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 ERIZDI 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 CETEvolutionary 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 dTsvetkova et al. 2012

2010-2011 seasons

Beta Ceti : ZDI MAP(Tsvetkova et al. 2012)

Prot = 128 dNo Diff. Rot.i = 42°Pol. at 95%

Dip. 62%Axi : 62%

Bmean = 12 G

Ap STAR DESCENDANTSPRESENT 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 MFStrugarek 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 INTERACTION

POLLUX : DETECTION OF THE

MAGNETIC FIELD

EK ERI: HRD + EVOLUTIONARY MODELS (of Charbonnel and Lagarde 2010)