<i>Herschel</i>/HIFI deepens the circumstellar NH<sub>3</sub>enigma
<i>Herschel</i>/HIFI deepens the circumstellar NH<sub>3</sub>enigma
Circumstellar envelopes (CSEs) of a variety of evolved stars have been found to contain ammonia (NH3) in amounts that exceed predictions from conventional chemical models by many orders of magnitude. The observations reported here were performed in order to better constrain the NH3 abundance in the CSEs of four, quite …