The Debris Disk Host beta Piscis Austrinus is a Rapidly Rotating Star Seen Nearly Pole-On

Previous studies of beta Piscis Austrinus (PsA) have speculated that the narrow and saddle-like shapes of some of its weak metallic lines are a consequence of it being a rapidly rotating star viewed nearly pole-on. Here we use the fastrot-spec spectral synthesis code to model high-dispersion (R = 115,000) HARPS spectra of beta PsA in order to determine its inclination and photospheric properties, with additional constraints on the surface temperature set by measures of Fe II/Fe I line ratios. The analysis confirms that beta PsA is oriented nearly pole-on (i = 4.75+0.75-0.50 o) and experiences substantial gravity darkening caused by its rapid rotation (/ crit=0.93 plus or minus0.17). beta PsA has a polar temperature of 10300+200-250 K that is 24% hotter than its equatorial temperature (8275+317-400 K). This results in its apparent luminosity being 48% larger than its actual luminosity of 26.2+1.9-2.4 L. When this methodology is applied to high-dispersion spectra of the star Vega, the analysis determines a nearly pole-on orientation that is consistent with interferometric measurements, validating the technique. Based on comparisons with PARSEC evolutionary models of stars rotating at similar velocities, beta PsA has a mass of 2.20 plus or minus0.03 M and an age of 141+113-49 Myr; this age is consistent with the age inferred for its G5V companion star, CD-32 17127, based on lithium depletion models. The analysis demonstrates the potential for both identifying and determining the stellar properties of rapidly rotating stars viewed nearly pole-on via spectroscopy alone.