The Central Star of NGC 2346 as a Clue to Binary Evolution through the Common Envelope Phase

TL;DR

This study analyzes the binary central star of NGC 2346 using UV and optical spectra, revealing details about its evolution and supporting the occurrence of a common envelope phase in its history.

Contribution

It provides a comprehensive spectral analysis combining UV and optical data to characterize the binary system and its evolutionary history, especially the common envelope phase.

Findings

Reclassified the companion star as A5IV.

Derived the ionizing star's temperature as 130,000K.

Supported the occurrence of a common envelope phase.

Abstract

We present an analysis of the binary central star of the planetary nebula NGC 2346 based on archival data from the International Ultraviolet Explorer (IUE), and new low- and high-resolution optical spectra (3700 - 7300{\AA}). By including in the spectral analysis the contribution of both stellar and nebular continuum, we reconciled long-time discrepant UV and optical diagnostics and derive $E(B-V)=0.18\pm0.01$. We re-classified the companion star as A5IV by analyzing the wings of the Balmer absorption lines in the high-resolution ($R=67\,000$) optical spectra. Using the distance to the nebula of 1400 pc from Gaia DR2, we constructed a photoionization model based on abundances and line intensities derived from the low-resolution optical spectra, and obtained a temperature of $T_{\rm eff}=130\,000$K and a luminosity $L=170$L$_\odot$ for the ionizing star, consistent with the UV continuum. This analysis allows us to better characterize the binary system's evolution. We conclude that the progenitor star of NGC 2346 has experienced a common envelope phase, in which the companion star has accreted mass and evolved off the main-sequence.