Near-Infrared Constraints on the Presence of Warm Dust at Metal-Rich, Helium Atmosphere White Dwarfs

TL;DR

This study uses near-infrared spectroscopy to investigate the presence of warm dust around helium atmosphere, metal-rich white dwarfs, finding a lower occurrence rate compared to hydrogen atmosphere white dwarfs, which informs understanding of planetary debris and evolution.

Contribution

It provides new near-infrared observational constraints on warm dust around helium atmosphere white dwarfs, refining the estimated frequency of such circumstellar material.

Findings

Less than 5% of helium atmosphere white dwarfs show warm dust signatures.

At least 20% of hydrogen atmosphere white dwarfs have warm circumstellar material.

No significant correlation between white dwarf mass and presence of disks.

Abstract

Here, we present near-infrared spectroscopic observations of 15 helium atmosphere, metal-rich white dwarfs obtained at the NASA Infrared Telescope Facility. While a connection has been demonstrated between the most highly polluted, hydrogen atmosphere white dwarfs and the presence of warm circumstellar dust and gas, their frequency at the helium atmosphere variety is poorly constrained. None of our targets show excess near-infrared radiation consistent with warm orbiting material. Adding these near-infrared constraints to previous near- and mid-infrared observations, the frequency of warm circumstellar material at metal-bearing white dwarfs is at least 20% for hydrogen-dominated photospheres, but could be less than 5% for those effectively composed of helium alone. The lower occurrence of dust disks around helium atmosphere white dwarfs is consistent with Myr timescales for photospheric metals in massive convection zones. Analyzing the mass distribution of 10 white dwarfs with warm circumstellar material, we search for similar trends between the frequency of disks and the predicted frequency of massive planets around intermediate mass stars, but find the probability that disk-bearing white dwarfs are more massive than average is not significant.