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# Copyright (c) 2017 Weitian LI <liweitianux@live.com>
# MIT license
"""
Cosmology calculator for Chandra ACIS.
"""
import math
from astropy.cosmology import FlatLambdaCDM
import astropy.units as au
from .acis import ACIS
class Calculator:
"""
Calculate various quantities under a specific cosmology, as well
as some values with respect to Chandra ACIS detector properties.
"""
def __init__(self, H0=71.0, Om0=0.27, Ob0=0.046):
self.H0 = H0 # [km/s/Mpc]
self.Om0 = Om0
self.Ode0 = 1.0 - Om0
self.Ob0 = Ob0
self._cosmo = FlatLambdaCDM(H0=H0, Om0=Om0, Ob0=Ob0)
def luminosity_distance(self, z, unit="Mpc"):
dist = self._cosmo.luminosity_distance(z)
return dist.to(au.Unit(unit)).value
def angular_diameter_distance(self, z, unit="Mpc"):
dist = self._cosmo.angular_diameter_distance(z)
return dist.to(au.Unit(unit)).value
def kpc_per_arcsec(self, z):
"""
Calculate the transversal length (unit: kpc) corresponding to
1 arcsec at the *angular diameter distance* of z.
"""
dist_kpc = self.angular_diameter_distance(z, unit="kpc")
return dist_kpc * au.arcsec.to(au.rad)
def kpc_per_pix(self, z):
"""
Calculate the transversal length (unit: kpc) corresponding to
1 ACIS pixel (i.e., 0.492 arcsec) at the *angular diameter distance*
of z.
"""
pix = ACIS.pixel2arcsec * au.arcsec
dist_kpc = self.angular_diameter_distance(z, unit="kpc")
return dist_kpc * pix.to(au.rad).value
def cm_per_pix(self, z):
"""
Calculate the transversal length (unit: cm) corresponding to
1 ACIS pixel (i.e., 0.492 arcsec) at the *angular diameter distance*
of z.
"""
return self.kpc_per_pix(z) * au.kpc.to(au.cm)
def norm_apec(self, z):
"""
The normalization factor of the XSPEC APEC model assuming
EM = 1 (i.e., n_e = n_H = 1 cm^-3, and V = 1 cm^3)
norm = 1e-14 / (4*pi* (D_A * (1+z))^2) * int(n_e * n_H) dV
unit: [cm^-5]
This value will be used to calculate the cooling function values.
References
----------
* XSPEC: APEC model
https://heasarc.gsfc.nasa.gov/docs/xanadu/xspec/manual/XSmodelApec.html
"""
da = self.angular_diameter_distance(z, unit="cm")
norm = 1e-14 / (4*math.pi * (da * (1+z))**2)
return norm
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