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Register a new userBeta Lyrae as seen by BRITE in 2016
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The BTr and UBr satellites observed $beta$ Lyrae from May to October 2016 to continuously monitor light-curve instabilities with the time resolution of about 100 mins. An instrumental problem affecting localized patches on the BTr CCD detector has been discovered by comparison with partly simultaneous UBr observations; the origin of the problem is being investigated. A zero-point offset permits utilization of the BTr data for a time-series characterization of deviations from the mean light curve defined to $simeq 0.0025$ mag.
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Observations of Beta Lyr in four months of 2018 by three BRITE Constellation satellites (the red-filter BTr and BHr, and the blue-filter BLb) permitted a first, limited look into the light-curve variability in two spectral bands. The variations were found to be well correlated outside the innermost primary minima with the blue variations appearing to have smaller amplitudes than the red; this reduction may reflect their presumed origin in the cooler, outer parts of the accretion disk. This result must be confirmed with more extensive material as the current conclusions are based on observations spanning slightly less than three orbital cycles of the binary. The assumption of an instrumental problem and the applied corrections made to explain the unexpectedly large amplitude of the red-filter light-curve observed with the BTr satellite in 2016 are fully confirmed by the 2018 results.
Photometric instabilities of $beta$ Lyr were observed in 2016 by two red-filter BRITE satellites over more than 10 revolutions of the binary, with $sim$100-minute sampling. Analysis of the time series shows that flares or fading events take place typically 3 to 5 times per binary orbit. The amplitudes of the disturbances (relative to the mean light curve, in units of the maximum out-of-eclipse light-flux, f.u.) are characterized by a Gaussian distribution with $sigma=0.0130pm0.0004$ f.u. Most of the disturbances appear to be random, with a tendency to remain for one or a few orbital revolutions, sometimes changing from brightening to fading or the reverse. Phases just preceding the center of the deeper eclipse showed the most scatter while phases around secondary eclipse were the quietest. This implies that the invisible companion is the most likely source of the instabilities. Wavelet transform analysis showed domination of the variability scales at phase intervals $0.05-0.3$ (0.65--4 d), with the shorter (longer) scales dominating in numbers (variability power) in this range. The series can be well described as a stochastic Gaussian process with the signal at short timescales showing a slightly stronger correlation than red noise. The signal de-correlation timescale $tau=(0.068pm0.018)$ in phase or $(0.88pm0.23)$~d appears to follow the same dependence on the accretor mass as that observed for AGN and QSO masses 5--9 orders of magnitude larger than the $beta$~Lyr torus-hidden component.
The unprecedented photometric precision along with the quasi-continuous sampling provided by the Kepler space telescope revealed new and unpredicted phenomena that reformed and invigorated RR Lyrae star research. The discovery of period doubling and the wealth of low-amplitude modes enlightened the complexity of the pulsation behavior and guided us towards nonlinear and nonradial studies. Searching and providing theoretical explanation for these newly found phenomena became a central question, as well as understanding their connection to the oldest enigma of RR Lyrae stars, the Blazhko effect. We attempt to summarize the highest impact RR Lyrae results based on or inspired by the data of the Kepler space telescope both from the nominal and the K2 missions. Besides the three most intriguing topics, the period doubling, the low-amplitude modes, and the Blazhko effect, we also discuss the challenges of Kepler photometry that played a crucial role in the results. The secrets of these amazing variables, uncovered by Kepler, keep the theoretical, ground-based and space-based research inspired in the post-Kepler era, since light variation of RR Lyrae stars is still not completely understood.
Context. Debris discs are thought to be formed through the collisional grinding of planetesimals, and can be considered as the outcome of planet formation. Understanding the properties of gas and dust in debris discs can help us to comprehend the architecture of extrasolar planetary systems. Herschel Space Observatory far-infrared (IR) photometry and spectroscopy have provided a valuable dataset for the study of debris discs gas and dust composition. This paper is part of a series of papers devoted to the study of Herschel PACS observations of young stellar associations. Aims. This work aims at studying the properties of discs in the Beta Pictoris Moving Group (BPMG) through far-IR PACS observations of dust and gas. Methods. We obtained Herschel-PACS far-IR photometric observations at 70, 100 and 160 microns of 19 BPMG members, together with spectroscopic observations of four of them. Spectroscopic observations were centred at 63.18 microns and 157 microns, aiming to detect [OI] and [CII] emission. We incorporated the new far-IR observations in the SED of BPMG members and fitted modified blackbody models to better characterise the dust content. Results. We have detected far-IR excess emission toward nine BPMG members, including the first detection of an IR excess toward HD 29391.The star HD 172555, shows [OI] emission, while HD 181296, shows [CII] emission, expanding the short list of debris discs with a gas detection. No debris disc in BPMG is detected in both [OI] and [CII]. The discs show dust temperatures in the range 55 to 264 K, with low dust masses (6.6*10^{-5} MEarth to 0.2 MEarth) and radii from blackbody models in the range 3 to 82 AU. All the objects with a gas detection are early spectral type stars with a hot dust component.
RR Lyrae stars for a long time had the reputation of being rather simple pulsators, but the advent of high-precision space photometry has meanwhile changed this picture dramatically. This article summarizes the results obtained for two remarkable Blazhko RR Lyrae stars and discusses how our view of RR Lyrae stars has changed since the availability of ultra-precise satellite photometry as it is obtained by CoRoT and Kepler. Both stars, CoRoT 105288363 and V445 Lyrae, show a multitude of phenomena that were impossible to observe from the ground, either because of the small amplitude of the effect, or because uninterrupted long-term monitoring was required for a detection. Not only was it found that strong and irregular cycle-to-cycle changes of the Blazhko effect can occur, and that seemingly chaotic phenomena need to be accounted for when modeling the Blazhko effect, but also a rich spectrum of low-amplitude frequencies was detected in addition to the fundamental radial pusation in RRab stars. The so-called period doubling phenomenon, higher radial overtones and possibly also non-radial modes make RR Lyrae stars more multifaceted than previously thought. This article presents the various aspects of irregularity of the Blazhko effect, questioning its long-standing definition as a periodic modulation, and also discusses the low-amplitude pulsation signatures that had been hidden in the noise of observations for centuries.
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