Gas distribution, kinematics, and excitation structure in the disks around the Classical Be Stars β Canis Minoris and ζ Tauri
ten Brummelaar, TA
American Astronomical Society / IOP Publishing
Using CHARA and VLTI near-infrared spectro-interferometry with hectometric baseline lengths (up to 330 m) and with high spectral resolution (up to λ/Δλ = 12, 000), we studied the gas distribution and kinematics around two classical Be stars. The combination of high spatial and spectral resolution achieved allows us to constrain the gas velocity field on scales of a few stellar radii and to obtain, for the first time in optical interferometry, a dynamical mass estimate using the position-velocity analysis technique known from radio astronomy. For our first target star, β Canis Minoris, we model the H+K-band continuum and Brγ-line geometry with a near-critical rotating stellar photosphere and a geometrically thin equatorial disk. Testing different disk rotation laws, we find that the disk is in Keplerian rotation (v(r)∝r –0.5 ± 0.1) and derive the disk position angle (140° ± 1fdg7), inclination (38fdg5 ± 1°), and the mass of the central star (3.5 ± 0.2 M ☉). As a second target star, we observed the prototypical Be star ζ Tauri and spatially resolved the Brγ emission as well as nine transitions from the hydrogen Pfund series (Pf 14-22). Comparing the spatial origin of the different line transitions, we find that the Brackett (Brγ), Pfund (Pf 14-17), and Balmer (Hα) lines originate from different stellocentric radii (R cont < R Pf < R Brγ ~ R Hα), which we can reproduce with an LTE line radiative transfer computation. Discussing different disk-formation scenarios, we conclude that our constraints are inconsistent with wind compression models predicting a strong outflowing velocity component, but support viscous decretion disk models, where the Keplerian-rotating disk is replenished with material from the near-critical rotating star.
This work was done in part under contract with the California Institute of Technology (Caltech), funded by NASA through the Sagan Fellowship Program (SK is a Sagan fellow). JDM and GHS acknowledge support for this work provided by the National Science Foundation under grants AST-0707927 and AST-1009080. The MIRC beam combiner was developed with funding from the University of 16 Michigan. The CHARA Array is funded by the Georgia State University, by the National Science Foundation through grant AST-0908253, by the W.M. Keck Foundation, by the NASA Exoplanet Science Institute, and the David and Lucile Packard Institute
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.
Vol. 744: 19