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Cycle 21 Phase II Proposal Instructions
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Chapter 3: Fixed and Generic Targets > 3.3 Target Brightness and Bright Object Checking

3.3 Target Brightness and Bright Object Checking
Flux information is required to support bright object (ACS/SBC, COS, FGS, and STIS/MAMA) and persistence (WFC3/IR) checking on the target.
All flux information relevant for bright object checking must be provided.
3.3.1 Flux Data [Flux and Other_Fluxes]
Flux information must be provided for all targets, and there can be more than one entry for a given target. STScI uses flux information to check for over-illumination of sensitive detectors. All entries are values as observed at the Earth, rather than intrinsic values.
COS, ACS/SBC and STI/MAMA proposals cannot be implemented without flux information for all targets because of the critical requirements to protect the detectors from damage by excessively bright objects. Note that all objects in the field need to be checked, and there is a Bright Object Tool in APT to support that checking.
The flux information is provided in two separate fields:
Other Fluxes (separated by commas), which is entered in free text.
In the “Other Fluxes” field, the spectral type and reddening could be provided if you think it’s important. As many additional flux values as appropriate for the requested exposures should be provided. For example, ultraviolet or emission-line fluxes should be given if the target is to be observed in the ultraviolet or through a narrow-band filter, or several magnitudes might be provided if the target is a variable star to be observed at various brightness levels. In some cases (Targets of Opportunity, variable objects, etc.) the estimated flux data may be very uncertain, but the best available estimates should nevertheless be given, along with appropriate uncertainties and comments.
It may be important to specify the flux of a background source as well as the target flux. For example, a globular cluster in M87 may be seen against the bright background of the galaxy. The suffix –BKG should be appended to a background flux specification in this case (e.g. SURF-BKG(B) = 20 +/– 0.2 mag/arcsec2). Use a comma to separate entries if more than one flux value is given.
Text Proposal File
If you are using the Text Proposal File, flux items in a list must be separated by commas.
3.3.1.1 General Guidelines on What Flux Data to Include
The following summary provides general guidelines for what flux information could be included in three general areas.
Target Flux
1.
2.
3.
4.
5.
Background Flux
1.
2.
Surface Flux
1.
2.
Dispersive spectral element: Continuum (point source) or surface (extended source) flux at wavelength of observation and size of the region specified,
or
Line flux (point source), line surface flux (extended source), and line width of brightest emission line in the wavelength range of observation
.
Note: Details of how the above flux information was derived should be given in the Observing Description or Target Comment, as appropriate. If any of the required flux data cannot be provided or are deemed to be unnecessary, these points must also be explained in that section. Incomplete flux information may delay the implementation of your proposal, especially in the case of ACS/SBC, COS and STIS/MAMA observations.
3.3.2 Radial Velocity or Redshift [RV_ or _Z]
Give, if known, the heliocentric radial velocity or redshift of the target. The format is <velocity in km/sec> or <redshift>; examples are +1198 (Radial Velocity) and 1.95 (Z). The units must not be specified.
Text Proposal File
In the Text Proposal File the format is V = +1198 and Z = 1.95.
3.3.3 Bright-Object Constraints
Several of the Scientific Instruments must be protected against over-illumination. Table 3.12 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 should be used to check on these constraints. Proposers should check the entire field using the Aladin interface provided in APT.
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, other fluxes 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.
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.
Time Calculator (ETC available at http://etc.stsci.edu/etc/input/acs/imaging) and with the Bright Object tool in APT. 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, other fluxes 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.
The FGS may view objects brighter than mV = 8.0 only if the neutral-density filter is in place.
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.
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, other fluxes must be provided for all
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.

1
see http://www.stsci.edu/hst/proposing/apt/using_apt for a description of the APT Bright Object tool.


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