# {\em Gaia}-derived luminosities of {\em Kepler} A/F stars and the pulsator fraction across the {\delta} Scuti instability strip

## TL;DR

This study uses Gaia DR2 parallaxes to accurately determine luminosities of Kepler A/F stars, analyzing their pulsation behavior across the delta Scuti instability strip and revealing that many stars in this region do not pulsate.

## Contribution

It introduces an empirical instability strip based on observed pulsator fractions, differing from existing theoretical models, and provides a comprehensive classification of pulsating and non-pulsating stars.

## Key findings

- 18% of delta Sct stars have dominant frequencies above the Nyquist frequency.
- 30% exhibit super-Nyquist variability.
- Pulsator fraction peaks at just over 70% within the instability strip.

## Abstract

We study the fraction of stars in and around the {\delta} Scuti instability strip that are pulsating, using {\em Gaia} DR2 parallaxes to derive precise luminosities. We classify a sample of over 15,000 {\em Kepler} A and F stars into {\delta} Sct and non-{\delta} Sct stars, paying close attention to variability that could have other origins. We find that 18 per cent of the {\delta} Sct stars have their dominant frequency above the Kepler long-cadence Nyquist frequency (periods < 1 hr), and 30 per cent have some super-Nyquist variability. We analyse the pulsator fraction as a function of effective temperature and luminosity, finding that many stars in the {\delta} Sct instability strip do not pulsate. The pulsator fraction peaks at just over 70 per cent in the middle of the instability strip. The results are insensitive to the amplitude threshold used to identify the pulsators. We define a new empirical instability strip based on the observed pulsator fraction that is systematically hotter than theoretical strips currently in use. The stellar temperatures, luminosities, and pulsation classifications are provided in an online catalogue.