def sfd_ebmv(ra, dec, equinox=2000, obsepoch=None, service='IRSA'):
"""
Fetch SFD Milky Way E(B-V) from IRSA or NED.
`IRSA <http://irsa.ipac.caltech.edu/>`_ (slow)
`NED <http://ned.ipac.caltech.edu/>`_.
:param service: can be 'IRSA' or 'NED'
"""
assert equinox in [1950, 2000], 'equinox should be 1950 or 2000'
if obsepoch is None:
obsepoch = datetime.utcnow().year
ra, dec = SkyCoord(ra, dec, unit='deg').to_string('hmsdms').split()
equinox = {1950: 'B1950.0', 2000: 'J2000.0'}[equinox]
if service.lower() == 'ned':
query = dict(in_csys='Equatorial',
in_equinox=equinox,
obs_epoch=str(obsepoch),
lon=ra.__str__(),
lat=dec.__str__(),
pa='0.0',
out_csys='Equatorial',
out_equinox=equinox)
try: # python 2
items = query.iteritems()
except: # python 3
items = query.items()
url = urlparse.urlunparse(('http', 'ned.ipac.caltech.edu',
'cgi-bin/nph-calc', '',
'&'.join(['%s=%s' % (i, j)
for i, j in items]),
''))
html = urllib.urlopen(url).read()
# grep into the HTML
mwebv = re.search(r'(?<=E\(B-V\)\s=\s)\d+\.\d+(?=\smag)', html)
if mwebv is not None:
return float(mwebv.group(0))
else:
return None
elif service.lower() == 'irsa':
query = dict(locstr=urllib.quote('%s %s Equatorial %s' %
(ra.__str__(), dec.__str__(), equinox)))
try: # python 2
items = query.iteritems()
except: # python 3
items = query.items()
url = urlparse.urlunparse(('http', 'irsa.ipac.caltech.edu',
'cgi-bin/DUST/nph-dust', '',
'&'.join(['%s=%s' % (i, j)
for i, j in items]),
''))
# parse the XML
opened_url = urllib.urlopen(url)
if 'read' in dir(opened_url):
# python 2
infos = xml_parser(opened_url.read())
else:
# python 3
infos = xml_parser(opened_url)
if infos is not None:
# the other 'result' are not in mag
mwebv = infos['results']['result'][0]['statistics']['refPixelValueSFD']
return float(mwebv.split()[0])
else:
return None
