brightness_temperature

astropy.units.equivalencies.brightness_temperature(beam_area, disp)

Defines the conversion between Jy/beam and “brightness temperature”, , 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).

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_sigma = 50*u.arcsec
>>> beam_area = 2*np.pi*(beam_sigma)**2
>>> freq = 5*u.GHz
>>> equiv = u.brightness_temperature(beam_area, freq)
>>> u.Jy.to(u.K, equivalencies=equiv)  
3.526294429423223
>>> (1*u.Jy).to(u.K, equivalencies=equiv)  
<Quantity 3.526294429423223 K>

VLA synthetic beam:

>>> bmaj = 15*u.arcsec
>>> bmin = 15*u.arcsec
>>> fwhm_to_sigma = 1./(8*np.log(2))**0.5
>>> beam_area = 2.*np.pi*(bmaj*bmin/fwhm_to_sigma**2)
>>> freq = 5*u.GHz
>>> equiv = u.brightness_temperature(beam_area, freq)
>>> u.Jy.to(u.K, equivalencies=equiv)  
7.065788175060084