1. PCEBs from the SDSS testing disrupted magnetic braking Matthias Schreiber Tucson, March-2009 Boris T. Gaensicke, John Southworth, S. Stylianos (Warwick) A. Rebassa-Mansergas (Valparaiso) M. Zorotovic-Fiebig, C. Tappert (PUC Santiago) L. Schmidtobreik (ESO) A. D. Schwope, A. Nebot Gomez-Moran (AIP)

2. The orbital period distribution of CVs Ritter & Kolb (2003)

3. 1983: Disrupted magnetic braking (DMB) Paczynski & Sienkiewicz; Spruit & Ritter; Rappaport et al. (1983) Two angular momentum loss mechanisms: magnetic wind braking & gravitational radiation MWB+GRGR

4. DMB: believe it or not Cons: -Spin down rates of low-mass stars in open clusters (Sills et al. 2000) -Large scale magnetic fields in fully convective stars (Donati et al. 2006) Pros: -Mean mass transfer rates of CVs (Townsley & Gaensicke 2008) -Donor star mass-radius relation (e.g. Knigge 2006)

5. Predicted PCEB fractions Politano & Weiler (2006)

6. WDMS and PCEBs from the SDSS -SEGUE and SDSS identified ~2000 WDMS -We followed-up 285 -111 PCEBs identified (~39%) -54 orbital periods measured (see next talk)

7. PCEB fraction versus secondary spectral type

8. PCEB fraction versus secondary mass

9. Comparing predictions and observations Politano & Weiler (2006)

10. -fast fully convective rotators in old field stars -not a single early M fast rotator (Reiners et al. 2008) -change in the magnetic field topology at ~M3.5 (Donati et al. 2008) Disrupted braking in single old field M dwarfs

11. Conclusion Disrupted braking confirmed!

12. Remaining questions Why does braking get disrupted? How strong is AML below the gap? Why is it different in young stars?

13. For questions

14. Gemini PCEB identifications (2007B, 2008A)

15. 3 good reasons to believe in DMB -Mean mass transfer rates of CVs (Townsley & Gaensicke 2008) -Expanded secondaries above the gap (e.g. Knigge et al. 2006)

16. Selection effects Bias towards short orbital periods Bias towards low mass secondaries

17. Disrupted braking in single field M dwarfs?