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Disrupted Magnetic Braking in Close Binary Systems: Insights from PCEBs and Angular Momentum Loss

This study explores the phenomenon of disrupted magnetic braking (DMB) in pre-cataclysmic binaries (PCEBs) utilizing data from the SDSS. We analyze the orbital period distribution of cataclysmic variables (CVs) and consider two angular momentum loss mechanisms: magnetic wind braking and gravitational radiation. With over 285 identified PCEBs and 54 measured orbital periods, we compare theoretical predictions against observations. Key findings reveal the impacts of magnetic fields in M dwarf stars and raise questions about the mechanisms behind braking disruptions in older stars.

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Disrupted Magnetic Braking in Close Binary Systems: Insights from PCEBs and Angular Momentum Loss

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  1. PCEBs from the SDSStesting disrupted magnetic braking Matthias Schreiber • 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) Tucson, March-2009

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

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

  4. DMB: believe it or not • Pros: • - Mean mass transfer rates of CVs • (Townsley & Gaensicke 2008) • Donor star mass-radius relation • (e.g. Knigge 2006) • 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)

  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. Disrupted braking in single old field M dwarfs • 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)

  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 low mass secondaries Bias towards short orbital periods

  17. Disrupted braking in single field M dwarfs?

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