SpeX mounted on IRTF May 9 2000 SpeX mounted on IRTF May 9 2000

SpeX: 0.7-5.3 micron medium-resolution spectrograph and imager


SpeX is a medium-resolution 0.7-5.3 micron spectrograph built at the Institute for Astronomy (IfA), for the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. The instrument saw first light in May 2000 and was upgraded in 2014. The primary reason for the upgrade was to replace obsolete array control and instrument control electronics although the opportunity was taken to upgrade the arrays as well. The Raytheon Aladdin 3 1024x1024 InSb array in the spectrograph was replaced by a Teledyne 2048x2048 Hawaii-2RG array and the engineering grade Aladdin 2 512x512 InSb array in the IR slit viewer was replaced by the science grade Aladdin 3 array from the spectrograph (only a 512x512 quadrant is used). Astronomical Research Cameras, Inc. controllers run both arrays. Most of the warm electronic hardware was also replaced: motors, motor controllers, Hall effect sensor control, power supplies, computers and GUIs.

For most observing programs guiding is done with the IR slit viewer on spillover flux from the object in the slit. However, for optically visible objects selectable IR transmitting and visible reflecting dichroics in SpeX feed the MORIS CCD camera attached to the side of SpeX to enable guiding in the visible. MORIS is also used as a scientific CCD imager and for simultaneous optical and IR observations in conjunction with SpeX.

The upgrade has resulted in increased simultaneous (one shot) wavelength coverage in all spectral modes and improved spectral sensitivity (0.25-0.5 mags). Due to the faster computers instrument control is more robust and there are fewer software problems.

SpeX was originally funded by the National Science Foundation (NSF) in 1996 with additional funding from NASA for the detector arrays in 1998. The SpeX Upgrade was funded by NSF in 2008 but delays in procurement of a science grade H2RG array delayed completion until 2014.

Old SpeX (2000-Jan 2014)

New SpeX (Aug 2014-)

Archive of past quarterly reports.

SpeX News


IRTF Spectral Library

SpeX has been used to observe several hundred stars in order to compile a library near-infrared spectra (R=2000, ~0.8-5 micron). Currently FGKM stars, carbon stars, LT dwarfs, and the planets Jupiter, Saturn, Uranus, and Neptune, are available for general use and download.

SpeX Prism Library

The SpeX Prism Libraries hosts over 1000 low-resolution, near-infrared spectra of low-temperature dwarf stars and brown dwarfs obtained with the prism mode. All are available for general use and download.


Observers publishing results obtained with SpeX are requested to reference the following paper:

SpeX: A Medium-Resolution 0.8-5.5 micron Spectrograph and Imager for the NASA Infrared Telescope Facility
J. T. Rayner, D. W. Toomey, P. M. Onaka, A. J. Denault, W. E. Stahlberger, W. D. Vacca, M. C. Cushing and S. Wang
(2003, PASP 115, 362).

Observers who use Spextool are also kindly asked to reference the following papers:

Spextool: A Spectral Extraction Package for SpeX, a 0.8-5.5 micron Cross-Dispersed Spectrograph
Michael C. Cushing, William D. Vacca and John T. Rayner
(2004, PASP 116, 362).

A Method of Correcting Near-Infrared Spectra for Telluric Absorption
William D. Vacca, Michael C. Cushing and John T. Rayner
(2003, PASP 115, 389).

Note: The general version of the telluric correction routines, xtellcor_general, previously available as a stand alone package, has now been incorporated into the Spextool package. Users must download the full Spextool package in order to use xtellcor_general.

Two other papers maybe of interest to SpeX users:

Four years of good SpeX
John T. Rayner, Peter M. Onaka, Michael C. Cushing and William D. Vacca
(2004, SPIE 5492, 1498-1509).

Nonlinearity Corrections and Statistical Uncertainties Asociated with Near-Infrared Arrays
William D. Vacca, Michael C. Cushing and John T. Rayner
(2004, PASP 116, 352).

Observer Documentation

These pages are updated irregularly.


SpeX MANUAL (06 October 2017).

  • Observing Logs for the Spectrograph and the Guider/Imager
  • Parallactic angle calculator
  • Form to locate A0V Stars and G2V Stars near a target.

  • Spectrograph limiting flux calculator

    SpeX Data

    With the 1024x1024 Aladdin 3 array originally in SpeX the file size was 4.2MB (and sometimes 2.1 MB at low flux). Now, with the 2048x2048 H2RG array in the spectrograph the individual file size is 16.8MB. However, we now store three files per image: pedestal minus signal, pedestal, and signal, for a total image size of 50MB. The reason for the extra fiiles, which are stored as extensions to each image, is to accurately compute corrections for non-linearity. Consequently, observers should note that spectrograph images will take about ten times longer to ftp and require ten times more disk space to store than with the old SpeX.

    Guidedog images (512x512) are the same size as before (1.05MB).

    Observers can compress data for transfer and uncompress on arrival by using the -C flag: 'sftp -C yourname@yourhost'. This should only be used for slow links since it requires extra CPU time.


    Spextool is an IDL-based spectral reduction program to reduce SpeX cross-dispersed and prism data. It is written and maintained by Mike Cushing and Bill Vacca.

    25 January 2016 Spextool version v4.1. Spextool v4.1 reduces data obtained with the pre-upgraded SpeX and the upgraded SpeX. This new version includes bug fixes, reduces data using the two dichroics and adds features to 'xvspex'. All users should read Sections 1 and 2 of the manual (found in Spextool/manuals/) before attempting to run the software, if only because some new IDL libraries are required. A gzipped tar file uSpeXdata.tar.gz. containing raw SXD+LXD_Long SpeX data can be used to test drive the downloaded Spextool package. Comments, suggestions for improvements, and bug reports should be directed to Mike Cushing at michael.cushing@gmail.com.

    Technical Documentation

    Back to IRTF Homepage

    Last modified 25 January 2016
    Questions to John Rayner rayner@ifa.hawaii.edu