SEQUOIA, photograph of one of the assembled 16-pixel arrays.
SEQUOIA is a cryogenic focal-plane array of 16 pixels, arranged in a 4×4 array, that operates in the range 85 – 115 GHz. The array, which is feed by square horns separated by 2 f λ, is cooled to 18K and use low-noise Indium Phosphide (InP) monolithic microwave integrated circuit (MMIC) preamplifiers designed at UMass to provide a characteristic receiver noise of 55K in the range 85-107 GHz, increasing to 90K at 115 GHz.
SEQUOIA was the workhorse facility instrument for the FCRAO 14-m telescope for many years. Installed at the LMT in 2017, the refurbished SEQUOIA has a new digital spectrometer with a total bandwidth options of 200, 400, and 800 MHz. All pixels of the array track the same frequency window, so nominally a single spectral line is observed at a time by the array. However, we note that in some cases two lines may fall within the same spectral window so that they may be imaged simultaneously (e.g. HCO+ J=1-0 and HCN J=1-0 in the 800 MHz bandwidth mode of the spectrometer).
Sensitivity and integration time calculators for SEQUOIA are available in LMT-Hedwig, the LMT’s proposal submission system. Documentation and a simple example on how to use this calculators are available here.