Composite Spectra, Paper XXI: 14 Serpentis

We separate the component spectra of the composite-spectrum binary 14 Serpentis, derive a precise double-lined (SB2) orbit for the system, and investigate the physical properties and evolutionary states of its component stars. The 260-day binary is comprised of an early-K giant plus a late-Am star that is rotating at ∼60–70 km s−1. We find that the system has a mass ratio (M1/M2) of 1.14 ± 0.01, and that the cool star is ∼1.7 times as bright as its hot companion in V, though ∼2.5 times brighter bolometrically. We derive individual masses and logarithmic luminosities of the cool star and the hotter one as 2.05 and 1.8 M⊙, and 1.57 and 1.18 log L⊙, respectively, with corresponding uncertainties close to 0.1 M⊙ and 0.07 log L⊙. Fitting evolutionary tracks to the H–R diagram positions of the two stars suggests that the cool primary is part-way up the red-giant branch and that the system has been evolving for more than 109 years; the absence of Li from its spectrum may support the latter statement. The hotter, less massive companion appears to have left the zero-age main sequence, which accords with the log g<4.0 indicated by comparisons with synthetic spectra, though its radius is currently only 2.5 R⊙.