SpeX: 0.7-5.3 Micron Medium-Resolution Spectrograph and Imager
NASA InfraRed Telescope Facility(IRTF), Institute for Astronomy, University of Hawaii

@ Observer Documentation


SpeX Manuals and Tools

  • SpeX manual 02Mar21.pdf
  • The SpeX Observing Manual (02 March 2021). Previous editions avaiable here.
  • SpeX FITS Keyword Reference
  • This directory contains the SpeX FITS Keyword Reference document, including previous edition.
  • Spectrograph Logs (PDF)
  • Spectrograph Log Template
  • Guider/Imager (PDF)
  • Spectrograph Guider/Imager Log Template
  • Parallactic Angle Calculator Form
  • Web form to estimate angle and differential atmospheric refraction for observations with SpeX
  • A0V Stars and G2V Stars Form
  • Web form to locate A0V and/or G2V stars near a target object
  • Spex Observing Calculator
  • This form can be used to estimate the limiting fluxes, ITIME for requested S/N, and S/N from flux, temperature, and ITIME for the spectrograph

    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.

    SpeX Libraries

  • 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.
  • IRTF Extended Spectral Library
  • The Extended IRTF Library expands the metallicity coverage of the original IRTF Spectral Library (Rayner et al. 2009) from mainly solar metallicity to -1.7 < [Fe/H] < 0.3. The current release is mainly for late-type stars.
  • 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).

    Contact Mike Connelley for further information or assistance