NSV 11749: Symbiotic Nova, Not a Born-Again Red Giant

TL;DR

NSV 11749, previously thought to be a born-again red giant, is actually a symbiotic binary with a nova outburst, challenging prior classifications and expanding understanding of such stellar phenomena.

Contribution

The paper reclassifies NSV 11749 as a symbiotic nova, providing new spectral evidence that contradicts earlier born-again red giant hypotheses.

Findings

Spectral analysis shows strong emission lines and a cool red giant companion.

The 1903 outburst was a symbiotic nova event, not a final helium shell flash.

NSV 11749 is only the fourth known symbiotic nova with such a long outburst history.

Abstract

NSV 11749 is a little-studied variable star, discovered by W. J. Luyten, which had a long-duration outburst around the year 1903, reaching blue magnitude 12.5 at maximum. Following the outburst, it has apparently been quiescent at about blue magnitude 17 for the past century. It was recently suggested that NSV 11749 may have been a low- or intermediate-mass star that underwent a final helium shell flash, making it temporarily a "born-again" red giant. If so, it would be only the fourth known member of this class, along with V605 Aql, FG Sge, and V4334 Sgr. However, our newly obtained optical and near-IR spectra of the object show that it is instead a symbiotic binary, with strong Balmer and He I-II emission lines, combined with a cool red-giant companion of spectral type M1-2 III. The 1903 outburst was most likely a symbiotic nova event, of which less than a dozen are known at present.