High-frequency A-type pulsators discovered using SuperWASP★†

Abstract

We present the results of a survey using the WASP archive to search for high frequency pulsations in F-, A-and B-type stars. Over 1.5 million targets have been searched for pulsations with amplitudes greater than 0.5 millimagnitude. We identify over 350 stars which pulsate with periods less than 30 min. Spectroscopic follow-up of selected targets has enabled us to confirm 10 new rapidly oscillating Ap stars, 13 pulsating Am stars and the fastest known δ Scuti star. We also observe stars which show pulsations in both the high-frequency domain and in the low-frequency δ Scuti range. This work shows the power of the WASP photometric survey to find variable stars with amplitudes well below the nominal photometric precision per observation.

HD 24355 observed by theKepler K2mission: a rapidly oscillating Ap star pulsating in a distorted quadrupole mode

“…HD 24355 is a bright (V = 9.65) rapidly oscillating Ap star, discovered by Holdsworth et al (2014a). Their data show a pulsation at 224.31 d −1 (2596.18 µHz; P = 6.4 min) with an amplitude of 1.51 mmag in the WASP broadband filter.…”

“…They show pulsations in the range of 6 − 23 min with amplitudes up to 18 mmag in Johnson B (Holdsworth 2015), and are found at the base of the classical instability strip on the Hertzsprung-Russell (HR) diagram, from the zero-age main-sequence to the terminal-age main-sequence in luminosity. Since their discovery by Kurtz (1982), only 61 of these objects have been identified (see Smalley et al 2015 for a catalogue).…”

“…Savanov, Malanushenko & Ryabchikova 1999;Kochukhov & Ryabchikova 2001;Hatzes & Mkrtichian 2004;Mkrtichian et al 2008;Elkin et al 2010;Elkin, Kurtz & Mathys 2011;Kochukhov et al 2013). Most recently, the use of the Super-WASP (Wide Angle Search for Planets) ground-based photometric survey led to the identification of 11 roAp stars (Holdsworth et al 2014a;Holdsworth 2015).…”

“…Indeed, many of these projects have been employed for that purpose (e.g. Pepper et al 2008;Hartman et al 2011;Ulaczyk et al 2013;Holdsworth et al 2014a). The ability of these surveys to achieve mmag precision provides an extensive all-sky database in which to search for lowamplitude stellar variability, which can then be observed at much higher precision by space-based missions such as K2 (Howell et al 2014) and TESS (Ricker et al 2015).…”

Triennial Report (2012-2015): The Legacy Issue

“…They reveal over 350 stars which pulsate with periods less than 30 minutes; among them 10 new roAp, 13 pulsating Am stars and the fastest known pulsating δ Scuti stars. Holdsworth et al (2014b) reported the safe detection in the Kepler and WASP data sets of pulsation frequency variations in the roAp star KIC 7582608. They concluded that one possibility for the frequency variation is intrinsic variability in the pulsation cavity or the binary motion.…”