Australian-led Spectrograph Operating on Gemini South Telescope

An international team of experts, led by the Australian Astronomical Optics (AAO) from Macquarie University and the Australian National University have announced the installation of a new spectrograph on one of the largest telescopes in the southern hemisphere. 

The new spectrograph, named Gemini High-resolution Optical SpecTrograph (GHOST), is a high-resolution spectroscopic tool that allows the spectra of astronomical objects, like stars and other bodies, to be analysed in detail. 

Electromagnetic radiation (like visible light) is made up of a variety of different wavelengths, each with its own unique band. Visible light, for example, is subdivided into six major bands that have wavelengths that stretch between 380 nanometres and through to 750 nanometres (nm). Wavelengths that correspond lower than 380 nm fall in the ultraviolet range, and wavelengths that are above 750 nm, fall into the infrared portion of the spectrum. 

When light from astrophysical objects, like stars, passes through a gaseous medium, elements within the gas will absorb certain wavelengths of light, presenting as gaps or dark bands in a continuous spectrum. This information tells astronomers what elements are present (as each has its own unique spectral fingerprint) and how the material is behaving in the presence of gravity, magnetic fields, and dynamical movement. 

Spectrographs are the instruments that allow the analysis of this data - and the higher the resolution of the instrument, the finer detail it can pull apart when it comes to the unique features of each individual star. 

GHOST’s wavelength coverage extends a little further outside the visible range, running from 363 nm - 950 nm, with the instrument having two resolution (R) modes - R ~50,000 for standard, and R ~75,000 for the high-resolution capabilities. GHOST will also be able to observe two targets simultaneously, speeding up the rate of data and information that is acquired from the large GEMINI telescope, located in Chile. And it’s already captured its first light, looking at a star (HD 222925) roughly 1,400 light-years away in the southern constellation of Tucana. 

Tony Farrell, Software Technical Lead from Australia Astronomical Optics-Macquarie says GHOST will expand the types of science the Gemini Telescope can accomplish.                       

“GHOST’s extremely high-resolution viewing capabilities will allow astronomers to get much more detail from their observations. The spectrograph’s ability to view HD 222925 is a prime example of this,” says Mr Farrell.

“The reason Gemini didn’t have this type of instrument before was due to a design feature of the telescope which causes the instruments to move and flex in ways that make instruments of this type impractical.”

The team has solved this long-standing problem by using an optical cable feed from the Gemini telescope to the large and very stable GHOST technology located in a room well underneath the telescope. Ultimately, this remoteness allows an instrument to be built which is both extremely physically and temperature stable

“The result is a spectrograph which is stable within fractions of micrometres.  At the telescope, there are two input probes on a robotic system, feeding the optical cable, which allows observations of two stars to take place at the same time, doubling the efficiency of the telescope compared to common solutions,” says Mr Farrell.

Australian Astronomical Optics-Macquarie leads the GHOST team, which includes the Australian National University (ANU) leading the instrument control system and data reduction software, the National Research Council of Canada (NRC) for the construction of the spectrograph, and the US National Science Foundation’s NOIRLab which manages the International Gemini Observatory.

“GHOST is primarily designed to help astronomers measure the abundance of a large number of elements in the spectra of stars, more efficiently than other large telescopes. By taking precise, high-resolution spectra, it will also be able to measure the reflex motion of stars due to the effects of exoplanets,” Professor Michael Ireland from the ANU Research School of Astronomy and Astrophysics.

“The Big Bang only produced Hydrogen and Helium, with a tiny amount of other light elements. GHOST will measure the elements formed in the first supernovae in the Universe, by measuring the spectra of the oldest stars.”

“Early elements produced in supernovae and retained in the next generation of stars vary between different environments. GHOST can not only measure stars in our Galaxy, but also in small galaxies orbiting our own,” says Professor Ireland.