A New Sample of Warm Extreme Debris Disks from the ALLWISE Catalog

Abstract

Extreme debris disks (EDDs) are rare systems with peculiarly large amounts of warm dust that may stem from recent giant impacts between planetary embryos during the final phases of terrestrial planet growth. Here we report on the identification and characterization of six new EDDs. These disks surround F5-G9 type main-sequence stars with ages >100 Myr, have dust temperatures higher than 300 K and fractional luminosities between 0.01 and 0.07. Using time-domain photometric data at 3.4 and 4.6 µm from the WISE all sky surveys, we conclude that four of these disks exhibited variable mid-infrared emission between 2010 and 2019. Analyzing the sample of all known EDDs, now expanded to 17 objects, we find that 14 of them showed changes at 3-5 µm over the past decade suggesting that mid-infrared variability is an inherent characteristic of EDDs. We also report that wide-orbit pairs are significantly more common in EDD systems than in the normal stellar population. While current models of rocky planet formation predict that the majority of giant collisions occur in the first 100 Myr, we find that the sample of EDDs is dominated by systems older than this age. This raises the possibility that the era of giant impacts may be longer than we think, or that some other mechanism(s) can also produce EDDs. We examine a scenario where the observed warm dust stems from the disruption and/or collisions of comets delivered from an outer reservoir into the inner regions, and explore what role the wide companions could play in this process.

Planetesimal/Debris discs

“…This is especially favoured in systems with fractional luminosities above 1%, which are termed extreme debris discs (EDDs Balog et al, 2009), and systems displaying mid-IR spectroscopic features that indicate the presence of very small crystalline dust particles (Rhee et al, 2008;Lisse et al, 2009;Olofsson et al, 2012). Some systems even display variability in their mid-IR emission as expected in a giant collision scenario (Meng et al, 2014(Meng et al, , 2015Su et al, 2019;Moór et al, 2021;Rieke et al, 2021), or even have short-lived gas (Marino et al, 2017a;Schneiderman et al, 2021).…”

Demographics of young stars and their protoplanetary disks: lessons learned on disk evolution and its connection to planet formation

“…This proposal is supported by recent theoretical modeling work (Najita et al 2022) and studies of large samples of exoplanet properties and ALMA disk observations (van der Marel and Mulders 2021). Recent multiwavelength and time-domain observations have also codified the existence of so-called "Extreme debris disks" (EDDs), which are characterized by unusually high excess luminosity and time variability in the near-to mid-IR even at relatively late (> 100 Myr) ages (e.g., Balog et al 2009;Meng et al 2014Meng et al , 2015Su et al 2019;Moór et al 2021;Melis et al 2021). While these systems have infrared excess luminosities higher than the 8 × 10 −3 level typical of debris disks, they are classified as debris disks based on the age of the central star and their lack of gas.…”

First detection of a disk free of volatile elements around a young A-type star: A possible sign of collisions between rocky planets

“…In addition, simulations of tidal disruption of giant planets due to interactions with their host star show that remnants of exomoons can end up in orbits that are similar to the disk seen in HD 152384 (Martinez et al 2019). Interestingly, the relatively low fractional infrared luminosity (L IR /L = 0.05) places HD 152384 within the group of extreme debris disks defined recently by Moór et al (2021), for which large amounts of warm dust may stem from recent giant impacts between planetary embryos during the final phases of terrestrial planet growth. Although cool molecular gas has been found at relatively large distances in a number of these objects (Moór et al 2017;Marino et al 2020), our analysis on HD 152384 constitutes the first detection of gas solely consisting of refractory elements around such an object, leading further support for the hypothesis of the destruction of planetary embryos.…”