The Pickering series ( also known as the Pickering–Fowler series ) consists of three lines of singly ionized helium found , usually in absorption , in the spectra of hot stars like Wolf–Rayet stars .
DET PROPN NOUN ( ADV VERB ADP DET NOUN NOUN ) VERB ADP NUM NOUN ADP ADV VERB NOUN VERB , ADV ADP NOUN , ADP DET NOUN ADP ADJ NOUN ADP PROPN NOUN .