The new generation of instruments at APEX have large bandwidths, up to 8 GHz per sideband, and many of them are 2SB, which means that you can get the two sidebands simultaneously during the same observation.
These are powerful features which allow the PI to strategically select the tuning frequency of the instrument so that it can cover two, three or more astronomical lines in the same setup.
We have created the instrument setup tool to help PIs finding the right tuning for the science goal of their interest, keeping in mind the large bandwidth. The tool allows to visualise simultaneously the atmospheric transmission over Chajnantor plateau and the frequency span covered by the different instruments. You can select the pwv content of the atmosphere and see where the strong atmospheric absorptions lie within your bandwidth
- You can select the LSB or USB tuning for your sky frequency and see which is less affected by the atmosphere in the image sideband.
- If your astronomical line lies on top of one atmospheric absorption by ozone or water, you can slightly shift your tuning frequency to move the line away. You can use the buttons +100 MHz or -100 MHz for this purpose.
- Try to avoid placing your line too close (<200 MHz) to the edges of the bands or in the overlap region between the 4-GHz backend groups (for those instruments with 8 GHz bandwidth). You could have in those regions some aliasing effects.
- When you select a given source elevation you will see in the plot both the transmissions at zenith and at that elevation, so you can compare what is the expected loss of transmission due to the airmass.
- You have some drop-down menus with typical astronomical lines found in space at the frequencies covered by the instrument you selected. You can play to see how many you can get inside your tuning. For instance, if you tune nFLASH230 at 249.9 GHz LSB you will get in your bandwidth SiO(6-5) @ 260.52, HCN(3-2) @ 265.89, HCO+(3-2) @ 267.56, H13CO+(3-2) @ 260.26 and CS(5-4) @ 244.94.