Cataclysmic Variables in the UV D.de Martino INAF-Osservatorio Astronomico di Capodimonte Napoli & B.T. Gaensicke (Warwick), K.Long (STScI), T.R.Marsh (Warwick), E. Sion (Villanova), P. Szkody (Washington)

Hot Topics THE UV RANGE PLAYS A KEY ROLE HST SM4 recovery of UV capabilities Angular Momentum Loss Mechanisms Role of Novae in evolution Non-standard paths Close Binary Evolution: CVs as test cases Properties:WDs in CBs vs single WDs Accretion and outflow processes Mass, Temperature, Abundances, Rotation rate, Magnetism Rates, kinematics, energetics Effects on stellar parameters -> evolution

White Dwarf Late type Star CATACLYSMIC VARIABLES

Questions on CV Evolution Angular Momentum Loss mechanisms? Standard Theory: - Magnetic Braking (Porb>3hr) - Gravitational Radiation (Porb<2hr) Rappaport et al.1983; Patterson 1984; Kolb 1993; Sills et al. 2000; Ivanova&Taam, 2003 AML drives evolution From Ivanova &Taam, 2003

BUT Observed Orbital Period Distribution  99% present day CVs should Porb<2hr!  P min (obs)  80min > P min (th)  65min OK 2-3hr GAP ! RK Catalogue 2007 A Missing Population? Poor knowledge of AML? Both?

Understanding CV Evolution  Binary components properties Study of WD properties difficult in the optical but easier in the UV! Teff, log g, Vrot, Abundances from WD model fits Can be done for systems accreting at low-rates e.g.:DNe in quiescence, Magnetics in low states

Optically thick discs (TLUSDISK -Hubeny & Lanz 1995 ) + WD: IUE & HST/FOS/STIS/GHRS archival spectra:  100 objects in different states most low-res.  50% are disc dominated (Fdisc> 60%)  25% areWD dominated  25% equal contribution of WD & accretion disc For DNe not always easy…. Modelling of Accretion Discs to be included: But sometimes Disc+WD & 2-T WDs do the job (Sion et al.2008) TT Crt HST/STIS/G140L Teff=30000K log g=8.7 Mdot=3E-11 Msun/yr from Sion et al i=60deg V436 Cen DA WD (32%) + DISC (68%) Teff=24000K log g=8.3 Mdot=8E-11 Msun/yr from IUE Urban & Sion 2006 i=18deg

….& in Magnetic CVs…. No WD Signatures in high state From Araujo-Betancor et al but in low state models require 2 WD components Accretion Heated Pole + Bare WD

From Sion 1999, Araujo-Betancor et al 2005; Urban & Sion 2006; Sion et al WDs Probe Accretion History WD cooling down to Teff  K in  4Gyr until secondary fills Roche Lobe and mass transfer starts WDs reheated due to accretion compressional heating WD Teff systematically lower in short period systems

Observables From Townsley & Bildstein 2003 using Teff from Winter & Sion 2003 WD Teff can be used to test predictions: Teff 4  dm/dt M WD = 0.6, 1.0, 1.2 M sun M WD = 0.7, 1.0 M sun Mass Accretion rate decreases by 10 below Gap Models overestimate accretion rates at long Porb AML due to G.R. favours high WD masses

MCVs  25% of all CVs against MWDs  10% of all WDs Why MCVs overabundant? Evolution:influence of magnetic fields

Selection effects: MCVs bright sources in X-ray surveys Reduced Magnetic Braking (Lee & Wickramasinghe 1998) Lower accretion rates in MCVs (From HST/STIS Araujo-Betancor et al.2005) -> Longer evolutionary timescales ->Overabundance of MCVs

High field CVs emit cyclotron radiation in optical/nIR In low states Zeeman components might be detected High (B>100MG) can be detected in the UV! Magnetic fields in CVs Twd  20000K Log g=8.0 Bwd  144MG From HST/STIS Gaensicke et al. 2004

What about other WD properties? WD Rotation rates and abundances unknown prior HST Teff=18000K log g=8.5 Metals=1.1sun from HST/STIS E140M Long et al 2004 Vrot=360km/s High resolution UV spectra for 12 systems so far…..

WD Rotation rates: V rot sin i  km/s but Single WDs Vsini<40km/s V rot sin i  % V break  Accreted angular momentum lost in Nova eruptions  Relation with Porb?  L BL  L disc if V rot <0.45V break L BL <<L disc if V rot  V breakup but L x <<L disc for many systems. 2-T WDs in UV would solve BL mistery in some systems. Chemical Composition: Wide range of subsolar and suprasolar abundances Many systems show Carbon, Oxygen, Si  sun but some metals reach high values: e.g.Al  2  Mass transferred from donors not expected  Nova TNRs affect abundances but too large than theory

“Normal” CVs hiding their true face in the UV IUE discovered a few systems with “normal” optical spectra but with anomalous NV/CIV>>1 HST/STIS further increased the number to 12 From HST STIS Gaensicke et al. 2003;

From FUSE Mouchet et al Also in the Far UV…….. FUSE spectra show enhanced NIV/OVI Signature of CNO processed core of evolved secondary suggests TTSMT evolution similar to Super Soft X-ray Sources (Failed SNIa?) Evolutionary TTSMT (Shencker et al. 2003) model predicts 1/3 of CVs have started from companions with M>Mwd No relation with Porb No relation with B RXJ de Martino et al. inprep BD Pav Sion et al. 2008

COS & STIS UV Spectroscopic Capabilities Role of HST/SM4 For Fuv  erg/cm 2 /s/A One orbit (2400sec) Exposure COS/G130M S/N  STIS/E140M S/N  Abundances and Rotational velocities require R  20000

COS/G140L more appropriate to gain resolution Snapshot CV HST/STIS Programme Cycle 11, (withdrawn) (PI: Gaensicke) 70 CVs observed (DNe,NL, Magnetics) over  1000 CVs known to date Many new faint systems: Fuv  1E-15 erg/cm2/s/A

HST/SM4 will re-open spectroscopic access in the UV COS will provide great step ahead to understand Angular Momentum history of WD binaries (CVs, pre-CVs,AM CVn) High sensitivity and higher resolution will allow to: Determine Vrot, Chem.Abundances, Teff, log g, Kwd,B Determine Accretion parameters Prospects for the near future  Improve Teff vs Porb relation (Magnetics, pulsators, long Porb including pre-CVs)  Determine dependency of Rotation rates vs Porb  Address Chemical abundances in a large sample  Constraints on Mwd

New challenge to evolution theory: WD+MS binaries 101 SDSS WD+MS discovered (Rebassas-Mansergas et al. 2007) 18 identified as Post-Common-Envelope Binaries Galex found thousands of WD+MS objects (Bianchi et al. 2007) UV & SDSS colours in “bridge” and evolved star regions (Seibert et al. 2005) Prospects for the near future (ctd) SDSS SDSS UV spectroscopic follow-ups to constrain WD parameters