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WEAVE (WHT Enhanced Area Velocity Explorer) is a powerful new multi-object spectrograph for the 4.2-m William Herschel = Telescope at the Observatori= o del Roque de los Muchachos, on La Palma in the Canary Islands. It will al= low astronomers to take spectra of up to 1000 stars and galaxies in a singl= e exposure. This huge leap in observing efficiency (currently a maximum of = 100 objects can be observed simultaneously) will allow astronomers to tackl= e several ast= rophysical problems that unt= il now have remained out of reach.
One of the most exciting of these is find= ing out how our Galaxy (the Milky Way) was assembled. To do this, astronome= rs need first to measure the current positions and motions of the galaxy's = stars and then, in effect, run the clock backwards. The positions in three = dimensions of about 1000 million of the Galaxy's stars will be measured by = the European Space Agency's GAI= A satellite, launched in 2013. The speeds of th= e stars towards or away from us can more accurately be measured from a grou= nd-based telescope than by GAIA, and this is where WEAVE comes in. WEAVE wi= ll measure the speeds of several million of the stars mapped by GAIA. Astro= nomers will then be able to unravel the sequence of events which brought in= to being the Milky Way galaxy (and us).
The Milky Way galaxy, as viewed from the Roque de los Muchachos =
Observatory. Credit: Nik Szymanek.
Another key project for WEAVE will be stu= dying how galaxies have evolved over the aeons. To do this, astronomers wil= l take spectra of galaxies up to several billions of light years away, effe= ctively looking back in time to see each galaxy as it was when the light st= arted out on its journey towards us. From these spectra, astronomers will b= e able to deduce the chemical composition of the galaxy at that time and th= e rate at which new stars were forming.
European astronomers are in broad agreeme= nt about the need for a powerful multi-object optical spectrograph on a med= ium-sized telescope in the northern hemisphere to tackle such questions (se= e for example a recent report&nb= sp;by ASTRONET's European Telescope Strategy Review Committee).
In March 2010, 90 astronomers from across= Europe met in London for a workshop on "Science with the William Herschel Telescope 2010-2020", and pla= ns for WEAVE were hatched at this meeting. Fabrication of WEAVE is now well= -advanced, and the goal is to have it operational by mid-2018 (see timeline).
To increase the field of view of t= he William Herschel Telescope, new optics (including a lens more than 1 met= re across) will be installed at its prime focus (top end). These optics wil= l create an image of a patch of sky about 2 deg in diameter (4 times the di= ameter of the full moon). Light from 1000 individual stars and galaxies wit= hin this area will then be picked off by 1000 robotically-positioned optica= l fibres in the focal plane, and fed to the spectrograph, located on a plat= form lower down the telescope.
The prime focus of the William Hers= chel Telescope with the dummy WEAVE top-end assembly mounted.
Optical fibres of the WHT's current m=
ulti-object spectrograph, AUTOFIB-2/WYFFOS.=
a> Up to 100 fibres (out of a total of 150) can be positioned over a 5=
0-arcmin field of view in the focal plane of the telescope, each picking up=
the light from an individual star or galaxy, and feeding it to the spectro=
graph. (Here, the fibre heads have been positioned to outline the shape of =
the island of La Palma.)
WEAVE will have seven times as many fibre=
s as AUTOFIB-2/WYFFOS, and will be able to position them over an area six t=
imes larger.
WEAVE's spectrograph disperses the light = from each star or galaxy into its component colours (wavelengths) from red = through to blue and measures the intensity of the light at each of about 50= 00 separate wavelengths. Armed with this information, astronomers can measu= re accurately the speed at which the star or galaxy is travelling, and also= its chemical makeup.
WEAVE stands for WHT Enhanced Area Veloci= ty Explorer. The acronym aptly reflects the challenge of positioning correc= tly, in a 2-dimensional plane, a large number of fibres. Weaving also happe= ns to be a long-standing traditional handicraft on the island of La Palma!<= /p>
Further information:
ESA vid=
eo presentation 'Charting the Galaxy - from Hipparcos to Gaia'