Systematic Effects on the Brightness of Type Ia Supernovae

Transcription

1 Systematic Effects on the Brightness of Type Ia Supernovae Alan Calder D. Willcox, A. Jackson, B. Krueger (Stony Brook) D. Townsley, B. Miles (Alabama), E. Brown (MSU), F. Timmes (ASU) P. Denissenkov, F. Herwig (U. Victoria) 18 th Workshop on Nuclear Astrophysics, Ringberg Castle March 17,

2 Single Degenerate M Chandra Scenario Mass accretes from a companion onto a white dwarf that then ignites thermonuclear burning. Nature of the burn is a fundamental problem. Deflagration? Detonation? Can models reproduce observed nuclear abundances and light curves? Can models go a step further and capture systematic effects on the brightness of events? 21

3 Observation compared with W7 model 22 Mazzali et al. (2008)

4 Flame Model Implemented in Flash ADR scheme propagates a model flame. Flame speeds from tables, include effects of RTI and TFI. Set of variables captures consumption of C, evolution to Si-group, relaxation to NSE, Weak reactions included. Implemented in Flash (and recently CASTRO) Packages available on Dean Townsley s Homepage,

5 Role of Neutron Enrichment Simplest model of burning is an alpha chain 12 C 56 Ni (NSE: α + 56 Ni) Including neutron-rich metals and weak reactions, burning proceeds to more neutron-rich ash of stable nuclei lower 56 Ni yield. C fusion is rapid, ~ 1 s to burn the star. Depending on density, electron captures may or may not have time to adjust the fraction of neutrons (Y e ). Investigate the role of neutron-rich material on models using 22 Ne as a proxy for metals. initial composition dynamics of burning boosted flame speed decreased deflagration to detonation transition density. 45

6 Fluid Instability in a Type Ia Supernova Fluid dynamics are very important. The simmering progenitor and Rayleigh-Taylor instabilities (RTI) generate turbulence, which boosts burning rate. RTI perturbs the flame front on large and small scales. Note- multi-dimensional event stresses the need for 3-d models. 46

7 Deflagration Models: Incomplete Burning Khokhlov (2001) Energy of explosion is too small Significant mass of unburned C+O No composition stratification: complete mixing of Ni, Si, C+O throughout the star 48

8 3-D Delayed Detonation Model Average chemical composition as function of radius Ni C/O Mg Si 3-D pure deflagration Ni Si C/O 3-D deflagration followed by detonation Ignited by hand at the center of the pre-expanded star. Mg Gamezo et al. (2003) Resulting stratified compositions are in better agreement with observations! Classic delayed detonation scenario. 49

9 DDT mechanism The mechanism by which a deflagration to detonation transition (DDT) might occur is not well understood. One proposed way follows from the wrinkling of the flame with decreasing density. At some point, the net burning rate is fast enough that the equivalent flame would be supersonic DDT! 1.5 x 10 7 g/cm x 10 7 g/cm x 10 6 g/cm 3 fuel Carbon mass fraction ash M. Zingale 51

10 Simulations in the DDT paradigm Jackson, et al. (2010) 54

11 Simulations in the DDT paradigm Jackson, et al. (2010) 55

12 DDT Density Study Jackson et al. (2010) 62

13 Metallicity Results Jackson et al. (2010) 64

14 Central Density Study Krueger et al. (2010) 66

15 wikipedia 67

16 Trend confronted with observations. Krueger et al. (2012) 70

17 Central Density Study Krueger et al. (2010) 71

18 Current Work Hybrid progenitors Currently studying more advanced hybrid progenitors that more naturally approach the Chandrasekhar limit (Denissenkov et al. 2013, 2015). Improved the flame model to include 20 Ne produced by partial C fusion. 72 Denissenkov et al. 2013

19 Hybrid Progenitor Willcox et al. (2016) 73

20 Hybrid Progenitors Willcox et al. (2016) 76

21 Hybrid Progenitors Willcox et al. (2016) 77

22 Hybrid Progenitors Ignition configuration Willcox et al. (2016) 78

23 Hybrid Progenitors Willcox et al. (2016) 79

24 Hybrid Progenitors Willcox et al. (2016) 80

25 Hybrid Progenitors Willcox et al. (2016) 81

26 Hybrid Progenitors Central region shows delayed burning. Willcox et al. (2016) 82

27 Hybrid Progenitors Willcox et al. (2016) 87

28 Hybrid Progenitors Willcox et al. (2016) 88

29 Conclusions By considering the DDT density, we find the change in 56 Ni yield with metallicity to be a decrease 0.09 M_sol for a 1 Z_sol increase. We find a significant dependence of 56 Ni yield on progenitor central density, a systematic effect on the brightness. Considering prior evolution of the progenitor white dwarf, this result suggests a cooling time/age dependence. Such a relationship is consistent with observations. Hybrid progenitors produce less 56 Ni, implying a slightly dimmer Ia events than C/O models. But see considerable scatter. Ejecta from hybrid progenitors consistently more weakly expelled. 93

30 and that leads us to QUESTIONS AND DISCUSSION 94

31 Bibliography Fryxell, et al. ApJS 131, 273 (2000) [Flash Code] Calder, et al. ApJ 635, 313 (2007) Seitenzahl, et al. ADNDT, 95, 96 (2009) Townsley, et al. ApJ 688, 1118 (2007) Townsley, et al. ApJ 701, 1582 (2009) Krueger et al. ApJ 719, L5 (2010) Jackson, et al. ApJ 720, 99 (2010) Krueger, et al. ApJ 757, 175 (2012) Willcox, et al. ApJ, submitted, arxiv: