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1
SIGNS OF ACCRETION IN THE ABUNDANCE PATTERNS OF THE COMPONENTS OF THE RS CVn-TYPE ECLIPSING BINARY STAR LX PERSEI

Kang, Young-Woon,Yushchenko, Alexander V.,Hong, Kyeongsoo,Guinan, Edward F.,Gopka, Vira F. American Institute of Physics 2013 The Astronomical journal Vol.145 No.6
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We present spectroscopic observations of LX Per carried out using the Korean Bohyunsan Observatory Echelle Spectrograph (BOES) with spectral resolving power R = 80, 000. The spectrograph was attached to the 1.8 m telescope. The fit of synthetic spectra to the observed spectrum of the system allowed us to find the component parameters and the abundances of chemical elements in the atmospheres of the components. The strong Ca II H&K emissions are confirmed; we also found emission lines in the Ca II reversals' triplet absorptions at the wavelengths of 8498, 8542, and 8662 Å in the spectrum of the cooler component of LX Per. A unique photometric solution using the distorted light curves of three different epochs was made. The spot model light curves were fitted to the 1981, 1982, and 1983 observations successfully by adjusting only spot parameters. We could infer that the variation of spot location and size was the main reason for the changing shape of light curves. The main feature of the abundance patterns of both components was the apparent deficiency of heavy (Z > 30) elements. Only elements with strong lines, namely Y and Ba, were detected. Correlations of relative abundances of chemical elements with condensation temperatures and second ionization potentials of these elements, which can be explained by the accretion of dust and gas, were found.
2
X-Ray, UV and Optical Observations of Classical Cepheids: New Insights into Cepheid Evolution, and the Heating and Dynamics of Their Atmospheres

Engle, Scott G.,Guinan, Edward F. 한국우주과학회 2012 Journal of Astronomy and Space Sciences Vol.29 No.2
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To broaden the understanding of classical Cepheid structure, evolution and atmospheres, we have extended our continuing secret lives of Cepheids program by obtaining XMM/Chandra X-ray observations, and Hubble space telescope (HST) / cosmic origins spectrograph (COS) FUV-UV spectra of the bright, nearby Cepheids Polaris, δ Cep and β Dor. Previous studies made with the international ultraviolet explorer (IUE) showed a limited number of UV emission lines in Cepheids. The well-known problem presented by scattered light contamination in IUE spectra for bright stars, along with the excellent sensitivity & resolution combination offered by HST/COS, motivated this study, and the spectra obtained were much more rich and complex than we had ever anticipated. Numerous emission lines, indicating 104 K up to ~3 x 105 K plasmas, have been observed, showing Cepheids to have complex, dynamic outer atmospheres that also vary with the photospheric pulsation period. The FUV line emissions peak in the phase range φ ≈ 0.8-1.0 and vary by factors as large as 10x. A more complete picture of Cepheid outer atmospheres is accomplished when the HST/COS results are combined with X-ray observations that we have obtained of the same stars with XMM-Newton & Chandra. The Cepheids detected to date have X-ray luminosities of log LX ≈ 28.5-29.1 ergs/sec, and plasma temperatures in the 2-8 x 106 K range. Given the phase-timing of the enhanced emissions, the most plausible explanation is the formation of a pulsation-induced shocks that excite (and heat) the atmospheric plasmas surrounding the photosphere. A pulsation-driven α2 equivalent dynamo mechanism is also a viable and interesting alternative. However, the tight phase-space of enhanced emission (peaking near 0.8-1.0 φ) favor the shock heating mechanism hypothesis.
3
X-Ray, UV and Optical Observations of Classical Cepheids: New Insights into Cepheid Evolution, and the Heating and Dynamics of Their Atmospheres

Scott G. Engle,Edward F. Guinan 한국우주과학회 2012 Journal of Astronomy and Space Sciences Vol.29 No.2
To broaden the understanding of classical Cepheid structure, evolution and atmospheres, we have extended our continuing secret lives of Cepheids program by obtaining XMM/Chandra X-ray observations, and Hubble space telescope (HST) / cosmic origins spectrograph (COS) FUV-UV spectra of the bright, nearby Cepheids Polaris, δ Cep and β Dor. Previous studies made with the international ultraviolet explorer (IUE) showed a limited number of UV emission lines in Cepheids. The well-known problem presented by scattered light contamination in IUE spectra for bright stars, along with the excellent sensitivity & resolution combination offered by HST/COS, motivated this study, and the spectra obtained were much more rich and complex than we had ever anticipated. Numerous emission lines, indicating 104 K up to ~3 × 105 K plasmas, have been observed, showing Cepheids to have complex, dynamic outer atmospheres that also vary with the photospheric pulsation period. The FUV line emissions peak in the phase range φ ? 0.8-1.0 and vary by factors as large as 10×. A more complete picture of Cepheid outer atmospheres is accomplished when the HST/COS results are combined with X-ray observations that we have obtained of the same stars with XMM-Newton & Chandra. The Cepheids detected to date have X-ray luminosities of log LX ? 28.5-29.1 ergs/sec, and plasma temperatures in the 2-8 × 106 K range. Given the phase-timing of the enhanced emissions, the most plausible explanation is the formation of a pulsation-induced shocks that excite (and heat) the atmospheric plasmas surrounding the photosphere. A pulsation-driven α2 equivalent dynamo mechanism is also a viable and interesting alternative. However, the tight phase-space of enhanced emission (peaking near 0.8-1.0 φ) favor the shock heating mechanism hypothesis.