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HIGH ENERGY ASTROPHYSICS -ray emission from galactic radioactivity

HIGH ENERGY ASTROPHYSICS -ray emission from galactic radioactivity. Relevant radioactive nuclei for galactic -ray line emission : how and where they are synthesized: nucleosynthesis (hydrostatic and explosive), in stars interaction with cosmic rays, in the interstellar medium

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HIGH ENERGY ASTROPHYSICS -ray emission from galactic radioactivity

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  1. HIGH ENERGY ASTROPHYSICS-ray emission from galactic radioactivity • Relevant radioactive nuclei for galactic -ray line emission: • how and where they are synthesized: • nucleosynthesis (hydrostatic and explosive), in stars • interaction with cosmic rays, in the interstellar medium • Electron-positron annihilation emission (line and continuum): • e+ from +- unstable nuclei • BUT other sources of e+ ( radioactivity) exist • Type of emission: point-source or diffuse

  2. 1.8 MeV line of 26Al • Already seen: historical (flux and width of the line) • General comments on the map, regions of enhanced emission • Different maps depending on type of analysis • Correlations with all-sky maps at other energies • Sites of 26Al production

  3. COMPTEL map of the 1.8 MeV line of 26Al • Regions of enhanced emission: • central galaxy • Cygnus (star formation region) • Carina (spiral arm) • Vela (star formation region) Complete CGRO mission (9 years) – Plüschke et al. 2001 Inner Galaxy Carina Vela Cygnus

  4. COMPTEL map of the 1.8 MeV line of 26Al • COMPTEL map allows to discard • unique central source • important contribution from the bulge (related with old stars population) • class of objects involving a large number of sites with low individual yield (smooth distribution expected  observed) Prantzos & Diehl, 1996 COMPTEL map clearly indicates: irregular asymmetric emission, with some hot spots related to spiral arms, or to star forming regions (Cygnus), or to regions with particular sources (Vela: SNR, close WR star 2 Vel ??)

  5. COMPTEL map of the 1.8 MeV line of 26Al Extended emission Contributions from point sources: Vela SNR 2 Vel (WR; but less than expected) Signs of nucleosynthesis activity COMPTEL team, Diehl 2000

  6. COMPTEL map of the 1.8 MeV line of 26Al Knödlseder et al. 2002: census of candidate sources: OB associations, WR stars, supernova remnants… Knödlseder et al. 2004: INTEGRAL observations COMPTEL team, Diehl 2000

  7. 1.8 MeV line of 26Al • Already seen: historical (flux and width of the line) • General comments on the map, regions of enhanced emission • Different maps depending on type of analysis • Correlations with all-sky maps at other energies • Sites of 26Al production

  8. 1.8 MeV line of 26Al • Different methods of image reconstruction lead to different maps: • maximum entropy • multiresolution • maximum likelihood Knödlseder, 1997, Oberlack,1997, Plüschke, 2001

  9. 1.8 MeV line of 26Al • Already seen: historical (flux and width of the line) • General comments on the map, regions of enhanced emission • Different maps depending on type of analysis • Correlations with all-sky maps at other energies • Sites of 26Al production

  10. 1.8 MeV line of 26Al Search for correlation with all-sky maps at other wavelengths Knödlseder, 1999: best correlation with radio map tracing ionised gas (free electrons) Diehl, 2000

  11. CO survey of the Milky Way 115 GHz Dame et al. 2001

  12. COBE/DIRBE dust maps COBE: Cosmic Background Explorer (1989) DIRBE: Diffuse Infrared Background Experiment

  13. COBE/DIRBE starlight maps

  14. COBE/DMR maps DMR: Differential Microwave Radiometer 53 GHz; 4 year sky maps (1GHz: 3 cm)

  15. Knödlseder, 1999, A&A

  16. 1.8 MeV line of 26Al: correlation with e- distribution • Longitude profiles of 1.8 MeV line (combination of WR stars, SNe II, SNe Ib/c) and free-free emission (distribution of HII regions) • Line of sight integrated 1.8MeV emission and free-free emission correlated • Short recombination timescale of ionized gas • massive stars are the main contributors to galactic 26Al Knödlseder, 1999, ApJ

  17. 1.8 MeV line of 26Al • Already seen: historical (flux and width of the line) • General comments on the map, regions of enhanced emission • Different maps depending on type of analysis • Correlations with all-sky maps at other energies • Sites of 26Al production

  18. Possible sites of 26Al production Massive stars contribution Knödlseder, 1999, ApJ not definitive numbers!

  19. Possible sites of 26Al production Mowlavi, 1999 not definitive numbers! General agreement: around 10% contribution of NON-massive stars is plausible

  20. Possible sites of 26Al production • Core collapse supernovae: see SNe course • Production through 25Mg(p,); destruction via: + decay, (n,p) (n,) (p,) • 26Al yield depends on free nucleon abundances and T • Pre-supernova: H-burning shell • O-Ne burning shells • Explosion: - O-Ne burning shells: 26Al  • - -spallation on (20Ne, 16O, 23Na, 24Mg) liberates p • ==> 25Mg(p,)26Al Diehl, 2000 M=25M

  21. REMINDER

  22. Possible sites of 26Al production • Wolf Rayet stars: bare cores of initially massive stars, which have lost their H envelope by stellar winds (or Roche lobe overflow if in close binaries). Progenitor masses larger than ~30 M¤ • Teff : 25 000-50 000 K; L: 105 to 106 L¤ • Duration of WR phase: few 106 years, typically (very short) • Surface composition is extremely exotic, being dominated by helium rather than hydrogen, and typically showing broad wind emission lines of elements like carbon (WC type), nitrogen (WN type), or oxygen: the products of core nucleosynthesis. • Impact of rotation: formationof WR stars favored, longerdurationof WR star phase,larger surface enrichment of 26Al, larger mass loss  larger contribution of WR stars to galactic 26Al • Impact of metallicity: 26Al yields increase(larger 25Mg and enhanced mass loss)

  23. Possible sites of 26Al production • AGB (asymptotic giant branch) stars: phase through which all stars with M 8-10 M¤ pass, after core He exhaustion Le Grand Atlas de l’Astronomie; Encyclopedia Universalis, 1983

  24. Possible sites of 26Al production Lattanzio Schematic structure of an AGB during the thermally pulsing phase

  25. Possible sites of 26Al production Mowlavi & Meynet

  26. BIBLIOGRAFIA • Prantzos, N., Diehl, R., 1996, Radioactive 26Al in the galaxy: observations versus theory, Physics Reports, 267, 1-69 • Diehl, R., Timmes, FX., 1998, Gamma-ray line emission from radioactive isotopes in stars and galaxies, Publications of the Astronomical Society of the Pacific, 110, 637-659 • Knödlseder, J. et al., 1999, A multiwavelength comparison of COMPTEL 18 MeV26Al line data, Astonomy & Astrophysics, 344, 68-82 • Knödlseder, J., 1999, Implications of 1.8 MeV gamma-ray observations for the origin of 26Al, Astrophysical Journal, 510, 915-929 • Diehl, R. et al., 2003, SPI measurements of Galactic 26Al, Astron. & Astrophys., 411, L451-L455 • Astronomy with Radioactivities, Workshop Proceedings (1999 and successive), WEB page at Max Planck Institut für Extraterrestrische Physik (www.mpe-garching.mpg.de/gamma/science/lines/workshops/radioactivity.htm)

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