1. Extrasolar planet detection: a view from the trenches
Alex Wolszczan
(Penn State)
01/23/06
Collaborators:
A. Niedzielski (TCfA)
M. Konacki (Caltech)

2. Ways to find them…

3. Methods that actually work …
Radial velocity
Pulse timing
Microlensing
Transit photometry

4. Some examples… Neptune-mass planet The transit classic: HD209458
Microlensing planet
A “super-comet” around PSR B ?

5. 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

6. …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:

7. Determining binary orbits…
Collect data: measure Vr’s, TOA’s, P’s
Estimate orbital period, Pb (see below)
Use Vr’s to estimate a1sini, e, T0, Pb,  (use P’s to obtain an “incoherent orbital solution”)
Use TOA’s to derive a “phase-connected” orbital solution

8. 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-1> 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

9. The pulsar planet story…

10. … 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

11. Examples of Vr time series “under construction”

12. 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

13. …and the best orbital solutions
P~340 (e~0.35) appears to be best (lowest rms residual, 2 ~ 1)
This case will probably be resolved in the next 2 months, after >2 years of observations

14. 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