+--------------------------------------------------------+ ACS SBC Bright Object Limit Revisions As discussed in the ACS Instrument Handbook for Cycle 17, Sections 4.4.2 and 5.5.2, during 2007 it was found that the SBC sensitivity to near-UV and optical light (the "red leak") is significantly greater than previously recognized (or alternatively, it has increased with time). Since the release of the current Handbook, further analysis has shown that the effect is somewhat less than specified there, but still much larger than previously recognized. Further details will be provided by Boffi et al. in ACS ISR 2008-02. *** (UPDATE NOTE: This will not be in an ISR, but is shown here and on the ACS Bulletin Board with subsequent posts, and will be updated for the next version of the ACS Instrument Handbook as well.) Also, see more details about "brightest pixe"l calculations and "IUE Stellar Spectra used for determining the KM III star bright object Vmag limits" in the last postings in the ACS Bulletin Board on this topic. The second pdf file there is the best-formatted source to look at or print for yourself. (Click on the link for this subject under "What's new on the Bulletin Board" on the top-level ACS page to get to this.) *** A revised sensitivity curve has been delivered to the calibration database, and since November 2007, that has been reflected in the ETC. Hence, the V-magnitude screening limits in Table 7.4, Section 7.2.2 of the Handbook are now fainter for stars later than type F0 V. Revised values are given in the following table. Revised bright-limit V-band magnitudes for observations with the SBC filters and prisms (no reddening). ---------------------------------------------------------- Spec F122M F115LP F125LP F140LP F150LP F165LP PR110L PR130L ---- ----- ------ ------ ------ ------ ------ ------ ------ F0 V 4.8 10.1 10.0 10.0 10.0 9.9 8.3 8.3 F2 V 4.0 9.3 9.3 9.2 9.2 9.1 7.6 7.5 F5 V 2.2 7.7 7.6 7.6 7.6 7.5 5.9 5.9 F8 V 0.9 6.8 6.8 6.7 6.7 6.7 4.7 4.7 G2 V 2.2 6.3 6.0 6.0 5.9 5.8 3.2 3.1 G8 V ... 5.6 5.6 5.4 5.2 4.8 2.2 2.1 K2 V ... 5.7 5.7 5.2 5.0 4.3 3.2 3.0 KM III ... 4.5 4.5 4.2 4.0 3.6 2.7 2.3 ---------------------------------------------------------- All values have been calculated with the ETC to satisfy the local countrate screening limit of 50 counts/second/pixel (Table 7.3), and all other input sources are also as specified in the Handbook, except that the KM III values are now the faintest for each spectral element among IUE data for 8 objects with spectral types from G8 through M5. +--------------------------------------------------------+
