Extrasolar planet detection: a view from the trenches

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Extrasolar planet detection a view from the
trenches

• Alex Wolszczan
• (Penn State)
• 01/23/06
• Collaborators
• A. Niedzielski (TCfA)
• M. Konacki (Caltech)

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Ways to find them
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Methods that actually work
Pulse timing
Radial velocity
Microlensing
Transit photometry
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Some examples
Neptune-mass planet
The transit classic HD209458
A super-comet around PSR B125712?
Microlensing planet
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Orbits from Vr measurements

• Observations are given in the form of a time
  series, Vr(i),
• at epochs t(i), i 1,,n

• A transition from t(i) to ?(i) is accomplished
  in two steps

Equation for eccentric anomaly, E

• From the fit (least squares, etc.), one
  determines parameters
• K, e, ?, T, P

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and from pulsar timing

• In phase-connected timing, one models pulse phase
  in terms of spin frequency and its derivatives
  and tries to keep pulse count starting at t0
• A predicted time-of-arrival (TOA) of a pulse at
  the Solar System barycenter depends on a number
  of factors

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Determining binary orbits

• Collect data measure Vrs, TOAs, Ps
• Estimate orbital period, Pb (see below)
• Use Vrs to estimate a1sini, e, T0, Pb, ? (use
  Ps to obtain an incoherent orbital solution)
• Use TOAs to derive a phase-connected orbital
  solution

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Figuring out the orbital period

• Go Lomb-Scargle! If in doubt, try this procedure
  (borrowed from Joe Taylor)
• Get the best and most complete time series of
  your observable (the hardest part)
• Define the shortest reasonable Pb for your data
  set
• Compute orbital phases, ?I mod(ti/Pb,1.0)
• Sort (Pi, ti, ?I) in order of increasing ?
• Compute s2 ?(Pj-Pj-1)2 ignoring terms for which
  ?j- ?j-1gt 0.1
• Increment Pb 1/Pb-0.1/(tmax-tmin)-1
• Repeat these steps until an acceptable Pb has
  been reached
• Choose Pb for the smallest value of s2

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The pulsar planet story
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and the latest puzzle to play with

• Timing (TOA) residuals at 430 MHz show a 3.7-yr
  periodicity with a 10 µs amplitude
• At 1400 MHz, this periodicity has become evident
  in late 2003, with a 2 µs amplitude
• Two-frequency timing can be used to calculate
  line-of-sight electron column density (DM)
  variations, using the cold plasma dispersion law.
  The data show a typical long-term, interstellar
  trend in DM, with the superimposed low-amplitude
  variations
• By definition, these variations perfectly
  correlate with the timing residual variations in
  (a)
• Because a dispersive delay scales as ?2,
  the observed periodic TOA variations are most
  likely a superposition of a variable propagation
  delay and the effect of a Keplerian motion of a
  very low-mass body

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Examples of Vr time series under construction
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One of the promising candidates

• Periods from time domain search 118, 355 days
• Periods from periodogram 120, 400 days
• Periods from simplex search 118, 340, also 450
  days

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and the best orbital solutions

• P340 (e0.35) appears to be best (lowest rms
  residual, ?2 1)
• This case will probably be resolved in the next 2
  months, after gt2 years of observations

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Summary

• Given a time series of your observable
• Sought a stable orbital solution to get orbital
  parameters and planet characteristics
• Question astrophysical viability of the model
  (e.g. stellar activity, neutron star seismology,
  fake transit events by background stars)
• Future new challenges with the advent of
  high-precision astrometry from ground and space
  and planet imaging in more distant future