New Water Opacity for Cool Stars
Bob Barber
Water is the third most common molecule in the universe and
its spectrum is particularly rich. H2O is the principal source of
opacity in M, L and T dwarfs where it may account for in excess of 60% of
absorption in the IR.
Only a very small proportion of the lines in the water spectrum are known
experimentally and consequently all model atmospheres and much
spectroscopic work depend on line lists that have been generated ab initio
using quantum mechanical modelling.
None of the earlier line lists has been accurate enough to allow accurate
modelling of stellar atmospheres. In addition, the new generation of IR
telescopes will require a spectroscopically accurate line list.
We have produced a new line list which contains approx. 620 million
transitions (more than twice the number in earlier lists). Moreover,
the BT1 list sets new standards in accuracy as the calculations utilise
superior physics. This list is being employed in new spectral analyses
and models of M dwarfs and giants, brown dwarfs, and comets.