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CV and pre-CV populations in the SDSS era

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)

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CV and pre-CV populations in the SDSS era

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  1. CV and pre-CV populations in the SDSS era Ulrich Kolb with Phil Davis (OU), Bart Willems (NWU)

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

  3. 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

  4. 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)

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

  6. Model A n(q)1 αCE=1

  7. Dependence on CE description (for n(q)=1) Model A αCE=1 αCE(M2)2 proper  total energy WD mass 1.1- 1.4 Msun IK Peg AM budget

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

  9. 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?

  10. 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

  11. Reconstructing pre-CE parameters A PDF for reconstructed CE values 0137-3457

  12. Reconstructing pre-CE parameters Red: Young PCEBs Blue: M2<0.35Msun Gravitational waves only Green: M2>0.35Msun Magnetic braking

  13. SDSS CVs

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

  15. SDSS CVs (Gänsicke et al 2009)

  16. New SDSS CVs vs model A

  17. Kolb & Baraffe 1999

  18. 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

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