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PostPosted: Tue Feb 14, 2012 9:45 pm 
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In your latest blog post, you look at fixing 2300 AD's star map. You mention some "invention" of stars.

Do you have any thoughts about the distances from Sol one might reasonably start inventing various star types?

Frank


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PostPosted: Tue Feb 14, 2012 9:49 pm 
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I'd say it's safe to add them beyond the RECONS limit (22.8 ly). Within that, it's unlikely that there are many more M V stars or BDs since they've probably found most of them. I do know that there are more M V stars and WDs in the southern part of the sky between 20 and 25 ly from Sol (see the TSN papers at http://www.recons.org/Publications.htm ), but they haven't had trigonometric parallaxes confirmed for them so I've not included them. There are a few mentioned in there with confirmed ground-based parallaxes that I may add later though (once I've read up on them a bit more).

So I would say that one shouldn't add stars within 22.8 ly, but one could add them beyond that.

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PostPosted: Tue Feb 14, 2012 10:10 pm 
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I was also curious when one might think it is ok to add K V, G V, and F V. And slightly curious on adding even brighter stars (since F-K V covers the stars one would want to add for habitability, though far enough away, one might not always want to solve a route between two distant stars with smaller stars).

Of course if one is absolutely desperate to make some connection even close to Sol, one might be able to invent a rogue planet, though if rogue planets are findable and usable, it would be hard to create "rifts"...

Frank


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PostPosted: Tue Feb 14, 2012 10:31 pm 
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I haven't really pinned down where the brighter stars would be yet. Obviously, one would start inserting the dimmer stars closer to 22.8 lightyears and start to include the brighter ones at a further distance away. The trick is that you have to keep the same number of dimmer stars at the full range of distances (they'd be undetectable at all ranges), and then start adding the brighter ones as you go out.

Very roughly (with only cursory research, looking at solstation.com) it looks like G V and F V stars still seem to be visible around 100ly from Sol (they may be harder to find beyond that) - subgiants are detectable from a bit further away. I would say that K V stars seem to peter out from the "easily detectable" star lists around 50ly. M V stars become harder to detect around 20-25 ly.

We're seeing only the very bright stars - the O/B Vs and giants at ranges beyond a few hundred ly.

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PostPosted: Tue Feb 14, 2012 11:43 pm 
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I guess the trick would be to come up with some range where one would expect to find say 95% of a particular brightness of star, then compute actual densities for that type of star based on the number of said stars within that distance of Sol. Then in some random chunk of space farther away, if you want to add that type of star, determine how many might be expected to be found in your chunk of space and subtract the number actually known.

In practice, for my purposes, I'm mostly happy to add dim stars when connection stars are missing. And I add F-K when I want to add a habitable system. Maybe I add some F-K closer to Sol than there could be expected to be missing stars, but in the end, does it really matter? Sure, I'm not going to put stars too close to Sol, but then my jump ranges are 10 pc or 30 pc, so I don't need to invent stars 20-25 ly from Sol, and the Sol polity has 30 pc jump distance, so I don't need to invent habitable systems within 100 ly of Sol...

I have a thought of going back to my Sol polity, and playing around with very early jump systems that maybe didn't even have 10 pc distance, and look for connections to the various habitable systems, and then perhaps I can decide which was the most likely first extra-solar habitable system (which might not be the closest).

Frank


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PostPosted: Wed Feb 15, 2012 2:27 pm 
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The relative percentages of different types of stars are pretty well known for our part of the galaxy. Looking only at MAIN SEQUENCE stars, the numbers are approximately:

M - 76.5%
K - 12.1%
G - 7.6%
F - 3%
A - 0.6%
B - 0.13%
O - 0.00003%

Brown Dwarfs (L, T and possibly Y stars) are not listed, but could represent as much as 15% to 20% of all stars.

Non-Main Sequence stars are less common, but White Dwarfs seem to represent about 10% of the stellar population distribution.

Of course, B and O stars are usually only going to be found in star clusters since they go nova very quickly and don't really have time to travel very far.

If you are interested, read the Stellar Classification entry in Wikipedia, it is pretty good.

SO, back to your question. If you were to randomly try to create a complete star map, you could use those numbers above for your main sequence stars.

If you were mapping existing stars and just trying to fill in the voids, the relative percentages would give you a good feel for how to do that.

As EDG suggested, I would not add anything within the RECONS data, maybe a T-type brown dwarf or two, but not anything else.

<25 ly: maybe a T-type BD or two but that would be it
25-50 ly: Add a M-type Red star if needed
50-100 ly: Add a K-type Orange star if needed
100-200 ly: Add a G-type Yellow star if needed
200-300 ly: Add a F-type Yellow-White star if needed

For each of the longer distances, remember to add extra dimmer stars for each brighter star you add.

So, for every F-type star you add, you should add 2 G-types, 3 K-types and about a dozen M-type stars.

Hope that helps.

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PostPosted: Sun Feb 19, 2012 8:22 am 
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I downloaded the RECONS data (file GAL_RECONS.csv) with the thought of using it to correct the positions of stars within 22.8 LY in my merged set of ISDB with HYG, and as the data set to map for my little #D map building project. I found that it did not contain luminosity, mass, and radius data, which the page said it would.

As GAL_RECONS.txt says: "Format: Star, ID#, Star Name, Galactic X (ly), Galactic Y (ly), Galactic Z (ly), mass, (blank), (blank), Spectral Type/Size, (blank), distance (ly)."

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PostPosted: Sun Feb 19, 2012 8:27 am 
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Bugger.

I think I got a bit confused in my editing there. The RECONS files just have accurate mass and spectral types, not luminosity and radius. The Further Stars dataset is the one with (generally) accurate luminosity and radius as well, but it only has a selection of HIP stars in it. Sorry! The description on the webpage is edited now.

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PostPosted: Sun Feb 19, 2012 9:08 am 
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Attachment:
density of stars in space in RECONS.png
density of stars in space in RECONS.png [ 50.94 KiB | Viewed 560 times ]
Cyborg IM1 wrote:
So, for every F-type star you add, you should add 2 G-types, 3 K-types and about a dozen M-type stars.

Yeah, but closer in you add M-types without adding any Gs, and a little further out, Ks without Fs.

I had a bit of a look at the trend of the space density of stars in the RECONS set, and after allowing for a freakish spike between 11.27 and 11.83 light-years from Sol (there are six multiple systems all in that narrow range of distances from Sol: EZ Aquarii, 61 Cygni, Procyon, Gliese 725, GX & GQ Andromedae, and Epsilon Indi) it looks as though the trend is flat (and therefore no stars missing because of distance) at 0.0033 stars per cubic light-year. The volume covered by the RECONS set is 49,647 cubic light years, and contains 8 white dwarfs, 98 M-type stars, 18 K-type, 7 G-type, 1 F-type, and 2 A-type. You have to be careful about the small numbers because of sampling error, but the catalogues ought to be fairly complete for O, B, A, and perhaps F types anyway, at least as far as they are good for anything. That said, it basically looks as though you ought to add sufficient stars at each distance to maintain an average of about 0.00016 D-type, 0.00197 M-type, 0.000363 K-type, and 0.00014 G-type stars per cubic light-year.

I'm off to have a look at density trends by type in the HYG catalogue.

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Last edited by Agemegos on Sun Feb 19, 2012 1:12 pm, edited 1 time in total.

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PostPosted: Sun Feb 19, 2012 9:29 am 
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EDG wrote:
Bugger.

I think I got a bit confused in my editing there. The RECONS files just have accurate mass and spectral types, not luminosity and radius. The Further Stars dataset is the one with (generally) accurate luminosity and radius as well, but it only has a selection of HIP stars in it. Sorry! The description on the webpage is edited now.

No worries. I can get those data from the ISDB collection. I just thought you'd like to know about the discrepancy between the word and the deed.

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