Source code for astropy.analytic_functions.blackbody
# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""Functions related to blackbody radiation."""
from __future__ import (absolute_import, division, print_function,
unicode_literals)
# STDLIB
import warnings
# THIRD-PARTY
import numpy as np
# LOCAL
from .. import constants as const
from .. import units as u
from ..utils.exceptions import AstropyUserWarning
__all__ = ['blackbody_nu', 'blackbody_lambda']
# Units
FNU = u.erg / (u.cm**2 * u.s * u.Hz)
FLAM = u.erg / (u.cm**2 * u.s * u.AA)
# Some platform implementations of expm1() are buggy and Numpy uses
# them anyways--the bug is that on certain large inputs it returns
# NaN instead of INF like it should (it should only return NaN on a
# NaN input
# See https://github.com/astropy/astropy/issues/4171
_has_buggy_expm1 = np.isnan(np.expm1(1000))
[docs]def blackbody_nu(in_x, temperature):
"""Calculate blackbody flux per steradian, :math:`B_{\\nu}(T)`.
.. note::
Use `numpy.errstate` to suppress Numpy warnings, if desired.
.. warning::
Output values might contain ``nan`` and ``inf``.
Parameters
----------
in_x : number, array-like, or `~astropy.units.Quantity`
Frequency, wavelength, or wave number.
If not a Quantity, it is assumed to be in Hz.
temperature : number, array-like, or `~astropy.units.Quantity`
Blackbody temperature.
If not a Quantity, it is assumed to be in Kelvin.
Returns
-------
flux : `~astropy.units.Quantity`
Blackbody monochromatic flux in
:math:`erg \\; cm^{-2} s^{-1} Hz^{-1} sr^{-1}`.
Raises
------
ValueError
Invalid temperature.
ZeroDivisionError
Wavelength is zero (when converting to frequency).
"""
# Convert to units for calculations, also force double precision
with u.add_enabled_equivalencies(u.spectral() + u.temperature()):
freq = u.Quantity(in_x, u.Hz, dtype=np.float64)
temp = u.Quantity(temperature, u.K, dtype=np.float64)
# Check if input values are physically possible
if np.any(temp < 0):
raise ValueError('Temperature should be positive: {0}'.format(temp))
if not np.all(np.isfinite(freq)) or np.any(freq <= 0):
warnings.warn('Input contains invalid wavelength/frequency value(s)',
AstropyUserWarning)
log_boltz = const.h * freq / (const.k_B * temp)
boltzm1 = np.expm1(log_boltz)
if _has_buggy_expm1:
# Replace incorrect nan results with infs--any result of 'nan' is
# incorrect unless the input (in log_boltz) happened to be nan to begin
# with. (As noted in #4393 ideally this would be replaced by a version
# of expm1 that doesn't have this bug, rather than fixing incorrect
# results after the fact...)
boltzm1_nans = np.isnan(boltzm1)
if np.any(boltzm1_nans):
if boltzm1.isscalar and not np.isnan(log_boltz):
boltzm1 = np.inf
else:
boltzm1[np.where(~np.isnan(log_boltz) & boltzm1_nans)] = np.inf
# Calculate blackbody flux
bb_nu = (2.0 * const.h * freq ** 3 / (const.c ** 2 * boltzm1))
flux = bb_nu.to(FNU, u.spectral_density(freq))
return flux / u.sr # Add per steradian to output flux unit
[docs]def blackbody_lambda(in_x, temperature):
"""Like :func:`blackbody_nu` but for :math:`B_{\\lambda}(T)`.
Parameters
----------
in_x : number, array-like, or `~astropy.units.Quantity`
Frequency, wavelength, or wave number.
If not a Quantity, it is assumed to be in Angstrom.
temperature : number, array-like, or `~astropy.units.Quantity`
Blackbody temperature.
If not a Quantity, it is assumed to be in Kelvin.
Returns
-------
flux : `~astropy.units.Quantity`
Blackbody monochromatic flux in
:math:`erg \\; cm^{-2} s^{-1} \\AA^{-1} sr^{-1}`.
"""
if getattr(in_x, 'unit', None) is None:
in_x = u.Quantity(in_x, u.AA)
bb_nu = blackbody_nu(in_x, temperature) * u.sr # Remove sr for conversion
flux = bb_nu.to(FLAM, u.spectral_density(in_x))
return flux / u.sr # Add per steradian to output flux unit