CV and pre-CV populations in the SDSS era

Ulrich Kolbwith Phil Davis (OU), Bart Willems (NWU)

Post-common envelope binaries• PCEBs• create full population synthesis models• Davis, Kolb & Willems 2009

What’s new about it?

• cf. Willems & Kolb (2004), Politano & Weiler (2007)

• First proper present-day post-CE population model

• Compare in (Porb M1 M2)-space

• Focus on CE prescription and secondary star IMF

• There is a growing PCEB sample to compare against– here: Ritter & Kolb (2003; RKcat7.10 , 2008), with

2008 SDSS updates

Model assumptions• BiSEPS

• Classical magnetic braking (Mconv < M2 < 1.25 Msun), calibrated

• IMF of M2: same as for M1, or mass ratio correlated n(q) qν (ν=-1,0,1)

• common envelope: energy budget, or AM budget (Nelemans & Tout

2005)

Multi-panel representation of PCEB distribution over M2 - log Porb plane for different MWD

Model A

n(q)1αCE=1

Dependence on CE description (for n(q)=1)

Model AαCE=1

αCE(M2)2 proper

total energy

AM budget

WD mass1.1-1.4 Msun

IK Peg

Dependence on IMF of M2 (WD mass 0.4 - 0.5 Msun)

Summary of featuresObserved post-CE sample falls in populated regionsOutliers are probably not post-CE, except: IK Peg:

– needs αCE=3, i.e. additional energy sources

– description based on AM budget would work, too, but generates overabundance of long-period systems

Models extend to (and peak at) large M2 and long Porb where no systems are observed– May favour n(q) q-1 models– This also gives the lowest space densities (10-5 pc-3)– Selection effects or missing physics?

A selection effect? (with model A, n(q) q-1 )

All PCEBs

M2 < 0.50Msun

M2 < 0.35Msun

Using detection probability by Rebassa-Mansergas et al 2008

Reconstructing pre-CE parameters

0137-3457

A PDF for reconstructedCE values

Reconstructing pre-CE parameters

Red:Young PCEBs

Blue:M2<0.35Msun

Gravitational waves only

Green:M2>0.35Msun

Magnetic braking

SDSS CVs

Barker & Kolb 2003

Minimum period problem

For standard MB/GR evolutionary tracks convergeto universal track

Period bounce spikes add up

PPN

1)(

SDSS CVs (Gänsicke et al 2009)

New SDSS CVsvs model A

Kolb & Baraffe 1999

Conclusions

• All PCEB model populations extend to long periods and large companion masses – these are not seen in the observed sample

• There may be a relation CE (af)

• SDSS period spike too wide for GR only populations• Where is the age cut-off? • Consistent with remnant orbital braking a few times GR

below period gap