UKIDSS Queries (astroquery.ukidss)

Getting started

This module allows searching catalogs and retrieving images from the UKIDSS web service. Some data can on UKIDSS can be accessed only after a valid login. For accessing such data a UKIDSS object must first be instantiated with valid credentials. On the other hand, to access the public data, the various query functions may just be called without logging in. Below are examples that illustrate both the means for accessing the data.

Case 1 : Access only public data - No login

>>> from astroquery.ukidss import Ukidss
>>> images = Ukidss.get_images("m1")

Found 1 targets
|===========================================| 174k/174k (100.00%)        02s

Case 2 : Login to access non-public data

>>> from astroquery.ukidss import Ukidss

# Now first instantiate a new Ukidss object with login credentials

>>> u_obj = Ukidss(username='xyz', password='secret', 
...                community='your_community')        

>>> # The prompt appears indicating successful login

Note that at login time you may also optionally set the database and the survey that you would like to query. By default the database is set to ‘UKIDSSDR7PLUS’ and the programme_id is set to ‘all’ - which includes all the surveys. A word of warning - for region queries you should explicitly set the programme_id to the survey you wish to query. Querying all surveys is permitted only for image queries.

>>> from astroquery.ukidss import Ukidss
>>> u_obj = Ukidss(username='xyz', password='secret',                    
...                community='your_community', database='UKIDSSDR8PLUS', 
...                programme_id='GPS')                                   

At any given time you may if you wish check your login status (continuing from the above example):

>>> u_obj.logged_in() 


If you want to change your programme_id and database after you have already instantiated the object - say u_obj then you should do:

>>> u_obj.programme_id = 'new_id_here'   
>>> u_obj.database = 'new_database_here' 

The above examples mention programme_id that specifies the catalog or survey you wish to query. If you would like to get a list of the commonly available UKIDSS survey - either the abbreviations or the complete names, you can do so by using list_catalogs():

>>> from astroquery.ukidss import Ukidss
>>> Ukidss.list_catalogs()

['UDS', 'GCS', 'GPS', 'DXS', 'LAS']

>>> Ukidss.list_catalogs(style='long')

['Galactic Plane Survey',
 'Deep Extragalactic Survey',
 'Galactic Clusters Survey',
 'Ultra Deep Survey',
 'Large Area Survey']

Now we look at examples of the actual queries that can be performed.

Get images around a target

You can fetch images around the specified target or coordinates. When a target name is used rather than the coordinates, this will be resolved to coordinates using astropy name resolving methods that utilize online services like SESAME. Coordinates may be entered using the suitable object from astropy.coordinates. The images are returned as a list of HDUList objects.

>>> from astroquery.ukidss import Ukidss
>>> images = Ukidss.get_images("m1")

Found 1 targets
|===========================================| 174k/174k (100.00%)        07s

>>> print(images)

[[< object at 0x40f8b10>, < object at 0x41026d0>]]

Note if you have logged in using the procedure described earlier and assuming that you already have a UkidssClass object u_obj instantiated:

>>> images = u_obj.get_images("m1") 

There are several optional parameters that you can specify in image queries. For instance to specify the image size you should set the image_width and the image_height keyword arguments. If only the image_width is set then the image_height is taken to be the same as this width. By default the image_width is set to 1 arcmin. To set this to your desired value, you should enter it using a Quantity object with appropriate units or as a string that is parsable by Angle. Another parameter you may set is radius. This may be specified in the same way as the image_height and image_width with the radius keyword. By specifying this multi-frame FITS images will be retrieved. Note that in this case the image height and width parameters will no longer be effective.

>>> from astroquery.ukidss import Ukidss
>>> import astropy.units as u
>>> import astropy.coordinates as coord
>>> images = Ukidss.get_images(coord.SkyCoord(49.489, -0.27,
...                                           unit=(u.deg, u.deg),
...                                           frame='galactic'),
...                            image_width=5 * u.arcmin)

    Found 6 targets
|===========================================| 518k/518k (100.00%)        06s
|===========================================| 517k/517k (100.00%)        06s
|===========================================| 654k/654k (100.00%)        06s
|===========================================| 647k/647k (100.00%)        06s
|===========================================| 586k/586k (100.00%)        06s
|===========================================| 587k/587k (100.00%)        04s

Again the query may be performed similarly with a log-in.

If you haven’t logged-in then you could also specify the programme_id as a keyword argument. By default this is set to ‘all’. But you can change it to a specific survey as mentioned earlier. The same goes for the database which is set by default to ‘UKIDSSDR7PLUS’. Some more parameters you can set are the frame_type which may be one of

'stack' 'normal' 'interleave' 'deep_stack' 'confidence' 'difference'
'leavstack' 'all'

and the waveband that decides the color filter to download. This must be chosen from

'all' 'J' 'H' 'K' 'H2' 'Z' 'Y' 'Br'

Note that rather than fetching the actual images, you could also get the URLs of the downloadable images. To do this simply replace the call to get_images() by a call to get_image_list() with exactly the same parameters. Let us now see a complete example to illustrate these points.

>>> from astroquery.ukidss import Ukidss
>>> import astropy.units as u
>>> import astropy.coordinates as coord
>>> image_urls = Ukidss.get_image_list(coord.SkyCoord(ra=83.633083,
...          dec=22.0145, unit=(u.deg, u.deg), frame='icrs'),
...          frame_type='interleave',
...          programme_id="GCS", waveband="K", radius=20*u.arcmin)
>>> image_urls


Query a region

Another type of query is to search a catalog for objects within a specified radius of a source. Again the source may be either a named identifier or it may be specified via coordinates. The radius may be specified as in the previous cases by using a Quantity or a string parsable via Angle. If this is missing, then it defaults to 1 arcmin. As before you may also mention the programme_id and the database. The query results are returned in a Table.

>>> from astroquery.ukidss import Ukidss
>>> import astropy.coordinates as coord
>>> import astropy.units as u
>>> table = Ukidss.query_region(coord.SkyCoord(10.625, -0.38,
...                                            unit=(u.deg, u.deg),
...                                            frame='galactic'),
...                             radius=6 * u.arcsec)

|===========================================| 4.6k/4.6k (100.00%)        00s

>>> print(table)

     sourceID    framesetID        RA      ... H2AperMag3Err     distance
------------ ------------ ------------- ... ------------- ---------------
438758381345 438086690175 272.615581037 ...  -9.99999e+08 0.0864656469768
438758381157 438086690175   272.6178395 ...  -9.99999e+08 0.0717893063941
438758381256 438086690175 272.616581639 ...  -9.99999e+08 0.0725261678319
438758399768 438086690175 272.618154346 ...  -9.99999e+08 0.0800819201056
438758399809 438086690175 272.617630209 ...  -9.99999e+08 0.0996951205267
438758399828 438086690175 272.617238438 ...  -9.99999e+08 0.0435480204348
438758399832 438086690175 272.617034836 ...  -9.99999e+08 0.0665854385804
438758414982 438086690175 272.616576986 ...  -9.99999e+08 0.0214102038115


If you are repeatedly getting failed queries, or bad/out-of-date results, try clearing your cache:

>>> from astroquery.ukidss import Ukidss
>>> Ukidss.clear_cache()

If this function is unavailable, upgrade your version of astroquery. The clear_cache function was introduced in version 0.4.7.dev8479.


astroquery.ukidss Package

UKIDSS Image and Catalog Query Tool


UkidssClass(*[, username, password, ...])

The UKIDSSQuery class.


Configuration parameters for astroquery.ukidss.