CFHT, Current Image of the Week


June 19th, 2000

The Young and Active DG Tauri

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The Young and Active DG Tauri

Credit: CFH12k: all the Astronomers at CFHT; PUEO: C.Dougados1,3, S.Cabrit2, C.Lavalley3

1 Canada-France-Hawaii Telescope
2 DEMIRM, Observatoire de Paris, France
3 Laboratoire d'Astrophysique de l'Observatoire de Grenoble France

(for more details on the insert see: Dougados et al. 2000, Astronomy & Astrophysics Letters, Vol. 357, p.L61-L64)

Stars come in a variety of flavors: from young to old, and from well-behaved to bad-tempered. As for many humans, stars in their youth exhibit many contradictory and exhuberant behaviours that are inherent to their formation process.

This week's image features DG Tauri, a 2 million year old star that is currently forming in a large molecular cloud located in the constellation Taurus. To gather enough material to reach its "adult" mass, a star must accrete dust and gas from the nearby medium. That's common sense! Starting from nothing, the star has to grow by accreting from its neighbourhood. Signatures of this process are well identified in the so-called T Tauri stars, a group of young solar-like stars to which DG Tauri belongs.

Contradictory to this picture of mass accretion, many young stars also lose mass at the same time, sometimes dramatically. Astronomers can witness and study a fine example of this dual phenomenon of simultaneous mass loss and mass accretion in DG Tauri. This week's featured images were obtained with two of CFHT's leading instruments: CFH12k, the prime focus wide-field imager, and PUEO, the high resolution adaptive optics imager. On the large scale CFH12k image (at top right), DG Tauri is visible, together with its surrounding nebulosity and jet outflow. DG Tauri is actually hidden inside the bright red spot, together with a jet (seen in the insert). These and other features of the DG Tauri environement are identified here.

At the bottom of this image, DG Tauri B, the young companion of DG Tauri is also showing signs of mass loss! Indeed, a fine streak of material, a bipolar jet, is also clearly visible on both sides of a zone apparently devoid of material. In reality, DG Tauri B is hidden inside , in a dust cocoon dense enough to make the star invisible in this wavelength range.

A closer view of the inner parts of DG Tauri, close to the base of the arrows, is presented in the insert, at bottom left. This high resolution image shows details of the ionised outflow close to the star. The stellar position is indicated by the cross and a large emission knot, tracing emission of a shock as the outflow rams into previously ejected material, is seen at two different epochs. Clearly the shock front is moving outward with a large velocity (200 km/s). Another strong shock is also seen farther out in the CFH12k image, to the lower-right of DG Tauri. The presence of such strong shocks within the outflow is interpreted as signs of variability in the ejection process.

Technical description:

The wide-field image of DG Tauri and DG Tauri B is presented here for the first time. It was obtained during a survey of Taurus cloud by the Astronomers of the CFHT corporation. The image was obtained in a filter centered on the Hydrogen H-alpha line. This emission line is a good tracer of shock emission and a powerful tool to seearch for mass loss. Exposure time was 20 minutes in this single image obtained in January 2000.

The insert images were obtained with the PUEO adaptive optics systems in January 1997 and TIGER imaging spectrograph in November 1994. The images were obtained in a forbidden emission line of Oxygen centered at 630nm in both cases. Exposure time were typically 20 minutes with PUEO.

next week: To be announced shortly

editors: François Ménard & Jean-Charles Cuillandre
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