The Stellar Parameters and Evolutionary State of the Primary in the d' Symbiotic System StHα 190

We report on a high-resolution spectroscopic stellar parameter and abundance analysis of a d' symbiotic star: the yellow component of StHα190. This star has recently been discovered, and confirmed here, to be a rapidly rotating (vsini=100+/-10 km s^-1) subgiant, or giant, that exhibits radial velocity variations of probably at least 40 km s^-1, indicating the presence of a companion (as in many symbiotic systems, the companion is a hot white dwarf star). An analysis of the red spectrum reveals the cool stellar component to have an effective temperature of T_eff=5300+/-150 K and a surface gravity of logg=3.0+/-0.5 (this corresponds to an approximate spectral type of G4 III/IV). These parameters result in an estimated primary luminosity of 45 L_solar, implying a distance of about 780 pc (within a factor of 2). The iron and calcium abundances are found to be close to solar; however, barium is overabundant, relative to Fe and Ca, by about 0.5 dex. The Ba enhancement reflects mass transfer of s-process-enriched material when the current white dwarf was an asymptotic giant branch star, of large physical dimension (>=1 AU). The past and future evolution of this binary system depends critically on its current orbital period, which is not yet known. Concerted and frequent radial velocity measurements are needed to provide crucial physical constraints to this d' symbiotic system. Based on observations made with the 2.1 m telescope of McDonald Observatory, University of Texas.