NATURE|Vol 447|28 June 2007 NEWS & VIEWS ASTRONOMY as a result of the Doppler effect, Ziurys et al. were also able to derive the kinematic struc- tures of the different components of the winds A new molecular factory from the emission profiles of lines. Imaging of Sun Kwok VY CMa by the Hubble Space Telescope has shown that the winds have complicated Carbon-rich stars are known to be prolific producers of molecules. Against morphologies (Fig. 1), and the origin of the expectations, astronomers have identified an old, oxygen-rich star that can different molecules can be traced to different morphological features3. So these observations also synthesize a chemically varied molecular cocktail. can also be used as probes to help elucidate the physics of the winds. For 30 years, astronomers’ favourite star in Our interest in old stars is not confined to the search for molecules was a nearby, old, the molecules they may be producing. In the carbon-rich star called CW Leo. This star gas phase, molecules are in turn believed to be produces such a variety of molecules that it the building-blocks of more complex inorganic constitutes a veritable ‘molecular factory’. On and organic solids that consist of hundreds of page 1094 of this issue, Ziurys et al.1 describe atoms. These solids have been detected by how they have discovered another stellar infrared spectroscopy through their vibrational molecular factory that is almost as prolific. modes. Planetary nebulae, the descendants of VY Canis Majoris (VY CMa) is a cool, old old red-giant stars such as CW Leo, have been star like CW Leo, and like CW Leo it is in our seen to contain carbonaceous compounds Galactic neighbourhood. But it is different in with both ring and chain structures typical of one crucial respect: it is rich in oxygen. Appar- complex organic substances4. The detection ently, then, oxygen-rich stars can also produce of additional gas-phase molecules will help a wide variety of molecules when they are near us draw a more complete picture of chemical the ends of their lives. synthesis in stars. Most people think of stars as sources of light. Ziurys and colleagues’ report1 shows that But since the early 1970s, and the development there is much more to be learnt about the use of infrared and microwave astronomy, stars of old stars as laboratories for studying inter- have also proved to be sources of matter. We stellar chemistry. How do these stars manage now know that old stars generate strong stellar to make complex molecules in the extreme Figure 1 | Stellar performance. This colour- winds that eject material from the parent star composite picture of VY CMa consists of low-density environment? Do physical shocks, into interstellar space. Because many heavy separate images, taken in blue, green, red radiation or even grain-surface chemistry con- elements are synthesized by nuclear processes and near-infrared light, obtained with the tribute to the molecular-formation process? in the interior of old stars, stellar winds are a Hubble Space Telescope (HST) Wide Field and What chemical pathways lead from the simple major avenue for feeding those elements into Planetary Camera 2. The image reveals complex gas-phase molecules to complex organic the interstellar medium. circumstellar ejecta, with arcs, filaments and solids? And what roles do these molecules have What kinds of matter are in the stellar winds? knots of material formed by the massive outflows in the enrichment of the Galaxy and maybe 1 In addition to atomic nuclei, it turns out that created during several outbursts. As Ziurys et al. even the early Solar System? Such questions the stellar winds have very rich chemical con- recount, the observed emission from different have broad implications beyond astronomy molecular species can be traced to the different tents. Spectroscopic observations at millimetre and chemistry — winds from old stars will optical features. (Composite image created from and submillimetre wavelengths have resulted HST data taken by R. Humphreys.) be an enticing target of observations for some in the detection of more than 60 types of mol- time to come. ■ ecule. These include inorganic molecules (for Sun Kwok is in the Department of Physics, example, CO, SiO, SiS, NH3, AlCl), organic of molecules is striking as well. Among the University of Hong Kong, Pokfulam, Hong Kong. molecules (C2H2, CH4, H2CO, CH3CN), seven are molecules containing sulphur (NS), e-mail: [email protected] + radicals (CN, C2H, C3, HCO ), rings (C3H2) phosphorus (PN), silicon (SiS) and even met- 2 1. Ziurys, L. M., Milam, S. N., Apponi, A. J. & Woolf, N. J. and chains (HC5N, HC7N) . The winds are dis- als (NaCl, or salt). Phosphorus is of particular Nature 447, 1094–1097 (2007). persing fast, so the formation processes must interest because this element has an essential 2. Olofsson, H. in Molecules in Astrophysics: Probes and take place on timescales as short as hundreds role in the biochemistry of life, in spite of its Processes IAU Symp. 178 (ed. Van Dishoeck, E.) 457–468 (Kluwer, Dordrecht, 1997). of years. low abundance in the cosmos. The authors’ dis- 3. Humphreys, R. M., Helton, L. A. & Jones, T. J. Astron. J. 133, Conventional wisdom suggests that if oxy- covery also reveals unexpected physical com- 2716–2729 (2007). gen is more abundant than carbon, most of the plexity. They found the molecular ion HCO+, 4. Kwok, S. Nature 430, 985–991 (2004). carbon atoms in the wind of VY CMa should even though it is not expected to be present in be locked up in the CO molecule, a simple the low-temperature, neutral environment of and stable molecular species that forms in a cool star. Robert Cahn (1924–2007) the atmosphere of the star. Given the lack of The molecules in VY CMa were identified Robert Cahn, who died on 9 April 2007, was available carbon atoms, an oxygen-rich star is through their rotational transitions. When a a much-valued and prolific contributor to not expected to have the chemical versatility molecule decays to a lower rotational state, Nature, and to News & Views in particular. His of a carbon-rich star and is therefore much having been excited by collisions or radiation articles first appeared in the mid-1960s, and less likely to have a chemically rich molecular to a higher rotational state, it emits microwaves ranged widely across the discipline of materi- content. at specific wavelengths. Modern spectrometers als science. The July issue of Nature Materials So it comes as a surprise that Ziurys et al.1 can have high spectral resolution, so different includes a full obituary by A. Lindsay Greer, announce seven newly discovered molecules molecular species can be uniquely identified which is freely available at http://dx.doi. in the stellar wind of VY CMa. Not only is by the wavelengths of the observed spectral org/10.1038/nmat1941 the production of these increased numbers lines. Because the observed line wavelengths Editor, News & Views of molecules a feat in itself1, but the variety are shifted by the velocities of the emitting gas, 1063.