The IRMS concept is for a near diffraction-limited multi-slit near-infrared spectrometer and imager. The concept is modeled closely after the MOSFIRE instrument on the Keck Telescope and would be fed by the Narrow-Field Infrared Adaptive Optics System (NFIRAOS). See schematic of the instrument in the following figure. The development of the IRMS instrument concept and the accompanying science case has highlighted the extremely exciting science that would be enabled with a highly sensitive slit based multi-object near-IR spectrograph.
The IRMS concept instrument would provide near-infrared imaging and multi-object spectroscopy at Y (0.97–1.12 micron), J (1.15–1.35 micron), H (1.46–1.81 micron), and K (1.93–2.45 micron) bands. Operating with NFIRAOS on the TMT, it would be used as a near-diffraction-limited imager and multi-slit spectrograph with moderate resolution with a circular field-of-view (FoV) of 2.27 arcmin in imaging mode, and elliptical FoV of 2.0'x0.6' in spectroscopy mode. The spatial scale would be 0.06" per pixel, or 0.08" per pixel in the dispersion direction. The spectral resolution would be R=3270 for a 3 pixel or 0.24" wide slit, or R = 4660 for a 2 pixel or 0.16" wide slit. The multiplex capability would be up to 46 slits using a slit mask system on a cryogenic configurable slit unit as used presently in MOSFIRE where each slit width can be adjusted arbitrarily. For IRMS minimum slit width would be 0.16". The IRMS detector would be a 2048x2048 Teledyne Technologies Hawaii-2RG with a long wavelength cut-off at 2.5 micron.
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The science areas that will be advanced with IRMS observations include, but are not limited to, the following:
NFIRAOS Wide Field Mode will deliver images to IRMS that will produce almost an order of magnitude gain in encircled energy within 160″ slits over the entire of 2′ diameter field. These IRMS performance estimates were generated by the TMT AO analyst Luc Gilles in 2010. The solid curves are performance predictions for atmospheric turbulence and WFS noise effects only. Please note that enclosed energies are plotted as a function of the full (not half) slit width. The dashed and dotted curves include the additional wavefront errors due to implementation effects based on two models. Notice that the dashed curves aren't that much different from the solid curves for a 160 mas slit width, although more work is needed to estimate the actual structure function for these implementation errors.
Dotted: Errors have a white spatial frequency spectrum, and the impact on the enclosed energies is estimated using Marechel's approximation. Dashed: Errors have a Kolmogorov spectrum, and the impact on the enclosed energies is estimated by multiplying the OTF by a transfer function in the spatial frequency domain.
IRMS Science Team
IRMS Technical Team
