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School of Physics amp Astronoy Cataclysmic Variables 10 Breakthroughs in 10 Years P Marenfeld and NOAOAURANSF Christian Knigge University of Southampton University of Southampton School of Physics amp Astronoy ID: 177171

amp cvs university physics cvs amp physics university astronoy southamptonschool evolution period dwarf accretion breakthrough nova gap knigge xrbs 2006 gcs 2011

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Slide1

University of SouthamptonSchool of Physics & Astronoy

Cataclysmic

Variables:10 Breakthroughs in 10 Years

P. Marenfeld and NOAO/AURA/NSF

Christian

Knigge

University of SouthamptonSlide2

University of SouthamptonSchool of Physics & Astronoy

Outline

IntroductionCataclysmic variables: a primer10 breakthroughs in 10 years

(a personal and hugely biased perspective...)

Evolution

Accretion

Outflows

The Role of UV AstronomySummary

35 minutes

9 8 7 6 5 4 3 2 1

XX XXXXX

Links to Other Systems

(BH/NS LMXBs)Slide3

University of SouthamptonSchool of Physics & Astronoy

Cataclysmic Variables: A PrimerThe Physical Structure of CVs

White Dwarf

Accretion Disk

Red Dwarf

White dwarf

primary

UV bright

“Main-sequence”

secondary

75 mins < Porb

< 6 hrs Roche-lobe overflow Accretion usually via a diskUV-bright

Disk accretion is unstable if below critical rate

dwarf novae

Mass transfer and evolution driven by angular momentum

loss

Evolution is (initially) from long to short periods

Credit: Rob HynesSlide4

University of SouthamptonSchool of Physics & Astronoy

Cataclysmic Variables: A Primer

The Orbital Period Distribution and the Standard Model of CV EvolutionClear “Period Gap” between 2-3 hrs

Suggests a change in the dominant angular momentum loss mechanism:

Above the gap:

Magnetic Braking

Fast AML

 High

Below the gap:

Gravitational RadiationSlow AML  Low Minimum period at Pmin ≈ 80 mindonor transitions from MS

 BD

beyond this, Porb increases again This disrupted magnetic braking scenario is the standard model for CV evolution

 

Knigge 2006Slide5

Breakthrough I: Evolution

Disrupted Angular Momentum Loss at the Period Gap

Standard model predictionThe period gap is caused by a disruption in AML when the donor becomes fully convectiveMagnetic braking drives high above the gap

Donor is slightly out of TE and thus oversizedAt , donor becomes fully convectiveMB ceases (or is severely reduced)

drops

--> d

onor relaxes (shrinks) to TE radius

Donor loses contact with RLCV evolves through gap as detached binaryResidual AML (e.g. GR) shrinks orbit (and RL)

Contact with donor re-established at Observational reality pre-2005

No direct empirical support for this picture (other than the existence of the gap itself)University of SouthamptonSchool of Physics & AstronoyHowell et al. 2001Slide6

University of SouthamptonSchool of Physics & Astronoy

Patterson et al. (2005),

Knigge (2006)

Donors are significantly larger than MS stars both above and below the gap

Clear discontinuity at M

2

= 0.20 M

☼, separating long- and short-period CVs!Direct evidence for disrupted angular momentum loss!

M-R relation based on eclipsing and “

superhumping” CVs Breakthrough I: EvolutionDisrupted Angular Momentum Loss at the Period GapSlide7

University of Southampton

School of Physics & Astronoy

We can even use the donor

relation to quantitatively reconstruct CV evolution

CV Donors are significantly larger than MS stars because they are bloated by mass loss

Higher

Larger

So we can use the

degree of donor bloating at given to infer

Above the gap: slightly reduced “standard” MB recipes work well

Below the gap: need enhanced AML,

 significant revision of the standard model!

 

Breakthrough II: Evolution

Reconstructing CV Evolution Empirically

Knigge

(2006)

Knigge

,

Baraffe

&

Patterson (2011)Slide8

Breakthrough III: Evolution

Period Bouncers with Brown Dwarf Secondaries

Standard model predictions 99% of CVs should be found below the period gapA full 70% should be “period bouncers” with brown dwarf secondaries

Observational reality pre-2006

Not a single definitive period bouncer

Only ~10 candidates out of ~1000 CVs

No secondary with a well-established mass below the H-burning limit

Is this a selection effect or model failure?

University of Southampton

School of Physics & AstronoyHowell et al. 2001Slide9

Breakthrough III: Evolution

Period Bouncers with Brown Dwarf Secondaries

SDSS has yielded a deep new sample of ~200 CVs (Szkody et al. 2002-9)......including a sub-set of faint, WD-dominated systems near P

min (Gaensicke et al. 2009; see later)

A few of these are eclipsing, allowing precise system parameter determinations

At least 3 of these have M

2

< 0.072 M☼

(Littlefair et al. 2006, 2008)

At least some post-period-minimum systems with brown dwarf donors do exist!But one of them is very strange…University of SouthamptonSchool of Physics & AstronoyLittlefair et al. 2006, Science, 314, 1578Slide10

Stehle

et al. (1999)

Breakthrough III: Evolution

Period Bouncers with Brown Dwarf

Secondaries

SDSS J1507 is one of the three eclipsing CVs with sub-stellar donors…

but

i

ts

for other CVs

Two ideas:

J1507

is young -- born

with a

sub-stellar donor

(

Littlefair

et al. 2007)

J1507 is a low

metallicity

halo CV

(Patterson et el. 2008)

How can we test which is correct?

UV astronomy to the rescue!

FUV spectroscopy shows that [Fe/H] = -1.2

SDSS J1507 is an eclipsing period bouncer in the Galactic halo!

Rosetta stone for studying e

ffects of

metallicity

on accretion and evolution?

 

University of Southampton

School of Physics & Astronoy

Littlefair

et al. (2007)

Patterson et al. (2008)

Littlefair

et al. (2007)

Uthas

et al. (2011)Slide11

Breakthrough IV: Evolution

The Period Spike at

PminStandard model prediction

The number of CVs found in a particular Porb range is inversely proportional to the speed with which they evolve through it

So there should be a spike at

P

min

, in the period distribution since

Observational reality pre-2009No convincing spike anywhere near Pmin

in the CV Porb distributionUniversity of SouthamptonSchool of Physics & AstronoyBarker & Kolb 2003Slide12

Previously known CVs

SDSS CVs

Breakthrough IV: Evolution

The Period Spike at

P

min

Boris

Gaensicke

and collaborators have obtained orbital periods for most of the new SDSS CVs

The resulting period distribution does show a spike at Pmin for the first time (Gaensicke et al. 2009)CVs do in fact “bounce” at Pmin!

University of Southampton

School of Physics & AstronoyGaensicke et al. 2009Slide13

Breakthrough V: Evolution

CVs in Globular Clusters

A typical GC should contain ~100 CVs purely based on its stellar mass content

But

b

right X-ray binaries are overabundant in GCs by ~100x

(Clark 1975, Katz 1975)

New

dynamical

formation channels are available in GCstidal capture (Fabian, Pringle & Rees 1976)3- and 4-body interactionsCould CV numbers also be enhanced?Theory says yes, but “only” by a factor of ~2 (di Stefano & Rappaport 1994, Davies 1995/7,

Ivanova et al. 2006)There should be hundreds of accreting WDs in GCs!

Important and useful:Large samples of CVs at known distancesDrivers and tracers of GC dynamical evolution Are GCs SN Ia factories? (Shara & Hurley 2006)

So where are they?

University of Southampton

School of Physics &

Astronoy

CV

space

density:

(e.g

. Pretorius &

Knigge

2007, 2011)

Effective volume of

MW:

Expected # of

CVs in

MW:

Fraction of MW mass in GCs:

# of GCs

in

MW:

→ expected # of CVs per GC:

3-body exchange encounter

White DwarfSlide14

Breakthrough V: Evolution

CVs in Globular ClustersUniversity of Southampton

School of Physics & Astronoy

Shara

et al. (1996)

Difference Imaging of the Core of 47

Tuc

Early searches typically found only a handful per GC

(e.g.

Shara

et al. 1996,

Bailyn

et al. 1996, Cool et al. 1998)

Are CVs not formed or maybe even destroyed in CVs?

Significant implications for GC dynamics!

Selection effects?

Survey depth?

Dwarf nova duty cycle?

X-rays would be a great way to find CVs in GCs

But this used to be really hard!

Chandra has revolutionized the field

Deep X-ray surveys typically find tens per cluster

Numbers scale with collision rate

 dynamical formation matters!

GCs do

harbour

significant populations of dynamically-formed CVs!

47

Tuc

with the ROSAT HRI

(

Hasinger

et al. 1994)

Shara

et al. (1996)

Pooley

& Hut (2006)

47

Tuc

with Chandra

(

Grindlay

et al. 2001;

Heinke

et al. 2005)

47

Tuc

with Chandra

(

Grindlay

et al. 2001;

Heinke

et al. 2005) Slide15

UV astronomy has also played a key role

Efficient way of finding new CVs and confirming X-ray-selected candidates

(

Knigge

et al. 2002,

Dieball

et al. 2005, 2009, 2010, Thomson et al. 2012)

Even

slitless

multi-object spectroscopic identification/confirmation is possible!Still many key unsolved questions!Are there enough CVs in GCs?Are they different from field CVs?Where are the double WDs? Are there SN Ia progenitors?

The core of 47

Tuc

: U-band

The core of 47

Tuc

: FUV (~1500A)

University of Southampton

School of Physics &

Astronoy

Knigge

et al (2002, 2003, 2008)

Breakthrough V: Evolution

CVs in Globular ClustersSlide16

Dwarf nova eruption (optical): SS

Cyg

Wheatley et al (2003)

X-ray transient outburst (X-ray): GX 339

Gallo et al (2004)

Adapted from Fender,

Belloni

& Gallo 2004

Breakthroughs VI and VII:

Accretion /

OutflowsOutburst Hysteresis and Jets

University of SouthamptonSchool of Physics & AstronoyGallo et al. 2004

GX339: Gallo et al. (2004)

SS

Cyg

:

Koerding

et al. 2008, Science

Both

CVs (dwarf novae) and XRBs (X-ray transients) exhibit

outbursts

Thermal/viscous disk instability

XRBs

Outbursts trace a q-shape in the X-ray hardness

vs

intensity plane

(Fender,

Belloni

& Gallo 2004)

 h

ysteresis

Collimated (radio) jets are seen (almost only) in the hard state

Hard-soft transition produces a powerful jet ejection episode

CVs (pre-2008)

No evidence for collimated jets in any CV

Constraint on theories of jet formation (e.g.

Livio

1999)?

No constraints on outburst hysteresis

Elmar

Koerding

et al. (2008)

Do dwarf novae also execute a q-shaped outburst pattern?

Yes they do!

Best chance to see a powerful jet is during the “hard-to-soft” transition during the rise to a dwarf nova outburst

D

iscovery of the first CV radio jet!Slide17

Both XRBs and CVs often exhibit (quasi-)periodic oscillations on short (~dynamical) time-scales

Origin is poorly understood, but intimately connected to accretion/outflow processes in the innermost disk regions

Key result in XRBs (accreting NSs and BHs):strong correlations between different types of oscillations, especially LKO and HBO

CVs also exhibit two types of oscillations

Is there a direct connection to

LMXBs?s

Yes!

(Warner & Woudt [2002...2010], Mauche [2003])

DNOs : QPOs in CVs ↔ LKOs : HBOs in LMXBsUniversality of accretion physics extends to periodic variabilityModels relying on ultra-strong gravity or B-fields are ruled outUniversity of SouthamptonSchool of Physics & AstronoyBreakthrough

VIII: Accretion

Periodic Variability: Oscillations

Psaltis, Belloni & van der Klis 1999

Warner &

Woudt

2004

NS & BH

LMXBs

26 CVs

DNOs in VW

Hyi

Woudt

& Warner (2002)Slide18

An XRB (

Churazov

et al. 2003)

A CV (Pretorius & Knigge 2007)

University of Southampton

School of Physics & Astronoy

Breakthrough

IX:

Accretion

Non-Periodic Variability: The RMS-Flux Relation

Black Hole XRB (

Uttley & McHardy 2001)Neutron Star XRB (Uttley & McHardy 2001)

AGN (Vaughan et al. 2011)

NGC 4051

(

Seyfert

1)

What about

non-periodic

accretion-induced variability (“flickering”)?

Stochastic variability has been closely studied in XRBs

Key discovery: the

rms

-flux relation

(

Uttley

&

McHardy

2001)

Rules out “additive” models

(e.g. shot-noise)

What about CVs?

Non-trivial to study: variability time-scales are much longer, so need high-cadence, uninterrupted long-term light curves

-->

Kepler

!

CVs also show the

rms

-flux relation!

(

Scaringi

et al. 2011)

Accretion-induced variability is universal!

Key properties shared by supermassive BHs, stellar-mass BHs, NSs and WDs

MV

Lyr

(

Scaringi

et al. 2011)

MV

Lyr

(

Scaringi

et al. 2011)Slide19

Shara

et al. 2007, Nature 446, 159

We all “know” that CVs burn accreted matter explosively

(Fujimoto,

Iben

,

Starrfield

,

Shaviv

, Shara, Townsley, Bildsten, Yaron...)→ Nova Eruptions (typical recurrence time ~10,000 yrs)But all known novae were actually discovered as suchHow can we establish the general link empirically ?

Ejected nova

shells may be detectable for ~1000 yrs!So Shara et al. (2007) searched for resolved nebulae around ordinary CVs in the GALEX imaging archive.......and

disovered

an ancient nova shell around the proto-typical dwarf nova Z Cam

→ o

rdinary CVs do undergo nova eruptions!

Postscript: Chinese astronomers would have disagreed with the classification of Z Cam as an “ordinary CV”...

University of Southampton

School of Physics & Astronoy

r

Breakthrough X: Evolution /

Accretion

/

Outflows

Do all CVs go nova?Slide20

University of SouthamptonSchool of Physics & Astronoy

Summary

The last decade has seen several breakthroughs in our understanding of CVs, many of which were made possible by ultraviolet observations

Evolution

The basic disrupted-angular-momentum-loss picture of CV evolution is correct !

We know how to reconstruct CV evolution from both primary and secondary properties

CVs do exist in significant numbers in GCs

CVs

not discovered as novae can still have nova shells -->

all CVs experience nova eruptionsAccretion, Outflows and Links to Other SystemsCV outbursts exhibit hysteresis (“turtlehead” diagram) – just like XRBs and AGN

CVs can drive radio jets – just like XRBs and AGN

Accretion-induced oscillations in CVs are… – just like those in XRBsStochastic variability in CVs follows an rms-flux relation –

just like XRBs and AGN

The physics of disk accretion is universal

CVs provide excellent, nearby, bright accretion laboratories