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Single-Object Slitless Spectroscopy with NIRISS

JWST FGS. Single-Object Slitless Spectroscopy with NIRISS. Kevin Volk, STScI / HIA With help from Loïc Albert (U. Montreal). TIPS Meeting, 18 April 2013. Single-Object Grism Spectroscopy.

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Single-Object Slitless Spectroscopy with NIRISS

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  1. JWST FGS Single-Object Slitless Spectroscopy with NIRISS Kevin Volk, STScI/ HIA With help from Loïc Albert (U. Montreal) TIPS Meeting, 18 April 2013

  2. Single-Object Grism Spectroscopy • In mid-2011 the TFI instrument was re-designed to NIRISS, and at that time a grism mode specific to exo-planet spectroscopy around bright stars was added. Unlike normal grism modes, it is intended for single objects. The goal is to observe stars known to have exo-planets in-eclipse and out-of-eclipse, and take the difference to extract the exo-planet spectrum. • A medium-resolution grism is used, with a prism to separate the orders: note that no blocking filter is used. • Estimated resolution λ/Δλ varies from ~300 to ~800 in 1st order, from 0.6 to 3 μm. • Control of systematic effects is going to be important for the exo-planet science. TIPS 18 April 2013

  3. Current Flight Grism (Bach Corp.) Recess Unruled Perimeter TIPS 18 April 2013

  4. NIRISS GR700XD Point Spread Function With weak lens: ~35 pixels wide in the cross-dispersion direction No lens (divided by 11) PSF simulations from David Lafernière (Montreal) TIPS 18 April 2013

  5. Flight (Bach) Grism Blaze Function TIPS 18 April 2013

  6. Spare (LLNL) Grism Blaze Function TIPS 18 April 2013

  7. The cross-dispersion direction is always (close to) along the y axis. Hence it is not perpendicular to the trace direction. order 0

  8. For brighter objects a 2048×256 pixel sub-array will be used to speed up the read-out. For the brightest objects a 2048×80 pixel sub-array will be used, sacrificing wavelength coverage for fast read-out. TIPS 18 April 2013

  9. GR700XD Bright Limit Estimates 2MASS J-band Magnitude Limits 10000 ADU/frame TIPS 18 April 2013

  10. TIPS 18 April 2013

  11. Final Remarks • The SOSS mode provides a unique and powerful capability for JWST exo-planet observations. • First light through the instrument will be later this year during ISIM CV1RR testing (nominally in the early fall). • Calibration of this mode will be challenging, particularly in terms of working to reduce the systematic effects – i.e. pixel-to-pixel variations, non-linearity effects, persistence, etc. – to achieve very high S/N in a series of spectra over a period of order 10 hours. TIPS 18 April 2013

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