Two planets orbiting the post-common
envelope binary NN Serpentis
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
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
Two planets orbiting the post-common
envelope binary NN Serpentis
Exoplanets
• ≤ 500 exoplantes
• Various methods
• Growing number
of planets around
evolved stars
• ≈ 10% in binaries
• Recently: circumbinary planets
Two planets orbiting the post-common
envelope binary NN Serpentis
A school project …
Two planets orbiting the post-common
envelope binary NN Serpentis
NN Serpentis
• PG1550+131 (Wilson et al. 1986)
• Porb = 3.12 hr (Haefner et al. 1989; MCCP)
• VLT imaging, spectroscopy (Haefner et al. 2004)
Haefner et al. 1989
Orbital Parameters
Two planets orbiting the post-common
envelope binary NN Serpentis
Parsons et al. 2010a
a
MWD
Msec
i
= 0.934 R
= 0.535 M
= 0.111 M
= 89.6°
TWD = 57,000 K
D
= 512 pc
Age of WD ~ 106 yr
Eclipse Timing Residuals
Two planets orbiting the post-common
envelope binary NN Serpentis
Qian et al. 2009
MCCP
VLT
Bialkow
UltraCam
Lijiang
P = 7.6 years, a < 3.3 A.U., M = 11 MJupiter
Eclipse Timing Residuals
Two planets orbiting the post-common
envelope binary NN Serpentis
Parsons et al. 2010b
• Planetary solution rejected
• No satisfactory fit with linear
ephemeris
• VLT point suspicious
MCCP
VLT
Bialkow
UltraCam
Lijiang
Two planets orbiting the post-common
envelope binary NN Serpentis
Revisiting the VLT Observations
• Trailed FORS images (Haefner et al. 2004)
1125.7462 secs
(±0.2 secs !)
Two planets orbiting the post-common
envelope binary NN Serpentis
MONET/North Observations
Two planets orbiting the post-common
envelope binary NN Serpentis
Timing Residuals
MCCP
VLT
UltraCam
Bialkow
Lijiang
MONET
Two planets orbiting the post-common
envelope binary NN Serpentis
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
Two planets orbiting the post-common
envelope binary NN Serpentis
McDonald Observations
Two planets orbiting the post-common
envelope binary NN Serpentis
UltraCam Observations
Two planets orbiting the post-common
envelope binary NN Serpentis
Model #1 : 3rd Body
P = 22.6 years, e > 0.65
a = 6.9 A.U., M = 8.4 MJupiter
Two planets orbiting the post-common
envelope binary NN Serpentis
Model #2 : 2 Bodies
Two planets orbiting the post-common
envelope binary NN Serpentis
The 2+2-Body Solutions
• Binary
– Pdot < -10-13 (GR angular momentum loss OK)
• Two stable 2+2 solutions (grid search)
– Pb:Pc
– Reduced 2
≈ 2:1
0.90
≈ 5:2 (±15%)
0.91
0
0
15.50±0.45
5.38±0.20
6.89±0.54
16.73±0.26
5.65±0.06
5.93±0.40
0.20±0.02
7.75±0.35
3.39±0.10
2.24±0.38
0.22±0.02
6.69±0.40
3.07±0.13
1.61±0.27
• NN Ser b
–
–
–
–
eb
Pb [years]
ab [A.U.]
Mb sin i [MJupiter]
• NN Ser c
–
–
–
–
ec
Pc [years]
ac [A.U.]
Mc sin i [MJupiter]
Two planets orbiting the post-common
envelope binary NN Serpentis
Orbital Histories of NN Ser A,B
Red Giant
Envelope
0.7 A.U.
0.9 A.U.
Common
Envelope
Ejection
Two planets orbiting the post-common
envelope binary NN Serpentis
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
Two planets orbiting the post-common
envelope binary NN Serpentis
A Primitive Evolution Simulation
Two planets orbiting the post-common
envelope binary NN Serpentis
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
Two planets orbiting the post-common
envelope binary NN Serpentis
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
Two planets orbiting the post-common
envelope binary NN Serpentis
Common Envelope