Source code for pyhetdex.het.flux_conversions

# Misc python library to support HETDEX software and data analysis
# Copyright (C) 2016  "The HETDEX collaboration"
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.
"""
Module to deal with converting between flux and
counts on the detector
"""

import numpy as np


def virus_eff(lbda):
    """
    Model fit to Virus + HET 

    Parameters
    ----------
    lbda : float
        wavelength in Angstroms

    Returns
    -------
    virus_eff : float
        the efficiency of Virus + HET 
    """

    l = lbda/1000.0
    return (-4.2490646 + 2.7864084*l - 0.57810372*l*l + 0.039241072*l*l*l)


def extinction(lbda, airmass):
    """Model fit to the atmospheric detection, taken from projector.cpp
    (automatically applied to input/output fluxes in Cure).

    Parameters
    ----------
    lbda : float
        wavelength in Angstroms
    airmass : float
    """
    lam = lbda / 1000.0

    l2 = lam*lam
    l3 = l2*lam
    l4 = l2*l2
    l5 = l2*l3
    l6 = l3*l3
    l7 = l3*l4

    ext_mag = (-323.131 + 481.712*lam - 303.375*l2 + 105.294*l3 - 21.8203*l4 +
               2.70452*l5 - 0.185798*l6 + 0.00545958*l7)

    ext = np.power(10.0, -0.4*ext_mag*airmass)

    return ext


def flambda_to_electrons(flbda, lbda, tint):
    """Convert flux to electrons assuming a 10 m clear aperture. Also taken
    from Cure.

    Parameters
    ----------
    flbda : float
        flux / lambda
    lbda : float
        wavelength
    tint : float
        exposure time
    """
    h = 1.054572e-34*2.*np.pi*1e7  # Planck's constant in erg
    c = 2.997925e+18  # c in A/s
    nu = c/lbda
    A = np.pi*(10.0/2.*100.)*(10.0/2.*100.)  # 10m clear aperture in cm^2

    # number of detected electrons for an object of spectrum flambda
    return A*tint*flbda/(h*nu)