# Summary of the impact on instrument calibration

Figure 10: Brightness temperature ratio as a function of frequency for Mars ( ), Uranus ( ) and Neptune ( ), the planets that are the most used for IRAM flux calibration. Mars is representend with two lines in order to represent the minimum and maximum values reached during the time variation of its brightness temperature.

The use of 2024 planet models for data calibration will have its strongest effect at lower end of the IRAM frequency ranges (below 100 GHz), where the brightness temperatures of the 3 mostly used planets are on the order of 5–10% lower in the 2024 model than in the Legacy version (see Fig. 10).

The difference between the 2024 and Legacy models is also large in the presence of planet atmospheric lines. This concerns mainly the CO lines in Neptune, where the 2024 model give lower brightness temperatures than the Legacy one. However, the presence of these lines is well known and in general taken into account.

In these two cases, 2024 brightness temperatures are lower than the Legacy values, so the instruments are more performant than it was deduced using the Legacy ASTRO models (higher beam efficiency at 30m and lower secondary calibrator flux, and so Jy/K efficiencies, for NOEMA). This will have to be taken into account into calibration software like MRTCAL () and CLIC PIPELINE (lightcurves of secondary calibrators).

The Mars brightness light curve is globally below the Legacy Mars brightness up to almost 300 GHz, where it gets symmetric around the Legacy values (5%).

Above 120 GHz Netpune and Uranus 2024 models give temperatures closer to the Legacy values, with offset of 2–4%, which is smaller than the model absolute accuracy (5%).

There are two cases in which the brightness temperature is higher in the 2024 models: i/ for Mars, at frequencies above 230 GHz, during half of the long term variation, where the offset can reach 5%; ii/ for Neptune, at frequencies above 130 GHz, but with a very small effect of 2%.