White Dwarfs in Binary Systems

White Dwarfs in Binary Systems

Tom Marsh

Department of Physics, University of Warwick

Collaborators: Steven Parsons, Madelon Bours, Boris Gansicke, Stelios

Pyrzas, Danny Steeghs, Chris Copperwheat, Vik Dhillon, Stu Littlefair

Tom Marsh, Department of Physics, University of Warwick Slide 1 / 39

White dwarfs in binaries . . .

• the sites of classical nova and Type Ia supernova explosions;

• provide easily-observed examples of accretion, both discs andmagnetically-dominated;

• widened range of white dwarf properties (bulk composition,mass, spin, surface pollution, magnetism);

• precision parameters of white dwarfs and their companions;

• dominant gravitational wave sources for eLISA.


Types & Numbers

Type Number known Total in Galaxy(×106)

Accreting WD+MS (CVs) 3000 2 – 10WD+MS (detached) 2300 100 – 300WD+WD 100 100 – 300

(other combinations possible: WD+RG, WD+sdB, WD+NS, . . . )

Progress:

In 2000 we knew of 4 eclipsing WD+dM stars; we now know 86.


The Rise of White Dwarf Binaries

Progress has been driven byspectroscopic and variabilitysurveys (SDSS, CSS, PTF).

GAIA & LSST will have amajor future impact. e.g.GAIA will find ∼ 300,000 WDswith G < 19 cf ∼ 10,000today.

Number of eclipsers known vs time, upto 2011


Talk Plan

• Precision parameters, white dwarf masses in binaries

• Circumbinary debris, timing & planets

• Recent highlights


Some background on single white dwarfs

Physics of Starkbroadening + opticalspectra → Teff andlog g .

Physics of degeneratematter, evolutionarymodel + Teff and log g→ mass and cooling age

Narrow massdistribution from massloss on AGB. Liebert et al (2005)


Growing white dwarfs

A key problem of Type Ia SNmodels is how to ensurelong-term increase of the massof white dwarfs. CVs areusually ruled out because it isbelieved that nova explosionsremove most of the accretedmass.

Through precisionmeasurements we can test thisobservationally.


Evolution of CVs

Mass transfer implies ashortening orbital period. Ifwhite dwarf masses grow ordecrease with time, expect astratification of white dwarfmass with period.

Due to nova explosions,expect mass to decrease alongwith the period

Only become testable in pastfew years from new systemsfrom the SDSS.

Orbital period distribution of CVs


Measuring the masses of CV components

(Work of the 1980s by Wood, Horne, Smak, Cook, Warner)


Only widely applicableafter SDSS & CRTSdiscoveries.

Light curve modelling ⇒MW , MR and TW

Savoury et al (2011)

Typical cadence 2 – 6 sec,g = 17 – 20. Requires 3– 8 m aperture telescopes& repeat observations tobeat flickering.












Masses of white dwarfs in CVs

No clear evidence forstratification with period,but CV white dwarfs aremassive cf isolated whitedwarfs.

[NB. WDs in CVs tendonly to be easily seen atthe short period end, somany of these may haveevolved from longerperiods where M ishigher.] Savoury et al (2011)


1.1M� white dwarf in the system IP Peg

−0.1 0.1

Re

sid

ua

ls

−0.1 0.1−0.1 0.1

−0.12 −0.10 −0.08 −0.06 −0.04 −0.02 0.00 0.02 0.04 0.06

Phase

White dwarf

Accretion disc

Bright spot

0.5

1

1.5

2

2.5

3

3.5

4

mJy

Copperwheat et al (2010): massive white dwarf is small andeclipsed in just 10 seconds.


The problem of CV white dwarf masses

The high-masses of thewhite dwarfs in CVs arehugely problematic.

Could they be high frombirth due to evolutionaryeffects?

Why are there no lowmass He white dwarfs,which are expected inabundance? −→

Test with detached“pre-CVs”.

Politano (1996), predicted white dwarfmass distribution in CVs at birth. Those on

the left are He white dwarfs.


Detached WD+MS systems

Simple systems withspectra which are acombination of whitedwarfs and M dwarfs.

Around 2300 now known,mostly from SDSS, with86+ eclipsers.

Pyrzas et al (2009), spectra of 4 eclipsingWD/dM systems.


Detached eclipsers

Eclipsing WD+dMbinaries enable exquisitemeasurements(VLT+ULTRACAM here)

Parsons et al (2010a), GK Vir, a hot WD+ 0.1M� dM eclipser.


Detached eclipsers

In the best cases,complete solution ofMW , RW , MR , RR and iis possible. e.g NN Ser

MW = 0.535± 0.013M�

RW = 0.0211± 0.002R�

MR = 0.111± 0.004M�

RR = 0.149± 0.002R�

i = 89.6◦ ± 0.2.

Parsons et al (2010b), NN Ser.


White Dwarf mass: CVs vs pre-CVs

The masses of WDs in pre-CVs (andrelated post-CE binaries) are notsystematically large.

The CV white dwarf mass problemremains. Hard to avoid conclusionthat white dwarf masses in CVs doin fact grow with time.

Zorotovic et al. (2011)


Side product I. brown dwarf donor stars

Nice side-products areprecise masses of themass donors.

These are close topredictions of binaryevolution models, andconstrain the long-termangular momentum lossrate.



Side product II. Electron degeneracy EoS

The best mass–radius measurementstest structure models of whitedwarfs and very low mass stars (and,potentially, brown dwarfs).

Parsons et al (2010b)


Side product III. Ancient systems

Starting to find systems withcool, very old white dwarfs.

In the system on the right, afeeble star of just 0.13M�outshines its “white” dwarfcompanion.

With T ≈ 3600 K, the latterhas been cooling for 9.5 Gyr

Such white dwarfs are hardto characterise when isolated. Parsons et al (2013)


Talk Plan





White dwarf debris disks

The existence of debris disksaround some single white dwarfsis now well-established.

Signatures: pollutedatmospheres; emission lines fromaccretion disks; excess IR fluxfrom dust.

Thought to be asteroidal incomposition, and to imply thepresence of planetary perturbers.

Metal (Mg) pollution and accretiondisc emission (CaII) of the single

white dwarf SDSS1228+1040(Gansicke et al 2006).


White dwarf debris disks

The existence of debris disksaround some single white dwarfsis now well-established.

Signatures: pollutedatmospheres; emission lines fromaccretion disks; excess IR fluxfrom dust.

Thought to be asteroidal incomposition, and to imply thepresence of planetary perturbers.

IR dust emission from the debris diskaround SDSS1228+1040(Brinkworth et al 2009).


Circumbinary debris?

Similar evidence for debrisdisks around white dwarfbinary stars has been largelyunconvincing as it isvulnerable to intrinsic binaryeffects.

Witness the case of SDSSJ0303+0054, a P = 3.2 h,WD+dM eclipser.

Apparent debris disk emission aroundthe WD+dM binary SDSS0303+0054

(Debes et al 2012)


SDSS0303+0054: optical eclipse

The system is opticallyindistinguishable from otherWD+MS eclipsers, soaccretion does not appear atfirst sight to be responsiblefor the IR excess.

Eclipse of the white dwarf in SDSS g’(WHT+ULTRACAM), (Parsons et al

2013).


SDSS0303+0054: near infrared eclipse

However, the NIR (KS)eclipse of the white dwarfshows that the IR excesscomes from concentratedspots of emission on thewhite dwarf.

=⇒ cyclotron emission frommagnetic poles accretingfrom the M star companion’swind.

. . . not circumbinary debris.

Eclipse of the white dwarf in KS

(VLT+HAWKI), (Parsons et al 2013).


Circumbinary planets via timingEclipsers enable precise period

measurement. Potential todirectly measure angularmomentum loss (gravitationalradiation, magnetic braking).

A steady rate of period changeP alters the times of eclipse by aquadratic function of time

∆t =1

2

P

Pt2.

In practice, rather erraticvariations always seem to be therule. −→


Circumbinary planets via timingEclipsers enable precise period

measurement. Potential todirectly measure angularmomentum loss (gravitationalradiation, magnetic braking).

A steady rate of period changeP alters the times of eclipse by aquadratic function of time

∆t =1

2

P

Pt2.

In practice, rather erraticvariations always seem to be therule. −→

Period changes in WD/dM systemQS Vir, O’Donoghue et al (2003)


Applegate’s Mechanism

Applegate (1992) suggestedthat such variations are drivenby variations in the quadrupolemoment of the MS star drivenby internal angular momentumexchange.

No angular momentum is lost inthe process; it is not a driver ofevolution.

Applegate’s mechanism doesrequire energy however.

Variations in quadrupole momentchange the gravitational attraction

between the stars


Perturbation by “third” bodies

Unseen object

Unseen object

different time Eclipse arrival time

delayed or advanced


Stress-testing Applegate

Some systems show too large aperiod change for Applegate’smechanism to work.

Here the eclipses in QS Vir areseen to arrive ∼ 200 sec earlierthan expected from O’Donoghueet al.’s data.

Seems certain that there is a “thirdbody” orbiting the binary, in thiscase a brown dwarf

Last 3 O’Donoghue

times

QS Vir, Parsons et al (2010)


Two planets around NN Ser

The M dwarf in the 3.1 h binaryNN Serpentis is so feeble, that itdoes not even have the oomphto drive its much smaller timingchanges via Applegate.

Instead, two planets, withmasses of 6.9 and and 2.2MJ in15.5 and 7.7 yr orbits provide anexcellent fit.

. . . but is this just a visit fromMr G. Ive-Me-Enough-Free-Parameters-And I-Will-Fit-Anything?

Two planet fit to NN Ser times,Beuermann et al (2010)


Extrapolating NN Ser . . .

Last 10 years of data from Beuermann et al (2010)



Last 10 years of data plus MCMC sample of possible orbits.



. . . with 2 years of new data


Up to May 2014, expanded scale

First successful prediction of eclipse times based upon planetaryorbit model (Marsh et al 2014)


Talk Plan





NLTT 11748, first eclipsing double white dwarf

A 0.2M� and 0.7M� pair of whitedwarfs in a 5.6-hour, i = 89.9◦ orbit.

6% and 3% deep eclipses.

Steinfadt et al. (2010), Kaplan et al.(2014)


CSS 41177, second known DWD eclipser

0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 0.0035+5.5943994e4

0.8

0.9

1.0

1.1

1.2

1.3

1.4

40% & 10% deep eclipses, lasting 2 minutes. Two ∼ 0.3M�helium white dwarfs, P = 2.8 hour orbit.

Parsons et al (2011), Bours et al (2014)Tom Marsh, Department of Physics, University of Warwick Slide 35 / 39

SDSS J0651+2844, fourth DWD eclipser

Brown et al. (2011) discovereda remarkable P = 12.7 minuteeclipsing DWD.

GWR-driven decay detectedafter a little more than one year:one of the two best eLISA“calibrators” known.

Hermes et al. (2012)


New data, new effects: beaming & lensing

KPD 1946+4340 is an WD+sdBbinary. Component stars are radiativeand stable.

Kepler data show eclipses and ellipsoidalmodulation, but also Doppler beamingand gravitational lensing (althoughdegenerate with other parameters).

Bloemen et al (2010)


Indisputable lensing

KOI-3278 shows apparenttransits of an Earth-sized object,once every P = 88 days, raisingthe interest of planet hunters.

In fact, the dips are eclipses of a0.63M� white dwarf whichhalf-a-cycle later lenses itscompanion G star.

Kruse & Agol (2014)


Conclusions

• Large surveys have hugely increased the number of whitedwarf binaries known.

• Many new eclipsers discovered leading to high-precisionparameters.

• The white dwarf masses in CVs emerging from this are inserious discord with theory.

• Some detached systems show timing anomalies which appearto imply circum-binary planets.

• High-quality data are revealing white dwarfs in hard-to-findlocations and subtle new physical effects.


SDSS0303+0054: Zeeman-split line emission

The system provides thesecond-known example ofZeeman-split line emissionfrom a white dwarf.

This leads to a surface fieldof B ∼ 8 MG. This ismoderately strong by whitedwarf standards. The systemis a likely progenitor of the.“intermediate polar” class ofCVs.

. . . but no debris disk.

Parsons et al (2013)


Common envelope efficiency

Most post-CE WD+MSbinaries have orbital periodsshort of one day.

These can be matched withcommon envelope efficiencyαCE = 0.2 – 0.3 (Zorotovicet al. 2010)

Periods from Ritter & Kolb


Documents

White Dwarfs in Binary Systems