An Overview of Exocomets

TL;DR

Exocomets are sublimation-driven minor bodies orbiting stars other than the Sun that display tails or comae; interstellar objects are not considered exocomets in this work. The paper provides a broad survey of detection pathways, comparing exocomets seen as bodies via spectroscopy and photometry with exocometary material in debris discs and around white dwarfs. It compiles a census of exocomet candidate detections around main-sequence stars and white dwarfs, identifying beta Pictoris as the canonical system and WD 1145+017 as an illustrative white-dwarf analog. The discussion highlights biases, detection limits, and the need for future high-precision surveys to robustly characterize exocomet demographics and compositions.

Abstract

We give a general overview of what the scientific community refers to as "exocomets". The general definition of exocomets, as presented in this work, is discussed and compared with Solar System comets and interstellar objects, addressing their detection around main-sequence stars as well as orbiting white dwarfs. We introduce the different types of exocomet observations, highlighting the difference between exocometary 'bodies' and exocometary 'material'. We provide a census of all exocometary system candidates detected so far, both via spectroscopy and photometry, including detections around white dwarfs.

Figures (2)

• Figure 1: The distribution of planets, main comet and asteroid belts around the Sun, and the equivalent analogues for Beta Pictoris and WD 1145+017. All distances are logarithmic, scaled such that they all have the same equilibrium temperature for a blackbody, meaning that the various sublimation lines are at the same x-axis locations for comparison. Distances from each star are labelled in stellar radii (upper scale) and astronomical units (lower scale). For the Sun, Solar system comets are shown with notable associated distances, belts and planets. For $\beta$ Pictoris, the planets and main belts are noted. For the white dwarf WD 1145+017 the locations for the six transiting bodies are indicated, with a zoomed-in panel showing their labelled order from Vanderburg2015.
• Figure 2: Overview of ages and T$_{\rm eff}$ for stars with reported exocomet detections for main sequence and white dwarf systems. Stellar T$_{\rm eff}$ have been adopted from the spectral types in Tables \ref{['tab:exocomet_candidatesSP']} and \ref{['tab:exocomet_candidatesPH']} using the conversion from Pecaut_Mamajek2013. Unclear and false positive detections are excluded from the figure. White dwarf objects are also listed in Table \ref{['tab:exocomet_candidatesPHWD']}.