1 / 30

Development of A Near-Infrared Camera for use at RBO

Development of A Near-Infrared Camera for use at RBO. A Preliminary defense by Andy Monson. Motivations for Instrumentation Thesis. Develop NIR camera expertise Cryo-mechanical techniques Electronics and array performance Camera control software NIR observational strategies

yehudi
Download Presentation

Development of A Near-Infrared Camera for use at RBO

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Development of A Near-Infrared Camera for use at RBO A Preliminary defense by Andy Monson

  2. Motivations for Instrumentation Thesis • Develop NIR camera expertise • Cryo-mechanical techniques • Electronics and array performance • Camera control software • NIR observational strategies • Demonstrate camera capabilities • Synoptic photometry of bright stars

  3. NIR Characteristics • CMOS detectors using HgCdTe have reached 2048x2048 pixels. EXPENSIVE !!! $350,000.00 • Atmospheric H2O absorption defines near-infrared bands • Filters designed to fit in atmospheric windows • Thermal emission from sky dominates past 2.5 microns and emission from OH in atmosphere contributes to flux in H band

  4. What are the benefits of the NIR? • Less sensitivity to extinction • Less sensitivity to heavy metal abundance • Systematic errors are less by an order of magnitude

  5. BIRCAM was developed to gain insight and develop techniques for constructing the mechanics, electronics, and software interfaces for a larger camera currently under development at UW. BIRCAM is a capable instrument in its own right. Buttes Infra-Red CAMera (BIRCAM)

  6. Optical Design • IR cameras need internal optics and a cold stop to prevent thermal background from telescope structure from reaching the detector • Re-imaging optics folded to fit in the dewar using an Offner relay • All mirror design reduced cost, low emissivity and no chromatic aberration • Designed in ZEMAX to determine optimum spacing

  7. Optics Bench • Everything inside the dewar is at -200°C to minimize thermal background. • Designed to minimize effect of thermal contraction. • Allows for each mirror to be tip/tilted and positioned relative to each other for alignment. • The filter wheel (from BABE) mounts to the bench. • A cryo-conditioned stepper motor moves the filter wheel via LabView GUI. • Micro-switches sense the position of the filter wheel mechanically.

  8. Detector Fanout-Board • Provided by John Geary (CfA/Harvard) • Seats the H2 array in ziff socket and fans out signal lines from each quadrant to connector • Heaters and temperature sensor allow for temperature control of the detector. • Enables use of off-chip amplifiers for each of the 32 channels • 128 signals to / from the board to the outside. Wire as fine as hair used for all detector signals.

  9. BIRCAM Interior • Fanout-board is spring loaded and referenced to optical bench • Optics bench mounts to cold plate and squares detector to the optical axis • Cold straps facilitate cooling • CaF2 window protects array. • Temperature sensors on optics bench monitor temperature

  10. Pre-amp & Array Controller • GUMP is a 32 channel, pre-amplifier for providing 5x gain from fanout board to controller (IRLABS). Added resistors to each channel to reference ground. • Controller electronics (Leach / ARC) provides all voltages to array and converts analog signal from GUMP to digital signal to computer. Replaced current limiting resistors to supply adequate power to GUMP and the array • Ground for the controller is isolated from the power supply (different chassis). Huge floating ground problem eliminated by supplying isolated ground from GUMP power supply.

  11. Signal Chain • Developed MultiSim model of signal chain. • Allowed simulation of signal chain • Verification of array performance

  12. Output Waveforms of H2 • 0V(full well) to 0.4V(no light) output from the detector/fanout-board • GUMP applies -3.7V DC offset and 5x gain • Controller applies inverting gain of 5x and A/D offset. • Integrator applies (t/RC)=0.5 gain to 16bit A/D • A/D input = -2.5V(full well) to +2.5V(no light) • Gain = 82,800e/65,536ADU = 1.26e/ADU (theory) • Camera and Electronics Work!

  13. Verification and Testing • Bare CMOS multiplexer provided by Rockwell / Teledyne for testing • Safely verify the electronics • Adjust voltages for 32 independent channels • Adjust bias and offset voltages to tune gain to fit dynamic range of the A/D converters. • Create subroutines to reconstruct (de-interlace) the 32 channels to form an image.

  14. BIRCAM in Cleanroom • BIRCAM during final assembly in the Cleanroom • Clean all surface of fingerprints and other volatiles to minimize outgases in a vacuum • Prevent dust and particulate matter from contaminating the inside.

  15. Hawaii-2 HgCdTe Detector Arrives • 2048 x 2048 array (Rockwell / Teledyne) • 18 micron pixels • CMOS HgCdTe • Full Well 84,000e- • 4 independent quadrants • Capable of 32 channel read-out (8 per quad) • Read out time ~1.3s • QE of 0.85, 0.68, 0.78 at J, H, K

  16. Wiring for BIRCAM • ~100 ft inside dewar (All done here by myself and electronics shop) • ~1000 ft outside dewar (50% done here by myself and electronics shop)

  17. Software for BIRCAM • Voodoo (Java/C) software modified to de-interlace the 32 outputs and write header information and image. • Voodoo configured for Correlated Double Sampling (CDS) • Read array (image1) • Expose • Read array (image2) • Net image = image2 - image1 • LabView GUI developed to control filter wheel position, monitor temperatures and control detector temperature

  18. Cool down at RBO • 30 liters of LN2 brought to RBO every 5 days • It takes about 3 hours to cool the array to 78K and an additional 3 hours for the optics bench to reach 80K • BIRCAM is kept continuously cold to be ready at a moments notice.

  19. BIRCAM at RBO • BIRCAM mounts to telescope through the use of an adapter ‘boot’ • Controller mounts to boot but is electrically isolated from telescope • Power Supplies and external controllers ride on cart next to telescope.

  20. First Light Dec,17 2007 • Field of View = 13x13 arc-minutes, pixel scale = 0.76 “/pix • Optical Image of M42 Orion Star Forming Region from RBO (credit: Chris Rodgers). BIRCAM Near-Infrared view of same region.

  21. BIRCAM Performance at RBO • Linear to 56,000 counts • Gain = 0.95 e- / ADU • Read Noise = 18 e-

  22. Science Opportunities with BIRCAM at RBO • Sensitivity of BIRCAM is comparable to the 2 Micron All Sky Survey (2MASS). • BIRCAM allows for synoptic surveys of relatively bright stars. • Gamma Ray Bursts • Nearby Supernovae • Variable Stars (esp. Cepheid Variables)

  23. Cepheid Variable Stars • More massive more intrinsically luminous Cepheids have longer periods. Plot intrinsic luminosity versus period to obtain the PL relation • Mechanism for pulsation due to opacity (kappa-mechanism) • As star contracts the density and temperature rise • The increase in temperature causes a shell of helium to ionize • Kramers law kappa = density * T^(-3.5), since temperature is driving ionization, the density is the dominant term and the opacity increases. • Radiation is ‘trapped’ in high opacity conditions and the radiation pressure forces the star to expand • As the star expands, the density and temperature decrease. The Helium shell recombines with free electrons and the opacity falls • Radiation ‘flows’ through low opacity conditions and radiation pressure loses to gravity causing contraction.

  24. The Cepheid PL relation • The form of the PL relation is M = a Log(P) + b • Infer the intrinsic luminosity by measuring the period • Compare measured apparent brightness to inferred intrinsic luminosity to determine the distance. • Measured apparent brightness effected by: extinction, line blanketing and binarity. • Observe in the NIR where these systematic effects are small compared to the optical. • Example from http://sci.esa.int

  25. Cepheids and The Distance Ladder • Cepheids will link (via GAIA) trigonometric parallax to tertiary distance indicators (they link relative distance measures to absolute distance measure). • By observing in the NIR, systematic effects are reduced. • Future distances to galaxies will be improved. • Measurements of the Hubble Constant will be better constrained. • See for example: Jacoby etal (1992)

  26. Cepheids observed in the NIR • Samples Based on Cepheids that had known distances based on methods other than trigonometric parallax • Laney & Stobie 1992 • Welch 1984 • Barnes 1997 • A combined total of 59 quality Cepheids

  27. BIRCAM survey • BIRCAM will enable Northern Hemisphere survey of nearly 120 Cepheids in the J, H and K bands with periods between 4 and 40 days. • Well sampled light-curves produces standard NIR templates • The light-curves will provide for a future calibration of the NIR PL relation once GAIA data is available. • Detailed light-curves will enable a comparison to LMC Cepheids to identify systematic differences (if any).

  28. Data Analysis • Simple image reduction techniques (IRAF) • Standard star calibration • NIR standards (Elias) and 2MASS. • Cepheid photometry • Differential aperture photometry of isolated Cepheids and secondary standards • Periods are known • Optimization of phase coverage for each star • Construct template light-curves

  29. Timeline • Fall 2007 : Finish building camera and begin observations at RBO (Complete). Write Instrument paper for PASP. • Spring / Summer 2008 : Continue observing at RBO while reducing data and submit instrument paper. Finish observation and continue to reduce data and begin analysis. Write observations paper for AJ. • Fall 2008 : Complete analysis of light-curves shapes including a comparison with the LMC sample. Start writing results and thesis defense. Finish all tasks and defend thesis.

More Related