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 MechanismsRole of Novae in evolutionNon-standard paths

Close Binary Evolution: CVs as test cases

Properties:WDs in CBs vs single WDs

Accretion and outflow processesMass, Temperature, Abundances,

Rotation rate, Magnetism

Rates, kinematics, energeticsEffects 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 be @ Porb<2hr!

Pmin(obs) 80min > Pmin(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 opticalbut

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:

Butsometimes Disc+WD & 2-T WDs do the job (Sion et

al.2008) TT Crt HST/STIS/G140L Teff=30000Klog g=8.7Mdot=3E-11 Msun/yr from Sion et al.

2008i=60deg

V436 Cen DA WD (32%) + DISC (68%)Teff=24000Klog g=8.3Mdot=8E-11 Msun/yr from IUE Urban & Sion 2006i=18deg

….& in Magnetic CVs….

No WD Signatures in high state

From Araujo-Betancor et al. 2005

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. 2008

WDs Probe Accretion History

WD cooling down to Teff4500-5000K 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: Teff4 dm/dt

MWD = 0.6, 1.0, 1.2 Msun MWD = 0.7, 1.0 Msun

Mass Accretion rate decreases by 10 below Gap Models overestimate accretion rates at long Porb AML due to G.R. favours high WD masses

MCVs25% of all CVs against MWDs10% 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

Twd20000K Log g=8.0 Bwd144MG From HST/STIS Gaensicke et al. 2004

What about other WD properties?

WD Rotation rates and abundances unknown prior HST

Teff=18000Klog g=8.5Metals=1.1sun from HST/STIS E140M Long et al

2004Vrot=360km/s

High resolution UV spectra for12 systems so far…..

WD Rotation rates:

Vrotsin i 40-1200 km/s but Single WDs Vsini<40km/s

Vrotsin i 0.7-20% Vbreak Accreted angular momentum lost in Nova eruptions

Relation with Porb? LBLLdisc if Vrot<0.45Vbreak LBL<<Ldisc if VrotVbreakup

but Lx <<Ldisc 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 0.3-

0.5sun 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. 2003

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 PorbNo relation with B

RXJ0625+73 de Martino et al. inprep

BD Pav Sion et al. 2008

COS & STIS UV Spectroscopic Capabilities

Role of HST/SM4

For Fuv10-14 erg/cm2/s/A One orbit (2400sec) Exposure

COS/G130MS/N10-14

STIS/E140MS/N1.5-2.1

Abundances and Rotational velocities require R20000

COS/G140L more appropriate to gain resolution

Snapshot CV HST/STIS Programme

Cycle 11, 12 13 (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,BDetermine 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 binaries101 SDSS WD+MS discovered (Rebassas-Mansergas et al. 2007)18 identified as Post-Common-Envelope BinariesGalex 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)

SDSS005208-0051SDSS005457-0025

UV spectroscopic follow-ups to constrain WD parameters