Instrumentation

DPhil Projects 2021: Instrumentation Development

Building the HARMONI spectrograph – a first light instrument for the ELT.
John Capone, Ian Lewis & Niranjan Thatte

The Extremely Large Telescope (ELT) currently being built by the European Southern Observatory is a revolutionary scientific project for a 39m diameter primary mirror telescope that will allow us to address many of the most pressing unsolved questions about our Universe: discovering planets around other stars, probing the first objects in the Universe, unveiling the nature and distribution of the dark matter and dark energy which dominate the Universe. The ELT will be the largest optical/near-infrared telescope in the world and will gather 13 times more light than the largest optical telescopes existing today.
The University of Oxford is leading the construction of HARMONI, an integral field spectrograph that will be one of the two “first-light” instruments for the ELT. Integral field spectroscopy, also called 3D spectroscopy, is a recent instrumental technique which allows observers to simultaneously obtain the full set of spectra from all astrophysical sources in a small region of sky. In addition to managing the overall project, the visible and infrared instrumentation group at Oxford is responsible for building a key system of the instrument: the spectrograph units.
We are looking for a motivated D.Phil student who has a keen interest in state-of-the-art instrumentation, to work collaboratively with the spectrograph team. The successful candidate will design and execute laboratory measurements to align and demonstrate the performance of spectrographs in vacuum and at cryogenic temperatures. This will require designing, constructing, and utilising an optical test system which will provide light representative of the broader instrument into the spectrographs. The successful candidate will gain expertise in optical metrology, cryogenic systems, and instrument assembly, integration, and testing. They will be part of constructing the ELT - the world’s biggest ground based optical observatory. The project work also involves an opportunity to work with astronomical data sets.

Measuring grating efficiency for HARMONI – the first light ELT spectrograph
John Capone, Matthias Tecza & Niranjan Thatte

The Extremely Large Telescope (ELT) currently being built by the European Southern Observatory is a revolutionary scientific project for a 39m diameter primary mirror telescope that will allow us to address many of the most pressing unsolved questions about our Universe: discovering planets around other stars, probing the first objects in the Universe, unveiling the nature and distribution of the dark matter and dark energy which dominate the Universe. The ELT will be the largest optical/near-infrared telescope in the world and will gather 13 times more light than the largest optical telescopes existing today.
The University of Oxford is leading the construction of HARMONI, an integral field spectrograph that will be one of the two “first-light” instruments for the ELT. Integral field spectroscopy, also called 3D spectroscopy, is a recent instrumental technique which allows observers to simultaneously obtain the full set of spectra from all astrophysical sources in a small region of sky. In addition to managing the overall project, the visible and infrared instrumentation group at Oxford is responsible for building a key system of the instrument: the spectrograph units.
We are looking for a motivated D.Phil student who has a keen interest in state-of-the-art instrumentation, to work with the spectrograph team in characterising the performance of Volume Phase Holographic Gratings (VPHGs). The HARMONI spectrographs contain 42 VPHGs which are critical to the instrument’s overall performance. The successful candidate will develop and utilise an automated radiometric test bench to measure the performance of delivered gratings, in a spectrally and spatially resolved manner. This will require designing, constructing, and programming a motorised optomechanical setup and using this setup to measure the diffraction efficiencies of gratings. The successful candidate will gain expertise in optomechanical design, radiometry, and test automation. The project work also involves an opportunity to work with astronomical data sets.

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Very high-energy gamma ray astrophysics.
Garret Cotter

Very high-energy (VHE) gamma-ray astrophysics is an exciting field spanning fundamental physics and extreme astrophysical processes. We detect the Cherenkov light emitted when VHE gamma rays from space hit the Earth’s atmosphere, using optical telescopes on the ground fitted with high-speed detectors similar to those used by the Large Hadron Collider, and also with water-filled Cherenkov detectors at high-altitude sites. Our science goals include
• Understanding the natures and variety of particle acceleration around black holes.
• Understanding the origin of cosmic rays and their role in the Universe.
• Searching for the ultimate nature of matter and physics beyond the Standard Model
At Oxford we are involved in three major international experiments. The High Energy Stereoscopic System (H.E.S.S.) consists of five telescopes in the Khomas Highlands of Namibia, one of the darkest sites for astronomy in the world. H.E.S.S. is at present the world’s largest gamma-ray observatory. The international Cherenkov Telescope Array (CTA) is the next-generation ground-based observatory, which has just commenced construction. It will have two arrays, totalling one hundred telescopes. One array is in the Northern Hemisphere, on La Palma in the Canary Islands, and one in the Southern Hemisphere, at Cerro Paranal in Chile. Then at the very highest photon energies, the proposed Southern Wide-Field Gamma-ray Observatory (SWGO) will have water Cherenkov detectors at an extremely-high-altitude site in the Andes.
There are openings for both experimental and theoretical work. We are developing software and data analysis techniques for CTA’s small-sized unit telescopes. These will have 2k pixel detectors and front-end amplifiers which feed into custom high-speed electronics. This gives a system that can image at a rate of a billion frames per second. We are also leading the efforts on machine learning techniques for the large volumes of data that will be generated when the new experiments become operational. These techniques allow us to use large datasets, in large-dimensioned parameter spaces, with very high entropy, and still undertake precise calibration of the astrophysical signals.
On the theoretical/observational side of the programme, recently we have developed new theoretical models for the broad-spectrum emission from steady-state jets that let us use the gamma-ray observations and those at other wavelengths to investigate the physical properties of the jet and the black hole at its base. We now propose to extend these models to look in particular at the entrainment of heavy particles as the jets propagate through their host galaxy, and the resulting possibility of hadronic particle processes within the jets. We will investigate the physical conditions that lead to flaring and the presence, and extent, of emission from hadronic processes.
We will offer the possibility of joint supervision with the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg. All students will have the opportunity to gain experience on observing shifts at the H.E.S.S. site, and opportunities are available to participate in our projects on education, outreach and socio/economic capacity building in Namibia.
H.E.S.S. website https://www.mpi-hd.mpg.de/hfm/HESS/
CTA website https://www.cta-observatory.org
SWGO website https://www.swgo.org/
Background reading: https://www.worldscientific.com/doi/pdf/10.1142/10986

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Left: H.E.S.S. 28-m telescope in Namibia (Credit: G.Cotter) Right: Artist’s impression of CTA-South site in Chile (Credit: Gabriel Pérez Diaz (IAC)/Marc-André Besel (CTAO)/ESO/ N. Risinger (skysurvey.org)

For more information please contact Professor Garret Cotter (garret.cotter@physics.ox.ac.uk)

Can the E-ELT detect super-Earths? Determining the lower mass limit of HARMONI and PCS through simulation and experiment.
Matthias Tecza, Niranjan Thatte

One of the E-ELT's highest scientific priorities is to characterise exo-planets and to take images of Earth-like planets. For this purpose the E-ELT will be equiped with a dedicated planetary camera and spectrograph, called PCS, to be commissioned in the 2030s. The overriding factor in directly imaging exo-planets is the contrast ratio between the faint planet and the bright star it orbits.

In Oxford we are leading the R&D effort to establish which spectrograph design offers the best performance. Using a bench mounted spectrograph we will measure the achievable contrast ratio of an image-slicer based and a lenslet-array based spectrograph.

We are looking for motivated D.Phil student who has a keen interest in state-of-the-art instrumentation. She/he will be involved in the design and set-up of the experiment, including opto-mechanical design, and data acquisition using CCD detectors. The student will also reduce, process, and analyse the data collected to determine and optimise the achievable contrast, including applying and/or developing novel algorithms to exploit the advantages of image-slicer or lenslet-array based spectrographs.