+--------------------------------------------------------+ | STScI Analysis Newsletter (STAN) | Cosmic Origins Spectrograph (COS) | Space Telescope Imaging Spectrograph (STIS) | June 2011 +--------------------------------------------------------+ In this Newsletter we provide some updates of interest to COS and STIS users who will be drafting and submitting Phase 2 HST programs over the next several weeks. -------------------------------------------------------------- Using Multiple FP-POS positions with COS observations The use of multiple FP-POS positions is recommended to improve the quality of all COS spectroscopic data, especially for observations using the FUV channel. -------------------------------------------------------------- New Options for COS FUV Target Acquisitions Recent changes to the PEAKXD algorithm allow the use of all three FUV gratings for dispersed-light target acquisitions with COS. We discuss these changes and provide instructions for estimating the exposure time necessary to perform a successful PEAKXD exposure. -------------------------------------------------------------- Operational voltage of Segment B of the COS/FUV detector raised to mitigate effects of gain sag On March 10, 2011 the operational voltage of Segment B of the COS/FUV detector was increased to the value used initially in SMOV and during routine ground testing. The operational voltage of Segment A was not modified. This change was needed to mitigate the effects of gain sag, which had become particularly severe on Segment B, leading to the appearance of absorption-like features, i.e. gain sag "holes", in the regions of the detector illuminated by geocoronal Lyman alpha emission when observing with G130M settings. -------------------------------------------------------------- COS G130M 1055 and 1096 Wavelengths are Corrected for OSM Drift and Zero-point Offsets As is the case for other modes, observations done using the new 1055 and 1096 cenwaves of the G130M grating will normally have their wavelength zero-points corrected using wavelength calibration spectra, but for these settings there are some special issues to consider. -------------------------------------------------------------- The STIS CCD E1 aperture positions Observers planning STIS CCD spectroscopy are reminded that use of the E1 aperture positions may dramatically improve the quality of their data. -------------------------------------------------------------- Need for ACQ/Peak Exposures with Small STIS Slits As STIS ACQ exposures only center the target in the aperture with an accuracy of about 0.01", when using a slit 0.1" in width or smaller, an additional ACQ/PEAK exposure sequence is strongly recommended. The use of ACQ/PEAK exposures is described in Section 8.3 of the STIS Instrument Handbook; however, observers should be aware that APT does not currently provide any warning if these recommended ACQ/PEAK exposures are omitted. -------------------------------------------------------------- Warning for COS and STIS Target Acquisitions on Systems with Large Orbital Motions The cataloged position and proper motion of some visual binaries with large angular separations and significant orbital motion may not characterize the target's location to the accuracy required by the target acquisition aperture. For such objects, a custom proper motion calculation, tailored to approximate the object's position and motion at the expected time of the observation is recommended to ensure the the target will be in the target acquisition aperture. Timing requirements, such as BETWEENS, should be specified if needed to ensure that the visit can execute only when this custom proper motion specification is sufficiently close to the target's true position to satisfy the recommended positional accuracy for the type of acquisition specified. -------------------------------------------------------------- ETC ID in APT The ETC ID(s) used to simulate your observations is now a required field in APT. +----------------------------------------------------------+ | 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. +----------------------------------------------------------+
