The first view of δ Scuti and γ Doradus stars with the TESS mission

Abstract

We present the first asteroseismic results for δ Scuti and γ Doradus stars observed in Sectors 1 and 2 of the TESS mission. We utilize the 2-min cadence TESS data for a sample of 117 stars to classify their behaviour regarding variability and place them in the Hertzsprung–Russell diagram using Gaia DR2 data. Included within our sample are the eponymous members of two pulsator classes, γ Doradus and SX Phoenicis. Our sample of pulsating intermediate-mass stars observed by TESS also allows us to confront theoretical models of pulsation driving in the classical instability strip for the first time and show that mixing processes in the outer envelope play an important role. We derive an empirical estimate of 74 per cent for the relative amplitude suppression factor as a result of the redder TESS passband compared to the Kepler mission using a pulsating eclipsing binary system. Furthermore, our sample contains many high-frequency pulsators, allowing us to probe the frequency variability of hot young δ Scuti stars, which were lacking in the Kepler mission data set, and identify promising targets for future asteroseismic modelling. The TESS data also allow us to refine the stellar parameters of SX Phoenicis, which is believed to be a blue straggler.

On the first δ Sct–roAp hybrid pulsator and the stability of p and g modes in chemically peculiar A/F stars

“…Our blue edge lies near that of Antoci et al (2019), who employed a different convection theory and used models with a smaller helium depletion. However, Antoci et al (2019) found turbulent pressure to be the mechanism driving p modes in Am stars, whereas we find that the 'edge-bump' is able to drive these modes without turbulent pressure and with more extreme helium depletion. A detailed comparison over a broad parameter space is required, but is beyond the scope of this paper.…”

“…The driving of low-overtone pulsations persists in Am stars, despite the gravitational settling of helium, albeit in a narrower instability strip and at lower incidence than for normal stars (Vauclair 1976;Kurtz 1989;Smalley et al 2011Smalley et al , 2017). It appears that turbulent pressure contributes to pulsational driving in these stars (Houdek 2000;Antoci et al 2014Antoci et al , 2019, offering one explanation why some of them pulsate. The suppression of convection in roAp stars by their magnetic fields further explains why these stars have not been observed with low-overtone p modes.…”

Very regular high-frequency pulsation modes in young intermediate-mass stars

“…1 shows some of the pulsation spectra, which have remarkably regular patterns of peaks. The small amplitudes of the highest-frequency modes may indicate that turbulent pressure, rather than the standard opacity mechanism, is responsible for driving them 15 . About one-third of the stars in our sample (for example, the bottom half of Fig.…”

Highlights of Discoveries for δ Scuti Variable Stars From the Kepler Era

“…The pixel size for the TESS cameras is larger, making crowding and contamination from nearby stars in the field an issue that must be taken into account in data analyses. The redder TESS bandpass reduces the observed amplitudes of δ Sct pulsations by about 25% compared to the amplitudes of the Kepler mission (Antoci et al, 2019).…”

“…The TESS first-light papers have been published, including a first view of δ Sct and γ Dor stars with the TESS mission (Antoci et al, 2019). This paper contains up-to-date descriptions of δ Sct and related stars, including pre-main-sequence δ Sct stars that were not studied in detail using Kepler observations, λ Boo stars not discussed in this review, TESS observations of very bright stars such as α Pic, and the pulsation class prototypes SX Phe (see also Daszyńska-Daszkiewicz et al, 2020a,b) and γ Dor that were not targeted by Kepler.…”