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Dalit EngelhardtBoston University
Summer 2006 REUObservational CosmologyAdvisor: Prof. Peter TimbieUniversity of Wisconsin-Madison
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Outline
• Objectives
• CMB anisotropies and detection
• beam-combination techniques
• WSTAR design– Personal contributions
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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
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The Big Bang and the CMB
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
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CMB Anisotropies (II)
WMAP image of the CMB. Courtesy of CASA, University of Colorado at Boulder
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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
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Correlation (Multiplying) Interferometer
• Signal loss due to voltage dividing need good amplifiers
• Computational complexity: n(n-1)/2 correlations needed for n antennas
…
E1 E2 En
Voltage / electronic divider
Amplifier
×
×
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+
E1 + E2 + … + En
Detector
(E1 + E2 + … + En )2
Adding Interferometer
• No signal loss due to voltage splitting
• Computational algorithm less complicated feasible for large arrays necessary for CMB
…
E1 E2 En
Phase shifter
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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
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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
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WSTAR Hardware
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WSTAR Software
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• Software (java-based code) modifications
• OS environment alteration
• Hardware changes
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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
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Special Thanks
• Peter Timbie
• ObsCos group
• UW-Madison REU
• National Science Foundation (NSF)
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…
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CMB Anisotropies
WMAP image of the CMBCourtesy of NASA / WMAP Science Team