CP stars – Introduction II
CP subgroups
Classical
name
Prestons’s
group
Discovery criteria Spectral
types
Magnetic
Field
Am – Fm CP1 weak Ca II and/or Sc II;
enhanced metals
A0 – F4 N
Bp – Ap CP2 enhanced Sr, Cr, Eu, and/or Si B6 – F4 Y
HgMn CP3 enhanced Hg II and/or Mn II B6 – A0 N
He – weak CP4 weak He I compared with
colours
B2 – B8 Y
He – strong enhanced He I compared with
colours
B0 – B2 Y
Preston (1974, ARA&A, 12, 257), Pedersen & Thomsen (1977, A&AS, 30, 11)
Diffusion in stellar atmospheres
• Standard book: Michaud et al., 2015, Atomic
Diffusion in Stars, Astronomy and
Astrophysics Library, ISBN 978-3-319-19853-8.
Springer International Publishing Switzerland
• Here, we look at the upper main sequence
Diffusion in stellar atmospheres
Hui-Bon-Hoa et al., 2002, A&A, 381, 197
Raising
Sinking
Diffusion in stellar atmospheres
Hui-Bon-Hoa et al., 2002, A&A, 381, 197
Raising
Sinking
Alecian et al., 2011, MNRAS, 418, 986
Diffusion works on
rather short
timescales
Stratification in the stellar atmosphere
Alecian, 1998, Contributions
of the Astronomical
Observatory Skalnate Pleso,
27, 290
Stratification in the stellar atmosphere
O. Kochukhov: HD 24712
Diffusion in stellar atmospheres
• What can destroy the pattern from diffusion?
1. Rotation as meridional circulation: limit 100 km/s
2. Convection: not significant, low mass boundary
3. Mass-loss: high mass boundary
The Rotation of BAF stars
Abt et al., 2002, ApJ, 573, 359
v (Sun) = 2 km/s; v (Jupiter) = 12,7 km/s
v (Earth) = 0,465 km/s
The Rotation of BAF stars
Abt & Morrell, 1995, ApJS, 99, 135
The Rotation of A-type stars
Abt & Morrell, 1995, ApJS, 99, 135
The Rotation of A-type stars
Abt & Morrell, 1995, ApJS, 99, 135
The Rotation of BAF stars
• Mixing wins over diffusion for v > 100 km/s
Zorec&Royer,2012,A&A,537,A120
The origin of the magnetic field
Alecian et al., 2019, EAS
Publications Series, 82, 345
Schneider et al., 2019, Nature,
574, 211
Featherstone et al., 2009, ApJ,
705, 1000
The origin of the magnetic field
Only for low rotational
velocities
Many known binary CP stars
known
No differential rotation
detected
Takes several hundred Myrs
Some open questions
• Are CP stars just the slow rotating “normal
stars”?
• Are all slow rotating stars also CP stars?
• Are there also “fast rotating” CP stars?
• Is there a dynamo working in magnetic CP
stars?
• On which time scales work the dynamo?
• Is there a magnetic breaking?