the role of sw sex stars in the evolution of cvs · 2009. 4. 7. · magnetic ﬁeld of the white...

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The role of SW Sex stars in the evolution of CVs

Linda Schmidtobreick

European Southern ObservatoryChile

Wild Stars in the West II, Tucson 2009

Linda Schmidtobreick The role of SW Sex stars in the evolution of CVs

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The orbital period distribution


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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 expectedvelocity 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


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The orbital period distribution


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RR Pic

old nova with Porb = 3.5 h

inclination of ∼ 65 deg, noteclipsing, or only marginally

line wings with velocities of1200 km

Hα line profile in RR Pic changesfrom single-peaked tocentrally-absorbed over the orbitalcycle

offset of about 0.2 cycles betweenthe velocities of the line wings andthose of the line core


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The project

The hypothesis:As the physical properties of SW Sex stars have nothing to do withtheir inclination, all non- or weakly-magnetic CVs in the 2.8–4 hperiod range are physically SW Sex stars.

The method:Obtain time-resolved spectroscopy of CVs in the 2.8–4 h periodrange to test for the presence of the defining SW Sex characteristics

The team:Boris Gansicke (Warwick University, UK)Pablo Rodriguez (IAC, Spain)Linda Schmidtobreick (ESO, Chile)


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The Observations so far

three observing runs in 2005at NTT (ESO, La Silla) andWHT (La Palma)

one run in 2007 at NTT

one run in 2009 at NTT

15 SW Sex candidatesobserved spectroscopicallycovering about 1 orbitalperiod


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Trailed spectra: LQPeg, AHPic, V992 Sco, LNUMa


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Trailed spectra:HLAqr, BO Cet, V849Her, V393Hya


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Trailed spectra: AHMen, V380Oph, AQMen, BBDor


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Some radial velocity curves: HLAqr


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Some radial velocity curves: V849Her


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Some radial velocity curves: BO Cet


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Results so far

System single peak S–wave 0.5–abs. phases flaring SW Sex?

HLAqr√a √ √ √ √

yesBO Cet

√ √ √ √ √yes

BBDor√ √ √ √

? yesIM Eri

√ √ √ √? yes

V849 Her√

x x x x noV393 Hya x x x x x noAQ Men

√ √ √? ? yes

AHMen√ √ √ √ √

yesKQMon

√ √ √ √ √yes

V380 Oph√ √ √ √ √

yesV1193 Ori

√ √ √ √ √yes

LQ Peg√

x x x x noAHPic

√a √ √ √ √yes

V992 Sco - - - - - - b

LNUMa√ √ √

xc √yes

a: In absorption.b: spectrum still dominated by shell emission lines from recent nova explosionc : Better spectral resolution needed


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Conclusion:

SW Sex type stars are the dominantCV population in the 3–4 h periodrange.


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Consequences for the evolution of CVs


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Consequences for the evolution of CVs

If the disruptive braking model holds, all CVs that are formedabove the gap must evolve to an SW Sex type star before enteringthe gap.

Question: Does the high accretion rate of this state force the CVsinto the gap?


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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:


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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.


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Some conclusions and many questions

SW Sex type stars are the dominant population of CVs with periodsbetween 3 h and 4 h.

If the disruptive braking model is true, all CVs have to go through anSW 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?


the role of sw sex stars in the evolution of cvs · 2009. 4. 7. · magnetic ﬁeld of the white...

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