The Pole Star and the Moon were used to test the instrument
The HORS spectrograph, belonging to the IAC, was successfully installed on the Large CANARIAS Telescope (“Gran Telescopio CANARIAS”) last week, and observed its “first light” through the telescope last Saturday. The new instrument will enable the GTC to analyze light with a resolution ten times higher than any of the other instruments on the telescope. “HORS will let us measure with precision the abundances of the chemical elements in stars, determine the masses of black holes in binary systems, or the composition of the atmospheres of exoplanets” explained Carlos Allende, the scientist in charge of the project.
HORS, which weighs a little more than one and a half tonnes, left the IAC on Tuesday of last week in a lorry which embarked for La Palma in the port of Los Cristianos in the south of Tenerife. On Wednesday the instrument was carried by road to the Roque de los Muchachos Observatory, and it was mounted on the GTC on Thursday. After a battery of tests of the optics, the electronics, and the software, on Saturday night the big telescope pointed at the Pole Star, and its light was analyzed by HORS. Félix Gracia, the optical engineer on the project was satisfied when first light was obtained with the instrument during the first two hours of tests on the sky. “Although we still have some months of work ahead of us, we are very happy to be able to observe a real star, after a year of experiments with laboratory lamps”.
The HORS spectrograph is based on the optical elements (mirrors, lenses and prisms) of the old instrument Utrecht Echelle Spectrograph (UES), built by the University of Utrecht (Netherlands) and operated by the Isaac Newton Group (ING) since 1992 on the William Herschel Telescope (WHT) on La Palma. UES was donated by the ING to the IAC in 2002 in order to give it a second life in a more powerful telescope. Therefore, one could describe HORS as a “recycled” instrument, and this has meant an enormous reduction in cost. The IAC has adapted its design, making it more compact, and equipping it with a new CCD camera, which operates at 110 degrees below zero to be able to detect the extremely weak signals of astronomical sources. The new instrument is linked to the “Gran Telescopio CANARIAS” using a robot arm with a fibre optic bundle. “HORS is in many senses a peculiar instrument” says Juan Calvo, the technical director of the project. It has gone from the drawing-board to the telescope in record time with a tiny budget. José Peñate, the mechanical engineer on HORS admits that “there were components designed and made in the same day. It has been done in a rush, but it works”.
With its diameter of 10.4 metres the GTC is at the moment the biggest optical telescope in the world. Telescopes capture the light which was emitted by astronomical objects a long time ago, years for the nearest stars, millions of years for the galaxies in the Local Group, to which the Milky Way belongs, and thousands of millions of years for the most distant galaxies. “We will be using HORS to measure the chemical compositions of the first stars born in the Milky Way, some 13,000 million years ago, not long after the Big Bang” declared Carlos Allende. After a few more months of trials it is hope that HORS will begin routine use as a Visiting Instrument on the GTC early in 2016, at which time it will be on offer to all the scientific community of the GTC.
Video of the mounting of HORS on the GTC. Credits: Félix Gracia (IAC).
Technical team of the HORS instrument: