cataclysmic variables in the uv d.de martino inaf-osservatorio astronomico di capodimonte napoli...
TRANSCRIPT
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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)
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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
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White Dwarf
Late type Star
CATACLYSMIC VARIABLES
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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
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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?
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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
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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
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….& 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
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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
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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
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MCVs25% of all CVs against MWDs10% of all WDs
Why MCVs overabundant?
Evolution:influence of magnetic fields
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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
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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
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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…..
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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
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“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;
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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
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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
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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
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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
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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