use airmass fill_value=999 for more intuitive use
@@ -1166,6 +1166,9 @@ class HorizonsClass(BaseQuery):
data.add_column(Column([phcof] * len(data),
name='phasecoeff'), index=7)
+ # replace missing airmass values with 999 (not observable)
+ data['a-mass'] = data['a-mass'].filled(999)
+
# set column definition dictionary
if self.query_type is 'ephemerides':
column_defs = conf.eph_columns
