Gaia-derived luminosities ofKeplerA/F stars and the pulsator fraction across the δ Scuti instability strip

Abstract

We study the fraction of stars in and around the δ Scuti instability strip that are pulsating, using Gaia DR2 parallaxes to derive precise luminosities. We classify a sample of over 15 000 Kepler A and F stars into δ Sct and non-δ Sct stars, paying close attention to variability that could have other origins. We find that 18 per cent of the δ 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 δ 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.

Forward Modeling the Orbits of Companions to Pulsating Stars from Their Light Travel Time Variations

“…A linear fit to the SNR vs. a sin i scatter yields the relation, ln (σ a sin i ) = −1.0048 ln (SNR) + 6.6173. To place these values in the context of known δ Sct stars, we calculated the SNR of the strongest pulsation peak within the Kepler δ Sct catalogue of Murphy et al (2019) (Fig. 9).…”

Finding binaries from phase modulation of pulsating stars with Kepler – VI. Orbits for 10 new binaries with mischaracterized primaries

“…We then used the trained GMM to calculate posterior probabilities for each of the seven classes and focused on the 56 860 stars in the "cool stars" subsample. We generated an automated short list of 1203 candidates whose most likely variable class was δ Sct, which included 960 δ Sct stars already known from Murphy et al (2019). By manually inspecting all stars on this list, we identified 93 new δ Sct stars.…”

“…The false-positive rate during short-listing was ∼9%, with the primary sources of false positives being, in order of occurrence: harmonics of g mode pulsations, Kepler data artefacts, apparent non-pulsators with noise spikes, and very low amplitude pulsators of borderline significance. Stars in the latter category could be considered δ Sct stars, depending on the chosen significance threshold (see Murphy et al 2019 for a discussion), but the amplitudes would be too low to detect any phase modulation.…”

“…Since the new δ Sct stars have temperatures much cooler than the red edge of the δ Sct instability strip (Dupret et al 2005;Murphy et al 2019), their temperatures must be mischaracterised. Of the 93 δ Sct stars, 91 had pulsation amplitudes high enough for a phase modulation analysis.…”

“…With a reasonable estimate of the masses of the δ Sct primaries, we can estimate the nature of their companions. Given that the systems have been photometrically (mis-)classified with temperatures just cooler than the δ Sct red edge, we assume that the primaries are low-mass δ Sct stars near the instability strip's red edge, which suggests that they have masses of ∼1.5 M (Dupret et al 2004;Murphy et al 2019). Alternatively, these δ Sct stars could have low metallicities and lower masses (∼1.2 M ), but that does not greatly affect the following calculations.…”