fix cos(delta) bug

sblunt · Feb 9, 2024 · 98148b7 · 98148b7
1 parent e20eaf4
commit 98148b7
Show file tree

Hide file tree

Showing 2 changed files with 5 additions and 3 deletions.
diff --git a/orbitize/hipparcos.py b/orbitize/hipparcos.py
@@ -63,8 +63,8 @@ def compute_astrometric_model(self, samples, param_idx):
 
         Returns:
             tuple of:
-                - float: predicted RA position offsets from the measured position
-                    at alphadec0_epoch, calculated for each input epoch [mas]
+                - float: predicted RA*cos(delta0) position offsets from the measured 
+                    position at alphadec0_epoch, calculated for each input epoch [mas]
                 - float: predicted Dec position offsets from the measured position
                     at alphadec0_epoch, calculated for each input epoch [mas]
         """

diff --git a/orbitize/system.py b/orbitize/system.py
@@ -654,7 +654,9 @@ def compute_model(self, params_arr, use_rebound=False):
                 params_arr, self.param_idx
             )
 
-            model[self.radec[0], 0] += ra_pred.reshape(model[self.radec[0], 0].shape)
+            # divide by cos(delta0) because orbitize! input is delta(ra), not
+            # delta(ra)*cos(delta0)
+            model[self.radec[0], 0] += ra_pred.reshape(model[self.radec[0], 0].shape) / np.cos(np.radians(self.pm_plx_predictor.delta0))
             model[self.radec[0], 1] += dec_pred.reshape(model[self.radec[0], 0].shape)
 
         if n_orbits == 1: