A Triple-Planet System Orbiting Ups Andromedae
A diagram of the orbits of the 3 planets
around Upsilon Andromedae. The red dots mark the
orbits of planets b,c and d. The dashed circles show
the orbits of Mercury, Venus, Earth and Mars
to give the scale of the orbits.
The inner planet was announced by Butler et al. in Jan 1997.
A velocity plot containing a few months of data looks clean
( Fig 1 ), during a few months.
However, a larger duration of velocities reveals additional
velocity variations. Recognizing that the velocity variations
could be due to a second companion, Butler and Marcy immediately
alerted the astronomical community to this possibility.
The second companion appeared to have an orbital period of
about 3.5 years from the long-term excursions of the velocities. These
velocity variations were also found by the AFOE team of Drs. R.Noyes, T.Brown,
S.Korzennik, S.Horner, A.Contos et al.
A Keplerian orbital model was constructed to fit the data. However, the best
solution still left velocity points scattering above and below
the 2-planet theoretical curve. After
subtracting the theoretical velocities that would be produced by
a 2-planet system from the observed velocities, a periodic pattern
was observed in the "residual" velocities, suggesting the possibility
of one more companion. A 3-planet model
was found to produce a dramtically superior fit to the data, reducing the
residual velocities to the expected variations,
with no periodicity in the residuals.
With the orbital solution for 3 planets that fit our observed
velocities, we can subtract the predicted velocities for any one planet,
to reveal the velocities caused by the remaining two planets:
Similarly, by removing two planets, the velocities vs. orbital phase can be viewed
for each companion individually:
Our collaborators on this work are the AFOE team.
Simulated view of Planets around Upsilon Andromedae by Sylvain Korzennik.
The Doppler Evidence for Three Planets:
The measured Velocities for Upsilon Andreomdae are fit with a model containing
three Jupiter-mass companions. The inner planet is subtracted (4.6-day sine wave)
to render more visible the wobble caused by the outer two planets.
"Evidence for Multiple Companions to Upsilon Andromedae ",
,
Submitted to the Astrophysical Journal.
