A CHARA Array Survey of Circumstellar Disks around Nearby Be-type Stars

TL;DR

This study uses high-resolution interferometry to measure the sizes and orientations of circumstellar disks around 24 Be stars, revealing that most stars rotate near their critical velocity and disks are typically 4.4 times larger than the star.

Contribution

First high angular resolution survey of Be star disks using CHARA Array, providing detailed disk size, shape, and orientation measurements with spectral energy distribution analysis.

Findings

Disks are on average 4.4 times larger than stellar diameters.

Most Be stars in the sample rotate near critical velocity.

Disk sizes are generally smaller than those measured in Halpha emission.

Abstract

We report on a high angular resolution survey of circumstellar disks around 24 northern sky Be stars. The K-band continuum survey was made using the CHARA Array long baseline interferometer (baselines of 30 to 331 m). The interferometric visibilities were corrected for the flux contribution of stellar companions in those cases where the Be star is a member of a known binary or multiple system. For those targets with good uv coverage, we used a four parameter Gaussian elliptical disk model to fit the visibilities and to determine the axial ratio, position angle, K-band photospheric flux contribution, and angular diameter of the disk major axis. For the other targets with relatively limited uv coverage, we constrained the axial ratio, inclination angle, and or disk position angle where necessary in order to resolve the degeneracy between possible model solutions. We also made fits of the ultraviolet and infrared spectral energy distributions to estimate the stellar angular diameter and infrared flux excess of each target. The mean ratio of the disk diameter (measured in K-band emission) to stellar diameter (from SED modeling) is 4.4 among the 14 cases where we reliably resolved the disk emission, a value which is generally lower than the disk size ratio measured in the higher opacity Halpha emission line. We estimated the equatorial rotational velocity from the projected rotational velocity and disk inclination for 12 stars, and most of these stars rotate close to or at the critical rotational velocity.