Interacting Binary Stars and Astronomical Instrumentation
Academic staff: Professor Vik Dhillon, Dr Stuart Littlefair, Dr Steven Parsons
Postdoctoral researchers: Dr Martin Dyer
PhD students: James Wild
Honorary/Visiting researcher: Dr Dave Sahman, Dr Simon Tulloch
Interacting binary stars
Some of the most interesting binary stars are close pairings, where one compact component, typically a white dwarf, neutron star or black hole, is accreting mass from the other component, typically a white dwarf, brown dwarf or main-sequence star.
These interacting binary stars, which include Cataclysmic Variables (CVs) and X-ray Binaries, are responsible for some of the most exotic phenomena observed in the Universe, such as Type Ia Supernovae, short Gamma-Ray bursts, millisecond pulsars and micro-quasars.
At Sheffield, we investigate these objects using a series of high-speed cameras and robotic telescopes that we have developed, as described below.
The ancient Greeks believed the Universe to be perfect and unchanging, whereas we now know that astronomical objects vary in brightness on timescales ranging from milliseconds to billions of years.
Although astronomy has made great strides in recent years, the study of the most rapidly varying phenonema (on timescales of milliseconds to seconds) has been largely ignored.
To address this situation, we have built a series of high-speed cameras (ULTRACAM, ULTRASPEC, HiPERCAM) and mounted them on the world's largest telescopes to study astronomical objects which eclipse, transit, occult, flicker, flare, pulsate, oscillate, erupt, outburst or explode, thereby opening up a new region of observational parameter space for discovery.
We are also interested in observing the gravitational-wave sources in the Universe discovered by LIGO/Virgo, most likely emitted by merging binary neutron stars. The group's effort in this area is currently focused on the construction of GOTO, a wide-field survey telescope on La Palma that will search for electromagnetic counterparts to gravitational-wave transients.
ULTRACAM is an ultra-fast, triple-beam imaging photometer, which we use at the 4.2-m William Herschel Telescope (WHT) on La Palma, the 8.2-m Very Large Telescope (VLT) in Chile, and the 3.5m New Technology Telescope (NTT) in Chile.
The instrument was built by a consortium involving the Universities of Sheffield and Warwick, and the UK Astronomy Technology Centre (UKATC), Edinburgh.
ULTRACAM has been used to study white dwarfs, brown dwarfs, red dwarfs, pulsars, black-hole/neutron-star X-ray binaries, gamma-ray bursts, cataclysmic variables, eclipsing binary stars, extrasolar planets, active galactic nuclei, asteroseismology and occultations by Solar System objects (Titan, Pluto and Kuiper Belt objects).
ULTRASPEC is a high-speed camera employing a frame-transfer electron-multiplying CCD (EMCCD) and the data acquisition system of ULTRACAM. The project is a collaboration between the Universities of Sheffield, Warwick and the UKATC.
ULTRASPEC is permanently mounted on the 2.4m Thai National Telescope (TNT), providing Sheffield and Warwick with 25 nights per year of time to pursue a programme of research into high-speed astrophysics.
HiPERCAM is a quintuple-beam imager that saw first light on the 4.2m William Herschel Telescope (WHT) in 2017 and on the 10.4m Gran Telescopio Canarias (GTC) in 2018.
The instrument uses re-imaging optics and 4 dichroic beamsplitters to record ugriz (300-1000nm) images simultaneously on its five CCD cameras.
The detectors in HiPERCAM are frame-transfer devices cooled thermo-electrically to -90°C, thereby allowing both long-exposure, deep imaging of faint targets, as well as high-speed (over 1000 windowed frames per second) imaging of rapidly varying targets.
The GOTO project consists of multiple wide-field telescopes on a single mount, necessary to map the large source regions on the sky that accompany detections of gravitational waves with LIGO and Virgo.
An initial prototype phase using a single mount with 4 telescope units have made observations from 2017 onwards, including throughout the 3rd LIGO/Virgo observing period (O3). The second phase will deploy a full-scale instrument at the La Palma site, as well as developing a second site in Australia.
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