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| -rw-r--r-- | fg21sim/utils/convert.py | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/fg21sim/utils/convert.py b/fg21sim/utils/convert.py new file mode 100644 index 0000000..1212780 --- /dev/null +++ b/fg21sim/utils/convert.py @@ -0,0 +1,63 @@ +# Copyright (c) 2016 Weitian LI <liweitianux@live.com> +# MIT license + +""" +Utilities for conversion among common astronomical quantities. +""" + +import astropy.units as au + + +def Fnu_to_Tb(Fnu, omega, freq): + """Convert flux density to brightness temperature, using the + Rayleigh-Jeans law, in the Rayleigh-Jeans limit. + + Parameters + ---------- + Fnu : `~astropy.units.Quantity` + Input flux density, e.g., `1.0*au.Jy` + omega : `~astropy.units.Quantity` + Source angular size/area, e.g., `1.0*au.sr` + freq : `~astropy.units.Quantity` + Frequency where the flux density measured, e.g., `1.0*au.MHz` + + Returns + ------- + Tb : `~astropy.units.Quantity` + Brightness temperature, with default unit `au.K` + + References + ---------- + - Brightness and Flux + http://www.cv.nrao.edu/course/astr534/Brightness.html + - Wikipedia: Brightness Temperature + https://en.wikipedia.org/wiki/Brightness_temperature + - NJIT: Physics 728: Introduction to Radio Astronomy: Lecture #1 + https://web.njit.edu/~gary/728/Lecture1.html + - Astropy: Equivalencies: Brightness Temperature / Flux Density + http://docs.astropy.org/en/stable/units/equivalencies.html + """ + equiv = au.brightness_temperature(omega, freq) + Tb = Fnu.to(au.K, equivalencies=equiv) + return Tb + + +def Sb_to_Tb(Sb, freq): + """Convert surface brightness to brightness temperature, using the + Rayleigh-Jeans law, in the Rayleigh-Jeans limit. + + Parameters + ---------- + Sb : `~astropy.units.Quantity` + Input surface brightness, e.g., `1.0*au.Jy/au.sr` + freq : `~astropy.units.Quantity` + Frequency where the flux density measured, e.g., `1.0*au.MHz` + + Returns + ------- + Tb : `~astropy.units.Quantity` + Brightness temperature, with default unit `au.K` + """ + omega = 1.0 * au.sr + Fnu = Sb * omega + return Fnu_to_Tb(Fnu, omega, freq) |