AAS Meeting #193 - Austin, Texas, January 1999
Session 36. HST Instrumentation
Display, Thursday, January 7, 1999, 9:20am-6:30pm, Exhibit Hall 1

## [36.05] Photometry with NICMOS

D. Calzetti, M. E. Dickinson, L. E. Bergeron (STScI), L. Colina (STScI/ESA)

We summarize the performance of the NICMOS instrument and discuss the measured sensitivity, and the photometric performance and stability. We also present a method for removing an instrument artifact termed pedestal'', a bias instability that is present at a low level in most NICMOS images. The characteristics of dark frames will also be discussed, in particular as they relate to pedestal correction.

NICMOS is capable of achieving the advertised performance in most areas. As an example, typical 3~\sigma detection limits for a 5 orbit observation with NIC2 are 1.47~mJy~arcsec-2 in F110W, 1.67~mJy~arcsec-2 in F160W, and 12.6~mJy~arcsec-2 in F222M. The absence of time-dependent backgrounds makes infrared photometry from NICMOS highly stable, reaching an accuracy of 2% or better. NICMOS absolute calibration has been accomplished with a combination of solar analog stars and white dwarf standard stars and achieves 5% absolute photometry. An exception to these accuracies occurs for NIC3 at short wavelengths where intra-pixel sensitivity variations produces variations in relative photometry as large as 20%.