April NUI GALWAY ASTRONOMERS MEASURE STAR DIAMETERS

Astronomers at NUI Galway are part of an international team which for the first time have used the VERITAS gamma-ray telescopes to measure the angular diameter of stars. The study was published today (15, April 2019) in the journal Nature Astronomy.

VERITAS is an array of four 12-metre gamma-ray telescopes located at the F.L. Whipple Observatory in southern Arizona.  They are used to detect very-high-energy gamma radiation from exotic objects in space. They do this by measuring the brief flashes of visible light produced when gamma rays enter the Earth’s atmosphere.

Dr Gary Gillanders of the School of Physics, Centre for Astronomy at NUI Galway, explains: “Stars are so far away from us that they appear as points of light in the sky. Their diameters are usually estimated indirectly using measurements of temperature and brightness.”

The VERITAS team have directly measured the angular diameter of two stars by using an asteroid occultation method in which the shadow cast on the Earth when an asteroid passes between the star and the Earth is measured. This is a first for telescopes of the type used by VERITAS, and opens up a new window for direct measurement of the size of stars.

Amy Joyce, then an MSc student at NUI Galway was part of the observing crew which measured one of the occultations.  Supported by the Irish Research Council, she is now based at the European Space Agency in Madrid. According to Amy Joyce: “The occultation is like a mini solar eclipse, although it is extremely faint and only lasts a few seconds, VERITAS is an ideal instrument to detect it.”

Dr Mark Lang of the School of Physics, Centre for Astronomy at NUI Galway welcomed the results: “Normally we use VERITAS to observe objects like the supermassive black hole in M87, recently imaged by the Event Horizon Telescope. Now we have shown that VERITAS can make other types of measurements”.

The study was led by Dr Michael Daniel of the Harvard-Smithsonian Center for Astrophysics and Dr Tarek Hassan of DESY, the German high-energy physics institute. The VERITAS collaboration includes colleagues at UCD and Cork IT.

To read the full study on Monday, 15 April at 16:00 London time in Nature Astronomy, visit: https://www.nature.com/articles/s41550-019-0741-z

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