import os
from gzip import GzipFile
from io import BytesIO
import numpy as np
from .tools import download_with_progress_bar
from . import get_data_home
DATA_URL = ('https://github.com/astroML/astroML-data/raw/master/datasets/'
'stripe82calibStars_v2.6.dat.gz')
DATA_URL_2MASS = ('https://github.com/astroML/astroML-data/raw/master/datasets/'
'stripe82calibStars_2MASS_v2.6.dat.gz')
ARCHIVE_FILE = 'sdss_S82standards.npy'
ARCHIVE_FILE_2MASS = 'sdss_S82standards_2mass.npy'
DTYPE = [('RA', 'f8'),
('DEC', 'f8'),
('RArms', 'f4'),
('DECrms', 'f4'),
('Ntot', 'i4'),
('A_r', 'f4')]
for band in 'ugriz':
DTYPE += [('Nobs_%s' % band, 'i4')]
DTYPE += map(lambda s: (s + '_' + band, 'f4'),
['mmed', 'mmu', 'msig', 'mrms', 'mchi2'])
DTYPE_2MASS = DTYPE + [('ra2MASS', 'f4'),
('dec2MASS', 'f4'),
('J', 'f4'),
('Jerr', 'f4'),
('H', 'f4'),
('Herr', 'f4'),
('K', 'f4'),
('Kerr', 'f4'),
('theta', 'f4')]
# first column is 'CALIBSTARS'. We'll ignore this.
COLUMNS = range(1, len(DTYPE) + 1)
[docs]def 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 astroML data is stored in '~/astroML_data'.
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)
Examples
--------
>>> data = fetch_sdss_S82standards() # doctest: +IGNORE_OUTPUT +REMOTE_DATA
>>> u_g = data['mmed_u'] - data['mmed_g'] # doctest: +REMOTE_DATA
>>> print(u_g[:4]) # doctest: +REMOTE_DATA
[-22.23500061 1.34900093 1.43799973 2.08200073]
References
----------
Ivesic et al. ApJ 134:973 (2007)
"""
data_home = get_data_home(data_home)
if crossmatch_2mass:
archive_file = os.path.join(data_home, ARCHIVE_FILE_2MASS)
data_url = DATA_URL_2MASS
kwargs = dict(dtype=DTYPE_2MASS)
else:
archive_file = os.path.join(data_home, ARCHIVE_FILE)
data_url = DATA_URL
kwargs = dict(usecols=COLUMNS, dtype=DTYPE)
if not os.path.exists(archive_file):
if not download_if_missing:
raise IOError('data not present on disk. '
'set download_if_missing=True to download')
print("downloading cross-matched SDSS/2MASS dataset from %s to %s"
% (data_url, data_home))
zipped_buf = download_with_progress_bar(data_url, return_buffer=True)
gzf = GzipFile(fileobj=zipped_buf, mode='rb')
print("uncompressing file...")
extracted_buf = BytesIO(gzf.read())
data = np.loadtxt(extracted_buf, **kwargs)
np.save(archive_file, data)
else:
data = np.load(archive_file)
return data
