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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