+--------------------------------------------------------+ | STScI Analysis Newsletter (STAN) | Cosmic Origins Spectrograph (COS) | Space Telescope Imaging Spectrograph (STIS) | January 2011 +--------------------------------------------------------+ In this Newsletter we provide some updates of interest to COS and STIS users who will be drafting and submitting Phase 1 HST programs over the next several weeks. -------------------------------------------------------------- Obtaining COS FUV spectra with a S/N > 100/1 per resolution element Because the COS FUV detectors are subject to position and time dependent fixed pattern noise, we do not foresee producing routine pipeline processed data with a S/N much larger than 30. However, S/N > 100 (per resolution element) spectra can be achieved by using the iterative FPPOS technique (e.g., Bagnulo & Gies, 1991, ApJ, 376, 266, and Lambert et al., 1994, ApJ, 470, 756) as long as the source spectrum and the observational sequence meet certain conditions. -------------------------------------------------------------- Incorrect Resolution Element Used by COS ETC for new G130M Modes The resolution element used in the calculations performed with the COS spectroscopic ETC for the new FUV/G130M modes (cenwave=1055 and cenwave=1096) does not correspond to the real resolution element of the two new modes. To calculate the correct exposure time per real resolution element, divide the exposure time returned by the ETC by 5 (for calculations at 950 Å) or 19 (for calculations at 1150 Å). To calculate the correct S/N per real resolution element, multiply the S/N returned by the ETC by 2.2 (for calculations at 950 Å) or 4.4 (for calculations at 1150 Å). -------------------------------------------------------------- Gain Sagged Regions on the COS FUV Detector The gain sag on the COS FUV detector can lead to artifacts (absorption-like features) in the extracted spectra. The locations of the most seriously affected regions are listed. Users should inspect their data for these effects. -------------------------------------------------------------- Gain Sag and FUV Dispersed Light Target Acquisitions The gain sag of the COS FUV detector leads to mis-registration of events along the cross-dispersion or y-direction (y-walk) which can affect the centering of the target on the aperture when FUV dispersed light target acquisitions are used. Users preparing Cycle 19 phase I proposals are strongly encouraged to consider target acquisition strategies that do not use FUV dispersed light, such as Imaging TA or NUV dispersed light TA. -------------------------------------------------------------- Release of CALCOS v2.13.6 CALCOS v2.13.6 was released as part of STSDAS 3.13 in December 2010 and was installed in the Operations Archive on January 19, 2011 (OPUS Release 2010.4). A detailed list of changes related to CALCOS v2.13.6 can be found on the "CALCOS Release Notices" web page at http://www.stsci.edu/hst/cos/pipeline/CALCOSReleaseNotes/notes/). -------------------------------------------------------------- COS NUV Dark Rate Update The dark rate of the COS NUV detector has been increasing with time following an approximately linear trend. At the present date, the mean dark rate is about 4.5 x 10^-4 cts/sec/pix, but if the established trend continues, by April 2012, (approximately the mid-point of Cycle 19), the mean dark rate will have reached a level of about 7.3 x 10^-4 cts/sec/pix. Users with active Cycle 17 and Cycle 18 programs using the COS NUV detector should evaluate whether this increasing dark rate will have an impact on their planned program. -------------------------------------------------------------- Verification of Proper Motion Specifications We continue to experience some HST observation failures caused by erroneous proper motion entries. We remind proposers that the specification of correct HST pointing information is their responsibility and observations that fail because of incorrect pointing specifications will not be repeated. Changes to APT and acceptable units are discussed. +----------------------------------------------------------+ | 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. +----------------------------------------------------------+
