Super-slowly rotating Ap (ssrAp) stars: New spectroscopic observations

The rotation periods of Ap stars range over five to six orders of magnitude. The origin of their differentiation remains unknown. We carry out a systematic study of the longest period Ap stars to gain insight into their properties. We analysed newly obtained spectra of a sample of super-slowly rotating Ap (ssrAp) star candidates identified by a TESS photometric survey to confirm that their projected equatorial velocity, ši, is consistent with (very) long rotation periods; to obtain a first determination of their magnetic fields; and to test their binarity. The value of ši in 16 of the 18 studied stars is low enough for them to have moderately to extremely long rotation periods. All stars but one are definitely magnetic; for five of them, the magnetic field was detected for the first time. Another set of five new stars with resolved magnetically split lines were discovered. Five of the stars that were not previously known to be spectroscopic binaries were found to show radial velocity variations, and in one of them, lines from both components were observed.