| Popis: |
Ap stars have the strongest magnetic fields of any main sequence star. As a group they rotate more slowly than superficially normal stars of similar temperatures. In recent years, it has been shown that several percent of the Ap stars must have rotation periods longer than one year, that some of them definitely have periods of the order of 300yr, and that Ap stars with much longer periods (perhaps ~1000 yr) may exist. The astrophysical cause of their slow rotation – the braking mechanism – is not known with certainty. To constrain the theoretical models, achieving as complete and exact knowledge of the period distribution as possible is essential. Until now, the vast majority of the very slowly rotating Ap stars known were strongly magnetic. Recently, we have shown that TESS data lend themselves well to the identification of long-period Ap stars (Mathys et al. 2020, A&A, 639, A31). We have used the southern ecliptic hemisphere TESS data to build a list of 60 Ap stars that do not show rotational variability over 27d, almost all of which must have much longer rotation periods. We shall present the results of this work, together with a status report on the progress of a similar, complementary study based on the northern ecliptic hemisphere TESS data. The identification of long-period Ap stars using this approach is fully independent of the strengths of their magnetic fields. We shall also discuss the existence of a correlation between the roAp phenomenon and rotation. |
