Abstract We examine the evolution of the disk surrounding the Be star in the highly eccentric 10.8 yr binary system δ Scorpii over its three most recent periastron passages. V -band and B − V ...photometry, along with H α spectroscopy, are combined with a new set of extensive multiband polarimetry data to produce a detailed comparison of the disk's physical conditions during the time periods surrounding each closest approach of the secondary star. We use the three-dimensional Monte Carlo radiative transfer code HDUST and a smoothed particle hydrodynamics code to support our observations with models of disk evolution, discussing the behavior of the H α and He i 6678 Å lines, V -band magnitude, and polarization degree. We compare the characteristics of the disk immediately before each periastron passage to create a baseline for the unperturbed disk. We find that the extent of the H α emitting region increased between each periastron passage, and that transient asymmetries in the disk become more pronounced with each successive encounter. Asymmetries of the H α and He i 6678 Å lines in 2011 indicate that perturbations propagate inward through the disk near periastron. When the disk’s direction of orbit is opposite to that of the secondary, the parameters used in our models do not produce spiral density enhancements in the H α emitting region because the tidal interaction time is short due to the relative velocities of the disk particles with the secondary. The effects of the secondary star on the disk are short-lived and the disk shows independent evolution between each periastron event.
Abstract
We acquired H
α
spectroscopic observations from 2005 to 2019 showing Pleione has transitioned from a Be phase to a Be-shell phase during this period. Using the radiative transfer code
hdust
..., we created a grid of ∼100,000 disk models for Pleione. We successfully reproduced the observed transition with a disk model that varies in inclination while maintaining an equatorial density of
ρ
0
(
r
)
=
3
×
10
−
11
(
r
/
R
eq
)
−
2.7
g
cm
−
3
, and an H
α
-emitting region extending to 15
R
eq
. We use a precessing disk model to extrapolate the changing disk inclination over 120 yr and follow the variability in archival observations. The best-fit disk model precesses over a line-of-sight inclination between ∼25° and ∼144° with a precessional period of ∼80.5 yr. Our precessing models match some of the observed variability but fail to reproduce all of the historical data available. Therefore, we propose an ad hoc model based on our precessing disk model inspired by recent smoothed particle hydrodynamics simulations of similar systems, where the disk tears due to the tidal influence of a companion star. In this model, a single disk is slowly tilted to an angle of 30° from the stellar equator over 34 yr. Then, the disk is torn by the companion’s tidal torque, with the outer region separating from the innermost disk. The small inner disk returns to the stellar equator as mass injection remains constant. The outer disk precesses for ∼15 yr before gradually dissipating. The process repeats every 34 yr and reproduces all trends in Pleione’s variability.
Abstract
We present the results of a multiplicity survey for a magnitude-limited sample of 31 classical Be stars conducted with the Navy Precision Optical Interferometer and the Mark III Stellar ...Interferometer. The interferometric observations were used to detect companions in 10 previously known binary systems. For two of these sources (66 Oph and
β
Cep) new orbital solutions were obtained, while for a third source (
υ
Sgr) our observations provide the first direct, visual detection of the hot companion to the primary star. Combining our interferometric observations with an extensive literature search, we conclude that an additional four sources (o Cas, 15 Mon,
β
Lyr, and
β
Cep) also contain wider binary components that are physical companions to the narrow binaries, thus forming hierarchical multiple systems. Among the sources not previously confirmed as spectroscopic or visual binaries, BK Cam was resolved on a number of nights within a close physical proximity of another star with relative motion possibly suggesting a physical binary. Combining our interferometric observations with an extensive literature search, we provide a detailed listing of companions known around each star in the sample, and discuss the multiplicity frequency in the sample. We also discuss the prospects for future multiplicity studies of classical Be stars by long-baseline optical interferometry.
We demonstrate that the angle between a star’s rotation axis and the observer’s line of sight, usually called the inclination angle, can be reliably determined for Be stars via Hα emission line ...profile fitting. We test our method on a sample of 11 Be stars with available long-baseline interferometric data from the Navy Precision Optical Interferometer. We fit the Hα emission line profile of each star to obtain a spectroscopic inclination angle i Hα . We then obtain an independent inclination angle estimate, \({i}_{{{\rm{V}}}^{2}}\), by fitting the observed interferometric visibilities with model visibilities based on a purely geometric representation of the light distribution on the sky. The sample differences, \({\rm{\Delta }}i\equiv {i}_{{\rm{H}}\alpha }-{i}_{{{\rm{V}}}^{2}}\), are normally distributed with a mean of zero and a standard deviation of 6.°7, and the linear correlation coefficient between i Hα and \({i}_{{{\rm{V}}}^{2}}\) is r = 0.93. As Be stars comprise upwards of one-fifth of all main-sequence B-type stars, this Hα line profile fitting technique has the potential to provide an efficient method for detecting correlated stellar spin axes in young open clusters. Furthermore, if the orientation of the Be star’s circumstellar disk on the plane of the sky can be constrained by polarization measurements, it is possible to determine the full 3D stellar rotation vector of each Be star.
Spiral density enhancements in Be binary systems Cyr, Isabelle H; Jones, C E; Carciofi, A C ...
Monthly notices of the Royal Astronomical Society,
09/2020, Volume:
497, Issue:
3
Journal Article
Peer reviewed
Open access
ABSTRACT
We use a smoothed particle hydrodynamics (SPH) code to examine the effects of a binary companion on a Be star disc for a range of disc viscosities and misalignment angles, i.e. the angle ...between the orbital plane and the primary star’s spin axis. The density structures in the disc due to the tidal interaction with the binary companion are investigated. Expanding on our previous work, the shape and density structure of density enhancements due to the binary companion are analysed and the changes in observed interferometric features due to these orbiting enhancements are also predicted. We find that larger misalignment angles and viscosity values result in more tightly wound spiral arms with densities that fall-off more slowly with radial distance from the central star. We show that the orbital phase has very little effect on the structure of the spiral density enhancements. We demonstrate that these spiral features can be detected with an interferometer in H α and K-band emission. We also show that the spiral features affect the axis ratios determined by interferometry depending on the orientation of these features and the observer. For example, our simulations show that the axis ratios can vary by 20 per cent for our co-planar binary disc system depending on the location of the disc density enhancements.
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.
Aims.
Both components of the bright eclipsing binary
α
Dra have been resolved using long baseline interferometry and the secondary component has been shown to contribute approximately 15% of the ...total flux; however, a spectroscopic detection of the companion star has so far been unsuccessful. We aim for a firm spectroscopic detection of the secondary component of
α
Dra using state-of-the-art spectroscopic analysis methods for very high-quality spectroscopic observations. This will allow the determination of fundamental and atmospheric properties of the components in the system with high precision and accuracy.
Methods.
To achieve our goals, we use a combined data set from interferometry with the Navy Precision Optical Interferometer (NPOI), photometry with the TESS space observatory, and high-resolution spectroscopy with the H
ERMES
fibre-fed spectrograph at the La Palma observatory. We use the method of spectral disentangling to search for the contribution of a companion star in the observed composite H
ERMES
spectra, to separate the spectral contributions of both components, and to determine orbital elements of the
α
Dra system. TESS light curves are analysed in an iterative fashion with spectroscopic inference of stellar atmospheric parameters to determine fundamental stellar properties and their uncertainties. Finally, NPOI interferometric measurements are used for determination of the orbital parameters of the system and angular diameters of both binary components.
Results.
We report the first firm spectroscopic detection of the secondary component in
α
Dra and deliver disentangled spectra of both binary components. The components’ masses and radii are inferred with high precision and accuracy, and are
M
A
= 3.186 ± 0.044
M
⊙
,
R
A
= 4.932 ± 0.036
R
⊙
, and
M
B
= 2.431 ± 0.019
M
⊙
,
R
B
= 2.326 ± 0.052
R
⊙
for the primary and secondary components, respectively. Combined astrometric and spectroscopic analysis yields the semi-major axis of the system, which is ultimately used to derive the dynamical parallax of
π
= 11.48 ± 0.13 mas, and the distance
d
= 87.07 ± 1.03 pc to the
α
Dra system. Evolutionary analysis of both binary components with M
ESA
stellar structure and evolution models suggests the primary is an evolved post-TAMS A-type star, while the companion is a main-sequence A-type star with a convective core mass of
M
cc
= 0.337 ± 0.011
M
⊙
. Positions of both binary components in the Kiel- and HR-diagrams suggest a value of the convective core overshooting parameter
f
ov
well below 0.010
H
p
, and we infer the age of the system to be 310 ± 25 Myr.
Conclusions.
The inferred near-core mixing properties of both components do not support a dependence of the convective core overshooting on the stellar mass. At the same time, the
α
Dra system provides extra support to hypothesise that the mass discrepancy in eclipsing spectroscopic double-lined binaries is associated with inferior atmospheric modelling of intermediate- and high-mass stars, and less so with the predictive powerof stellar structure and evolution models as to the amount of near-core mixing and mass of the convective core.
THE Hα PROFILES OF Be SHELL STARS Silaj, J; Jones, C E; Sigut, T A A ...
The Astrophysical journal,
11/2014, Volume:
795, Issue:
1
Journal Article
Peer reviewed
A new set of theoretical H alpha emission line profiles of Be stars has been computed using the code BERAY, which solves the transfer equation along a series of rays passing through the star+disk ...system, representing an improved treatment over earlier work done by the authors. The new profiles were compared with the previous work, and general trends (such as line profile shapes and correlations between line equivalent widths as a function of initial density rho sub(0) and power law index n) were recovered. Additionally, BERAY was employed to model the spectra of eight well-known Be shell stars. Some degeneracy was found in the choice of model parameters, highlighting the need to employ alternate observables to constrain the models. However, the inclination angle of the model seemed relatively insensitive to the choices of other parameters, and we show that, with our models, only a very small range of inclination angles can adequately reproduce the observations. Five of our eight targets were found to have inclination angles of 70degrees or higher, and two more were found to have inclination angles of 67degrees and 65degrees. The observation of one target-4 Aquilae-could only be reproduced by models created at an inclination angle of approximately 45degrees.
This work presents a novel method to estimate the effective opening angle of CBe star disks from projected axis ratio measurements, obtained by interferometry using a statistical approach. A Monte ...Carlo scheme was used to generate a large set of theoretical axis ratios from disk models using different distributions of disk densities and opening angles. These theoretical samples were then compared to observational samples, using a two-sample Kolmogorov-Smirnov test, to determine which theoretical distribution best reproduces the observations. The results suggest that the observed ratio distributions in the K, H, and N band can best be explained by the presence of thin disks, with opening half-angles of the order of 0.degrees15-4.degrees0. Results for measurements over the H alpha line point toward slightly thicker disks, 3.degrees7-14degrees, which is consistent with a flaring disk predicted by the viscous disk model.
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