2020ApJ...902....4R

We present two new epochs of Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph coronagraphic imaging, along with multi-epoch optical, near-IR, and radio monitoring, of the HD 163296 system. We find that ansae features identified in earlier-epoch HST imagery are a fourth ring that resides at a semimajor axis distance of 3.''25 (330 au). We determine that the scale height of the dust is 64 au at a radial distance of 330 au. We observe surface brightness variations in the fourth ring on <3 month timescales, including large-scale, azimuthally asymmetric changes. This variability resembles earlier studies of the innermost disk ring (0.''66, 67 au), suggesting a common origin. We find no evidence for the ejection of new HH knots predicted to occur in 2018. Moreover, our nondetection of older HH knots indicates that the knots could be experiencing less shock heating. We also detect one clear dipper event in our optical light curve from 2018. Using the timescale and spatial extent of the disk illumination changes we observe, we estimate that the source of this shadowing resides within 0.5 au from the star, must extend at least 0.08 au above the midplane of the disk, and has an azimuthal extent of 0.26 au. We estimate that the source of the dipper event reaches a scale height of 0.37 au above the midplane at 0.41 au and has an azimuthal extent of 0.3 au. We suggest that these similarities could indicate that the same (or similar) mechanisms are responsible for producing both dippers and variable ring illumination in the system.