Definition of a Cut for Multiplexing between Bolocam and High - Frequency Observations at the CSO Version 3 Sunil

It is expected that the CSO’s observatory efficiency can be increased by weather-multiplexing highand low-frequency observations. We define schemes for multiplexing between Bolocam lowfrequency (150 and 275 GHz) and high-frequency (850 GHz) SHARC-II or heterodyne observations. The SHARC-II multiplexing scheme is a simple cut in τ225. The heterodyne multiplexing scheme makes use of the wide range of Bolocam mapping speeds obtained for a given atmospheric opacity to define a cut in the plane of τ225 vs. Bolocam mapping speed. With these multiplexing schemes, the observing speeds of the individual instruments are typically degraded by 20-30% relative to the speeds that would be achieved without multiplexing, so multiplexing is expected to improve observatory efficiency for high-priority scientific programs by about 50%. 1 Motivation and rough scheme Due to the rarity and lack of predictability of low-opacity observing conditions at Mauna Kea (or elsewhere, for that matter), there is a great advantage to be gained in allocating observing time in a weatheror frequency-multiplexed fashion. In such a scheme, observing time is allocated directly to a low-frequency program (ν < 350 GHz) that can make use of most reasonable observing conditions (τ225 < 0.15, for example), with the stipulation that the telescope be handed over to a high-frequency program in low τ225 conditions. There should be significant improvement in observatory efficiency and science output: high-frequency programs will have access to all lowopacity periods, rather than only those low-opacity periods occuring during time allocated explicitly to such programs; and, periods of moderate to high opacity that are useless to high-frequency observations will be available to low-frequency observations rather than letting the telescope sit idle (or devoting such periods to relatively low-priority low-frequency backup programs). Such a multiplexing scheme can only succeed if it is implemented for long enough stretches of time that many different weather conditions are averaged over. The extended (' 30-night) survey runs that are frequently allocated to Bolocam, the CSO’s 275 GHz and 150 GHz facility camera, meet this length criterion. This averaging ensures a predictable time split between high-frequency and low-frequency observations; the lost low-frequency observing time can be corrected for by simply allocating an equal additional fraction of time to the multiplexed program. 2 Mapping speed and opacity The conventional scheme for such multiplexing uses a simple cut on τ225. However, an additional empirical fact of relevance is that the Bolocam mapping speed shows a large dispersion for any given