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)A. Rebassa-Mansergas (Valparaiso)

M. Zorotovic-Fiebig, C. Tappert (PUC Santiago)

L. Schmidtobreik (ESO)

A. D. Schwope, A. Nebot Gomez-Moran (AIP)

The orbital period distribution of CVs

Ritter & Kolb (2003)

1983: Disrupted magnetic braking (DMB)

Paczynski & Sienkiewicz; Spruit & Ritter; Rappaport et al. (1983)

Two angular momentum loss mechanisms:

magnetic wind braking & gravitational radiation

MWB+GR GR

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)

Predicted PCEB fractions

Politano & Weiler (2006)

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)

PCEB fraction versus secondary spectral

type

PCEB fraction versus secondary mass

Comparing predictions and observations

Politano & Weiler (2006)

- 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

Conclusion

Disrupted braking confirmed!

Remaining questions

Why does braking get disrupted?

How strong is AML below the gap?

Why is it different in young stars?

For questions

Gemini PCEB identifications (2007B, 2008A)

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)

Selection effects

Bias towards short orbital periods

Bias towards low mass secondaries

Disrupted braking in single field M dwarfs?