Extreme Red Sensitivity of ACS/WFC
Abstract
Establishing the instrumental sensitivity as a function of wavelength within the domain covered by the F850LP (z) filter is critical for a number of ACS science programs. Absolute sensitivity calibrations with hot white dwarfs showed that substantial updates up to 20% in the blue were needed relative to pre-flight estimates, and were suggestive of a significant gradient in the far-red (0.85-1.1 microns) QE update needed (but did not suffice to constrain this well). We report here observations of several hot white dwarfs; as well as a M7 V, a L3.5 V and a T6.5 V star in F625W, F814W and F850LP with ACS/WFC. The concentration of flux for the coolest stars to the longest wavelengths probed with F850LP provide a means of defining the quantum efficiency curve underlying this broad filter. We find, unique to the z-band filter, that over the range O, M, L, T stars that the encircled energy for small-to-moderate apertures can vary at the level of 10s of percent. Attempts to separate out underlying QE variations and wavelength dependent PSF effects are reported on here. For an L dwarf, similar in SED to a high redshift Type Ia SN, these effects can reach half a magnitude for small apertures.
- Publication:
-
HST Calibration Workshop : Hubble after the Installation of the ACS and the NICMOS Cooling System
- Pub Date:
- 2003
- Bibcode:
- 2003hstc.conf...61G