Stellar Evolution II: Overview of Stellar Models

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1 Stellar Evolution II: Overview of Stellar Models The Origin of Cosmic Elements Satellite School Barcelona 10 & 11 June, 2013 Aldo Serenelli (ICE/CSIC-IEEC)

2 Stars: a rigid society Stellar life and work is determined by: «ini6al M «ini6al composi6on (X,Y,Z) ««ini6al angular momentum environmental factors, e.g. couple to an accre6on disk affects angular momentum Binarity (close) introduces mobility «mass transfer «stellar mergers «angular momentum transfer «evapora6on of stellar atmospheres (irradia6on) Most stars belong to mul6ple systems, but to a large degree, interact very ligle à evolu6on of single stars the fundamental building block in stellar evolu6on

3 Stars: life in a slide Mass (M 8 ) D Burning stages Transi6on object Remnant Planets Brown Dwarfs 0.48 H He- WD Low Mass Stars 2.0 H, He He- flash Planetary nebula (all?) CO- WD Intermediate Mass Stars M c = H, He, C H, He, C Ne, O, Si, C- flash e- - capture SNe Type II, Ib, Ic SNe ONe- WD NS NS/BH Super- AGB Stars Massive Stars

4 Low- mass stars: 1M 8 star evolunon Pre- MS evolu6on: driven by contrac6on L determined by g KH ~ 10-30Myr From virial theorem: Ω + U/2 =0 L = Ω/2 D- burning and par6al Li- burning Credit: A. Weiss

5 Low- mass stars: 1M 8 star evolunon MS evolu6on: H- core burning n ~ 10Gyr radia6ve core convec6ve envelope General rule of thumb τ n M/L M 2

6 Low- mass stars: 1M 8 star evolunon Red Giant Branch H- shell burning rgb ~ 2Gyr He- core degeneracy Cool convec6ve envelope 1 st dredge- up (change of surface composi6on) 1 R 8 10 R R 8 Core mass- luminosity rela6on: L~ (M c ) 7 Close to RGB- 6p, - cooling close to center à max. T not in center

7 Low- mass stars: 1M 8 star evolunon He- core flash when M c =0.47 M 8 (weak dependence on M and composi6on) Off- center igni6on He- core is degenerate à thermal runaway Nuclear energy used to lif degeneracy in the core- does not show up in the surface L

8 Low- mass stars: 1M 8 star evolunon He- core flash when M c =0.47 M 8 (weak dependence on M and composi6on) Off- center igni6on He- core is degenerate à thermal runaway Nuclear energy used to lif degeneracy in the core- does not show up in the surface L Subflashes un6l stable He- burning sets in the center

9 Low- mass stars: 1M 8 star evolunon Horizontal Branch He- core burning 1 st order: single core mass (0.47 M 8 ) à horizontal HB =10 8 yr but H- shell burning is relevant à L= L He +L H L H depends on thickness of H- envelope à mass loss on the RGB impacts HB

10 Interlude on Horizontal Branch NGC 2808 Hot HB HB Different morphology: composi6on (1 st parameter metal- poor HB stars are bluer) age, Y (2 nd parameter?)

11 Low- mass stars: 1M 8 star evolunon Asympto6c Giant Branch 1 st phase (Early- AGB): He- shell burning Degenerate CO core 2 nd phase (thermally- pulsing AGB; TP- AGB) H & He shells burning alternates He- ignites under moderate degeneracy condi6ons Large mass loss and ejec6on of envelope

12 Interlude on TP- AGB L T eff L He L H Herwig (2005) Althaus et al. (2001)

13 Low- mass stars: 1M 8 star evolunon Post- AGB phase Quick evolu6on at constant L, generally driven by fast H- burning of a thin shell (this depends on when the star leaves the AGB) Star surrounded by ejected material Rapid contrac6on very high T eff T eff +ejecta à planetary nebula (always?)

14 Low- mass stars: 1M 8 star evolunon White dwarf Evolu6on driven by cooling (nuclear reac6ons negligible) Fast ini6al - cooling phase L > L!! Evolu6on slows down. From beginning of WD phase ~300 Myr to ~10000K but several Gyr to ~5000K

15 Solar structure & models Main Sequence star half- way through its life M 8 = g R 8 = cm L 8 = erg/s Teff= 5777K Z/X= (AGSS09, GS98) Z i /X (individual elements) 8 = yr

16 Solar structure: helioseismology Non- radial p- modes (pressure is the restoring force): acous6c waves Decomposi6on in spherical harmonics (l,m); observed up to l~1500

17 Solar structure: helioseismology Inversion of frequencies for determina6on of solar structure 2 δωi i δc i = K 2 ( r) ( r) dr + K 2 c 2 ρ, c ω c i δρ ( r) ( r) dr ρ + F, ρ surf i ( ω ) δc 2 ( r) δρ( r) R CZ Y SUP ( X SUP ) GS98 R CZ Y SURF δc δρ 0.01 AGSS Helioseism ± ±

18 Solar structure: helioseismology Large devia6on in sound speed due to mismatch in CE boundary, determined by condi6on rad ( κ) = ad Lower Z leads to lower Is there a case for missing opaci6es in stellar interiors? Solar structure and models fundamental tests for stellar physics

19 Solar neutrinos 8 reac6ons produce neutrinos (p, ) 13 C 14 N (p, ) 17 O (,e + ) (p, ) (,e + ) 13 N 15 O 17 F (p, ) 12 C (p, ) (,e + ) (p, ) (p, ) 15 N 16 O

20 Solar neutrinos Produc6on regions reflect temperature and composi6on dependence

21 Solar neutrinos 8 B and 7 Be fluxes measured by neutrino experiments: SuperKamiokande, SNO, Borexino

22 Solar structure Credit: A. Weiss

23 IniNal Mass Final Mass relanon Ini6al Mass Func6on is a Salpeter- like distribu6on of masses dn dm M 2.35 Hot (T>13000 K) WD mass distribu6on from SDSS DR7 White dwarf masses distribu6on does not look like it at all!! Kleinman et al. 2013

24 IniNal Mass Final Mass relanon Semi- empirical IMFM rela6on (WDs in clusters) strong mass loss affects stellar evolu6on Very important rela6on, not just for stellar theory, but also for galac6c chemical evolu6on

25 IniNal Mass Final Mass relanon Semi- empirical IMFM rela6on from proper mo6on pairs (da6ng the companion can be tricky) Catalan et al. (2008)

26 Dominant role of core convecnon As mass increases convec6on in core takes larger frac6on of star in Main Sequence Evolu6on affected by modeling of convec6on subject to uncertain6es, most important is amount of overshoo6ng (OV) Core OV affects all stages of evolu6on, even the fuzzy mass threshold leading to e- capture SNe (numerous according to IMF)

27 Intermediate Mass Stars He- igni6on under non- degenerate condi6ons no constant He- core mass A. Weiss Blue loops during He- core burning: Cepheids Very sensi6ve to model details

28 AGB Stars: 3 rd dredge- up During the TP- AGB phase, mager processes in He- burning can be brought to the surface M Maeder (2009) M

29 AGB Stars: 3 rd dredge- up During the TP- AGB phase, mager processes in He- burning can be brought to the surface 3 rd dredge- up: penetra6on of convec6ve envelope down to ashes of He- shell Strongly modifies surface composi6on: C/O, 12 C/ 13 C, C/N ~ half 12 C has AGB origin Maeder (2009)

30 AGB Stars: 3 rd dredge- up & s- process s- process elements, peaks at magic neutron numbers

31 AGB Stars: 3 rd dredge- up & s- process Main ingredient: free neutrons / Not easy to come by Basic s(slow)- process: neutron flux low à if unstable decay Herwig (2005)

32 AGB Stars: 3 rd dredge- up & s- process Main ingredient: free neutrons / Not easy to come by Basic s(slow)- process: neutron flux low à if unstable decay In reality branching point exist; depend on neutron flux and local condi6ons and are poten6al tests of stellar physics

33 AGB Stars: 3 rd dredge- up & s- process Main ingredient: free neutrons / Not easy to come by Two main sources: 13 C(,n) 16 O & 22 Ne(,n) 25 Mg At the deepest penetra6on point H envelope in contact with 12 C (from 3 ) Subsequent evolu6on 12 C(p, γ) 13 N(β + ) 13 C C(p, γ) 14 N How to prevent 14 N produc6on? Scarcity of protons, so only 1 capture takes place

34 AGB Stars: 3 rd dredge- up & s- process Temperature increases when reaching next pulse and at T~ K, 13 C(,n) 16 O becomes ac6ve and s- process takes place 13 C pocket

35 AGB Stars: 3 rd dredge- up & s- process Small caveat: stellar models DO NOT produce 13 C pocket using standard physics. Mild mixing of protons below the convec6ve envelope has to be induced (no clear physical mechanism has been iden6fied yet) doged: 12C solid: 13C dashed: 14N long- dashed: p Increase in mixing below the CZ 13 C pocket Cristallo et al. (2009)

36 Massive stars Evolu6on very sensi6ve to overshoo6ng and mass loss (even in MS) OV extends CC à life6me Chieffi et al.

37 Massive stars Evolu6on very sensi6ve to rota6on massive stars tend to rotate faster (no efficient braking during MS) Maeder & Meynet (2000)

38 Stars: the high- mass end Heger et al. (2003)

39 The end is where we start from Mass (M 8 ) D Burning stages Transi6on object Remnant Planets Brown Dwarfs 0.48 H He- WD Low Mass Stars 2.0 H, He He- flash Planetary nebula (all?) CO- WD Intermediate Mass Stars H, He, C H, He, C Ne, O, Si, C- flash e- - capture SNe Type II, Ib, Ic SNe ONe- WD NS NS/BH Super- AGB Stars Massive Stars

As the central pressure decreases due to the increase of μ, the stellar core contracts and the central temperature increases. This increases the

As the central pressure decreases due to the increase of μ, the stellar core contracts and the central temperature increases. This increases the Stellar Evolu,on Stars spend most of their lives on the main sequence. Evidence for this is provided by the fact that 90% of stars observable from Earth are main- sequence stars. Stellar evolu,on during