Hokupa'a team science observations

1. Hokupa'a team scienceobservations Hokupa'a UH team : Pierre Baudoz (baudoz@ifa.hawaii.edu) Faint stellar companions (brown dwarfs, Hipparcos and/or radial velocity doubles) Olivier Guyon (guyon@ifa.hawaii.edu) Host galxies around QSOs Dan Potter (potter@ifa.hawaii.edu) Polarimetry imaging of youg stars (Ttau, Pre-main sequence)

2. Polarimetry imaging ( Dan Potter) Speckle noise caused by the atmosphere and telscope optics cause PSF's to change from exposure to exposure on varying timescales. Racine et al. (1999) showed that this noise dominates by a factor of ~100 over photon noise within the central regions of the PSF where planets and debris disks would be found for stars >5 PC away. Debris disks are seen in scattered light in near IR wavelengths so one can take advantage of their polarization signature using a dual channel polarimeter that simultaneously creates two orthoganal polarization images. These two images will have the same speckle pattern, assuming the central source is unpolarized, so the subtraction of the two images reveals either a stokes Q or U vector image of the debris that is uninhibited by speckel noise.

3. This figure shows a ten minute exposure of GG tau using this technique compared to the HST/NICMOS image from Silber et al. (2000). The Hokupa'a image comfirms the suspected gap in the disk that fell in the diffraction spikes of HST/NICMOS as well as revealing new structure in the disk.

4. QSO host imaging • Host morphology • QSO fueling • Host history (recent star formation ?) • Are QSOs a byproduct of mergers ? J,H and Kp imaging.

5. Observing strategy • The filter is chosen according to the seeing and magnitude of the quasar Kp : high sky background level and good AO correction. Used when seeing is average or worse than average. H : For average of above average conditions, FWHM < 0.2" on most quasars of the observing list. Background is lower and allows detection of fainter surface brightness. J : Used when seeing is very good and corrected images have FWHM <0.2".

6. PG 1001+054 Distance star/QSO = 10.18" H filter R magn : 16.4, z =0.161 AO guide star : QSO (0.2") & magn 12 star 32" away (0.2")

7. PG 0804+761 Magn R : 14.04, Magn V : 14.71, z=0.100 McLeod & Rieke, ApJ, 420,58-67, 1994 Jan 1. "Near-Infrared Imaging of Low-redshift Quasar Host Galaxy" Host detected by PSF profile fitting on a 2.3m telescope (Kitt Peak) without AO (H band). 0 5 15 10 38"x38"

8. PG0804+761 10" x 10" Kp H H : QSO (49mn) - PSF (16mn)

9. Gemini+Hokupa'a PSF From data taken Feb. 19, 2001 (Hokupa'a engineering night) H band Imaging of Landolt 104490 (V=12.572, R=12.254) 1s, 10s & 100s exposure time with 5 dither positions. Cass rotator angles : 0, 5, 20, 30, 70 & 160 deg. Relative rotation angles : 0,5,10,15,20,25,30,40,50,65,70,90,130,140,155,160 deg (perfect Golomb ruler from 0 to 30 deg) Study the behaviour of speckles (fast speckles, super-speckles ?) Investigate the effect of the Cass rotator.

10. PSF structure

11. Time variation of Speckles A program was written to compute mean and RMS variation of speckle structure.

12. 100s-scale time variation

13. Time - variability : (preliminary) conclusion From 1s to 10s : SNR x 0.63 From 10s to 100s : SNR x 0.47 Most speckles have lifetimes shorter than 1mn and average out well in long exposures. Need to explore longer timescales and build a power spectrum of speckles' lifetimes.

14. 5 deg. H band 100s 2.5"x2.5" 20 deg.

15. Cassegrain rotation 15 deg rotation of the instrument port is responsible for a ~10% variation of the PSF (relative to radial profile). 2 solutions : Switch PSF/Target very frequently or reproduce the rotation of cass rotator during target imaging on PSF. Turn off the Cass rotator during observations of PSF and object.