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Focus on primordial stars

Spectrograph manufactured in Brazil may be able to observe typical elements of the first stars in the Universe

The STELES spectrograph...

LNAThe STELES spectrograph…LNA

Brazilian astronomers should soon have access to a new instrument to observe radiation emitted by celestial bodies in the visible wavelength spectrum, from the ultraviolet to the near-infrared region: the STELES high-resolution spectrograph, designed and manufactured in Brazil. The equipment can obtain detailed data on the chemical composition, temperature, speed of rotation and gravitational force of stars, including those formed during the primordial stage of the Universe, shortly after the Big Bang. The project is a success, despite a delay of five years. Bureaucratic problems, related to the import of components, parts supplier delays and errors, and insufficient experience in managing such a complicated undertaking contributed to the delay. “We had to learn by trial and error how to manage the construction of such a complex instrument,” admits astrophysicist Bruno Vaz Castilho, director of the National Astrophysics Laboratory (LNA) and coordinator of construction of the spectrograph.

In the coming days, STELES is scheduled to leave LNA headquarters in Itajubá, Minas Gerais State, and travel to the Andean municipality of Vicuña, in Northern Chile. The final destination of the instrument, which cost R$2.5 million, is the top of a mountain located 2,700 meters above sea level, Cerro Pachón. At this privileged sky observation point, STELES will be installed inside the dome of the Southern Astrophysical Research Telescope (SOAR), a telescope with a 4.1 meter (m) mirror, built and maintained thanks to investments from Brazil, the United States and Chile. “In September, STELES is scheduled to begin making observations,” says Castilho. If all goes as planned, researchers from the countries associated with the telescope should be allowed access to the instrument by the end of 2016. As a partner in the SOAR project, Brazil has the right to 30% of the telescope’s observation time.

...will be coupled to the SOAR telescope...

LNA…will be coupled to the SOAR telescopeLNA

STELES is the third instrument produced in Brazil for the international observatory. The first two were the SIFS spectrograph, with a smaller resolution than STELES, and the Brazilian Tunable Filter Imager (BTFI), both installed in the Andean telescope in 2010. Inspired by FEROS and UVES, two of the most powerful spectrographs operating at Chilean sites run by the European Southern Observatory (ESO), STELES is a more modern version of its siblings. It weights 830 kilograms, nine times less than UVES. It is also half the size of similar spectrographs. It is almost a cube, with a height of 1.8 m, a width of 1.9 m and a depth of 60 cm. The instrument has more than 5,000 parts, and most were designed at LNA. However, all of the optics and a good percentage of the electronics were imported. Machined mechanical structures and some of the electronic components were manufactured in Brazil, where the instrument was designed, assembled and tested before being declared ready for shipment to Chile.

Ten Brazilian companies were involved in building the spectrograph. For example, Equitecs, in São Carlos, created the bench structure and supports to hang on the telescope. Erominas, in Piranguçu, Minas Gerais State, built mechanical parts and MedTron, in Santa Rita do Sapucaí, Minas Gerais State, manufactured electronic boards for STELES. “In addition to preparing Brazilian companies to become suppliers of parts and services for other sophisticated technological projects, the manufacture of STELES allowed several students to learn optomechanical techniques and some even did their master’s degree theses on topics related to the issue of instrumentation,” comments Castilho.

Absorption lines recorded in the instrument’s red channel

LNAAbsorption lines recorded in the instrument’s red channelLNA

Building a spectrograph like STELES in Brazil costs significantly less than if it had been manufactured abroad, according to researchers involved in the project. “The objective was to build a cutting-edge instrument at a cost much lower than if it had been built abroad,” says astrophysicist Augusto Damineli, of the Institute of Astronomy, Geophysics and Atmospheric Sciences of the University of São Paulo (IAG-USP).  FAPESP financed about half the cost of the construction of STELES. The rest came from the Ministry of Science, Technology, Innovation and Communication (MCTIC), from the National Council for Scientific and Technological Development (CNPq), and from the Minas Gerais Research Foundation (FAPEMIG).

According to Castilho, STELES’ competitive price was due to a few factors: the administrative costs and salaries, in dollars, of the researchers and engineers involved in the project are lower in Brazil than abroad; manufacturing mechanical parts in Brazil is also much cheaper; and the smaller size of the instrument allowed them to use smaller, less expensive optical components. “STELES is going to have a strong impact on Brazilian astrophysics. Few spectrographs observe absorption lines in the ultraviolet region,” says Beatriz Barbuy, a professor at IAG-USP. “With it, scientific production based on SOAR should double.”

This optimism is due to the instrument’s characteristics. Like all spectrographs, STELES captures the light from a star and separates it, initially, into two main channels (blue and red), and then into different colors (wavelengths). Some chemical elements emit radiation in very specific wavelengths, which are difficult to detect. This is the case with beryllium, which formed in the first stars to appear after the Big Bang, 13.7 billion years ago. Its radiation is in a narrow band of the ultraviolet region that should be clearly “visible” to STELES. The resolution of SOAR’s new spectrograph is greater than that of its competitors. It can “discern” a signal up to 50,000 times smaller than the wavelength observed. FEROS, for example, has recorded an absorption line a maximum of 48,000 times smaller than the wavelength.

STELES: High-resolution spectrograph for SOAR (nº 2007/02933-3); Grant Mechanism Thematic Project; Principal Investigator Augusto Damineli (IAG-USP); Investment R$1,104,780.00.