The spots on Ap stars

Abstract

The upper main sequence magnetic chemically peculiar (Ap) stars exhibit a non-uniform distribution of chemical elements across their surfaces and with height in their atmospheres. These inhomogeneities, responsible for the conspicuous photometric and spectroscopic variation of Ap stars, are believed to be produced by atomic diffusion operating in the stellar atmospheres stabilized by multi-kG magnetic fields. Here I present an overview of the current state-of-the-art in understanding Ap-star spots and their relation to magnetic fields. In particular, I highlight recent 3-D chemical spot structure studies and summarize magnetic field mapping results based on the inversion of the full Stokes vector spectropolarimetric observations. I also discuss a puzzling new type of spotted stars, HgMn stars, in which the formation and evolution of heavy element spots is driven by a poorly understood mechanism, apparently unrelated to magnetic fields.

6 pages, 3 figures; invited review to appear in the proceedings of IAU Symp. 273 "Physics of Sun and Star Spots"

References in corpus (8)

• Weak magnetic fields in Ap/Bp stars: Evidence for a dipole field lower limit and a tentative interpretation of the magnetic dichotomy
• Evolutionary state of magnetic chemically peculiar stars
• Rare-earth elements in the atmosphere of the magnetic chemically peculiar star HD 144897. New classification of the Nd III spectrum
• Chemical stratification in the atmosphere of Ap star HD 133792. Regularized solution of the vertical inversion problem
• Pulsation tomography of rapidly oscillating Ap stars. Resolving the third dimension in peculiar pulsating stellar atmospheres
• A search for magnetic fields in the variable HgMn star $\alpha$ Andromedae
• Magnetic fields and chemical peculiarities of the very young intermediate-mass binary system HD 72106
• Magnetic field, chemical composition and line profile variability of the peculiar eclipsing binary star AR Aur

Cited by in corpus (6)

• A Third Hot White Dwarf Companion Detected by Kepler
• An Investigation of the Rotational Properties of Magnetic Chemically Peculiar Stars
• A search for photometric variability in magnetic chemically peculiar stars using ASAS-3 data
• TESS Cycle 1 observations of roAp stars with 2-min cadence data
• Detectability of small-scale magnetic fields in early-type stars
• An Investigation of Four Chemically Peculiar Stars with Photometric Periods below 12 Hours