Spectral rule to measure stars

Astronomers have developed a spectral ruler as a means of measuring stars. It is the first standardised set of measurement guidelines for analysing and cataloguing stars: there was previously no uniform system of reference for calibrating the heavens, and this ‘ruler’ will make it much easier to classify and compare data on star discoveries. The scale is an important first step in the Gaia satellite mission to map over a billion stars in the Milky Way, and will ensure that analysis of data – expected to be in the petabyte range – is completed in the most effective and efficient way. To create the stellar scale, researchers selected 34 initial benchmark stars, including some of the most studied in the galaxy. They represent the different kinds of stellar populations and metallicities – the chemical patterns which reveal a star’s age – that can be found. “We took stars which had been measured a lot so the parameters are very well-known, but needed to be brought to the same scale for the new benchmark – essentially, using the stars we know about most to help measure the stars we know nothing about,” said Dr Paula Jofre from the Institute of Astronomy at the University of Cambridge. Jofre concentrated on determining metallicity using spectroscopic data. She created a spectral library by combining the best data on the atmospheric structure of benchmark stars to determine a uniform scale. Together with scales for the stars’ temperatures and surface gravities determined by colleagues at the Universities of Uppsala and Bordeaux, her work completes the measuring system that will be used to gauge data from Gaia. “Now this set of data scales for the benchmark stars can be used as a way of making definitive measurements of other stars – invaluable to astronomers working on a wide range of projects,” Jofre said. UK Gaia lead, Professor Gerry Gilmore said: “Advances in understanding the history and structure of our Galaxy with ambitious projects are possible only because, like Newton, we see farther by standing on the shoulders of giants. For reliably determining what chemical elements the stars are made of, those giants are the benchmark stars. All our vastly expanding knowledge depends on really understanding the few.” The work has been published in Astronomy & Astrophysics. Gaia FGK benchmark stars: Metallicity Fact: The petabyte is 10¹⁵ bytes of digital information and is roughly the equivalent of all the information held in all the libraries of the world today.