We present a new Bayesian approach to constrain the intrinsic parameters (stellar mass and age) of the eclipsing binary system-CEP0227-in the Large Magellanic Cloud (LMC). We computed several sets of evolutionary models covering a broad range in chemical compositions and in stellar mass. Independent sets of models were also constructed either by neglecting or by including a moderate convective core overshooting (beta(ov) = 0.2) during central hydrogen-burning phases. Sets of models were also constructed either by neglecting or by assuming a canonical (eta = 0.4, 0.8) or an enhanced (eta = 4) mass-loss rate. The most probable solutions were computed in three different planes: luminosity-temperature, mass-radius, and gravity-temperature. By using the Bayes factor, we found that the most probable solutions were obtained in the gravity-temperature plane with a Gaussian mass prior distribution. The evolutionary models constructed by assuming a moderate convective core overshooting (beta(ov) = 0.2) and a canonical mass-loss rate (eta = 0.4) give stellar masses for the primary (Cepheid)-M = 4.14(-0.05)(+0.04) M-circle dot-and for the secondary-M = 4.15+(0.04)(-0.05) M-circle dot-that agree at the 1% level with dynamical measurements. Moreover, we found ages for the two components and for the combined system-t = 151(-3)(+4) Myr-that agree at the 5% level. The solutions based on evolutionary models that neglect the mass loss attain similar parameters, while those ones based on models that either account for an enhanced mass loss or neglect convective core overshooting have lower Bayes factors and larger confidence intervals. The dependence on the mass-loss rate might be the consequence of the crude approximation we use to mimic this phenomenon. By using the isochrone of the most probable solution and a Gaussian prior on the LMC distance, we found a true distance modulus-18.53(-0.02)(+0.02) mag-and a reddening value-E(B - V) = 0.142+(+0.005)(-0.010) mag-that agree quite well with similar estimates in the literature.
ON THE EVOLUTIONARY AND PULSATION MASS OF CLASSICAL CEPHEIDS. III. THE CASE OF THE ECLIPSING BINARY CEPHEID CEP0227 IN THE LARGE MAGELLANIC CLOUD
PRADA MORONI, PIER GIORGIO;
2012-01-01
Abstract
We present a new Bayesian approach to constrain the intrinsic parameters (stellar mass and age) of the eclipsing binary system-CEP0227-in the Large Magellanic Cloud (LMC). We computed several sets of evolutionary models covering a broad range in chemical compositions and in stellar mass. Independent sets of models were also constructed either by neglecting or by including a moderate convective core overshooting (beta(ov) = 0.2) during central hydrogen-burning phases. Sets of models were also constructed either by neglecting or by assuming a canonical (eta = 0.4, 0.8) or an enhanced (eta = 4) mass-loss rate. The most probable solutions were computed in three different planes: luminosity-temperature, mass-radius, and gravity-temperature. By using the Bayes factor, we found that the most probable solutions were obtained in the gravity-temperature plane with a Gaussian mass prior distribution. The evolutionary models constructed by assuming a moderate convective core overshooting (beta(ov) = 0.2) and a canonical mass-loss rate (eta = 0.4) give stellar masses for the primary (Cepheid)-M = 4.14(-0.05)(+0.04) M-circle dot-and for the secondary-M = 4.15+(0.04)(-0.05) M-circle dot-that agree at the 1% level with dynamical measurements. Moreover, we found ages for the two components and for the combined system-t = 151(-3)(+4) Myr-that agree at the 5% level. The solutions based on evolutionary models that neglect the mass loss attain similar parameters, while those ones based on models that either account for an enhanced mass loss or neglect convective core overshooting have lower Bayes factors and larger confidence intervals. The dependence on the mass-loss rate might be the consequence of the crude approximation we use to mimic this phenomenon. By using the isochrone of the most probable solution and a Gaussian prior on the LMC distance, we found a true distance modulus-18.53(-0.02)(+0.02) mag-and a reddening value-E(B - V) = 0.142+(+0.005)(-0.010) mag-that agree quite well with similar estimates in the literature.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
