A Survey for C II Emission-Line Stars in the Large Magellanic Cloud. II. Final Results and the Origin of C II Emission in [WC] Spectra

TL;DR

This survey identifies and analyzes C II emission-line stars in the Large Magellanic Cloud, clarifying their origins and spectral characteristics, and providing insights into their classification and physical mechanisms.

Contribution

It offers the final results of a comprehensive search for C II emission-line stars in the LMC, revealing the origin of C II emission and distinguishing between stellar wind and nebular sources.

Findings

Identification of new [WC11] stars in the LMC.

C II emission originates from either stellar wind or surrounding nebula.

Spectral features enable future detailed modeling.

Abstract

We present the final results of an imaging and spectroscopic search for stars in the Large Magellanic Cloud (LMC) with C II 7231, 7236 emission lines. The goal is to identify and study [WC11] stars, the coolest of the low-mass Wolf-Rayet sequence, and a subset of central stars of planetary nebulae where the C II lines are known to be especially prominent. A recent serendipitous discovery of an LMC [WC11] raised the possibility that these objects, although difficult to identify, might in fact be more common than previously believed. Several new members of this rare class have been found in this survey. It now seems clear, however, that a significant number of these stars are not hiding amongst the general [WC] population. We point out that the C II doublet intensity ratio observed in our spectra proves to neatly divide the objects into two distinct groups, with the C II emission likely originating from either the stellar wind or a surrounding nebula. The physics of the C II emission mechanism correctly explains this bifurcation. Spectral subtypes are suggested for most of the objects. The numerous spectroscopic clues now available for these objects should facilitate future detailed modeling.