Gaia Parallax Zero Point From RR Lyrae Stars

TL;DR

This paper proposes using RR Lyrae stars' infrared period-luminosity relation to independently determine Gaia's parallax zero-point error, which is crucial for accurate distance measurements in astrophysics.

Contribution

It introduces a novel method leveraging RR Lyrae stars to precisely measure Gaia's parallax zero-point error, addressing limitations of Gaia's internal measurements.

Findings

RR Lyrae stars provide competitive parallax data despite their scarcity.

The method is mathematically robust and applicable over a wide distance range.

Using RR Lyrae stars can improve the accuracy of key astrophysical distance measurements.

Abstract

Like Hipparcos, Gaia is designed to give absolute parallaxes, independent of any astrophysical reference system. And indeed, Gaia's internal zero-point error for parallaxes is likely to be smaller than any individual parallax error. Nevertheless, due in part to mechanical issues of unknown origin, there are many astrophysical questions for which the parallax zero-point error $\sigma(\pi_0)$ will be the fundamentally limiting constraint. These include the distance to the Large Magellanic Cloud and the Galactic Center. We show that by using the photometric parallax estimates for RR Lyrae stars (RRL) within 8kpc, via the ultra-precise infrared period-luminosity relation, one can independently determine a hyper-precise value for $\pi_{0}$. Despite their paucity relative to bright quasars, we show that RRL are competitive due to their order-of-magnitude improved parallax precision for each individual object relative to bright quasars. We show that this method is mathematically robust and well-approximated by analytic formulae over a wide range of relevant distances.