Laser Guide Star Adaptive Optics without Tip-tilt Richard Davies1, C. Lidman2, M. Le Louarn3, M. Kasper3, V. Roccatagliata4, N. Ageorges2, P. Amico2 1

Max Planck Institute for Extraterrestrial Physics, Garching, Germany 2 European Southern Observatory, Paranal, Chile 3 European Southern Observatory, Garching, Germany 4 Max Planck Institute for Astronomy, Heidelberg, Germany

¾ Why use LGS-AO without tip-tilt? ¾ What do simulations predict? ¾ What do the observations show? photo: comet McNaught & PARSEC laser (Guillaume Blanchard)

Introducing 2 characters representing Adaptive Optics Engineers

representing Astronomers

from “Pettersson und Findus” by Sven Nordqvist

from “Ivor the Engine” by Oliver Postgate & Peter Firmin

The AO Language Barrier

what the AO engineer means

what the astronomer really wants

limiting magnitude

AO/tip-tilt loop is just about stable & closed at this limit

so I’ll get excellent correction even if I push it a bit fainter still

off axis correction

it is possible to correct up to 60” off axis, but performance is reduced

so it should work with a star 70” away that is at the limiting magnitude…

Deep extragalactic observations: often no tip-tilt stars e.g. the classic deep fields: HDF-North: HDF-South: Chandra DFS: Lockman Hole: COSMOS field:

small red circles: targets large red circle: 60” radius tip-tilt limit blue circles: star at 75”, R~17mag star at 115”, R~15mag

12 37, 22 34, 03 32, 10 45, 10 00,

+62 13 -60 33 -27 48 +58 00 +02 12

LGS-AO: high sky coverage at low Strehl ratios ¾ at low strehl, flux in core is the same but FWHM of core is larger ¾ sky coverage is nearly complete ¾ resolution much better than seeing

Simulations for the VLT seeing set at 0.8” at 500nm wavefront sensing with NAOS 7×7 array with full AO, FWHM of PSF is ~70mas max Strehl for full LGS-AO ~35%

LGS without tip/tilt, FWHM ~120mas

seeing limit

Simulations for the VLT LGS-AO without tip-tilt is much better than no AO at all 50% energy is within 0.3”×0.3” for LGS-AO both with & without tip-tilt

full AO no TT no AO

young star cluster in NG1313

14mag tip-tilt star is 50” from the star cluster

K-band LGS-AO + NACO

resolution ~0.3”, PSF elongated… An isolated galaxy with intense star formation occuring in dense regions scattered around the spiral arms

perhaps would be better without tip-tilt?

ULIRG IRAS11095-0238 LGS observation without tip-tilt class IVb compact galaxy merger at z=0.1066 (~400Mpc, 1”~1.8kpc) nuclei are 0.53” apart

K-band image (Kim+ 2002)

I-band image (Bushouse+ 02)

K-band NACO image with LGS-AO but no tip-tilt

ULIRG: Arp220 a prototypical advanced merger D=70Mpc; 1”~350pc

HST/ACS

60” radius

optical & HI: courtesy of NRAO/AUI; Hibbard et al. 2000

10”

HST/NICMOS

ULIRG: Arp220 the same structures are visible in HST/NICMOS and VLT/SINFONI data → resolution is comparable in both → SINFONI has the advantage of yielding distribution and kinematics of many diagnostics: 1-0S(1), Brγ, Si[VI], [FeII], stars, etc…

Scoville+ (2000) SINFONI + LGS-AO (effectively without tip-tilt) Erin Hicks will say more about the SINFONI data on Arp220 on Friday

Circumstellar Disks around Young Stellar Objects V.Roccatagliata, Th.Henning, S.Wolf, W.Brandner, MPIA

scattered light seen above & below an edge-on disk around the YSO

• Dense accretion disks form in T Tauri & Herbig Ae/Be stars • Key process in planet formation • High resolution multicolour infrared images yield • dust distribution → disk geometry • grain properties → how they grow & settle towards midplane

Circumstellar Disks around Young Stellar Objects V.Roccatagliata, Th.Henning, S.Wolf, W.Brandner, MPIA The Butterfly Star Wolf+ 03 J & K band images from HST/NICMOS; images 900AU across; resolution 0.09”-0.15”; higher resolutions won’t teach you anything more models (images 600AU across) based on near-IR & 1.3/2.7mm maps grain size (e.g. 100 or 0.25 μm) disk mass (7×10-3 Msun) outer disk radius (300AU) disk flaring & density profile scale height (15AU)

Circumstellar Disks around Young Stellar Objects V.Roccatagliata, Th.Henning, S.Wolf, W.Brandner, MPIA

60” radius around butterfly star no tip-tilt star available For L & M bands where exposures are short, one can use shift-and-add to recover at least some of the resolution

LGS-AO effectively without a tip-tilt star 1 hour integration on a compact K=18.7 source

5”

Effectively there was no tip-tilt, since the brightest star within 60” has V~19 resolution achieved ~0.22” 3”×3”

z=2.2 galaxy

12.3” from the MPE SINS project

tip-tilt star B=20.4, R=18.3, K=14.8

High redshift galaxies

from the MPE SINS project

Resolution attainable is limited by signal-to-noise BzK-6004 at z = 2.38 SINFONI LGS (no tip-tilt)

BzK-15504 at z = 2.38 SINFONI NGS data (Genzel+ 2006)

NACO +LGS-AO Stellar mass NACO+Laser Guide Star AO K band continuum

SINFONI+AO Hα

1″ 8 kpc

«

0.15″=1.2kpc

Line flux

• LGS used to improve seeing • resolution limited by pixel scale • large pixel scale improves efficiency (dither within field)

0.2″ = 1.6 kpc

• R~16mag star only 17” away • source has K-19.2 (but extended over ~1”) • resolution in NACO image is only 0.2” • despite 2 hrs on source integration at large pixel scale, still need to smooth to increase S/N

High redshift galaxies Do you lose out by not reaching the diffraction limit? simulations of a z=2 galaxy, based loosely on IC342 0.6” FWHM

200mas FWHM

50mas FWHM

Conclusions ¾ Many astronomical targets do not have suitable tip-tilt stars for full LGS-AO correction ¾ Simulations show that LGS-AO without tip-tilt will still yield resolutions of order 0.1-0.2arcsec ¾ For many science cases, higher resolution is not needed or not possible (e.g. due to S/N) ¾ There is already considerable data taken without tip-tilt, and it would be good if this mode was offered at the VLT