Searching for magnetic fields in pulsating A-type stars: the discovery of a strong field in the probable delta Sct star HD340577 and a null result for the gamma Dor star HR8799

TL;DR

This study investigates magnetic fields in pulsating A-type stars, discovering a strong magnetic field in a delta Sct star and finding no magnetic field in a gamma Dor star, to understand magnetic influence on stellar pulsations.

Contribution

First spectropolarimetric detection of a strong magnetic field in a delta Sct star, providing empirical data to test theories of magnetic damping of pulsations.

Findings

HD340577 has a magnetic field of several hundred Gauss.

No magnetic field detected in HR8799.

Potential for the strongest magnetic field measured in a delta Sct star.

Abstract

Numerous delta Sct and gamma Dor pulsators are identified in the region of the Hertzsprung-Russell diagram that is occupied by chemically peculiar magnetic Ap stars. The connection between delta Sct and gamma Dor pulsations and the magnetic field in Ap stars is however not clear: theory suggests for magnetic Ap stars some critical field strengths for pulsation mode suppression by computing the magnetic damping effect for selected p and g modes. To test these theoretical considerations, we obtained PEPSI spectropolarimetric snapshots of the typical Ap star HD340577, for which delta Sct-like pulsations were recently detected in TESS data, and the gamma Dor pulsator HR8799, which is a remarkable system with multiple planets and two debris disks. Our measurements reveal the presence of a magnetic field with a strength of several hundred Gauss in HD340577. The measured mean longitudinal field would be the strongest field measured so far in a delta Sct star if the pulsational character of HD340577 is confirmed spectroscopically. No magnetic field is detected in HR8799.