+--------------------------------------------------------+ | STScI Analysis Newsletter (STAN) | Cosmic Origins Spectrograph (COS) | Space Telescope Imaging Spectrograph (STIS) | April 2011 +--------------------------------------------------------+ In this newsletter we provide information on reference files, updates to the STIS NUV TDC Table, the COS FUV TDS Table, the COS NUV Flat Field, the COS Dispersion and Lamp Tables, and the delivery of a COS FUV Flat Field. Additionally, changes to the COS PeakXD Target Acquisition Strategy and the results of the alignment of two STIS modes are discussed. Finally we present updates to the calibration software. -------------------------------------------------------------- Changes to PEAKXD Acquisitions with COS To combat the effects of gain sag, we have modified the algorithm used for PEAKXD acquisitions with the COS FUV detector. The new algorithm will require no changes to (most) Phase II proposals already in the system. It has the added benefit of enabling the use of all FUV gratings for target acquisitions. -------------------------------------------------------------- Partial flat field corrections for G130M and G160M spectra and their limiting signal-to-noise. This article describes the newly implemented COS FUV grid- wire flats, which correct the largest contribution to fixed- pattern noise in COS FUV spectra. It also provides estimates for the remaining fixed-pattern noise and the limiting S/N that can be achieved with standard pipeline processed data. -------------------------------------------------------------- New COS Far Ultraviolet Time-Dependent Spectroscopic Sensitivity Reference File As part of routine monitoring of spectrophotometric white dwarf standard stars, a change in the time dependence of the spectroscopic sensitivity of the COS FUV detector has been determined. A new reference file has been delivered and is now routinely used in pipeline processing of data. -------------------------------------------------------------- Vignetting Removed from COS NUV Flat Field The vignetting on the COS NUV detector has been shown to vary with time. The static vignetting correction has therefore been removed from the NUV flat field. The new NUV flat field (v2e20129l_flat.fits) was delivered to CDBS on February 14, 2011. -------------------------------------------------------------- Updated Wavelength Dispersion Solutions for G140L/1280 setting COS/FUV wavelength dispersion (v3g18194l_disp.fits) and lamp template (v3g18195l_lamp.fits) reference files were delivered to CDBS on Mar 16 2011. These files contain updated zero-point offsets for the G140L/1280 dispersion solutions, based on Cycle 17 on-orbit data obtained in September 2010. The lamp template reference file was also updated with lamp spectra obtained on-orbit for all FP-POS positions of the G140L/1280 setting. -------------------------------------------------------------- New TDC Reference File Delivered for STIS NUV The dark rate of the STIS NUV MAMA detector was surprisingly high after SM4, and its decline over time has been complicated by another surge in the Fall of 2010 due to the STIS MAMA hiatus. A new TDC (temperature dependent dark correction table) reference file was delivered in February, to provide accurate dark subtraction within ~5% for the NUV MAMA. -------------------------------------------------------------- Adjustment to the Alignment of Two STIS Central Wavelength Settings In March 2010, errors in the cross-dispersion alignment of the STIS G430M 5216 and G750M 6094 settings were corrected. Previously these offsets could cause problems when attempting to center the target in small subarrays, requiring awkward workarounds in the phase 2 implementation. These workarounds should no longer be necessary, and the alignment of these central wavelength settings is now comparable to that of other STIS modes. -------------------------------------------------------------- CALCOS Version 2.14.4 Available for Download CALCOS v2.14.4 was installed in STSCI_PYTHON 2.11 Patch 1 on April 4, 2011. The rest of STSCI_PYTHON remains unchanged. Some of the changes in this version include a fix to a bug that prevented using a corrtag file as input to CALCOS. It also adds a TIMELINE extension to corrtag files, giving the altitude of the Sun, the longitude and latitude of HST, and other information at one-second intervals throughout the exposure. This new extension can be used to filter COS data based on orbital day or night, which can be used to decrease the contamination of spectra by geocoronal emission lines. For a complete list of the changes and instructions on how to download this version go to www.stsci.edu/institute/software_hardware/pyraf/stsci_python/current/stsci-python-download /patch_install -------------------------------------------------------------- Development version of the STScI STSDAS software now available to the community The development version of STScI STSDAS (called IRAFX), with the latest improvements to the HST calibration software, is currently available to the general astronomical community. IRAFX is presumed to be fairly reliable, but anyone using this software should be aware that it is not supported and has not been fully tested. For more information and details on how to download the software go to http://stsdas.stsci.edu/irafx/ +----------------------------------------------------------+ | Need help? http://www.stsci.edu/hst/cos/help.html +----------------------------------------------------------+ | To subscribe or unsubscribe to the STAN, send a message | to majordomo@stsci.edu with a blank subject line and | the following in the body: [un]subscribe cos_news | or [un]subscribe stis_news +----------------------------------------------------------+ | The Space Telescope Science Institute is operated by the | Association of Universities for Research in Astronomy, | Inc., under NASA contract NAS5-26555. +----------------------------------------------------------+
