Instrument Science Reports (ISRs)

We report on a new IRAF task called finesky that removes higher order sky residuals in NICMOS images by creating a masked median image of the observed sky. This median sky image is thereafter subtracted from the science images. A residual signal after image processing using the calibration software calnica may be present due to reference files that do not sufficiently match the conditions of the observations. This includes a slight mismatch in the dark current or the flat-field corrections. The task described here can also used to create sky flat-field images.

This ISR describes the CalTempFromBias program which was developed to estimate the temperature of each of the three NICMOS detectors individually. Unlike previous NICMOS temperature estimates, which are derived from a mounting cup sensor, these temperatures are derived using the bias level of the detectors themselves. The uncertainty associated with these temperature-from-bias values are 0.05K and are the basis for the new temperature-dependent calibration products for NICMOS data. This ISR describes the program CalTempFromBias, its options, and its applications.

The focus of the NICMOS cameras is monitored on a regular basis. In order to achieve consistency in the focus determination, several effects have to be taken into consideration. The main ones affecting NICMOS are: (1) thermally induced movement of the secondary mirror (a.k.a. breathing), and (2) a curved focal plane for all three cameras. The latter is known as NICMOS Focus Field Variation and affects both the measurement of the focus and gives a position dependent Point Spread Function. In this Instrument Science Report we discuss the breathing corrections in the context of the NICMOS Focus Monitoring Program, and re-measure the Focus Field Variations.

The bias-derived detector temperature for all three NICMOS cameras showed a variation of about ~2K in both the era before the installation of the NICMOS Cooling System (NCS) 1997-1998, as well as in the post-NCS era, 2002-2008. This temperature variation affected the detector quantum efficiency (DQE) and hence the structure of the flat-fields. In this ISR we discuss the creation of new temperature dependent flat-field reference files that correct for the effect of temperature on the DQE. Temperature dependent flat-fields (*_tdf.fits) populate the keyword TDFFILE in the headers of post-NCS data retrieved after November 19, 2008 and pre-NCS data retrieved after January 23, 2009. The temperature dependent flat-fields are used by the FLATCORR step in calnica version 4.4 and later. For consistency check we also created epoch dependent flatfields for postNCS data and compared them with the temperature dependent flatfields. The result of this analysis is also included here.

As part of the Cycle 16 NICMOS calibration program, new observations of planetary nebulae were obtained using all three NICMOS grisms (G096, G141, and G206). The aim of these observations was to re-derive the dispersion relations for the grism modes of NICMOS as well as to examine and parametrize any field dependence of the dispersion relation within the field of view of the instrument. In this ISR, we present updated versions of the dispersion relations of the G096, G141, and G206 grisms. While the field dependence is small (1-2% peak to peak variation), we also compute two dimensional polynomial solutions to compute more exact dispersion relations anywhere in the field of view of NICMOS.

We present the details of the NICMOS Photometric Calibration Pipeline used to generate aperture photometry. We present an overview of the different corrections employed, explain components of the pipeline and also outline the types of photometric and statistical data products created. In de Jong et al. (in preparation) this photometry will be used to determine the photometric calibration constants stored in the PHOTTAB reference files.

This report describes how the calnica data reduction software implements temperature dependent reference files in order to correct for temperature dependent variations in the dark current, the flat-fields, and the flux calibration. We describe in detail the logic used by the software to decide when to apply a temperature dependent correction and which temperature to use in that case.

This report describes the investigation of the temperature dependence of the linear dark and amplifier glow components of the NICMOS temperature dependent *_tdd.fits dark reference files in the post-NCS era, 2002-2008. We find a significant temperature dependence of the amplifier glow signal with higher counts at higher temperature when using the bias-derived detector temperature. The linear dark should also be dependent on temperature, however, the expected change in dark current should to be smaller than the scatter introduced from the read noise. This is consistent with what we find. We also describe how the calnica reduction software uses the temperature dependent dark components when calibrating NICMOS images.

The last determined bad pixel masks for the three NICMOS cameras were made in September 2002. Those masks were created using data from calibration programs following the installation of the NCS and are therefore based on the relatively limited data set available at the time. Since then, the NICMOS calibration monitoring programs have regularly obtained calibration images of both flat-fields and darks, images used to create the mask reference files. With numerous images taken during a long base-line (2002-2008), this data set allows us to create high signal-to-noise reference files, as well as investigate any temporal dependence of the mask files. In this ISR we describe the creation of new mask files based on this extended data set and compare the new masks with the previous versions. The new masks created contain a higher number of bad pixels compared to the old versions, while the number of pixels thought to be affected by “grot” is lower.

This ISR outlines the NICMOS plan for Servicing Mission Observatory Verification 4 (SMOV4). It presents the NICMOS requirements, the planned activities to fulfill these requirements and a brief plan for the data reduction and analysis.

We re-investigate the NICMOS count dependent non-linearity, using the flat field lamps to reach high count regimes. The NICMOS count dependent non-linearity has been previously quantified and is currently corrected in NICMOS pipeline. In this document we show that the count dependent correction is still accurate to within 1.2% of true linearity for counts above 100 ADU independent of filter used. This is a response to the count-rate dependent non-linearity investigations, to eliminate questions about the current count dependent corrections.

This ISR describes a number of improvements to calnica, the STSDAS task that performs routine instrumental calibration of NICMOS raw images. We report two major and a number of minor updates to the code. The major updates consist of changes in the way the count rate is calculated from up-the-ramp fitting and changes in the cosmic rays rejection algorithm. All updates have been extensively tested and analysis shows improvement in the S/N of output images by 6-15% compared to the previous calnica version. A further improvement is that the error extension in the calibrated images now represents the true errors in a more consistent way compared to the old implementation of the software.

We report the presence of image persistence in NICMOS data due to prior saturation of the array by the bright Earth as well as an algorithm to remove its impact. BEP (Bright Earth Persistence) may occur when ACS and NICMOS are used in parallel, and the data dump of ACS delays the insertion of the NICMOS filter blank as long as 6 minutes beyond the Bright Earth avoidance angle. We have constructed a BEP frame which can be used to model and remove the presence of BEP in NICMOS data. The algorithm is seen to remove 99.5% of the variance in the background of BEP impacted Camera 2 data. Ongoing work involves broadening the applicability of the BEP correction to Camera 1 and 3 and making it available as a pyraf script through STSDAS.

This document summarizes the NICMOS Calibration Plans for Cycle 15. The monitoring programs from the previous Cycle 13 and 14 are carried out in Cycle 15. Additional calibration is included in order to improve the accuracy of previously archived NICMOS data.

This ISR will address a number of changes in the way the NICMOS focus is monitored. It will provide a detailed explanation of those changes and a step-by-step description of the new procedure. The ISR also highlights the results of the focus checks after the HST safing event, which caused the NICMOS cooling system (NCS) anomalous shutdown in February of 2007.