NIRSpec - the JWST Multi-Object Spectrograph P. Jakobsen (ESA), S. Arribas (CSIS), T. Beck (STScI), S. Birkmann (ESA), T. Böker (ESA), A. Bunker (Oxford), S. Carpano (ESA), S. Charlot (IAP), G. De Marchi (ESA),P. Ferruit (CRAL), M. Franx (Leiden), R. Maiolino (INAF), H. Moseley (NASA), J. Muzerolle (STScI), B. Rauscher (NASA), M. Regan (STScI), H.W. Rix (MPIA), M. Sirianni (ESA), J. Valenti (STScI), C. Willott (Ottawa) Abstract The Near-Infrared Spectrograph (NIRSpec), to be launched in 2014 on the James Webb Space Telescope, will be the first slit-based multi-object spectrograph used in space, and is designed to simultaneously provide spectra of faint objects in the range µm at resolutions of R=100, R=1000 and R=2700. The all-reflective wide-field optics, a novel MEMS-based programmable micro-shutter array slit selection device, and large format low-noise HgCdTe detectors combine to allow simultaneous observations of >100 objects within a 3.4x3.4 arcmin 2 field. A 3x3 arcsec 2 integral field unit and five fixed slits are also available. The NIRSpec sensitivity is expected to allow detection of a continuum flux of 20 nJy (AB>28) in R~100 mode, and a line flux of 6x erg s -1 cm -2 in R~1000 mode, both at S/N > 3 in 10 4 s. NIRSpec is being built for the European Space Agency by EADS Astrium as part of the European contribution to the JWST mission, with the micro-shutter and detector arrays being provided by NASA/GSFC. NIRSpec Highlights wavelength range: µm spectral resolutions: R~100, R~1000, and R~2700 field of view: 3.4 x 3.6 arcmin (9 arcmin 2 for MOS) programmable slit mask: MEMS-based micro-shutter array Integral-field spectroscopy: 3”x3” image slicer 5 individual “long” slits for single-object, high-contrast spectroscopy all-reflective optics athermal design based on ceramic material for structure and optics 8 Positions: 1. Clear (CaF substrate) 2. Closed (for use with CAA) 3. Long Pass l > 0.7 µm 4. Long Pass l > 1.0 µm (Band I) 5. Long Pass l > 1.7 µm (Band II) 6. Long Pass l > 2.9 µm (Band III) 7. TA A (1.0 < l < 1.3 µm, for Target Acquis.) 8. TA B (0.8 < l < 2.0 µm) Flight model shown Filter Wheel Re-Focussing Mechanism penta-prism design large focus range no lateral image shifts Structural & Thermal Model shown All-ceramic design: bench & mirrors of SiC athermal, very low CTE at 37 K light-weight, yet extremely stiff polished to optical quality (qualification model shown) Fore Optics Three Mirror Anastigmat NIRSpec field of view NIRSpec status and schedule Instrument design consolidated during ISR in July 2007 CDR successfully completed in December 2008 Demonstration model built, tested and modified for delivery to NASA for early test at ISIM level First thermal vacuum calibration campaign successfully held in May/July 2009 (see adjacent poster) Flight model thermal vacuum calibration campaign in Fall 2010, followed by delivery to NASA ISIM-level integration and test campaign in 2011/12 Observatory-level test campaign in 2012/13 JWST launch in 2014 NIRSpec optical path Telescope aperture & PSFPSF at MSA & truncationPupil at gratingPSF at FPA & pixelisation 11 calibration lamps: bulbless Tungsten filaments filaments combined with transmission filters for passband selection temperature-monitored Fabry-Perot filters for dispersion calibration rare-Earth filter for absolute reference qualification model shown Calibration Assembly Spectrometer light shield 8 Positions: 1. R=100 Prism 2. R=1000 Grating (Band I) 3. R=1000 Grating (Band II) 4. R=1000 Grating (Band III) 5. R=3000 Grating (Band I) 6. R=3000 Grating (Band II) 7. R=3000 Grating (Band III) 8. Flat mirror for imaging mode Grating wheel Focal Plane Assembly (FPA) 2 Rockwell SCAs 2048 x 2048 pixels 2 each physical pixel size 18 mm pixel scale 100 mas thermally controlled data locally digitized by 2 SIDECAR ASICs: Camera housing FPA Harness Radiator interface Collimator Optics TMA Coupling Optics Target alignment Microshutter detail Microshutter Sub-Assembly (MSA) 4 MSA quadrants with 365x171 shutters each Physical slit size: 179 x 80 mm 2 Aperture size on sky: 460 x 200 mas 2 Total FOV: 3.4 x 3.6 arcmin 2 Mounting structure also houses IFU optics IFU design made from SiC flight model shown actual size 110 cm ~ 3’ 7”