How To Sort Through A List Of Observable Coordinates?

I am struggling to find the best way of removing unwanted targets from a list of coordinates. My coordinates (Ra, Dec) are formed using astropy.coordinates.SkyCoord but I have a la

Solution 1:

I'll just illustrate how you can use numpy indexing with boolean masks on some arbitary coordinates:

from astropy.coordinatesimportSkyCoordimport astropy.unitsas u
import numpy as np
phi = np.linspace(0,2*np.pi,20)
theta = np.linspace(0, np.pi, 20)
radecs = SkyCoord(ra=phi*u.rad, dec=(0.5*np.pi - theta)*u.rad)
radecs

giving me radecs:

<SkyCoord (ICRS): (ra, dec) indeg
    [(0.0, 90.0), (18.94736842, 80.52631579), (37.89473684, 71.05263158),
     (56.84210526, 61.57894737), (75.78947368, 52.10526316),
     (94.73684211, 42.63157895), (113.68421053, 33.15789474),
     (132.63157895, 23.68421053), (151.57894737, 14.21052632),
     (170.52631579, 4.73684211), (189.47368421, -4.73684211),
     (208.42105263, -14.21052632), (227.36842105, -23.68421053),
     (246.31578947, -33.15789474), (265.26315789, -42.63157895),
     (284.21052632, -52.10526316), (303.15789474, -61.57894737),
     (322.10526316, -71.05263158), (341.05263158, -80.52631579),
     (0.0, -90.0)]>

to get the dec (declination) of your radecs you can acces the property:

radecs.dec

[90, 80.526316, 71.052632, 61.578947, 52.105263, 42.631579, 33.157895, 23.684211, 14.210526, 4.7368421, −4.7368421, −14.210526, −23.684211, −33.157895, −42.631579, −52.105263, −61.578947, −71.052632, −80.526316, −90]

so we can access all targets with a declination above -10 degree by creating a mask:

radecs.dec > - 10 * u.degree

and then index all targets which satisfy this mask:

radecs2 = radecs[radecs.dec > - 10 * u.degree]

Giving me the following radecs2:

<SkyCoord (ICRS): (ra, dec) indeg
    [(0.0, 90.0), (18.94736842, 80.52631579), (37.89473684, 71.05263158),
     (56.84210526, 61.57894737), (75.78947368, 52.10526316),
     (94.73684211, 42.63157895), (113.68421053, 33.15789474),
     (132.63157895, 23.68421053), (151.57894737, 14.21052632),
     (170.52631579, 4.73684211), (189.47368421, -4.73684211)]>

essentially all you do is the last step (radecs2 = radecs[radecs.dec > - 10 * u.degree]), all the other steps are just explanatory.