UV and Optical Variability of the Young Star T Cha Produced by Inner Disk Obscuration

The young (7 Myr) 1.5 M⊙ T Tauri star T Cha shows dramatic variability. The optical extinction varies by at least 3 magnitudes on few hour time-scales. The obscuration is produced by material at the inner edge of the circumstellar disk and therefore characterizing the absorbing material can reveal important clues regarding the transport of gas and dust within such disks. The inner disk of T Cha is particularly interesting, because T Cha has a transitional disk with a large gap at 0.2- 15 AU in the dust disk and allows study of the gas and dust structure in the terrestrial planet formation zone during this important rapid phase of protoplanetary disk evolution. For this reason we have conducted a comprehensive, multi-spectral- region, observing campaign to study the UV/X-ray/optical variability of T Cha. During 2018 February/March we monitored the optical photometric and spectral variability using LCOGT and the SMARTS telescopes. These optical data provide a broad context within which to interpret our shorter UV and X-ray observations. We observed T Cha during 3 coordinated observations (each 5 HST orbits + 25 ksec XMM; on 2018 Feb 22, Feb 26, Mar 2) using HST COS/STIS to measure the UV-optical spectra and XMM-Newton to measure the X-ray energy distribution. The observed spectral changes are well correlated and demonstrate the influence of the same absorbing material in the different spectral regions. In this poster we examine which spectral features in the different spectral regions (FUV/NUV/optical/X-ray) change and by how much, and thereby determine the location of different emitting regions within the complex stellar/inner disk system relative to the absorbers along the line-of-sight to the stellar photosphere. Understanding these contributions is vital for estimating the properties of the absorbing gas and dust. (This work is supported by grant HST-GO-15128 and time awarded by HST, XMM-Newton, LCOGT, and SMARTS.)