COS ETC Cycle 19 Warnings
(last updated: 11/15/2011 )
The two new COS/FUV G130M modes (cenwave=1055 and cenwave=1096) have resolution of R ~ 3000 at 950 A, decreasing to R ~ 1000 at 1150 A and dispersion of ~ 0.01 A/pixel, similar to the dispersion of the other, higher resolution, modes. This implies that at 950 A one resolution element is around 30 pixels. Since the ETC uses a resolution element that is 5 times smaller (6 pix), it will overestimate the time required to achieve a certain S/N per 30 pixel resolution element, while underestimating the S/N per 30 pixel resolution element for a given time. To calculate the correct exposure time per real 30 pix resolution element, divide the exposure time returned by the ETC by 5 (= 30/6). To calculate the correct S/N per real 30 pix resolution element, multiply the S/N returned by the ETC by 2.2 (= 5^0.5).
COS ETC Cycle 18 Warnings
(last updated: 11/15/2011 )
COS BOA Calculations for Wavelengths <1200 Å
The transmission of the BOA aperture at the short wavelengths seen by the G140L 1105 and 1280 cenwaves, while not fully characterized, is expected to be close to zero (due to MgF2 cutoff for wavelengths shorter than 1200 A). The values reported by the Spectroscopic COS ETC, for calculations using the BOA at wavelengths shorter than 1200 A, are not accurate and should not be used for planning any COS observations.
COS Web Form Bug
Version 18 of the ETC, which was installed in the Fall of 2009, contained a bug in the web forms for COS imaging ETC that affected calculations performed using a point source with a size other than the default. A fix to this problem was installed on 2/17/2010. Users who think their previous ETC calculations may have been affected by this problem should repeat their calculations.
The problem corrected by this new version of the ETC occurred when the "Point Source" option is selected in section 2 of the ETC input form and "circular region" is selected via the pull down menu option, the calculation is performed using a circular region of radius 0.4 arcsec, regardless of the value selected in the pull down menu.
ETC Calculations Using COS Spectroscopic TA with G285M/2739
Using this mode in the ETC will cause a JavaNullPointerException error. Although not available in the ETC, there is a workaround for this problem. If you need to use this mode, please contact the helpdesk help@stsci.edu.
Warning regarding G140L cenwaves in ETC vs APT
Cycle 18 users are advised that the "1250" G140L cenwave in ETC 18.0.5 is identical and refers to the same mode as the cenwave called "1280" in APT and the Cycle 18 COS Instrument Handbook. GOs preparing Cycle 18 phase II should do ETC calculations with G140L/1250, but use G140L/1280 setting in their APT phase II. Cycle 17 users should NOT change and re-submit their phase IIs in relation to this change in cenwave name. All Cycle 17 phase IIs should use the G140L/1230 nomenclature instead.