CRUSH Supported Instruments

SHARC 2

Documentation

User's Manual Extension for SHARC-2 (README.sharc2).
Notes for CRUSH-1.xx Users (README.crush-1.xx).

Pointing Corrections

You can specify the CSO pointing offsets (FAZO and FZAO) during reduction, and CRUSH will make the realignments as necessary (see fazo and fzao in the GLOSSARY). To help you determine the correct offsets to use, you can download

Darren's pointing tool (pointsharc).

The suggested values can be used in CRUSH-2 without precondition. For CRUSH-1.xx you may also need to specify the -pcenter=16.5,4.5 command-line option to set a non-standard pointing center during 2004 September and 2005 January (see Darren's readme).

Calibration

CRUSH will produce SHARC-2 images that are crudely calibrated (to ~20% rms) using a fixed conversion factor (from data units to Jy/beam). The actual flux conversion is dependent on the in-band, line-of-sight opacity τ and a number of other factors (e.g. detector temperature, optical configuration, cleanliness of the mirrors, focus quality and DSOS status).

You should never blindly trust the fluxes until you have applied order-of-unity corrections (see scale option in the GLOSSARY) based on observed calibrator sources. For more information, please refer to the

SHARC-2 calibration page

Atmospheric opacity (τ) correction

The atmospheric opacity correction is automatic. As configured, CRUSH tries to contact the MaiTau server for an appropriate τ value based on daily polynomial fits to the measured 225GHz radiometer or 350μm tipper data (see tau and maitau options in the GLOSSARY). If the MaiTau lookup fails, CRUSH-2 will calculate τ directly from the total-power loading of the bolometers. The direct method has been much improved since CRUSH-1.xx, and is very accurate under typical observing conditions (τ_225GHz < 0.1).