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 (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)1
αCE=1
Dependence on CE description (for n(q)=1)
αCE(M2)2
Model A
αCE=1
WD
mass
1.11.4 Msun
proper 
total energy
IK Peg
AM budget
Dependence on IMF of M2 (WD mass 0.4 - 0.5 Msun)
Summary of features
Observed post-CE sample falls in populated regions
Outliers 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
A PDF for
reconstructed
CE values
0137-3457
Reconstructing
pre-CE
parameters
Red:
Young PCEBs
Blue:
M2<0.35Msun
Gravitational waves
only
Green:
M2>0.35Msun
Magnetic braking
SDSS CVs
Minimum period problem
For standard MB/GR
evolutionary tracks converge
to universal track
Period bounce spikes add up
1
N ( P) 
P
Barker & Kolb 2003
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 (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