Transcript Slide 1

A Test for the Disruption of Magnetic Braking
in Cataclysmic Variable Evolution
P. Davis1, U. Kolb1, B. Willems2, B. T. Gänsicke3
1Department
2Department
of Physics & Astronomy, Open University, Walton Hall, Milton Keynes, MK7
6AA, UK
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
Ritter & Kolb (2003), Edition 7.9 (2008)
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)
Method
■ 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
Common Envelope ejection efficiency,
αCE
Initial Mass Ratio Distribution
+
Primary
mass
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
Calibrate strength  ~10-9
Msun yr-1 at 3 hr (e.g. McDermot & Taam
Disrupting Magnetic
Braking
■ Gap width of ~ 1 hour
1989)
Angular momentum loss rate
R3Ω3 (Menv/M)
Hurley, Pols &
Tout (2002)
R2Ω3M
R4Ω3M
Rappaport,
Verbunt &
Joss (1983)
■ 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”
gPCEB
dCV
Total
■ Flat initial mass ratio
distribution
(Goldberg, Lazeh & Latham 2003
■ αCE = 1
■ Flat initial mass ratio
“Mirror Gap”
distribution
(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
■ The ratio
dCV:gPCEB 
indicator of size of
mirror gap
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)
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.
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