Download Ap stars

HUNTING THE RG DESCENDANTS
OF Ap STARS
Michel Aurière
Renada Konstantinova-Antova
Corinne Charbonnel
Sophie Van Eck
Pascal Petit
Svetla Tsvetkova
et al.
Ap stars
Magnetic Ap/Bp stars
Slow rotators
Chemically peculiar
Strong large scale MF (of fossil origin ?)
Progenitors of magnetic white dwarves ?
About 2-5 % of A-type stars
A dozen of Ap star descendants inside D<100 pc from sun ?
Could be outstanding magnetically active slow rotators
THE HISTORICAL CASE
EK ERI = HR1362
(Stepien 1993)
- G8 III-IV
- Very magnetically active in X-rays (~1030 ergs/s),
CaII H&K in emission, photometric variability...
- Slow rotator: Prot = 308.8 d
- Suspected to be an Ap-star descendant
- Rossby number ~ 2
EKERI: V, V-I PHOTOMETRY
(Dall et al. 2010)
EKERI: LONGITUDINAL MAGNETIC FIELD
EK ERI :
Variations of Bl with phase
EK ERI
ZDI MAP
A Dominant
Magnetic
Dipole
EK ERI : A DOMINANT MAGNETIC DIPOLE
i = 60° beta = 45° Bmax = 200 G
Axisymetry: 79 %
Poloidal: 98% Dipolar: 90% Quadripolar : 6%
magnetic/photometric spot = negative pole of the dipole
= remnant from Ap-star dipole?
14 CET :
The Outstanding F Star
F5IV
Studied during 25 years by the HK survey
(M cycle of 5 y?)
Vsini < 4-5 km/s
Zeeman detected : Bl~ -30 G
Known magnetic F * : Fp or later than F7
14 CET
Evolutionary models of
Charbonnel and Lagarde 2010
14 CET : Be abundance
14 CET : Vrot
VARIATIONS OF Bl OF 14 CET
July-November 2011
STRENGTH OF MF
VERSUS Prot
Beta Ceti
K0III
M ~ 3M_sun
During 1st DUP
Activity of a star of Prot about 50-60 d
Prot ~ 120d
Beta Ceti : Bl variations 2010-2011
(Tsvetkova et al. 2012)
Beta Ceti Prot=128 d
Tsvetkova et al. 2012
2010-2011 seasons
Beta Ceti : ZDI MAP
(Tsvetkova et al. 2012)
Prot = 128 d
No Diff. Rot.
i = 42°
Pol. at 95%
Dip. 62%
Axi : 62%
Bmean = 12 G
Ap STAR DESCENDANTS
PRESENT STATUS
OF OBSERVATIONS
- CP wipped out
- 3 stars with outstanding MF (2 with polo. topology)
- Other active « slow rotators » have MF strength
coherent with Prot (look to their MF topology)
TO LOOK TO RG WITH VERY WEAK MF
AND VERY LONG PERIODS
HISTOGRAM OF Prot
POLLUX : HD 62509
- K0 III
- Pvrad = 589.64 d : hosted planet?
- Weak X-ray luminosity (solar level)
- Rossby number ~ > 2 ?
POLLUX: VARIATIONS OF RV AND Bl
THE MODELISATION SIDE
TO STUDY THE INTERACTION OF :
- A RIGID MAGNETIC FIELD
- CONVECTION
DONE MAINLY IN THE SOLAR CASE
EVOLVING Ap STARS =
EXCELLENT LABORATORY ? !
INTERACTION BETWEEN
CONVECTION AND MF
Cattaneo et al. 2003
SUN + FOSSIL MF
Strugarek et al. 2011
Base of the CE : 0.72 R_sun
Dipolar fossil MF buried deep
in the radiative interior.
The dipolar fossil MF spreads
into the CE !
FUTURE WORK
- TO STUDY THE ZDI TOPOLOGY OF
SLOW ROTATORS
- STABLE RV VARIATIONS VERSUS
PLANETS/STABLE MF TOPOLOGY
- MODELING EVOLUTION OF SLOW
ROTATORS WITH MAGNETIC
BRAKING
- MODELING
OF A DIPOLE
/CONVECTION
POLLUX : DETECTION OF THE
MAGNETIC FIELD
EK ERI: HRD + EVOLUTIONARY MODELS
(of Charbonnel and Lagarde 2010)