900 “Eyes” in Optical Fiber To Study the Universe (Astronomy)

On the Canary Islands, the assembly and preliminary tests of Weave are being completed, a sophisticated instrument that will provide invaluable data to be able to understand how our galaxy was formed and the evolution of its stars, but also the evolution of galaxies outside the ours and the nature of dark matter and dark energy. The international project sees the scientific participation of INAF

Work in progress at the William Herschel (Wht) telescope at the Roque de los Muchachos Observatory in the Canary Islands: the technical and scientific staff are completing the assembly and preliminary tests of Weave (Wht Enhanced Area Velocity Explorer), an advanced instrument that it will provide invaluable data to be able to understand how our galaxy was formed and the evolution of its stars, but also the evolution of galaxies outside ours and the nature of dark matter and dark energy. Weave will see the first light by 2021 and, as soon as the commissioning phase is completed , it will begin its observation campaign. In 1200 nightsdistributed over the next five years, Weave will collect an enormous amount of data, including measuring the speeds of over 10 million celestial objects, including stars in our galaxy and outer galaxies. The Weave project, led by the Rutherford Appleton Laboratory (Ral) Space and the University of Oxford, also sees the participation of the National Institute of Astrophysics (Inaf).

“The construction of the instrument involves the Inaf institutes in Italy in Bologna, Cagliari, Catania, Florence, Milan, Naples, Palermo, Rome and Turin,” says Antonella Vallenari , INAF researcher and Italian principal investigator of Weave. «In addition, the Galileo National Telescope houses the Weave archive for the distribution of data to the entire international scientific community. Eight surveys have already been planned : two involve the main components of our galaxy, while the others involve external galaxies (both in the local universe and more distant), clusters of galaxies and absorption systems of quasars. Two surveys they are Italian-led, called ‘Star Clusters’ and ‘StePS’, respectively intended to study the structure of the galaxy’s disk and provide the most detailed view of the properties of intermediate redshift galaxies ».

The Weave spectrograph has already been installed at the Wht. The observed spectra are sent on two different optical paths (arms), for the blue and the red part of the spectra respectively. Each arm houses a mosaic of two Ccd detectors, each with 36 megapixels. Weave, with a field of view of 3 square degrees , will allow to obtain, in just one hour of exposure, data for about 900 objects simultaneously .

After a year of painstaking installation of nearly 100km of fiber optic assemblies, the fiber positioner was tested and calibrated. The positioner is capable of making complete configurations of over 900 optical fibers in less than an hour using its two high-speed industrial robots. Each fiber collects the light emitted by a single star or galaxy present in the field of view of the spectrograph. Operational tests of the new prime focus corrector have already produced high quality astronomical images at all wavelengths, from ultraviolet to the limit of visible light. With good seeing, each fiber will collect 80% of the light from a celestial source.

Image of the galaxy M74 obtained during the tests of the first focus corrector for the Weave instrument with the red, green blue and H-alpha filters. Credits: Darío González Picos, Lara Monteagudo, Chris Benn and Ovidiu Vaduvescu

The principal investigator of Weave, Gavin Dalton , of the University of Oxford and Ral Space, says: «It is fantastic to finally see all the different elements that make up Weave, the result of the work of so many groups of people, gathered together at the telescope, and to finally be able to put the positioning system in operation. Weave’s development spanned 10 years, with a myriad of complex moving and non-moving parts designed and built in workshops across Europe. The complete instrument that we have today here at the Roque de los Muchachos Observatory and which works correctly, is ready to be made available to the astronomical community and become a new, formidable eye for studying the universe ».

“This tool will be fundamental in the coming years,” continues Vallenari. «Weave is the only high-resolution multifiber spectrograph in the northern hemisphere: it will complete the surveys of Gaia and 4Most (which will operate in the southern hemisphere in a few years) as radial velocities and chemical abundances for the study of the Milky Way. As for the study of external galaxies, Weave will provide the missing information in the Lofar (Low Frequency Array) and Aperitif at Westerbork Synthesis Radio Telescope surveys , together with the study of stellar populations of intermediate redshift galaxies ».

The commissioning of Weave will begin after the integration of the tool. It will last from 2 to 3 months and will be followed by scientific verification observations. Weave will be managed by the Isaac Newton Group of Telescopes which will then begin routine observations and open-time observations.

Featured image: A WEAVE field completely configured with 700 optical fibers posed by two robots (not visible in the photo), at the WHT telescope site. Credits: Gavin Dalton / U. Oxford and STFCRAL Space

Provided by INAF

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