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11.4.4. astroML.datasets.fetch_sdss_S82standards

astroML.datasets.fetch_sdss_S82standards(data_home=None, download_if_missing=True, crossmatch_2mass=False)

Loader for SDSS stripe82 standard star catalog

Parameters :

data_home : optional, default=None

Specify another download and cache folder for the datasets. By default all scikit learn data is stored in ‘~/astroML_data’ subfolders.

download_if_missing : bool, optional, default=True

If False, raise a IOError if the data is not locally available instead of trying to download the data from the source site.

crossmatch_2mass: bool, optional, default=False :

If True, return the standard star catalog cross-matched with 2mass magnitudes

Returns :

data : ndarray, shape = (313859,)

record array containing sdss standard stars (see notes below)


Information on the data can be found at Data is described in Ivezic et al. 2007 (Astronomical Journal, 134, 973). Columns are as follows:

RA Right-ascention of source (degrees) DEC Declination of source (degrees) RArms rms of right-ascention (arcsec) DECrms rms of declination (arcsec) Ntot total number of epochs A_r SFD ISM extinction (mags)

for each band in (u g r i z):

Nobs_<band> number of observations in this band mmed_<band> median magnitude in this band mmu_<band> mean magnitude in this band msig_<band> standard error on the mean

(1.25 times larger for median)

mrms_<band> root-mean-square scatter mchi2_<band> chi2 per degree of freedom for mean magnitude

For 2-MASS, the following columns are added:

ra2MASS 2-mass right-ascention dec2MASS 2-mass declination J J-band magnitude Jerr J-band error H H-band magnitude Herr H-band error K K-band magnitude Kerr K-band error theta difference between SDSS and 2MASS position (arcsec)


Ivesic et al. ApJ 134:973 (2007)


>>> data = fetch_sdss_S82standards()
>>> u_g = data['mmed_u'] - data['mmed_g']
>>> print u_g[:5]
[-22.23500061   1.34900093   1.43799973   2.08200073 -23.03800011]