Science with AO

A. Bouchez

for the Keck AO team

Topics

Sample scientific programs. Observing strategies. Technical issues.

Keck AO, K'

Sample scientific programsRequirements Technical issues

Planetary imaging/spec.

Achieve high Strehl. Pointing requirements for spectroscopy.

No differential tracking rates allowed. Direction of NIRC2/WFS sky must be controlled.

Dense star fields Achieve high contrast. Good sky subtraction.

High-contrast imaging High Strehl stability. Precise placement behind coronographic spot.

Observing in vertical angle mode

Deep imaging Precise pointing during long exposures. Good sky subtraction.

FSM range limited.

Off-axis spectroscopy Precise pointing during long exposures. Slit orientation.

FSM limits may constrain slit orientation.

Surveys High observing efficiency. Avoid using auto-acquisition when possible.

M and L band imaging Rapid dithering

Program 1: Planetary imaging and spectroscopyExample: 24 December 2003

PI: M. Brown (CIT)

Program: "Oceans, Mountains & Rivers on Titan".

OA: Steven Magee

Observing strategy: Use quick 3-position dither pattern for imaging. Cycle through 5 filters. Repeat ad nauseum for 8 hours. Once per night, take spectra of each location on Titan's disk by scanning the slit across Titan:

Image (10s) Image through slit (10s) Spectrum (120s) Dither 5" along slit and 0.04" perpendicular Spectrum (120s) Image through slit (10s) image (10s)

Operational issues: Make sure that target list has no differential tracking rates. WFS background should be taken in a direction perpendicular to Titan-Saturn vector (e.g. N or S). Use centroid origin scaling in acquisition widget.

M. Brown and A. Bouchez, "Evolution of a storm on Titan", GRL 2004, submitted.

11/11/03 11/12/03 11/13/03 11/14/03

K’ (1.95 – 2.30 μm) H2 (2.11-2.14 μm)

K’ (1.95 – 2.30 μm)

Program 2: Crowded star field imagingExample: 6 June 2003

PI: A. Ghez (UCLA)

Program: "Imaging and spectroscopy of the Galactic Center's stellar population: Studying the properties and environs of the central supermassive black hole."

OA: Joel Aycock

Observing strategy: Use R=13.2 guidestar 30" from galactic center (GC). Center target (GC) on NIRC2 narrow field. Image with 5-position dither patter, 1" throw.

Operational issues: FSM range should not be exceeded (FSM fault) Beware of source confusion on WFS (binary or multiple guide star, etc.), which could lead to tip-tilt oscillations.

A. Ghez et al., "Variable Infrared Emission from the Supermassive Black Hole at the Center of the Milky Way", ApJ 601, 2004.

Program 3: High-contrast imagingExample: November 30, 2001

PI: Zuckerman (UCLA)

Program: "Measuring the border between brown dwarfs and planets".

OA: Chuck Sorenson

Observing strategy: Use wide field (0.04"/pix) for highest sensitivity & area. Star positioned off detector to minimize ghosts. 15 x 90s images in 5-position dither pattern, pointed 24" N,S,E,W of ε Eridani. Sky frames taken separately, offset 600" from star.

Alternate technique: Use coronographic spot and medium/small lyot stop. AO rotator in vertical angle mode: PSF artifacts will be fixed, while astronomical objects rotate around guide star. DAR would be on.

Operational issues: Observer will probably redefine FSM pointing origin if using coronographic spot.

B. Macintosh et al., "Deep Keck Adaptive Optics Searches for

Extrasolar Planets in the Dust of Eridani and Vega", ApJ 594, 2003.

Program 4: Deep imagingExample: October 3, 2003

PI: J. Larkin (UCLA)

Programe: "CfAO Treasury Survey: AO imaging in the GOODS field"

OA: Terry Stickel

Observing strategy: Place bright guide-star near corner of NIRC2 wide field. Take long (300s) integrations in tight 15-position dither pattern. 2 filters (H, K') Use faint stars in field to map out distortion and PSF.

Operational issues: none

T. Glassman et al., "Morphological Evolution of Distant Galaxies

from Adaptive Optics Imaging", ApJ 581, 2002.

Program 5: Off-axis spectroscopyExample:08/17/03 August 17, 2003

PI: C. Max (UCSC)

Program:"AO observations of nearby active galactic nuclei"

AO: Gary Puniwai

Observing strategy: Use R=12.5 guide star 35" from target (interacting galaxies with active nucleii). Align slit on both nucleii. DAR must be on. Take long (300s) integrations. Offset to sky for sky spectra.

Operational issues: FSM range may constrain slit PA. Cannot change rotator angle while FSMs are off pointing center.

1.6 arc sec35 arc sec

Off-axis spectroscopyConstraints on slit PA due to FSM limits

Off-axis spectroscopyConstraints on slit PA due to FSM limits

Off-axis spectroscopyConstraints on slit PA due to FSM limits

HST: J,H,K composite

1.6 arc sec

Bright nucleus

Faint nucleus

Gas in betweenx

2.00 m 2.08 m 2.17 m

H2 emission line from shocked or ionized gas (v=580 km/s)

Keck: K-band

NIRSPECImage & spectra

R = 12.5 NGS,35” separation

C. Max et al., "Adaptive optics observations of NGC 6240 at the Keck and Lick Observatories", BAAS 32, 2000.

Program 6: SurveysExample: Last night!

PI: B. Merline (NASA)

Program: "Searching for asteroid satellites using AO."

OA: Chuck Sorenson

Observing strategy: Group targets by sky position (minimize slew time). Group targets by magnitude (minimize acquisition time). Take 4 x 60s integrations in 4-position dither pattern. Move on…

Operational issues: Center target on WFS by ACAM pixel position. Avoid running auto-acquisition script on each target.

Kaliope (Margot and Brown, 2001)

Pulkova (B. Merline et al., 2000)

Binary asteroids discovered with Keck AO

Sylvia (Brown and Margot, 2001)

Antiope (Merline et al., 2001)