The new orbital elements and properties of $\vec{\varepsilon}$ Persei

Abstract

A detailed analysis of a large collection of electronic spectra from three observatories, together with radial velocities published earlier, were used to derive a new ephemeris and improved orbital elements for the e Per binary. Observations covering a time interval of about 37 000 days (101.3 years) can be reconciled with a constant orbital period of 14$\fd$06916$\,\pm\,$0$\fd$00004. The high orbital eccentricity of 0.555$\,\pm\,$0.009 was also confirmed. New spectral observations confirm that there is a periodic variation of the systemic velocity. Together with new evidence from astrometric observations (also analyzed here), they confirm the existence of a third body in the system with an orbital period of about 9600 days (26.3 years), rather than 4156 days, as reported earlier. Application of the disentangling technique to the H α spectra with good $S/N$ ratios did not allow detection of spectral lines of either the secondary or tertiary components. For plausible inclinations between 30° and 90°, the observed mass function implies a mass of the secondary $M_2=0.85{-}1.77$ $M_{\odot}$, if a primary mass is adopted of 13.5$\,\pm\,$2.0 $M_{\odot}$. Attempts to detect the third body via interferometric observations should continue in spite of this first negative result.