SDSS Queries (astroquery.sdss)

Getting started

This example shows how to perform an object cross-ID with SDSS. We’ll start with the position of a source found in another survey, and search within a 5 arcsecond radius for optical counterparts in SDSS. Note use of the keyword argument spectro, which requires matches to have spectroscopy, not just photometry:

>>> from astroquery.sdss import SDSS
>>> from astropy import coordinates as coords
>>> pos = coords.SkyCoord('0h8m05.63s +14d50m23.3s', frame='icrs')
>>> xid = SDSS.query_region(pos, spectro=True)
>>> print(xid)
    ra         dec           objid        run  rerun camcol field    z    plate  mjd  fiberID     specobjid      specClass
---------- ----------- ------------------ ---- ----- ------ ----- ------- ----- ----- ------- ------------------ ---------
2.02344483 14.83982059 587727221951234166 1739    40      3   315 0.04541   751 52251     160 211612124516974592         3

The result is an astropy.Table.

Downloading data

If we’d like to download spectra and/or images for our match, we have all the information we need in the elements of “xid” from the above example.

>>> sp = SDSS.get_spectra(matches=xid)
>>> im = SDSS.get_images(matches=xid, band='g')

The variables “sp” and “im” are lists of HDUList objects, one entry for each corresponding object in xid.

Note that in SDSS, image downloads retrieve the entire plate, so further processing will be required to excise an image centered around the point of interest (i.e. the object(s) returned by query_region).

Spectral templates

It is also possible to download spectral templates from SDSS. To see what is available, do

>>> from astroquery.sdss import SDSS
>>> print(SDSS.AVAILABLE_TEMPLATES)

Then, to download your favorite template, do something like

>>> template = SDSS.get_spectral_template('qso')

The variable “template” is a list of PyFITS HDUList objects (same object as “sp” in the above example). In this case there is only one result, but in a few cases there are multiple templates available to choose from (e.g. the “galaxy” spectral template will actually return 3 templates).

Reference/API

astroquery.sdss Package

SDSS Spectra/Image/SpectralTemplate Archive Query Tool

Classes

Conf Configuration parameters for astroquery.sdss.
SDSSClass()