## Line vs continuum system temperature

In the online estimator (to be used for proposal preparation), the is interpolated in frequency, airmass, amount of precipitable water vapor, and ambient temperature from tabulated values (see Fig. ). The airmass is estimated using the maximum elevation of a source at the chosen Declination. The values are different for summer and winter due to the different atmospheric characteristics. Moreover, the chosen amount of precipitable water vapor depends on the receiver band (in addition to the season) because the NOEMA operation team schedule the different receiver bands according to the actual weather (high frequency bands are scheduled only during the best weather conditions).

The system temperature for a given LO frequency can be computed using an atmospheric model in ASTRO (ASTRO ATMOSPHERE command) with ambient temperature and precipitable water amount as input. The overall computing time of the continuum system temperature would be prohibitive because of the computation of the atmospheric model over the GHz IF bandwidth sampled every 100 MHz. Instead the computation is done off-line on a grid of LO frequency sampled every 1 GHz.