I present a personal view of Wojtek Dziembowski's scientific career, derived mainly from my direct interactions with Wojtek. Necessarily this presentation is biased towards the earlier days, partly because we interacted more then, and partly because the presentation after mine is by a local admirer who has been much more involved than I with Wojtek's later work.

Selected events of the scientific biography of Wojtek Dziembowski are briefly described, and several related photos are presented. The full version of the presentation is available at the IAU Symposium 301 webpage.

Precision asteroseismology is the determination of accurate stellar parameters from oscillation data. At first successful for pulsating white dwarf stars, it is now applied to more and more types of stars. We give a number of selected examples where precision asteroseismology, but also asteroseismology based on few observables may lead to considerable improvement of stellar astrophysics in the near future.

We present some results of long-term studies of pulsating stars conducted in the course of the OGLE and Araucaria projects. In particular, very scarce eclipsing binaries containing pulsating stars are discussed. Such systems provide a unique opportunity to improve calibration of the cosmic distance scale and to better calibrate stellar evolutionary models.

The All-Sky Automated Survey (ASAS) appeared to be extremely useful in establishing the census of bright variable stars in the sky. A short review of the characteristics of the ASAS data and discoveries based on these data and related to pulsating stars is presented here by an enthusiastic user of the ASAS data.

The highly successful SuperWASP planetary transit finding programme has surveyed a large fraction of both the northern and southern skies. There now exists in its archive over 420 billion photometric measurements for more than 31 million stars. SuperWASP provides good quality photometry with a precision exceeding 1% per observation in the approximate magnitude range 9 < V < 12. The archive enables long-baseline, high-cadence studies of stellar variability to be undertaken. An overview of the SuperWASP project is presented, along with results which demonstrate the survey's asteroseismic capabilities.

We summarize the properties of the new periodic, small-amplitude, variable stars recently discovered in the open cluster NGC 3766. They are located in the region of the Hertzsprung-Russell diagram between δ Sct and slowly pulsating B stars, a region where no sustained pulsation is predicted by standard models. The origin of their periodic variability is currently unknown. We also discuss how the Gaia mission, launched at the end of 2013, can contribute to our knowledge of those stars.

Since its launch in December 2006, the CoRoT satellite has provided photometric data precise down to the micro-magnitude level for about 150 bright stars and 150 000 fainter ones. These stars have been observed over runs covering up to 160 days with a 90% duty cycle. Seismic data of such precision had been longed for by the scientific community for decades, and expected as a way of making progress in our understanding of stellar structure and evolution. The analysis and interpretation of CoRoT seismic data have indeed made it possible to place observational constraints on several key aspects of stellar structure and evolution, such as the size of mixed convective cores, magnetic activity, mass loss. . . We here present some highlights of the CoRoT results and their implications in terms of internal stellar structure.

Fundamental mode classical Cepheids have light curves which repeat accurately enough that we can watch them evolve (change period). The new level of accuracy and quantity of data with the Kepler and MOST satellites probes this further. An intriguing result was found in the long time-series of Kepler data for V1154 Cyg the one classical Cepheid (fundamental mode, P = 4.9 d) in the field, which has short term changes in period (≃20 minutes), correlated for ≃10 cycles (period jitter). To follow this up, we obtained a month long series of observations of the fundamental mode Cepheid RT Aur and the first overtone pulsator SZ Tau. RT Aur shows the traditional strict repetition of the light curve, with the Fourier amplitude ratio R1/R2 remaining nearly constant. The light curve of SZ Tau, on the other hand, fluctuates in amplitude ratio at the level of approximately 50%. Furthermore prewhitening the RT Aur data with 10 frequencies reduces the Fourier spectrum to noise. For SZ Tau, considerable power is left after this prewhitening in a complicated variety of frequencies.

The star HD 51844 was observed in the CoRoT LRa02 as a target in the seismology field, which turned out to be an SB2 system. The 117-day light curve revealed δ Scuti pulsations in the range of 6 to 15 d−1 where four frequencies have amplitudes larger than 1.4 mmag, and a rich frequency spectrum with amplitudes lower than 0.6 mmag. Additionally, the light curve exhibits a 3-mmag brightening event recurring every 33.5 days with a duration of about 5 days. The radial velocities from spectroscopy confirmed that the star is an eccentric binary system with nearly identical masses and physical parameters. The brightening event in the light curve coincides with the maximum radial-velocity separation showing that the brightening is in fact caused by tidal distortion and/or reflected light. One component displays large line-profile variations, while the other does not show significant variation. The frequency analysis revealed a quintuplet structure of the four highest-amplitude frequencies, which is due to the orbital motion of the pulsating star.

We examine the light curves of over 2700 stars observed in long cadence by the Kepler spacecraft as part of the Guest Observer program. Most of these stars are faint (Kepler magnitude > 14), and fall near or within the effective temperature and log g range of the γ Dor and δ Sct instability strips. We find that the pulsating stars are obvious from inspection of the light curves and power spectra, even for these faint stars. However, we find that a large number of stars are ‘constant’, i.e. show no frequencies in the 0.2 to 24 d−1 range above the 20 ppm level. We discuss the statistics for the constant stars, and some possible physical reasons for lack of pulsations. On the other hand, γ Dor and δ Sct candidates have been found in the Kepler data spread throughout and even outside of the instability regions of both types that were established from pre-Kepler ground-based observations. We revisit mechanisms to produce g- or p-mode pulsations in conditions when these modes are not expected to be unstable via the He-ionization κ effect (δ Sct) or convective blocking (γ Dor) pulsation driving mechanisms.

BRITE-Constellation (where BRITE stands for BRIght Target Explorer) is an international nanosatellite mission to monitor photometrically, in two colours, brightness and temperature variations of stars brighter than V ≈ 4, with precision and time coverage not possible from the ground. The current mission design consists of three pairs of 7 kg nanosats (hence “Constellation”) from Austria, Canada and Poland carrying optical telescopes (3 cm aperture) and CCDs. One instrument in each pair is equipped with a blue filter; the other, a red filter. The first two nanosats (funded by Austria) are UniBRITE, designed and built by UTIAS-SFL (University of Toronto Institute for Aerospace Studies-Space Flight Laboratory) and its twin, BRITE-Austria, built by the Technical University Graz (TUG) with support of UTIAS-SFL. They were launched on 25 February 2013 by the Indian Space Agency, under contract to the Canadian Space Agency.

Each BRITE instrument has a wide field of view (≈ 24 degrees), so up to 15 bright stars can be observed simultaneously in 32 × 32 sub-rasters. Photometry (with reduced precision but thorough time sampling) of additional fainter targets will be possible through on-board data processing. A critical technical element of the BRITE mission is the three-axis attitude control system to stabilize a nanosat with very low inertia. The pointing stability is better than 1.5 arcminutes rms, a significant advance by UTIAS-SFL over any previous nanosatellite.

BRITE-Constellation will primarily measure p- and g-mode pulsations to probe the interiors and ages of stars through asteroseismology. The BRITE sample of many of the brightest stars in the night sky is dominated by the most intrinsically luminous stars: massive stars seen at all evolutionary stages, and evolved medium-mass stars at the very end of their nuclear burning phases (cool giants and AGB stars). The Hertzsprung-Russell diagram for stars brighter than mag V=4 from which the BRITE-Constellation sample will be selected is shown in Fig. 1. This sample falls into two principal classes of stars:

(1) Hot luminous H-burning stars (O to F stars). Analyses of OB star variability have the potential to help solve two outstanding problems: the sizes of convective (mixed) cores in massive stars and the influence of rapid rotation on their structure and evolution.

(2) Cool luminous stars (AGB stars, cool giants and cool supergiants). Measurements of the time scales involved in surface granulation and differential rotation will constrain turbulent convection models.

Mass loss from these stars (especially the massive supernova progenitors) is a major contributor to the evolution of the interstellar medium, so in a sense, this sample dominates cosmic “ecology” in terms of future generations of star formation. The massive stars are believed to share many characteristics of the lower mass range of the first generation of stars ever formed (although the original examples are of course long gone).

BRITE observations will also be used to detect some Jupiter- and even Neptune-sized planets around bright host stars via transits, as expected on the basis of statistics from the Kepler exoplanet mission. Detecting planets around such very bright stars will greatly facilitate their subsequent characterization. BRITE will also use surface spots to investigate stellar rotation.

The following Table summarizes launch and orbit parameters of BRITE-Constellation components.

The full version of this paper describing in more detail BRITE-Constellation will be published separately in a journal. The symposium presentation is available at http://iaus301.astro.uni.wroc.pl/program.php

The prototype telescope and instruments for the Stellar Observations Network Group (SONG) are nearing completion at the Observatorio del Teide on Tenerife. In this contribution we describe the current status (autumn 2013) of the telescope and its instrumentation. Preliminary performance characteristics are presented for the high-resolution spectrograph based on daytime observations of the Sun and a 4 hour test series obtained for the sub-giant β Aquilae.

Asteroseismology depends absolutely on the detection of authentic pulsation signatures in stars. A variety of mathematical and statistical tools have been developed to extract such signatures from photometric and spectroscopic time series. The earliest tools were developed on the platform of Fourier analysis, and Fourier-based methodology still plays a major part in the detection of pulsation signatures in the present day. Alternative approaches have been gaining ground in recent years. This article offers a brief but broad review of the various methodologies for detecting authentic periodic signals that have been developed over the past few decades, including examples of their pitfalls and successes.

The power of asteroseismology relies on the ability to infer the stellar structure from the unambiguous frequency identification of the corresponding pulsation mode. Hence, the use of a Fourier transform is in the basis of asteroseismic studies. Nevertheless, the difficulties with the interpretation of the frequencies found in many stars lead us to reconsider whether Fourier analysis is the most appropriate technique to identify pulsation modes. We have found that the data, usually analyzed using Fourier techniques, present a non-analyticity originating from the lack of connectivity of the underlying function describing the physical phenomena. Therefore, the conditions for the Fourier series to converge are not fulfilled. In the light of these results, we examine in this talk some stellar light curves from different asteroseismology space missions (CoRoT, Kepler and SoHO) in which the interpretation of the data in terms of Fourier frequencies becomes difficult. We emphasize the necessity of a new interpretation of the stellar light curves in order to identify the correct frequencies of the pulsation modes.

We study the theoretical properties of the regular spacings found in the oscillation spectra of δ Scuti stars. A linear relation between the large separation and the mean density is predicted to be found in the low-frequency domain (i.e. radial orders spanning from 1 to 8, approximately) of the main-sequence δ Scuti stars' oscillation spectrum. This implies an independent direct measure of the average density of δ Scuti stars, analogous to that of the Sun, and places tight constraints on the mode identification and hence on the stellar internal structure and dynamics, and allows a determination the radii of planets orbiting around δ Scuti stars with unprecedented precision. This opens the way for studying the evolution of regular patterns in pulsating stars, and its relation to stellar structure and evolution.

The identification of the detected pulsation modes in terms of the spherical harmonic quantum numbers is crucial for asteroseismology. Light curves obtained in different passbands have become an important tool for mode identifications, which rely on wavelength-dependent amplitudes and phase shifts. We demonstrate this for different types of pulsators and review recent successes from earth-based measurements, especially in determining the important l values. The extensive amount of accurate data needed to determine small phase shifts and accurate amplitude ratios suggests multicolor measurements using space satellites. This motivated the multicolor BRITE satellite project, for which the first two satellites have already been launched successfully. We demonstrate the potential from models computed for the BRITE wavelengths. Most of the excellent presently available satellite photometry is not multicolor, although frequencies with amplitudes as small as a few parts-per-million have been detected and confirmed. We briefly discuss mode identifications from frequency patterns, including the use of correlations between phase and amplitude changes.

Time-series of high-resolution spectra of massive main-sequence pulsators contain information on the degree l and azimuthal number m of a pulsation mode. I present an overview of existing mode-identification techniques that have been developed to derive l and m from spectroscopic data. I also discuss the data quality needed to perform such a study. Through some examples from the literature I show that the optimal way to identify modes in heat-driven non-radial pulsators is by 1) using multi-site campaign data, 2) combining different spectroscopic mode-identification techniques, and 3) combining results from photometric and spectroscopic mode-identification studies.

Attempts to interpret the observed oscillation spectrum of the SPB star HD 50230 are reported. We argue that a nearly equidistant period spacing found in the oscillation spectrum of the star is most likely accidental. The observed period distribution requires excitation of modes with the degree l > 4. Much more may be learned from the rich oscillation spectrum of the star but most of the work is still ahead of us.

The musician programme at the University of Canterbury has been successfully identifying pulsation modes in many γ Doradus stars using hundreds of ground-based spectroscopic observations. This paper describes some of the successful mode identifications and emerging patterns of the programme. The hybrid γ Doradus/δ Scuti star HD 49434 remains an enigma, despite the analysis of more than 1700 multi-site high-resolution spectra. A new result for this star is apparently distinct line-profile variations for the γ Doradus and δ Scuti frequencies.