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

IRTF Spectral Library


The Instrument:

SpeX is a 0.8-5.4 μm, medium-resolution, cross-dispersed spectrograph equipped with a 1024 x 1024 Aladdin 3 InSb array.  The entire 0.8 to 5.4 μm wavelength range can be covered with two cross-dispersed modes, the short-wavelength cross-dispersed mode (SXD), and the long-wavelength cross-dispersed mode (LXD).  The SXD mode provides simultaneous coverage of the 0.8-2.4 μm wavelength range, while the LXD1.9, LXD2.1, and LXD2.3 modes cover the 1.9-4.2, 2.20-5.0 and 2.38-5.4 μm wavelength ranges, respectively.  For nearly all stars in the Library, the 0.3 arcsec (2 pixel) slit was used for both the SXD and LXD modes, providing resolving powers of 2000 and 2500, respectively. Measurements of arclines confirm that the design resolving power is obtained (a full width half maximum of 2.0 pixels for the 0.3 slit at all wavelengths.  The length of the slit for these modes is 15.0 arcsec and the spatial scale is 0.15 arcsec/pixel.  The spectrograph also includes a high-throughput low-resolution R~200 prism mode and a single-order 60 arcsec long-slit R~2000 mode.  An autonomous infrared slit viewer employing a 512 x 512 Aladdin 2 InSb array is used for object acquisition, guiding, and imaging photometry. The slit viewer covers a 60 x 60 arcsec field-of-view at a spatial scale of 0.12 arcsec/pixel. An internal K-mirror image rotator enables the field to be rotated on the slit.  Spectral calibration is done with a calibration unit consisting of flat field and arc lamps, integrating sphere, and illumination optics which reproduce the beam from the telescope.