brightness_temperature¶

astropy.units.equivalencies.brightness_temperature(beam_area, disp)[source] [edit on github]¶

Defines the conversion between Jy/beam and “brightness temperature”, $T_B$ , in Kelvins. The brightness temperature is a unit very commonly used in radio astronomy. See, e.g., “Tools of Radio Astronomy” (Wilson 2009) eqn 8.16 and eqn 8.19 (these pages are available on google books).

$T_B \equiv S_\nu / \left(2 k \nu^2 / c^2 \right)$

However, the beam area is essential for this computation: the brightness temperature is inversely proportional to the beam area

Parameters:

beam_area : Beam Area equivalent

Beam area in angular units, i.e. steradian equivalent

disp : Quantity with spectral units

The observed spectral equivalent Unit (e.g., frequency or wavelength)

Examples

Arecibo C-band beam:

>>> import numpy as np
>>> from astropy import units as u
>>> beam_area = np.pi*(50*u.arcsec)**2
>>> freq = 5*u.GHz
>>> equiv = u.brightness_temperature(beam_area, freq)
>>> u.Jy.to(u.K, equivalencies=equiv)  
7.052588858846446
>>> (1*u.Jy).to(u.K, equivalencies=equiv)  
<Quantity 7.052588858846446 K>

VLA synthetic beam:

>>> beam_area = np.pi*(15*u.arcsec)**2
>>> freq = 5*u.GHz
>>> equiv = u.brightness_temperature(beam_area, freq)
>>> u.Jy.to(u.K, equivalencies=equiv)  
78.36209843162719

Navigation

brightness_temperature¶

Page Contents