2009 Aug 20 — SAC update WFOS/MOBIE1 WFOS/Multi-Object Broadband Imaging Echellette MOBIE Team, to date: PI / optical designer: Rebecca Bernstein Project Manager: Bruce Bigelow Project Scientist: Chuck Steidel Science Team: Bob Abraham (U. Toronto) Jarle Brinchmann (Leiden) Rebecca Bernstein (UCSC) Judy Cohen (Caltech) Sandy Faber (UCSC) Raja Guhathakurta (UCSC) Jason Kalirai (STScI) Jason (Xavier) Prochaska (UCSC) Connie Rockosi (UCSC) Alice Shapley (UCLA) Chuck Steidel (Caltech)

2009 Aug 20 — SAC update WFOS/MOBIE2 Minimize complexity & moving parts — Maximize coverage, resolution, field, transmission. MOBIE overview: Design Principles

2009 Aug 20 — SAC update WFOS/MOBIE3 ADC – always used, fused silica prisms Slit-mask fed Mirror collimator Dichroic split at ~550nm 300mm pupils Prism cross-dispersion Reflection gratings 3 options (1 low blaze, 2 high-blaze angle) R = / ∆ = 1000, 3000, 5000, or 8000 Refracting cameras Diameter < 400mm lenses Blue: all fused silica, CaF2 (perfect internal transmission) Red: fused silica, glass, CaF2, 400 mm diameter elements max. RTV-bonded multiplets o field of view F/1.9 High transmission (~40%) R rms < 0.1arcsec MOBIE summary: a multi-slit red/blue echellette. Slit mask collimator dichroic Fold mirror Red grating Blue grating (dummy Surface)

2009 Aug 20 — SAC update WFOS/MOBIE4 MOBIE overview: 3 Spectroscopic Modes Low: R~1000Only dispersion elements change Medium: R~ 2,500 and/or 5000Each grating is fixed. High: R ~ 8,000 TMT focal plane. (mask not visible) collimator grating Fold mirror (red side) Dichroic (blue side)

2009 Aug 20 — SAC update WFOS/MOBIE5 MOBIE overview: 3 Spectroscopic Modes Low: R~1000Only dispersion elements change. Medium: R~ 2,500 and/or 5000Each grating is fixed. High: R ~ 8,000 TMT focal plane. (mask not visible) collimator grating Fold mirror (red side) Dichroic (blue side)

2009 Aug 20 — SAC update WFOS/MOBIE6 MOBIE overview: 3 Spectroscopic Modes Low: R~1000Only dispersion elements change. Medium: R~ 2,500 and/or 5000 Each grating is fixed. High: R ~ 8,000 TMT focal plane. (mask not visible) collimator grating Fold mirror (red side) Dichroic (blue side)

2009 Aug 20 — SAC update WFOS/MOBIE7 MOBIE overview: Example Configuration Options 7 R~1000 (single order) R~2500 (3 orders) R~5000 (5 orders) R~8000 (7-8 orders) Prism cross-dispersion sets the slit length: 2” – 4” (for multiple orders) MOBIE OCDD

2009 Aug 20 — SAC update WFOS/MOBIE8 MOBIE overview: Echellette spectroscopy Echelle advantages: Always “on blaze” Standard ruled reflection grating No grating tilt or camera articulation required High resolution with modest beam size (300 mm on TMT)

2009 Aug 20 — SAC update WFOS/MOBIE9 MOBIE overview: field of view Field of view is similar to DEIMOS if placed on Keck. Field dimensions: Slit length: 9.6 arcmin (max) Area: ~40.3 sq. arcmin Off-axis Required with reflective collimator Achromatic, high throughput Contiguous field: Simple, cheap, better for surveys. (Empirically, multiple fields work badly.)

2009 Aug 20 — SAC update WFOS/MOBIE10 MOBIE overview: field of view

2009 Aug 20 — SAC update WFOS/MOBIE11 This slide intentionally left blank.

2009 Aug 20 — SAC update WFOS/MOBIE12 CDP upcoming: Background Subtraction Some sort of beam-switching is mandatory — short slit pairs or within a longer slit. minimal systematics if cadence is faster than variability timescale (2-30 sec for rms sky variance < 0.1%) ideally no fitting/interpolating required (measure sky / target at same time, same slit) Short exposures or nod+shuffle both possible. limit set by overhead+detector noise. A A B B ~4” ~2”

2009 Aug 20 — SAC update WFOS/MOBIE13 ADC and collimated field of view CDP progress: Fused silica, linear ADC