Astroquery SIMBAD : Obtaining coordinates for all frames

Question

I'm trying to obtain coordinates for all frames using the Simbad class from astroquery, just like it is shown on the SIMBAD web page (Basic data section)

I have the following code :

from astroquery.simbad import Simbad

def get():
    Simbad.reset_votable_fields()
    Simbad.remove_votable_fields('coordinates')

    Simbad.add_votable_fields('ra(:;A;ICRS;J2000)', 'dec(:;D;ICRS;2000)')
    Simbad.add_votable_fields('ra(:;A;FK5;J2000)', 'dec(:;D;FK5;2000)')

    table = Simbad.query_object("Betelgeuse", wildcard=False)

but I'm getting the error:

KeyError: 'ra(:;A;FK5;J2000): field already present. Fields ra,dec,id,otype, and bibcodelist can only be specified once. To change their options, first remove the existing entry, then add a new one.'

Everything I could find in the doc about manipulating votable fields, especially coordinates is this :

http://astroquery.readthedocs.io/en/latest/simbad/simbad.html#specifying-the-format-of-the-included-votable-fields

Is there a way to get coordinates for all frames sending one query to SIMBAD?

Answer 1

Instead of querying multiple coordinates (which seems impossible with astroquery) from SIMBAD you could convert the coordinates by using astropy.coordinates.SkyCoord.

For example:

from astroquery.simbad import Simbad
from astropy.coordinates import SkyCoord

Simbad.reset_votable_fields()
Simbad.remove_votable_fields('coordinates')
Simbad.add_votable_fields('ra(:;A;ICRS;J2000)', 'dec(:;D;ICRS;2000)')
table = Simbad.query_object("Betelgeuse", wildcard=False)
coords = SkyCoord(ra=['{}h{}m{}s'.format(*ra.split(':')) for ra in table['RA___A_ICRS_J2000']], 
                  dec=['{}d{}m{}s'.format(*dec.split(':')) for dec in table['DEC___D_ICRS_2000']],
                  frame='icrs', equinox='J2000')

Which is a now a SkyCoord object that can be transformed to other frames:

>>> coords
<SkyCoord (ICRS): (ra, dec) in deg
    ( 88.79293875,  7.40706389)>
>>> coords.fk4
<SkyCoord (FK4: equinox=J2000.000, obstime=B1950.000): (ra, dec) in deg
    ( 88.79274075,  7.40705223)>
>>> coords.fk5
<SkyCoord (FK5: equinox=J2000.000): (ra, dec) in deg
    ( 88.79294545,  7.40705842)>

This can be converted to strings again, for example in hms dms formatting:

>>> coords.fk5.to_string('hmsdms')
['05h55m10.3069s +07d24m25.4103s']

If you want these as additional columns in your table, you can simply add these:

>>> table['RA FK5'] = coords.fk5.ra
>>> table['DEC FK5'] = coords.fk5.dec
>>> table['FK4'] = coords.fk4.to_string('hmsdms')
>>> table
 MAIN_ID  RA___A_ICRS_J2000 DEC___D_ICRS_2000     RA FK5       DEC FK5                 FK4             
               "h:m:s"           "d:m:s"           deg           deg     
--------- ----------------- ----------------- ------------- ------------- -----------------------------
* alf Ori     05:55:10.3053     +07:24:25.430 88.7929454548 7.40705841559 05h55m10.2578s +07d24m25.388s