Searching for magnetic fields in pulsating A-type stars

Numerous δ Sct and γ Dor pulsators are identified in the region of the Hertzsprung-Russell diagram that is occupied by chemically peculiar magnetic Ap stars. The connection between δ Sct and γ 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 HD 340577, for which δ Sct- like pulsations were recently detected in TESS data, and the γ Dor pulsator HR 8799, 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 HD 340577. The measured mean longitudinal field would be the strongest field measured so far in a δ Sct star if the pulsational character of HD 340577 is confirmed spectroscopically. No magnetic field is detected in HR 8799.

LSD Stokes I, V, and diagnostic null N spectra (from bottom to top) calculated for HD340577, for the mask with all lines and the masks for individual ions. The numbers in brackets relate to the number of lines used in each individual mask. The grey horizontal lines in the Stokes V and N spectra indicate the ±1σ error bars. Stokes V spectra are highlighted in red.

Read more: Hubrig et al. 2023, MNRAS 526, L83; arXiv 2308.09441