Simultaneous emission from dust and gas in the planetary debris orbiting a white dwarf

TL;DR

This study presents the first near-simultaneous observations of dust and gas around a polluted white dwarf, revealing correlated variability that suggests a common origin in collisions, with the shortest timescales observed to date.

Contribution

It provides the first concurrent optical and infrared data showing correlated dust and gas variability, indicating a simultaneous production likely from collisions.

Findings

Gas emission lines vary significantly over weeks.

Dust emission changes occur on similar short timescales.

Correlated variability suggests a common origin for dust and gas.

Abstract

There is increasing evidence for the presence and variability of circumstellar dust and gas around white dwarfs that are polluted with exoplanetary material, although the origin of this dust and gas remains debated. This paper presents the first near-simultaneous observations of both circumstellar dust (via broadband emission) and gas (via emission lines) around a polluted white dwarf. From the optical spectra the gaseous emission lines, notably the calcium infrared triplet and magnesium lines, show significant increases and decreases in their strength over timescales of weeks, while the oxygen and iron lines remain relatively stable. Near-infrared JHKs photometry reveals dust emission changes of up to 0.2 magnitudes in the Ks band over similar timescales, marking the shortest variability timescales observed to date. The two epochs with the strongest emission were correlated between the dust (Ks band brightening) and gas (strengthened calcium and magnesium lines), showing for the first time that the dust and gas must be produced near-simultaneously with a common origin, likely in collisions.