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# -*- mode: python -*-
#
# Weitian LI
# Created: 2016-06-24
# Updated: 2016-06-24
#
# Change logs:
# 2016-06-24:
# * Add class 'ChandraPixel', moved from 'deproject_sbp.py'
#
"""
This module contains the parameters/constants used in astronomy
and astrophysics.
"""
import astropy.units as au
from astropy.cosmology import FlatLambdaCDM
class AstroParams:
"""
The parameters/constants used in astronomy.
References:
[1] ref. [4], eq.(9) below
"""
# Hubble constant at z=0
H0 = 71.0 # [ km/s/Mpc ]
# density of non-relativistic matter in units of the critical density
# at z=0
OmegaM0 = 0.27
# ratio of electron density (n_e) to proton density (n_p) [1]
ratio_ne_np = 1.211
# molecular weight per electron (0.3 solar abundance; grsa table) [1]
mu_e = 1.155
# atomic mass unit
m_atom = au.u.to(au.g) # [ g ]
class ChandraPixel:
"""
Chandra pixel unit conversions.
"""
angle = 0.492 * au.arcsec
z = None
# cosmology calculator
cosmo = None
# angular diameter distance
D_A = None
# length of one pixel at the given redshift
length = None
def __init__(self, z=None):
self.z = z
self.cosmo = FlatLambdaCDM(H0=AstroParams.H0,
Om0=AstroParams.OmegaM0)
if z is not None:
self.D_A = self.cosmo.angular_diameter_distance(z)
self.length = self.D_A * self.angle.to(au.radian).value
def get_angle(self):
return self.angle
def get_length(self, z=None):
if z is None:
length = self.length
else:
D_A = self.cosmo.angular_diameter_distance(z)
length = D_A * self.angle.to(au.radian).value
return length
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