Periodic Variability of the Barium Central Star of the Planetary Nebula Abell 70

TL;DR

This study reports a 2.061-day periodic variability in the central star of planetary nebula Abell 70, attributed to starspots on a chromospherically active, rapidly rotating companion, revealing insights into binary interactions and stellar activity.

Contribution

First detection of periodic variability in Abell 70's central star, linking it to starspots and rapid rotation in a barium star companion within a planetary nebula.

Findings

Periodic 2.061-day variation observed

Variability amplitude is variable, indicating starspots

Central star's companion is a chemically peculiar, rapidly rotating star

Abstract

Abell 70 is a planetary nebula (PN) whose nucleus at optical wavelengths is a G8 star with enhanced carbon and s-process abundances--a "barium star." The cool star is a binary companion of the true, hot central star. In several other members of this rare class, the cool star is known to rotate with a period of only a few days. This is attributed to a spin-up that occurred due to accretion from the wind of the central star during its post-AGB PN ejection; this also accounts for the unusual chemical composition of the companion's photosphere. We obtained photometry of the central star of Abell 70 on 104 nights in 2010-11, and find a periodic 2.061-day variation, but with a variable amplitude--indicating that the variability is due to starspots on a chromospherically active star. Abell 70 thus joins other members of this class in having a rapidly rotating and chemically peculiar late-type companion of the hot central star.