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Published on 22 June 2018
Vol. 614
In section 6. Interstellar and circumstellar matter
Interstellar bromine abundance is consistent with cometary ices from Rosetta
by N.F.W. Ligterink and M. Kama, A&A 614, A112
This paper presents a unique, intriguing study of the abundance of a
rare halogen, bromine, in the gas phase by the Rosetta mission in
comet 67P/Churyumov-Gerasimenko. Obtaining the abundance of rare heavy elements
has been a challenge for interstellar medium studies for decades and untill now, it has not been possible to measure this
element in the diffuse gas phase. For comet 67P, the detection of HBr and the
measured elemental ratio Br/O = (1 − 7) × 10^−6 is
consistent with the ratios found for its cousin
Cl (for which the Br/Cl ratio is consistent with terrestrial values), and consistent with all of the Br
being sequestered in cometary ice mantles. The derived abundances are
compared with upper limits for HBr and HBr^+ from infrared spectra of
several star forming regions and employ chemical network modeling to
understand the molecular abundances. This study represents the first
direct measurement of the bromine abundance in a cosmic environment
other than meteorites.