Gravitational waves from double whitedwarfs and AM CVn binaries

Gijs NelemansInstitute of Astronomy, Cambridge

Simon Portegies ZwartAmsterdamLev YungelsonMoscowFrank VerbuntUtrecht

Outline

� Introduction: double white dwarfs and AM CVnsystems as GWR sources

� A model for the double white dwarf and AM CVnpopulation and their GWR signal

� New double white dwarf observations, the SPYproject

� New AM CVn observations: short period systems

� Update on LISA sources: resolved double whitedwarf and AM CVn systems

� Conclusions

Gijs Nelemans

Introduction: GWR from binary white dwarfs

� Most stars become white dwarfs and many arepart of (close) binary system

� Theoretical expectation is lots of close double whitedwarfs

� After GWR brings them together, stable mass trans-fer may ensue; AM CVn systems

� Observational problem: they are faint

� Close double white dwarfs and AM CVn systemsare low-frequency gravitational wave sources

� Double white dwarfs are so numerous that theyform an unresolved noise for LISA, most AM CVnsystems are very weak and don’t add to the noise.

Gijs Nelemans

A model for the double white dwarf andAM CVn population and their GWR signal

� Population synthesis for double white dwarfs andAM CVn systemsNelemans et al. 2001, A&A, 365, 491 and 368, 939

� Large uncertainty for AM CVn systems: direct im-pact accretion for initial phases mass transfer

� Limited comparison to observations: reasonableagreement

� Model for the Galactic distribution of stars

� Gravitational waves from (all) compact binariesNelemans et al. 2001, A&A, 375, 890

Gijs Nelemans

from Marsh & Steeghs 2002, MNRAS, 331, L7

‘‘Observable’’ double w

hite dwarf population

Nelemans, Yungelson, Portegies Zwart, Verbunt 2001, A&A, 365, 491

GW

R signal of G

alactic double white dw

arfs

Nelemans, Yungelson, Portegies Zwart, 2001, A&A, 375, 890

New double white dwarf observations,the SPY project

� � 15 were known

� ESO VLT survey of � 1500 white dwarfs for radialvelocity variations (PI Napiwotzki)

� Current status:

– Surveyed 497 white dwarfs

– 94 with radial velocity variations� 80 with white dwarf companion� 14 with main sequence companion

– 9 double lined systems (see both white dwarfs)

– 5 already have period determinationsbetween 0.3 and 1.5 d

Gijs Nelemans

HE

1414-0848 P =

0.52 d

Napiwotzki, Koester, Nelemans et al., 2002, A&A, 378, 957

New AM CVn observations:short period systems

� Three new (possible) AM CVn systems(7 were known)

� V407 Vul (RX J1914.4+2456)

– P = 9.5 min, X-ray source,“No lines” spectrumDirect impact?Cropper et al. 1998, Ramsay et al. 2002, Mash & Steeghs 2002

� KUV 01584-0939

– P = 10.3 min, previously classified as Cata-clysmic VariableWarner & Woudt, 2002

� RX J0806.3+1527

– P = 5.3 min, X-ray source,He(+H?) emission line spectrumDirect impact?Israel et al. 2002, Ramsay et al. 2002

Gijs Nelemans

Israel et al. 2002, A&A, 386, L13

Update on LISA sources: resolved doublewhite dwarfs and AM CVn systems

� AM CVns do not contribute (much) to confusionlimited noise

� However, many AM CVn systems might be re-solved.

� Point mass approximation?

� Resolved systems:

Type resolved systems(wd, wd) 7171�wd, wd) 14225

(ns, wd) 19(ns, ns) 3(bh, wd) 0(bh, ns) 0total 21421

Gijs Nelemans

HP LibAM CVn

V407 VulKUV 01584

RX J0806

Resolved double w

hite dwarfs and A

M C

Vns

Nelemans et al. in preparation

Conclusions

� Models of double white dwarf and AM CVn popu-lation agree qualitatively with observations

� New observations will lead to quantitative test ofmodels

� New short period AM CVn systems are “guaran-teed” LISA sources

� LISA will resolve thousands of double white dwarfsand AM CVn systems and a few neutron star sys-tems

Gijs Nelemans