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

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.

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.

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

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.

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~ 0.05-1 M Gas stream Accretion disc

CVs have magnetic fields…

…accretion discs…

…or both!

The intermediate polar CVs

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)

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

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)

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

The ‘period gap’

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

The minimum orbital period

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

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

The minimum orbital period

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

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

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

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!

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

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.

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.

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

A likely magnetic nature DW UMa (Smith et al., unpublished) V533 Her (Rodríguez-Gil & Martínez-Pais 2002) Emission-line flaring also characteristic of IPs.

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

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)

A likely magnetic nature RX J1643.7+3402 Strong HeII l4686 emission, typical of mCVs. (Martínez-Pais, de la Cruz & Rodríguez-Gil, submitted)

A likely magnetic nature RX J1643.7+3402 Discovery of circular polarisation. P1 = 19.4 min (Martínez-Pais, de la Cruz & Rodríguez-Gil, submitted)

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

A likely magnetic nature HS 0728+6738 Light curve oscillations (QPOs).

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.

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.

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).

Weighing the components Photometric monitoring campaigns in the North and South. ToO programmes at the VLT, and the WHT and NOT. HS 0220+0603 Sp(2)=dM3-4 V T1 > 25000 K d ~ 0.7-1.0 kpc VLT

Weighing the components First donor star radial velocity curve at the WHT (R = 19.4). HS 0220+0603 K2 = 330 km/s i = 83º M2 = 0.3 M M1 = 1.0 M

Weighing the components WD exceeds the average mass of 0.65 M. T1 is unusually high. DW UMa has ~ 50000 K. Secular heating of the WD. Why such a high transfer rate? Fundamental to measure the physical parameters of a large sample of systems!

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.

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

A growing family AH Mensae NTT P = 2.97 hr

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.

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 HQS: 53 new CVs, 35 Porb SW Sextantis excess @ 215 min (20%)

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.

The SDSS: 120 new CVs, 45 Porb

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…

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