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 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.

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 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=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 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

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 15 - 20 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: 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)

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: 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)

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)

Redshift J band H band K band

~ 1.2 H and NII

~ 1.5 OIII H and NII

~ 2.5 OII OIII H and NII

~ 3.2 OII OIII

~ 4.1 OII

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? 6 - 12 IFU heads

Type of Object Approx density

per square arc minute

SCUBA sub-mm galaxies

to 8 mJy 0.1

Old and red galaxies wit h 0.85 < z < 2.5 and R < 24.5

2

Field galaxies w/ em ission lines in JHK windows

0.8 < z < 2.6 & R < 25

> 25

Center of distant rich cluster of galaxies at z > 0.8

> 20

All galaxies K < 23 > 40

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: 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

Slide 19

Spreadsheet summary

Next Generation Adaptive Optics - Science Requirements November 14, 2006

Science Case

Wave-length

(microns)

Instan-tan-eous FOV

(")Image quality

Imag Sampli

ng (mas)

Spec Sampli

ng (mas)

Spectral Reso-lution

Photo-metric accur. (mag)

Astro-metric accur. (mas)

IFU Multipli

cityBkgnd level

Contrast ( )mag

1 Science Inst stpriority Additional Requirements

Solar System Multiple Asteroidal Systems (<70"/ )Differential tracking hr

( : 87 )Main Belt Multiples ex Sylvia0.7-2.5 2 170 nm OK Nyq na na 0.05 ( )rel /4Nyq 1 na > 5.5 0.5"at Vis camera ; <10 - Service observing min overhead to acquire new LGS on axis targetGalactic

Galactic Center Dynamics confusion limited Astrometry K band 10 170 nm OK Nyq na na na 0.1 na ? =4 0.05"K @ NIR imager - ( )IR Tip Tilt needed consider H or K band Radial Velocities K band 1 170 nm OK na 20 35or 3 - 4K K na na 1 ? =4 0.05"K @ NIR IFU 10 / ; ~15,000 km s accuracy needed an R spectrometer would also be nice

Direct Imaging of Planets ~ ( ); ; - Static wfe XX nm needed must quantify coronagraph needed L band imaging would be useful & ( , * )Search detection BDs young s0.9-2.5 5 10to 140 nm OK 5-10 na na 0.05 ( )rel < 5 na na =10 0.5"H @ /NIR imager coronagraph - ( ); <10 - IR tip tilt both on and off axis min overhead to acquire new LGS on axis target

Extragalactic Field Galaxies

2 < < 3z JHK 3 1 3 3x to x50 mas for

*optimal TT s na 503000 to4000 na na 6 12to

10 to20% >

+atm tel na deployable NIR IFUs ; . low backgrounds are crucial no of IFUs should be determined by cost

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?)