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PostPosted: Sun Feb 19, 2012 11:20 am 
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Attached is a chart in which I graphed for each five-light-year-thick shell centred on Sol the number of stars listed in the Internet Stellar Database in that shell per thousand cubic light-years of the shell. I omitted the three innermost shells because their figures were small enough for sampling error to be seriously misleading, but star lists for the shell 15–20 light-years are essentially complete.

Each coloured line represents a different spectral type of star, as shown by the key, and the downward slope of the lines show how the detectability (or measurability, really) of each spectral type declines with distance.


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ISDB density as a function of distance, by spectral type.png
ISDB density as a function of distance, by spectral type.png [ 62.62 KiB | Viewed 714 times ]

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Last edited by Agemegos on Sun Feb 19, 2012 12:54 pm, edited 1 time in total.
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PostPosted: Sun Feb 19, 2012 12:30 pm 
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The attached graph shows an estimate of the completeness of the ISDB sources as a function of distance by spectral type (for types F to M and D).

The less common types jink around a bit, especially close to Sol when the sample numbers are small: never mind that. Observe that the catalogues of F types are essentially complete out to about 70 light-years, and Gs to 60 LY, but that K and M types seem to be seriously under-catalogued from about 25 light-years.

This graph ought to supply some idea of how many stars of each spectral type have to be invented at given distance from Sol.


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ISDB completeness.png
ISDB completeness.png [ 89.37 KiB | Viewed 714 times ]

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PostPosted: Sun Feb 19, 2012 2:02 pm 
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ffilz wrote:
I was also curious when one might think it is ok to add K V, G V, and F V.

Here is my estimate of the number of invented stars it would be appropriate to add (to the composite catalogue used by the Internet Stellar Database), tabulated by spectral type in shells five light-years thick, out to 200 light-years. These estimates are based on subtracting the number of stars of each spectral class recorded as being in the shells from the expected number (the volume of the shell times the estimated average density with which stars of said spectral type are distributed in space). Of course, if you used these actual numbers a statistician would observe that there was too little random variation in the density of stellar types, but you'll have to deal with that yourself.

Observe that the numbers get rather large.


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star defect in ISDB.png
star defect in ISDB.png [ 376.81 KiB | Viewed 713 times ]

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PostPosted: Mon Feb 20, 2012 7:39 am 
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Cool, that's very helpful.

Thanks

Frank


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PostPosted: Mon Feb 20, 2012 9:25 am 
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The RECONS guys did have tables like that up on their site at some point, I guess they must be updating them for 2012 because they're down right now.

Incidentally, I am working on adding the CTIOPI dataset (also on RECONS) to my page, but it's fiddly. This will provide about 200 of M dwarfs, brown dwarfs, and white dwarfs to about one whole hemisphere around Sol (unfortunately it doesn't cover the other side). I'll be updating the DENSE dataset too since CTIOPI includes duplicates or updated values fo several of the WDs in there. It'll also have spectral types (which is the fiddly part, I have to look them all up individually!).

Hopefully it'll be released within the week.

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PostPosted: Mon Feb 20, 2012 4:42 pm 
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It seems that much past 100 lys you might as well go completely random (adding in only the really bright stars).

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PostPosted: Mon Feb 20, 2012 8:26 pm 
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Cyborg IM1 wrote:
It seems that much past 100 lys you might as well go completely random (adding in only the really bright stars).

Yeah, the known stars out there are just a scattering of landmarks in a vast territory in which the likely primaries of inhabited planets are mostly unknown. Even at about 75 LY half of all habitable planets ought to circle fictitious stars.

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PostPosted: Mon Feb 20, 2012 8:32 pm 
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There are still quite a lot of known stars between 100 and 300 lightyears in the Hipparcos data (17771 of them, to be precise...)

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PostPosted: Mon Feb 20, 2012 8:43 pm 
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EDG wrote:
There are still quite a lot of known stars between 100 and 300 lightyears in the Hipparcos data (17771 of them, to be precise...)

Yes, but RECONS lists 161 objects within 22.8 LY, for a density of 3.24 stars per thousand cubic light-years. At that rate there ought to be 353,000 stars in that volume, about twice as many as Hipparcos lists.

How many of those stars have usuably-accurate magnitudes and colour indices?

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PostPosted: Mon Feb 27, 2012 1:18 pm 
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I've now added 164 stars from the CTIOPI dataset (available on the RECONS website), and also updated the DENSE data. See http://evildrganymede.net/2012/02/27/stellar-mapping-ctiopi-added/ for details. The Stellar Mapping page has also been reorganised!

Image

If you've downloaded the datasets previously, you'll need to download the updated versions rom the Stellar Mapping page!

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