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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)

Notes

Information on the data can be found at http://www.astro.washington.edu/users/ivezic/sdss/catalogs/stripe82.html 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)

References

Ivesic et al. ApJ 134:973 (2007)

Examples

>>> 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]