Archivi tag: binary stars

Living Together: Planets, Host Stars and Binaries

The scientific meeting will be organized in the city of Litomyšl, Czech Republic, on the week of September 8 – 12, 2014. The city will be honouring Zdenek Kopal, one of the foremost investigators of binary stars who was born in this city in 1914. A similar, smaller-scale conference in the same city took place in 2004 (http://var.astro.cz/kopal/). Continua a leggere Living Together: Planets, Host Stars and Binaries

KASC-6: A new era of stellar astrophysics with Kepler

KASC-6, the 6th Kepler Asteroseismic Science Consortium Conference, will take place in Sydney, Australia, in June 2013. It will be the first KASC conference after all Kepler data became public in 2012 — marking a new era in science with Kepler. We therefore welcome everyone to attend KASC-6, both members and non-members of KASC, who are interested in the stellar astrophysics that we can investigate with Kepler data. The main themes of the conference will be Stellar structure and evolution using asteroseismology, Stellar activity and rotation, Binary stars, and connections to Extrasolar planets. This conference offers great opportunities to establish new collaborations in these scientific fields, which are currently experiencing dramatic progress driven by the vast amounts of exquisite photometric data from space missions like Kepler.

Measuring the Universe More Accurately Than Ever Before

After nearly a decade of careful observations an international team of astronomers has measured the distance to our neighbouring galaxy, the Large Magellanic Cloud, more accurately than ever before. This new measurement also improves our knowledge of the rate of expansion of the Universe, the Hubble constant, and is a crucial step towards understanding the nature of the mysterious dark energy that is causing the expansion to accelerate. The team used telescopes at ESO’s La Silla Observatory in Chile as well as others around the globe. These results appear in the 7 March 2013 issue of the journal Nature.

Astronomers survey the scale of the Universe by first measuring the distances to close-by objects and then using them as standard candles to pin down distances further and further out into the cosmos. But this chain is only as accurate as its weakest link. Up to now finding an accurate distance to the Large Magellanic Cloud (LMC), one of the nearest galaxies to the Milky Way, has proved elusive. As stars in this galaxy are used to fix the distance scale for more remote galaxies, it is crucially important. But careful observations of a rare class of double star have now allowed a team of astronomers to deduce a much more precise value for the LMC distance: 163 000 light-years. “I am very excited because astronomers have been trying for a hundred years to accurately measure the distance to the Large Magellanic Cloud, and it has proved to be extremely difficult,” says Wolfgang Gieren (Universidad de Concepción, Chile) and one of the leaders of the team. “Now we have solved this problem by demonstrably having a result accurate to 2%.” The improvement in the measurement of the distance to the Large Magellanic Cloud also gives better distances for many Cepheid variable stars. These bright pulsating stars are used as standard candles to measure distances out to more remote galaxies and to determine the expansion rate of the Universe, the Hubble constant. This in turn is the basis for surveying the Universe out to the most distant galaxies that can be seen with current telescopes. So the more accurate distance to the Large Magellanic Cloud immediately reduces the inaccuracy in current measurements of cosmological distances. The astronomers worked out the distance to the Large Magellanic Cloud by observing rare close pairs of stars, known as eclipsing binaries. As these stars orbit each other they pass in front of each other. When this happens, as seen from Earth, the total brightness drops, both when one star passes in front of the other and, by a different amount, when it passes behind. By tracking these changes in brightness very carefully, and also measuring the stars’ orbital speeds, it is possible to work out how big the stars are, their masses and other information about their orbits. When this is combined with careful measurements of the total brightness and colours of the stars remarkably accurate distances can be found. This method has been used before, but with hot stars. However, certain assumptions have to be made in this case and such distances are not as accurate as is desirable. But now, for the first time, eight extremely rare eclipsing binaries where both stars are cooler red giant stars have been identified. These stars have been studied very carefully and yield much more accurate distance values — accurate to about 2%. “ESO provided the perfect suite of telescopes and instruments for the observations needed for this project: HARPS for extremely accurate radial velocities of relatively faint stars, and SOFI for precise measurements of how bright the stars appeared in the infrared,” adds Grzegorz Pietrzyński (Universidad de Concepción, Chile and Warsaw University Observatory, Poland), lead author of the new paper in Nature. “We are working to improve our method still further and hope to have a 1% LMC distance in a very few years from now. This has far-reaching consequences not only for cosmology, but for many fields of astrophysics,” concludes Dariusz Graczyk, the second author on the new Nature paper.

ESO: Measuring the Universe More Accurately Than Ever Before
Research paper in Nature: An eclipsing binary distance to the Large Magellanic Cloud accurate to 2 per cent

1st Doha International Astronomy Conference: “Gravitational Microlensing – 101 years from theory to practice”

1st Doha International Astronomy Conference: “Gravitational Microlensing – 101 years from theory to practice” – 2013 marks the 101st anniversary of Einstein’s notebook entry in which he first discussed the transient brightening of an observed distant star caused by the bending of light due to the gravitational field of an intervening foreground star – a phenomenon now commonly known as ‘gravitational microlensing’. Continua a leggere 1st Doha International Astronomy Conference: “Gravitational Microlensing – 101 years from theory to practice”