14.8 MAMA Imaging Bright Object Limits

As described in Section 7.7, the MAMAs are subject to absolute brightness limits, above which sources cannot be observed or they would potentially damage the detectors. In Table 14.40, we present the complete set of bright object point source and integrated magnitude screening limits for the MAMA imaging modes. These screening magnitudes are presented as a guide. Whether or not an individual source can be observed is determined by whether the desired configuration and the spectrum of that source is predicted to exceed the global and local absolute observing count rate limits, as described in Chapter 7. Remember, sources cannot be observed in configurations where they exceed the absolute bright object limits. The information presented here should be used in conjunction with the material presented in Chapter 7.

A few important points to note:

• Limits are given as Johnson V Vega magnitudes, ergs/s/cm²/Å, or ergs/s/cm²/Å/arcsec².
• The limits were derived assuming zero slit loss.
  
• The imaging table includes a single point source limit. No single source in the field of view can exceed this limit.
  
• The limits in the tables assume zero extinction. If your source, when corrected for interstellar extinction, does not exceed the absolute limits, then you will be allowed to observe your source.
  
• The imaging table also includes an integrated magnitude limit. Remember that the global limit of 200,000 counts/s applies to all sources imaged onto the MAMA detector. The integrated magnitude limit gives the total magnitude from all stars (or galaxies, or diffuse objects) of spectral type O which can appear in the MAMA field of view. Initial screening of all MAMA imaging observations will be done assuming all stars are O stars, however, ultimately for the final decision, the colors of the stars are taken into account whenever such information is available (see Chapter 7).
  
• Be aware of the additional limitations that exist for crowded fields and slightly-resolved stellar clusters (see Section 7.7.3).
  
• M dwarf flaring is a potential issue for MAMA imaging observations. For more information, see STIS ISR 2017-02.
  

• This table is provided for general guidance, but deference should be given to ETC calculations, particularly for stars which deviate significantly from the spectral type template (e.g., accretion, chromospheric emission, etc.).

Table 14.40: MAMA Bright-Object limits (V magnitudes and cgs units). V magnitudes include NO additional safety factor to account for extrapolation uncertainties from the optical to the UV spectral range.

¹ Maximum allowed flux for a point source in ergs/s/cm²/Å.

² Maximum peak allowed flux for an extended source in ergs/s/cm²/Å/arcsec².

³ V magnitude limit for unreddened single stars. O5 V through F8 V are based on Kurucz (1993) models.
⁴ The magnitudes listed for G2 V are for the Solar template in the STIS ETC.
⁵ The magnitudes listed for G8 V are from IUE data for the star Tau Ceti.
⁶ The magnitudes listed for K2 V are from IUE data for the star Epsilon Eri.
⁷ The magnitudes listed for KM III are from IUE data for 9 stars of these types.
⁸ Maximum integrated V magnitude for stars in the field assuming all are of O5 V spectral type.
⁹ Maximum allowed flux for an extended source which covers the full detector in erg/s/cm²/Å/arcsec²