The inner radius of T Tauri disks estimated from near-infrared interferometry: the importance of scattered light

TL;DR

This paper demonstrates that neglecting scattered light in models causes overestimation of T Tauri star disk inner radii from near-infrared interferometry, emphasizing the importance of including scattered light for accurate measurements.

Contribution

The study shows that incorporating scattered light into radiative transfer models significantly improves the accuracy of disk inner radius estimates for T Tauri stars.

Findings

Scattered light contributes significantly to near-infrared emission in T Tauri disks.

Neglecting scattered light leads to overestimating disk sizes by a factor of 2-3.

Including scattered light aligns models with observed interferometric data for T Tauri stars.

Abstract

For young Herbig Ae/Be stars, near-infrared interferometric measurements have revealed a correlation between the luminosity of the central object and the position of the disk inner rim. This correlation breaks down for the cooler T Tauri stars, a fact often interpreted in terms of disks with larger inner radii. In most cases, the conversion between the observed interferometric visibility and the calculated disk inner radius was done with a crude disk emission model. Here, we examine how the use of models that neglect scattered light can lead to an overestimation of the disk sizes. To do so, synthetic disk images (and visibilities) are calculated with a full treatment of the radiative transfer. The relative contributions of thermal emission and scattered light are compared. We find that the latter can not be neglected for cool stars. For further comparison, the model visibilities are also converted into inner disk radii using the same simple disk models as found in the literature. We find that reliable inner radii can only be estimated for Herbig Ae/Be stars with these models. However, they lead to a systematic overestimation of the disk size, by a factor of 2 to 3, for T Tauri stars. We suggest that including scattered light in the models is a simple (and sufficient) explanation of the current interferometric measurements of T Tauri stars.