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.