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.

• 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

• The current default detector of UES is SITe1, which has 2048x2048 24 micron pixels. This chip samples the full length of the orders of the E31 echelle. In the cross-dispersion direction the echellogram is affected by camera vignetting. A resolution of about R=55000 can be reached with this chip (1 arcsec slitwidth = 2 pixel).
  Detector characteristics can be found here .
• As of semester 2000B we also offer the choice of using the twin EEV42 mosaic camera with 2x2kx4k 13.5 micron pixels. With this camera we have reached about R=85000 (0.6 arcsec slitwidth = 2 pixel). The two chips are nicely alligned with a 39-pixel gap in between them ( see ING Tech Note 119 ). As the orders run along the long side of the chips, the gap results in the loss of one central order for the 79 echelle. Along the spectral direction there is a 3 pixel offset between the two chips. Camera vignetting is the same as for the SITe1 detector. A flatfield image with e79 centred on Halpha looks like this (only the part of the chips that sample the echellogram is displayed).
  Red fringing is terrible (50% peak-to-peak at 9000 Angstrom, but practically zero bluewards from Halpha) on the EEV42 chips. As the lightpath of the flatfield lamp in the AG box is a bit different than that of the stellar light, acceptable fringe correction (using the standard flatfielding method) can only be achieved for wavelengths shorter than 7000 Angstrom.

Echelle gratings

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

• Target acquisition and slit guiding is difficult for stars fainter than V=15.5. See the section on derotators.

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

• 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

• When setting up, a couple of useful routines to set UES to a standard setup and also to aid in focussing are available. For setup, at the ICL prompt LOAD DISK$USER1:[NAW]UES_CHECKUP.PROC and then type UES_CHECKUP. Once the spectrograph has been configured go ahead and take a 20s arc frame.
• UES_CHECKUP sets UES up to its standard test position, ie E79 at 4521.8A. Taking a THAR arc of 20s (ARC UES 20 "thar 4521.8A 20s") should produce an image similar to this.
• Then, you can do UES quality control as described in the UES Quality Control Folder

Determining the GAIN and RON of SITe1 on UES

• Read the help on IRAF task ues_gain_ron for instructions and the required UES setup. An image with that setup will look like this .

ThAr arc maps

• To quickly identify the main ThAr lines in the echellogram use ING Technical note 116 , which is made with SITe1 and the 31 lines/mm echelle of MUSICOS. The old UES ThAr arc map is very useful for finding lines in detail (ING Technical note 91).

  Technical note 116 does not contain these blue (3700-4000) orders: order 152 , order 151 , order 150 , order 149 , order 148 , order 147 , order 146 , order 145 , order 144 , order 143 , order 142 , order 141 , order 140 . Thanks to Daniel Folha (Centro de Astrofisica da Universidade do Porto) for sending these ThAr maps.

Known problems