Keck NGAO Science Requirements

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

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

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 2006. • 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.

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 0.6-5 µm • 2.2 x 2.2 arc-minute field of view, pixel scale of 0.035 arc sec for 0.6-2.3 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=1000 or 3000; not clear which) • 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.

5. ALMA Capabilities • Very powerful new facility for mm and sub-mm astrophysics • Currently scheduled to begin science operations in 2012 • Consists of 54 12-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

6. Science case: Size and shape of minor planets Ceres, K band, Keck NGS AO • 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 15 - 20 largest asteroids will provide strong constraints on frequency of large collisions • NGAO should be able to resolve ~800 main-belt asteroids Eros

7. Science case: Multiplicity of minor planets Simulation of fake moonlet around 87 Sylvia • 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

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

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

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: 5 - 10 arc sec, 5 - 10 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)

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

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: 3000 - 4000 • 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)

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.

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.

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)

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? 6 - 12 IFU heads

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?

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: 3000 - 4000 • 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

19. Spreadsheet summary

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?)