radiation_fields.py
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# -*- coding: utf-8 -*-
"""
Created on Thu Jun 23 09:55:18 2022
@author: frede
"""
import numpy as np
from astropy.table import Table
'''
This program calculates the scaling factor of the radiation field G0 relative
to the data of an object or a set of objects radiating for given distances
A file containing my G0 values with the associated distance will then be created
We take the standard Habing value for the interstellar medium 5.6x10^-14 ergs cm-3
between 91.2 and 240nm as normalization factor of G0
The file to be used must contain in column 1 the wavelength in nm,
and in column 2 the intensity per wavelength per sr (in erg cm-2 s-1 nm-1 sr-1).
Each column should not have a name
Example of execution of the program for the star of 10 solar radius HD200775,
for a distance to the star at 20pc :
radiation_field(filename='HD200775_RF.txt', star_radius=10, parsec=20)
If I want to generate a hundred values of G0 :
radiation_field('HD200775_RF.txt', 10, 20, ISRF=False, RF_list=True)
The program will tell me that for 20pc my first value of G0 is not of the order of 1e6,
and will make me enter a new value of distance (in pc) until finding G0 of the order of 1e6
If I want to calculate G0 for the interstellar medium
with an approach described by Habing (1968),
(using Habing file with datas of wavelength and intensity per wavelength per sr) :
radiation_field('habing1968.txt', 1, 1, ISRF=True)
For the interstellar medium, the parameters star_radius, parsec and RF_list
are no longer important;
the part of the program executed will be independent of them
'''
''' Constants '''
h = 6.62607015e-34 #Planck constant in J s
c = 299792458 #Light speed in m s-1
''' Conversions '''
ev = 1.602176634e-19 # 1 ev = 1.602176634e-19 J and value of electron charge
def radiation_field(filename, star_radius , parsec, ISRF=False, RF_list=False):
"""
----------
filename : str,
name of the .txt containing intensity and wavelength data
parsec : float,
distance in parsec from the star
star_radius : float,
star radius, in unit of solar radius
ISRF : bool,
Interstellar Radiation Field; if true, then the filename is a file for ISRF
if false, the radiation field of a star is studied
RF_list: bool,
If false, the calculation of G0 is done for a given distance,
if true, it is done for a hundred distances whose input distance
will correspond to a G0 of the order of 1e6
returns the value of G0 for a given distance, the distance,
wavelengths from 91.2nm (13.6ev) to 2 microns, the corresponding intensity
at a distance d_0, the energy intensity, the energy, the values of ISRF and RF_list
-------
"""
''' association of file data '''
wave_intensity = Table.read( filename, format='ascii' )
wavelength = wave_intensity['col1'] #in nm
wavelength_intensity = wave_intensity['col2'] #in erg cm-2 s-1 nm-1 sr-1
#=> intensity per nm per sr
''' useful parameters '''
radiation_field = []
distance = []
energy = ( ( (h/ev) * (c*1e2) ) / (wavelength*1e-7) )[::-1] #in ev
r = star_radius*7e10 #radius of the star in cm
d_0 = 3.086e18*parsec #1pc = 3.086e18cm
''' energy intensity in erg s-1 cm-2 sr-1 eV-1 '''
energy_intensity = wavelength_intensity[::-1] * ( (h/ev) * (c*1e9) )/(energy**2)
''' indentation '''
i=0
if ISRF :
''' Radiation Field '''
intensity_range = (wavelength >= 91.2) & (wavelength <= 240)
#far UV range, 91.2nm corresponding to 13.6ev
g_0 = np.trapz( 2*np.pi * wavelength_intensity[intensity_range], wavelength[intensity_range])/(5.6e-14 * c*1e2)
#g_0 dimensionless
radiation_field.append(g_0)
distance.append(0)
else:
if RF_list :
while i < 100:
''' distance '''
if i == 0 :
d = d_0
else:
d = 5*i * d_0
''' initialization '''
g_0 = 0
''' geometrical dillution '''
diluted_intensity = wavelength_intensity*(r/d)**2
#intensity diluted and extincted in erg cm-2 s-1 nm-1 sr-1
'''energy intensity in erg s-1 cm-2 sr-1 eV-1'''
energy_intensity = diluted_intensity[::-1] * ( (h/ev) * (c*1e9) )/(energy**2)
''' Radiation Field '''
intensity_range = (wavelength >= 91.2) & (wavelength <= 240)
g_0 = np.trapz(2 * np.pi * diluted_intensity[intensity_range], wavelength[intensity_range])/(5.6e-14 * c * 1e2)
distance.append(d)
radiation_field.append(g_0)
if (radiation_field[0] >= 2e6 or radiation_field[0] < 1e6):
radiation_field = []
parsec = float(input('radiation_field[0] = {}, set a value of parsec such that radiation_field[0] is proportional to 1e6 : '.format(g_0),))
distance = []
d_0 = 3.086e18*parsec
i = 0
else:
i = i + 1
else:
d = d_0
''' geometrical dillution '''
diluted_intensity = wavelength_intensity*(r/d)**2
'''energy intensity in erg s-1 cm-2 sr-1 eV-1'''
energy_intensity = diluted_intensity[::-1] * ( (h/ev) * (c*1e9) )/(energy**2)
''' Radiation Field '''
intensity_range = (wavelength >= 91.2) & (wavelength <= 240)
g_0 = np.trapz(2 * np.pi * diluted_intensity[intensity_range], wavelength[intensity_range])/(5.6e-14 * c * 1e2)
distance.append(d)
radiation_field.append(g_0)
''' creation of data files '''
document_1 = Table([wavelength , wavelength_intensity] , names =('col1','col2'))
document_1.meta['comments'] = ['wavelength (nm)' , 'intensity (erg s-1 cm-2 nm-1 sr-1)']
document_1.write('intensity_per_wavelength.txt', format = 'ascii', overwrite=True)
document_2 = Table([distance , radiation_field], names =('col1', 'col2'))
document_2.meta['comments'] = ['distance (cm)' , 'radiation field (dimensionless)']
document_2.write('radiation_field_per_distance.txt', format = 'ascii', overwrite=True)
return radiation_field[0], distance[0], wavelength, wavelength_intensity, energy_intensity, energy, ISRF, RF_list