Using find_nearby_stars.py¶
Introduction¶
The “script find_nearby_stars.py” handles finding a star within a specified distance from a RA/DEC position with constraints on brightness. It is normally used by the “autofocus_auto_star.py” script but can also be invoked indepently.
Invocation¶
The invocation of autofocus_auto_star.py is:
usage: find_nearby_stars.py [-h] [--minmag MINMAG] [--maxmag MAXMAG]
[--verbose] [--outfile OUTFILE] [--force]
[--lst LST] [--onlyside ONLYSIDE]
[--meridianthres MERIDIANTHRES] [--lon LON]
cat ra2000 dec2000 dist
positional arguments:
cat Catalog to search
ra2000 RA J2000
dec2000 DEC J2000
dist Max distance in degrees
optional arguments:
-h, --help show this help message and exit
--minmag MINMAG
--maxmag MAXMAG
--verbose
--outfile OUTFILE Output file with candidates
--force Overwrite output file
--lst LST Local sidereal time
--onlyside ONLYSIDE EAST or WEST side only
--meridianthres MERIDIANTHRES
How close to meridian is allowed (hh:mm:ss)
--lon LON Location longitude
Program Output¶
The program outputs the list of candidate stars to the console and if the argument “–outfile” is given it will also write CSV output to this file. The file includes a header that explains the columns.
Explanation of specifying side of pier¶
The “cat” argument should reference a binary SAO Catalog created with the utilities in the “find_star” directory. One such file is in the “data” directory and is called “SAO_Catalog_m5_p11_filtered.bin” and has stars down to magnitude 11. It has been filtered of stars that are close to one another to reduce the chance of having a another star interfere with the autofocus routine.
The “–lon” argument allows the specification of the observing latitude. Then script can then compute the local sidereal time. Optionally the local sidereal time can be given with the “–lst” argument.
Once the local sidereal time has been determined then the “–onlyside” parameter can be used to retrict the star to one side of the meridian or the other. It can take a value of “EAST” or “WEST” (capitalized!).
The “–meridianthres” argument can be used to create a “keep out” area near the meridian that excludes choosing a focus star in that area.