Variability of Disk Emission in Pre-Main Sequence and Related Stars. III. Exploring Structural Changes in the Pre-transitional Disk in HD 169142

TL;DR

This study investigates the variability and structural changes in the pre-transitional disk of HD 169142 over 24 years, combining observations and modeling to explore disk activity and potential planetary formation signatures.

Contribution

It provides a detailed analysis of disk variability, models the impact of planetary bodies on disk structure, and links observed features to possible planet formation processes.

Findings

Disk exhibits up to 45% variability over 10 years.

Inner disk edge shifts by 0.05 AU, affecting NIR flux.

Dark ring structure may be caused by planetary clearing.

Abstract

We present near-IR and far-UV observations of the pre-transitional (gapped) disk in HD 169142 using NASA's Infrared Telescope Facility and Hubble Space Telescope. The combination of our data along with existing data sets into the broadband spectral energy distribution reveals variability of up to 45% between ~1.5-10 {\mu}m over a maximum timescale of 10 years. All observations known to us separate into two distinct states corresponding to a high near-IR state in the pre-2000 epoch and a low state in the post-2000 epoch, indicating activity within the <1 AU region of the disk. Through analysis of the Pa {\beta} and Br {\gamma} lines in our data we derive a mass accretion rate in May 2013 of (1.5 - 2.7) x 10^-9 Msun/yr. We present a theoretical modeling analysis of the disk in HD 169142 using Monte-Carlo radiative transfer simulation software to explore the conditions and perhaps signs of planetary formation in our collection of 24 years of observations. We find that shifting the outer edge (r = 0.3 AU) of the inner disk by 0.05 AU toward the star (in simulation of accretion and/or sculpting by forming planets) successfully reproduces the shift in NIR flux. We establish that the ~40-70 AU dark ring imaged in the NIR by Quanz et al. (2013) and Momose et al. (2013) and at 7 mm by Osorio et al. (2014) may be reproduced with a 30% scaled density profile throughout the region, strengthening the link to this structure being dynamically cleared by one or more planetary mass bodies.