Physics
Scientific paper
Jul 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004hst..prop10709b&link_type=abstract
HST Proposal ID #10709
Physics
Hst Proposal Id #10709
Scientific paper
In cycle 12, 24 orbits were used to measure the NICMOS grism mode sensitivities and to establish a set of IR flux standards with a goal of 1% accuracy. However, the short wavelength response shows a 5.6%/dex apparent non-linearity in the overlap region with STIS {Bohlin, Lindler, & Riess NICMOS ISR 2005-02}. Studies of the _ima files for both the grism data and for stellar photometry suggest that the NICMOS count rates are a monotonically rising function of integration time. The typical integration time of the grism observations are typically 1-2min with a maximum of 3min, while the most interesting science observations are typically 5-10x longer. At a declination of +72deg, a previous observation of WD1057+719 obtained 04Apr2 reached at an exposure time of 3min for each of 15 dither positions. By reducing the dithers to 2, exposure times of 20-25min will be obtained. This program addresses the NICMOS count rate growth from 0.8-1.9microns as a function of integration times that are relevant for faint source science. Results will include count rate growth curves for several wavelength bins covering the range of maximum non-linearity around 1micron to where the previously measured non-linearity disappears around 1.7microns. The count rates for the existing short integrations can be attached seamlessly to those for the new long integrations, because NICMOS sensitivities are constant with time to <1%. A definitive answer is expected to the question of whether the count rates rise enough with exposure time to explain the full apparent grism non-linearity for short exposure times and whether the rise is enough to explain the apparent lack of any non-linearity in the prime science from photometry of faint point sources. II. NICMOS Non-Linearity Measurement as a Function of Wavelength WD1057+719 is one of two faint stars used by {Bohlin, Lindler, & Riess NICMOS ISR 2005-02} to establish the wavelength dependence of the non-linearity. However, the uncertainty in the linearity correction vs. wavelength is as big as 3%/dex at 1.8microns. These new data should reduce that uncertainty by sqrt{2} and answer the crucial question of whether the non-linearity changes slope from positive to negative longward of 1.7microns.
No associations
LandOfFree
Linearity Test for Long Grism Integrations does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Linearity Test for Long Grism Integrations, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Linearity Test for Long Grism Integrations will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1011521