1. SDSS finds the period minimum spike Boris Gänsicke John Southworth John Thorstensen M Dillon, P Rodríguez-Gil, A Aungwerojwit, TR Marsh, P Szkody, SCC Barros, J Casares, D de Martino, PJ Groot, P Hakala, U Kolb, SP Littlefair, IG Martínez-Pais, G Nelemans, MR Schreiber Ilse Decoster

2. CV Evolution in a nutshell Howell et al. (2001) Angular momentum loss MB/GR MB GR Porb decreases down to Pmin Donor becomes degenerate BD Porb increases again

3. Period bouncing

4. CV evolution in a nutshell Howell et al. 2001, ApJ 550, 897Kolb & Baraffe 1999, MNRAS 309, 1034 70% 29% 1% Most systems post-bounce Spike at Pmin MB GR Angular momentum loss MB/GR At Pmin: donor  BD MB disrupted at P=3h

5. Ritter 5 (1990): 167 CVs

6. Ritter & Kolb 6 (1998): 314 CVs

7. Ritter & Kolb 7.2 (2004): 518 CVs

8. CV evolution: theory & observations P min ≈65min 80 min! (Ritter & Kolb 2004) Spike @ P min selection effects?

9. Of spikes and small numbers Hameury et al. (1990) 114min 80 polars today

10. The PG CVs - 35 CVs, of which 31 new - 31 periods determined (Ringwald PhD 1993, Thorstensen, and others) no spike (see Pretorius)

11. CVs from the Hamburg Quasar Survey - 96 CVs, of which 53 new - 86 periods determined (Gänsicke, Rodríguez-Gil, Aungwerojwit, Hagen, Engels,...)... 24 HQS CVs with P orb =3-4h... spike?

12. SDSS CVs (Szkody et al. 2002, 2003, 2004) - 101 CVs, of which 90 new - 45 periods determined ITP time 2004/5 for SDSS CV follow-up: 70 nights WHT, TNG, INT, NOT & LT (Gänsicke et al.) Recycled slide detected … recycled slide detected …

13. SDSS CVs in DR7 (Szkody et al. 2002, 2003, 2004, 2005, 2006, 2007, 2009) - 281 CVs, of which 90 new - 126 periods determined ?

14. 10 years effort in 2 minutes Period accurate to better than 3%

15. 10 years effort in 2 minutes Period accurate to better than 3%

16. 10 years effort in 2 minutes Period accurate to better than 3%

17. SDSS CVs differ significantly from previous samples new SDSS CVs old SDSS CVs non-SDSS CVs - old vs non: 52.2% - new vs non: 0.065% two-sided Kolmogorov-Smirnov test Gänsicke et al. 2008, MNRAS, submitted why?

18. Properties of SDSS CVs

19. “active” CVs in the spike V844 Her T Leo SW UMa EV UMa GG Leo

20. Old (active) SDSS CVs with 80min<Porb<86min SW UMaT Leo V844 HerEV UMa

21. New SDSS CVs with 80min<Porb<86min

22. New (inactive) SDSS CVs with 80min<Porb<86min

24. eclipsing poor dataeclipsing polar

25. New (inactive) SDSS CVs with Porb>86min

27. Some comments on the space density -WD-dominated, or “WZ Sge” are often considered post-period-bounce (candidate) systems… -Yes, SDSS finds many new “WZ Sge”… but, they are all faint (g>17.6) and far (>150pc) away… -…yet, no bias against finding nearby “WZ Sge”… - “WZ Sge”s, bouncers or not, are not very common - While Littlefair found good evidence for bouncers, they are all at P min - Even SDSS has not found the predicted large population of period bouncers

28. SDSS finds the period spike because of depth “Palomar Green” “Hamburg Quasar Survey” “SDSS Quasar Survey” “SDSS all”

29. Completeness: the QSO exclusion boxes -WD box: one faint CV -A-star box: no CV -WMDS box: 5 CVs with P orb >150min while excluded from the QSO programme, there are sufficient spectra to inspect the kind of objects they contain.  no effect on the period spike discussed here

30. non-SDSS-discovered CVs in the SDSS footprint QSO survey limit

31. SDSS CV (re)identification efficiency CV has re-discovered ~90% of the previously known CVs with 17<g<19 QSO survey limit

32. Testing CV completeness by colour proximity i<19.1: 66% complete 19.1<i<23: 13% complete

33. Selecting CV candidates via p.m. from GALEX/SDSS 1437 objects with - 5  p.m. - GALEX fluxes - SDSS spectra all WD-cut QSO-cut CV 67 67 63 11.3% WD 601 169 113 31.5% WDMS 398 368 308 55.2% QSO 371 363 74 13.3% Total 1437 967 558

34. Selecting CV candidates via p.m. from GALEX/SDSS 3713 objects with - 5  p.m. - GALEX fluxes - no SDSS spectra 1689 candidates, expect - 191 CVs - 532 WDs - 932 WDMS binaries - 225 QSO

35. Summary SDSS goes deeper than any survey before, and the SDSS CV population exhibits a period spike at P min =80min, but need accurate orbital periods The spectra of the majority of “spike” CVs are WD dominated, “WZ Sge”-like, but SDSS has still not found the predicted large population of period-bouncers. The SDSS CV population is 66-90% complete for 17<i<19, but completeness drops quickly below i=19.1 … and that’s where the WD-dominated CVs become more numerous! The “missing” SDSS CV population can be targeted via a selection combining optical/UV colours and proper motion