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.

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 HERMES 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 HERMES 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 MA = 3.186 ± 0.044 M⊙, RA = 4.932 ± 0.036 R⊙, and MB = 2.431 ± 0.019 M⊙, RB = 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 MESA 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 Mcc = 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 fov well below 0.010 Hp, 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.

We acquired Hα 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 ρ0(r)=3×10−11(r/Req)−2.7gcm−3 , and an Hα-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.

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 ten 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 sdO companion to the Be 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 star's rotation axis and the observer's line-of-sight, usually called the inclination angle, can be reliably determined for Be stars via H$\alpha$ 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~(NPOI). We fit the H$\alpha$ emission line profile of each star to obtain a spectroscopic inclination angle $i_{\rm H\alpha}$. 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, $\Delta i \equiv i_{\rm H\alpha} - i_{\rm V^2}$, are normally distributed with a mean of zero and a standard deviation of $6.7$ degrees, and the linear correlation coefficient between $i_{\rm H\alpha}$ 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 H$\alpha$ 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 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.

We model the circumstellar disk of delta Sco using the three-dimensional Monte Carlo radiative transfer code HDUST in order to quantify the large-scale changes in the disk through the years 2000-2018, and to see if these changes can be attributed to the secondary star affecting the disk throughout its orbit. We determine our best-fitting models through matching simulated observations to actual H alpha spectroscopy and V-band photometric observations. Our modeling results confirm previous findings that the disk of delta Sco was forming early in the century. We also find a period of disk dissipation when the companion is at apastron, as well as a significant growth of the disk between 2009 and 2011, prior to the periastron of 2011. Due to the steady-state nature of the disk after 2011, it is difficult to say whether the variations seen are due to the effect of the close passage of the binary companion.

We use a smoothed particle hydrodynamics (SPH) code to examine the effects of a binary companion on a Be star disk for a range of disk viscosities and misalignment angles, i.e. the angle between the orbital plane and the primary’s spin axis. The density structures in the disk 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 analyzed 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 Hα 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% for our co-planar binary disk system depending on the location of the disk density enhancements.

We present the results of a multiplicity survey for a volume-limited sample of 29 main-sequence F0–G0 stars within 17 pc conducted with the Navy Precision Optical Interferometer (NPOI). Four companions were detected in previously known binary systems. The results for these stars show good agreement with previously published orbits. For one of these sources, ι Peg, the modeling of our data, which includes closure phase information, confirms the quadrant of the orbit. No new companions were detected in the sample (within separations of 3–860 mas and contrasts down to 3.5 mag at 700 nm). Combined with an extensive literature search, we provide a detailed listing of companions known around each star in the sample from prior spectroscopic and imaging/speckle observations, and we discuss the multiplicity frequency in the sample. We also discuss the prospects for future stellar multiplicity studies with the NPOI.

We present the fundamental properties of 87 stars based on angular diameter measurements from the Navy Precision Optical Interferometer, 36 of which have not been measured previously using interferometry. Our sample consists of 5 dwarfs, 3 subgiants, 69 giants, 3 bright giants, and 7 supergiants, and span a wide range of spectral classes from B to M. We combined our angular diameters with photometric and distance information from the literature to determine each star’s physical radius, effective temperature, bolometric flux, luminosity, mass, and age.

Context. The viscous decretion disk (VDD) model is able to explain most of the currently observable properties of the circumstellar disks of Be stars. However, more stringent tests, focusing on reproducing multitechnique observations of individual targets via physical modeling, are needed to study the predictions of the VDD model under specific circumstances. In the case of nearby, bright Be star beta CMi, these circumstances are a very stable low-density disk and a late-type (B8Ve) central star.Aims. The aim is to test the VDD model thoroughly, exploiting the full diagnostic potential of individual types of observations, in particular, to constrain the poorly known structure of the outer disk if possible, and to test truncation effects caused by a possible binary companion using radio observations.Methods. We use the Monte Carlo radiative transfer code HDUST to produce model observables, which we compare with a very large set of multitechnique and multiwavelength observations that include ultraviolet and optical spectra, photometry covering the interval between optical and radio wavelengths, optical polarimetry, and optical and near-IR (spectro) interferometry.Results. A parametric VDD model with radial density exponent of n = 3.5, which is the canonical value for isothermal flaring disks, is found to explain observables typically formed in the inner disk, while observables originating in the more extended parts favor a shallower, n = 3.0, density falloff. Theoretical consequences of this finding are discussed and the outcomes are compared with the predictions of a fully self-consistent VDD model. Modeling of radio observations allowed for the first determination of the physical extent of a Be disk (35(-5)(+10) stellar radii), which might be caused by a binary companion. Finally, polarization data allowed for an indirect measurement of the rotation rate of the star, which was found to be W greater than or similar to 0.98, i.e., very close to critical.

We utilize a multi-step modeling process to produce synthetic interferometric and spectroscopic observables, which are then compared to their observed counterparts. Our extensive set of interferometric observations of the Be star 48 Per, totaling 291 data points, were obtained at the Navy Precision Optical Interferometer from 2006 November 07 to 23. Our models were further constrained by comparison with contemporaneous Ha line spectroscopy obtained at the John S. Hall Telescope at the. Lowell Observatory on 2006 November 1. Theoretical spectral energy distributions, SEDs, for 48. Per were confirmed by comparison with observations over a wavelength regime of 0.4-60 mu m from Touhami et al. and Vieira et al. Our best-fitting combined model from Ha spectroscopy, Ha interferometry, and SED fitting has a power-law density fall off, n, of 2.3 and an initial density at the stellar surface of rho(0)= 1.0 x 10(-11) g cm(-3) with an inclination constrained by Ha spectroscopy and interferometry of 45 degrees +/- 5 degrees. The position angle for the system, measured east from north, is 114 degrees +/- 18 degrees. Our bestfit model shows that the disk emission originates in a moderately large disk with a radius of 25 R*,. which is consistent with a disk mass of approximately 5. x. 10(24) g or 3 x 10(-10) M-*. Finally, we compare our results with previous studies of 48. Per by Quirrenbach et al. and find agreement, whereas our disk size does not agree with Delaa et al., based on a much smaller visibility set.

We present the first results from an ongoing survey for multiplicity among the bright stars using the Navy Precision Optical Interferometer (NPOI). We first present a summary of NPOI observations of known multiple systems, including the first detection of the companion of beta Scuti with precise relative astrometry, to illustrate the instrument's detection sensitivity for binaries at magnitude differences Delta m less than or similar to 3 over the range of angular separation 3-860 milliarcseconds (mas). A limiting Delta m(700) similar to 3.5 is likely for binaries where the component spectral types differ by less than two. Model fits to these data show good agreement with published orbits, and we additionally present a new orbit solution for one of these stars, sigma Her. We then discuss early results of the survey of bright stars at delta >= -20 degrees. This survey, which complements previous surveys of the bright stars using speckle interferometry, initially emphasizes bright stars of spectral types F0 through K2. We report observations of 41 stars of apparent visual magnitude m(V) <= 4.30, all having been observed on multiple nights. Analysis of these data produces fitted angular separations, position angles, and component magnitude differences for six previously known visual binaries. Three additional systems were examined as possible binaries, but no conclusive detection could be made. No evidence of close stellar companions within our detection limit of Delta m approximate to 3 was found for the remaining 32 stars observed; however, uniform-disk angular diameters are reported for 11 of the resolved stars in this last group.

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, display shell characteristics in their spectra, and 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 years, which agrees with the observed period, and the behavior 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.

48 Librae is a well-known Be shell star that exhibits spectacular cyclic V/R asymmetries in its Balmer emission lines. In this work, we use the HDUST code to investigate the disk density structure required to produce this signature. By modelling one representative Ha profile, we obtain the two initial densities required to match each peak, and from this we infer the average initial disk density. Furthermore, we investigate the parameters of the central star by modelling the SED, and we constrain the inclination angle of the system with polarization measurements. We find 48 Lib is best represented by a B3V central star surrounded by a very dense disk with an average initial density of 1.1 x 10(-10) g cm(-3), and that the system is oriented at 85.

The B-emission stars 48 Per (HD 25940, HR 1273) and psi, Per(HD 22192, HR 1087) share similar stellar parameters with their disks viewed near pole-on in the case of 48 Per, and near edge-on for psi Per. An extensive set of high-quality interferometric observations were obtained for both stars between 2006 and 2011 with the Navy Precision Optical Interferometer (NPOI) in the H alpha emitting region. Using a three-step modelling process, model visibilities are compared to observations with a view toward achieving better constraints on the disk models than were possible with previous studies.