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A Test for the Disruption of Magnetic Braking in Cataclysmic Variable Evolution

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  1. A Test for the Disruption of Magnetic Braking in Cataclysmic Variable Evolution P. Davis1, U. Kolb1, B. Willems2, B. T. Gänsicke3 1Department of Physics & Astronomy, Open University, Walton Hall, Milton Keynes, MK7 6AA, UK 2Department of Physics & Astronomy, Northwestern University, 2131 Tech Drive, Evanston, Illinois, USA 3Department of Physics, University of Warwick, Coventry, UK MNRAS, 2008, 389, 1563-1576

  2. Talk Overview ■ The period gap ■ The disrupted magnetic braking hypothesis ■ Our method ■ Summary of results ■ Future work: the SDSS ■ Conclusions

  3. The Period Gap & The Disrupted Magnetic Braking Hypothesis The Period Gap & The Disrupted Magnetic Braking Hypothesis

  4. Ritter & Kolb (2003), Edition 7.9 (2008)

  5. Magnetic braking drives rapid mass transfer  donor star swells Evolution driven by gravitational radiation. Donor fully convective → magnetic braking ceases System becomes “dCV” Mass transfer resumes ~ 2 h Rappaport, Verbunt & Joss (1983) Spruit & Ritter (1983)

  6. Method Method

  7. ■ Calculate present day populations of: ● “detached CVs” (dCVs) ● “gap post-common envelope binaries” (gPCEBs)  0.17 <M2 / Msun < 0.36 ■ BiSEPS (Binary System Evolution and Population Synthesis) ● Stellar evolution package: Hurley, Pols & Tout 2000 ● Binary Evolution based on Hurley, Tout & Pols 2002 ● Open University developed code (Willems & Kolb 2002, 2004) ● Significant modifications: □ Realistic treatment of mass transfer in CVs □ Reaction of donor star due to mass loss □ Evolution of dCV across period gap

  8. Common Envelope ejection efficiency, αCE Initial Mass Ratio Distribution ? αCE = constant = 0.1 – 5.0 (e.g. Willems & Kolb 2004) αCE = (M2/Msun)p, p = 0.5, 1, 2 (Politano & Weiler 2007) + Primary mass Disrupting Magnetic Braking Magnetic Braking Strength Calibrate strength  ~10-9 Msun yr-1 at 3 hr ■ Gap width of ~ 1 hour ■ R2 ~ 1.3RMS at 3 hr ■ Disrupt magnetic braking once M2 = 0.17Msun ■  lower edge at ~ 2 hr (e.g. McDermot & Taam 1989) Angular momentum loss rate R3Ω3 (Menv/M) R2Ω3M R4Ω3M Hurley, Pols & Tout (2002) Rappaport, Verbunt & Joss (1983)

  9. Results

  10. Excess of dCVs over PCEBs in the period gap → “Mirror Gap” ■ Flat initial mass ratio distribution gPCEB dCV (Goldberg, Lazeh & Latham 2003 Total ■ αCE = 1

  11. ■ Flat initial mass ratio distribution “Mirror Gap” (Goldberg, Lazeh & Latham 2003) ■ Significant Mirror Gap. Ratio dCV/gPCEB in gap: ● ~ 13 for αCE = 0.1 ● ~ 4 for αCE = 0.6 αCE = 0.6 Iben & Livio 1993 αCE = 0.1

  12. ■ The ratio dCV:gPCEB  indicator of size of mirror gap

  13. How about… ■ Different Magnetic braking strengths? dCV:gPCEB=3.5 dCV:gPCEB=5.5 dCV:gPCEB=6.0  Still obtain a mirror gap with a significant peak height, irrespective of MB law ■ Narrower period gap? From a weaker magnetic braking law? (Ivanova & Taam 2003) Gap width of ½ hr dCV:gPCEB ~ 2.1  mirror gap still expected. ■ CVs from thermal timescale mass transfer Contribute an extra ~40% to calculated dCV population (Kolb & Willems 2005)

  14. SDSS ■ ~ 50 PCEBs identified with determined orbital periods. ~10 from SDSS (Rebassa-Mansergas et al 2008, Schreiber et al. 2008) ■ 3 dCV candidates so far identified. □ At 164.2, 129.5 and 130 minutes ■ Require few hundred white dwarf-main sequence binaries to adequately resolve mirror gap.

  15. Conclusions ■ Dearth of CVs with Porb ≈ 2 and 3 hours. ■ Standard explanation  disrupted magnetic explanation… ■ Test: Orbital period distribution of gPCEB and dCV population  “Mirror Gap”  excess of dCV over gPCEBs there. ■ Expect dCV:gPCEB ~ 4 to 13  mirror gap with a significant peak height ■ Observationally feasible  SDSS

  16. References ■ Goldberg D., Mazeh T., Latham D. W., 2003, ApJ, 591, 397 ■ Hurley J. R., Pols O. R., Tout C. A., 2000, MNRAS, 315, 543 ■ Hurley J. R., Tout C. A., Pols O. R., 2002, MNRAS, 329, 897 ■ Iben I. J., Livio M., 1993, PASP, 105, 1357 ■ Ivanova N., Taam R. E., 2003, ApJ, 599, 516 ■ Jones B. F., Fischer D. A., Stauffer J. R., 1996, AJ, 112, 1562 ■ Knigge C., 2006, MNRAS, 373, 484 ■ Kolb U., Willems B., 2005, ASP Conf. Ser., 330, 17 ■ Politano M., Weiler K. P., 2007, ApJ, 665, 663 ■ Rappaport S., Verbunt F., Joss P. C., 1983, ApJ, 275, 713 ■ Rebassa-Mansergas A., et al., 2007, MNRAS, 382, 1377 ■ Rebassa-Mansergas A., et al., 2008, MNRAS, 390, 1635 ■ Ritter H., Kolb U., 2003, A&A, 404, 301 ■ Schreiber M. R., et al., 2008, A&A, 484, 441 ■ Spruit H. C., Ritter H., 1983, A&A, 124, 267 ■ Willems B., Kolb U., 2002, MNRAS, 337, 1004 ■ Willems B., Kolb U., 2004, A&A, 419, 1057