Spitzer Spectroscopy of the Circumprimary Disk in the Binary Brown Dwarf 2MASS J04414489+2301513

TL;DR

This study uses Spitzer spectroscopy to analyze a young binary brown dwarf's disk, revealing significant grain growth and a small, possibly truncated disk lacking silicate emission, indicating advanced dust evolution.

Contribution

First mid-infrared spectral analysis of a young binary brown dwarf's disk showing grain growth and disk truncation effects.

Findings

Absence of silicate emission suggests significant grain growth.

Disk likely truncated at 0.2-0.3 AU, possibly by the secondary.

Disk shows signs of advanced dust evolution with micron-sized grains.

Abstract

Using the Spitzer Infrared Spectrograph, we have performed mid-infrared spectroscopy on the young binary brown dwarf 2MASS J04414489+2301513 (15 AU) in the Taurus star-forming region. The spectrum exhibits excess continuum emission that likely arises from a circumstellar disk around the primary. Silicate emission is not detected in these data, indicating the presence of significant grain growth. This is one of the few brown dwarf disks at such a young age (~1 Myr) that has been found to lack silicate emission. To quantitatively constrain the properties of the disk, we have compared the spectral energy distribution of 2MASS J04414489+2301513 to the predictions of our vertical structure codes for irradiated accretion disks. Our models suggest that the remaining atmospheric grains of moderately depleted layers may have grown to a size of $\gtrsim5$ micron. In addition, our model fits indicate an outer radius of 0.2-0.3 AU for the disk. The small size of this circumprimary disk could be due to truncation by the secondary. The absence of an outer disk containing a reservoir of small, primordial grains, combined with a weak turbulent mechanism, may be responsible for the advanced grain growth in this disk.