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
Linda Schmidtobreick The role of SW Sex stars in the evolution of CVs
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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
Linda Schmidtobreick The role of SW Sex stars in the evolution of CVs
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The orbital period distribution
Linda Schmidtobreick The role of SW Sex stars in the evolution of CVs
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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
Linda Schmidtobreick The role of SW Sex stars in the evolution of CVs
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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)
Linda Schmidtobreick The role of SW Sex stars in the evolution of CVs
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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
Linda Schmidtobreick The role of SW Sex stars in the evolution of CVs
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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
Linda Schmidtobreick The role of SW Sex stars in the evolution of CVs
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Some radial velocity curves: V849Her
Linda Schmidtobreick The role of SW Sex stars in the evolution of CVs
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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
Linda Schmidtobreick The role of SW Sex stars in the evolution of CVs
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Consequences for the evolution of CVs
Linda Schmidtobreick The role of SW Sex stars in the evolution of CVs
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Consequences for the evolution of CVs
Linda Schmidtobreick The role of SW Sex stars in 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?
Linda Schmidtobreick The role of SW Sex stars in 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?
Linda Schmidtobreick The role of SW Sex stars in the evolution of CVs
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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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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.
Linda Schmidtobreick The role of SW Sex stars in the evolution of CVs
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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?
Linda Schmidtobreick The role of SW Sex stars in the evolution of CVs