# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""This module defines reddening laws and extinction curves."""
# STDLIB
import numbers
# THIRD-PARTY
import numpy as np
from astropy import units as u
# LOCAL
from synphot import exceptions, specio, units
from synphot.compat import HAS_DUST_EXTINCTION
from synphot.config import Conf
from synphot.models import Empirical1D
from synphot.spectrum import BaseUnitlessSpectrum
__all__ = ['ExtinctionModel1D', 'ReddeningLaw', 'ExtinctionCurve',
'etau_madau']
[docs]
class ExtinctionModel1D(Empirical1D):
"""Model to handle extinction curve.
This is like :class:`~synphot.models.Empirical1D` except that
its ``sampleset`` will not be propagated to composite spectrum.
"""
[docs]
def sampleset(self):
"""This simply returns `None`. Use ``numpy.squeeze(self.points)``
instead for array (in Angstrom) that samples the model.
"""
return None
[docs]
class ReddeningLaw(BaseUnitlessSpectrum):
"""Class to handle reddening law.
Parameters
----------
modelclass, kwargs
See `~synphot.spectrum.BaseSpectrum`.
"""
[docs]
def extinction_curve(self, ebv, wavelengths=None):
"""Generate extinction curve.
.. math::
A(V) = R(V) \\; \\times \\; E(B-V)
THRU = 10^{-0.4 \\; A(V)}
Parameters
----------
ebv : float or `~astropy.units.quantity.Quantity`
:math:`E(B-V)` value in magnitude.
wavelengths : array-like, `~astropy.units.quantity.Quantity`, or `None`
Wavelength values for sampling.
If not a Quantity, assumed to be in Angstrom.
If `None`, ``self.waveset`` is used.
Returns
-------
extcurve : `ExtinctionCurve`
Empirical extinction curve.
Raises
------
synphot.exceptions.SynphotError
Invalid input.
"""
if isinstance(ebv, u.Quantity) and ebv.unit.decompose() == u.mag:
ebv = ebv.value
elif not isinstance(ebv, numbers.Real):
raise exceptions.SynphotError('E(B-V)={0} is invalid.'.format(ebv))
x = self._validate_wavelengths(wavelengths)
header = {'E(B-V)': ebv}
# Duck-typing dust-extinction package API.
if HAS_DUST_EXTINCTION and hasattr(self.model, 'extinguish'):
y = self.model.extinguish(x, Ebv=ebv)
header['ReddeningLaw'] = '{!r}'.format(self.model)
else:
y = 10 ** (-0.4 * self(x).value * ebv)
header['ReddeningLaw'] = self.meta.get('expr', 'unknown')
return ExtinctionCurve(ExtinctionModel1D, points=x, lookup_table=y,
meta={'header': header})
[docs]
def to_fits(self, filename, wavelengths=None, **kwargs):
"""Write the reddening law to a FITS file.
:math:`R(V)` column is automatically named 'Av/E(B-V)'.
Parameters
----------
filename : str
Output filename.
wavelengths : array-like, `~astropy.units.quantity.Quantity`, or `None`
Wavelength values for sampling.
If not a Quantity, assumed to be in Angstrom.
If `None`, ``self.waveset`` is used.
kwargs : dict
Keywords accepted by :func:`~synphot.specio.write_fits_spec`.
"""
w, y = self._get_arrays(wavelengths)
kwargs['flux_col'] = 'Av/E(B-V)'
kwargs['flux_unit'] = self._internal_flux_unit
# No need to trim/pad zeroes, unless user chooses to do so.
if 'pad_zero_ends' not in kwargs:
kwargs['pad_zero_ends'] = False
if 'trim_zero' not in kwargs:
kwargs['trim_zero'] = False
# There are some standard keywords that should be added
# to the extension header.
bkeys = {'tdisp1': 'G15.7', 'tdisp2': 'G15.7'}
if 'expr' in self.meta:
bkeys['expr'] = (self.meta['expr'], 'synphot expression')
if 'ext_header' in kwargs:
kwargs['ext_header'].update(bkeys)
else:
kwargs['ext_header'] = bkeys
specio.write_fits_spec(filename, w, y, **kwargs)
[docs]
@classmethod
def from_file(cls, filename, **kwargs):
"""Create a reddening law from file.
If filename has 'fits' or 'fit' suffix, it is read as FITS.
Otherwise, it is read as ASCII.
Parameters
----------
filename : str
Reddening law filename.
kwargs : dict
Keywords acceptable by
:func:`~synphot.specio.read_fits_spec` (if FITS) or
:func:`~synphot.specio.read_ascii_spec` (if ASCII).
Returns
-------
redlaw : `ReddeningLaw`
Empirical reddening law.
"""
if 'flux_unit' not in kwargs:
kwargs['flux_unit'] = cls._internal_flux_unit
if ((filename.endswith('fits') or filename.endswith('fit')) and
'flux_col' not in kwargs):
kwargs['flux_col'] = 'Av/E(B-V)'
header, wavelengths, rvs = specio.read_spec(filename, **kwargs)
return cls(Empirical1D, points=wavelengths, lookup_table=rvs,
meta={'header': header})
[docs]
@classmethod
def from_extinction_model(cls, modelname, **kwargs):
"""Load :ref:`pre-defined extinction model <synphot_reddening>`.
Parameters
----------
modelname : str
Extinction model name. Choose from 'lmc30dor', 'lmcavg', 'mwavg',
'mwdense', 'mwrv21', 'mwrv40', 'smcbar', or 'xgalsb'.
kwargs : dict
Keywords acceptable by :func:`~synphot.specio.read_remote_spec`.
Returns
-------
redlaw : `ReddeningLaw`
Empirical reddening law.
Raises
------
synphot.exceptions.SynphotError
Invalid extinction model name.
"""
modelname = modelname.lower()
# Select filename based on model name
if modelname == 'lmc30dor':
cfgitem = Conf.lmc30dor_file
elif modelname == 'lmcavg':
cfgitem = Conf.lmcavg_file
elif modelname == 'mwavg':
cfgitem = Conf.mwavg_file
elif modelname == 'mwdense':
cfgitem = Conf.mwdense_file
elif modelname == 'mwrv21':
cfgitem = Conf.mwrv21_file
elif modelname == 'mwrv40':
cfgitem = Conf.mwrv40_file
elif modelname == 'smcbar':
cfgitem = Conf.smcbar_file
elif modelname == 'xgalsb':
cfgitem = Conf.xgal_file
else:
raise exceptions.SynphotError(
'Extinction model {0} is invalid.'.format(modelname))
filename = cfgitem()
if 'flux_unit' not in kwargs:
kwargs['flux_unit'] = cls._internal_flux_unit
if ((filename.endswith('fits') or filename.endswith('fit')) and
'flux_col' not in kwargs):
kwargs['flux_col'] = 'Av/E(B-V)'
header, wavelengths, rvs = specio.read_remote_spec(filename, **kwargs)
header['filename'] = filename
header['descrip'] = cfgitem.description
meta = {'header': header, 'expr': modelname}
return cls(Empirical1D, points=wavelengths, lookup_table=rvs,
meta=meta)
[docs]
class ExtinctionCurve(BaseUnitlessSpectrum):
"""Class to handle extinction curve.
Parameters
----------
modelclass, kwargs
See `~synphot.spectrum.BaseSpectrum`.
"""
pass
# TODO: Find a better way to handle so many magic numbers.
# See https://github.com/spacetelescope/synphot_refactor/issues/77
[docs]
def etau_madau(wave, z, **kwargs):
"""Madau 1995 extinction for a galaxy at given redshift.
This is the Lyman-alpha prescription from the photo-z code BPZ.
The Lyman-alpha forest approximately has an effective
"throughput" which is a function of redshift and
rest-frame wavelength.
One would multiply the SEDs by this factor before
passing it through an instrument filter.
This approximation is from Footnote 3 of
:ref:`Madau et al. (1995) <synphot-ref-madau1995>`.
This is claimed accurate to 5%.
The scatter in this factor (due to different lines of sight)
is huge, as shown in Madau's Fig. 3 (top panel);
The figure's bottom panel shows a redshifted version of the
"exact" prescription.
Parameters
----------
wave : array-like or `~astropy.units.quantity.Quantity`
Redshifted wavelength values.
Non-redshifted wavelength is ``wave / (1 + z)``.
z : number
Redshift.
kwargs : dict
Equivalencies for unit conversion, see
:func:`~synphot.units.validate_quantity`.
Returns
-------
extcurve : `ExtinctionCurve`
Extinction curve to apply to the redshifted spectrum.
"""
if not isinstance(z, numbers.Real):
raise exceptions.SynphotError(
'Redshift must be a real scalar number.')
if np.isscalar(wave) or len(wave) <= 1:
raise exceptions.SynphotError('Wavelength has too few data points')
wave = units.validate_quantity(wave, u.AA, **kwargs).value
ll = 912.0
c = np.array([3.6e-3, 1.7e-3, 1.2e-3, 9.3e-4])
el = np.array([1216, 1026, 973, 950], dtype=float) # noqa
tau = np.zeros_like(wave, dtype=float)
xe = 1.0 + z
# Lyman series
for i in range(len(el)):
tau = np.where(wave <= el[i] * xe,
tau + c[i] * (wave / el[i]) ** 3.46,
tau)
# Photoelectric absorption
xc = wave / ll
xc3 = xc ** 3
tau = np.where(wave <= ll * xe,
(tau + 0.25 * xc3 * (xe ** 0.46 - xc ** 0.46) +
9.4 * xc ** 1.5 * (xe ** 0.18 - xc ** 0.18) -
0.7 * xc3 * (xc ** (-1.32) - xe ** (-1.32)) -
0.023 * (xe ** 1.68 - xc ** 1.68)),
tau)
thru = np.where(tau > 700., 0., np.exp(-tau))
meta = {'descrip': 'Madau 1995 extinction for z={0}'.format(z)}
return ExtinctionCurve(ExtinctionModel1D, points=wave, lookup_table=thru,
meta=meta)
