STScI Logo

Hubble Space Telescope
June 2011 STAN

| 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.


The ETC ID(s) used to simulate your observations is now a 
required field in APT.

| Need help?
| To subscribe or unsubscribe to the STAN, send a message
| to 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.