Three Challenges

Rosanne Di Stefano, 27 September 2013

ThreeChallengesto standard assumptions

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ThreeOpportunities

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A new way to discover progenitors in the Galaxy.

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Spin-up/spin-down changes our perspective.

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Spin-up/spin-down changes our perspective.

Extensive data-based investigations helps model input for population synthesis simulations.

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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.

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Rosanne Di Stefano, 27 September 2013 Di Stefano 2011

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Rosanne Di Stefano, 27 September 20139/27/13

Rosanne Di Stefano, 27 September 20139/27/13


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.

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Angular Momentum Is Important

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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.

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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



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.

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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.

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Spin-Up/Spin-Down

Mass transfer needs to slow down or stop on order for the WD to spin down.

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Spin-Up/Spin-Down

The explosion occurs when the spin-down has decreased the mass of the WD to its current value.

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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.)

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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.

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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.

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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.

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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.

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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 theOGLE 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

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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).9/27/13


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 = M2/M1 with increasing P.9/27/13


Using detailed light curve models and Monte Carlo simulations, we fit the intrinsic mass-ratio distribution fq as a function of P.We find the power-law slope infq =qγ 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).

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Most binary population synthesis studies assume a uniform fq = 1 for all M1 and P, and fP = 0.1 companions per primary per decade of orbital period.

Observations give fq = q-2.3 and fP = 0.2 for M1 = (5-20)M at intermediate P.

Single degenerate (SD) SN Ia with late delay times derive from subgiant/giant donors at intermediate periods with M2 = 1M (so that τ2 = 10 Gyr) and massive WD MWD = 1.1M (M1 = 7M) considering accretion is inefficient.

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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!

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×200

Simulated SD SN Ia (Meng & Yang 2010)

vs. observed SN Ia DTD(Totani et al. 2008)

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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.

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Three Challenges