CV and pre-CV populations in the SDSS era Ulrich Kolb with 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 (P orb M 1 M 2 )-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 (M conv < M 2 < 1.25 M sun ), calibrated IMF of M 2 : same as for M 1, or mass ratio correlated n(q)  q ν (ν=-1,0,1) common envelope: energy budget, or AM budget (Nelemans & Tout 2005)

Multi-panel representation of PCEB distribution over M 2 - log P orb plane for different M WD

Model A n(q)  1 α CE =1

Dependence on CE description (for n(q)=1) Model A α CE =1 α CE  (M 2 ) 2 proper total energy AM budget WD mass M sun IK Peg

Dependence on IMF of M 2 (WD mass Msun)

Summary of features Observed post-CE sample falls in populated regions Outliers are probably not post-CE, except: ´IK Peg: –needs α CE =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 M 2 and long P orb 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 M 2 < 0.50M sun M 2 < 0.35M sun Using detection probability by Rebassa-Mansergas et al 2008

Reconstructing pre-CE parameters A PDF for reconstructed  CE values

Reconstructing pre-CE parameters Red: Young PCEBs Blue: M 2 <0.35M sun Gravitational waves only Green: M 2 >0.35M sun Magnetic braking

SDSS CVs

Barker & Kolb 2003 Minimum period problem For standard MB/GR evolutionary tracks converge to universal track Period bounce spikes add up

SDSS CVs (Gänsicke et al 2009)

New SDSS CVs vs 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 (a f ) 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