Student Colloquium with Ann Gaedie and Modiri Mokaila

Date
Time
-
Venue
NWU Potchefstroom, Building G5 - Room 310
Description

You are cordially invited to attend a student colloquium presented by Ann Gaedie and Modiri Mokaila.

Ann Gaedie's talk:

Title: Development of Fiber Instrument Cable for AMASE Survey

Abstract: The Affordable Multiple-Aperture Spectroscopy Explorer Prototype (AMASE-P) is an innovative initiative designed to enhance high-resolution integral field spectroscopy for studying ionised gas in the Milky Way and nearby galaxies. In this project, AMASE-P will pioneer the use of multimode fibres with 50 micron diameter and octagonal cores in a fibre array consisting of 1519 fibres. However, for this prototype study, only 547 fibres are incorporated to form the fibre bundle array, making them the smallest of their kind in the field of astronomy. This specific fibre size is critical for the resolution of individual hydrogen lines and the analysis of kinematics and metallicity by merging high spatial resolution (σ ≈ 8.5 km s−1) with high spectral resolution (R = 15000). The deployment of small fibres is necessary because a small telescope covers a larger sky area, whereas large fibres would be impractical to position on such a telescope and difficult to store.

 
Although the title highlights the creation of a fibre cable, this research concentrates on the precise positioning and alignment of optical fibres within a hexagonal opening, alongside the development of a computational imaging algorithm to assess fibre positioning accuracy. A compact fibre bundle necessary for the fibre cable’s creation was not realised. The production process involves placing 547 fibres in a hexagonal hole with a diagonal diameter from corner to corner of 1.894 mm, achieving a fibre fill factor of about 35.8% to improve photon collection. The fibre ends are polished to a surface roughness of 0.3 microns, which aligns with the optical wavelength. Positioning errors beyond ±3µm can result in a decrease of more than 10% in observation efficiency. Furthermore, stress-free fibre mounting is crucial to prevent degradation of the output focal ratio. To address these challenges, we have developed a fibre assembly technology that combines high-accuracy fibre positioning with a metrology system. This system achieves a positioning precision of ±3µm. The high-precision algorithm images the fibre bundles and translates the pixel data into micron-scale measurements, accounting for detector resolution, pixel dimension, and magnification. This approach automates fibre alignment verification, reduces manual effort, and improves overall assembly efficiency.
 
Our method for developing and characterising fibre bundles for AMASE-P ensures minimal light loss, uniform signal capture, and compact design, establishing a new benchmark for precision assembly in fibre-fed spectrographs for large-scale astrophysical studies.

 

Modiri Mokaila's talk:

Title: Exploring long-term Trends of Ionospheric Total Electron Content over South Africa.

Abstract: The ionosphere is a dynamic, inhomogeneous, and electrically conductive plasma formed through the interaction of solar extreme ultraviolet (EUV) and X-ray radiation with the Earth’s upper atmosphere at altitudes of approximately 50–1000 km. Variations in ionisation levels within this region significantly influence radio wave propagation and satellite-based communication systems. Total Electron Content (TEC), the integral of electron density between satellite and receiver, a parameter for studying ionospheric behaviour because of its impact on radio communication, navigation, and Global Navigation Satellite System (GNSS) signal propagation, was used in this study. The long-term trends in TEC over South Africa using observations from three GNSS stations were analysed. To isolate long-term ionospheric variability, solar-cycle influence was removed using different solar activity proxies: F10.7 solar radio flux, the MgII core-to-wing index, and sunspot numbers. Monthly and yearly averaged TEC data spanning 16 to 25 years were analysed using regression techniques to estimate long-term trends after correcting for solar activity. Results indicate a persistent negative trend in TEC across the South African mid-latitudes after accounting for solar activity. Differences in the trend magnitude obtained highlight the importance of proxy selection when estimating long-term ionospheric trends.

 

Join meeting here 

Meeting ID: 317 533 300 088 38

Passcode: 3v277Hq3

Contact Details

For more information, kindly contact Joseph Magwanya.