Early scientific goals for the MMT’s multi-laser-guided adaptive optics Michael Lloyd-Hart, Thomas Stalcup, Christoph Baranec, N. Mark Milton, Matt Rademacher, Miguel Snyder, Michael Meyer, and Daniel Eisenstein Steward Observatory, The University of Arizona

Drivers for LGS AO Laser guide stars are now helping us get the most out of current generation large telescopes. –Keck II now devotes 25% of its time to LGS AO, and is producing science papers at the rate of ~1 per month. –Gemini North has just begun operating with a laser guide star. –Palomar closed the loop on a sodium LGS for the first time two nights ago. –VLT, Subaru, Gemini South, Keck I are all actively working to deploy lasers. Extremely large telescopes with apertures of m will need qualitatively different techniques: multiple LGS with tomographic wavefront analysis.

Multi-LGS at MMT Motivation is twofold: provide a facility LGS capability for the MMT, and understand the tools needed to succeed with adaptive optics for the Giant Magellan Telescope. First closed-loop operation of ground-layer adaptive optics (GLAO) at the MMT is anticipated this autumn. We are planning the first science programs that will take advantage of GLAO.

Modelling closed-loop PSFs To quantify expected closed-loop GLAO performance, we have computed synthetic PSFs from the open-loop wavefront measurements. Seeing at the time had mean r 0 = 22.5 cm (500 nm). Mean L 0 was 19 m. Tip-tilt (not sensed by LGS) is modeled on image motion observations of a 2 asterism, and assumes a single tilt star at the center of the LGS constellation.

GLAO PSFs: K band Encircled energy graphs for synthetic GLAO PSFs at three different radii within the LGS constellation. The results for 25 and 50 arcsec radius are almost indistinguishable. Also shown are curves for PSFs at the diffraction limit and the seeing limit at r 0 = 22.5 cm

GLAO PSFs: H band Encircled energy graphs for synthetic GLAO PSFs at three different radii within the LGS constellation. The results for 25 and 50 arcsec radius are almost indistinguishable. Also shown are curves for PSFs at the diffraction limit and the seeing limit at r 0 = 22.5 cm

PSF summary Reduction of FWHM and increase in peak intensity lead to improved imaging Energy concentration inside 0 .15 is 55% at K and 40% at H J band results coming… Metric Field angle (arcsec) Diffraction limit Seeing limit HKHKHKHKHK FWHM (arcsec)  50 (arcsec)  80 (arcsec) Peak intensity

Science instruments for GLAO PISCES –A  m imager for wide field imaging with a 1024 Hawaii array. –Field of view at the MMT f/15 focus is 1.9, at a pixel scale of 0 .11. Proposed GLAO imager (ATI proposal this year) –2x2 mosaic of JWST NIRCam devices (4kx4k focal plane array). –Pixel scale of 0 .06 critically samples the GLAO PSF in H and K. –Field of view is 4 on a side, well matched to the planned 5 circular corrected field.

Early science program: high redshift galaxies Near IR is a key spectral region: ground-based optical observations and thermal IR data from Spitzer leave a gap at 1-3  m. Near IR SED probes photometric redshifts and stellar population distributions, and morphology of older stars. Wide-field optical and Spitzer data are currently acquired much faster than NIR - improved GLAO image quality can help relieve this bottleneck. GLAO offers the chance of consistently good imaging quality, well matched to the sizes of high-redshift galaxies, to integrate down to the required faint flux levels. This is particularly true in K band, where GLAO will perform well and where HST has little capability.

Early science program: constraining the low-mass IMF GLAO observations can potentially confirm evidence from nearby star-forming regions (e.g. NGC 1333) that sub-stellar objects are distributed differently from stars in the cluster. This would test theories of cluster formation and subsequent dynamical evolution. GLAO could survey ~200 sq. arcmin per night with sensitivity for objects 3 Myr old down to 2 M J at 10 . Companions would be resolved at the peak of the binary separation distribution of 30 AU at the distance of NGC 1333 (300 pc). Follow-up GLAO observations of candidate 2 M J mass objects with a J/H grism at resolution 300 could be obtained for dozens of objects per pointing with SNR > 10 in 6 hours. Would provide estimates of T eff and surface gravity to discriminate bona fide association members from reddened background L and T dwarfs. Photometric detections at SNR > 100 for all sources with m K 20 M J at the age of NGC 1333) would enable astrometry constraining velocity dispersions to 1 km/s over a baseline of two years. These observations would provide fundamental tests of models for the dynamical evolution of brown dwarfs and stars in forming clusters.

Summary Experiments with multi-LGS at the MMT are very encouraging so far in open-loop work. GLAO is the easiest multi-laser technique to implement, and so that is where our closed-loop work will start. GLAO also offers low-hanging scientific fruit that we will attempt to pluck. There is a window of opportunity for unique return at the MMT since it will for several years be the only telescope with multi-LGS. The next on line is expected to be Gemini South. The MMT results are already providing critical input to the design of GMT’s adaptive optics systems.