NOTE: For the most up-to-date information on TRISPEC and its operating modes at UKIRT, please visit the TRISPEC Homepage, which is maintained by the TRISPEC team at Nagoya University.


TRISPEC (the Triple Range Imager and SPECtrograph) contains three optical channels, each with its own detector, to cover the wavelength range 0.46 to 2.5 microns simultaneously. One CCD and two near-IR InSb arrays are used. The incoming beam from the telescope is focused, collimated and then split into three beams by two dichroic mirrors (see below). Each of the three channels has a filter wheel-box containing three or five wheels equiped with broad-band filters, grisms and polarization analysers (Wollaston prisms). TRISPEC is thus capable of imaging, spectroscopy and spectro/imaging polarimetry at three bands simultaneously. Spectral resolutions are around 100, depending on the slit widths. Linear and circular polarimetry can be carried out using an upstream (warm) waveplate(s) followed by Wollaston prisms (cold) inside TRISPEC. The polarization mode is provided by Prof. J. Hough (University of Hertfordshire, U.K.) and is available on a collaborative basis (contact Chris Davis at JAC [] for further details).

The first trial with TRISPEC at UKIRT was carried out on February 4-7, 2000. Imaging and spectro-polarimetry data were obtained, although some aberration and light loss were experienced in the infrared channels, due to the misalignment of the optical axes, specially the pupil stops and focal planes, relative to the secondary mirror. These problems have since been overcome. TRISPEC has since had a very successful two-period visit to UKIRT in February and March 2001, when PATT and UH observers obtained data for a number of projects.

To illustrate the unique capabilities of TRISPEC we show some of the spectrophotometric data obtained last year at UKIRT here.

Technical specifications summary

The detectors used by TRISPEC are an SITe 512×512 pixel CCD and two SBRC 256×256 pixel InSb arrays (engineering grade). The simultaneous wavelength coverages are; optical 0.46-0.90 microns; J-H band 0.90-1.90 microns; K-L band 1.90-2.50 microns. The Field of View measures 56 arcsec on UKIRT (F/36: f=135m). Pixel scales are 0.1 arcsec/pixel in the optical and 0.2 arcsec/pixel in the infrared. Note that 1) the beam of F/36 or the focal length of 135 m of UKIRT currently makes the pixel scales slightly oversampled for the typical slit-width of 0.9arcsec in the spectrophotometry mode, and that 2) atmospheric dispersion degrades photometric accuracies at zenith angles larger than 30 degrees due to the wide coverage of wavelengths.

TRISPEC and the polarimetry unit are occassionally available to PATT observers on a collaborative basis (the polarimetry waveplates were purchased by the University of Hertfordshire). Thus, any publications resulting from TRISPEC time should include the appropriate TRISPEC (and Univ. of Hertfordshire) staff as co-authors.

Please consult the Nagoya University TRISPEC PAGE for the most up to date information on TRISPEC, or Chris Davis ( at the JAC.

Acknowledgements Since 1996 TRISPEC has been developed by three graduate students, H. Nakaya, M. Watanabe and T. Yamamuro, from Nagoya University.



Visible : 512×512 CCD (SITe)

IR – 1 : 256×256 InSb (SBRC)

IR – 2 : 256×256 InSb (SBRC)

Slit viewer : 512×512 CCD (SITe)

(These detectors can be exposed simultaneously.)

Mode change

Changing the modes can be done anytime during observations. Frequent changes in a short time are not recommended.  




Visible : (B),V,R,I
IR – 1 : J, H
IR – 2 : K, Ks

Filters can be changed during observations. Note, however, that the colours of the B,V,R and I filters are somewhat non-standard. Observers wishing to do high-precision photometry should take time to acquire sufficient calibration observations (and should discuss this issue with the TRISPEC team while at UKIRT).


57 arcsec x 57 arcsec square

Pixel scale

Visible : 0.11 arcsec/pixel

IR : 0.22 arcsec/pixel

Sensitivities for TRISPEC imaging are give here.



Slits available

(0.44 arcsec)
0.66 arcsec
0.88 arcsec

Note: 0.66 arcsec and 0.88 arcsec slits will be installed. These two slits can be changed during observations. Use of the 0.44 arcsec slit is not planned at this time.

Spectral coverage

Visible: 0.46 – 0.90 um (0.0012 um/pixel)
IR – 1 : 0.90 – 1.80 um (0.0046 um/pixel)
IR – 2 : 1.85 – 2.50 um (0.0031 um/pixel)
(Slit viewer : V-band)

FOV of slit viewer

35 arcsec x 35 arcsec square

Resolving power (R = lambda / delta lambda)

Visible(at 0.665um):1389269
IR – 1 (at 1.30 um):1429571
IR – 2 (at 2.22 um):360240180

  Sensitivities for TRISPEC spectroscopy are give here.





Focal plane mask

57 arcsec x 11 arcsec x 2

Sensitivities for TRISPEC imaging-polarimetry are give HERE.


  • This mode has been tested both in the laboratory and at the telescope. Imaging-polarimetry is available through collaboration with the University of Hertfordshire. Please contact Chris Davis at the JAC ( for further details.




0.88 arcsec x 11 arcsec x 2

Sensitivities for TRISPEC spectro-polarimetry are give here.


  • This mode is available through collaboration with the University of Hertfordshire. Please contact Chris Davis at the JAC ( for further details. TRISPEC Spectropolarimetry has been successfully tested in the laboratory and at UKIRT.
  • With the slit currently available, there are some overlapped regions due to unexpectedly narrow dispersion of the Wollaston prisms. Point sources or small objects are recommended as targets.

Last modification date: 1 April 2001
Last modification author: Chris Davis