Download - The SW Sextantis stars and the evolution of cataclysmic variables Pablo Rodríguez Gil 5 January 2006
The SW Sextantis starsand the
evolution ofcataclysmic variables
Pablo Rodríguez Gil
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 Detached binary
Common envelope
AML; a decreases
Envelope ejection
AML: magnetic braking or gravitational radiation
Contact
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
Bright spot
White dwarf
Gas stream
Accretion disc
~ Main sequence
Secondary star
Late type (K-M)
M2~ 0.05-1 M
White dwarf
Primary component
<M1> ~ 0.7 M
CVs have magnetic fields…
…accretion discs…
…or both!
The intermediate polar CVs
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)
Magnetic accretion
Orbital period distribution
Ritter & Kolb (2003): 496 systems
Gives observational input on the AML rate
Flashback – 1983: ‘Disrupted magnetic braking’
Paczynski & Sienkiewicz; Spruit & Ritter; Rappaport et al. (1983)
Two AML mechanisms:
Magnetic braking (stellar wind) & gravitational radiation
MB+GR GR
Standard theory predictions
- Paucity of the number of CVs in the range Porb=2-3 hr
The ‘period gap’
Standard theory predictions
- Minimum Porb of ~ 65 min
- Paucity of the number of CVs in the range Porb=2-3 hr
The minimum orbital period
~80 min!
Standard theory predictions
- Minimum Porb of ~ 65 min X
- Paucity of the number of CVs in the range Porb=2-3 hr
- Pile-up of systems at Pmin
Population syntheses: the minimum period
Kolb & Baraffe (1999)
The minimum orbital period
~80 min!
Standard theory predictions
- Minimum Porb of ~ 65 min X
- Paucity of the number of CVs in the range Porb=2-3 hr
- 99% of all CVs should have Porb < 2 hr
- Pile-up of systems at Pmin X
Orbital period distribution
191=38%250=51%
55=11%
Standard theory predictions
- Minimum Porb of ~ 65 min X
- Paucity of the number of CVs in the range Porb=2-3 hr
- Pile-up of systems at Pmin X
- 99% of all CVs should have Porb < 2 hr X
Standard theory predictions
- Minimum Porb of ~ 65 min X
- Paucity of the number of CVs in the range Porb=2-3 hr
- 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
- Unusual spectral features, inconsistent with a standardoptically thick, geometrically thin accretion disc.
- Extremely high mass accretion rates.
- ~50% of all CVs in the 3-4 hr strip are SW Sextantis stars.
- No place for such maverick systems in the standardevolution theory.
Trailed spectra. Pulsed S-wave (Rodríguez-Gil et al. 2001)
LS Pegasi
Pulse separation
~ 0.1 Porb
A likely magnetic nature
A likely magnetic nature
V533 Her (Rodríguez-Gil & Martínez-Pais 2002)
DW UMa (Smith et al., unpublished)
- Emission-line flaring also characteristic of IPs.
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
A likely magnetic nature
LS Pegasi
(Rodríguez-Gil et al. 2001)
Strong HeII 4686 emission, typical of mCVs.
A likely magnetic nature
RX J1643.7+3402
(Martínez-Pais, de la Cruz & Rodríguez-Gil, submitted)
Discovery of circular polarisation.
P1 = 19.4 min
RX J1643.7+3402
(Martínez-Pais, de la Cruz & Rodríguez-Gil, submitted)
A likely magnetic nature
Variable HeII 4686 EW.
P =25.5 min (coherent for at least 15 cycles).
V1315 Aql
A likely magnetic nature
Light curve oscillations (QPOs).HS 0728+6738
A likely magnetic nature
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!).
A comprehensive study of the SW Sextantis stars is therefore mandatory.
1) Masses involved.
2) Search for more systems.
3) Circular polarimetry.
Weighing the components
- SW Sextantis stars ocassionally fade. ’LOW STATES’.
- The absence of DN-type outbursts during the low statessupports a magnetic scenario (Hameury & Lasota 2002).
(Honeycutt & Kafka 2004)
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 4686 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, DNoutbursts, 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, DNoutbursts, 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
- The current CV population is a mixed bag (novae, DNoutbursts, 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 afundamental test to the standard theory.
Major revision is expected…
The SW Sextantis starsand the
evolution ofcataclysmic variables
Pablo Rodríguez Gil
5 January 2006