Transcript Stellar angular momentum evolution in the CoRoT Mission - IAG-Usp

Stellar angular momentum
evolution in the COROT Mission
Jose Dias do Nascimento
PROFIX / CNPq
(Natal / Brazil)
COROT : Rotation of solar-type stars from the main
sequence to the Red Giant Branch
Jose Renan de Medeiros UFRN
José D. do Nascimento
UFRN
Igor F. dos Santos
UFRN
Bruno L. Canto Martins UFRN
Izan C. Leão
UFRN
Lício da Silva
Gustavo P. Mello
Eduardo F. Del Peloso
Beatriz Barbuy
Cláudio Melo
ON
Obs. Valongo
Obs. Valongo
USP
ESO
COROT : Rotation of solar-type stars from the main sequence
to the Red Giant Branch
•
The behavior of surface rotation of solar-type stars (masses
between 0.9 and 1.4 solar masses) along an evolutionary track
from the main sequence to the RGB.
•
This may have deep impact on our understanding of stellar
angular momentum evolution, in particular on solar rotation
evolution.
The evolving Sun
• Geneva - Toulouse Code
• Standard Evolution
do Nascimento et.al 1999
In addition to evolutionary
expansion, which physical
processes control the behavior of
rotation along the HR Diagram?
The Rotation evolution (vsini)
Over the past 10 years it has become possible to measure projected rotational velocities with high
ecision and, as a result, some very interesting new features on the behavior of stellar rotation are emergi
Figure shows the well established
rotational discontinuity around the spectral
type F8IV corresponding to (B-V) ~ 0.55
(logTeff = 3.78).
do Nascimento et.al 1999,
We can see clearly that single subgiants
redward of the discontinuity with high vsin i
are unusual.
The root cause for such a discontinuity
seems to be a strong magnetic braking
associated with the rapid increase of the
moment of inertia, due to evolutionary
expansion, once the star evolves along the
late F spectral region ( De Medeiros and
1990).
Fig.1 Distribution of subgiant stars in the HR diagram, withMayor
the rotational
behavior as a function of luminosity and
effective temperature. Luminosities have been derived from the HIPPARCOS parallaxes. Evolutionary tracks at
[Fe/H]=0 are shown
for stellar masses between 1 and 4 M (do Nascimento et al 2000 for a more detailed description). The dashed line
indicates the beginning of the subgiant branch and the dotted line represents the beginning on the red giant branch.
The evolving Sun
do Nascimento et.al 1999, do Nascimento et.al 2003
Mixing in Low Mass Stars
A(Li) and on the subgiant
branch
do Nascimento et.al 1999
Portion around 1 transit
For most of the stars we find good
agreement with the dilution
prediction
The evolutionary status
of the sample as well as the
individual masses have been
determined
4 transits summed together
Time (hrs)
However, some stars show a
significant discrepancy with
the theoretical prediction,
even if the Non-LTE effects
are taken into account
Meridional circulation
Gradients of

Shear instabilities
Zahn 1992: strong horizontal turbulence
Transport of the chemical species
X i 1   2
X i 

 2
r ( Deff  Dschear )


t
r r 
r 
Transport of the angular momentum
(r )
1 
1  4
 
4

 2
r U  2  r Dschear

t
5r r
r r 
r 
2


Palacios et al. 2004 A&A
A(Li), Vsini and Convection
do Nascimento et.al 1999
Portion around 1 transit
4 transits summed together
Time (hrs)
The deepening (in mass) of the
convective envelope as a function of the
effective temperature (first dredge--up)
and [Fe/H] = 0.
No transport processes except for the
classical convective mixing (with a value
of 1.6 for the mixing length parameter)
are taken into account.
The predicted dilution factor at the end of
the dredge-up ranges between 20 and 60
low lithium content of some
subgiants cannot be accounted by
dilution alone
Mixing model have some free parameters
A(Li), Vsini and F(Ca)
do Nascimento et.al 2002 A&A
We have analyzed the behavior of the vsini,
chromospheric flux and lithium abundance
across the subgiant branch.
Portion around 1 transit
A sample of 121 stars, along the spectral
region F, G and K, with rotational velocity,
flux of CaII and A(Li)
Flux index catalogue by Rutten (1987)
4 transits summed together
Time (hrs)
Different authors have reported for a
rotation-activity relation for evolved stars
based on the linear behavior of the
chromospheric flux against
stellar rotation (e.g.: Rutten 1987; Rutten and
Pylyser 1988; Simon and Drake 1989; etc)
The evolving Sun
Markers spaced by 250 million years
The left-hand side of the disk shows the size
with time.
Portion around 1 transit
The right half of the sphere shows the
radiative core and the depth of the
convective envelope (dark).
4 transits summed together
Time (hrs)
Three half-circles show where 25%, 50%,
and 75% of the mass is contained
The mass fraction in the convective
envelope and the moment of intertia for the
convective envelope are shown
do Nascimento et.al., A&A 1999
The evolving Sun
Description of the Targets
The main goal has been to select solar-type
stars loosely defined as bona-fide dwarfs,
subgiants and giants stars aligned along the
theoretical evolutionary tracks of stars
with 0.9-1.4 solar masses.
This translates approximately in the limits
+0.5 < (B-V) < +0.8 and 6.0 < MV <
+2.0. The apparent magnitude limit is V =
9.0, as a guarantee towards completeness
of photometric data for the targets as well
as to facilitate the subsequent acquisition
of spectroscopic data by ground-based
telescopes.
The result of this selection is a sample of
30 and 22 targets, respectively, in the
06h50m and 18h50m COROT fields.
do Nascimento et.al., A&A 1999
Rotation Connection with Activity
and Mixing
Which physical processes control the behavior of rotation along the HR
Diagram?
There is some conjecture that the mixing maybe driven by rotation and thus
depend upon the rotational history of the star.
How is the angular momentum transported and is it related to particles
transports ?
How does magnetic braking affect rotation?
How does rotation affect internal mixing processes?
Does rotation controls dynamo process and stellar activity?
The evolving Sun
Anticenter positions_V9 Description of the Targets
V<8
8<V<9
+
11 < V < 16 ExoField
The evolving Sun
center positions_V9 Description of the Targets
V<8
8<V<9
+
11 < V < 16 ExoField