Keck NGAO Science Requirements Claire Max UC Santa Cruz Caltech NGAO Meeting November 14, 2006

Slide 2 Outline Background JWST and ALMA Science requirements for selected key areas –Multiplicity and size of minor planets –Imaging extrasolar planets around brown dwarfs and low mass stars –General relativistic effects in the Galactic Center –Galaxy assembly and star formation history Other science cases are in progress Roll-up of requirements to date Some key issues that have emerged

Slide 3 Background Science Requirements Document (SRD) is a “living document” and will be updated as the science case is developed with increasing fidelity. Initially, SRD will heavily reference the science cases developed for Proposal to Keck SSC in June Key issues: –Importance of science enabled by NGAO system and accompanying instruments –Advances offered by NGAO relative to existing systems and new AO systems being developed on other telescopes –Complementarity to JWST and ALMA, which will be commissioned on the same timescale as Keck NGAO will be commissioned.

Slide 4 JWST Capabilities Cryogenic 6.5m space telescope to be launched in 2013 Higher faint-source sensitivity than Keck NGAO (very low backgrounds) NIRCAM will image from µm –2.2 x 2.2 arc-minute field of view, pixel scale of arc sec for µm, and coronagraphic capability NIRSpec multi-object spectrograph with an IFU –In R~100 and R~1000 modes will obtain simultaneous spectra of >100 objects in 3.4 x 3.4 arcmin field of view –Has an IFU with field of view 3” x 3” (R=100, 1000, or 2700) –Spatial pixel size will be 0.1 arc sec in all cases Conclusions for NGAO? We can compete at higher spatial resolution (<0.1 arc sec) and shorter wavelengths (<2 µm) where JWST will not be diffraction limited or Nyquist sampled.

Slide 5 ALMA Capabilities Very powerful new facility for mm and sub-mm astrophysics Currently scheduled to begin science operations in 2012 Consists of m and 12 7-m antennas located at 5000m (16,500 feet) in the Atacama desert Typical spatial resolution 0.1 arc-second (down to 0.01 arc- seconds at high frequencies) Chemical evolution in star-forming regions at z~3, dust-gas interactions, molecules surrounding stars, molecular clouds, dust emission out to z=20, kinematics of obscured galactic nuclei and quasi-stellar objects on spatial scales smaller than 100 pc Conclusions for NGAO? A renaissance in star formation studies near and far; new insights into highly obscured distant galaxies

Slide 6 Science case: Size and shape of minor planets Shape and size –Some are round, many are not –IAU planet definition debate! Surface features –Ceres is one example: low contrast will be helped by high NGAO Strehl ratio Observations of the largest asteroids will provide strong constraints on frequency of large collisions NGAO should be able to resolve ~800 main-belt asteroids Ceres, K band, Keck NGS AO Eros

Slide 7 Science case: Multiplicity of minor planets Recent data suggest that primary asteroid of most binary asteroid systems has rubble-pile structure, weak shear strength Hence shape is directly related to angular momentum at formation Moonlet orbit plus shape of primary gives mass of primary NGAO, particularly at R band, increases detection rate of moonlets dramatically Simulation of fake moonlet around 87 Sylvia

Slide 8 Minor planets: science requirements Driver for visible wavelengths: 0.7 < < 2.4 microns –Reflected sunlight, important spectral bands Preferred instrument: visible imager Other instruments: visible IFU Instantaneous FOV: 2 arc sec, Nyquist-sampled Image quality: 170 nm OK, still doing simulations Photometric accuracy: 5% for satellite relative to primary Astrometric accuracy: Nyquist/4 Contrast ratio:  m > 5.5 at 5 arc sec from primary Other important considerations: –Need non-sidereal tracking; need rapid retargeting in LGS mode (≤10 min compared with 25 min today); request service observing

Slide 9 Science case: Extrasolar planets around nearby stars Gemini + ESO “extreme AO” systems very powerful, but can’t look around low-mass stars or brown dwarfs –Too faint for wavefront sensing Low-mass stars are much more abundant than higher mass stars; they might be most common hosts of planetary systems Survey of young T Tauri stars will constrain planet formation timescales

Slide 10 Extrasolar planets: Science Requirements Wavelength range: 0.9 < < 2.4 microns Preferred instrument: NIR imager Other instruments: Low-resolution (R~100) near-IR spectroscopy (could this be done with narrow-band filters?), L-band imager Instantaneous FOV: arc sec, mas sampling Image quality: 140 nm OK, still doing simulations of ≥170 nm Photometric accuracy: 5% for planet relative to primary Astrometric accuracy: < 5 mas Contrast ratio:  H=10 at 0.5” separation Other important considerations: –Need coronagraph; Need low residual static WFE (how low?); Need rapid retargeting in LGS mode (≤10 min compared with 25 min today); Need IR tip-tilt (both on and off axis)

Slide 11 Science Case: General Relativistic Effects at Galactic Center Detect deviations from Keplerian orbits around black hole Highest priority: strong-field GR precession Can be measured even for single orbits of known stars (S0-2) if astrometric precision is ~100 μas coupled with radial velocity precision of ~10 km/s If NGAO allows discovery of other (fainter) close-in stars, may be able to measure other effects too

Slide 12 Galactic Center: science requirements Wavelength range: K band Preferred instruments: NIR imager and NIR IFU Imager instantaneous FOV: 10 arc sec (now 20 km/s), Nyquist samp IFU instantaneous FOV: 1 arc sec, 20 or 35 mas sampling Other instruments: R=15,000 IR spectrograph would be good Spectral resolution: Image quality: 170 nm OK, doing simulations of other WFEs Astrometric accuracy: 0.1 mas Radial velocity accuracy: 10 km/s Contrast ratio:  K=4 at 0.05” separation Other important considerations: –Need IR tip-tilt (consider H or K band, because of very high extinction at J band)

Slide 13 We need to understand what is limiting astrometric accuracy today Uncertainty decreases as expected for brighter stars, then hits a floor. Why the floor? Tip-tilt anisoplanatism? Work is underway.

Slide 14 Comment on astrometric accuracy and AO design MCAO systems are known to suffer from focal plane distortions. In addition to tip and tilt, differential astigmatism and defocus between the DMs is unconstrained. These three unconstrained modes do not influence on-axis image quality, but produce differential tilt between the different parts of the field of view. Our Point Design has a large DM for high stroke correction, and a smaller DM (MEMS or other) for high- order correction. Need to analyze interaction of the two DMs to avoid or minimize focal plane distortions.

Slide 15 Science Case: Galaxy assembly and star formation history Overview –Study galaxies at z > 1 via their emission lines –Star formation: H  –Metallicity: NII / H  –Excitation: OII, OIII (star formation, AGN activity)

Slide 16 Space densities of types of galaxies Tens of galaxies per square arc min Clear benefit to deployable IFUs How many? Decide based on total cost and design issues (e.g. all fit into one dewar) Reasonable number? IFU heads

Slide 17 Low backgrounds are key Backgrounds are current limit for OSIRIS science in this field Requirement: background AO system less than 10 to 20% of that from sky and telescope We need to address cooling issues vigorously –What is practical, what are costs?

Slide 18 High z Galaxies: science requirements Wavelength range: JHK bands Preferred instruments: deployable NIR IFUs (6 - 12) IFU instantaneous FOV: 3 x1 arc sec requirement, 3 x 3 arc sec goal Spectral resolution: Spatial sampling: 50 mas Image quality: 50 mas enclosed energy (what fraction?) for optimal tip-tilt star configuration Sky coverage fraction: > 30% on average, if consistent with above image quality spec. If not, iterate. Sky background: less than 10-20% above sky + telescope Other important considerations: –No. of IFUs should be determined by total cost, and by design issues

Slide 19 Spreadsheet summary

Slide 20 Key issues that have emerged Keep asking “how does this science complement JWST capabilities?” or “where is NGAO’s sweet spot relative to JWST?” Need non-sidereal tracking (asteroids) Need rapid retargeting in LGS mode (≤10 min compared with 25 min today) Need coronagraph and low residual static WFE (how low?) (planet detection) Need IR tip-tilt (think about H or K for Galactic Ctr) Need to understand what is limiting astrometric accuracy for Galactic Center today (need 0.1 mas) Need to understand astrometric implications of having > 1 DM Need sky background less than 10-20% above sky + telescope Determine # of IFUs from total cost and from design issues (below what # is it possible to fit all into one dewar?)