Non stationary features in light curves of AM CVn and HP Lib

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Non stationary features in light curves of AM CVn
and HP Lib

• Jan-Erik Solheim
• University of Oslo
• Institute of Theoretical Astrophysics

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Content

• The double humped light curve
• Period change
• Harmonics
• Negative superhump or pulsation?
• Nonstationary random processes
• Pulsed superhump or tidal shock
• Active density wave model

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First variability, Feb 4, 1962P 18 min (Double
humped)
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The first P18 min double humped light curve
(Smak 1967a)
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Smak autocorrelation functions gives P
0.0122d 1054s
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B. Paczynski (1967) Prediction of Period
changes for HZ 29 if two equal mass WDs
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Flickering sign of mass transfer
AM CVn CFHT1990
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What is the period 1982-83?
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Decreasing period 1962-83 dP/dt -3.2 10-12ss-1
Not possible if binary orbit for He WDs with mass
transfer!! But as predicted if two non
transferring WDs M2/M1 lt 0.1 (Paczynski 1967)
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No sign of a 1051s period but 1011.4s and 525.5 s
First FT of data 1982/83
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The Period Controversy
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WET campaign 1990 (XCov4)
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WET campaign 1990 (XCov4)
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P525.5s becomes a triplet with equal frequency
spacing (XCov4)
Other harmonics also showed equal frequency
splitting of 21 µHz or a periode of 13.3 hrs
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The 1050s region
periods 1050 1028 1011
957 s
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1903 µHz variations (XCov4)
P 525.6
519.9 514.3
s
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AM CVn XCov4
?- O ? ? N
All peaks from 3 periods
? orbit O disc precession (apsidal advance)
NNodal regression or f2 pulsation?
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AM CVn 1990 Harmonics and sidebands
The fundamental frequency f0 is not observed
Splitting 21µHz? 13.23h
1028s1011s
h5
h1
h2
h3
h4
f0
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Average pulse shape XCov4
Positive superhump
POrbit
Negative superhump Or pulsation
Second harmonic
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The amplitude of the first harmonics (525.5s) is
modulated with period 13.4 hours
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A simple modelstationary disc withtwo armed
spiral structure and an accreting WD in a hole
and a cold irradiatedsecondary A
Solheim et al 1998
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Disc AM CVns all have harmonics
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AM CVn Photometry 1978-92

• Three independent frequencies
• 1902.5µHz (525.6s)
• 988.7 µHz (1011.5s)
• 972.3µHz (1028.5s)
• Harmonics of a fundamental frequency 951 µHz
• Variable amplitudes

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HP Lib much more stable
Po1117s harmonics
1998 photometry
3 sucessive nights, Kazakstan
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Why do we see harmonics ?

• NON-Cicular shape
• of disc with spiral arms
• Harmonics of superhump frequency
• Higher amplitudes at higher angles
• Mixed with harmonics of orbital period at exteme
  angels

0
85
30
60
90
75
Wood Simpson 1995
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P1011 Negative Superhump or pulsation?

• Negative superhump (JP)
• Geometrical effect disc warp regress with a
  periode of 16.7 hrs
• Why?
• No colours
• Pulsation on the accreting white dwarf
• DB or Pg 1159 type pulsator
• Pulsation is a response to the orbital tidal
  force
• May show chromatic effect
• Light from the WD or reflected from disc?

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The 1011s period varies with time
Optical region
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Colour variations and the amplitude ratio
diagram for pulsations of l 0, 1, 2
Simon Jeffery 2005
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Hubble spectroscopy of AM CVn
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AM CVn Lightcurve 1450-1550Å
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A hopeless FT
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The light curve with 4 peaks subtracted
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Result Strongest Peak 1011spulsation or
negative superhump?
?
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There is something more in the light curve of AM
CVns than stable structures A nonstationary
contribution
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A search for non stationary random processes in
light curves of AM CVn and HP Lib

• Wavelet analysis

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Wavelet analysis (Morlet order 6)
HP Lib 19
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fo 1117 s
HP Lib 19
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HP Lib 21
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HP 21
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WET campaign 1990 (XCov4)
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AM R13D
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R13D Pulse Train
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AM R17C Pulse Train
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AM R17C
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R17C Pulse Train
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R18B Strong pulse train
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R13C
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28C Low high whistles?
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R09B
superhump signal turned offf
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Active Density Wave (DW) Model

• Intereaction between the 2 armed spiral wave and
  the disc
• Areas with supersonic shocks
• First harmonic
• Combination of tidal stress and shock
• Pulses because the DW dissipate after a few
  cycles
• The double hump structure in lc disappears
• Second harmonic
• Active density wave at higher angles
• Spriral arm seen 3 times per superhump period
• Disc change from circular to elliptical (spiral
  arms shorten)
• Coupling or non linear behaviour (Non stationary)

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Interpretation of the burst of the
harmonicSpiral shocks at certain orbital phases
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Conclusions for AM CVn

• Period variation before 1982 explained by cycle
  count errors
• Harmonics related to superhump period
• P1011s is stronger in UV ? pulsation or
  negagtive superhump?
• Tidal shocks are related to the superhump period
  come in groups
• Nontstationary random processes and inhomogenous
  random fields must be investigated (in progress)