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Hubble Space Telescope
NICMOS Observing Strategies

A summary of general recommendations for both Phase I and Phase II proposal preparation is available in Chapter 1 of the NICMOS Instrument Handbook; observers are strongly urged to review the material therein.

APT Phase II examples for coronagraphy, polarimetry, and grism spectroscopy are available for download in pdf format.

A new syntax for dither patterns has been developed which now allows multiple exposures (e.g. in different filters) to be taken at each dither position (for details, refer to Appendix D of the NICMOS Instrument Handbook for Cycle 14).

In order to reduce the degrading impact of cosmic ray persistence (see Chapter 4 of the NICMOS Instrument Handbook for details) after passage through the South-Atlantic Anomaly (SAA), a pair of ACCUM dark exposures will be obtained immediately after each HST orbit through the SAA. The scheduling of these dark exposures is automatic and transparent to the user. The darks yield a map of the persistence pattern, and can be used to subtract a significant amount of the unwanted persistence signal. Software for implementing this correction and are being tested and distributed since the start of Cycle 11 observations.

Observers are strongly advised to dither their observations as much as possible. This general advice regarding dithering is generally not applicable to observations of faint sources around/near bright ones. Dithering generally aids in the processes of removing cosmic rays, photon and cosmic-ray persistence, detector artifacts, and in averaging out flat-field sensitivity variations. HST absolute pointing is only good to about 1 arcsecond; dithering patterns should be designed to place science targets away from the edges of the cameras by at least this amount.

In the case of crowded fields, observers are advised to dither their observations with sub-pixel sampling.

Observers proposing to use the NICMOS coronagraphic hole may want to consider back-to-back visits, possibly within one orbit, of their targets with an in-between roll of the spacecraft for optimal PSF subtraction. Contemporary flat-field observations should also be considered for coronagraphic programs. Coronagraphic hole movements and HST focus changes (breathing) will result in residual noise during PSF subtraction. PSF stars should be observed close in time to the primary target.

The bottom 10-15 rows of the three cameras' field of views are somewhat vignetted and interesting targets should not be placed there.