AUGUST 1, 2016

August 2016 STAN

This newsletter shares new read noise values for the STIS/CCD and information on how to subscribe to COS STANs after the COS-STIS split in 2016.

Updated Read Noise Values for the STIS/CCD in the CCDTAB Released

Read noise values of the STIS/CCD have been updated in the CalSTIS pipeline's CCDTAB to better reflect read noise measurements taken throughout the operation of STIS. These new values will give better estimates of errors in the error extension of the CCD data files.

The STIS/CCD read noise levels contained in the pipeline's CCDTABs have been updated to reflect measurements taken throughout operation of STIS. The previous version of these files contained averages that were often based on only the initial part of the time-span to which a given file was applied. See the STIS read noise monitoring website for measurements of the ongoing "CCD Bias and Read Noise Monitor" programs used to make this update.

The updated read noise values are expected to give more realistic error values in STIS CCD data product error extensions. Furthermore, read noise is used to calculate the cosmic ray rejection thresholds when combining multiple CCD exposures, and so will lead to small differences in CR-rejected data products (i.e. _crj, _sx1, _sx2 files).

While the magnitude of the change depends on the particular amplifier, gain, binning mode, and date of observation, probably the most relevant change made reflects the May 2014 read noise jump in amplifier D at gain=1 from 5.71 DN (Data Number = # electrons/gain) to 6.24 DN reported in the August 2014 STAN. The amplifier D gain=4 read noise has also gradually increased from 1.99 DN to 2.06 DN since 2010. Due to its lower read noise, amplifier D is the only amplifier used in science operations.

Users wishing to obtain updated data taken after the instrument recovery in 2009 can simply re-retrieve the observations from the Hubble Space Telescope Archive, hosted by MAST, at http://archive.stsci.edu/hst/. Observations taken prior to 2009 are statically archived, and so will not receive this update in the pipeline. To recalibrate these earlier data, users are advised to update raw data headers and download needed reference files using the CRDS command line tool before recalibrating with CalSTIS.

Splitting the COS & STIS STANs

In the past, COS and STIS updates have been sent out in a single newsletter. However, now we are splitting the COS and STIS STANs. Updates to COS can be found in COS STANs and updates to STIS in STIS STANs. In the event you would also like to subscribe to receive COS newsletters, simply send an email to listserv@maillist.stsci.edu with a blank subject line. The body of the email should say "subscribe cos_news". You should then receive an email asking you to confirm with similar text to the following:

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Select this link or reply to the message saying "OK", and you will then be on the mailing list for COS newsletters.