RE: starship-design: Stars_within_16_light_years_of_the_Sun

["L. Parker" <lparker@cacaphony.net>]

Zenon, I found this while browsing from one of the links that you sent:

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Date: Fri, 10 May 1996 17:20:01 +0002

From: Jean.Schneider@obspm.fr

Subject: possible planet in Lalande 21185

To: exoplanets@gag.observ-gr.fr

Message-Id: <01I4JRB7UTV60011GX@MESIOB.OBSPM.FR>






Lalande 21185
George Gatewood


We report the detection of accelerations in the astrometric
motion of Lalande 21185 that indicate the presence of a planetary
system. The clearest indication is an excess in the apparent
perspective acceleration of the star, detected at two wavelengths
in the data gathered with two independent telescopic optical
systems and with detectors of two different types. Superimposed
upon this multidecade effect are possibly two shorter term
perturbations each near the detection sensitivity of the system
with which it is espied. Alone, either of the latter effects
would simply result in an increased rate of observation, but some
evidence of each effect is detected in the signal of the other
astrometric instrumentation and neither seems to explain the long
term acceleration. An initial pass to the data indicates that
the disturbing masses would usually be more than 0.8 arcsec from
this frequently observed star. Thus companions of significant
luminosity are effectively ruled out. The approximate nature of
a relatively short period component is suggested by data
obtained, over the last 8.5 years, with the University of
Pittsburgh Multichannel Astrometric Photometer (MAP). We find: a
low eccentricity orbit, a period of approximately 5.8 yrs, a
semimajor axis of 0.0022 arcsec, and a probable mass of 0.9 times
that of Jupiter. Residuals from this orbital analysis, and from
data obtained from the Allegheny Observatory's plate series,
indicate the presence of at least one additional component, but
its exact nature is unclear. A possible solution involves a
second companion with a period of approximately 30 years, however
the period is not well established and the residuals to this
solution also indicate a remaining acceleration. The source of
the latter may be a substantial underestimation of the period of
the second mass or it may indicate the presence of a yet longer
period 3rd planetary body.

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I know there have been lots of planets "found" lately, but this one is practically next door - Lalande is only a little over 8 light years away!

Lee Parker

Long experience has taught me not to believe in the limitations indicated by purely theoretical considerations. These - as we well know - are based on insufficient knowledge of all the relevant factors." 

Guglielmo Marconi