Simultaneous Infrared-Visible Imager/Spectrograph a Multi-Purpose Instrument for the Magdalena Ridge Observatory 2.4-m Telescope

The Simultaneous Infrared-Visible Imager/Spectrograph (SIRVIS) is a planned multi-purpose instrument for the Magdalena Ridge Observatory 2.4-m telescope located west of Socorro, NM. The primary science drivers are asteroid studies, the rapid response to astrophysical transient phenomena and observations of artificial targets such as satellites. For asteroid science, the wavelength range 0.39-2.5 μm gives the most mineralogically diagnostic information on surface compositions using standard filters and low-resolution, R ~ 200, spectroscopy. For transients, the telescope's rapid 10° /second slew rate will facilitate acquisition of data on any target within one minute of receipt of notice. For artificial targets, simultaneous two-color imaging will assist in unique determinations and overall condition monitoring. SIRVIS has two channels, a cryogenic NIR channel covering 0.85-2.5 μm at 0.27 arcsec/pixel, and an ambient temperature-pressure visible channel covering 0.39-1.0 μm at 0.15 arcsec/pixel. The beam is split by a cryogenic, redpass dichroic mirror located between the telescope focal plane and the respective collimators. Both channels use refractive optics. The instrument is being designed to initially phase in the visible channel, then the NIR channel, and readily accommodate upgrades. For sky subtraction, the telescope is nodded between 30-60 second NIR integrations. Long visible integrations are made possible by shifting the CCD charge in sync with the nod. SIRVIS Serves Three Scientific Functions 1) Photometry to measure the brightness of a target in selected filters. * Simultaneous visible and NIR photometry to derive colors. * Atmospheric extinction corrections are simplified as both channels observe through the same airmass. * 3 σ detections of V (0.55 μm) ≈ 22.5 and J (1.25 μm) ≈ 19.0 targets in 10 second long images. * 3 σ detections of V ≈ 25.0 and J ≈ 21.5 targets in 10 minute long images. * 1% photometry on V ≈ 21.5 and J ≈ 18.0 targets in 10 minute long images. 2) Spectroscopy for surface material characterization and temperature measurements. * The visible and NIR spectra offer continuous coverage from 0.39-2.5 μm. * Overlap in the ~ 0.85-1.00 μm range simplifies cross-calibration of the visible and NIR spectra. * Low resolution spectra maximizes sensitivity to faint targets, or shortens exposures of brighter targets. * R~200 (R is λ/Δλ) spectroscopy is sufficient to identify the mineral content of small bodies or surface materials of artificial satellites. * Can measure the black body temperature of warm and hot targets. 3) Astrometry to measure the position and motion of targets. * The low, <0.1%, geometric distortion simplifies the measurement of a target's position with respect to reference objects in the same field. * Relative astrometry accurate to <0.1 arcseconds across the full field of either channel.