Re: One Face Gas Giant confusions

Erik Max Francis (max@xxxxxxxxxxx) writes:
John Park wrote:
Mike Williams (nospam@xxxxxxxxxxxxxxxxxx) writes:
Wasn't it John Park who wrote:

Well we've had decent radial velocity data for over a decade now--good
enough to detect a Jupiter mass in a Jovian orbit, and few candidates
if any have turned up. Indeed relatively few multi-AU, near-circular
orbits have turned up.
We've had radial velocity data good enough to detect Jupiter mass
objects in close orbits for about a decade, but good enough to detect
Jupiter mass objects in Jupiter-like orbits for considerably less than
that.

Are you sure of that? (As I recall, Jupiter produces a reflex velocity in
the Sun of about 15 m/s; I thought detection limits had been in the 3-5 m/s
range for over a decade. Current [ideal] state of the art is close to cm/s
[!!].)

Even if your figures are right (they don't sound like it), that still
misses the point: To detect a planet in orbit, you need to be able to
pull it out of the noise. It's not like if you have a resolution of x,
then you can instantly see everything bigger than x but nothing smaller
than x. It's that x is the present limit for being able to pull the
periodic pattern out of the noise given enough data. The given enough
data is the key; if you're exploring near the resolution, then you need
multiple orbits to be able to have high confidence in the results. So
even though techniques are improving, it still takes time to pick the
patterns out of the data in order to find planets further and further
from their parent star.

(And, as mentioned above, you need data for more than one 12-year
orbit to convincingly demonstrate that it's a planet.)

I think people will report if they can show the orbit is closed, particularly
if they seem to have found a real "Jupiter". (And I'd settle for an 8-year
period.)

No, they're report it when they have statistical significance that
they've found a pattern. That will take multiple orbits if it's on the
limit of detection.

Two examples from a very quick look at the web:

HD160691 e

Msini = 1.814 M_J

a = 5.235 AU; P = 4206 days [~11.5 yr]] ; e < 0.1

according to the Geneva site
[http://obswww.unige.ch/~udry/planet/hd160691.html], the residuals to the
fit from three different observatories range from 1.4 to 6.0 m/s


HD154345 b

Msini = 0.947 M_J

a = 4.10 AU; P = 3340 d [9.15 yr]; e = 0.044


Both were reported in 2006.

In other words, we CAN find Jupiters because we found a couple three years
ago.


--John Park
.

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