Abundance analysis of roAp stars. IV. HD24712

Wepresenttherstabundanceanalysisoftherapidly oscillating chemically peculiar star HD24712, and determine a Teff =7250K, log g =4.3, and t =1kms 1 . Microturbulence seems to be entirely simulated by a magnetic eld with a polar eld strength of 4.4kG and of dipolar structure, both of which are supported by our polarimetric observations. Rotation of HD24712 and a spotty surface distribution of the elements result in different mean abundances for different (magnetic) phases. Our results do not support the hypothesis of a monotonic correlation between the amplitude of abundance variations and the atomic number Z, and we present arguments in favour of one of the rotation periods (Prot=12: 4610) discussed in the literature. Rareearthelementsarethemostoverabundantelementsrel- ative to the sun, and they have the largest abundance amplitude during a rotation cycle; only Mg has a larger amplitude. For HD24712 we nd a clear overabundance of Co while most of the other iron peak elements are underabundant. A comparison of the abundance pattern with the other three roAp stars analyzed so far by us concludes the paper. A systematic difference between surface gravities obtained from spectroscopy and from both asteroseismology and evolu- tionary tracks is found for the roAp stars HD 24712, Cir and Equ.