brightness_temperature¶
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astropy.units.equivalencies.
brightness_temperature
(beam_area, disp)[source] [edit on github]¶ 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 unitsExamples
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) 217.2658703625732