Yazar "Frasca, A." seçeneğine göre listele

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    A spectroscopic study of some Algol systems
    (2005) Soydugan, Faruk; Frasca, A.; Catalano, S.; Ibano?lu, C.; Demircan, O.; Soydugan, Esin
    We present and discuss here new high-resolution (R? 22000) optical spectra of three Algol binaries, namely KO Aql, S Equ and AT Peg, obtained with the echelle spectrograph of Catania Astrophysical Observatory. In this work, we obtained new radial velocity curves for the hotter primary components with a much better precision than the previous data in the literature, mainly coming from old plate spectra. Thanks to the cross-correlation procedure, we were able to obtain, for the first time to our knowledge, radial velocities also for the cool secondary components of KO Aql and S Equ. We have also measured, with a rather good accuracy (2-4 km/s), the rotational velocity of the hotter components of these three systems and found that, with the exception of AT Peg, the primary stars are rotating faster than the synchronization velocity, consistently with a mass transfer scenario. In addition, preliminary results on the mass-transfer effects displayed by the H? and H? extra-absorption/emission components are presented.
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    A spectroscopic study of the Algol-type binaries S Equulei and KO Aquilae: absolute parameters and mass transfer
    (Blackwell Publishing, 2007) Soydugan, Faruk; Frasca, A.; Soydugan, Esin; Catalano, S.; Demircan, O.; Ibanoglu, C.
    We present and analyse high-resolution optical spectra of two Algol binaries, namely S Equ and KO Aql, obtained with the echelle spectrograph at Catania Astrophysical Observatory. New accurate radial velocities (RVs) for the hotter primary components are obtained. Thanks to the cross-correlation procedure, we were able to measure, for the first time to our knowledge, RVs also for the cool secondary components of S Equ and KO Aql. By combining the parameters obtained from the solution of the RV curves with those obtained from the light-curve analysis, reliable absolute parameters of the systems have been derived. The rotational velocity of the hotter components of S Equ and KO Aql has been measured and it is found that the gainers of both systems rotate about 30 per cent faster than synchronously. This is likely due to mass transfer across the Lagrangian L-1 point from the cooler to the hotter component. The lower luminosity of the mass-gaining components of these systems compared to normal main-sequence stars of the same mass can also be an effect of the mass transfer. The H alpha profiles were analysed with the 'synthesis and subtraction' technique and reveal clear evidence of mass transfer and accretion structures. In both systems, especially before the primary eclipses and afterwards, we clearly observed extra absorption lines. From the integrated absorption and the RV variations of these features, we found that the mass accretion is very dense around the impact region of the hotter components. A double-peaked emission in the spectra of S Equ was seen outside the eclipses. One of these peaks is likely originated in a region between the centre of mass and the cooler component, which is occupied by the flowing matter. Furthermore, the H alpha difference spectra of S Equ and KO Aql also display emission features, which should be arising from the magnetic activity of the cooler components.
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    A spectroscopic survey of algol-type binary S Equ
    (Astronomical Soc Pacific, 2007) Soydugan, Faruk; Soydugan, Esin; Frasca, A.
    This study presents the results of the medium-resolution optical spectra of S Equ obtained with the echelle spectrograph of the Catania Astro-physical Observatory. In this work, new radial velocity curves for the components of the system with a precision better than in previous works are obtained using the cross-correlation technique. We have determined the absolute parameters of S Equ combining the orbit and light curve solutions. The preliminary results of the Ha line analysis indicate an extra emission and absorption as a likely result of a mass-transfer process and chromospheric activity of the cooler component.
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    Öğe
    An algol type binary with a ? Scuti component
    (Wiley-V C H Verlag Gmbh, 2006) Soydugan, Esin; Soydugan, Faruk; Ibanoglu, C.; Frasca, A.; Demircan, O.; Akan, M. C.
    We present new BV photometry and spectroscopic observations of RZ Cassiopeiae. The light and radial velocity curves were formed by the new observations which have been analyzed simultaneously by using the Wilson-Dewinney code. The non-synchronous rotational velocity v(1) sin i = 76 +/- 6 km s(-1), deduced for the primary component from the new spectroscopic observations, was also incorporated in the analysis. A time-series analysis of the residual light curves revealed the multi-periodic pulsations of the primary component of RZ Cas. The main peak in the frequency spectrum was observed at about 64.197 c d(-1) in both B and V bands. The pulsational constant was calculated to be 0.0116 days. This value corresponds to high overtones (n similar to 6) of non-radial mode oscillations. We find significant changes in the pulsational amplitude of the primary component from year to year. The peak-to-peak pulsational amplitude of the main frequency displays a decrease from 0.(m)-013 in 2000 to 0.(m)002 in 2001 and thereafter we have found an increase again in the amplitude to 0.(m)01 in the year 2002. We propose the mass transfer from the cool secondary to the pulsating primary as a possible explanation for such remarkable changes in the pulsational behavior of the primary component. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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    Öğe
    Preliminary results on the fundamental parameters of the eclipsing binary V398 Lacertae*
    (Wiley-V C H Verlag Gmbh, 2007) Cakirli, Oe.; Frasca, A.; Ibanoglu, C.; Soydugan, Faruk; Degirmenci, Oe.
    The Hipparcos Space Astrometry Mission photometric observations of V398 Lac, led to the discovery of its variability, allowing to classify it as an eclipsing binary with an orbital period of about 5.4 days. This prompted us to acquire high-resolution echelle spectra with the aim of performing accurate radial velocity measurements and to determine the main physical parameters of the system's components. We present, for the first time, a double-lined radial velocity curve and determine the orbital and physical parameters of the two components, that can be classified both as late B-type stars. In particular, we obtained an orbital inclination i similar to 85 degrees. With this value of the inclination, we deduced masses M-1 = 3.83 +/- 0.35 M-circle dot and M-2 = 3.29 +/- 0.32 M-circle dot, and radii R-1 = 4.89 +/- 0.18 R-circle dot and R-2 = 2.45 +/- 0.11 R-circle dot for the more massive and less massive components, respectively. Both components are well inside their own Roche lobes. The mass ratio is M-2/M-1, similar to 0.86. We derived also the projected rotational velocities as v(1) sin i = 79 +/- 2 km s(-1) and v(2) Sin i = 19 +/- 2 km s(-1). Our measurements indicate that the rotation of the primary star is essentially pseudo-synchronized with the orbital velocity at the periastron, while the secondary appears to rotate very slowly and has not yet attained synchronization. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.