The role of SW Sex stars in the evolution of CVs

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Lindsey Rich
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1 European Southern Observatory Chile Wild Stars in the West II, Tucson 2009

2 The orbital period distribution

3 SW Sextantis stars in a nutshell Original definition (Thorstensen et al. 1991, AJ 102, 272): novalike stars eclipsing velocity of Balmer emission lines lags behind the expected velocity of the WD (about 0.2 phases) transient absorption in the emission lines at phase Φ 0.5 strong He II emission no polarisation Other features that were found later: most objects have periods between 3 and 4 h high velocity wings extend to up to 4000 km/s extremely high accretion rates

4 The orbital period distribution

5 RR Pic old nova with P orb = 3.5 h inclination of 65 deg, not eclipsing, or only marginally line wings with velocities of 1200 km Hα line profile in RR Pic changes from single-peaked to centrally-absorbed over the orbital cycle offset of about 0.2 cycles between the velocities of the line wings and those of the line core

6 The project The hypothesis: As the physical properties of SW Sex stars have nothing to do with their inclination, all non- or weakly-magnetic CVs in the h period range are physically SW Sex stars. The method: Obtain time-resolved spectroscopy of CVs in the h period range to test for the presence of the defining SW Sex characteristics The team: Boris Gänsicke (Warwick University, UK) Pablo Rodriguez (IAC, Spain) (ESO, Chile)

7 The Observations so far three observing runs in 2005 at NTT (ESO, La Silla) and WHT (La Palma) one run in 2007 at NTT one run in 2009 at NTT 15 SW Sex candidates observed spectroscopically covering about 1 orbital period

8 Trailed spectra: LQ Peg, AH Pic, V992 Sco, LN UMa

9 Trailed spectra:hl Aqr, BO Cet, V849 Her, V393 Hya

10 Trailed spectra: AH Men, V380 Oph, AQ Men, BB Dor

11 Some radial velocity curves: HL Aqr

12 Some radial velocity curves: V849 Her

13 Some radial velocity curves: BO Cet

14 Results so far System single peak S wave 0.5 abs. phases flaring SW Sex? HL Aqr a yes BO Cet yes BB Dor? yes IM Eri? yes V849 Her x x x x no V393 Hya x x x x x no AQ Men?? yes AH Men yes KQ Mon yes V380 Oph yes V1193 Ori yes LQ Peg x x x x no AH Pic a yes V992 Sco b LN UMa x c yes a : In absorption. b : spectrum still dominated by shell emission lines from recent nova explosion c : Better spectral resolution needed

15 Conclusion: SW Sex type stars are the dominant CV population in the 3 4 h period range.

16 Consequences for the evolution of CVs

17 Consequences for the evolution of CVs

18 Consequences for the evolution of CVs

19 Consequences for the evolution of CVs If the disruptive braking model holds, all CVs that are formed above the gap must evolve to an SW Sex type star before entering the gap.

20 Consequences for the evolution of CVs If the disruptive braking model holds, all CVs that are formed above the gap must evolve to an SW Sex type star before entering the gap. Question: Does the high accretion rate of this state force the CVs into the gap?

21 What role does irradiation play? Irradiation by the White Dwarf Irradiation by the disc Runaway mass transfer? Ritter, Zhang, Kolb 2000, A&A 360, 969:

22 What role do magnetic fields play? Magnetic field of the White Dwarf -line flaring -polarisation Magnetic field of the secondary star -low states, e.g. BB Dor

23 What role do magnetic fields play? Magnetic field of the White Dwarf -line flaring -polarisation Magnetic field of the secondary star -low states, e.g. BB Dor see Poster by Rodriguez Gil et al.

24 Some conclusions and many questions SW Sex type stars are the dominant population of CVs with periods between 3 h and 4 h. If the disruptive braking model is true, all CVs have to go through an SW Sex phase before entering the gap. Does irradation after all play a major role for the existence of the gap? Does the secondary s magnetic field trigger the low states of VY Scl stars? Can it also trigger the entering into the gap? Is the SW Sex state the end phase of the CVs above the gap? Is the peak of SW Sex stars a pile up?

Two projects without apparent connection?

Two projects without apparent connection? SW Sextantis stars SW Sextantis stars The golden age of surveys, Gänsicke 2005, Strassbourg SW Sextantis stars an introduction Original definition (Thorstensen