arXiv subjects

O. Cakirli

Publications and source records attributed to O. Cakirli.

23 records · Page 2Linked to original sources

arXiv2009

A new low-mass eclipsing binary: NSVS 02502726

We present optical spectroscopy and extensive $RI$ differential photometry of the double-lined eclipsing binary NSVS 02502726 (2MASS J08441103+5423473). Simultaneous solution of two-band light curves and radial velocities permits determination of precise emprical masses and radii for both components of the system. The analysis indicates that the primary and secondary components of NSVS 02502726 are in a circular orbit with 0.56-day orbital period and have stellar masses of M$_1$=0.714$\pm$0.019 \Msun, and M$_2$=0.347$\pm$0.012 \Msun. Both of the components have large radii, being R$_1$=0.67$\pm$0.01 \Rsun, and R$_2$=0.76$\pm$0.01 \Rsun. The principal parameters of the mass and radius of the component stars are found with an accuracy of 3% and 1%, respectively. The secondary component's radius is significantly larger than model predictions for its mass, similar to what is seen in almost all of the other well-studied low-mass stars which belong to double-lined eclipsing binaries. Strong H$_α$ emission cores and considerable distortion at out-of-eclipse light curve in both $R$ and $I$ bandpasses, presumably due to dark spots on both stars, have been taken as an evidence of strong stellar activity. The distance to system was calculated as 173$\pm$8 pc from the $BVRIJHK$ magnitudes. The absolute parameters of the components indicate that both components are close to the zero-age main-sequence. Comparison with current stellar evolution models gives an age of 126 $\pm$30 Myr, indicating the stars are in the final stages of pre-main-sequence contraction.

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↗

arXiv2008

Photometric/spectroscopic analyses and magnetic activity in young late-type stars

We present the work in progress of a study based on photometric and spectroscopic observations of young Weak-line T Tauri and Post T Tauri stars just attiving on the Zero Age Main Sequence. This study is part of a project based on high-resolution spectra obtained with FOCES@CAHA (Spain) and SARG@TNG (Spain) and contemporaneous photometry performed at Catania (Italy) and Ege (Turkey) observatories. The main aim is to investigate the topology of magnetic active regions at photospheric and chromospheric levels in young single stars. Since our targets are slow rotators (vsini < 25 km/s), corresponding to rotation periods larger than about 2 days, we are able to apply the spectroscopic technique based on line-depth ratio for the measure of the photospheric temperature modulation. These stars, possible members of Stellar Kinematic Groups, display emission cores in the CaII H&K and IRT lines, as well as a conspicuous filling-in of the Halpha core. Moreover, we detect absorption of the HeI-D3 line, coming from the upper chromospheric layers, derive the lithium abundance (age indicator), and measure the rotational and radial velocities. We find a clear rotational modulation, due to photospheric spots, both in the light and the temperature curves. The Halpha and the CaII-IRT emissions display a fair variation correlated with the rotation. Finally, we are developing a spot/plage model to reproduce the data and derive the spot parameters (namely, filling factor and temperature) and to recover information about the chromospheric inhomogeneities (flux contrast and filling factor). This study is very important to explore the correlations between global stellar parameters (e.g., surface gravity, effective temperature) and spot/plage characteristics in stars with different activity level and evolutionary stage.

astro-ph↗

arXiv2008

Magnetic activity in the young star SAO 51891

We present preliminary results on a study based on contemporaneous photometric and spectroscopic observations of the young K0-1V star SAO 51891. We find that SAO 51891, a possible member of the Local Association, shows emission cores in the CaII H&K and fillings in the Halpha and CaII Infra-Red Triplet (IRT) lines. Moreover, we detect absorption lines of HeI-D3 and LiI and measure a v sini of 19 km/s. A clear rotational modulation of both the light and the photospheric temperature, due to photospheric spots, has been detected. The net Halpha chromospheric emission does not show any detectable variation, while the CaII IRT emission displays a fair modulation.

astro-ph↗

arXiv2007

Follow-up observations of pulsating subdwarf B stars: Multisite campaigns on PG 1618+563B and PG 0048+091

We present follow-up observations of pulsating subdwarf B (sdB) stars as part of our efforts to resolve the pulsation spectra for use in asteroseismological analyses. This paper reports on multisite campaigns of the pulsating sdB stars PG 1618+563B and PG 0048+091. Data were obtained from observatories placed around the globe for coverage from all longitudes. For PG 1618+563B, our five-site campaign uncovered a dichotomy of pulsation states: Early during the campaign the amplitudes and phases (and perhaps frequencies) were quite variable while data obtained late in the campaign were able to fully resolve five stable pulsation frequencies. For PG 0048+091, our five-site campaign uncovered a plethora of frequencies with short pulsation lifetimes. We find them to have observed properties consistent with stochastically excited oscillations, an unexpected result for subdwarf B stars. We discuss our findings and their impact on subdwarf B asteroseismology.

astro-ph↗