Probing the field of Radio Astronomy with the SKA and the Hartebeesthoek

Radio Observatory:An Engineer’s perspective

Sunelle OttoHartebeesthoek Radio Astronomy

Observatory (HartRAO)

July 2011

Outline

• Introduction• The Square Kilometre Array - Background, Pathfinders , Key Science Projects, System design

• Hartebeesthoek Radio Astronomy Observatory - Background, Research work

• Conclusion

Introduction

• MSc (Electronic Engineering) at Stellenbosch University - thesis work on SKA

• Intern at HartRAO (Hartebeesthoek Radio Astronomy Observatory) - research work

Stellenbosch University

Background• Square Kilometre Array (SKA) • largest, most sensitive radio telescope• thousands of small dishes and aperture arrays• total collecting area of 1 km²• South Africa vs. Australia• International project • smaller projects to assist in research• SKA pathfinders to demonstrate the technologies

The Square Kilometre Array

SKA configuration design

Pathfinders• MeerKAT (South Africa)• Started with the XDM

(eXperimental Development Model)

• 15m diameter parabolic reflector dish

• 7 horn cluster feed• Located at HartRAO

The Square Kilometre Array

XDM antenna

7 horn feed

Pathfinders• KAT-7 (Karoo Array Telescope)• Array of 7 parabolic reflector antennas each 12m in diameter• Wide-band single pixel feeds (WBSPFs)• Demonstrates working of an interferometer

The Square Kilometre Array

KAT-7

Pathfinders• MeerKAT: final phase of KAT• 64 offset Gregorian antennas • 13.5m diameter• unblocked aperture• multiple receiver systems

The Square Kilometre Array

MeerKAT antenna design(credit: SKA fact sheet 1: MeerKAT, June 2011, www.ska.ac.za)

Pathfinders• ASKAP (Australian Square

Kilometre Array Pathfinder)• Goal: 36 parabolic reflectors• each 12m diameter• Phased array feeds (PAFs)• Multiple beam formation

capability

The Square Kilometre Array

ASKAP

Phased Array Feed

Pathfinders• EMBRACE (Electronic Multi Beam

Radio Astronomy Concept)• THEA (Thousand Element Array)• Dense Aperture Arrays • Vivaldi antennas

• LOFAR (Low Frequency Array)• Sparse Aperture Arrays• Dipole antennas

The Square Kilometre Array

Dense Aperture Array

Sparse Aperture Array

Key Science Projects• Science observations requested by the radio astronomers, SKA drivers• The Cradle of Life

- terrestrial planet formation, molecular chemistry and the search for intelligent life

• Strong-Field Tests of Gravity using Pulsars and Black Holes - Pulsar search and timing, test relativistic gravity and detect gravitational waves

• The Origin and Evolution of Cosmic Magnetism - map the origin and evolution of magnetic fields• Galaxy Evolution, Cosmology and Dark Matter - study the cosmic evolution of HI (neutral hydrogen), dark energy and

dark matter• Probing the Dark Ages - study the epoch of reionisation (EoR)

The Square Kilometre Array

System designThe Square Kilometre Array

Hartebeesthoek Radio Astronomy Observatory (HartRAO)

Background• HartRAO is the only major radio astronomy observatory in Africa; KAT-7 is still in testing, MeerKAT in design phase• 26m radio telescope• Single dish observations• VLBI (very large baseline interferometry)

26 m Telescope at HartRAO

Pointing model• Telescope needs to find and track sources accurately• Need good pointing model• Pointing scans for various sources• Data used to improve the pointing model

HartRAO – research work

Hour Angle pointing error vs HA Declination pointing error vs HA

Rubidium and Hydrogen Maser clocks• Hydrogen Maser - frequency standard, accurate timing

• Rubidium clock, GPS10RB - Less accurate, corrects time by periodically comparing it with GPS (global positioning system) satellites

• Measure difference between : Maser and Rubidium clock times Maser and GPS clock times• performance of Rubidium

HartRAO – research work

Rubidium and Hydrogen Maser clocks• slope in the graph : frequency drift of the Maser clock• Phase noise: due to GPS signal path variations through the atmosphere

HartRAO – research work

Rubidium vs Hydrogen maser GPS vs Hydrogen maser

Rubidium and Hydrogen Maser clocks• 5min averages made, see how Rubidium follows the GPS• Look at frequency stability: Rubidium has short term stability, while GPS has long term

stability

HartRAO – research work

5min averages (Rubidium, GPS) Frequency stability (Rubidium, GPS)

Building a 1.4GHz receiver• Receiver for a satellite TV antenna• 3m diameter• Testbed for demonstrating

practical radio astronomy at school and University level

• Cylindrical waveguide horn feed with choke ring

HartRAO – research work

3 m dish with 1.4 GHz receiver

H₂0 Maser in Orion KL• Observations of H₂0 Masers in the Orion KL source region• 22GHz• March 2011 to present• Why? Flares occurred in 1984, 1998 • Flux density reached millions of Janskys

HartRAO – research work

Orion KL

H₂0 Maser in Orion KL• Average spectrum• Flux Density: 80,000 Jy• compare with data from 2007 when maser was not flaring (light blue)

HartRAO – research work

Average spectrum (lcp and rcp added)

H₂0 Maser in Orion KL• Time series plot at main peak velocities

HartRAO – research work

Time series plots (lcp)

Conclusion

• The Square Kilometre Array - Pathfinders - Key Science Projects - System design

• Hartebeesthoek Radio Astronomy Observatory - Pointing model - Rubidium and Hydrogen Maser clocks - 1.4GHz receiver - H₂0 Maser in Orion KL

Thank you!