-------------------------------------------------------------------- EGS NICMOS README File located in /net/marc/raid2/egs_nicmos_reduced Susan Kassin 9/15/2005 kassin@ucolick.org updated 1/20/2006 -------------------------------------------------------------------- In this directory you will find reduced and calibrated images from the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) onboard HST for the Extended Groth Strip (EGS) Survey. These data consist of 63 pointings in each the J (F110V) and the H (F160V) band filters. The final multidrizzled files are those with the suffixes '110_drz*.fits' and '160_drz*.fits' for the J and H bands, respectively. Each multidrizzled image is created from 4 individual images and is given the name of one of its constituent images. To find the name of the other 3 files, look in the list file that corresponds to the image (list* files in this directory). For example, n90r1picq_160_drz_sci.fits is the final multidrizzled image that contains the data from the n90r1picq_raw.fits image and 3 other images which looked at the same area of the sky. The corresponding list file is called list160.n90r1picq and tells you that the 3 other images are: n90r1pieq_raw1_clean.fits n90r1pivq_raw1_clean.fits n90r1piyq_raw1_clean.fits. *You will want to look at these *clean.fits images to see what went into the final multidrizzled image.* The final drizzled science and weight images have the extensions 'drz_sci.fits' and 'drz_weight.fits', respectively Do not trust the zero-points in the headers. Up-to-date zero-points can be found at: http://www.stsci.edu/hst/nicmos/performance/photometry/postncs_keywords.html Currently they are -21.10 mag (Vega) for both F110W and F160W. As a function as aperture size, the 5-sigma limits are... 26.5 - 2.5 * log_10 (d_aper / 0.52") in the F110W band (AB) 26.3 - 2.5 * log_10 (d_aper / 0.52") in the F160W band (AB) Instrument: NIC-3 (there are 3 NICMOS cameras), F110W and F160W filters It has a field of view of view of 51.2 x 51.2 arcseconds and 200 milliarcsec pixels. Filter Curve: see F110W_filtercurve.txt and F160W_filtercurve.txt files in this directory NIC-3 Instrument Handbook: http://www.stsci.edu/hst/nicmos/documents/handbooks/current_NEW/nicmos_instr_handbookTOC.html The following reductions were applied: -dark correct (applied HST's 'calnica' routine, but used the darks from the UDF); includes corrections for amplifier glow, bias, and shading -removing the 'pedistal' effect (variable quadrant bias) -correction for South Atlantic Anomaly impacted images (basically got rid of the cosmic ray persistence in these images using Space Telescope's model for our particular orbits) -create inverse variance maps..., apply static mask (mask of bad pixels on the detector) -subtract median image from itself (like removing variations in 'sky' brightness), median combine all images in the same filter and subtract that median image from each of the input images (like a 'sky' subtraction), shift the cleaned images to remove dithers and register them per visit; during this process sources are masked for sky medians -mutidrizzle... For more details, see the NICMOS Data handbook, and in particular sections 3 and 4: http://www.stsci.edu/hst/nicmos/documents/handbooks/DataHandbookv6/NICMOS_longdhbTOC.html ---------------------------------