The Surprising Evolution of the Shadow on the TW Hya Disk*

We report new total-intensity visible-light high-contrast imaging of the TW Hya disk taken with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope. This represents the first published images of the disk with STIS since 2016, when a moving shadow on the disk surface was reported. We continue to see the shadow moving in a counterclockwise fashion, but in these new images the shadow has evolved into two separate shadows, implying a change in behavior for the occulting structure. Based on radiative-transfer models of optically thick disk structures casting shadows, we infer that a plausible explanation for the change is that there are now two misaligned components of the inner disk. The first of these disks is located between 5 and 6 au with an inclination of 5.5 degrees and position angle (PA) of 170 degrees, and the second between 6 and 7 au with an inclination of 7 degrees and PA of 50 degrees. Finally, we speculate on the implications of the new shadow structure and determine that additional observations are needed to disentangle the nature of TW Hya's inner-disk architecture.

Automated summary

We present new visible-light imaging of the TW Hya disk using the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope. The images show two separate shadows, indicating a change in behavior of the occulting structure. Based on radiative-transfer models, we suggest that the change is due to two misaligned components of the inner disk. More observations are needed to understand the nature of TW Hya's inner-disk architecture.