# Asteroseismology and Gaia: Testing Scaling Relations Using 2200 Kepler Stars with TGAS Parallaxes

## TL;DR

This study compares asteroseismic and Gaia parallaxes for 2200 Kepler stars, confirming the accuracy of asteroseismic radii within 5% and exploring systematic differences, thereby enhancing stellar distance measurements and understanding of stellar properties.

## Contribution

It provides an empirical validation of asteroseismic radii accuracy and refines the understanding of parallax offsets, improving stellar scaling relations and distance estimates.

## Key findings

- Asteroseismic radii are accurate to ~5% for stars 0.8-8 Rsun.
- No significant parallax offset for main-sequence and low-luminosity RGB stars.
- Systematic underestimation (~5%) of radii for subgiants (~1.5-3 Rsun).

## Abstract

We present a comparison of parallaxes and radii from asteroseismology and Gaia DR1 (TGAS) for 2200 Kepler stars spanning from the main sequence to the red giant branch. We show that previously identified offsets between TGAS parallaxes and distances derived from asteroseismology and eclipsing binaries have likely been overestimated for parallaxes <~ 5-10 mas (~ 90-98% of the TGAS sample). The observed differences in our sample can furthermore be partially compensated by adopting a hotter Teff scale (such as the infrared flux method) instead of spectroscopic temperatures for dwarfs and subgiants. Residual systematic differences are at the ~ 2% level in parallax across three orders of magnitude. We use TGAS parallaxes to empirically demonstrate that asteroseismic radii are accurate to ~ 5% or better for stars between ~ 0.8-8 Rsun. We find no significant offset for main-sequence (<~ 1.5 Rsun) and low-luminosity RGB stars (~ 3-8 Rsun), but seismic radii appear to be systematically underestimated by ~5% for subgiants (~ 1.5-3 Rsun). We find no systematic errors as a function of metallicity between [Fe/H] ~ -0.8 to +0.4 dex, and show tentative evidence that corrections to the scaling relation for the large frequency separation (Dnu) improve the agreement with TGAS for RGB stars. Finally, we demonstrate that beyond ~ 3 kpc asteroseismology will provide more precise distances than end-of-mission Gaia data, highlighting the synergy and complementary nature of Gaia and asteroseismology for studying galactic stellar populations.