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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 • 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
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
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
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 ??)
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
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
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
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
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
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
CO survey of the Milky Way 115 GHz Dame et al. 2001
COBE/DIRBE dust maps COBE: Cosmic Background Explorer (1989) DIRBE: Diffuse Infrared Background Experiment
COBE/DMR maps DMR: Differential Microwave Radiometer 53 GHz; 4 year sky maps (1GHz: 3 cm)
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
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
Possible sites of 26Al production Massive stars contribution Knödlseder, 1999, ApJ not definitive numbers!
Possible sites of 26Al production Mowlavi, 1999 not definitive numbers! General agreement: around 10% contribution of NON-massive stars is plausible
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
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)
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
Possible sites of 26Al production Lattanzio Schematic structure of an AGB during the thermally pulsing phase
Possible sites of 26Al production Mowlavi & Meynet
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)