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Dalit Engelhardt Boston University

The Wisconsin Small Telescope Array for Radio Waves (WSTAR). Dalit Engelhardt Boston University. Summer 2006 REU Observational Cosmology Advisor: Prof. Peter Timbie University of Wisconsin-Madison. Outline. Objectives CMB anisotropies and detection beam-combination techniques

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Dalit Engelhardt Boston University

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  1. The Wisconsin Small Telescope Array for Radio Waves (WSTAR) Dalit Engelhardt Boston University Summer 2006 REU Observational Cosmology Advisor: Prof. Peter Timbie University of Wisconsin-Madison

  2. Outline • Objectives • CMB anisotropies and detection • beam-combination techniques • WSTAR design • Personal contributions

  3. WSTAR Objectives • Investigate alternate beam-combination techniques to minimize systematic errors in detecting CMB anisotropies. • Map 21-cm emission line • Use in undergraduate education and training in radio astronomy

  4. The Big Bang and the CMB

  5. CMB Anisotropies (I) • Matter distribution • Temperature variations < 100 μK • Polarization: “E modes” variation < 1 μK • Spatial effects / gravitational waves • Polarization: “B modes” variation of tens of nK

  6. CMB Anisotropies (II) WMAP image of the CMB. Courtesy of CASA, University of Colorado at Boulder

  7. Detecting the CMB • Current detection methods  different systematic effects • Imaging systems (e.g. WMAP) • Interferometers: combine signals by means of wave interference to produce higher-resolution, clearer images • Problems: • CMB frequencies up to 140 GHz  no appropriate low-noise amplifiers • CMB detection requires large arrays  amount of computation needed

  8. Correlation (Multiplying) Interferometer E1 E2 • Signal loss due to voltage dividing  need good amplifiers • Computational complexity: n(n-1)/2 correlations needed for n antennas En Amplifier … Voltage / electronic divider × ×

  9. Adding Interferometer E1 E2 En • No signal loss due to voltage splitting • Computational algorithm less complicated  feasible for large arrays necessary for CMB Phase shifter … + E1 + E2 + … + En Detector (E1 + E2 + … + En )2

  10. 21-cm Emission Line • Emission mechanism • Transition at ground state • f = 1420.4 MHz • E = 5.9 ×10-6 eV • RARE transition, but many H atoms in the universe • Why 21-cm line? • Clear sky (low atmospheric interference) • Large signals • Availability of data from other experiments • Relatively low frequency (but still in CMB range)  easy to build equipment • Computational data analysis algorithms same at low and high frequencies

  11. WSTAR Design • Array setup • 30 ft initial spacing (but variable) • 3 small radio telescopes • Haystack Observatory design, built from scratch by undergraduates at ObsCos • Control boards on roof of Chamberlin, manual control planned from lab • Hardware • Software

  12. WSTAR Hardware

  13. WSTAR Software

  14. Personal Contributions / Design Modifications • Software (java-based code) modifications • OS environment alteration • Hardware changes

  15. Looking ahead… • Receiver board to Haystack Observatory • Remote access to the telescope via TCP/IP • Testing • Remaining two array telescopes • Testing in different interferometry configurations

  16. Special Thanks • Peter Timbie • ObsCos group • UW-Madison REU • National Science Foundation (NSF)

  17. References • Center for Astropohysics and Astronomy, University of Colorado at Boulder,http://casa.colorado.edu/ • Minnesota State University, Mankato, http://Odin.physastro.mnsu.edu • MIT Haystack Observatory, http://www.haystack.mit.edu/edu/undergrad/srt/ • Various papers and articles read in the course of the program that have gradually entered the subconscious…

  18. CMB Anisotropies WMAP image of the CMB Courtesy of NASA / WMAP Science Team

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