README web version of /home/usg/OPS/MTS/readme_xml/readme_79009400

Principal Investigator Email Address

• Paul.Crowther@sheffield.ac.uk

Estimated Total Execution Time (hours, including overheads)

• 6h

General Description

• We are performing spectropolarimetry on Oxygen-sequence Wolf-Rayet stars.
   We require a precision of 0.1%, and hence a SNR of 1000 per resolution element.
   We use the 300V grism with no order-filter to observe the wavelength range 3300-6600A.
   The stars have strong emission lines, so to avoid saturation we have broken up the
   observations into 4 repeat observations at 3 offset positions.
  
  We will arrange adjacent even-numbered MOS stripes into 1" slits (the odd-numbered
   stripes are closed to prevent overlap of the O and E rays). We will put the star
   in the centre of slit 10 to begin with (default setting), then offset the telescope
   by +44", +44" to move the star into the 2 adjacent open slits (8 and 6), in order
   to identify & eliminate any bad pixels. Note that we require the star to be
   in the centre of each slit to characterize the sky either side of the star.
  
  For the 3 slits through which we observe - (A, B, C), where A is the centre slit
   (slit 10), B is slit 8, and C is slit 6 - we use the offset pattern A, B, C, and
   hence the telescope offset pattern [0, +44", +44"]. We will do 4 repeats at each
   offset to check for result-repeatability and to avoid saturating the detector.
  
  Finally, we would request that Co-I Ben Davies be the technical contact, and be
   copied in on all e-mails regarding these observations: davies@cis.rit.edu

Waiver Requests

• As targets are V~14 and we require a high SNR for high-precision spectropolarimetry,
   we need to integrate for longer than 1hr per target. As each science OB consists
   of 6 separate exposures, we would ask that, should conditions degrade such that
   an OB must be aborted mid-way through, the OB be restarted where it was left off.
  
  Also, as we are aiming for high S/N, we use readout mode (200KHz, 2x2, low) to allow
   us to integrate for longer without saturating and spend less time reading out.

Critical Observing Condition Constraints

• none

Time-Critical Aspects

• none

Special Execution Requirements

• We have taken care to choose exposure times that avoid saturation at the
   bright emission lines. However, if the seeing were to become extremely good (say
   < 0.4") there is a possibility that the emission lines may saturate the detector.
   We ask that the astronomer look out for this, and decrease the exposure times if
   necessary.

Special Calibration Information

• polarized/unpolarized standards must be observed for the purposes of instrumental
   polarization and position-angle calibration. The details of the standards are...
  
  HD155197 - pol std - V=9.6 - A0V
  HD161056 - pol std - V=6.3 - B1.5V
  HD176425 - zeropol - V=6.2 - A0V
  
  Due to the brightness of the latter two stds, we opt for individual exposure times
   of 0.5sec. Should this cause major problems, let us know. 
  
  We also require that the flat-fields and wavelength calibration frames be taken
   through the polarization optics, to compensate for any difference in focussing/alignment
   of the O and E beams. As to the best way to achieve these calibrations, we seek
   advice from the instrument specialist (the 'switch-on times' and 'flat/arc exp times'
   in the cal block need altering).

ToO Information

• n/a

ToO Activators List

• n/a

Is this a Pre-imaging run ?

• false

Pre-imaging Requirements

• n/a

Source(s) of Pre-imaging

• ---(Empty)---

Pre-imaging sources not listed above

• ---(Empty)---

Do all your OBs comply with the instrument-specific requirements listed
 on the instrument-specific Phase 2 web page ?

• YES

If this is a pre-imaging run, did you select PRE-IMAGING for the Observing
 Category for each Observing Template ?

• N/A

Do all your finding charts comply with both the general and instrument-specific
 Phase 2 Web Pages ?

• YES

If you submitted OBs for standard stars, did you specify the magnitude
 and spectral type of all standard stars in the OBs ?

• YES

Have you included OBs for any calibrations that you need but which are
 not part of the Calibration Plan ?

• N/A

If you are observing Moving Targets, have you attached suitable ephemeris
 files to your OBs?

• N/A

If you have preferences which OBs should be executed first, did you make
 use of the User Priority field in the OBs ?

• N/A

If this is a run that requires coordinated observations with other facilities,
 did you give proper instructions in the Time-Critical Aspects Section ?

• N/A

If you have prepared your finding charts with tools other than FIMS,
 do they comply with the specifications on the FORS1 Phase 2 web page ?

• N/A