A Test for the Disruption of Magnetic Braking in Cataclysmic Variable Evolution P. Davis 1, U. Kolb 1, B. Willems 2, B. T. Gänsicke 3 1 Department of Physics.

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

Talk Overview

■ The period gap

■ The disrupted magnetic braking hypothesis

■ Our method

■ Summary of results

■ Future work: the SDSS

■ Conclusions

The Period Gap & The Disrupted Magnetic Braking Hypothesis

The Period Gap & The Disrupted Magnetic Braking Hypothesis

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

Donor fully convective → magnetic braking ceases

System becomes “dCV”

Mass transfer resumes ~ 2 h

Evolution driven by gravitational radiation.

Rappaport, Verbunt & Joss (1983)

Spruit & Ritter (1983)

Magnetic braking drives rapid mass transfer donor star swells

MethodMethod

■ 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

Primary mass ?

Initial Mass Ratio DistributionCommon Envelope ejection efficiency,

αCE

αCE = constant = 0.1 – 5.0

(e.g. Willems & Kolb 2004)

αCE = (M2/Msun)p, p = 0.5, 1, 2

(Politano & Weiler 2007)

Magnetic Braking Strength

+

Hurley, Pols & Tout (2002)

Rappaport, Verbunt & Joss (1983)

R3Ω3 (Menv/M) R2Ω3M R4Ω3M

Angular momentum loss rate

Calibrate strength ~10-

9 Msun yr-1 at 3 hr(e.g. McDermot & Taam 1989)

Disrupting Magnetic Braking

■ Gap width of ~ 1 hour

■ R2 ~ 1.3RMS at 3 hr

■ Disrupt magnetic braking once M2 = 0.17Msun

■ lower edge at ~ 2 hr

Results

Excess of dCVs over PCEBs in the period gap → “Mirror Gap”

■ Flat initial mass ratio distribution

(Goldberg, Lazeh & Latham 2003

■ αCE = 1

gPCEBdCVTotal

“Mirror Gap”

αCE = 0.6

αCE = 0.1

■ Flat initial mass ratio distribution(Goldberg, Lazeh & Latham 2003)

■ Significant Mirror Gap. Ratio dCV/gPCEB in gap:

● ~ 13 for αCE = 0.1

● ~ 4 for αCE = 0.6

Iben & Livio 1993

■ The ratio dCV:gPCEB indicator of size of mirror gap

How about…

■ Different Magnetic braking strengths?

■ 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)

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

■ ~ 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.

SDSS

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

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