1 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

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 Signal loss due to voltage dividing  need good amplifiers Computational complexity: n(n-1)/2 correlations needed for n antennas … E1E1 E2E2 EnEn Voltage / electronic divider Amplifier × ×

9 + E 1 + E 2 + … + E n Detector (E 1 + E 2 + … + E n ) 2 Adding Interferometer No signal loss due to voltage splitting Computational algorithm less complicated  feasible for large arrays necessary for CMB … E1E1 E2E2 EnEn Phase shifter

10 21-cm Emission Line Emission mechanism –Transition at ground state –f = MHz –E = 5.9 × 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

14 WSTAR Software

15 Software (java- based code) modifications OS environment alteration Hardware changes

16 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

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

References Center for Astropohysics and Astronomy, University of Colorado at Boulder, Minnesota State University, Mankato, MIT Haystack Observatory, Various papers and articles read in the course of the program that have gradually entered the subconscious…

19 CMB Anisotropies WMAP image of the CMB Courtesy of NASA / WMAP Science Team