1. The SW Sextantis stars and the evolution of cataclysmic variables
Pablo Rodríguez Gil
The SW Sextantis stars and the evolution of cataclysmic variables
5 January 2006

2. Summary Introduction. Cataclysmic variable structure and evolution.
The SW Sextantis stars: new insights on their accretion structure.
Towards a global understanding.
The HQS and SDSS and CV evolution.

3. Astrophysical context
Most of the stars are born in binary or multiple systems.
~50% of the binaries will interact at some point (Iben 1991).
Many exotic astrophysical objects (e.g. binary pulsars, black holes, LMXBs, symbiotics…) are descendent from binary systems.
Type Ia supernovae: accretion on to white dwarfs. Cosmological distance scale.

4. Compact binaries
They harbour a compact stellar remnant (i.e. WD, NS or BH).
Their evolution critically depends on the angular momentum loss rate (dJ/dt). t
Envelope ejection
AML: magnetic braking or gravitational radiation
Contact
Common envelope
AML; a decreases
Detached binary

5. Summary Introduction. Cataclysmic variable structure and evolution.
The SW Sextantis stars: new insights on their accretion structure.
Towards a global understanding.
The HQS and SDSS and CV evolution.

6. What is a cataclysmic variable?
Donor star
White dwarf
Primary component
<M1> ~ 0.7 M
Bright spot
White dwarf
~ Main sequence
Secondary star
Late type (K-M)
M2~ M
Gas stream
Accretion disc

7. CVs have magnetic fields…

8. …accretion discs…

9. …or both!

10. The intermediate polar CVs

11. Magnetic accretion
The height of the shock front depends on the cooling mechanisms in the column.
The emission spectrum of the column:
108 K
105 K
Bremsstrahlung: Hard X rays (kTbr ~ 30 keV)
Compton: UV and soft X rays (kTBB ~ 40 eV)
Cyclotron: IR-optical-UV (POLARISED)

12. Orbital period distribution
Gives observational input on the AML rate
Ritter & Kolb (2003): 496 systems

13. Flashback – 1983: ‘Disrupted magnetic braking’
Two AML mechanisms:
Magnetic braking (stellar wind) & gravitational radiation
MB+GR GR
Paczynski & Sienkiewicz; Spruit & Ritter; Rappaport et al. (1983)

14. Standard theory predictions
- Paucity of the number of CVs in the range Porb=2-3 hr

15. The ‘period gap’

16. Standard theory predictions
- Paucity of the number of CVs in the range Porb=2-3 hr 
- Minimum Porb of ~ 65 min

17. The minimum orbital period

18. Standard theory predictions
- Paucity of the number of CVs in the range Porb=2-3 hr 
- Minimum Porb of ~ 65 min X
- Pile-up of systems at Pmin

19. Population syntheses: the minimum period
Kolb & Baraffe (1999)

20. The minimum orbital period

21. Standard theory predictions
- Paucity of the number of CVs in the range Porb=2-3 hr 
- Minimum Porb of ~ 65 min X
- Pile-up of systems at Pmin X
- 99% of all CVs should have Porb < 2 hr

22. Orbital period distribution
191=38%
250=51%
55=11%

23. Standard theory predictions
- Paucity of the number of CVs in the range Porb=2-3 hr 
- Minimum Porb of ~ 65 min X
- Pile-up of systems at Pmin X
- 99% of all CVs should have Porb < 2 hr X

24. Standard theory predictions
- Paucity of the number of CVs in the range Porb=2-3 hr 
- Minimum Porb of ~ 65 min X
- Pile-up of systems at Pmin X
- 99% of all CVs should have Porb < 2 hr X
- CV density ~
Observed ~ X
We are in deep trouble!

25. An alternative AML prescription
Verbunt & Zwaan (1981) vs. Sills et al. (2000).
Nevertheless, something is happening above the gap……………

26. Summary Introduction. Cataclysmic variable structure and evolution.
The SW Sextantis stars: new insights on their accretion structure.
Towards a global understanding.
The HQS and SDSS and CV evolution.

27. The SW Sextantis stars
~50% of all CVs in the 3-4 hr strip are SW Sextantis stars.
Unusual spectral features, inconsistent with a standard
optically thick, geometrically thin accretion disc.
Extremely high mass accretion rates.
No place for such maverick systems in the standard
evolution theory.

28. A likely magnetic nature
LS Pegasi
Trailed spectra. Pulsed S-wave (Rodríguez-Gil et al. 2001)
Pulse separation
~ 0.1 Porb

29. A likely magnetic nature
DW UMa (Smith et al., unpublished)
V533 Her (Rodríguez-Gil & Martínez-Pais 2002)
Emission-line flaring also characteristic of IPs.

30. A likely magnetic nature
LS Pegasi
PEW = 33.5  2.2 min

31. A likely magnetic nature
LS Pegasi
Circularly polarised continuum.
P1 = 29.6  1.8 min
1/ P1 - 1/PEW = 1/Porb
(PEW  synodic period)
Cyclotron radiation
B1 ~ 10 MG
(Rodríguez-Gil et al. 2001)

32. A likely magnetic nature
RX J
Strong HeII l4686 emission, typical of mCVs.
(Martínez-Pais, de la Cruz & Rodríguez-Gil, submitted)

33. A likely magnetic nature
RX J
Discovery of circular polarisation.
P1 = 19.4 min
(Martínez-Pais, de la Cruz & Rodríguez-Gil, submitted)

34. A likely magnetic nature
V1315 Aql
Variable HeII l4686 EW.
P =25.5 min (coherent for at least 15 cycles).

35. A likely magnetic natureHS
Light curve oscillations (QPOs).

36. Summary Introduction. Cataclysmic variable structure and evolution.
The SW Sextantis stars: new insights on their accretion structure.
Towards a global understanding.
The HQS and SDSS and CV evolution.

37. Magnetism and CV evolution
Magnetic fields can play a crucial role in CV evolution.
At least half the CVs in the 3-4 h range can be magnetic
(only 3% of isolated WDs are!).
1) Masses involved.
A comprehensive study of the SW Sextantis stars is therefore mandatory.
2) Search for more systems.
3) Circular polarimetry.

38. Weighing the components
SW Sextantis stars ocassionally fade. ’LOW STATES’.
(Honeycutt & Kafka 2004)
The absence of DN-type outbursts during the low states
supports a magnetic scenario (Hameury & Lasota 2002).

39. Weighing the components
Photometric monitoring campaigns in the North and South.
ToO programmes at the VLT, and the WHT and NOT. HS
Sp(2)=dM3-4 V
T1 > K
d ~ kpc
VLT

40. Weighing the components
First donor star radial velocity curve at the WHT (R = 19.4). HS
K2 = 330 km/s
i = 83º
M2 = 0.3 M
M1 = 1.0 M

41. Weighing the components
WD exceeds the average mass of 0.65 M.
T1 is unusually high. DW UMa has ~ K.
Secular heating of the WD. Why such a high transfer rate?
Fundamental to measure the physical parameters of a large sample of systems!

42. A growing family Search programmes in both hemispheres.
Linda Schmidtobreick (ESO), Boris Gänsicke (Warwick, UK).
Targets: CVs in the 3-4 h orbital period range.
Asymmetric line profiles with enhanced wings.
Short-time scale photometric variability (QPOs).
Presence of the HeII l4686 line and Bowen.
Low states.
...
Preliminary results in the south show great success.

43. A growing family
V380 Ophiuchi
NTT + WHT
P = 3.72 hr

44. A growing family
AH Mensae
NTT
P = 2.97 hr

45. Summary Introduction. Cataclysmic variable structure and evolution.
The SW Sextantis stars: new insights on their accretion structure.
Towards a global understanding.
The HQS and SDSS and CV evolution.

46. The HQS and the SDSS
The current CV population is a mixed bag (novae, DN
outbursts, rapid variablility, blue colour, X rays).
Need for an UNBIASED CV sample.
The HQS and the SDSS CVs are spectroscopically selected.

47. The HQS: 53 new CVs, 35 Porb
SW Sextantis 215 min (20%)

48. The HQS and the SDSS
The current CV population is a mixed bag (novae, DN
outbursts, rapid variablility, blue colour, X-rays).
Need for an UNBIASED CV sample.
The HQS and the SDSS CVs are spectroscopically selected.
The SDSS (g < 21) have provided ~120 new CVs.

49. The SDSS: 120 new CVs, 45 Porb

50. The HQS and the SDSS Major revision is expected…
The current CV population is a mixed bag (novae, DN
outbursts, rapid variablility, blue colour, X-rays).
Need for an UNBIASED CV sample.
The HQS and the SDSS CVs are spectroscopically selected.
The SDSS (g < 21) have provided ~120 new CVs.
The period distribution of the SDSS CVs will serve as a
fundamental test to the standard theory.
Major revision is expected…

51. The SW Sextantis stars and the evolution of cataclysmic variables
Pablo Rodríguez Gil
The SW Sextantis stars and the evolution of cataclysmic variables
5 January 2006