TU Tau B: The Peculiar 'Eclipse' of a possible proto-Barium Giant

TL;DR

This paper reports the unusual eclipse-like dimming of the A-type secondary in the binary system TU Tau, suggesting active accretion of s-process material and potential evolution into a Barium giant, providing insights into stellar evolution.

Contribution

It documents the first observation of a peculiar eclipse in TU Tau and proposes the A-star is accreting material, offering a new perspective on binary star evolution.

Findings

A-star secondary experienced irregular dimming with brief brightenings.

Evidence of active accretion of s-process enriched material by the A-star.

The system offers a unique case to study the evolution into a Barium giant.

Abstract

TU Tau (= HD 38218 = HIP 27135) is a binary system consisting of a C-N carbon star primary and an A-type secondary. We report on new photometry and spectroscopy which tracked the recent disappearance of the A-star secondary. The dimming of the A-star was gradual and irregular, with one or more brief brightenings, implying the presence of nonhomogeneities in the carbon star outflow. We also present evidence that the A-star is actively accreting s-process enriched material from the carbon star and suggest that it will therefore eventually evolve into a Barium giant. This is an important system as well because the A-type star can serve as a probe of the outer atmosphere of the carbon star.