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Astronomers observe mysterious winds from a T Tauri star

Artist impression of the T Tauri star AS 205 N and its companion. New ALMA data suggest that the disk around the star may be expelling gas via a wind. Credit: P. Marenfeld (NOAO/AURA/NSF)
Artist’s impression of the T Tauri star AS 205 N and its companion. Scientists now believe the planet-forming disk in this very young solar system may be expelling gas via a wind. Illustration via P. Marenfeld/ NOAO/AURA/NSF

Astronomers using the ALMA telescope in Chile have observed what they say may be the first-ever signs of winds around a T Tauri star. That’s a star that is an infant version of our own sun. These winds might help explain why some T Tauri stars have disks that glow weirdly in infrared light while others shine in a way that’s more expected.

T Tauri stars are a class of variable stars, named for their prototype T Tauri, discovered in 1852. T Tauri stars have been known for decades as relatively normal, medium-sized, extremely young main-sequence stars. At one point, some 4.5 billion years ago, our Sun was a T Tauri star. T Tauri stars are thought to be surrounded by protoplanetary disks, containing the raw materials to build both rocky and gaseous planets. Though nearly invisible in optical light, these disks shine in both infrared and millimeter-wavelength light.

Some T Tauri stars emit infrared radiation in unexpected ways. Those stars were the focus of this study, led by astronomer Colette Salyk at the National Optical Astronomical Observatory (NOAO) in Tucson, Arizona. Many T Tauri stars have been thought to have extremely powerful stellar winds – predicted by astronomers, but never clearly detected – and Salyk and her team proposed that, for some T Tauri stars, the winds may be emanating from within the stars’ protoplanetary disks. They say these winds could have important implications for planet formation, potentially robbing the disk of some of the gas required for the formation of giant Jupiter-like planets, or stirring up the disk and causing the building blocks of planets to change location entirely.

Salyk and her colleagues used the ALMA telescope (Atacama Large Millimeter/submillimeter Array) in Chile to look for evidence of a possible wind in the star known as AS 205 N. This T Tauri star is located 407 light-years away at the edge of a star-forming region located in the direction of the constellation Ophiuchus the Snake Bearer. This star seems to exhibit the strange infrared signature that has intrigued astronomers.

ALMA is a relatively new telescope, with exceptional resolution and sensitivity. Using this telescope, the researchers were able to study the distribution of carbon monoxide around the star. Carbon monoxide is an excellent tracer for the molecular gas that makes up stars and their planet-forming disks. These studies confirmed that there was indeed gas leaving the disk’s surface, as would be expected if a wind were present. The properties of the wind, however, did not exactly match expectations.

This difference between observations and expectations could be due to the fact that AS 205 N is actually part of a multiple star system. The companion has been dubbed AS 205 S. It is itself a binary star.

This multiple star arrangement may suggest that the gas is leaving the disk’s surface because it’s being pulled away by the binary companion star rather than ejected by a wind. Salyk said:

We are hoping these new ALMA observations help us better understand winds, but they have also left us with a new mystery. Are we seeing winds, or interactions with the companion star?

The study’s authors are not pessimistic, however. They plan to continue their research with more ALMA observations, targeting other unusual T Tauri stars, with and without companions, to see whether they show these same features.

Bottom line: T Tauri stars – infant solar systems – have been known for decades and many have been predicted to have extremely powerful stellar winds. Now astronomers using the ALMA telescope in Chile say they’ve observed T Tauri winds in the star system AS 205 N, and they are speculating on the source of the winds.

Read more about the new research on T Tauri stars from NRAO

September 24, 2014
Science Wire

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