The narrow and moving HeII lines in nova KT Eridani

¹ INAF Osservatorio Astronomico di Padova, 36012 Asiago (VI), Italy
e-mail: ulisse.munari@oapd.inaf.it
² INAF Osservatorio Astronomico di Trieste, 34143 Trieste, Italy
³ ANS Collaboration, c/o Osservatorio Astronomico, 36012 Asiago (VI), Italy

Received: 3 December 2013
Accepted: 28 February 2014

Abstract

We present outburst and quiescence spectra of the classical nova KT Eri and discuss the appearance of a sharp HeII 4686 Å emission line, whose origin is a matter of discussion for those novae that showed a similar component. We suggest that the sharp HeII line, when it first appeared toward the end of the outburst optically thick phase, comes from the wrist of the dumbbell structure characterizing the ejecta. When the ejecta turned optically thin, the already sharp HeII line became two times narrower and originated from the exposed central binary. During the optically thin phase, the HeII line displayed a large change in radial velocity that had no counterpart in the Balmer lines (both their narrow cores and the broad pedestals). The large variability in radial velocity of the HeII line continued well into quiescence, and it remains the strongest emission line observed over the whole optical range.