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minor planet checking

Project description

pympc

perform checks for the presence of minor bodies at astronomical locations for a given epoch.

installation

pip install pympc

or download source and:

python setup.py install

setup

frst import the package and grab the orbit element catalogue - this must be done at least once prior to doing any searches and can be run to overwrite the catalogues with the latest versions. the default call signature is shown

>>> import pympc
>>> pympc.update_catalogue()

by default the catalogues downloaded will be the mpcorb catalogue from the Minor Planet Center. astorb from Lowell Observatory may be downloaded instead or as well. this behaviour can be changed using the cat argument.

the Near Earth Asteroid and Comets catalogues will be downloaded and used to update the mpcorb entries based on the values of the include_nea and include_comets arguments (both default to True).

it will create a csv file for each catalogue downloaded in the xephem database format.

example 1 (searching)

define our search location, epoch and radius and run the check

>>> import astropy.units as u
>>> from astropy.time import Time
>>> ra = 230.028 * u.deg
>>> dec = -11.774 * u.deg
>>> epoch = Time("2019-01-01T00:00")
>>> search_radius = 0.5 * u.arcmin
>>> pympc.minor_planet_check(ra, dec, epoch, search_radius)
example 2 (assumed units)

here we use float arguments, and the program assumes the units (see pympc.minor_planet_check() docstring)

>>> ra = 230.028  # assumed degrees
>>> dec = -11.774  # assumed degrees
>>> epoch = 58484.  # assumed MJD
>>> search_radius = 30  # assumed arcseconds
>>> pympc.minor_planet_check(ra, dec, epoch, search_radius)
example 3 (using a specific catalogue)

to use a specific orbit catalogue, specify the location of the xephem database , e.g.:

minor_planet_check(ra, dec, epoch, search_radius, xephem_filepath='/path/to/astorb_xphem.csv')

if omitted, it will attempt to use /tmp/mpcorb_xephem.csv.

speed and multiprocessing

the check should take of order a second or two, depending on multiprocessing capabilities.

the private function which actually performs the calculation is _minor_planet_check() (note leading underscore). this can be called to avoid the overhead associated with converting input arguments to minor_planet_check(), if you can provide them directly as required (see _minor_planet_check() docstring).

by default the program will calculate positions of bodies in the catalogue multiprocessed. to switch this off set chunk_size = 0, i.e.:

>>> pympc.minor_planet_check(ra, dec, epoch, search_radius, chunk_size=0)

limitations

the orbits are propagated following xephem (via the pyephem package), and this does not account for perturbations of the orbits. thus the accuracy of the position is dependant on the time difference between the epoch of the orbit elements and the epoch at which the search is being performed. epoch differences between orbital elements calculation and observation of around a month or two should be fine for typical positional accuracies of a few arcsecond for most minor bodies - note however that a small number of bodies (those under going strong perturbations) may be quite inaccurate (arcminutes).

the xephem package can only provide geocentric astrometric positions. as such, parallax effects for near-earth bodies will be significant, in addition to the lack of perturbation calculations above.

currently the epoch of the orbit elements is visible in the xephem db strings returned by minor_planet_check() as a decimal year format (e.g. ..,2019.317808,..). some diagnostic information and warning when using large time differences is to be implemented.

the filtering of matches based on magnitude via max_mag argument to minor_planet_check() is limited by the accuracy of the magnitude information in the database so some buffer should be applied to the desired magnitude cutoff to allow for this.

acknowledgments

this package makes use of data and/or services provided by the International Astronomical Union's Minor Planet Center.

orbit elements are also sourced from Lowell Observatory, which is funded by the Lowell Observatory Endowment and NASA PDART grant NNX16AG52G.

based from a package developed by Chris Klein and Duncan Galloway.

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