CFHT, Current Image of the Week


January 3rd, 2000

Spectacular Mass Loss Events in Young Stars

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Spectacular Mass Loss Events in Young Stars
Credit: Image courtesy of C. Dougados ¹², S. Cabrit ³, C. Lavalley ² & F. Ménard ¹

¹Canada-France-Hawaii Telescope Corporation
²Observatoire de Grenoble, France
³ DEMIRM, Observatoire de Paris, France

Stars form from the collapse, because of gravity, of molecular clouds. Dust and gas gradually accumulate in the center until the proto-stars get big enough and their internal temperature rises to millions of degrees, at which point nuclear fusion ignites, and a star is born.

In that process, the initial proto-star must acquire mass. It does so by accreting material from the nearby molecular. Before being "swallowed" by the star, a large fraction of the material transits via an accretion disk. Surprisingly, astronomer also found, about 15 years ago, that the accretion process is also very often coupled to the opposite process, ejection of mass. Stellar Duality? Nowadyas, theoretical models suggest that accretion actually cannot proceed without the help of mass loss to carry away angular momentum. Without both processes at work at the same time during the early phases of its evolution, a star would spin-up to so large velocities that it would spontaneously break-up! The image presented here shows the spectacular jet, a beam of ionised material,flowing out of RW Aurigae. RW Aur is a young star located in Taurus still in the early phases of its evolution. It is also a triple system. RW Aur A is the source of the collimated mass loss. RW Aur B is itself a binary (it should be named RW Aur BC really!), but the two objects are too close to be seen here. The mass loss associated to RW Aur A is seen in the form of a long streak of luminosity flowing in diagonal on this image. We are seeing the emission of the ejected material as it gets shocked and heated by ramming into the ambient cloud as it moves away from the star (located by the + sign).

Images like this one allow us to study the structure of the outflows and better understand the origin of the mass loss. In particular, the size of the jets, their morphology and also kinematics when coupled with spectroscopy are important. For example, in this image of RW Aur the jet appears knotty, having a non uniform brightness along its axis. See this image for a better view. But other outflows are also observed that look slightly different. See for example the images of the jets associated to two other young stars: DG Tau and CW Tau here.

Technical description: These images were obtained on January and December, 1997, with PUEO, the adaptative Optics Bonnette, attached to the Canada-France-Hawaii telescope. The images were obtained in the optical part of the electromagnetic spectrum, with the help of the FOCAM camera. Narrow filters centered on the wavelengths of emission lines typically found in stellar jets were used (i.e. an Oxygen line [OI]6300A, and a sulfur line [SII]6735A). Images in the adjacent continuum were also obtained and subtracted to isolate the pure emission from the jet. RW Aur, DG Tau and CW Tau are all located in the Taurus molecular cloud complex, about 450 light years away.

next week: A Close Look at ARP 299

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.