On the narrow emission line components of the LMC novae 2004 (YY Dor) and 2009a

TL;DR

This study analyzes the spectral line profiles of two LMC novae, revealing that narrow emission components originate in the ejecta and suggesting a separate, environmentally distinct line-forming region, with implications for nova structure understanding.

Contribution

It provides new insights into the origin of narrow emission lines in LMC novae, proposing a physical separation from the broad line region based on spectral evolution.

Findings

Narrow emission lines originate in the ejecta.

HeII 4686 A narrow emission appears at the nebular phase.

The line-forming region is likely physically separated from the ejecta.

Abstract

We present early decline spectra of the two Large Magellanic Cloud novae: LMC 2004 (YY Dor) and LMC 2009a and discuss their spectral an line profile evolution with special emphasis on the existence and appearance of a sharp component. We show that the narrow component that characterizes the emission lines in the maximum spectra of nova LMC 2004 originates in the ejecta. The HeII 4686 A, narrow emission which appears at the onset of the nebular phase in both novae is somewhat controversial. Our observations suggest that the corresponding line forming region is physically separated from the rest of the ejecta (the broad line region) and environmentally different. However, the lack of late time observations covering the super-soft source (SSS) phase, the post-SSS phase and the quiescence state does not allow to securely establish any non-ejecta origin/contribution as, instead, in the case of U Sco and KT Eri.