From: Henry Spencer <henry@zoo.toronto.edu>
Newsgroups: sci.space.tech
Subject: stellar close encounters (was Re: Nemesis - a.k.a. Dark Star)
Date: Tue, 9 Jan 1996 18:10:56 GMT

>>: As I noted, we know of 6 stars coming within 3 ly of Sol in next 1,000,000
>>: years and one of those has a CPA of .29 ly ...
>>Just out of curiosity, what are the stars names, CPA's and time to CPA ???
>The source I have lists only one: K5  DM+61366  CPA  .29ly time 815,000yr

There is a letter in the Nov 1985 JBIS which includes a table of such
encounters.  The four close ones are

DM+62274	1.61LY	478kY
DM+61366	0.29LY	815kY
DM+452014	1.54LY	222kY
DM+253719	1.66LY	176kY

The letter observes that given the very long times involved, there are
quite large uncertainties in the miss distances -- the one-sigma
dispersion ellipsoid is often several LY across for these far-future
encounters -- and additional errors are introduced because differential
galactic rotation was not allowed for.

More important still, though, is that these predictions are based on
current star catalogs (specifically, the Gliese nearby-stars catalog),
and it is quite likely that on this time scale, there would be other
encounters by currently-uncataloged stars.

Better predictions -- both more complete in star coverage and more precise
in trajectories -- should be possible when the Hipparcos star catalogs
appear.  They will be essentially-complete inventories of all nearby
stars, with quite precise positions and velocities.  As I recall, they're
scheduled to appear within a couple of years (as soon as the Hipparcos
data-reduction people get finished pouring their gigabytes of data
through their computers).  There will probably still be a few surprise
encounters with fast stars (like Barnard's Star) that are currently too
far away for cataloging.
-- 
Look, look, see Windows 95.  Buy, lemmings, buy!   |       Henry Spencer
Pay no attention to that cliff ahead...            |   henry@zoo.toronto.edu