Using FUV to IR Variability to Probe the Star-Disk Connection in the Transitional Disk of GM Aur

TL;DR

This study uses multi-epoch UV, optical, and IR observations of the GM Aur transitional disk to investigate variability in accretion rates and inner disk structure, revealing inhomogeneities and their impact on star-disk interactions.

Contribution

It provides new insights into the variability of accretion and inner disk properties in a transitional disk through multi-epoch UV to IR observations.

Findings

Accretion rates varied over time, with a decrease over three months.

Lower accretion rates correlated with reduced dust and gas in the inner disk.

Inner disk inhomogeneities influence accretion and disk structure.

Abstract

We analyze 3 epochs of ultraviolet (UV), optical and near-infrared (NIR) observations of the Taurus transitional disk GM Aur using the Hubble Space Telescope Imaging Spectrograph (STIS) and the Infrared Telescope Facility SpeX spectrograph. Observations were separated by one week and 3 months in order to study variability over multiple timescales. We calculate accretion rates for each epoch of observations using the STIS spectra and find that those separated by one week had similar accretion rates (~1E-8 solar masses/yr) while the epoch obtained 3 months later had a substantially lower accretion rate (~4E-9 solar masses/yr). We find that the decline in accretion rate is caused by lower densities of material in the accretion flows, as opposed to a lower surface coverage of the accretion columns. During the low accretion rate epoch we also observe lower fluxes at both far UV (FUV) and IR wavelengths, which trace molecular gas and dust in the disk, respectively. We find that this can be explained by a lower dust and gas mass in the inner disk. We attribute the observed variability to inhomogeneities in the inner disk, near the corotation radius, where gas and dust may co-exist near the footprints of the magnetospheric flows. These FUV--NIR data offer a new perspective on the structure of the inner disk, the stellar magnetosphere, and their interaction.