lms & ims: their evolution, nucleosynthesis and dusty end s. cristallo in collaboration with...
TRANSCRIPT
LMS & IMS: their evolution, nucleosynthesis and dusty end
S. Cristallo
in collaboration with Oscar Straniero and Luciano Piersanti
Osservatorio Astronomico di Teramo - INAF
AGBs: a theoretician perspective
Very luminous(103-104 our SUN)
Very cold(2000-3000 K)
AGB structure
CO CoreHe-shellH-shell
Earth radius(~10-2 RSUN)
Earth-Sun(~200 RSUN)
Practically, a nut
in a 300 mts hot air balloon
The s-process in AGB stars
Busso et al. 1999
13C(α,n)16O reaction 22Ne(α,n)25Mg reaction
HOT BOTTOM BURNING (Boothroyd & Sackmann 1991)
TDU
TDU
HYDROSTATIC, NO ROTATION, NO MAGNETIC FIELDS
Four
first-order non-linear
constant coefficients
differential equations
Three
characteristic relations
The FRANEC Code(Frascati RAppson-Newton Evolutionary Code)
(Chieffi & Straniero 1989; Straniero et al. 1997; Chieffi et al. 2001;Straniero et al. 2006; Cristallo et al. 2007; Cristallo et al. 2009)
Major uncertainty sources in stellar evolutionary codes and their link with grains
1. Opacities;2. Mass-loss law;3. Equation of State (IMS); 4. Convection treatment;5. Non convective mixing mechanisms (LMS).
Opacities
T2000 K4000-5000 K
Atomic opacities
Molecular opacities
Grains
C/O>1 CO – C2 – CN - C2H2 – C3 Marigo 2002; Cristallo et al. 2007
C/O<1 TiO – H2O - CO
Metallicity 12C & 14N enh. factors
2x10-2 1, 1.5, 1.8, 2.2, 5
Solar ≡ 1.4x10-2 1, 1.5, 1.8, 2.2, 4
1x10-2 & 8x10-3 1, 1.8, 2.2, 5, 10
3x10-3 & 6x10-3 1, 2, 5, 10, 50
1x10-3 1, 5, 10, 50, 200
1x10-4 1, 10, 100, 500, 2000
C and N enhancements
See also:Lederer & Aringer 2009; Weiss & Ferguson 2009Ventura & Marigo 2009; Marigo & Aringer 2009
Karakas et al. 2010
Results
The C-enhanced low temperature opacities
make the stars redder in the AGB phase
Effects on surface temperatures and, therefore, on mass-loss and nucleosynthetic yields
AGB PHASE
Vassiliadis&Wood 1993
Straniero et al. 2006
1. BCK - temperature (Fluks et al. 1994)2. Luminosity - MBOL
3. MK=MBOL-BCK
4. Period-MK (Whitelock et al. 2003)5. Period – Mass-loss
Mass loss law
GRAINSDRIVE THEMASS-LOSS
Grains: opacities and mass-lossWinds of carbon stars are considered to be dust-driven winds. Photons lead to a radiative acceleration of grains away from the star.Subsequently, momentum is transferred to the surrounding gas by gas-grains collisions.
UNKNOWNS
1.grains opacity (how they interact with radiation);2.grains growth process;3.grains nucleation phase (in particular for C/O>>1);4.stellar pulsation physics.
It is commonly assumed that grain sizes are small compared to the relative wavelenght: that’s not always true (see e.g. Mattsson et al. 2011)
The Luminosity function of Galactic C-stars
Guandalini et al. 2006 (A&A, 445, 1069)Cristallo et al. 2011 (ApJS, 197, 2)
The Luminosity function of Galactic C-stars
Guandalini & Cristallo, in preparation
Distances from van Leeuwen 2007 P-L from Whitelock et al. 2006
First attempt (to my knowledge) to evaluate the amount and type of dust production in AGB stars with a stellar evolutionary model
Total mass of dust as a function of the stellar mass
Ventura et al. 2012 (MNRAS 424, 2345)
Ventura et al. 2012 (MNRAS 420, 1442)
1. Amount of silicates scales with Z2. Silicates are produced in IMS (strongly
dependence on HBB)3. Mass-loss rate dtermines the dust condensation
degree4. For C-stars, the main source of uncertainty is
the amount of dredged up carbon
Mass of silicates Mass of carbon dust
EOS for IMSFor Intermediate Mass Stars, the temperature at the bottom of the convective
envelope is high enough (T>4e7 K) to allow proton captures: HOT BOTTOM BURNING (Boothroyd & Sackmann 1991)
Convection treatment• Schwarzschild criterion: to determine convective borders
• Mixing length theory: to calculate velocities inside the convective zones
• Mixing efficiency: proportional to the ratio between the convective time scale and the time step of the calculation (Spark & Endal 1980);
• ΔX depends linearly on Δr (NOT diffusive approach).
At the inner border of the convective At the inner border of the convective envelopeenvelope, we assume that the velocity , we assume that the velocity profile drops following an profile drops following an exponentially decaying lawexponentially decaying law
v = vbce · exp (-d/β Hp) • Vbce is the convective velocity at the
inner border of the convective envelope (CE)
• d is the distance from the CE
• Hp is the scale pressure height
• β = 0.1
REF: Freytag (1996), Herwig (1997),REF: Freytag (1996), Herwig (1997),Chieffi (2001), Straniero (2006), Chieffi (2001), Straniero (2006), Cristallo (2001,2004,2006,2009)Cristallo (2001,2004,2006,2009)
WARNING: vbce=0 except during Dredge Up episodes
Gradients profiles WITHOUT exponentially decaying velocity profileGradients profiles WITH exponentially decaying velocity profile
CONVECTIVEENVELOPE
RADIATIVE He-INTERSHELL
Duringa TDUepisode
An interesting by-product: the formation of the 13C pocket
13C-pocket
23Na-pocket
14N-pocket
Variation of the 13C-pocket pulse by pulse
X(13Ceff)=X(13C)-X(14N)*13/14
1st 11th
14N strong neutron poison via
14N(n,p)14C reaction
Cristallo et al. 2009
13C pocket and dredge up as a function of
Third TP of 2 MThird TP of 2 Mʘʘ at Z=Z at Z=Zʘʘ and Z=10 and Z=10-4-4
Convective 13C burning
Cristallo et al. 2009
He-intershell elements enrichments
J=Iω=mr2ω
F.R.U.I.T.Y.(Franec Repository of Updated Isotopic Tables & Yields)
August the 9th 2012: added 1.3 MSUN models at all metallicities
Z=10-4 models (within the end of November)
On line at www.oa-teramo.inaf.it/fruity
(1.5,2.0,2.5,3.0) MSUN with Z=(1x10-3,3x10-3,6x10-3,8x10-3,1x10e-2,sun,2x10e-2)
Dedicated mailing list with upgrades
Final AGB composition for 0.0001<Z<Z
A key quantity:the neutron/seed ratio, that is
n(13Ceff) /n(56Fe)
13C is primary like56Fe is secondary like
M=2Mʘ
[ls/Fe]
[Pb/Fe]
[hs/Fe]
s-process indexes (I)[ls/Fe]=([Sr/Fe]+[Y/Fe]+[Zr/Fe])/3
[hs/Fe]=([Ba/Fe]+[La/Fe]+[Nd/Fe] +[Sm/Fe])/4
Cristallo et al. 2011
[ls/Fe]=([Sr/Fe]+[Y/Fe]+[Zr/Fe])/3 [hs/Fe]=([Ba/Fe]+[La/Fe]+[Nd/Fe] +[Sm/Fe])/4
Ba & CH stars
Post-AGB
Intrinsic C-rich
Intrinsic O-rich
Observations vs theory (II): [hs/ls] distributions
FRUITY Models vs Grains (measurements from Barzyk et al. 2007)
FRUITY Models vs Grains (measurements from Barzyk et al. 2007)
FRUITY and MONASH models vs Grains (measurements from Avila et al. 2012)
The most interesting data are those that do not agreewith theoretical models.
Ernst Zinner (this morning)
A new set of FRANEC rotating AGB models
1. Centrifugal forces lead to deviations from spherical symmetry;2. Differential rotation is considered and, following Endal & Sofia (1976,1978), the evolution of
angular momentum (J) through the star is followed via a nonlinear diffusion equation (except at the inner border of the convective envelope, where we apply the same formalism of the chemical transport), by enforcing rigid rotation in convective regions (constant angular velocity);
3. Efficiency of both dynamical (Solberg-Hoiland, dynamical shear) and secular (Eddington-Sweet circulation, Goldreich-Shubert-Fricke, secular shear) instabilities are evaluated by computing the corresponding diffusion coefficients as described in Heger et al. (2000), but without their proposed fμ and fc;
4. Angular momentum transport equation is solved contemporary to the chemical evolution equations to take into account the feedback of chemical mixing on molecular weight profile, which could inhibit secular instabilities (μ-current);
5. In solving the angular momentum transport and chemical mixing equations, we computed the effective diffusion coefficient as the sum of the convective one and those related to secular and dynamical rotationally instabilities;
6. No magnetic braking is considered.
PRELIMIN
ARY
THANKS!