Accretion discs: Accretion discs: models vs realitymodels vs reality

Jean-Pierre LasotaJean-Pierre Lasota

Institut d’Astrophysique de ParisInstitut d’Astrophysique de Paris

Jean-Alain Jean-Alain MarckMarck

SS CygSS Cyg

Dwarf Dwarf novaenovae

accretion discaccretion disc

white dwarfwhite dwarf

red dwarfred dwarf

““hot spot”hot spot”

Cataclysmic Binary StarsCataclysmic Binary Stars

Discs (in CVs) are:Discs (in CVs) are:

• KeplerianKeplerian

• geometrically thin (but not geometrically thin (but not “infinitely” thin)“infinitely” thin)

• not always in equilibrium (thermal not always in equilibrium (thermal and/or viscous) and/or viscous)

• (almost ?) flat(almost ?) flat

• non-adiabatic non-adiabatic ((radiate like hell !)radiate like hell !)

• not always (?) axisymmetricnot always (?) axisymmetric

• non-selfgravitatingnon-selfgravitating

• jetlessjetless ! !

Smak 1994Smak 1994

Webb et al. 1999Webb et al. 1999

Doppler Doppler tomography: 2Dtomography: 2D

Steeghs 2001Steeghs 2001

Steeghs 2001Steeghs 2001

Steeghs 2001Steeghs 2001

Steeghs 2001Steeghs 2001

??

MODELSMODELS

De Villiers et al. De Villiers et al. 20042004

Balbus 2005Balbus 2005

For subsonic turbulence equivalent to prescription (Duschl et al 2000)

RadiRadialal

VerticaVerticall

QQ++ = Q = Q--

Local limit-cycleLocal limit-cycle

Menou, Menou, HameuryHameury, Stehle 1998, Stehle 1998

quiescencequiescence

Hameury et al.1998

Dubus 2001Dubus 2001

Buat-Ménard et al. 2001

*

Smak 2000*

Hameury 2001

Hameury 2001

new

old

Proposed solution (Gammie & Menou Proposed solution (Gammie & Menou 1997)1997)

Cannot work: there Cannot work: there isis accretion during accretion during quiecence !quiecence !

Accretion Accretion streamstream

Maybe it is not turbulence ?

V436 Cen V436 Cen (Semeniuk 1980)(Semeniuk 1980)

SuperoutbursSuperoutburststs

SuperhumpsSuperhumps

(AAVSO)(AAVSO)VW HyiVW Hyi

““Standard model”: superhumps due Standard model”: superhumps due to tidal, eccentric instability.to tidal, eccentric instability.

Mu

rray & A

rmitage 1998

Mu

rray & A

rmitage 1998

Condition:Condition: 2

1

Mq= <0.25

M

(3:1 eccentric inner Lindblad resonance; Lubow 1991)

< 0.33 for reduced mass- transfer

Superoutbursts due to a tidal-thermal instability

Osaki:

IsothermIsothermalal

Fully radiativeFully radiative

Kornet & Rożyczka (1998)

Superhumps in U Gem !Superhumps in U Gem ! (Smak (Smak 2005)2005)

0.364 0.017q

Superoutburst in U Superoutburst in U GemGem

TV Col

…and in any case no need for tidal-thermal instability in LMXB outbursts

ConclusioConclusionsns

• CVs are the best systems for studying CVs are the best systems for studying accretion discsaccretion discs

• Observations will bring a tremendous Observations will bring a tremendous amount of data on disc structure amount of data on disc structure

• There are (at least) two kinds of There are (at least) two kinds of “viscosity”“viscosity”

• Numerical simulations will play an Numerical simulations will play an important role but thinking should not be important role but thinking should not be abandonedabandoned

• The role of tidal forces has to be re-The role of tidal forces has to be re-examinedexamined

• 3D is essential but without radiative 3D is essential but without radiative cooling included it might be of little cooling included it might be of little relevancerelevance