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Nucléosynthèse dans les novae

Nucléosynthèse dans les novae. Margarita Hernanz Institut d’Estudis Espacials de Catalunya, IEEC-CSIC, Barcelona. Modèles de novae classiques : introduction; principales propriétés observationnelles scénario: combustion explosive de l´H et “thermonuclear runaway”

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Nucléosynthèse dans les novae

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  1. Nucléosynthèse dans les novae Margarita Hernanz Institut d’Estudis Espacials de Catalunya, IEEC-CSIC, Barcelona • Modèles de novae classiques: • introduction; principales propriétés observationnelles • scénario: combustion explosive de l´H et “thermonuclear runaway” • modèles de novae; incertitudes • nucléosynthèse génerale • Modèles d’emission : • nucleosynthèse noyaux radioactifs • spectres et courbes de lumière • revue des observations • prespectives futures de détection avec INTEGRAL et d’autres instruments

  2. Observation d’une nova Nova Cygni 1975

  3. Observations avec le Telescope Spatial Hubble (HST) Nova Cygni 1992

  4. Qu’est-ce que sait une nova? Une explosion d’une naine blanche dans un système stellaire double

  5. Observation des novae: courbe de lumière optique Luminosité temps

  6. Observation des novae: courbe de lumière optique Luminosité temps La luminosité augmente par des facteurs 104

  7. Observation des novae: courbe de lumière optique: relation luminosité maximum-taux tombée luminosité t2  L/10 t2=10 jours: nova rapide t2=250 jours: nova très lente Determination de distances Luminosité temps tombée L 20j 200j

  8. Observation des novae: courbes de lumière Satellite IUE (UV): Lbol(LV+LUV)=ct. FH Ser 1970 Lbol(LV+LUV+ LIR) =ct. Nova Cyg 1978

  9. Observation des novae: spectres, determination d’abondances Vitesses d’expansion ~ 102-103 km/s Enrichissements en C, N, O, Ne Metallicités >> Solaires

  10. Exemple: détermination d’abondances à partir d’observations dans l’IR

  11. Distribution des novae dans notre galaxie ~35 novae/an dans notre galaxie (mais seulement 3-5 sont découvertes)

  12. Qu’est-ce que sait une nova? Scénario Transfer de matière de l’étoile compagnone vers la naine blanche (variable cataclismique ) Combustion hydrogène conditions dégénerescence à la surface de la naine blanque “avalanche termique” Combustion explosive H Décroissance noyaux radioactifs de courte vie dans l’enveloppe (transport par convection) Expansion enveloppe, augmentation L et expulsionmatière

  13. Modèles de nova: Combustion termonucléaire de l’Hydrogène • Echelles de temps plus relevantes • accrétion~ Macc/M ~ 104 - 105 yr • nucléaire~ CpT/nuc ; au max. nuc: abondances solaires 1-10s; abondances >sol. <<1s • dynamique~ Hp/cs ~ (1/g)(P/)1/2 ; quand P et  maximum: ~ 1s • Phases évolutives plus importantes • Accrétion: accrétion < nucléaire : accumulation matière P critique (T<TFermi degener.) • TNR (avalanche termique): dégénérescence empêche exp. enveloppe • MAIS: T T> TFermi (~108K per MNB =1M) • CNO solaire: nuc~ dyn ; CNO >sol.: nuc<< dyn T & nuc avant expan.

  14. Modèles de nova: combustion termonu-cléaire de l’Hydrogène. Cycle CNO 18Ne 18F 17F 19F 14O 15O 16O 17O 18O 13N 14N 15N (p,) AX (p,) 12C 13C (+) • Au début: +< (p,) • Cycle CNO “opère” en equ. • T ~108 K: +> (p,) • Cycle CNO +-limité • (goulot de bouteille) • Convection: • incorporation matière “fraîche” à la couche de combustion • conv < +: transport noyaux +-instables aux régions externes froides où ils ne sont pas détruits Sa décroissance postérieure à la surface provoque l’expansion et l’augmentation de luminosité ~ 93s 158min 102s 176s 862s

  15. Modèles de novae: nécessité de mélange coeur-enveloppe • Z observée >> solaire mélange CO ou ONe - enveloppe solaire accretée • Explosion elle-même surabondance initiale de CNO mélange Many classical nova ejectaare enriched in CNOand Ne. Rosner andcoworkers recently suggested thatthe enrichment might originatein the resonant interactionbetween large-scale shear flowsin the accreted H/Heenvelope and gravity wavesat the interface betweenthe envelope and theunderlying C/O white dwarf(WD).The shear flowamplifies the waves, whicheventually form cusps andbreak. This wave breakinginjects a spray ofC/O into the superincumbentH/He. In the absence ofenrichment prior to ignition,the base of theconvective zone, does not reach theC/O interface. As aresult, there is noadditional mixing, and therunaway is slow. Incontrast, the formation ofa mixed layer duringthe accretion of H/He,prior to ignition, causesa more violent runaway.The envelope can beenriched by  25% ofC/O by mass (consistentwith that observed insome ejecta) for shearvelocities, over the surface,with Mach numbers  0.4. Alexakis et al., 2004, ApJ

  16. Modèles de novae: calcul théorique HYDRODYNAMICAL CODE Lagrangian, one-dimensional, implicit Convection included Hydrostatic accretion phase also modelled Profiles of r, T, v ... along the envelope for each time & Detailed nucleosynthesis, including radioactive nuclei

  17. Modèles de novae: proprietés générales

  18. Modèles de novae: reactions nucléaires importantes

  19. Nucleosynthèse dans les novae et evolution chimique de la Galaxie Mejec(theor.) ~ 2x10-5 M/nova R(novae) ~ 35 novae/an Age Galaxie ~ 1010 années Mejec,total(novae) ~ 7x106 M = (7x10-4 M/an)  1/3000 Mgal(gaz+pous.) Novae peuvent être responsables des abondances galactiques des isotopes surproduits (par rap. Sol.) par des facteurs  3000

  20. Nucleosynthèse dans les novae: surproductions vs. solaires

  21. Nucleosynthèse dans les novae: surproductions vs. solaires

  22. Nucleosynthèse dans les novae: surproductions vs. solaires ONe 1.35M

  23. Other signatures of radioactivities in novae: presolar grains Amari et al. 2001, ApJ five SiC and one graphite grain from the Murchison meteorite show isotopic compositions indicating a nova origin

  24. Other signatures of radioactivities in novae: presolar grains

  25. Other signatures of radioactivities in novae: presolar grains

  26. Why novae emit gamma-rays? Explosive H-burning: synthesis of b+-unstable nuclei 13N 14O 15O 17F 18F t 862s 102s 176s 93s 158min. crucial for enve- lope expansion crucial for g-ray emission (through e--e+ annihilation) 7Be 22Na 26Al Other radioactive nuclei synthesized t 77days 3.75yrs 106yrs line 478keV 1275keV 1809keV e-capture e+-emission

  27. Main radioactive isotopes synthesized in classical novae

  28. Radioactivities in novae ejecta: some examples * 1 h after Tpeak Rates for 18F+p reactions from Utku et al. (1998)

  29. Modèles de novae: calcul théorique des spectres  Monte Carlo code for -ray production and transport (Ambwani & Sutherland 1988) Emission mechanisms: • Positron annihilation • e+ - e- (10 %) two 511 keV photons (90 %) positronium formation two 511 keV gs three <511 keV gs (25 %) (75 %) Positron-unstable nuclei included: 13N t = 862 s 18F t = 158 min 22Na t = 3.75 yrs

  30. Modèles de novae: calcul théorique des spectres  Emission mechanisms (cont.) • Nuclear decay 478 keV (t = 77 days) 7B (b-) 7Li 1275 keV (t = 3.75 yrs) 22Na (b+) 22Ne • Inverse Compton scattering Absorption mechanisms: • Photo-electric absorption (E < 100 keV) • e- - e+ production (E > 1022 keV) • Compton scattering (100 keV<E<5 MeV)

  31. Spectra of CO novae MWD = 1.15 M¤ • e+ annihilation and Comptonization • continuum and 511 keV line; e+ from 13N and 18F • predicted theoretically by Clayton & Hoyle 1974; Leising & Clayton 1987 • photoelectric absorption cutoff at 20 keV • 478 keV line from 7Be decay • transparent at 48 h d=1 kpc Gómez-Gomar, Hernanz, José, Isern,1998, MNRAS

  32. Spectra of CO novae MWD = 0.8 M¤ d=1 kpc • lower fluxes • longer duration: at 48 h there is still continuum and 511 keV line emission • larger opacities of the expanding shells than in 1.15 M¤ Gómez-Gomar, Hernanz, José, Isern,1998, MNRAS

  33. Spectra of ONe novae MWD = 1.15M¤(solid) 1.25M¤(dotted) d=1 kpc • photoelectric absorption cutoff at 30 keV • continuum and 511 keV as in CO novae • 1275 keV line from 22Na decay • similar behaviour for the 2 models, because of similar KE and yields Gómez-Gomar, Hernanz, José, Isern,1998, MNRAS

  34. Light curves: 478 keV (7Be) line Only in CO novae tmax: 13 days (0.8M) 5 days (1.15 M) duration: some weeks Flux  (1-2)x10-6 ph/cm2/s d=1 kpc

  35. Observations: 478 keV line (7Be) TGRS SMM Harris et al. 1991 and 2001 Theory: F<2.5x10-6/dkpc2 predicted theoretically by Clayton 1981

  36. Radioactivities in novae ejecta: some examples * 1 h after Tpeak Rates for 18F+p reactions from Utku et al. (1998)

  37. Light curves: 1275 keV (22Na) line Only in ONe novae Exponential decline Rise phase d=1 kpc tmax: 20 days (1.15M), 12 days (1.25 M) duration: some months Flux  2x10-5 ph/cm2/s

  38. Observations: 1275 keV line (22Na) CGRO/COMPTEL: no detection; upper limits Iyudin et al. 1995, A&A predicted theoretically by Clayton & Hoyle, 1974

  39. Observations : 1275 keV line (22Na) Upper limits in agreement with current theoretical predictions Iyudin et al. 1995, A&A

  40. Light curves: 511 keV line In CO and ONe novae • 511 keV line in ONe novae remains after 2 days until  1 week because of e+ from 22Na • Very early appearence, before visual maximum (i.e, before discovery) d=1 kpc

  41. The continuum and the 511 keV line,e--e+ annihilation, are the most intense emissions, but their duration is very short and they appear before visual discovery • detection requires “a posteriori” analyses with wide FOV instruments (BATSE, TGRS, RHESSI) • future hard X/soft -ray surveys like EXIST can provide unique information about the Galactic nova distribution

  42. Gamma-ray and visual light curves Visual maximum laterthan 511 keV and continuum maxima

  43. Observations of the 511 keV line WIND/TGRS:no detection; upper limits • Observation of 5 known Galactic novae in the broad TGRS FOV in the period 1995 Jan - 1997 June • High E-resolution Ge detector: ability to detect 511 keV line blueshifted w.r.t. background line Harris et al. 1999, ApJ

  44. Line profiles: 511 keV line CO nova MWD = 1.15M d=1 kpc The line is blueshifted, until the envelope reaches transparency: 518 keV (1h) 512 keV (24h) FWHM (12h)= 7 keV

  45. Observations of the 511 keV line WIND/TGRS: “constraining” the Galactic nova rate from a survey of the Southern Sky during 1995-1997 From the non detection, an upper limit of the Galactic nova rate was extracted: < 123 yr-1(CO novae; rdetect.: 0.9 kpc ) < 238 yr-1(ONe novae; rdetect.: 0.7 kpc ) Promising for future wide FOV instruments sensitive in the soft -ray range (20-511) keV Harris et al. 2000, ApJ

  46. Observations: 511 keV line CGRO/BATSE List of nearby novae (d < 3-4 kpc) since CGRO launch Refs.: IAU circulars and Shafter 1997, Ap. J. 487, 226 Other candidate novae: Cru96, Sco97, Sgr98, Oph98, Sco98, Mus98 Hernanz, Smith, Fishman, et al., 2000, Proc. 5th CGRO Symp.

  47. Light curves: 511 keV line and continuum ONe Nova, 1.15 M CO Nova, 1.15 M d=1 kpc

  48. Summary of BATSE observations: 3- upper limits to the fluxes (ph/cm2/s) Nova Cyg 1992(model: 1.25M¤ ONe nova at d=1.7 kpc) Nova Sco 1992 (model: 1.15M¤ CO nova at d=0.8 kpc) Nova Vel 1999 (model: 1.25 M¤ ONe nova at d=2 kpc) * using 250-511 keV data with assumed Comptonization; ** using 511 keV data only

  49. Light curves: 511 keV line. Influence of Mejected F when Mej F when Mej d=1 kpc e+: 13N and 18F e+: 13N, 18F and 22Na

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