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Star Spectral Type/Size distributions available online?

Psion

SOC-13
Malefant's modified stellar data generation makes for a better relationship between mainworld and star, but I was interested in a star-first generation sequence.

My college library had some excellent resources tabulating data from various catalogs and giving figures for spectral types and sizes of stars that would have been great for the basis of such a system. Alas, I am far from college now and google is giving me a flurry of unrelated data. Does anyone know of an online resource that gives approximate distributions of real star data?

TIA
 
If you want a star-first system, then you can use my tables with the following modifications - remove the following modifiers, but keep all the rest:

+4 on Size and Type for primary star only if Mainworld is atm 4-9 or pop 8+. This only applies to the primary star, not to any Companions. If it is applicable, this modifier is always applied before other size/type modifiers.

+2 modifier on Orbital Config. roll for first (and second, if present) Companions if Mainworld is atm 4-9 or pop 8+ and if system has more than one star in it. Do not apply this to third companion star if system is quadruple!
In effect, this makes all systems "unmodified", and doesn't allow the planet to influence the star type/size/orbits.

The distribution I was using for those was from something I wrote down a while back. I dunno the source though (might have been Carl Sagan's Cosmos?) - I just remember seeing this triangle that was filled in with different colours for each star type, and most of it was red ebcause most of the stars were type M.

IIRC, it's supposed to be something like 71% M, 14% K, 10% G, 4% F, 1% A, and trace amounts of B and even less O. The unmodified distribution that my tables generate is 69.4% M, 13.9% K, 8.3% G, 5.6% F, and 2.8% A - that's the best I could do with 2d6, but it's much closer than the system in Book 6 was. You can find all this info in parts 1 and 3 of the deluxe version of my tables.
 
Originally posted by Malenfant:
The distribution I was using for those was from something I wrote down a while back. I dunno the source though (might have been Carl Sagan's Cosmos?) - I just remember seeing this triangle that was filled in with different colours for each star type, and most of it was red ebcause most of the stars were type M.

IIRC, it's supposed to be something like 71% M, 14% K, 10% G, 4% F, 1% A, and trace amounts of B and even less O. The unmodified distribution that my tables generate is 69.4% M, 13.9% K, 8.3% G, 5.6% F, and 2.8% A - that's the best I could do with 2d6, but it's much closer than the system in Book 6 was. You can find all this info in parts 1 and 3 of the deluxe version of my tables.
That info's good though. I'm not necessarily restricting myself to 2d6 here. In fact, I am flat out not...

Do you have similar figures for size class distribution? Or for B and O stars? (I realize that its fractions of a percent, but when computer generating thousands of stars, it could come up.)

Edit: Have you ever seen ross smith's planet generation material? What do you think of his probabilities? They seem to jive with what I remember, albeit that the chance and number of planets seems generous for stars much more massive than Fx V:

(Sorry the link is messy, the board doesn't seem to want to let me fix it.)
http://216.239.39.104/search?q=cache:DYVJ-vAEibcJ:ftp.funet.fi/pub/doc/games/roleplay/texts/plangen.txt+%22ross+smith%22+%22planet+generation%22&hl=en&lr=lang_en
 
I'm not sure about size distribution (I don't even really think we know for sure, since we miss a lot of V stars in our surveys because the M Vs are so hard to spot). To some extent it'll follow the type distribution - most stars will be V because most are type K and M and they haven't had enough time to evolve off the main sequence yet (the giants are the ones that have, which means they must have been A, F, or G V).

I made my best guess for the revised tables and agai, the size probabilities can be found there (Table 6 of the deluxe version, in fact). Though there is some bias there - I'm probably ignoring some of the D stars since most probably won't have planets or be good places for settlements. But I think it's generally in the right ballpark.

As for O and B, ISTR it was something like 0.01% for B and 0.0001 for O. Some small fraction of a percent for each (with O being much smaller) anyway. Of course, we see lots of those in the sky because they're bloody luminous and we can see them pretty much wherever they are in the galaxy, so that's why you might think they're more common.

Also, you do get the odd OB Association (like the Pleiades), which is basically a clump of O and B stars that formed out of a nebula recently (you also get less massive stars too - the Pleiades has many of those, but you can't see them easily because they're so far away). I don't know what the chances are of that sort of thing showing up - there may be one or two in Charted Space, I'd imagine.
 
Originally posted by Malenfant:
I'm not sure about size distribution (I don't even really think we know for sure, since we miss a lot of V stars in our surveys because the M Vs are so hard to spot).
I sort of figured that. The reference I used to have access to had a more detailed near stars catalog, and at the time I had it in my mind to use that as a reference for the frequency of type M and K stars, since we can actually see them.


As long as I have you here: earlier you referred me to G:FI's temperature calculation, which had luminosity as a fourth root. Is that accurate, because I tried using it and it really shoved out the habital zone for an M class star's system I was trying to model?
 
Yep. To all intents and purposes, FI's blackbody temperature calculation is completely accurate. Well, actually the multiplier should be 278.3 instead of 278 to be completely accurate, but that makes such a tiny difference (a fraction of a degree at most) that it isn't noticeable. So you can stick with it as it is.

If you're using the luminosities from book 6, you should find that stars from about M3V to M9V don't have habitable zones - they lie within Orbit 0 (0.2 AU). Though that doesn't take into account the temperature multiplier for tidelocking.
 
I'm gonna have to check my numbers again. My next world on the list was:

Navarino 2538 A547424-E - Lo Ni 203 IC M3 V, D

Using the fourth-root-luminosity blackbody equation, the world came out too hot (ableit that G:FI says it should be in the habital zone). I had to use G:FI orbit generation instead of Traveller's "assume Bode's law applies universally" approach and it ended up with acceptable results in the second orbit with the following numbers:

IMTU orbital zones:

1 0.17
2 0.57 Navarino
3 0.97
4 1.77
5 3.37
6 6.57
7 12.97

Energy Absorption .7
Greenhouse: 1.09
Temp: 299 K (26 C; Earth normal)

Of course, that temp would be the base in the twilight zone; as in GT:FI, you get hotter or cooler away from the twilight band.

You mentioned a tidal locked multiplier. Perhaps that's what I am missing.
 
Yeah, the multiplier is tucked away at the top of the sidebar on page 63 of FI.
 
Regarding luminosity. Earlier, you mention that WDG doesn't use a root of luminosity. I found out that was because they don't use true luminosity in the table, but ~ the fourth root. The result is on the same magnitude of the fourth root as the tables in GT:FI, but not quite. I suspect one or the other table is not using bolometric luminosity.
 
Oh yeah, now you mention it that does sound familiar (I went through the WBH ages ago, but most of my notes are back home)... IIRC the orbit factors are something to do with how the orbits scale down. *digs through notes*

IIRC, wasn't the WBH temperature equation:

T = L * O * E * G

L was actually the fourth root of the real luminosity. E was (1-A). G was a greenhouse multiplier. O is defined as above. That's actually what the equation is on page 47 of Scouts (if you have the right edition. In the version in the CT reprints, their K constant is 374.025, in earlier editions it was two hundred and something).

However, the K=374.025 in the Scouts/WBH appears to be wrong. The 278 in the FI equation comes from converting the terms in the actual blackbody temperature equation from SI units into things like AU, solar luminosity units etc.

The only thing I can think of is that the 374.025 in the scouts equation is something to do with the fact that you're multiply by (1-A) in the full Scouts equation instead of (1-A)^(0.25) as you're supposed to do when you're incorporating the albedo into the temperature calculation. It's not obvious to me how you can get 278.3 from 374.025 because of this though, and I don't get the same results if I use 278.3 and (1-A)^0.25 or if I use 374.025 and (1-A).


I'm rambling. Either way, the correct (full) Scouts equation should be:

T = 278.3 * (L^0.25) * [(1-A)^0.25] / (D^0.5)


The correct blackbody-only Scouts equation (which produces results identical to the FI Blackbody equation) should be:

T = 278.3 * (L^0.25) / (D^0.5)


That means that you can actually calculate WBH orbit factors for non standard orbits now, because from this:

Orbit Factor = K/(D^0.5) = 278.3/(D^0.5)


I think that's right anyway... does that help?!
 
Well, if they factored some other thing into their luminosity, that would explain why my numbers aren't matching between GT:FI and WBH. I suppose I'll just assume that GT:FI is using the right luminosity and go from there.
 
If you want a book that will help you with TRAVELLER world generation and real world science, try getting your hands on WORLD-BUILDING by Stephan L. Gillette ISBN 0-89879-707-1 from Amazon.com. That is where I got my copy of the book. It varies somewhat from GURPS FIRST IN, but it has the advantage if you will, of explaining things very concretely such that you can add in information that is pertinent to you as a GM. For example, it gives you formulas for determining the apparant size of a body such as a moon or the sun or even a Gas Giant if your world were in orbit around such. It explains why things happened as they did to make earth's atmosphere as it is...
 
Originally posted by Hal:
If you want a book that will help you with TRAVELLER world generation and real world science, try getting your hands on WORLD-BUILDING by Stephan L. Gillette ISBN 0-89879-707-1 from Amazon.com.
Thanks. Will do.

That is where I got my copy of the book. It varies somewhat from GURPS FIRST IN, but it has the advantage if you will, of explaining things very concretely such that you can add in information that is pertinent to you as a GM. For example, it gives you formulas for determining the apparant size of a body such as a moon or the sun or even a Gas Giant if your world were in orbit around such.
There's a sidebar in GT:FI about that. IT's rapidly replacing WBH as my favorite world building book. ;)

It explains why things happened as they did to make earth's atmosphere as it is...
I thought that a lot of that was still largely conjecture.
 
portions are of course, still conjecture. Unfortunately, many of us somehow missed being around when the universe started its mad dance into existence ;)

As you can largely guess, a lot of what we know today invalidates what was known 20 years ago. As it will happen, what we learn 20 years from now will invalidate what we know today ;)

The thing to remember however is that if you look at that book with the idea that it embodies more of what we know today than what we did 20 years ago, it will be helpful in at least that regard. I am certain too, that the person to ask about what is now out of favor in that book would likely be Malefant himself - as much of his work I believe is based on just that field. I suspect too that he is more cutting edge than Gillett such that he can tell you what has changed since Stephan's time...

Just keep in mind that this book was not written for gamers, but for writers who wanted a real life basis for their writing. I also picked up a "primer" on astrophysics that you might find interesting. The only issue with buying it or borrowing it from the library is that much of what is in it is already contained in the likes of FIRST IN. I'm not sure if it contains the alternative method for determining a star's mass based on luminosity (or if that math formula is in yet another game book darn it - memory is a bad thing when you hit 40+!)
 
as far as I can see, Gillett's Worldbuilding book is still a perfectly valid resource for what it covers. Some details may have changed (but that said in practise there isn't really such thing as a consistent tables of stellar masses vs spectral type vs luminosities anyway - they change all the time over the course of a star's lifespan, so Scouts is about as good as FI is about as good as anything else you'll find where things are in the same sort of ballpark), but I can't recall anywhere that he's completely wrong about something - the general principles of the things he discusses still hold. Sure, we know more about extrasolar systems than we did when the book was written so there's info lacking on those there, but the rest is fine.
 
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