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December 7, 2023



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OSIRIS: The eye in the sky


A telescope would be nothing without the instruments it uses to observe. Developing instruments like these is vital to satisfy the needs of scientific programmes that could not be achieved without them. That is why the Gran Telescopio Canarias (GTC) has been designed from the outset with its scientific objectives in mind.

It will be fitted with instruments capable of investigating the formation and evolution of galaxies in the early days of the Universe and answering questions about faraway quasars, brown dwarfs, planets outside the solar system, and the interstellar matter that occupies most of space.

One of these instruments, OSIRIS, is being designed and built by the Instituto Astrofísica de Canarias. OSIRIS is scheduled for installation at the GTC in time for "Day One", the start of scientific operations.

OSIRIS, Egyptian god

We are not talking about the god of the underworld, even if he has now been transformed into an idol of vision in the overworld. The OSIRIS (Optical System for Imaging and low Resolution Integrated Spectroscopy or low and intermediate resolution integrated image and spectroscopy optical system) will produce direct images of the sky, carry out spectroscopy on several objects at once and will work in the visible range, that in which the human eye can make out objects in the sky.

Amongst other things, OSIRIS will deliver new data for the latest areas of investigation in astrophysics, like the atmospheres of planets in the solar system, compact x-ray emitting objects - possibly black holes - supernovas, which are very remote and which can be used to determine the age of the Universe, so-called gamma ray bursts (massive energy releases whose origins are unknown but important to discover) and other burning issues in astronomy like the formulation and evolution of galaxies and clusters of galaxies.

“OSIRIS has several interesting features” says José Miguel Rodríguez Espinosa, the GTC´s Scientific Director, “ such as tuneable filters.” These allow precise observation of a particular line in the light spectrum, situated anywhere in the range of visible light. “By using these filters we can get around phenomena like redshift, which affect very distant objects.” The objects he is talking about are so distant that we see them now as they were in the infancy of the Universe, when it was between just 1200 and 1500 million years old, or a tenth of the age it is now.

If he had to focus on just two of OSIRIS’ features, Rodríguez Espinosa would describe its high image resolution and magnitude limit - in other words, its ability to see such faint objects. OSIRIS will be fitted with very high quality sensors to reduce by half the ‘noise’ that goes with observation, so that it will be able to see distant objects clearly. OSIRIS, the ‘eye’, will also be able to look at several different objects at once, in a wider field of vision and with 80 to 90% efficiency.

Involved in designing and building OSIRIS are the IAC, which is the principal partner with responsibility for the development of the instrument, and the Institute of Astronomy of the National Autonomous University of Mexico (IA-UNAM). The engineering team is made up of twenty people from the two institutions, and a further 90 scientists from 27 institutions in 9 countries make up the project’s science team.

Jordi Cepa, the project’s Principal Investigator and Lecturer at the Astrophysics Department of the University of La Laguna, says that, having come through an early Conceptual Design Review (in which a committee of specialists assessed its progress and gave it their approval), OSIRIS progressed through Preliminary Design Review and is currently at the Detailed Design and Construction stage.

The “Keynote Project” OTELO (OSIRIS Tunable Emission Line Object Survey) which was unveiled at the “First workshop on Science with GTC” (February 2002) will require the widest, most detailed and numerous survey of objects ever to be undertaken. If it is approved, OTELO will will keep the GTC staff busy for several years: it will identify more than 10,000 different types of objects that are up to 25% of the age of the Universe, so that the evolution of the Universe can be studied.

Text: José Manuel Abad Liñán
Natalia R. Zelman

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