Experiences with Hokupa’a on Gemini

1. Experiences with Hokupa’a on Gemini Mark Chun USGP AO Workshop 26-27 Feb 2001

2. Highlight a few specific issues • Crowded stellar fields • M32 central stellar populations • M15 Anisoplanatism • Galaxy morphology & structural parameters • I. Jorgensen’s simulations • Detecting faint things near bright objects • Search for low-z DLA absorption systems • Residual aberrations in PSFs

3. 1. Stellar Photometry • M32 Program lead by Tim Davidge • Ref: Davidge et al. 2000, ApJL, 545, L89. • Goal: resolve stars to r~2” in the core and measure photometry • Represents the good and bad of AO images • non-diffraction-limited but decent FWHM PSFs varying across a crowded stellar field.

4. Central 20” in H & K-bands FWHM ~ 0.12” in H and K

5. 0-2” 2-4” 4-7.4” 7.4-13.1”

6. Anisoplanatic effects • We have been monitoring variations of anisoplanatic effects with observations of globular clusters during each run. • e.g. M15 data covers a large range of off-axis angles with a crowded field • Extracted PSFs in different radial (0,10,20,30”) and azimuthal (NW,NE,SW) bins. • PSFs are a combination of many stars in bin • bright, unsat stars, iterative sig-clip combination

7. M15 PSFs

8. Simple model for PSF variations • The majority of the anisoplanatic error is due to decorrelation of the tip/tilt. • Assume this introduces a gaussian smear. • Deconvolve the off-axis PSFs by the on-axis PSF and fit with a 2-D gaussian G(r,q) • For analysis construct an off-axis PSF from a convolution of the on-axis PSF and G(r,q).

9. Simple model for PSF variations

10. Simple model for PSF variations

11. 2. Measuring galaxy structural parameters • Example: Combine HST & Hokupa’a data to study stellar populations in A+E galaxy • Simulations from Inger Jorgensen (Gemini)

12. Seeing-limited off-axis (30”) on-axis Detection of individual sources • Simulations of 7”x7” z~0.6 field with AO • H, 6-hour

13. Distinguishing galaxy profiles Off-axis On-axis “raw” Fit r1/4 profiles Fit exponential

14. Measured total magnitude mtotal [output] mtotal [input]

15. Measured total magnitude Off-axis Dmtotal [output] On-axis: too faint mtotal [input]

16. Measuring galaxy sizes log re [output] log re [input]

17. Measuring galaxy sizes On-axis: too small Dlog re [output] Off-axis log re [input]

18. 3. Trying to detect faint objects • Principal problem: knowledge of residual high-order aberrations in PSF. • Example programs: • Detecting low-mass stellar/substellar companions. • We have imaged in K’ to look for origin of low-z DLA absorber systems with small impact parameters or LSB features.

19. Rao & Turnshek 1998, ApJL, 500, L115 zabs=0.0912, 0.2212 Cohen 2000, astro-ph/0012109 G1 & G10 match zabs

20. No LSB near Q2251+113 or Q0738+380 • with similar limiting surface brightnesses • SBlim ~ 17.8 mag/arcsec2, 3sigma • But small impact parameter space ??? G1

21. Residual aberrations in PSF • Residual high-order aberrations • Origin: atm, telescope, Hokupaa or QUIRC. • Telescope aberrations rotate with the pupil • atmospheric average out over time periods of ? • Hokupa’a and QUIRC fixed on detector/field. • Telescope aberrations • Determine by derotating images (fixed pupil) • Whether you see effect depends on level of correction

22. Static aberrations in PSF • diffraction spot have peaks ~few % of central peak

23. Summary • Stellar photometry in crowded fields • Need to deal with PSF fitting and anisoplanicity (Doug Currie’s and Eric Steinbring’s talks) • Measuring galaxy structural parameters • Need good SNR in PSF and its variations • Does simple anisoplanatic model improve fits? • Luc Simard’s talk • High-order static aberrations in telescope will limit faint object detection near bright objects • Can we deal with this if we characterize it? (Claude Roddier’s talk)