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Going from $T_A^*$ to $T_{\mathrm{mb}}$

In CLASS, the brightness scale is assumed to be expressed in $T_A^*$ when the forward and beam efficiencies are equal. To check this, you can type

LAS> EXAMINE R%HEAD%CAL%BEEFF R%HEAD%CAL%FOEFF
R%HEAD%CAL%BEEFF = 0.9600000    ! Real    GLOBAL RO
R%HEAD%CAL%FOEFF = 0.9600000    ! Real    GLOBAL RO
In this case, if the source properties are better represented by the main temperature scale ( $T_{\mathrm{mb}}$), you can convert the scale from $T_A^*$ to $T_{\mathrm{mb}}$ with
LAS> EXAMINE R%HEAD%HER%ETAL R%HEAD%CAL%FOEFF  ! Check that they have identical values
R%HEAD%HER%ETAL = 0.9600000     ! Real    GLOBAL RO
R%HEAD%CAL%FOEFF = 0.9600000    ! Real    GLOBAL RO
LAS> EXAMINE R%HEAD%HER%ETAMB                  ! Check that the beam efficiency is sensible
R%HEAD%HER%ETAMB =   0.6223738  ! Real    GLOBAL RO
LAS> MODIFY BEAM_EFF R%HEAD%HER%ETAMB          ! Scale conversion
I-MODIFY,  Former beam efficiency: 0.9600, new: 0.6224
The MODIFY BEAM_EFF command will multiply the spectrum by R%HEAD%CAL%FOEFF / R%HEAD%HER%ETAMB and change the associated header parameters accordingly, e.g. baseline rms and $T_{\mathrm{sys}}$.



Gildas manager 2023-06-01