On the Diversity of the Taurus Transitional Disks: UX Tau A & Lk Ca 15

TL;DR

This paper investigates the diversity of pre-transitional disks around young stars, analyzing their spectral energy distributions and dust compositions to understand disk gap formation and dust processing.

Contribution

It introduces the class of pre-transitional disks, analyzes two examples with Spitzer IRS spectra, and discusses dust composition and disk gap sizes, expanding knowledge of disk evolution.

Findings

UX Tau A has a ~56 AU gap with crystalline silicates beyond it.

LkCa 15 has a ~46 AU gap with amorphous silicates.

Dust processing varies significantly among pre-transitional disks.

Abstract

The recently recognized class of "transitional disk" systems consists of young starswith optically-thick outer disks but inner disks which are mostly devoid of small dust. Here we introduce a further class of "pre-transitional disks" with significant near-infrared excesses which indicate the presence of an optically thick inner disk separated from an optically thick outer disk; thus, the spectral energy distributions of pre-transitional disks suggest the incipient development of disk gaps rather than inner holes. In UX Tau A, our analysis of the Spitzer IRS spectrum finds that the near-infrared excess is produced by an inner optically thick disk and a gap of ~56 AU is present. The Spitzer IRS spectrum of LkCa 15 is suggestive of a gap of ~46 AU, confirming previous millimeter imaging. In addition, UX Tau A contains crystalline silicates in its disk at radii >~ 56 AU which poses a challenge to our understanding of the production of this crystalline material. In contrast, LkCa 15's silicates are amorphous and pristine. UX Tau A and LkCa 15 increase our knowledge of the diversity of dust clearing in low-mass star formation.