Brazilian Astronomers Identify Rare Star in Milky Way

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Below is an article published the day (02/17) in the website of the "Agency FAPESP", noting that Brazilian Astronomers identify rare star in Milky Way.

Duda Falcão

News

Brazilian Astronomers Identify

Rare Star in Milky Way

By Diego Freire

Agência FAPESP

February 17, 2016

(Photo: ESO/Beletsky/DSS1 + DSS2 + 2MASS)

The New Technology Telescope and ultra metal-poor

star 2MASS J18082002-5104378 (yellow rectangle).

Primitive stars dating from the infancy of the universe are hard to identify because of their brightness, which is typically very faint. However, this is not so in the rare case of 2MASS J18082002-5104378, recently found in the Milky Way by a group of Brazilian and US researchers led by astronomers at the University of São Paulo (USP). The discovery could be a major contribution to the understanding of our galaxy’s beginnings.

Minutes after the Big Bang, only the chemical elements hydrogen and helium were produced. The heaviest elements, classed as metals by astronomers, emerged much later in the interior of stars. The first stars ejected metal-rich matter into the interstellar medium when they exploded, such that new stars contained growing amounts of these elements. Astronomers therefore know that the stars with the smallest amounts of metals are the most primitive. An example is 2MASS J18082002-5104378, which has less than a ten-thousandth of the iron present in the Sun.

The search for metal-poor stars is a key activity for astronomers who study the beginnings of our galaxy. Currently, their efforts focus on faint stars that are hard to observe directly.

“There are quite a lot of metal-poor stars, but most of them are faint, and details can’t be seen with a telescope. They’re very old stars with chaotic orbits, dating from the stage in which the galaxy was collapsed, and they’re a long way away from our solar system. But, this one in particular is passing a little closer to the Sun, so that it’s a little brighter,” said Jorge Luis Meléndez Moreno, a professor at the University of São Paulo’s Institute of Astronomy, Geophysics & Atmospheric Sciences (IAG-USP).

Meléndez is principal investigator for the research project “High-precision spectroscopy: impact on the study of planets, stars, the galaxy and cosmology”. Conducted with support from FAPESP, the project aims to characterize certain types of stars with precision and to study planet formation, stellar evolution processes and galactic chemical evolution in unprecedented detail, as well as primordial nucleosynthesis, i.e., the formation of chemical elements by nuclear reactions during the Big Bang.

The “new” star is at least 13 billion years old, according to the researchers, who estimated its age by comparing it with the oldest star clusters in the galaxy, which are the same age but metal-rich. Its size is approximately 88% of the Sun’s mass, and its surface temperature is 5,440 K, almost the same as the Sun’s (5,778 K). The chemical elements detected in its atmosphere include iron, sodium, silicon, calcium and nickel, each in an amount corresponding to less than a ten-thousandth of the same element in the Sun.

Initial estimates suggest a distance from Earth of approximately 2,500 light years. According to the researchers, a more precise measurement will be obtained from the European Space Agency’s Gaia satellite, which is gauging the distance of many stars.

Galactic Archeology

The international collaboration led by Meléndez began its search for relatively bright metal-poor stars in 2013. In the following year, the team observed 2MASS J18082002-5104378 with the New Technology Telescope (NTT) at the European Southern Observatory’s La Silla site in northern Chile, identifying it as a promising metal-poor star formed in the galaxy’s infancy.

“Stars as poor in metals and as bright as this one are very rare,” Meléndez said. “They’re precious relics for galactic archeologists and help us greatly to understand the history of the Milky Way.”

Following the discovery, the star was observed in greater detail between 2014 and 2015 using the UVES spectrograph on the Very Large Telescope (VLT) at the European Southern Observatory’s Paranal facility in the Atacama Desert.

The VLT has a diameter of 8 m and is located at an altitude of 2,600 m. The spectrograph splits up the light from stars observed through the VLT into its constituent colors so that their chemical compositions can be studied in great detail.

The astronomers confirmed that the star contains very small amounts of heavy chemical elements, classifying it as ultra metal poor (UMP).

2MASS J18082002-5104378 is the brightest known UMP star, at magnitude 11.9, and is bright enough to be seen with small telescopes measuring as little as 10 cm across. Only CD-38 245, a UMP star discovered more than 30 years ago by Australian astronomers M. S. Bessell and J. Norris, has similar brightness. All other UMP stars are at least six times fainter.

The research group now plans to obtain detailed observations of the star at ultraviolet wavelengths using the Hubble Space Telescope to study a wide array of chemical elements without interference from Earth’s atmosphere.

The team’s findings have been published in the journal Astronomy & Astrophysics in the article entitled “2MASS J18082002-5104378: The brightest (V = 11.9) ultra metal-poor star”, authored by Meléndez, Gabriel Perez and Marcelo Tucci-Maia, IAG-USP; Vinicius Moris Placco, University of Notre Dame; Iván Ramírez, University of Texas at Austin; and Ting S. Li, Texas A&M University.

Source: Website of the Agência FAPESP - http://agencia.fapesp.br/