C. Aerts

Interpretation of the variability of the beta Cephei star lambda Scorpii : I: The multiple character

We derive accurate values of the orbital parameters of the close binary β Cephei star λ Scorpii. Moreover, we present the first determination of the properties of the triple system to which λ Scorpii belongs. Our analysis is based on a time series of 815 high-resolution spectra, covering a timespan of 14 years. We find a close orbit of 5. 9525 days (e = 0.26) and a wide orbit of approximately 1082 d days (e = 0.23). The orbital parameters of the triple star and a spectrum synthesis lead us to conclude that the system is composed of two early-type B stars and a low-mass pre-main-sequence star rather than containing an ultra- massive white dwarf as claimed before. Our proposed configuration is compatible with population synthesis. The radial velocity variations of the primary allow us to confirm the presence of at least one pulsation mode with frequency 4.679410 c d −1 which is subject to the light-time effect in the triple system. A detailed analysis of the complex line-profile variations is described in a subsequent paper.

Gaia Data Release 2: Summary of the variability processing and analysis results

Context. The Gaia Data Release 2 (DR2) contains more than half a million sources that are identified as variable stars. Aims: We summarise the processing and results of the identification of variable source candidates of RR Lyrae stars, Cepheids, long-period variables (LPVs), rotation modulation (BY Dra-type) stars, δ Scuti and SX Phoenicis stars, and short-timescale variables. In this release we aim to provide useful but not necessarily complete samples of candidates. Methods: The processed Gaia data consist of the G, GBP, and GRP photometry during the first 22 months of operations as well as positions and parallaxes. Various methods from classical statistics, data mining, and time-series analysis were applied and tailored to the specific properties of Gaia data, as were various visualisation tools to interpret the data. Results: The DR2 variability release contains 228 904 RR Lyrae stars, 11 438 Cepheids, 151 761 LPVs, 147 535 stars with rotation modulation, 8882 δ Scuti and SX Phoenicis stars, and 3018 short-timescale variables. These results are distributed over a classification and various Specific Object Studies tables in the Gaia archive, along with the three-band time series and associated statistics for the underlying 550 737 unique sources. We estimate that about half of them are newly identified variables. The variability type completeness varies strongly as a function of sky position as a result of the non-uniform sky coverage and intermediate calibration level of these data. The probabilistic and automated nature of this work implies certain completeness and contamination rates that are quantified so that users can anticipate their effects. Thismeans that even well-known variable sources can be missed or misidentified in the published data. Conclusions: The DR2 variability release only represents a small subset of the processed data. Future releases will include more variable sources and data products; however, DR2 shows the (already) very high quality of the data and great promise for variability studies.

Interpretation of the variability of the beta Cephei star Lambda Scorpii. II. The line-profile diagnostics

We present the results of our analysis of a time series of high-resolution spectra of the multiple β Cephei star λ Scorpii. The data set has a total time-span of more than 5000 days and includes an intensive monitoring campaign during 8 consecutive nights. We confirm the presence of a dominant frequency f1 = 4.679410 c d −1 in the data. We show that the amplitude is variable in time according to the light-time effect in the multiple system. The dominant frequency is identified as a prograde dipole pulsation mode. From modelling of the amplitudes and phases across the profiles we derive pulsational parameters, the inclination angle 70 ◦ ≤ i ≤ 90 ◦ and v sini ∼ 125 km s −1 . From a comparison between theoretically calculated forcing eigenfrequencies induced by the close companion and the eigenfrequencies of the observed oscillation mode we find no tidal enhancement or excitation of the pulsation mode of λ Scorpii. We find indications for the presence of additional frequencies with low amplitudes.

Latitude distribution of nonradial pulsations in rapidly rotating B stars

We present a method for the analysis of latitude distribution associated with temperature and/or velocity perturbations of the stellar surface due to non-radial pulsation (NRP) modes in rapidly rotating B stars. The technique is applied together with Fourier Doppler Imaging (FDI) to high resolution and high signal-to-noise ratio spectroscopic observations of ϵ Per. The main advantage of this approach is that it decomposes complex multi-periodic line profile variations into single components, allowing the detailed analysis of each mode separately. We study the 10.6-d −1 frequency that is particularly important for modal analysis of non-radial pulsations in the star.

Automated classification of periodic variable stars{Improved methodology for the automated classification of periodic variable stars}

We present a novel automated methodology to detect and classify periodic variable stars in a large database of photometric time series. The methods are based on multivariate Bayesian statistics and use a multi-stage approach. We applied our method to the ground-based data of the TrES Lyr1 field, which is also observed by the Kepler satellite, covering ~26000 stars. We found many eclipsing binaries as well as classical non-radial pulsators, such as slowly pulsating B stars, Gamma Doradus, Beta Cephei and Delta Scuti stars. Also a few classical radial pulsators were found.

Improved methodology for the automated classification of periodic variable stars: Automated classification of periodic variable stars

We present a novel automated methodology to detect and classify periodic variable stars in a large database of photometric time series. The methods are based on multivariate Bayesian statistics and use a multi-stage approach. We applied our method to the ground-based data of the TrES Lyr1 field, which is also observed by the Kepler satellite, covering ~26000 stars. We found many eclipsing binaries as well as classical non-radial pulsators, such as slowly pulsating B stars, Gamma Doradus, Beta Cephei and Delta Scuti stars. Also a few classical radial pulsators were found.

First results of Mercator observations of variable A and F stars

We report on the first results from observations of 31 variable A and F stars, obtained with the new Mercator telescope (La Palma). Besides confirming the γ Dor nature of known bonafide and candidate γ Dor stars, we also present new candidate γ Dor stars. In addition, we found a new short-period variable star.

Do temperature variations at the surface of a hot non-radial pulsator change significantly the line-profile variations ?

We present simulations of line-profile variations of Silicon lines in slowly-rotating non-radially pulsating β Cephei stars and SPB stars. Our goal is to examine how sensitive Si lines are to the non-adiabatic temperature variations at the surface of the star. We find that for realistic amplitudes of the velocity field, and for realistic amplitudes and phase differences for the non-adiabatic temperature and gravity variations, the Silicon lines variations are very little affected.

Long-term photometric and spectroscopic monitoring of slowly pulsating B stars

We review the current status of our long-term monitoring project on slowly pulsating B stars that we started in the course of 1996 and that was recently completed as far as the first part of our plan is concerned. In total, we have selected 17 southern and 8 northern stars. The idea is to fully exploit our current data in the near future and to select the most interesting targets for further very-long-term follow-up monitoring. A first conclusion is that half of the southern targets turn out to be spectroscopic binaries. Some of these have circular orbits and periods of the same order of magnitude as the intrinsic pulsation period(s) of the primary. The eccentric binaries have periods ranging from 12 to 460 d. For most stars the photometric behaviour is dominated by the same frequency as the intrinsic spectroscopic variability. Multiperiodicity in the expected frequency range is found for almost all stars. Two objects, however, turn out to have only one dominant pulsation mode.