Detection of forbidden line components of lithium-like carbon in stellar spectra

TL;DR

This paper reports the first astrophysical detection of forbidden line components from triply ionized carbon in the ultraviolet spectra of hot white dwarfs, expanding the understanding of forbidden lines beyond laboratory observations.

Contribution

It identifies forbidden line components of C IV in stellar spectra, a first in astrophysics, previously observed only in laboratory plasmas.

Findings

Forbidden C IV lines are visible in hot white dwarf spectra.

These lines appear in the wings of strong Stark-broadened lines.

Detected over a temperature range of 60,000-200,000 K.

Abstract

We report the first identification of forbidden line components from an element heavier than helium in the spectrum of astrophysical plasmas. As yet, these components were identified only in laboratory plasmas and not in astrophysical objects. Forbidden components are well known for neutral helium lines in hot stars, particularly in helium-rich post-AGB stars and white dwarfs. We discovered that two hitherto unidentified lines in the ultraviolet spectra of hot hydrogen-deficient (pre-) white dwarfs can be identified as forbidden line components of triply ionized carbon (C IV). The forbidden components (3p-4f and 3d-4d) appear in the blue and red wings of the strong, Stark broadened 3p-4d and 3d-4f lines at 1108 Angstroem and 1169 Angstroem, respectively. They are visible over a wide effective temperature range (60,000-200,000 K) in helium-rich (DO) white dwarfs and PG1159 stars that have strongly oversolar carbon abundances.