WFIRST Ultra-Precise Astrometry II: Asteroseismology

TL;DR

WFIRST will provide high-precision astrometry and photometry enabling extensive asteroseismic studies of giant stars in the Galactic bulge, improving stellar radius and mass measurements for about a million stars.

Contribution

This paper demonstrates the potential of WFIRST's microlensing observations for large-scale asteroseismology, a novel application of its high-precision data.

Findings

Detects oscillations in stars from red clump to red giant branch.

Enables external validation of stellar radii using astrometric data.

Allows mass measurements for fainter stars via asteroseismic parameter nu_max.

Abstract

WFIRST microlensing observations will return high-precision parallaxes, sigma(pi) < 0.3 microarcsec, for the roughly 1 million stars with H<14 in its 2.8 deg^2 field toward the Galactic bulge. Combined with its 40,000 epochs of high precision photometry (~0.7 mmag at H_vega=14 and ~0.1 mmag at H=8), this will yield a wealth of asteroseismic data of giant stars, primarily in the Galactic bulge but including a substantial fraction of disk stars at all Galactocentric radii interior to the Sun. For brighter stars, the astrometric data will yield an external check on the radii derived from the two asteroseismic parameters, <Delta nu> and nu_max, while for the fainter ones, it will enable a mass measurement from the single measurable asteroseismic parameter nu_max. Simulations based on Kepler data indicate that WFIRST will be capable of detecting oscillations in stars from slightly less luminous than the red clump to the tip of the red giant branch, yielding roughly 1 million detections.