
I created the data\fillgal\stars.dat file in order to produce the
Ragamuffin galaxy which has been included with Starmap. You may
also want to use this file (or an amended version) for the creation
of your own sf-rpg universe, however, before you do, there are a
few things you might want to know about it...

Data Source:

I used the preliminary version of the _Third Catalogue of Nearby
Stars_ (CNS3) (Gliese W., Jahreiss H., Astron. Rechen-Institut,
Heidelberg, 1991), which claims to contain all known stars with 25
parsecs (about 80 light years) of the Sun. Star names, locations,
and spectral class/type were taken from this catalog. Locational
data was converted from RA/Dec/Parallax coordinates to geocentric
galactic X,Y,Z coordinates using formulas found on Winchell Chung's
3d star mapping homepage (this method is highly suspect due to the
difficulty in obtaining accurate parallax measurements). Some
guesswork had to be done on the class/type data as well, with a
heavy leaning toward MV stars since these seem to be the most
common.

Star Naming:

Where a popular name existed (i.e. Capella), that was chosen above
any other form of designation. Stars with popular names were named
according to their constellation and their place within it (i.e.
Delta Leonis). In most cases, neither of these two were available,
so the star was next named according to its "Wolf" or "Ross"
designation number. If neither of these were available, then the
star was named according to its group (either its catalog number in
CNS3 or its random group).

          W = Woolley (1970)
          G = Gliese (CNS2, 1969)
          J = Gliese & Jahreiss (1979)
          N = Newly added to CNS3 (1991)
          R = Random star system (see below)
          B = Random brown dwarf system (see below)

Grouping:

After the stars were named, I grouped them according to location,
forming star systems (up to four stars per system). In the case of
Castor, there were six stars at one location, which I separated
into two star systems, Castor and YY Geminorum (I put the former
down as a binary, and the latter as a quarternary... that is two
sets of near binaries hovering about one another as far
companions). This grouping was done arbitrarily with little regard
to the Gliese (CNS3) data set, although I did make some effort to
put on a thin show of astronomical "correctness" (for example:
ensuring that 1st and 2nd generation stars aren't together within
the same stellar hub).

Analysis:

I had previously done an analysis of the data to see how the
stellar density (the number of stars per volume space) drops off
with increasing distance from the Sun. Since I now had the data
"grouped" into star systems, I re-analzyed the data, this time
looking at the star system density (number of star systems per
volume space), the idea here being that with increasing distance,
Gliese would show fewer and fewer stars, and hence I would be
forced to generate some random ones to take up the slack.

  Area       Sys    Volume    LYs/Sys    Expected      Missing
10 ly peel     9      4188       465           8            0 
20 ly peel    69     29321       424          58            0 
30 ly peel   139     79586       572         159           20 
40 ly peel   255    154985       607         309           54 
50 ly peel   439    255516       582         511           72 
60 ly peel   559    381179       681         762          203 
70 ly peel   699    531975       761        1063          364 
80 ly peel   676    707905      1047        1415          739 
90 ly peel   266    908966      3417        1817         1551 
100 ly peel   65   1135161     17464        2270         2205 
cube peel     74   3811213     51502        7622         7548 
total       3250   8000000 

Area: The peels are simply layers of an expanding sphere. The 10ly
peel is a sphere around the Sun 10 light years in radius. The 20ly
peel is a spere around the Sun 20 light years in radium minus the
10ly sphere. So on and so forth, so that the 100ly peel is a sphere
100ly in radius around the Sun minus the 10-90 ly peels. The cube
peel is a special peel, cubish in shape, and consists of a big
block, 200 light years to a side, with the Sun as its center, and
minus all the other peels.

Sys: Number of star systems in each peel.

Volume: Number of cubic light years per peel.

LYs/Sys: Number of cubic light years per star system per peel. The
higher the result, the lower the star system density.

Expected: The number of star systems expected assuming 500 LYs/Sys.
This is a highly speculative number and doesn't take into account
real differences in the local stellar cloud, however, I felt it was
necessary to arrive at some number given the state of the data set.

Missing: Number of expected star systems minus the number that
shows in the Gliese data. This is how many random star systems I
would have to place in the data file to get to the 500 LYs/Sys
figure which I'd previously assumed.

Reducing the Data Set:

The star system density analysis showed that there was a steep
increasing in "missing" stars the further one gets away from our
Sun. I had expected such an increase, but not so steep. My
conclusion was that assuming a 200 light year cube, I would have to
place over 10000 random star systems, whereas the data itself only
contained some 3250. Hence, the amount of "filler" would be around
75%. This was simply too high for my tastes, so I decided to be
less ambition and only shoot for a 100 light year cube. Re-analysis
produced the following table:

  Area       Sys    Volume    LYs/Sys    Expected      Missing
10 ly peel     9      4188       465           8            0 
20 ly peel    69     29321       424          58            0 
30 ly peel   139     79586       572         159           20 
40 ly peel   255    154985       607         309           54 
50 ly peel   439    255516       582         511           72 
cube peel    657    476401       725         952          295 
total       1568   1000000

This looked a lot more reasonable. I'd only have to pull 400-500
star systems out of a random hat, where as there were 1568 real
ones in the data (a filler rate of under 25%). It also fit better
with Gliese in the sense that Gliese only makes the claim of being
complete out to 25 parsecs (81.5 light years). The furthest corners
of a 100 light year cube would be roughly 86.5 light years from the
Sun, just slightly beyond the "sphere of completeness", so it
seemed like a good choice given the data set that I was using.

Placing Random Star Systems:

I decided to generate +/-10% of "missing" for each peel, producing
the following results:

  Area       Volume  Gliese  Random  Total   LYs/Sys
10 ly peel     4188      9       0       9     465
20 ly peel    29321     69       0      69     424
30 ly peel    79586    139      21     160     497
40 ly peel   154985    255      51     306     506
50 ly peel   255516    439      67     506     504 
cube peel    476401    657     313     970     491
total       1000000   1568     452    2020     495

My only problem with this is that 500 LYs/Sys may not have been a
very good number to use for approximate star system density.
Perhaps something a bit smaller (i.e. denser packing) would have
been more appropriate, but then again, this leaves some room for
growth in case GMs want to add a few star systems to the data set.

Adding Brown Dwarfs:

Another issue concerned the inclusion of brown dwarfs, stars that
never accumulated enough mass to ignite with sustainable nuclear
fusion. Current theories vary on the question of how many brown
dwarfs are out there, but a moderate guess seems to be that they
number about the same as the least luminous of the red dwarfs.
Using this as my basis, I figured, after a quick back-of-the-
envelope calculation, that there would probably be about as many
brown dwarf systems as one-sixth the number of red dwarf systems.
Analysis of the data pulled up 754 red dwarf solos and another 93
red dwarf binary pairs, so I decided to shoot an extra 138 brown
dwarfs systems (some solos, some binaries) into the data file.

Conclusion:

The data\fillgal\stars.dat file is the product of tons of work on
the part of Gliese & others and a few hours of goobering on the
part of yours truly. If you like it, use it. If you don't, use
something else. Amd if you have any questions or comments, feel
free to send me email...  jimv@empirenet.com / JimVassila@aol.com

