WFC3 Instrument Handbook for Cycle 24

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1.5	Special Considerations for Cycle 24

1.5.1 Current Instrument Status

1.5.2 Ongoing Calibration

1.5.3 New Capabilities

1.5.1 Current Instrument Status

WFC3 is operating as expected on HST, with its detectors at nominal setpoints of –83°C (UVIS) and –128°C (IR). There are no significant anomalies in its performance.

1.5.2 Ongoing Calibration

At the time of this writing, cycle 22 calibration observations have been nearly completed and cycle 23 calibration observations have begun. Descriptions of the calibration plan for each cycle are given in Appendix E and at:

http://www.stsci.edu/hst/wfc3/calibration.

Much of the analysis of the calibration programs from past cycles has already been documented in WFC3 Instrument Science Reports published on the WFC3 website; documentation of the remaining analysis is on-going.

Proposers and users of WFC3 should monitor the Cycle 24 announcement website for the latest information:

http://www.stsci.edu/hst/proposing/docs/cycle24announce

Additional information will be released as part of WFC3 Space Telescope Analysis Newsletters (STANs) and other updates posted directly to the WFC3 website:

http://www.stsci.edu/hst/wfc3

Throughout this handbook, a special “Online” symbol indicates information that is especially likely to be updated on the WFC3 website.

1.5.3 New Capabilities

UVIS SHUTTER BLADE: The capability of commanding the UVIS shutter to use exclusively one of the two sides of the shutter blade in short exposures, resulting in less vibration and PSF smearing, was implemented early in cycle 21. This option will be made available to the observer when it is critical to the scientific success of a program. See Section 6.11.4.

UVIS POST-FLASH: The major new capability of adding a flash at the end of a UVIS exposure (post-flash) was implemented for Cycle 20. APT began to issue diagnostic reports on exposures with inadequate or excessive flash in Cycle 23. Post-flash greatly increases the detection of faint sources in low background observations, where CTE losses would otherwise remove much or all of the flux from the sources. Most UVIS observers should consider using post-flash. It is useful for all UV, narrow band, and relatively short medium and broad band exposures where the detection of faint sources is required. It should replace Charge Injection in essentially all circumstances. (See Section 6.9.2) Those who are considering using Charge Injection rather than post-flash should consult STScI. See Section 5.4.11, Section 6.9, and the WFC3 UVIS CTE webpage for further information on CTE and post-flash.

SPATIAL SCANS: The observing technique of spatial scanning was introduced for WFC3 in cycle 19. (See Sections 6.12.3, 7.10.4, and 8.6.) Spatial scan mode was added to the ETC for UVIS and IR imaging and IR spectroscopy for cycle 24. This mode can be used to turn stars into well-defined streaks on the detector or to spread a stellar spectrum perpendicular to its dispersion. It is useful for:

•	Observations requiring high temporal sampling and/or time resolution

•	More efficient observation; higher S/N observations of exoplanet transits

•	High precision relative astrometric observations

•	Imaging and spectroscopy of brighter sources than previously possible

 

Information especially likely to be updated on the WFC3 website is indicated by this symbol.