add gc to Galaxy.py

ObservationSim/MockObject/Galaxy.py

 import numpy as np
 import galsim
+import gc
 import os, sys
 import astropy.constants as cons
 from astropy.table import Table
@@ -180,6 +181,7 @@ class Galaxy(MockObject):
             photons.x += x_nominal
             photons.y += y_nominal
             photons_list.append(photons)
+            del gal
 
         # print('xmax = %d, ymax = %d '%(xmax, ymax))
 
@@ -205,6 +207,7 @@ class Galaxy(MockObject):
                         sensor.accumulate(photons_list[i], stamp)
                     else:
                         sensor.accumulate(photons_list[i], stamp, resume=True)
+                del sensor
 
             chip.img[bounds] = stamp[bounds]
 
@@ -238,6 +241,7 @@ class Galaxy(MockObject):
         # # print("nphotons_sum = ", nphotons_sum)
         del photons_list
         del stamp
+        gc.collect()
         return True, pos_shear
 
     def drawObj_slitless(self, tel, pos_img, psf_model, bandpass_list, filt, chip, nphotons_tot=None, g1=0, g2=0,