Portal de Periódicos da CAPES

Warm water vapour in the sooty outflow from a luminous carbon star

2010; Nature Portfolio; Volume: 467; Issue: 7311 Linguagem: Inglês

10.1038/nature09344

1476-4687

L. Decin, M. Agúndez, M. J. Barlow, F. Daniel, J. Cernicharo, R. Lombaert, E. De Beck, P. Royer, B. Vandenbussche, R. Wesson, E. T. Polehampton, J. A. D. L. Blommaert, W. De Meester, Katrina Exter, H. Feuchtgruber, W. K. Gear, H. L. Gomez, M. A. T. Groenewegen, M. Guélin, Peter Hargrave, R. Huygen, P. Imhof, R. J. Ivison, C. Jean, C. Kahane, F. Kerschbaum, S. J. Leeks, T. Lim, M. Matsuura, G. Olofsson, Th. Posch, S. Regibo, G. Savini, B. Sibthorpe, B. M. Swinyard, J. A. Yates, C. Waelkens,

Astro and Planetary Science

The discovery in 2001 of water vapour around the ageing carbon star IRC+10216 was a surprise, because stellar evolution models predicted the virtual absence of water in carbon-rich stars. Several explanations were offered, but with only one water line detected in the spectrum of one carbon-rich evolved star, it was difficult to discriminate between the alternatives. Now observations with the European Space Agency's Herschel satellite have discovered dozens of water lines in the far-infrared and submillimetre spectrum of IRC+10216. These include high-excitation lines with energies corresponding to temperatures of around 1,000 K, which can be explained only if water is present in the warm inner sooty region of the envelope. Water has been predicted to be almost absent in carbon-rich stars, so the detection of water vapour around the ageing carbon star IRC + 10216 challenged our understanding of the chemistry in old stars. Several explanations for the water have been postulated, but with only one water line detected it is difficult to discriminate between them. Now, dozens of water vapour lines have been detected in the far-infrared and sub-millimetre spectrum of IRC + 10216. The detection1 of circumstellar water vapour around the ageing carbon star IRC +10216 challenged the current understanding of chemistry in old stars, because water was predicted2 to be almost absent in carbon-rich stars. Several explanations for the water were postulated, including the vaporization of icy bodies (comets or dwarf planets) in orbit around the star1, grain surface reactions3, and photochemistry in the outer circumstellar envelope4. With a single water line detected so far from this one carbon-rich evolved star, it is difficult to discriminate between the different mechanisms proposed. Here we report the detection of dozens of water vapour lines in the far-infrared and sub-millimetre spectrum of IRC +10216 using the Herschel satellite5. This includes some high-excitation lines with energies corresponding to ∼1,000 K, which can be explained only if water is present in the warm inner sooty region of the envelope. A plausible explanation for the warm water appears to be the penetration of ultraviolet photons deep into a clumpy circumstellar envelope. This mechanism also triggers the formation of other molecules, such as ammonia, whose observed abundances6 are much higher than hitherto predicted7.