摘要：Context. Knowing the distribution of strongly magnetic Ap stars in the Hertzsprung-Russell diagram (HRD) allows us to study the evolution of their magnetic fields across the main sequence (MS). With a newly extended Ap star sample from APOGEE and availableGaiaDR2 data, we can now critically review the results of previous studies based onHIPPARCOSdata.Aims. To investigate our targets in theGaiaDR2 HRD, we need to define astrometric and photometric quality criteria to remove unreliable data from the HRD.Methods. We used theGaiaDR2 renormalised unit weight error RUWE as our main quality criterion. We considered known (close) binaries in our sample compared to their (partly affected) astrometry and used theGaiaDR2 data to find common parallax and proper motion (CPPM) wide companions and open cluster members. We studiedG,BP, andRPvariability amplitudes and their significance as a function of magnitude. In colour-magnitude diagrams (CMDs) with absoluteGmagnitude (determined from inverted parallax) versusBP − RPcolour and HRDs, whereBP − RPis replaced by effective temperature, we studied the appearance of outliers with respect to their astrometric quality, binarity, and variability.Results. We present a catalogue of 83 previously known and 154 new strongly magnetic Ap stars withGaiaDR2 data, including astrometric quality parameters, binary flags, information on cluster membership, variability amplitudes, and data fromHIPPARCOS. Our astrometrically cleaned subsamples include 47 and 46 old and new Ap stars with parallaxes > 2 mas. Most of the known 26 binaries among all 237 stars and 14 out of 15 CMD/HRD outliers were excluded by astrometric criteria. The remaining 11 known binaries and a few highly variable objects mainly appear in the bright and red CMD/HRD parts. A CMD based onHIPPARCOSphotometry andGaiaDR2 parallaxes shows a much more narrow distribution in the absoluteVmagnitudes of 75 common Ap stars over the fullB − Vcolour range than the corresponding CMD based onHIPPARCOSparallaxes.
关键词：encatalogsbinaries: generalstars: distancesHertzsprung-Russell and C-M diagramsstars: magnetic fieldstars: variables: general
