Stellar angular momentum Stellar angular momentum evolution in the COROT evolution in the COROT

MissionMissionJose 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 UFRNJosé D. do Nascimento UFRNIgor F. dos Santos UFRNBruno L. Canto Martins UFRNIzan C. Leão UFRN

Lício da Silva ON Gustavo P. Mello Obs. ValongoEduardo F. Del Peloso Obs. ValongoBeatriz Barbuy USPCláudio Melo ESO

• 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.

COROT : Rotation of solar-type stars from the main sequence to the Red Giant Branch

In addition to evolutionary expansion, which physical processes control the behavior of rotation along the HR Diagram?

The evolving SunThe evolving Sun

do Nascimento et.al 1999

• Geneva - Toulouse CodeGeneva - Toulouse Code

• Standard EvolutionStandard Evolution

The Rotation evolution The Rotation evolution (vsini)(vsini)

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/H]=0 are shownfor 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.

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).

Over the past 10 years it has become possible to measure projected rotational velocities with highOver 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. precision and, as a result, some very interesting new features on the behavior of stellar rotation are emerging.

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The evolving SunThe evolving Sun

do Nascimento et.al 1999, do Nascimento et.al 2003

A(Li) and on the subgiant A(Li) and on the subgiant branchbranch

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

do Nascimento et.al 1999

4 transits summed together

Portion around 1 transit

Time (hrs)

Mixing in Low Mass StarsMixing in Low Mass Stars

rXDDr

rrtX i

scheareffi )(1 2

2

rDr

rrUr

rrtr

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24

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2 151)(

Meridional circulation Gradients of Shear instabilities

Zahn 1992: strong horizontal turbulence

Transport of the chemical species

Transport of the angular momentum

Palacios et al. 2004 A&A

A(Li), Vsini and Convection A(Li), Vsini and Convection

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 aloneMixing model have some free parameters

do Nascimento et.al 1999

4 transits summed together

Portion around 1 transit

Time (hrs)

A(LiA(Li), Vsini and F(Ca)), Vsini and F(Ca)

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)

do Nascimento et.al 2002 A&A

4 transits summed together

Portion around 1 transit

Time (hrs)

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

4 transits summed together

Portion around 1 transit

Time (hrs)

The evolving SunThe evolving Sun

do Nascimento et.al., A&A 1999

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.

The evolving Sun The evolving Sun Description of the Targets

do Nascimento et.al., A&A 1999

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?

Rotation Connection with Rotation Connection with Activity and MixingActivity and Mixing

The evolving Sun The evolving Sun Anticenter positions_V9 Anticenter positions_V9 Description of the Targets

V < 8V < 88 < V < 98 < V < 9

++

11 < V < 16 ExoField11 < V < 16 ExoField

The evolving Sun The evolving Sun center positions_V9 center positions_V9 Description of the Targets

V < 8V < 88 < V < 98 < V < 9

++11 < V < 16 ExoField11 < V < 16 ExoField