arXiv subjects

E. Sipahi

Publications and source records attributed to E. Sipahi.

22 records · Page 2Linked to original sources

arXiv2012

High-Level Magnetic Activity on a Low-Mass Close Binary: GSC 02038-0293

Taking into account results obtained from light-curve analysis and out-of-eclipse analyses, we discuss the nature of GSC 02038-00293 and also its magnetic activity behaviour. We obtained light curves of the system during observing seasons 2007, 2008 and 2011. We obtained its secondary minimum clearly in I-band observations in 2008 for the first time. Analysing this light curve, we found the physical parameters of the components. The light-curve analysis indicates that the possible mass ratio of the system is 0.35. We obtained the remaining V-band light curves, extracting the eclipses. We modelled these remaining curves using the spotmodel program and found possible spot configurations of the magnetically active component for each observing season. The models demonstrated that there are two active longitudes for the active component. The models reveal that both active longitudes migrate in the direction of decreasing longitude. We also examined the light curves in out-of-eclipse phases with respect to minimum and maximum brightness, amplitude, etc. The amplitude of the curves during out-of-eclipse phases varies in a sinusoidal way with a period of ~8.9yr the mean brightness of the system is dramatically decreasing. The phases of the deeper minimum during out-of-eclipse periods exhibit a migration toward decreasing phase.

astro-ph.SR↗

arXiv2011

Carbon deficiencies in the primaries of some classical Algols

The equivalent widths of C II $λ$ 4267 Åline were measured for the mass-gaining primary stars of the 18 Algol-type binary systems. The comparison of the EWs of the gainers with those of the single standard stars having the same effective temperature and luminosity class clearly indicates that they are systematically smaller than those of the standard stars. The primary components of the classical Algols, located in the main-sequence band of the HR diagram, appear to be C poor stars. We estimate $ [N_{C} /N_{tot}] $ relative to the Sun as -1.91 for GT Cep, -1.88 for AU Mon and -1.41 for TU Mon, indicating poorer C abundance. An average differential carbon abundance has been estimated to be -0.82 dex relative to the Sun and -0.54 dex relative to the main-sequence standard stars. This result is taken to be an indication of the transferring material from the evolved less-massive secondary components to the gainers such that the CNO cycle processed material changed the original abundance of the gainers. There appear to be relationships between the EWs of C II $λ$ 4267 Åline and the rates orbital period increase and mass transfer in some Algols. As the mass transfer rate increases the EW of the C II line decreases, which indicates that accreted material has not been completely mixed yet in the surface layers of the gainers. This result supports the idea of mixing as an efficient process to remove the abundance anomaly built up by accretion. Chemical evolution of the classical Algol-type systems may lead to constrains on the initial masses of the less massive, evolved, mass-losing stars.

astro-ph.SR↗

arXiv2011

V1898 Cygni: An interacting eclipsing binary in the vicinity of North America nebula

We present spectroscopic observations of the double-lined early type eclipsing binary V1898\,Cyg. The radial velocities were obtained by means of the cross-correlation technique. Analyses of the BV light curves and RVs led to determination of the fundamental stellar parameters of the V1898\,Cyg's components. We derived new ephemerides for the eclipsing pair using the observed times of mid-eclipses. The residuals between the observed and computed times of mid-eclipses were analysed and a rate of the period change $\dot{P}/P= 6.68 \times 10^{-7}\,yr^{-1}$ was obtained. The orbital period is increased by about 0.38 s in the last 24 years due to the mass transfer from less massive secondary to the more massive primary star with an amount of $1.88\times10^{-7}\,$ \Msun in a year, assuming conservative case. Results of the light and radial velocity curves' analyses were combined and the physical parameters of the components were revealed. The absolute parameters for the stars are derived as: M$_1$=6.054$\pm$0.037 M$_{\odot}$, M$_2$=1.162$\pm$0.011 M$_{\odot}$, R$_1$=3.526$\pm$0.009 R$_{\odot}$, R$_2$=2.640$\pm$0.010 R$_{\odot}$, T$_{eff_1}$=18\,000$\pm$600 K, and T$_{eff_2}$=6\,200$\pm$200 K. We have calculated the distance to the system of V1898\,Cyg as 501$\pm$5 pc using the infrared JHK magnitudes and bolometric corrections for the primary star. While the more massive star locates in the main-sequence band the less massive secondary appears in the giant branch which is common in the classical Algols. Any attempt for comparison with current stellar evolution models was made because the system seems in the phase of fast mass transfer. Moreover, the components of the system's proper motions present some indications about membership of the North America nebula.

astro-ph.SR↗

arXiv2009

Absolute parameters of the eclipsing binary V821 Cas from UBVRI light curves and radial velocities

We present UBVRI photometric measurements and spectroscopic observations of the double-lined eclipsing binary V821 Cas. The radial velocities were obtained by means of the cross-correlation technique. Simultaneous analyses of the multi-band light curves and RVs give the absolute parameters for the stars as: M$_1$=2.05$\pm$0.07 M$_{\odot}$, M$_2$=1.63$\pm$0.06 M$_{\odot}$, R$_1$=2.31$\pm$0.03 R$_{\odot}$, R$_2$=1.39$\pm$0.02 R$_{\odot}$, T$_{eff_1}$=9 400$\pm$400 K, and T$_{eff_2}$=8 600$\pm$400 K. Analysis of the O-C residuals yielded an apsidal motion in the binary at a rate of $\dotω$=0$^{\degr}$.0149$\pm0^{\degr}$.0023 cycle$^{-1}$, corresponding to an apsidal period of U=118$\pm$19 yr. Subtracting the relativistic contribution we find that $\log k_{2obs}$=-2.590 which is in agreement with the value predicted by theoretical models. Comparison with current stellar evolution models gives an age of $5.6\times10^{8}$ yr for the system.

astro-ph.SR↗