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Evidence for planets orbiting the post-common envelope binary NN Serpentis Stefan Dreizler Institut für Astrophysik Göttingen. Based on Two planets orbiting the recently formed post-common envelope binary NN Serpentis A&A submitted

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Evidence for planets orbiting the post-common envelope binary NN SerpentisStefan DreizlerInstitut für Astrophysik Göttingen

Based on

Two planets orbiting the recently formed post-common envelope binary NN Serpentis

A&A submitted

K. Beuermann1, F. V. Hessman1 , S. Dreizler1, T. R. Marsh2, S.G. Parsons2, D.E. Winget3, G. F. Miller3,

M. R. Schreiber4, W. Kley5, V. S. Dhillon6, S. P. Littlefair6, C.M. Copperwheat2, J. J. Hermes3

1) Göttingen, 2) Warwick, 3) Austin, 4) Valparaiso, 5) Tübingen, 6) Sheffield


Exoplanets
Exoplanets

≤ 500 exoplantes

Various methods

Growing number of planets around evolved stars

≈ 10% in binaries

Recently: circum-binary planets



Nn serpentis
NN Serpentis

Haefner et al. 1989

PG1550+131 (Wilson et al. 1986)

Porb = 3.12 hr (Haefner et al. 1989; MCCP)

VLT imaging, spectroscopy (Haefner et al. 2004)


Orbital parameters parsons et al 2010a
Orbital ParametersParsons et al. 2010a

a = 0.934 R TWD = 57,000 K

MWD = 0.535 M D = 512 pc

Msec = 0.111 M Age of WD ~ 106 yr

i = 89.6°


Eclipse timing residuals qian et al 2009
Eclipse Timing ResidualsQian et al. 2009

MCCP

VLT

Bialkow

UltraCam

Lijiang

P = 7.6 years, a < 3.3 A.U., M = 11 MJupiter


Eclipse timing residuals parsons et al 2010b
Eclipse Timing ResidualsParsons et al. 2010b

MCCP

VLT

Bialkow

UltraCam

Lijiang

Planetary solution rejected

No satisfactory fit with linear ephemeris

VLT point suspicious


Revisiting the vlt observations
Revisiting the VLT Observations

  • Trailed FORS images (Haefner et al. 2004)

1125.7462 secs

(±0.2 secs !)



Timing residuals
Timing Residuals

MCCP

VLT

UltraCam

Bialkow

Lijiang

MONET


What the timing variations are not
What the timing variations are not

  • Not due to complicated eclipse profile

  • Not due to stellar activity

  • Not due to Applegate’s mechanism

    • Spin-orbit coupling due to magnetic cycles and radius changes within the secondary

    • Time scale on decades or longer

    • Needs too much energy (Chen 2009)

  • Not due to apsidal motion

    • Precession of periastron due to tides

    • Amplitude t = Pbin ebin = 3577 s ebin OK with ebin~0.01

    • Variation of the FWHM not seen

    • Period would be ~0.4 years




Model 1 3rd body
Model #1 : 3rd Body

P = 22.6 years, e > 0.65

a = 6.9 A.U., M = 8.4 MJupiter



The 2 2 body solutions
The 2+2-Body Solutions

  • Binary

    • Pdot < -10-13 (GR angular momentum loss OK)

  • Two stable 2+2 solutions (grid search)

    • Pb:Pc ≈ 2:1 ≈ 5:2 (±15%)

    • Reduced 2 0.90 0.91

  • NN Ser b

    • eb 0  0

    • Pb [years] 15.50±0.45 16.73±0.26

    • ab [A.U.] 5.38±0.20 5.65±0.06

    • Mb sin i [MJupiter] 6.89±0.54 5.93±0.40

  • NN Ser c

    • ec 0.20±0.02 0.22±0.02

    • Pc [years] 7.75±0.35 6.69±0.40

    • ac [A.U.] 3.39±0.10 3.07±0.13

    • Mc sin i [MJupiter] 2.24±0.38 1.61±0.27


Orbital histories of nn ser a b
Orbital Histories of NN Ser A,B

0.7 A.U.

0.9 A.U.

Red Giant Envelope

Common Envelope Ejection


Orbital history of nn ser b c
Orbital History of NN Ser b,c

  • Binary Star System

    • ~2.1 Msun A star + M dwarf at ~1 A.U. (CE=0.25)

    • RGB expansion causes CE ejection ~1 million years ago

    • Planets around NN Ser A absorbed

  • 1st Generation (circumbinary):

    • NN Ser b,c at > ~3 A.U.

    • Drift outwards/near escape due to loss of 1.5 M from NN Ser A

    • Differential drift inwards due to frictional drag (gravitational), tidal forces

    • Dynamical evolution stops at radii ~3 & 5-6 A.U. with resonance condition between b & c



Orbital history of nn ser b c1
Orbital History of NN Ser b,c

  • 2nd Generation (circumbinary) :

    • Original planets at a < ~1 A.U. lost in RGB

    • Formation of planets in the metal rich and massive CE with 1.5 M

    • NN Ser b,c come into resonance as very young planets

  • Mixed :

    • Original planets at a < ~1 A.U. lost in RGB

    • Less massive planets at a ~ 2-6 A.U. survive CE and accretes from CE

    • 1st genaration plate might trigger planet formation in CE

    • NN Ser b,c come into resonance as rejuvinated/young planets


Conclusions
Conclusions

  • The task of observing the variations and constraining the origin of the timing variations is very difficult

  • It helps to have lots of access to 1m and occational access to 2-3m telescopes

  • The eclipse time variations in NN Ser A/B are most simply explained as the timing effect due to two massive, circumbinary planets

  • The planets could either be 1st or 2nd generation (or both), depending upon the details of their interaction with the CE and the CE’s long-term evolution

  • Potentially many more circum-binary, post-common envelope planets to come

http://solar-flux.forumandco.com/worlds-f12/edasich-s-work-t337.htm



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