The interest in interstellar carbon-rich molecules is again increasing, which may may have some astrobiological import. New mid-infrared data, from Spitzer, will open up the field. I once searched for evidence of the diffuse band carriers in optical spectra, taken towards a thick disk F-star seen through the circumstellar envelope of the extreme carbon star IRC+10 216 (CW Leonis). It’s only 140 light years away, and if anything is belching out carbon – in whatever form – this should be it.

But not according to my VLT spectrum, which showed no evidence of DIB absorptions. I remember trying first at the WHT (4 metre) with UES trying to get a high resolution spectrum of the V~16 target. Took all night – 6 hours of integration –  for a signal to noise ratio of roughly one! Not the WHT’s fault…just too faint! But a year later the VLT and UVES came up with the goods – S/N ~ 100, and the origin – the carrier molecules – of the diffuse interstellar bands remains a mystery. Only the strong band at 6283 Angstroms was detected and that only with an equivalent width commensurate with the intervening interstellar medium.

What does seem clear, though, is that the interstellar medium is full of gas, dust, all the remnants from the end of stellar evolution, which wind up back in star-forming regions where a new generation of stars – and planetary systems – are being born.

For the full peer-reviewed article see here.


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