3.10 Bright-Object Constraints

Several of the Scientific Instruments must be protected against over-illumination. Table 3.13 summarizes the safety restrictions by instrument. You should not propose observations which violate these guidelines. Non-linearity, saturation, or other temporary effects which may occur at substantially fainter limits than those identified below are described in the Instrument Handbooks.

APT contains a Bright Object Tool (BOT) that can be used to check on these constraints. Proposers should check both the target and the entire field (35" radius from the target for a single default pointing at any orientation, larger plus 5" buffer with POS TARGets or other displacements), using the Aladin interface provided in APT.

Table 3.13: Bright-Object Constraints 

Instrument	Description
STIS	The STIS MAMA (UV) detectors are subject to strict bright-object controls to prevent potentially fatal damage. Maximum permissible local and global count rates have been established for the STIS MAMA detectors, both for imaging and spectroscopy, and are given in the STIS Instrument Handbook. These limits have been translated into limiting magnitudes and fluxes for the various configurations and modes. Some of these limits are quite faint. All potential targets and field objects with in a certain field of view, which depends on the configuration selected, should be checked for safety with the STIS Exposure Time Calculator (ETC available at http://www.stsci.edu/hst/stis/software/etcs) and with the Bright Object tool in APT1. Measured UV fluxes must be provided for any object within 1 magnitude of the brightness limits; if not previously available, they must be first observed with a safe STIS mode. Unless they can be screened with GSC2/DSS, magnitudes and colors, or a UV image, must be provided for all objects in the fields of proposed STIS MAMA observations, including the background fields of solar-system targets. ORIENTs and/or POS TARGs may be used to avoid potentially problematic objects. There are no safety-related brightness limits for the STIS CCD. See the STIS Instrument Handbook for a description of saturation levels, residual charge, and other effects.
ACS	The ACS/SBC MAMA detector is subject to strict bright-object controls to prevent potentially fatal damage. Maximum permissible local and global count rates have been established for both imaging and spectroscopy; see the ACS Instrument Handbook (Section 7.2). These limits have been translated into a table of magnitudes as a function of spectral type for the various configurations and modes (ACS Instrument Handbook, Table 7.4). Some of these limits are quite faint. All potential targets should be checked for safety with the ACS Exposure Time Calculator (ETC available at http://etc.stsci.edu/etc/input/acs/imaging). Measured UV fluxes must be provided for any objects within one magnitude of the spectroscopic limits. This requirement extends to both targets and field objects on the detector. ORIENTs and/or POS TARGs may be used to avoid the latter. Unless they can be screened with GSC2/DSS, magnitudes and colors, or a UV image, must be provided for all objects in the fields of proposed SBC observations, including the background fields of solar-system targets. There are no safety-related brightness limits for the ACSWFC CCD cameras. See the ACS Instrument Handbook for a description of saturation levels, residual charge, and other effects.
FGS	The FGS may not be used to view objects brighter than mV = 1.8. The FGS may view objects brighter than mV = 8.0 only if the neutral-density filter is in place.
COS	The detectors used in the COS/FUV and COS/NUV channels are both subject to strict bright-object controls to prevent potentially fatal damage. The maximum permissible local and global count rates have been established and are given in the COS Instrument Handbook. These limits have been translated into equivalent limiting magnitudes and fluxes. Some of these limits are quite faint. All potential targets and field objects within a certain field of view must be checked for safety with the COS Exposure Time Calculator (ETC available at http://www.stsci.edu/hst/cos/software/etcs) and with the Bright Object tool in APT1. Measured UV fluxes must be provided for any object within one magnitude of the brightness limits. Unless they can be screened with GSC2/DSS, magnitudes and colors, or a UV image, must be provided for all objects in the fields of proposed COS observations, including the background fields of solar-system targets. ORIENTs and/or POS TARGs may be used to avoid potentially problematic objects.
WFC3	There are no safety-related brightness limitations for either the UVIS or IR channels. Please refer to the WFC3 Instrument Handbook, Appendix D for a description of persistence of saturated images.

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1

see http://www.stsci.edu/hst/proposing/apt/using_apt for a description of the APT Bright Object tool.