Salty brown dwarfs

I like American Scientist magazine very much. Somehow it just seems to carry the mix of articles I want.

However there was a curious error discussed in the letters column of the November-December 2013 issue.

The distinguished chemist, Roald Hoffmann, had remarked in an earlier issue that “the surface or interior of a star … is boring – there are no molecules there.” But a correspondent replied that the photosphere (surface) of our sun is a relatively “cool” 6,000 degrees kelvin, cool enough for molecular species to exist.

Hoffmann replied, agreeing that there is evidence for water (H2O) on the sun and H2 in white dwarf atmospheres.

However there is more out there of interest than Professor Hoffmann mentioned. If brown dwarfs are considered, there are a LOT of chemical species in their atmospheres, which are at about 2,000 degrees kelvin for the L class.

To take just one example, a volume in the Cambridge Contemporary Astrophysics series notes that “The lithium is eventually removed into molecules like LiCl (the brown dwarfs begin to be salty) somewhere at the cool end of the L sequence or cooler.”

“Artist’s vision of an L-dwarf”

#####################################################3L-dwarf-nasa-hurt

One could argue that brown dwarfs are not strictly stars. On the other hand, according to this article “Main-sequence stars vary in surface temperature from approximately 2,000 to 50,000 kelvin …” So, presumably some stars by this definition are as cool as brown dwarfs and might have equally interesting chemistry on their surfaces.

Also, sunspots are relatively cool being at about 3,000 K. Some information on the molecular lines seen in the spectra from sunspots and starspots is found here. One molecule observed in both sunspots and brown dwarfs is TiO. It would be interesting to make a general comparison of the chemistry of sunspots and brown dwarfs.

###############################ar1944_alean_mg_6384h900

Image with description of the sunspot here.

Roald Hoffmann won the Nobel Prize in Chemistry in 1981. Curiously his erroneous view is given as a statement in his Wikipedia article, although the error is corrected at this other Wikipedia article.

ADDENDUM: An interesting question is whether solar ejecta, which as Hoffmann notes contains molecules “in abundance”, could have reached the earth in the past, from the sun or from a nearby supernova.

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