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.