+--------------------------------------------------------+ | STScI Analysis Newsletter (STAN) | Cosmic Origins Spectrograph (COS) | Space Telescope Imaging Spectrograph (STIS) | November 2010 +--------------------------------------------------------+ In this Newsletter we provide information on the corrected STIS NUV TDS file and the COS FUV gain sag. -------------------------------------------------------------- Gain Sag in the COS FUV Detectors The COS FUV detector has exhibited gain sag in the regions illuminated by the bright airglow lines. This causes calcos to reject some target photons as background events and will eventually lead to the loss of target photons. Short and long term solutions have been developed by the team and are being implemented. -------------------------------------------------------------- New STIS NUV MAMA time-dependent sensitivity correction reference file. It was recently discovered that some rows of the STIS TDS reference file (u7c1846io_tds.fits) that was delivered on July 12 for the NUV MAMA were corrupted, leading to an incorrect flux calibration for post-SM4 observations using the STIS E230M, E230H, and G230M gratings. These files produced errors of 10-15% over much of the range of these gratings, and at some shorter wavelengths the errors were as large as 23%. Results for the STIS G230L were correct. Procedures for monitoring STIS time dependent sensitivity changes and for producing and testing these reference files have now been significantly revised to better ensure that final calibrated data products are scientifically correct. A new revised reference file that corrects the previous errors has now been delivered (ub920085o_tds.fits). For 1st order NUV MAMA modes, these revised files remove time dependent trends in the calibrated flux with about 2% accuracy. For echelle modes, the accuracy is about 6% or better, and future revisions may allow the repeatability of these modes to be further improved. +----------------------------------------------------------+ | 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. +----------------------------------------------------------+
