Telescope Guiding with a HyViSI H2RG Used in Guide Mode

1. Telescope Guiding with a HyViSI H2RG Used in Guide Mode Lance Simms Detectors for Astronomy 2009 10/2/09

2. Overview of Talk • Brief overview of Hybrid SiPIN CMOS and the HyViSI • Specs of our H2RG-32-147 in context of guiding • Persistence: the X-factor • Results from Kitt Peak 2.1m unguided • Results from guiding the Kitt Peak 2.1m telescope with a HyViSI H2RG

3. HyViSi SiPIN Arrays Teledyne’s Hybrid Visible Silicon (HyViSi) PIN (P-Intrinsic-N) Diodes H4RG MUX • H2RG Multiplexer (CMOS ReadOut IC = ROIC) • 2048 x 2048 Array, 32 outputs • 18 micron pixel size • Silicon Pin Array (Silicon Detector Array) • 2048 x 2048 Array of PIN diodes • 18 micron pixel size, 100 microns thick • Bias (VSUB) to deplete silicon of charge carriers • H2RG Detector = H4RG MUX + SiPINArray • Connected with Indium bump bonds p+ implant VSUB n- H4RG detector

4. H2RG-32-147 Specs and Fe55 Spectra for H2RG-32-147 Most of these specs can be folded into centroid accuracy calculations….so what’s the point of testing guide mode for an empirical result?

5. H2RG-32-147 Telescope Data • Picture taken of Saturn after Exposure + Dither shows Persistence • Very interesting that contrast is still detectable in persistent image even though all pixels in previous exposure were saturated Where Saturn is in this exposure Where Saturn was in last exposure Raw Read; No subtraction

6. Persistence from Stars • Persistence Effect seen in all HyViSIs • “Core” Pixels rapidly gain counts • “Halo” pixels see a decrease in counts, but eventually integrate positively • “Sky” pixels are unaffected, providing measure of what photocurrent should be • Effect lasts for ~200-300 seconds depending on offending star flux and fluence Where star is in this exposure Where star was in last exposure time Core Halo Sky *Image snippets have first read subtracted; Plot shows raw ADU

7. Effect on Centroid Measurement • “Wedges” in atmospheric turbulence can cause large displacements of image for hundreds of milliseconds • What happens if bright star light is displaced? • Does image persistence create large error in calculated centroid? 1st ramp 2nd ramp *Image snippets have first read subtracted 7

8. Persistence Model

9. Attempt to Simulate

10. Observing at Kitt Peak Lovely snow storm in December! • We brought the RIDL Dewar to the Kitt Peak 2.1m • Tested 3 HyViSi detectors on 3 separate runs • 4/24/07-5/1/07 H4RG-007 • 11/13/07-11/20/07 H1RG-022 • 12/11/07-12/19/07 H2RG-32-147

11. Kitt Peak 2.1m Details Above:Dewar attached to 2.1m Telescope Up Right: LSST Baseline Filters Right: Oscillations in Right Ascension and Declination caused by periodic error of worm gear in motors

12. Application of Guide Windows LSST Focal Plane • LSST • 8 2048x2048 HyViSI Guide sensors in corners • Large area covered by sensors ensures bright enough star will be available for guiding • Frame rate is independent of star location on detector and area Wouldn’t it be nice if all LSST detectors could be used for guiding? • In a CCD, frame rate depends on size of CCD even when using a “window” • In CMOS, window frame rate is independent of imager size

13. Guide Mode HxRG multiplexers have a “Guide Mode” - Full frame integration while subwindow is readout - Readout is interleaved …. Pixels integrating charge Full frame drop or read Window reset or read We used guide mode to guide 2.1m telescope with sequence on right

14. Short Exposures without Guiding NGC26813 • Combining multiple short exposures yields good point spread function • Image of NGC2681 from stack of 40 second exposures

15. Long Exposure Without Guiding 1800 second exposure of M=6.55 in V-band star SAO54817 taken with H1RG-022 Tracking error smears stars and makes them look like jelly beans

16. Long Exposure With Guiding 2600 second exposure of M=7 in V-band star IRAS 09595 taken with H2RG-32-147 PSF is reduced greatly. Guide window affects pixels in shared rows and columns Guide Window sampled at 25 hz for 8 seconds before moving telescope

17. Guide Mode Comparison

18. Summary Guide Mode of HyViSI offers unique feature to guide telescope while simultaneously taking deep field exposures Centroid accuracy for guide star can be predicted with standard signal to noise calculations that fold in read noise, dark current, etc. Effect of Persistence is less trivial since analytical fits to latent images have large errors Empirical results from using H2RG-32-147 at Kitt Peak 2.1m show that persistence of guide star does not negatively impact centroid measurements

19. Additional Slides

20. Dark Current H4RG-10-007 shows higher dark current than other SiPIN devices Teledyne indicates source of problem was found in unit cell and fixed New H4RG has order of magnitude less dark current

21. Read Noise • Total CDS Noise on H4RG ~ 15 e- • CDS Noise on H1RG and H2RG ~8 e- • Plot on left shows noise with multiple non-destructive samples

22. Detective Quantum Efficiency • Integrating sphere with monochromator and calibrated photodiode used to obtain QE vs. wavelength