncology Vol.20 No.7
<P>Preoperative differentiation between high-grade malignancy and others (benign or low-grade tumors) is more important than differentiation between malignant and benign tumors for surgical planning, treatment outcome, and prognosis in salivary gland tumors. Fine needle aspiration cytology (FNAC) has a relatively low sensitivity for differentiating malignant from benign salivary tumors. However, the diagnostic performance of FNAC has not been studied in predicting high-grade salivary malignancy, which can significantly affect patient care.</P>