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SUPERNOVAE (Thermonuclear supernovae)

SUPERNOVAE (Thermonuclear supernovae). SN 1994d HST. J. Isern Institut de Ciències de l’Espai IEEC - CSIC. SN 1998dh. SN 1998aq. SN 1998bu. Type Ia supernovae are the biggest thermonuclear explosions in the universe. For several weeks their luminosity rivals that of a large galaxy.

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SUPERNOVAE (Thermonuclear supernovae)

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  1. SUPERNOVAE (Thermonuclear supernovae) SN 1994d HST J. Isern Institut de Ciències de l’Espai IEEC - CSIC

  2. SN 1998dh SN 1998aq SN 1998bu Type Ia supernovae are the biggest thermonuclear explosions in the universe. For several weeks their luminosity rivals that of a large galaxy. HST SN 1994D

  3. Observational constraints. I • H must be absent at the moment of the explosion • There are some evidences (weak) of H-lines before maximum or at late epochs • Progenitors should be long lived to account for their presence in all galaxies, including ellipticals • The explosion should produce at least ~ 0.3 M0 of 56Ni to account for the light curve and late time spectra • The short risetime indicates that the exploding star is a compact object SNIa are caused by the explosion of a C/O white dwarf in binary systems (He white dwarfs detonate and are converted in Fe and ONe collapse to a neutron star)

  4. # As the supernova expands, the atmosphere becomes more and more transparent. # The different layers become exposed as the time goes on # This allows to study the structure as a function of time

  5. Spectrum at maximum light • Peak: absorption • CII OI SiII • SI CaII MgII • Incomplete burning 10000  15000 km/s Near-IR: SiII CaII MgII Fe peak Hatano et al. 1999

  6. Nebular spectra • Late time: emission • Fe Co • Complete burning < 10000 km/s Hatano et al. 1999

  7. B.Aschenbach, 2002, astro-ph/0208492 Tycho Remnant (SN 1572) XMM-Newton

  8. Big Bang Stars Supernovae Supernovae

  9. Solar system abundances SNII BBN SNII SNII ? AGB SNIa BBN AGB Anders & Grevesse 1989 Cameron 1982 (Arnett 1996)

  10. Observational constraints. II • Intermediate elements must be present in the outer layers to account for the spectrum at maximum light • The burning must be subsonic. It can be supersonic only if ρ < 107 g/cm3 The abundances of the iron peak elements (54Fe, 58Ni, 54Cr) must be compatible with the Solar System abundances after mixing with gravitational supernova products • Neutron excesses have to be avoided: • Post-burning e- -captures • Neutrons stored as 22Ne • Decrease ignition density • Decrease 22Ne content • Reduce the SNIa galactic contribution

  11. Thermonuclear runaways The necessary condition is that the energy must be released in a time shorter than the dynamical time Nuclear heating time: The hydrodynamical time: In hydrostatic equilibrium The instability condition is: Deflagration temperature

  12. Why typical stars are stable?: They stabilize the fuel by means of adiabatic expansions The efficiency of the adiabatic cooling is defined as the expansion, δρ, experienced to restore pressure equilibrium Where ΔX is the amount of burned fuel If the electronic degenerate component is dominant: In the gas ideal case: Since Q ~ 1 MeV and kT ~ 1-100 keV adiabatic cooling is very efficient and stars are stable Cooling is only efficient if Thermonuclear runaways occur if: Tdef < TF H is not a good explosive because it needs weak interactions to convert p in n (novae) He and C are good explosives (supernovae)

  13. The burning front Δ << l Burned Unburned Mass, momentum and energy conservation l (ρ,ε)0 (ρ,ε)1 Δ Two types of solutions Detonation: vfront supersonic versus the unburned material sonic or subsonic versus the burned material Deflagration: vfront always subsonic versus the unburned & burned material

  14. Deflagrations In spherical symmetry burned material is at rest at the center, v1 = 0 Assume unburned material at rest, v0 = 0 Mass and momentum conservation demands: V0 (P1 - P0) = u0 (u0 - u1) or V0 (P1 - P0) = u1 D in the frame at rest But if P1 - P0 < 0 & D > 0 then v1 < 0 in contradiction with the hypothesis A deflagration can only exist if it generates a shock precursor that burst matter outwards!

  15. Spectral and photometric homogeneity The B-light curve of 22 SNIA, showing the similarity among them (Cadonau 1987)

  16. Similitude of the spectra near the maximum light (Fillipenko)

  17. Type Ia The spectral homogeneity Is maintained over the time

  18. SN Ia Differences Light Curve Shape Relationships SN Ia are not all the same. Variations occur in their light curves and spectra. The following observations show the entire range in SN Ia brightness.

  19. Phillips (1993; ApJ 413, L105)

  20. SN Ia Explosion Energies Not all SNe Ia have the same KE Range from 6,000 – 25,000 km/s at photosphere Vast majority ~ 10,000 km/s

  21. Observational constraints. III • Homogeneity? • Differences in brightness: Overluminous (SN 1991T), underluminous (SN1991bg) • Differences in the expansion velocity (vexp ~ 10,000-15,000 km/s) • Two points of view: • There is a bulk of homogeneous supernovae plus some peculiars • SNIa display a continuous range of values • Is there a unique scenario & unique mechanism able to accommodate the normal behavior plus that of dissidents? • Is there a mechanism able to produce a continuous range of situations? • Can both mechanisms coexist? Anything able to explode eventually do it !!!

  22. Bolometric light curves • provide global parameters • size • nickel mass • ejecta mass • explosion energy • (distances) • indicate the total energy output/conversion from -rays

  23. UBVRIJHK Light Curves of a Typical SN Ia Primary maximum Secondary maximum Sources: UBVRI: Suntzeff et al. (1999) JHK: Mayya et al. (1998) Jha et al. (1999) Hernandez et al. (2000)

  24. The light curves of SN 1994D Vacca & Leibundgut 1996

  25. Accreting White Dwarfs The outcome depends on: Accretion rate Chemical composition of accreted matter Initial mass of the white dwarf As the WD accretes matter it contracts and heats up M ~ R-1/3 the thermonuclear runaway occurs

  26. The merging process The less massive star transfers mass to the most massive As R2 increases when M2 decreases, transfer accelerates Conservative transfer Since dM1 > 0, da >0 and the separation increases • There is a critical value Mc ~ 0.3 - 0.4 Mo • If M2 > Mc dynamic merging • If M2 < Mc self regulated merging

  27. Coalescence of two white dwarfs There are several double degenerate binary systems able to merge in a time shorter than the Hubble time. Which are the observational consequences? • Type Ia supernovae? • Accretion induced collapse? • Peculiar WD? • Gravitational wave emission?

  28. Chirping binaries From LIGO pages

  29. 3D temperature evolution Case: 0.6+0.8 Mo

  30. 0.6+0.8 case Density profiles of the disk 1000 g/cm3 Z (10-1 Ro) 1 0 R (10-1 Ro)

  31. 0.6+0.8 case Evolution of the tangential velocity respect to the center of masses The critical point is the intrinsic viscosity of the SPH methods

  32. He-accreting white dwarfs(merging of white dwarfs, CO WD + Helium star) • If 5x10-8 Mo/y  dMH/dt  10-9 Mo/yr. And MWD < 1.13 Mo an off center detonation forms

  33. Exploding mechanisms: Off center ignition detonation Shock wave MHe ~ 0.2 - 0.3 M0 MCO ~ 0.5 - 1.1 M0

  34. Off center detonations (E. Bravo et al IEEC/UPC)

  35. H-accreting white dwarfs(cataclysmic variables, symbiotic stars, supersoft X-ray sources) • dMH/dt < 10-9 Mo/yr.Nova explosions. Novae reduce the mass or produce a very inefficient increase of the total mass, except if MWD 1.2 Mo, but they are made of ONe • 10-6 Mo/y > dMH/dt > 10-9 Mo/yr. Hydrogen burns in X-ray flasshes, but produces He at a rate that can ignite under degenerate conditions. • MEdd > dMH/dt > 10-6 Mo/yr. Formation of a red giant Contamination by H? Where is the surviving star?

  36. The Eddington limit

  37. Neutrino Losses * Itoh et al 1996, ApJS,102, 411, see also Beaudet, Petrosian, & Salpeter 1967, ApJ, 147, 122

  38. Convection for 100 years, then formation of a thin flame sheet. Note that at: 7 x 108 K the burning time and convection time become equal. Can’t maintain adiabatic gradient anymore 1.1 x 109 K, burning goes faster than sound could go a pressure scale height Burning becomes localized T 0 radius

  39. Fuel Diffusion Burning Ash Temperature • This is the conductive • or sometimes “laminar” • flame speed. l

  40. Laminar Flame Speed km/s nb. these speeds are slower than the convective speeds prior to runaway cm Timmes and Woosley, (1992), ApJ,396, 649

  41. Heat Capacity Nuclear burning to the iron group gives qnuc = 7 x 1017 erg/gm “ “ “ silicon group “ “ 5 x 1017 erg/gm Above about 107 gm cm-3 burning will go to nuclear statistical equilibrium and make only iron group elements

  42. Exploding mechsanisms Detonation: supersonic flame If ρ > 107 g/cc  C,O  Ni If ρ 107 g/cc  C,O  Si,Ca, S, ... Other possibilities: Deflagration + detonation Pulsating delayed detonation The laminar flame becomes turbulent: * Rayleigh-Taylor instability * Kelvin- Helmholtz Deflagration: subsonic velocity laminar flame: v ~ 0.01 cs Turbulent flame: v ~ 0.1 - 0.3 cs Flame surface increases efective velocity increases

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