Hydrogen & Helium Burning in Stars

Transcription

1 Hydrogen & Helium Burning in Stars What remains to be done and how to do it! Hydrogen Burning: 4 He, 14 N Helium Burning: 12 C, 16 O, 22 Ne, n, s-nuclei Alba Formicola (on behalf of LUNA collaboration) 10 Si-ignition O-ignition Ne-ignition 9 C-ignition log (T c ) 8 He-ignition 7 H-ignition log ( c )

2 Solar system abundances M < 8 M star switches off (white black dwarf) M > 8 M star explodes (supernova) H burning He He burning C, O, Ne C/O Si burning Fe explosive burning relative abundance the ambitious task of Nuclear Astrophysics is to explain the origin and relative abundance of the elements in the Universe Atomic number 2

3 Globular cluster M 10 Red giant stars: H He via CNO cycles in H shell surrounding He core Horizontal branch stars: He C, O in core H He in shell Main sequence stars: H He via pp chains in core Accurate nuclear physics information is crucial for understanding of stars How do other stars produce energy? How do they evolve? Credner & Kohle, Sternwarte Bonn

4 Problem of extrapolation many orders of magnitude LOG SCALE S(E) (E) LINEAR SCALE sub-threshold resonance E G extrapolation needed! extrapolation E G direct measurement low-energy tail of broad resonance resonance non resonant process non-resonant direct measurements S(E)-FACTOR R lab = I p N av /A pb < < nb CROSS SECTION Interaction energy E ~ 10 % I P ~ ma ~ g/cm 2 event/month < R lab < event/day (E) = S(E)/Eexp(-2 ) -E r 0 E r interaction energy E

5 -ray spectra with HPGe detector surface underground underground passive shielding is more effective since μ flux, that create secondary γ s in the shield, is suppressed Pb Cu 3 orders of magnitude! 0.3 m 3 Pb-Cu shield suppression three orders of magnitude below 2MeV

6 LUNA II 400kV accelerator U terminal = kV I max = 500 A (on target) E = 0.07keV Allowed beams: H +, 4 He, ( 3 He)

7 Key reactions measured at LUNA 50kV-400kV pp chain p + p d + e + + e d + p 3 He % 13.8 % 3 He + 3 He + 2p 3 He + 4 He 7 Be % 0.02 % 7 Be+e - 7 Li + + e 7 Be + p 8 B + 7 Li + p + 8 B 2 + e + + e 25 Mg (p, 26Al e + 6 s e + 7 s 25 Al 26 Mg 27 Si (p, (p, 24 Mg (p, 27 Al

8 Study of the 17 O(p,γ) 18 F reaction 17 O+p is of paramount importance for understanding hydrogenburning in different stellar environments: Red Giants Classical Novae stars Massive Stars Asymptotic Giant Branch (AGB) E p = 193 kev 17 O+p E x (kev) 5789 Target profile F

9 -spectrum at resonance energy of the 17 O(p, ) 18 F reaction Total 17 O(p,γ) 18 F reaction cross section measured between E cm kev leading to a four-fold reduction in reaction rate uncertainty in novae region. A.Caciolli et al. Eur.Phys.J A48(2012)144 D. Scott et al. Phys.Rev.Lett. 109,202501, 2012 A.Di Leva et al. Submitted PRC

10 The LNGS Underground Laboratory LUNA I ( ) 50 kv LUNA MV ( >...) 3.5MV LUNA II ( ) 400 kv 12 C(, ) 16 O 13 C(,n) 16 O 22 Ne(,n) 25 Mg (, ) reactions on 14,15 N and 18 O These reactions are relevant at higher temperatures (larger energies) than reactions belonging to the hydrogen-burning studied so far at LUNA

11 Energy Sources in Helium Burning Oxygen-16 New low energy data are needed to improve reliability of cross section (S-factor) extrapolation taking all possible reaction components into account!

12 New R-Matrix calculation open problems S [kev-b] Interference Pattern? low energy region large uncertainties total 10 constructive E1 Casc destructive 1 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 E cm [MeV] E2

13 LUNA MV & JN & CASPAR Move towards higher energies and more intensity Nuclear Science Laboratory & Joint Institute for Nuclear Astrophysics Courtesy by Michael Wiescher University of Notre Dame

14 s-process nucleosynthesis during AGB 13 C(,n) 16 O 22 Ne(,n) 25 Mg max flux 10 9 n cm -3 few years During the AGB phase, alternatively H and Heshells switch on and off several times. Then, the convective H-envelope can penetrate the He-burning inter-shell, dredging-up the produced elements during the s-process.

15 13 C(,n) 16 O experimental status of the art Heil 2008 Big uncertainties in the R-matrix extrapolations. Presence of subthreshold resonances

16 22 Ne(,n) 16 O experimental status of the art Jaeger 2001 Unmeasured resonance at E=635 kev big uncertainties in the reaction rate.

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18 THE LUNA COLLABORATION THE LUNA COLLABORATION Laboratori Nazionali del Gran Sasso A.Formicola, M.Junker Helmoltz-Zentrum Dresden-Rossendorf, Germany M. Anders, D. Bemmerer, Z. Elekes INFN, Padova, Italy C. Broggini, A. Caciolli, R. De Palo, R. Menegazzo, C. Rossi Alvarez INFN, Roma 1, Italy C. Gustavino Institute of Nuclear Research (ATOMKI), Debrecen, Hungary Zs.Fülöp, Gy. Gyurky, E.Somorjai, T. Szucs Osservatorio Astronomico di Collurania, Teramo, and INFN, Napoli, Italy O. Straniero Ruhr-Universität Bochum, Bochum, Germany C.Rolfs, F.Strieder, H.P.Trautvetter Seconda Università di Napoli, Caserta, and INFN, Napoli, Italy F.Terrasi Università di Genova and INFN, Genova, Italy F. Cavanna, P.Corvisiero, P.Prati Università di Milano and INFN, Milano, Italy C. Bruno, A.Guglielmetti, D. Trezzi Università di Napoli ''Federico II'', and INFN, Napoli, Italy A.Di Leva, G.Imbriani, V.Roca Università di Torino and INFN, Torino, Italy G.Gervino University of Edinburgh M. Aliotta, T. Davinson, D. Scott