Comets sometimes result in a "ambiguous target name" error

[jessie-dotson]

When using tess_ephem to check on a comet, sometimes a ValueError is raised due to an ambiguous target name. For example:

tt = ephem("C/1995 O1", verbose=True)

Results in:

ValueError Traceback (most recent call last)
in
----> 1 tt = ephem("C/1995 O1", verbose=True)

/opt/anaconda3/lib/python3.8/site-packages/tess_ephem/ephem.py in ephem(target, time, verbose, id_type, interpolation_step)
175 start = time[0] - 7
176 stop = time[-1] + 7
--> 177 te = TessEphem(
178 target, start=start, stop=stop, step=interpolation_step, id_type=id_type
179 )

/opt/anaconda3/lib/python3.8/site-packages/tess_ephem/ephem.py in init(self, target, start, stop, step, location, id_type)
41 """
42 log.info(f"Started querying JPL/Horizons for for ephemeris (id='{target}')")
---> 43 eph = _get_horizons_ephem(
44 id=target,
45 id_type=id_type,

/opt/anaconda3/lib/python3.8/site-packages/tess_ephem/ephem.py in _get_horizons_ephem(id, start, stop, step, id_type, location, quantities)
127 )
128 t = Horizons(id=id, id_type=id_type, location=location, epochs=epochs)
--> 129 result = t.ephemerides(quantities=quantities)
130 log.debug(f"Received {len(result)} ephemeris results")
131 return result

/opt/anaconda3/lib/python3.8/site-packages/astroquery/utils/class_or_instance.py in f(*args, **kwds)
23 def f(*args, **kwds):
24 if obj is not None:
---> 25 return self.fn(obj, *args, **kwds)
26 else:
27 return self.fn(cls, *args, **kwds)

/opt/anaconda3/lib/python3.8/site-packages/astroquery/utils/process_asyncs.py in newmethod(self, *args, **kwargs)
27 if kwargs.get('get_query_payload') or kwargs.get('field_help'):
28 return response
---> 29 result = self._parse_result(response, verbose=verbose)
30 self.table = result
31 return result

/opt/anaconda3/lib/python3.8/site-packages/astroquery/jplhorizons/core.py in _parse_result(self, response, verbose)
1294 return None
1295 else:
-> 1296 data = self._parse_horizons(response.text)
1297
1298 return data

/opt/anaconda3/lib/python3.8/site-packages/astroquery/jplhorizons/core.py in _parse_horizons(self, src)
1153 end_idx = i
1154 break
-> 1155 raise ValueError(('Ambiguous target name; provide '
1156 'unique id:\n%s' %
1157 '\n'.join(src[idx + 2:end_idx])))

ValueError: Ambiguous target name; provide unique id:
Record # Epoch-yr >MATCH DESIG< Primary Desig Name
-------- -------- ------------- ------------- -------------------------
90002087 1996 C/1995 O1 C/1995 O1 Hale-Bopp
90002088 2008 C/1995 O1 C/1995 O1 Hale-Bopp

[jessie-dotson]

I have a list of more that generate this error if that would be useful. It looks like maybe Horizons considers different apparitions of comets as different objects? (Maybe the non-gravitational effects on their orbits is why horizons does this? If so, maybe we always want the most recent epoch. But I'm not quite sure how to specify that...)