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May 29th, 2000

T Tauri: A Prototype for Star Formation?

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T Tauri: A Prototype for Star Formation?

Credit: Image courtesy of C. and F. Roddier
Institute for Astronomy, Honolulu, Hawaii

(for more details see: C. Roddier, F. Roddier, J.E. Graves, et al. 1998, Proceedings of the ESO/OSA Topical Meeting on Astronomy with Adaptive Optics (ed., D. Bonaccini, ESO), pp. 389-399.

Stars form out of the gravitational collapse of large clouds of interstellar gas and dust. Originally very tenuous, the density of these clouds increases as they contract and a central star builds-up. As a consequence, the temperature at the center also increases as pressure goes up. After a while, many thousands of years actually, the temperature in the central protostar gets high enough that the "baby star" starts shining by itself. This is pretty much like a metal rod that "glows" red after being heated enough. At that stage, the original cloud of material as also dissipated, it becomes transparent. Most of it has been accreted by the star itself and the central object finally becomes visible to our telescopes. A star is born.

The first young stars were identified by Alfred Joy in 1945. He classified 11 objects into a new class he called the "T-Tauri Stars", after the brightest of the 11 peculiar stars he had just found, T Tauri. Since then, the name T Tauri stars has always been associated with newborn stars. We now know that these objects are very similar to what our own sun must have looked like when it was a few million years old only. By comparison our sun, in its midlife today, is about 5 billion years old, a thousand times older. A few thousands of T Tauri stars have been discovered to date.

This week's image provides a close view of T Tauri itself. As can be seen, T Tauri and its close environment are much more complicated than what is expected from the simplified scenario described above. First of all T Tauri is not single, it is a binary system. Two stars can be seen on the image, they are indicated more clearly here. The companion, T Tauri South, was detected in the near infrared J-band for the first time by the authors. It is the discovery image we present this week.

Circumstellar material, dust particles close to the stars that scatter light, is also visible as the extended Halo. It is a mixture of material leftover from the original cloud that gave birth to T Tauri (at large scale) and from material ejected by the stars as they formed (at small scales). The latter process is known as mass-loss, or "stellar winds". Our Sun looses material too, but at a much lower rate than the T Tauri stars do. It is this "wind" from the Sun that is responsible for the Northern light for example.

This week's images show us that T Tauri, and by analogy the whole star formation process, is very complicated. There is still a number of issues we just don't understand yet. Because our Sun and planetary system are most likely the outcome of the same process, it is mandatory that studies like the one presented this week be carried out if we hope to understand our origins one day.

Technical description:

This week's image is part of a series of images obtained at the Canada-France-Hawaii Telescope with adaptive optics since 1993 to monitor the evolution of the complicated T Tauri system. Different AO systems developed by the University of Hawaii adaptive optics group were used. Images were obtained mostly in the near-infrared, at 1.25, 1.65 and 2.2 microns, the so-called J-, H- and K-bands respectively. On all the images, North is up and East to the left, as we see in the sky.

next week: The CFHT Open Cluster Survey : NGC 2099

editors: François Ménard & Jean-Charles Cuillandre
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CFHT is funded by the Governments of Canada and France, and by the University of Hawaii.