ULTRASPEC wavelength range, resolution and pixel scale

Vik Dhillon, version: 29 May 2009

This document provides useful information on the wavelength range, resolution and pixel scale of ULTRASPEC when used on EFOSC2 on the NTT.

Contents

  1. Pixel scale
  2. Grisms
  3. Slits
  4. Filters

Pixel scale

ULTRASPEC has 1024 x 1024, 13 micron image pixels, each of 0.105" x 0.105" on the sky. Hence the field of view on the NTT when using EFOSC2 in its imaging mode is 1.8' x 1.8'. This compares with the ESO CCD#40 usually used with EFOSC2 on the NTT, which has 2048 x 2048, 15 micron image pixels.


Grisms

The available grisms for EFOSC2 are listed here. Note in particular grisms 19 and 20, which are the VPH grisms that we procured for the first ULTRASPEC science run in January 2008. A report on their use with ULTRASPEC can be found here.

A copy of the ESO table of grism parameters has been reproduced below, but all values have been converted to those for ULTRASPEC on EFOSC2 on the NTT. Note that these are all predicted values and will be verified during commissioning of ULTRASPEC on the NTT in early June 2009.


Grisms Range  Grating  Blaze angle  Dispersion 1 Resolution 2 Plots (PS Gzipped6 Tables6  Comments 
Name [Å]  gr/mm  wavelengh [Å]  [Å/pixel]  FWHM [Å] * Efficiency 
Response 
 Throughput [Å]  
Gr#01 
5382-8742
100
4500
5.77
48.0
gzipped ps
gzipped ps
   3 >9280Å
Gr#02 
6771-9328
100
6700
5.72
49.6
gzipped ps
 ps   3 >9850Å
Gr#03 
3914-5235
400
3900
1.30
11.6
gzipped ps
ps
 html
  
Gr#04 
5058-6546
360
4700
1.46
12.6
gzipped ps
gzipped ps
    
Gr#05 
6375-8174
300
6700
1.79
15.4
gzipped ps
gzipped ps
 html
  
Gr#06 
5052-6877
300
5000
1.79
15.5
gzipped ps
gzipped ps
 html
 3 >6280Å
Gr#07 
3828-4681
600
3800
0.83
7.4
gzipped ps
gzipped ps
  html 4
Gr#08 
4898-5781
600
5300
0.86
7.4
gzipped ps
ps
 html
  
Gr#09 
5286-6183
600
5600
0.87
7.6
  
ps
 html
 replaced by Gr#18
Gr#10 
6824-7655
600
6500
0.82
7.1
gzipped ps
ps
 html
 Gr#10 decommisioned
Gr#11 
4553-6346
300
4000
1.77
15.8
gzipped ps
ps
 html
  
Gr#12 
7234-9100
300
7900
1.84
16.0
  
ps
 html
 replaced by Gr#16
Gr#13 
5280-7719
236
4400
2.40
21.2
gzipped ps
gzipped fits
 html
  
Gr#14
3658-4521
600
4000
0.81
7.0
gzipped ps
ps
   4
Gr#15 
7424-8235
600
8300
0.75
6.5
  
ps
   replaced by Gr#17
Gr#16 
7234-9100
300
7900
1.84
16.0
gzipped ps
  
 
 3 >7170Å
Gr#17 
7424-8235
600
8300
0.80
6.5
gzipped ps
     3 >7000Å
Gr#18 
5286-6183
600
5600
0.87
7.6
gzipped ps
  
 
  
Gr#19 
4631-4923
1557
4777
0.29
1.5

 
 
 5                  
Gr#20
6358-6835
 1070
6597
0.48
2.0
 
  
 
  3 >6900Å     5 

1The pixel mentioned in the dispersion column is the 0.105 arcsec unbinned pixel of ULTRASPEC.
2The resolution depends on the slit used. Those quoted here are for a 1.0" slit.
32nd order contamination has been found for these grims at wavelengths longer than the indicated one. 
4Grisms 7 and 14 are almost identical; see the manual (section 2.4.5) for a comparison.
5Grism Dispersion and Resolution measured using a 0.5" slit and 1x1 binning. In an independent test Vik Dhillon found Grism dispersions of 0. 287 Å/pixel and 0.480 Å/pixel for Gr#19 and Gr#20, respectively. The corresponding resolutions are: 1.08 Å (Gr#19) and 1.77 Å (Gr#20). This test was performed using a 0.5" slit.

6All the plots and tables linked from this table are still for EFOSC2 @ 3P6


Slits

The EFOSC2 slit wheel has 10 positions which can be filled with the slits listed here. Note that the total slit length with ULTRASPEC is 1.8' and a 1" slit projects to approximately 10 pixels on the detector.


Filters

EFOSC2 has a filter wheel in which up to 10 different filters can be mounted. A list of the standard filters is given here, along with a link to the La Silla filter database if non-standard filters (e.g. order sorters) are required. A useful document looking at second-order contamination with the EFOSC2 grisms can be found here.