Recently I found a machine-readable copy of the data from the Royal
Observatory Catalog of Stars within 25 Parsecs and have been
massaging the data to allow for a Traveller:2300 like universe's
trade routes to be generated automatically. I have not had the time
to firm up my findings, but I have the raw data to look at and
comment on relative star densities and so forth.
Please bear in mind that parallaxes (distances) are very imprecise
beyond a range of 5-10 parsecs or so; 10% error in distance is
considered 'good' in this catalog.
The spectral type classifications started as observations of the
spectra themselves. They initially had no linking to anything that
we care about, such as brightness, which is why they appear to be in
no particular order. The numbers assigned as subclassifications,
rather than being a consistent scale wherein an O9 was close to a
B0, were judgements of the relative strengths of specific spectral
lines within that category. The I-VI 'size' descriptions started
out as a notation of the overall strength of the spectral lines --
the deeper they are the higher the number. The VI classification
was used rather spottily, and one astronomer's V might be another's
VI. It is only by coincidence (and the leap of faith of Hertzprung
and Russel) that these were linked to stellar size in a meaningful
way.
Of the last three (R, N, and S), they are specific subclasses of M
red dwarfs, which are used spottily. R and N were at one point
subsumed into a class C (carbon stars) by some astronomers because
of the strength of the carbon lines. Current observations have used
the more generic Me (M with strong emission lines) to describe all
three of these classes. It is my understanding that their surface
temperature (color and brighness) are not affected.
Within 25 parsecs there are 2,150 stars tabulated. With regard to
star type, there are 3 class B stars and no class O stars.
Also, binary systems are not _that_ popular -- the 2,150 stars are
grouped into about 1,700 star systems, with a few trinary and
quaternary systems.
I can add more later when I get home and look at the data and some
astrophysics texts, if anyone's interested.
Jack Dietz
// [email removed]