Spectroscopic Binary Cepheid V350 Sgr: Revision of Physical Characteristics and Evolutionary Status

Abstract

Based on the original version of the pulsating photosphere method that allows modeling the changes in the effective temperature, a revision of the physical characteristics of the unique binary Cepheid V350 Sgr was carried out. Previously published measurements of radial velocities were used, as well as new ones obtained by us, which allowed us to refine the parameters of the Cepheid orbit. The choice of the projection factor \(PF=1.34\) allowed us to reconcile our estimates of the cycle-averaged radius \(\langle{R}\rangle_{I}/R_{\odot}\approx 41.3{-}41.9\), luminosity \(M_{V}\approx-3\overset{\textrm{m}}{.}52{-}3\overset{\textrm{m}}{.}57\), normal color \((B-V)_{0}\approx 0\overset{\textrm{m}}{.}56\pm 0\overset{\textrm{m}}{.}01\), effective temperature \(\langle\log{}T_{\textrm{eff}}\rangle_{I}\approx 3.788\pm 0.002\), distance \(D\approx 992\pm 14\) pc and color excess \(E(B-V)\approx 0\overset{\textrm{m}}{.}35\pm 0\overset{\textrm{m}}{.}01\) with MESA theoretical evolutionary tracks for the mass \(5.1M_{\odot}\) and metallicity \([{\textrm{Fe}}/{\textrm{H}}]=-0.18\) dex (or mass \(5.2M_{\odot}\), \([{\textrm{Fe}}/{\textrm{H}}]\approx-0.10\) dex) and the PARSEC 2.0 track for the mass \(5.2M_{\odot}\), \(Z\approx 0.01\). The evolutionary age of the Cepheid, which is in the phase of the third crossing of the instability strip, is estimated at 100 Myr. It is shown that the Gaia eDR3/DR3 catalogues provide a distance overestimated by approximately 25%. Using the mass function for the available estimates of the Cepheid and companion masses, the relative orbital plane inclination angle \(i\approx 53^{\circ}\pm 3^{\circ}\) and the orbital semi-major axes \(a_{1}\approx 1.63\pm 0.05\) AU, \(a_{2}\approx 3.42\pm 0.09\) AU were determined for the first time, with the relative orbit size of about 5 AU.