The Absence of Cold Dust and the Mineralogy and Origin of the Warm Dust Encircling BD +20 307

TL;DR

This study reveals that the warm dust around the old star BD +20 307 originates from a recent catastrophic collision of rocky bodies within 1 AU, with no cold dust present, challenging steady-state dust models.

Contribution

It demonstrates that the dust around BD +20 307 results from a recent collision, not a steady-state process, and shows the absence of cold dust in an old star system.

Findings

All dust is within 1 AU, no cold dust detected.

Spectral features indicate small silicates that are rapidly removed.

The dust likely results from a recent planetary collision.

Abstract

Spitzer Space Telescope photometry and spectroscopy of BD +20 307 show that all of the dust around this remarkable Gyr-old spectroscopic binary arises within 1 AU. No additional cold dust is needed to fit the infrared excess. Peaks in the 10 and 20 micron spectrum are well fit with small silicates that should be removed on a timescale of years from the system. This is the dustiest star known for its age, which is >1 Gyr. The dust cannot arise from a steady-state collisional cascade. A catastrophic collision of two rocky, planetary-scale bodies in the terrestrial zone is the most likely source for this warm dust because it does not require a reservoir of planetesimals in the outer system.