Ian Berry 1, Stanley Owocki 1, Matt Shultz 1, Asif ud-Doula 2 Abstract: σ Ori E is a prototypical magnetic B star with a rapid 1.2 day rotation period. Two dips in brightness can be seen in its photometric light curve, which was well fit by the Rigidly Rotating Magnetosphere (RRM) model. This model shows that if a star is rotating rapidly enough, then material will become trapped in the centrifugal magnetosphere (CM). However, this model only considers considers absorption and as such does not fully explain the light curve of σ Ori E. We must take emission into account as well. To do this, we examine the possibility of electron scattering from the CM being responsible for extra emission seen in σ Ori E’s photometric light curve. These initial results could provide insight into explaining photometric light curves of other magnetic stars measured by measured by TESS. 1 University of Delaware 2 Penn State Scranton 13 - 17 July 2020 MOBSTER-1 ₋ Rotation, winds & outflows Conclusion: For this poster we set out to examine if simple electron scattering could be responsible for extra emission previously unaccounted for in the predicted light curve of σ Ori E. So far the results, which indeed show extra emission from electron scattering are encouraging. In the future we will tune the results to σ Ori E, as well as to other stars observed by TESS via fine-tuning of the oblique rotator model parameters. Finally, we will incorporate these results into the RRM model. will incorporate these results into the RRM model. S = 0 Pure Absorption Figure 4. Bottom: Surface intensity plotted at the same four phases as Fig. 3, with emission in red. The black disk represents the star, with the red cloud showing occultation of the star by the CM. Top: Resulting light curves, for both the scattering source function case (solid curve) and a pure absorption model (dotted curve). Note the scattering flux exceeds the continuum (dashed line) by a few percent in the scattering case at phases phases 0.1 and 0.6. The arrow connects the relevant phases of the light curve to their associated surface brightness panels. Figure 2. Diagram showing how a CM can form if a star is rotating fast enough such that Rk < RA , as is the case with the 3D MHD simulations used in this model. S = J Instead of RRM, we use 3D-MHD simulations (see ud-Doula contributed talk on Friday for more details) with Rk=1.25 R* < RA = 5.5 R* , and magnetic obliquity angle β = 45 degrees. This gives us the associated 3D distribution of mass density in the CM above the Kepler radius. Ignoring material below the Kepler radius, we use this to synthesize light curves wherein electron scattering from the CM both reduces the brightness from the star, but but also provides extra emission from outside the stellar limb. The plot below shows electron scattering optical depth at four different rotational phases for an observer viewing the star at an inclination angle i = 45 degrees. Can Magnetospheric Scattering Explain Inferred Emission in Photometric Light Curves of σ Ori E and Magnetic Stars Observed with TESS? Figure 3. Surface plot of electron scattering optical depth τ for the 3D MHD model with a magnetic obliquity angle β = 45 degrees at four rotational phases and an inclination angle i = 45 degrees. The observer is looking directly down onto the magnetic pole during phases 0.5 and 1, and along the magnetic equator at phases 0.25 and 0.75 . The rotation axis is vertical. This gives us a visual representaion of material in the CM rotating around the sta star, which is not shown. Figure 1. The photometric light curve for σ Ori E, with the solid line being the predicted light curve from the RRM model and the diamonds being observations (Townsend et. al 2005). Extra emission can be seen at phase 0.6, denoted by the red circle. where µ* = (1-R2/r 2) 1/2 is the cosine of the angular size for the stellar radius R at circumstellar radius r. S = J = ์⁄ ๗ I * (1-µ*) (2) We compute the surface intensity I from