Episodic Mass Loss from the Hydrogen-Deficient Central Star of the Planetary Nebula Longmore 4

TL;DR

This study reports recurrent episodic mass-loss events from the hydrogen-deficient central star of planetary nebula Longmore 4, occurring roughly every 100 days, likely driven by stellar pulsations, with no similar events observed in a comparable star.

Contribution

First long-term spectroscopic monitoring of Lo 4 reveals recurrent mass-loss episodes and suggests a pulsation-related mechanism, expanding understanding of stellar wind variability in hydrogen-deficient central stars.

Findings

Mass-loss episodes recur approximately every 100 days.

The star is in a high-mass-loss state about 5% of the time.

No similar outbursts observed in the comparison star NGC 246.

Abstract

A spectacular transient mass-loss episode from the extremely hot, hydrogen-deficient central star of the planetary nebula (PN) Longmore 4 was discovered in 1992 by Werner et al. During that event, the star temporarily changed from its normal PG 1159 spectrum to that of an emission-line low-luminosity early-type Wolf-Rayet [WCE] star. After a few days, Lo 4 reverted to its normal, predominantly absorption-line PG 1159 type. To determine whether such events recur, and if so how often, I monitored the optical spectrum of Lo 4 from early 2003 to early 2012. Out of 81 spectra taken at random dates, four of them revealed mass-loss outbursts similar to that seen in 1992. This indicates that the episodes recur approximately every 100 days (if the recurrence rate has been approximately constant and the duration of a typical episode is ~5 days), and that the star is in a high-mass-loss state about 5% of the time. Since the enhanced stellar wind is hydrogen-deficient, it arises from the photosphere and is unlikely to be related to phenomena such as a binary or planetary companion or infalling dust. I speculate on plausible mechanisms for these unique outbursts, including the possibility that they are related to the non-radial GW Vir-type pulsations exhibited by Lo 4. The central star of the PN NGC 246 has stellar parameters similar to those of Lo 4, and it is also a GW Vir-type pulsator with similar pulsation periods. I obtained 167 spectra of NGC 246 between 2003 and 2011, but no mass ejections were found.