We acquired Hα spectroscopic observations from 2005 to 2019 showing Pleione has transitioned from a Be phase to a Be-shell phase during this period. Using the radiative transfer code hdust, we created a grid of ∼100,000 disk models for Pleione. We successfully reproduced the observed transition with a disk model that varies in inclination while maintaining an equatorial density of ρ 0 ( r ) = 3 × 10 − 11 ( r / R eq ) − 2.7 g cm − 3 , and an Hα-emitting region extending to 15 R eq. We use a precessing disk model to extrapolate the changing disk inclination over 120 yr and follow the variability in archival observations. The best-fit disk model precesses over a line-of-sight inclination between ∼25° and ∼144° with a precessional period of ∼80.5 yr. Our precessing models match some of the observed variability but fail to reproduce all of the historical data available. Therefore, we propose an ad hoc model based on our precessing disk model inspired by recent smoothed particle hydrodynamics simulations of similar systems, where the disk tears due to the tidal influence of a companion star. In this model, a single disk is slowly tilted to an angle of 30° from the stellar equator over 34 yr. Then, the disk is torn by the companion’s tidal torque, with the outer region separating from the innermost disk. The small inner disk returns to the stellar equator as mass injection remains constant. The outer disk precesses for ∼15 yr before gradually dissipating. The process repeats every 34 yr and reproduces all trends in Pleione’s variability.

We use a time-dependent hydrodynamic code and a non-LTE Monte Carlo code to model disk dissipation for the Be star 66 Ophiuchi. We compiled 63 years of observations from 1957 to 2020 to encompass the complete history of the growth and subsequent dissipation of the star’s disk. Our models are constrained by new and archival photometry, spectroscopy, and polarization observations, allowing us to model the disk dissipation event. Using Markov Chain Monte Carlo methods, we find that the properties of 66 Oph are consistent with those of a standard B2Ve star. We computed a grid of 61,568 Be star disk models to constrain the density profile of the disk before dissipation using observations of the Hα line profile and spectral energy distribution. We find at the onset of dissipation the disk has a base density of 2.5 × 10−11 g cm−3 with a radial power-law index of n = 2.6. Our models indicate that after 21 yr of disk dissipation 66 Oph’s outer disk remained present and bright in the radio. We find an isothermal disk with constant viscosity with an α = 0.4 and an outer disk radius of ∼115 stellar radii best reproduces the rate of 66 Oph’s disk dissipation. We determined the interstellar polarization in the direction of the star in the V band is p = 0.63 ± 0.02% with a polarization position angle of θ IS ≈ 857 ± 07. Using the Stokes QU diagram, we find the intrinsic polarization position angle of 66 Oph’s disk is θ int ≈ 98° ± 3°.

We investigate variations in the linear polarization as well as in the V-band and B-band colourmagnitudes for classical Be star disks. We present two models: disks with enhanced disk density and disks that are tilted or warped from the stellar equatorial plane. In both cases, we predict variation in observable properties of the system as the disk rotates. We use a non-LTE radiative transfer code bedisk (Sigut & Jones) in combination with a Monte Carlo routine that includes multiple scattering (Halonen et al.) to model classical Be star systems. We find that a disk with an enhanced density region that is one order of magnitude denser than the disk's base density shows as much as ∼0.2% variability in the polarization while the polarization position angle varies by ∼8 • . The ∆V magnitude for the same system shows variations of up to ∼0.4 magnitude while the ∆(B-V) colour varies by at most ∼0.01 magnitude. We find that disks tilted from the equatorial plane at small angles of ∼30 • more strongly reflect the values of polarization and colour-magnitudes reported in the literature than disks tilted at larger angles. For this model, the linear polarization varies by ∼0.3%, the polarization position angle varies by ∼60 • , the ∆V magnitude varies up to 0.35 magnitude, and the ∆(B-V) colour varies up to 0.1 magnitude. We find that the enhanced disk density models show ranges of polarization and colour-magnitudes that are commensurate with what is reported in the literature for all sizes of the density enhanced regions. From this, we cannot determine any preference for small or large density enhanced regions.