Characterizing the IYJ Excess Continuum Emission in T Tauri Stars

TL;DR

This study characterizes the excess continuum emission in T Tauri stars from optical to near-infrared wavelengths, revealing a broad, featureless spectrum likely originating from hot gas inside the dust sublimation radius, impacting accretion rate estimates.

Contribution

First detailed analysis of IYJ excess emission in T Tauri stars, linking it to inner disk gas and accretion processes, challenging previous assumptions about its origin.

Findings

Excess emission correlates with V and K band excesses.

Spectrum is broad, featureless, resembling blackbody radiation.

Luminosity comparable to accretion luminosity from UV/blue excess.

Abstract

We present the first characterization of the excess continuum emission of accreting T Tauri stars between optical and near-infrared wavelengths. With nearly simultaneous spectra from 0.48 to 2.4 microns acquired with HIRES and NIRSPEC on Keck and SpeX on the IRTF, we find significant excess continuum emission throughout this region, including the I, Y, and J bands, which are usually thought to diagnose primarily photospheric emission. The IYJ excess correlates with the excess in the V band, attributed to accretion shocks in the photosphere, and the excess in the K band, attributed to dust in the inner disk near the dust sublimation radius, but it is too large to be an extension of the excess from these sources. The spectrum of the excess emission is broad and featureless, suggestive of blackbody radiation with a temperature between 2200 and 5000 K. The luminosity of the IYJ excess is comparable to the accretion luminosity inferred from modeling the blue and ultraviolet excess emission and may require reassessment of disk accretion rates. The source of the IYJ excess is unclear. In stars of low accretion rate, the size of the emitting region is consistent with cooler material surrounding small hot accretion spots in the photosphere. However, for stars with high accretion rates, the projected area is comparable to or exceeds that of the stellar surface. We suggest that at least some of the IYJ excess emission arises in the dust-free gas inside the dust sublimation radius in the disk.