Investigating the Circumstellar Disk of the Be Shell Star 48 Librae

TL;DR

This study models the circumstellar disk of the Be star 48 Librae using a global oscillation approach within the VDD framework, successfully reproducing key observational features and confirming the oscillation scenario.

Contribution

It provides a self-consistent 3D radiative transfer model of 48 Librae's disk incorporating global oscillations, extending the VDD model to this star.

Findings

The model reproduces the observed V/R cycle period of 12 years.

The perturbed disk model improves fit to photometric data.

The model captures key spectroscopic features of 48 Librae.

Abstract

A global disk oscillation implemented in the viscous decretion disk (VDD) model has been used to reproduce most of the observed properties of the well known Be star $\zeta$ Tau. 48 Librae shares several similarities with $\zeta$ Tau -- they are both early-type Be stars, they display shell characteristics in their spectra, and they exhibit cyclic $V/R$ variations -- but has some marked differences as well, such as a much denser and more extended disk, a much longer $V/R$ cycle, and the absence of the so-called triple-peak features. We aim to reproduce the photometric, polarimetric, and spectroscopic observables of 48 Librae with a self-consistent model, and to test the global oscillation scenario for this target. Our calculations are carried out with the three-dimensional NLTE radiative transfer code HDUST. We employ a rotationally deformed, gravity-darkened central star, surrounded by a disk whose unperturbed state is given by the VDD model. A two-dimensional global oscillation code is then used to calculate the disk perturbation, and superimpose it on the unperturbed disk. A very good, self-consistent fit to the time-averaged properties of the disk is obtained with the VDD. The calculated perturbation has a period $P = 12$ yr, which agrees with the observed period, and the behaviour of the $V/R$ cycle is well reproduced by the perturbed model. The perturbed model improves the fit to the photometric data and reproduces some features of the observed spectroscopic data. Some suggestions to improve the synthesized spectroscopy in a future work are given.