At present more than 6600 stars are known or suspected to be chemically
peculiar in the range of spectral types from B1 through F5 (Renson et al.
1991). Among them about 3480 stars are classified as Am or CP1,
according to Preston's (1974) scheme, and about 3160 stars are
Ap and Bp stars (i.e. CP2, CP3, CP4, and He-strong).
A period has been proposed only for 342 stars belonging to the CP2, CP3,
and CP4 groups of Preston's scheme, i.e. magnetic Ap (Si, CrEu, ...
stars), HgMn, and He-weak stars respectively. These stars are listed
in Table 1. Their variations are considered to be linked with nothing
but axial rotation (via the oblique rotator model), i.e. the quoted
periods are those of the star rotations. The very short periods,
attributed to pulsations or oscillations (roAp stars) are not included.
It is generally assumed that the He-strong stars constitute the extention
of the Ap phenomenon at higher temperatures. However it is often difficult
to know if their variations are of the same nature (rotation) or
originate from pulsations (pulsating He stars). Therefore 13 He stars
exhibiting a periodic variation probably originating from their rotation
are listed in another table: Table 2. Some probably pulsating He stars
with known periods (Rns 26510, 27090, 41964, 42920, 45230, 46600, 55266)
are not included.
The 9 Ap stars for which the periodic luminosity variations are ascribed
to a binary effect (eclipsing and/or ellipsoidal stars) are also gathered
in a separate table: Table 3. The distinction is not always obvious
because their periods are of the same order as for other Ap stars.