Resonant temperature fluctuations in nebulae ionized by short-period binary stars

TL;DR

This paper proposes that short-period binary stars induce resonant temperature fluctuations in nebulae, explaining observed ionic abundance discrepancies and providing a diagnostic tool for measuring these fluctuations.

Contribution

It demonstrates that periodic ionizing radiation from binary stars causes resonant temperature oscillations in nebulae, a novel explanation for temperature fluctuation phenomena.

Findings

Resonant temperature oscillations can significantly increase in nebulae with short-period binary stars.

A diagnostic plot combining line ratios effectively measures equilibrium and fluctuation temperatures.

Application to M 1-42 reveals large temperature fluctuations, impacting abundance estimates.

Abstract

A present prevailing open problem planetary nebulae research, and photoionized gaseous nebulae research at large, is the systematic discrepancies in ionic abundances derived from recombination and collisionally excited lines in many H II regions and planetary nebulae. Peimbert (1967) proposed that these discrepancies were due to 'temperature fluctuations' in the plasma, but the amplitude of such fluctuations remain unexplained by standard phtoionization modeling. In this letter we show that large amplitude temperature oscillations are expected to form in gaseous nebulae photoionized by short-period binary stars. Such stars yield periodically varying ionizing radiation fields, which induce periodic oscilla- tions in the heating-minus-cooling function across the nebula. For flux oscillation periods of a few days any temperature perturbations in the gas with frequencies similar to those of the ionizing source will undergo resonant amplification. In this case, the rate of growth of the perturbations increases with the amplitude of the variations of the ionizing flux and with decreasing nebular equilibrium temperature. We also present a line ratios diagnostic plot that combines [O III] collisional lines and O II recombination lines for diagnosing equilibrium and fluctuation am- plitude temperatures in gaseous nebulae. When applying this diagnostic to the planetary nebula M 1-42 we find an equilibrium temperature of ~6000 K and a resonant temperature fluctuation amplitude (Trtf ) of ~4000 K. This equilibrium temperature is significantly lower than the temperature estimated when temperature perturbations are ignored.