The Be phenomenon is present in about 20 per cent of B-type stars. Be stars show variability on a broad range of time-scales, which in most cases is related to the presence of a circumstellar disc of variable size and structure. For this reason, a time-resolved survey is highly desirable in order to understand the mechanisms of disc formation, which are still poorly understood. In addition, a complete observational sample would improve the statistical significance of the study of stellar and disc parameters. The ‘Be Stars Observation Survey’ (BeSOS) is a survey containing reduced spectra obtained using the Pontifica Universidad Católica High Echelle Resolution Optical Spectrograph (PUCHEROS) with a spectral resolution of 17 000 in the range 4260–7300 Å. BeSOS's main objective is to offer consistent spectroscopic and time-resolved data obtained with one instrument. The user can download or plot the data and obtain stellar parameters directly from the website. We also provide a star-by-star analysis based on photometric, spectroscopic and interferometric data, as well as general information about the whole BeSOS sample. Recently, BeSOS led to the discovery of a new Be star HD 42167 and facilitated study of the V/R variation of HD 35165 and HD 120324, the steady disc of HD 110335 and the Be shell status of HD 127972. Optical spectra used in this work, as well as the stellar parameters derived, are available online at http://besos.ifa.uv.cl.

Mass loss from massive stars plays a determining role in their evolution through the upper Hertzsprung–Russell diagram. The hydrodynamic theory that describes their steady-state winds is the line-driven wind theory (m-CAK). From this theory, the mass loss rate and the velocity profile of the wind can be derived, and estimating these properly will have a profound impact on quantitative spectroscopy analyses from the spectra of these objects. Currently, the so-called $\beta$ law, which is an approximation for the fast solution, is widely used instead of m-CAK hydrodynamics, and when the derived value is $\beta \gtrsim 1.2$, there is no hydrodynamic justification for these values. This review focuses on (1) a detailed topological analysis of the equation of motion (EoM), (2) solving the EoM numerically for all three different (fast and two slow) wind solutions, (3) deriving analytical approximations for the velocity profile via the LambertW function and (4) presenting a discussion of the applicability of the slow solutions.

Classical B emission (Be) stars are fast rotating, near-main-sequence B-type stars. The rotation and the presence of circumstellar discs profoundly modify the observables of active Be stars. Our goal is to infer stellar and disc parameters, as well as distance and interstellar extinction, using the currently most favoured physical models for these objects. We present BeAtlas, a grid of $61\, 600$ non-local thermodynamic equilibrium radiative transfer models for Be stars, calculated with the hdust code. The grid was coupled with a Monte Carlo Markov chain (MCMC) code to sample the posterior distribution. We test our method on two well-studied Be stars, α Eri and β CMi, using photometric, polarimetric, and spectroscopic data as input to the code. We recover literature determinations for most of the parameters of the targets, in particular the mass and age of α Eri, the disc parameters of β CMi, and their distances and inclinations. The main discrepancy is that we estimate lower rotational rates than previous works. We confirm previously detected signs of disc truncation in β CMi and note that its inner disc seems to have a flatter density slope than its outer disc. The correlations between the parameters are complex, further indicating that exploring the entire parameter space simultaneously is a more robust approach, statistically. The combination of BeAtlas and Bayesian-MCMC techniques proves successful, and a powerful new tool for the field: The fundamental parameters of any Be star can now be estimated in a matter of hours or days.

Double Periodic Variables (DPV) are among the new enigmas of semi-detached eclipsing binaries. These are intermediate-mass binaries characterized by a long photometric period lasting on average 33 times the orbital period. We present a spectroscopic and photometric study of the DPV V495 Cen based on new high-resolution spectra and the ASAS V-band light curve. We have determined an improved orbital period of 33.492 ± 0.002 d and a long period of 1283 d. We find a cool evolved star of M₂ = 0.91 ± 0.2M_⊙, T₂ = 6000 ± 250K and R₂ = 19.3 ± 0.5R_⊙ and a hot companion of M₁ = 5.76 ± 0.3M_⊙, T₁ = 16960 ± 400K and R = 4.5 ± 0.2R_⊙. The mid-type B dwarf is surrounded by a concave and geometrically thick disc, of radial extension R_d = 40.2 ± 1.3R_⊙ contributing ∼ 11 percent to the total luminosity of the system at the V band. The system is seen under inclination 84.°8 ± 0.°6 and it is at a distance d = 2092 ± 104.6 pc. The light curve analysis suggests that the mass transfer stream impacts the external edge of the disc forming a hot region 11% hotter than the surrounding disc material. The persistent V < R asymmetry of the Hα emission suggests the presence of a wind and the detection of a secondary absorption component in He I lines indicates a possible wind origin in the hotspot region.

Aims. We performed a spectral fitting for a set of O-type stars based on self-consistent wind solutions, which provide mass-loss rate and velocity profiles directly derived from the initial stellar parameters. The great advantage of this self-consistent spectral fitting is therefore the reduction of the number of free parameters to be tuned. Methods. Self-consistent values for the line-force parameters (k, α, δ)_sc and subsequently for the mass-loss rate, M_sc, and terminal velocity, υ_∞‚sc, are provided by the m-CAK prescription introduced in Paper I, which is updated in this work with improvements such as a temperature structure T(r) for the wind that are self-consistently evaluated from the line-acceleration. Synthetic spectra were calculated using the radiative transfer code FASTWIND, replacing the classical β-law for our new calculated velocity profiles v(r) and therefore making clumping the only free parameter for the stellar wind. Results. We found that self-consistent m-CAK solutions provide values for theoretical mass-loss rates of the order of the most recent predictions of other studies. From here, we generate synthetic spectra with self-consistent hydrodynamics to fit and obtain a new set of stellar and wind parameters for our sample of O-type stars (HD 192639, 9 Sge, HD 57682, HD 218915, HD 195592, and HD 210809), whose spectra were taken with the high-resolution echelle spectrograph HERMES (R = 85 000). We find a satisfactory global fit for our observations, with a good accuracy for photospheric He I and He II lines and a quite acceptable fit for H lines. Although this self-consistent spectral analysis is currently constrained in the optical wavelength range alone, this is an important step towards the determination of stellar and wind parameters without using a β-law. Based on the variance of the line-force parameters, we establish that our method is valid for O-type stars with T_eff ≥ 30 kK and log g ≥ 3.2. Given these results, we expect that the values introduced here are helpful for future studies of the stars constituting this sample, together with the prospect that the m-CAK self-consistent prescription may be extended to numerous studies of massive stars in the future.

Aims. In the context of Be stars, we re-studied the viscous transonic decretion disk model of these stars. This model is driven by a radiative force due to an ensemble of optically thin lines and viscosity considering the Shakura–Sunyaev prescription. Methods. The nonlinear equation of motion presents a singularity (sonic point) and an eigenvalue, which is also the initial condition at the stellar surface. Then, to obtain this eigenvalue, we set it as a radial quantity and performed a detailed topological analysis. We describe a numerical method for solving either nodal or saddle transonic solutions. Results. The value of the viscosity α barely determines the location of the sonic point, but it determines the topology of the solution. We found two nodal solutions, which are almost indistinguishable. Saddle solutions were found for lower values of α than required for the nodal solutions. In addition, rotational velocity does not play a determinate role in the velocity (and density) profile, because the viscosity effects collapse all the solutions to almost a unique one in a small region above the stellar surface. Conclusions. A suitable combination of line-force parameters and/or disk temperature gives the location of the sonic point lower than 50 stellar radii, describing a truncated disk. This could explain the SED turn-down observed in Be stars without needing a binary companion.