1 / 60

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”

shawna
Download Presentation

Nucléosynthèse dans les novae

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related