1. Three Challenges to standard assumptions 9/27/13Rosanne Di Stefano, 27 September 2013

2. Three Opportunities 9/27/13Rosanne Di Stefano, 27 September 2013

3.  A new way to discover progenitors in the Galaxy. 9/27/13Rosanne Di Stefano, 27 September 2013

4.  A new way to discover progenitors in the Galaxy.  Spin-up/spin-down changes our perspective. 9/27/13Rosanne Di Stefano, 27 September 2013

5.  A new way to discover progenitors in the Galaxy.  Spin-up/spin-down changes our perspective.  Extensive data-based investigations helps model input for population synthesis simulations. 9/27/13Rosanne Di Stefano, 27 September 2013

6. Searching for the Progenitors  We already look for WDs accreting mass, e.g., in symbiotics.  We already look for very close pairs of WDs, e.g., see contribution from Badenes.  Here’s something new: The WD may lens its companion during the epoch before mass transfer. Rosanne Di Stefano, 27 September 20139/27/13

7. Rosanne Di Stefano, 27 September 2013 Di Stefano 2011 9/27/13

8. Rosanne Di Stefano, 27 September 20139/27/13

9. Rosanne Di Stefano, 27 September 20139/27/13

10.  Kepler can detect transits of its target stars by white dwarfs.  Kepler can detect antitransits when its target stars are crossed by massive enough or distant enough white dwarfs. (Agol 2003, Farmer & Agol 2003, Sahu & Gilliland 2003)  We expect the event rate to be high enough that antitransits will indeed be discovered by Kepler. (Di~Stefano 2011)  Antitransits can be detected from the ground—for both possible progenitors and for their near cousins. This will also work for double white dwarfs.  The combination of transits and antitransits can constrain binary evolution models, including those for progenitors of Type Ia supernovae. Rosanne Di Stefano, 27 September 20139/27/13

11. Angular Momentum Is Important 9/27/13Rosanne Di Stefano, 27 September 2013

12. Spin-Up/Spin-Down  Incoming mass carries angular momentum.  This is not an “exotic” optional effect.  It is relevant to all accretion models and some merger models. 9/27/13Rosanne Di Stefano, 27 September 2013

13. Examples of rotating WDs  RX J0648.0 (13.2 s)  AE Aqr (33.06 s)  WZ Sge (27.87 s)  V842 Cen (56.82 s) 9/27/13 Rosanne Di Stefano, 27 September 2013

14. Spin-Up/Spin-Down  Incoming mass carries angular momentum.  We must consider the consequences to determine their effects. The consequences may be minimal or important. 9/27/13Rosanne Di Stefano, 27 September 2013

15. Spin-Up/Spin-Down  Some WDs spin up to near-critical rotation, increasing the value of the critical mass. Even a modest increase can be important.  Thus, even uniform rotation, which does not allow a large change in the critical mass, can alter time scales and appearances. 9/27/13Rosanne Di Stefano, 27 September 2013

16. Spin-Up/Spin-Down  Mass transfer needs to slow down or stop on order for the WD to spin down. 9/27/13Rosanne Di Stefano, 27 September 2013

17. Spin-Up/Spin-Down  The explosion occurs when the spin-down has decreased the mass of the WD to its current value. 9/27/13Rosanne Di Stefano, 27 September 2013

18. Spin-Up/Spin-Down  The explosion occurs when the spin-down has decreased the mass of the WD to its current value.  (See RD, Voss, and Claeys 2011 for details.) 9/27/13Rosanne Di Stefano, 27 September 2013

19. Spin-Up/Spin-Down Models  If the donor was a main-sequence star when accretion started, then  mass accretion decreases dramatically when the mass ratio reverses.  The result is a CV. 9/27/13Rosanne Di Stefano, 27 September 2013

20. Spin-Up/Spin-Down Models  If the donor was a subgiant or giant when accretion started, then  mass accretion stops when the donor’s  The result is a double WD system. 9/27/13Rosanne Di Stefano, 27 September 2013

21. Spin-Up/Spin-Down provides a new framework 1. The key element is that it can be tested. 2. In fact, the tests can help us to better understand the underlying physics. 3. We need to look for massive, fast-spinning WDs. They may be isolated, have WD companions, or else be in CVs. 4. We need to look for fast-moving low-mass and/or compact objects. 9/27/13Rosanne Di Stefano, 27 September 2013

22. Spin-Up/Spin-Down provides a new framework The widowed donor can be small. (SN 2011fe) The widowed donor can be dim.(SNR 0509-67.5; RD & Kilic 2011) The Kepler SNR is a potentially interesting test case. 9/27/13Rosanne Di Stefano, 27 September 2013

23. What Eclipsing Binaries Tell Us About Binary Formation and Evolution Maxwell Moe & Rosanne Di Stefano (Harvard-Smithsonian Center for Astrophysics) Example 1 : Unprecedentedly large samples of O and B- type eclipsing binaries in the OGLE MC catalogs. E.g., 2,327 MS systems with eclipse depths ΔI = 0.10-0.65 mag and orbital periods P = 2 – 200 days in the OGLE-III LMC eclipsing binary catalog (Graczyk et al. 2011). OGLE-III LMC 9/27/13Rosanne Di Stefano, 27 September 2013

24. What Eclipsing Binaries Tell Us About Binary Formation and Evolution Observed eclipse depth and period distributions are similar among the MW, LMC, and SMC, indicating the intrinsic close binary fractions, period distributions, and mass-ratio distributions do not vary with metallicity or environment (Moe & Di Stefano 2013). 9/27/13Rosanne Di Stefano, 27 September 2013

25. The eclipse depth distribution becomes weighted toward shallower eclipses with increasing orbital period at the 5.5σ confidence level. Indicates the mass-ratio distribution becomes weighted toward lower q = M 2 /M 1 with increasing P. 9/27/13Rosanne Di Stefano, 27 September 2013

26. Using detailed light curve models and Monte Carlo simulations, we fit the intrinsic mass-ratio distribution f q as a function of P. We find the power-law slope in f q =q γ dq rapidly approaches random pairings of the IMF (γ = -2.3) for P > 10 days and that the excess twin fraction with q > 0.9 is negligible for P > 5 days (consistent with results from spectroscopic binary observations by Abt et al. 1990). 9/27/13Rosanne Di Stefano, 27 September 2013

27. Most binary population synthesis studies assume a uniform f q = 1 for all M 1 and P, and f P = 0.1 companions per primary per decade of orbital period. Observations give f q = q -2.3 and f P = 0.2 for M 1 = (5-20)M  at intermediate P. Single degenerate (SD) SN Ia with late delay times derive from subgiant/giant donors at intermediate periods with M 2 = 1M  (so that τ 2 = 10 Gyr) and massive WD M WD = 1.1M  (M 1 = 7M  ) considering accretion is inefficient. 9/27/13Rosanne Di Stefano, 27 September 2013

28. Relative increase in late SD is: 2(1M  /7M  ) -2.3 = 200, consistent with observations! Low-mass X-ray binaries, which also derive from low-q progenitors, expected to increase by an order of magnitude, consistent with observations (Kiel & Hurley 2006). Increase in SD SN Ia and LMXB at the EXPENSE of DD SN Ia and HMXB! 9/27/13Rosanne Di Stefano, 27 September 2013

29. ×200 Simulated SD SN Ia (Meng & Yang 2010) vs. observed SN Ia DTD (Totani et al. 2008) 9/27/13Rosanne Di Stefano, 27 September 2013

30.  Antitransits may provide a new way to discover progenitors.  Spin-up/spin-down *must* be included. It changes things—esp. the *aftermath*.  Extensive data-based investigations may change the results of population synthesis studies, including the delay time distribution. 9/27/13Rosanne Di Stefano, 27 September 2013