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Fix parallax definition convention. #84

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Oct 10, 2023
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Fix parallax definition convention. #84

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811d490
Fix parallax definition convention.
schlafly Oct 10, 2023
9886355
Fix text.
schlafly Oct 10, 2023
1b2a069
Loosen tolerance of test to account for eccentricity of earth's orbit.
schlafly Oct 10, 2023
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5 changes: 2 additions & 3 deletions romanisim/gaia.py
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Original file line number Diff line number Diff line change
Expand Up @@ -53,10 +53,9 @@ def gaia2romanisimcat(gaiacat, date, refepoch=2016.0, boost_parallax=1,
newxyz = (
xyz + rahat * dt * radpermas * pmra + dechat * dt * radpermas * pmdec)
plx = gaiacat['parallax'].to(u.mas).value * boost_parallax
newxyz -= (rahat * earthcoord.dot(rahat) * plx / 2 * radpermas
+ dechat * earthcoord.dot(dechat) * plx / 2 * radpermas)
newxyz -= (rahat * earthcoord.dot(rahat) * plx * radpermas
+ dechat * earthcoord.dot(dechat) * plx * radpermas)
# stars move in the opposite direction of the earth -> minus sign
# divide by two: parallax is the diameter rather than radius of the circle
newunitspherical = coordinates.UnitSphericalRepresentation.from_cartesian(
coordinates.CartesianRepresentation(newxyz))
newra = newunitspherical.lon
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4 changes: 2 additions & 2 deletions romanisim/tests/test_gaia.py
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Expand Up @@ -29,9 +29,9 @@ def test_gaia():
# first source doesn't move it first catalog since it's observed at its
# epoch and has zero parallax
assert cats[0][field][0] == fakegaiacat[field][0]
# max separation when pm = 0 should be roughly parallax / 2
# max separation when pm = 0 should be roughly parallax
pm0 = (fakegaiacat['pmra'] == 0) & (fakegaiacat['pmdec'] == 0)
assert np.all(np.abs(maxsep[pm0] - fakegaiacat['parallax'][pm0] / 2)
assert np.all(np.abs(maxsep[pm0] - fakegaiacat['parallax'][pm0])
<= fakegaiacat['parallax'][pm0] * 0.01)
# sources with zero pmra and plx never move
assert np.all(sep[:, -1] == 0 * u.deg)
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