Predicting the incidence of planets and debris discs as a function of stellar mass

TL;DR

This study models the relationship between stellar mass and the likelihood of planets and debris discs, predicting their occurrence rates and suggesting many low-mass stars may host undetected planets or cold debris discs.

Contribution

It introduces a method to estimate planet and debris disc incidence based on dust observations and stellar mass, aligning predictions with existing data and proposing new observational targets.

Findings

20% of A-stars have gas giant or debris discs.

Predicted 2-3% planet occurrence around M-stars matches observations.

Deeper surveys may reveal more debris discs around low-mass stars.

Abstract

The mass of solids in a young circumstellar disc may be the key factor in its efficiency in building planetesimals and planetary cores, and dust observed around young T Tauri and Herbig Ae stars can be used as a proxy for this initial solid content. The dust-mass distributions are taken from recent millimetre-wavelength data and fitted using survival analysis to take into account upper limits, and threshold disc-masses for building planets and belts of comets are estimated. Amongst A-stars, 20% gas giant and 55% debris disc systems are predicted, in good agreement with observations. For M-stars, the predicted and observed planet-frequencies agree at ~2-3%, and this low incidence is explained by a lack of massive discs. However, debris is predicted around approx. 14% of M-stars, while only ~2% such systems have so far been found. This suggests that deeper searches such as with Herschel and SCUBA-2 may find a cold disc population previously missed around these low-luminosity stars. Also, an estimate of the efficiency of building millimetre-detected dust into planetary cores suggests that about a third of M-stars could host an Earth-mass planet -- but as the dust is spread over large disc areas, such planets may orbit far from the star.