Telescope Guiding with a HyViSI H2RG Used in Guide Mode

Lance Simms

Detectors for Astronomy 2009

10/2/09

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

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10/6/09

HyViSi SiPIN Arrays

H4RG MUX

H4RG detector

Teledyne’s Hybrid Visible Silicon (HyViSi)PIN (P-Intrinsic-N) Diodes

p+ implant

n-

VSUB

H2RG-32-147

8/2/09

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?

Most of these specs can be folded into centroid accuracy calculations….so what’s the point of testing guide mode for an empirical result?

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

Raw Read; No subtraction

Where Saturn is in this exposure

Where Saturn was in last exposure

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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

CoreHaloSky

*Image snippets have first read subtracted; Plot shows raw ADU

Where star is in this exposure

Where star was in last exposure

time

Effect on Centroid Measurement

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1st ramp

2nd ramp

*Image snippets have first read subtracted

• “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?

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Persistence Model

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Attempt to Simulate

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Observing at Kitt Peak

• 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

Lovely snow storm in December!

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Kitt Peak 2.1m Details

Up Right: LSST Baseline Filters

Above: Dewar attached to 2.1m Telescope

Right: Oscillations in Right Ascension and Declination caused by periodic error of worm gear in motors

Application of Guide Windows

• 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

8/2/09

LSST Focal Plane

Wouldn’t it be nice if all LSST detectors could be used for guiding?

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

Short Exposures without Guiding

8/2/09

NGC26813• Combining multiple short exposures yields good point spread function

• Image of NGC2681 from stack of 40 second exposures

Long Exposure Without Guiding

1800 second exposure of M=6.55 in V-band star SAO54817 taken with H1RG-022Tracking error smears stars and makes them look like jelly beans

Long Exposure With Guiding

8/2/09

2600 second exposure of M=7 in V-band star IRAS 09595 taken with H2RG-32-147PSF is reduced greatly. Guide window affects pixels in shared rows and columns

Guide Window sampled at 25 hz for 8 seconds before moving telescope

Guide Mode Comparison

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

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Additional Slides

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Dark Current

H4RG-10-007 shows higher dark current than other SiPIN devices

Teledyne indicates source of problem was found in unit cell and fixedNew H4RG has order of magnitude less dark current

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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

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Detective Quantum Efficiency

• Integrating sphere with monochromator and calibrated photodiode used to obtain QE vs. wavelength

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