Physical parameters and the projection factor of the classical Cepheid in the binary system OGLELMCCEP0227
Abstract
A novel method of analysis of doublelined eclipsing binaries containing a radially pulsating star is presented. The combined pulsatingeclipsing light curve is built up from a purely eclipsing lightcurve grid created using an existing modelling tool. For every pulsation phase, the instantaneous radius and surface brightness are taken into account, being calculated from the disentangled radial velocity curve of the pulsating star and from its outofeclipse pulsational light curve and the light ratio of the components, respectively. The best model is found using the Markov chain Monte Carlo method. The method is applied to the eclipsing binary Cepheid OGLELMCCEP0227 (P_{puls} = 3.80 d, P_{orb} = 309 d). We analyse a set of new spectroscopic and photometric observations for this binary, simultaneously fitting OGLE Vband, Iband and Spitzer 3.6 μm photometry. We derive a set of fundamental parameters of the system significantly improving the precision comparing to the previous results obtained by our group. The Cepheid mass and radius are M_{1} = 4.165 ± 0.032 M_{⊙} and R_{1} = 34.92 ± 0.34 R_{⊙}, respectively. For the first time a direct, geometrical and distanceindependent determination of the Cepheid projection factor is presented. The value p = 1.21 ± 0.03(stat.) ± 0.04(syst.) is consistent with theoretical expectations for a shortperiod Cepheid and interferometric measurements for δ Cep. We also find a very high value of the optical limb darkening coefficients for the Cepheid component, in strong disagreement with theoretical predictions for static atmospheres at a given surface temperature and gravity.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 December 2013
 DOI:
 10.1093/mnras/stt1529
 arXiv:
 arXiv:1308.5023
 Bibcode:
 2013MNRAS.436..953P
 Keywords:

 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 16 pages, 17 figures, accepted for publication in MNRAS