WELS - Ultraviolet Spectra and Expanding Atmosphere Models

TL;DR

This paper analyzes ultraviolet spectra of WELS stars, classifies them into groups based on P-Cygni profiles, measures wind velocities, compares them with [WC]-PG 1159 stars, and presents initial non-LTE atmosphere models for Hen 2-12.

Contribution

It provides a new classification of WELS stars based on UV spectral features and introduces the first non-LTE expanding atmosphere models for Hen 2-12.

Findings

WELS can be divided into three UV spectral groups.

WELS are distinct from [WC]-PG 1159 stars.

Initial non-LTE models for Hen 2-12 are presented.

Abstract

The ultraviolet spectra of all "weak emission line central stars of planetary nebulae" (WELS) with available IUE data is analyzed. We found that the WELS can be divided in three different groups regarding their UV: (1) Strong P-Cygni profiles (mainly in C IV 1549); (2) Weak P-Cygni features and (3) Absence of P-Cygni profiles. We have measured wind terminal velocities for all objects presenting P-Cygni profiles in N V 1238 and/or C IV 1549. The results obtained were compared to the UV data of the two prototype stars of the [WC]-PG 1159 class, namely, A30 and A78. They indicate that WELS are distinct from the [WC]-PG 1159 stars, in contrast to previous claims in the literature. In order to gain a better understanding about the WELS, we clearly need to determine their physical parameters and chemical abundances. First non LTE expanding atmosphere models (using the CMFGEN code) for the UV and optical spectra of the star Hen 2-12 are presented.