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# -*- mode: python -*-
#
# Weitian LI
# Created: 2016-06-24
# Updated: 2016-06-24
#
# Change logs:
# 2016-06-24:
# * Add some constants from `astropy.constants`
# * Add parameter 'mu'
# * Fix reference
# * Add class 'ChandraPixel', moved from 'deproject_sbp.py'
#
"""
This module contains the parameters/constants used in astronomy
and astrophysics.
"""
import astropy.units as au
import astropy.constants as ac
from astropy.cosmology import FlatLambdaCDM
class AstroParams:
"""
The parameters/constants used in astronomy.
NOTE:
The 'cgs' unit system is used.
References:
[1] Ettori et al, 2013, Space Science Review, 177, 119-154
"""
# Gravitational constant
G = ac.G.cgs.value # [ cm^3 g^-1 s^-2 ]
# Boltzmann constant
k_B = ac.k_B.cgs.value # [ erg K^-1 ]
# Atomic mass unit (i.e., a.m.u)
m_atom = ac.u.cgs.value # [ g ]
# 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)
# (Ref: [1], eq.(9) below)
ratio_ne_np = 1.211
# molecular weight per electron (0.3 solar abundance; grsa table)
# (Ref: [1], eq.(9) below)
mu_e = 1.155
# mean molecular weight (unit: a.m.u) [1] (Ref: [1], eq.(6) below)
mu = 0.6
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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