THE CIRCUMSTELLAR DISK OF THE Be STAR o AQUARII AS CONSTRAINED BY SIMULTANEOUS SPECTROSCOPY AND OPTICAL INTERFEROMETRY

ABSTRACT Omicron Aquarii is a late-type, Be shell star with a stable and nearly symmetric H emission line. We combine H interferometric observations obtained with the Navy Precision Optical Interferometer covering 2007 through 2014 with H spectroscopic observations over the same period and a 2008 ob...

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Bibliographic Details
Published in:The Astrophysical journal 2015-12, Vol.814 (2), p.1-12
Main Authors: Sigut, T. A. A., Tycner, C., Jansen, B., Zavala, R. T.
Format: Article
Language:English
Subjects:
Accretion disks
ANGULAR MOMENTUM
Aqr
Aquariums
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
circumstellar matter
COMPARATIVE EVALUATIONS
DENSITY
Disks
EMISSION SPECTRA
ENERGY SPECTRA
HYDROGEN
INCLINATION
Interferometers
INTERFEROMETRY
MAGNESIUM
MASS
Mathematical models
NEAR INFRARED RADIATION
ROTATION
SKY
Spectroscopy
STARS
stars: emission-line, Be
stars: individual
techniques: interferometric
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Summary:ABSTRACT Omicron Aquarii is a late-type, Be shell star with a stable and nearly symmetric H emission line. We combine H interferometric observations obtained with the Navy Precision Optical Interferometer covering 2007 through 2014 with H spectroscopic observations over the same period and a 2008 observation of the system's near-infrared spectral energy distribution to constrain the properties of o Aqr's circumstellar disk. All observations are consistent with a circumstellar disk seen at an inclination of 75° 3° with a position angle on the sky of 110° 8° measured East from North. From the best-fit disk density model, we find that 90% of the H emission arises from within 9.5 stellar radii, and the mass associated with this H disk is ∼1.8 × 10−10 of the stellar mass, and that the associated angular momentum, assuming Keplerian rotation for the disk, is ∼1.6 × 10−8 of the total stellar angular momentum. The occurrence of a central quasi-emission feature in Mg ii λ4481 is also predicted by this best-fit disk model and the computed profile compares successfully with observations from 1999. To obtain consistency between the H line profile modeling and the other constraints, it was necessary in the profile fitting to weight the line core (emission peaks and central depression) more heavily than the line wings, which were not well reproduced by our models. This may reflect the limitation of assuming a single power law for the disk's variation in equatorial density. The best-fit disk density model for o Aqr predicts that H is near its maximum strength as a function of disk density, and hence the H equivalent width and line profile change only weakly in response to large (factor of ∼5) changes in the disk density. This may in part explain the remarkable observed stability of o Aqr's H emission line profile.
ISSN:0004-637X
1538-4357
1538-4357
DOI:10.1088/0004-637X/814/2/159