Abstract
Before the launch of theKeplerSpace Telescope, most studies of the rapidly oscillating Ap (roAp) stars were conducted with ground-based photometricBobservations, supplemented with high-resolution time-resolved spectroscopy and some space observations with the WIRE, MOST, and BRITE satellites. These modes of observation often only provided information on a single star at a time, however,Keplerprovided the opportunity to observe hundreds of thousands of stars simultaneously. Over the duration of the primary 4 yearKeplermission, and its 4 year reconfigured K2 mission, the telescope observed at least 14 new and known roAp stars. This paper provides a summary the results of these observations, including a first look at the entire data sets, and provides a look forward to NASA'sTESSmission.
Highlights
The rapidly oscillating, chemically peculiar A stars are found at the base of the classical instability strip, where it intersects the main-sequence
It is the presence of the magnetic field which gives rise to the chemical peculiarities in the Ap stars; convection is suppressed by the magnetic field allowing for the radiative levitation of, most notably the rare earth elements, and the gravitational settling of others
The origin of the magnetic field is not conclusively known, but is suspected to be the result of the merger of close binary stars in the pre-main sequence phase of evolution where at least one star is still on the Henyey track (Ferrario et al, 2009; Tutukov and Fedorova, 2010). This scenario provides an explanation for the lack of Ap stars in close binary systems, and why the magnetic axis is inclined to the rotation axis
Summary
The rapidly oscillating, chemically peculiar A (roAp) stars are found at the base of the classical instability strip, where it intersects the main-sequence. In the case of the Ap stars, it is the magnetic field, which can be of order 30 kG (e.g., Babcock, 1960; Freyhammer et al, 2008; Mathys, 2017), that causes the most significant deviation from spherical symmetry, and so the pulsation axis is closely aligned to the magnetic one (e.g., Shibahashi and Saio, 1985a; Shibahashi and Takata, 1993; Bigot and Dziembowski, 2002; Bigot and Kurtz, 2011) This misalignment of the pulsation axis with the rotation one serves to provide an observer with a varying view of the pulsation, leading to amplitude modulation of the observed pulsation(s). It is hoped that the ongoing Transiting Exoplanet Survey Satellite (TESS) mission (Ricker et al, 2015) will provide insight to this
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