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jude_rookContinuing from yesterday…
Let’s say you have arbitrarily chosen a distance of 200 light years for the planet you want. Also, let’s say it’s going to be home to a species that can live comfortably on Earth, so you want a star fairly like Sol in terms of spectral class, age and metallicity.
Well, you’ll notice that some fields on the query page come pre-selected; you can de-select them and select others if you choose. For our purposes, we’ll stick with the pre-selected ones with the following exceptions:
Under “Maximum entries per table,” select “Unlimited.”
Enter the desired distance in the “Distance” field. Note that this database uses parsecs, so enter 61 (which is about 200 light years).
Select “Lower confidence limit on age” and “Upper confidence limit on age”. This will give you an idea of the possible age range of your star.
Press the “Submit query” button.
Wow, check it out! 149 possible stars at a distance of 61 parsecs!
Of course, you will need to narrow things down some before you pick a home star for the Rival Empire. Let’s take a look at some of the columns in our result page.
Start with age. A star much younger than four billion years is not likely to have an intelligent species living on one of its planets. So let’s eliminate those that are younger.
Next, Jill Tarter and Margaret Turnbull have said that a star with a metallicity of under 40% is not a good candidate to have planets. Let’s err on the side of caution and eliminate those with a metallicity of under 50% (which is -0.3 on the Fe/H scale used by the database.)
There is, by the way, an easier way to do this than printing out the list and drawing lines through the unsuitable candidates. Use your mouse to select the list, then copy it. Open Microsoft Excel, choose “Paste Special” and paste the list as unformatted text. Each data point should appear in a separate cell.
Don’t close the web page with the search results on it, though -- we’ll be going back to it.
In Excel, sort the list by age and eliminate all the candidates that are too young; then sort what is left by metallicity and eliminate the candidates that don’t have enough metals. Some stars won’t have data on one or both of these attributes; to be on the safe side again, let’s eliminate them too.
I’m also going to arbitrarily eliminate any stars that have ages given as over 8 billion years, simply because the older a star’s estimate age is, the wider the variations in its possible age, and even if it turns out I’m wrong in saying a given star is 5 billion years old for the purposes of my story, I don’t want to be too, too wrong.
Okay, having done all that, I still have 31 stars out of the original 149. Now let’s sort the list one more time, in order of the row numbers that the database assigned to the entries.
Now go back to the results page. The first star that is still in the Excel spreadsheet and on the original list is on line 2, HD 7326. Let’s click on the link that says “Simbad” at the end of the line and get some information on it from the Simbad database.
Well, according to Simbad, HD 705 is an F6V star with no companions. Not bad, but I feel like finding something a little closer to Sol in terms of spectral class.
Next is line 14, HD 21045. Another F star. Let’s keep trying.
Next is line 16, HD 22210. Aha, Simbad tells us this is a G5 dwarf! Getting closer, but can we find something even more sunlike?
I’m going to skip over the next few, which have companions, and number 40, another F star, and look at number 47, HD 52063. A G1V star, very close to Sol (which is G2V). No companion stars listed… older than Sol at between 7 and 8.5 billion years, metallicity of -0.23 (about 58% of Sol’s)… not an exact twin, but certainly a prime candidate. I say let’s go for it! Congratulations, new alien capital!
One more thing we need to check out. The database gives this star’s coordinates as right ascension 06 hours 56 minutes 23.2 seconds, and declination as -57 degrees 34 minutes 34 seconds. Taking my trusty star atlas off the shelf, I find this star is located in the constellation of Carina, practically on the border of Pictor. This can be useful knowledge in a number of ways; for example, if one of our exploration craft meets one of theirs somewhere in neutral space, you’ll want to pick a location that’s in the right direction.
Of course, if you want to, you can keep perusing the list. Maybe you want a star that is closer to Sol in age and/or metallicity; maybe you’ve decided you want to use an F star. And if you still don’t find a completely suitable star, well, these are just the ones at 61 parsecs. Try 60 or 62... Who knows what you’ll find?
Finally, just in case you need to use this resource in the future and something should happen to it, here’s a link to a text file giving the basic info on these stars: http://cdsarc.u-strasbg.fr/viz-bin/nph-Cat/txt?V/117A. Not as convenient as using the interactive database, but you can save it to your computer for use in an emergency.
Let’s say you have arbitrarily chosen a distance of 200 light years for the planet you want. Also, let’s say it’s going to be home to a species that can live comfortably on Earth, so you want a star fairly like Sol in terms of spectral class, age and metallicity.
Well, you’ll notice that some fields on the query page come pre-selected; you can de-select them and select others if you choose. For our purposes, we’ll stick with the pre-selected ones with the following exceptions:
Under “Maximum entries per table,” select “Unlimited.”
Enter the desired distance in the “Distance” field. Note that this database uses parsecs, so enter 61 (which is about 200 light years).
Select “Lower confidence limit on age” and “Upper confidence limit on age”. This will give you an idea of the possible age range of your star.
Press the “Submit query” button.
Wow, check it out! 149 possible stars at a distance of 61 parsecs!
Of course, you will need to narrow things down some before you pick a home star for the Rival Empire. Let’s take a look at some of the columns in our result page.
Start with age. A star much younger than four billion years is not likely to have an intelligent species living on one of its planets. So let’s eliminate those that are younger.
Next, Jill Tarter and Margaret Turnbull have said that a star with a metallicity of under 40% is not a good candidate to have planets. Let’s err on the side of caution and eliminate those with a metallicity of under 50% (which is -0.3 on the Fe/H scale used by the database.)
There is, by the way, an easier way to do this than printing out the list and drawing lines through the unsuitable candidates. Use your mouse to select the list, then copy it. Open Microsoft Excel, choose “Paste Special” and paste the list as unformatted text. Each data point should appear in a separate cell.
Don’t close the web page with the search results on it, though -- we’ll be going back to it.
In Excel, sort the list by age and eliminate all the candidates that are too young; then sort what is left by metallicity and eliminate the candidates that don’t have enough metals. Some stars won’t have data on one or both of these attributes; to be on the safe side again, let’s eliminate them too.
I’m also going to arbitrarily eliminate any stars that have ages given as over 8 billion years, simply because the older a star’s estimate age is, the wider the variations in its possible age, and even if it turns out I’m wrong in saying a given star is 5 billion years old for the purposes of my story, I don’t want to be too, too wrong.
Okay, having done all that, I still have 31 stars out of the original 149. Now let’s sort the list one more time, in order of the row numbers that the database assigned to the entries.
Now go back to the results page. The first star that is still in the Excel spreadsheet and on the original list is on line 2, HD 7326. Let’s click on the link that says “Simbad” at the end of the line and get some information on it from the Simbad database.
Well, according to Simbad, HD 705 is an F6V star with no companions. Not bad, but I feel like finding something a little closer to Sol in terms of spectral class.
Next is line 14, HD 21045. Another F star. Let’s keep trying.
Next is line 16, HD 22210. Aha, Simbad tells us this is a G5 dwarf! Getting closer, but can we find something even more sunlike?
I’m going to skip over the next few, which have companions, and number 40, another F star, and look at number 47, HD 52063. A G1V star, very close to Sol (which is G2V). No companion stars listed… older than Sol at between 7 and 8.5 billion years, metallicity of -0.23 (about 58% of Sol’s)… not an exact twin, but certainly a prime candidate. I say let’s go for it! Congratulations, new alien capital!
One more thing we need to check out. The database gives this star’s coordinates as right ascension 06 hours 56 minutes 23.2 seconds, and declination as -57 degrees 34 minutes 34 seconds. Taking my trusty star atlas off the shelf, I find this star is located in the constellation of Carina, practically on the border of Pictor. This can be useful knowledge in a number of ways; for example, if one of our exploration craft meets one of theirs somewhere in neutral space, you’ll want to pick a location that’s in the right direction.
Of course, if you want to, you can keep perusing the list. Maybe you want a star that is closer to Sol in age and/or metallicity; maybe you’ve decided you want to use an F star. And if you still don’t find a completely suitable star, well, these are just the ones at 61 parsecs. Try 60 or 62... Who knows what you’ll find?
Finally, just in case you need to use this resource in the future and something should happen to it, here’s a link to a text file giving the basic info on these stars: http://cdsarc.u-strasbg.fr/viz-bin/nph-Cat/txt?V/117A. Not as convenient as using the interactive database, but you can save it to your computer for use in an emergency.