Stellar angular momentum evolution in the COROT Mission

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Stellar angular momentum evolution in the COROT
Mission

• Jose Dias do Nascimento
• PROFIX / CNPq
• (Natal / Brazil)

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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
ON Gustavo P. Mello Obs.
Valongo Eduardo F. Del Peloso Obs.
Valongo Beatriz Barbuy
USP Cláudio Melo ESO
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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.

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The evolving Sun

• Geneva - Toulouse Code
• Standard Evolution

In addition to evolutionary expansion, which
physical processes control the behavior of
rotation along the HR Diagram?
do Nascimento et.al 1999
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The Rotation evolution (vsini)
Over the past 10 years it has become possible to
measure projected rotational velocities with
high precision and, as a result, some very
interesting new features on the behavior of
stellar rotation are emerging.

• Figure shows the well established rotational
  discontinuity around the spectral type F8IV
  corresponding to (B-V) 0.55 (logTeff 3.78).
  
• 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 Mayor 1990).

do Nascimento et.al 1999,
Fig.1 Distribution of subgiant stars in the HR
diagram, with the rotational behavior as a
function of luminosity and effective temperature.
Luminosities have been derived from the
HIPPARCOS parallaxes. Evolutionary tracks at
Fe/H0 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.
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The evolving Sun
do Nascimento et.al 1999, do Nascimento et.al
2003
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A(Li) and on the subgiant branch
Mixing in Low Mass Stars
do Nascimento et.al 1999

• 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
• However, some stars show a significant
  discrepancy with the theoretical prediction,
  even if the Non-LTE effects are taken into account

Portion around 1 transit
4 transits summed together
Time (hrs)
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Meridional circulation
Gradients of
Shear instabilities
Zahn 1992 strong horizontal turbulence
Transport of the chemical species
Transport of the angular momentum
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Palacios et al. 2004 AA
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A(Li), Vsini and Convection
do Nascimento et.al 1999

• 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

Portion around 1 transit
4 transits summed together
Time (hrs)
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A(Li), Vsini and F(Ca)
do Nascimento et.al 2002 AA

• We have analyzed the behavior of the vsini,
  chromospheric flux and lithium abundance across
  the subgiant branch.
• 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)
• Different authors have reported for a
  rotation-activity relation for evolved stars
  based on the linear behavior of the
  chromospheric flux againststellar rotation
  (e.g. Rutten 1987 Rutten and Pylyser 1988
  Simon and Drake 1989 etc)

Portion around 1 transit
4 transits summed together
Time (hrs)
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The evolving Sun

• Markers spaced by 250 million years
• The left-hand side of the disk shows the size
  with time.
• The right half of the sphere shows the radiative
  core and the depth of the convective envelope
  (dark).
• 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

Portion around 1 transit
4 transits summed together
Time (hrs)
do Nascimento et.al., AA 1999
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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
  lt (B-V) lt 0.8 and 6.0 lt MV lt 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., AA 1999
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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?

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The evolving Sun Anticenter positions_V9
Description of the Targets
V lt 8
8 lt V lt 9
11 lt V lt 16 ExoField
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The evolving Sun center positions_V9
Description of the Targets
V lt 8
8 lt V lt 9
11 lt V lt 16 ExoField
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