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Documentation:

UES characteristics:

Preparation:

Observing with UES:

Documentation

  • There are a number of documents to be found in the control room related to UES, the most important being the UES Users Guide and the UES Quality Control Folder.

About UES

Which derotator to use?

  • The UES Nasmyth platform supports two derotators . The old derotator has lower throughput than the new: approx 75% versus 95%. The field of view of the old derotator is 2.5arcmin diameter unvignetted, and 5 arcmin diameter with 50% light loss at the edge. The new derotator has an unvignetted FOV of 30 arcsec diameter, and 3.5 arcmin diameter FOV with 75% light loss at the edge. The new derotator has higher throughput than the old over a field of view of about 80 arcsec diameter. This means that for long-slit observations for objects larger than 80 arcsec the OLD derotator should be selected.
    Slit-view guiding can only be done on science targets brighter than 16th mag. When observing fainter stars off-axis guiding should be used. For off-axis guiding the old derotator provides a 5 arcmin diameter field, and the new derotator provides a 3.5 arcmin diameter field. For the new derotator stars at the edge of the field are obscured by 1.5 mags. Limiting mags for off-axis guiding are about 15 mags (for guide stars in the unvignetted field of the derotator).

Detectors

Echelle gratings

  • UES offers two Echelle gratings: E31, with 31 rules/mm, and E79, with 79 rules/mm. It is important to realise that both gratings give the same resolution, and the same wavelength range.

    The orders of E79 are 2.55 times as wide as those of E31 (in the spectral direction), and consequently the extracted continuum is less curved for E79. For E79 the interorder distance is 2.55 times as large as that of E31, allowing for longer slits, better sky subtraction, better flatfielding, better scattered light subtraction. Owing to these characteristics, the E79 data are easier to reduce with high precision than the E31 data.

    As the orders of E79 are wide, the far ends of the orders are affected by camera vignetting. In the red no order overlap is present because of this. The E31 Echelle offers a more complete wavelength range, with better order overlap. Use the ECHWIND program to investigate the effects of order overlap and the position on the echellogram of the lines you are interested in.

UES camera vignetting

  • A 4x4 binned FITS image showing SITe1 vignetting; E31 at central wavelength 6000. The camera reduces the echellogram to 1800 pixels in the cross dispersion direction (pixel range 200-2000). The pixel range affected by less than 50% vignetting is about 1400 pixels in the cross dispersion direction (pixel range 400-1800).
  • A 4x4 binned FITS image showing SITe1 vignetting; E79 at central wavelength 4700.
  • A 4x4 binned FITS image showing SITe1 vignetting; E79 at central wavelength 6000.
  • The vignetting in the dispersion direction is variable with the echelle angle. Rough rule: vignetting is least when centring the blaze at the centre of the chip.

Target limitations

Throughput and S/N

  • S/N estimates can be obtained with the SIGNAL program. Note that SIGNAL does NOT account for slit losses!!!
  • The on-blaze, chip-centre (i.e. no camera vignetting), wide-slit throughput has been measured in September 2000 for the following setup: WHT + UV-derotator + UES + Echelle31 + SITe1 . The results are listed in the table below. Exposure times for a U=B=V=R=I=14 star in typical observing conditions reaching S/N=50 at the blaze in the extracted unbinned spectrum are given as well.

    wavelength AB magnitude WHT+UES+SITe1 efficiency expo time for S/N=50 and m=14
    3800 ~16.4 ~1.0%
    4300 16.69 3.0% 6000s (41000 e-/Å)
    5500 16.93 4.7% 6000s (49000 e-/Å)
    6500 16.93 5.6% 6000s (45000 e-/Å)
    8200 16.02 3.0% 12000s (40000 e-/Å)
    9200 15.15 1.6%

  • The on-blaze, chip-centre (i.e. no camera vignetting), wide-slit throughput has been measured in January 2001 for the following setup: WHT + UV-derotator + UES + Echelle79 + 2EEV . The results are listed in the table below.

    wavelength AB magnitude WHT+UES+2EEV efficiency expo time for S/N=50 and m=14
    3600 16.99 3.2% 30000s (79000 e-/Å)
    4300 17.41 5.7% 8000s (73000 e-/Å)
    5500 17.28 6.5% 8000s (80000 e-/Å)
    6500 16.96 5.7% 9000s (73000 e-/Å)
    8200 fringes
    9200 fringes

Preparation

ECHWIND

  • The source of the planning program for determining echelle positions (ECHWIND) is available here . This gzipped tar file also contains the executable and libraries for SunOS 5.7.
  • On our Solaris cluster the ECHWIND program can be run by typing
      > use echwind
      > echwind
    at the shell prompt. One small defect, if you have a line list you must enter the full pathname:
      LINES - File containing line list? > /usr/local/bin/echwind/balmer.dat
  • To make the box as big as the unvignetted (less than 50% vignetted) part of the SITe1 chip (this is only accurate in the cross-disp direction), specify:
      Detector (IPCS, THOMSON, RCA, GEC, TEK, EEV6, SITE1 or xx,yy in mm)? > 50,34
  • To make the box as big as the full camera domain (this is only accurate in the cross-disp direction), specify:
      Detector (IPCS, THOMSON, RCA, GEC, TEK, EEV6, SITE1 or xx,yy in mm)? > 50,43

Observing

UES quality control

Determining the GAIN and RON of SITe1 on UES

ThAr arc maps

Known problems

  • Echellogram shifts: these have been observed to amount to up to 5 SITe pixels per 24 hours or so, both in the dispersion as in the cross-dispersion direction. These shifts are attributed to the unstable temperature environment inside UES. Make sure to take ThAr exposures regularly!!
  • Misallignment: from high precision observations it has become clear that there are slight misallignments in the coupling of UES to the telescope and the coupling of the calibration box to UES. Because of this it can be difficult to remove fringes with high precision using calibration lamp light. For the same reason, small hour-angle dependent shifts of an object with respect to the arc lines have been observed when following the object for a whole night.
  • At wavelengths longer than 8000A the ends of the orders are out of focus on the chip. This has been observed with the 79 echelle, and is due to optical aberrations.
  • The reflectivity of the UV collimator is the same as that of the WIDE collimator in the UV. Probably the coating of the UV collimator has deteriorated.


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Last modified: 18 December 2010