Description: The recent precise photometric observations and successes of the modelling efforts transformed our picture of the pulsation of RR Lyrae stars. The discovery of additional frequencies and the period doubling phenomenon revealed that a significant interaction may occur between pulsational modes. The signs of irregularities were detected both in observed light curves and hydrodynamic calculations. In this paper, we present the analysis of four peculiar hydrodynamic model solutions. All four solutions were found to be chaotic. The fractal (Lyapunov) dimensions of their attractors were calculated to be ~2.2. We also investigated possible resonances between the fundamental mode and the first overtone in the dynamical neighbourhood of these models. The most important is the 6:8 resonance that was also detected in the Kepler observations of RR Lyrae itself. These results reveal that the investigation of chaotic models is important in discovering and understanding resonances in RR Lyrae stars.

Description: We present a detailed non-linear dynamical investigation of the Blazhko modulation of the Kepler RR Lyrae star V783 Cyg (KIC 5559631). We used different techniques to produce modulation curves, including the determination of amplitude maxima, the O–C diagram and the analytical function method. We were able to fit the modulation curves with chaotic signals with the global flow reconstruction method. However, when we investigated the effects of instrumental and data processing artefacts, we found that the chaotic nature of the modulation cannot be proved because of the technical problems of data stitching, detrending and sparse sampling. Moreover, we found that a considerable part of the detected cycle-to-cycle variation of the modulation may originate from these effects. According to our results, even the four-year-long, unprecedented Kepler space photometry of V783 Cyg is too short for a reliable non-linear dynamical analysis aiming at the detection of chaos from the Blazhko modulation. We estimate that two other stars could be suitable for similar analysis in the Kepler sample and in the future TESS and PLATO may provide additional candidates.

Description: A detailed analysis is presented of 33 RR Lyrae stars in Pisces observed with the Kepler space telescope over the 8.9-d long K2 Two-Wheel Concept Engineering Test. The sample includes not only fundamental-mode and first-overtone (RRab and RRc) stars but the first two double-mode (RRd) stars that Kepler detected and the only modulated first-overtone star ever observed from space so far. The precision of the extracted K2 light curves made it possible to detect low-amplitude additional modes in all subtypes. All RRd and non-modulated RRc stars show the additional mode at P X / P 1  ~ 0.61 that was detected in previous space-based photometric measurements. A periodicity longer than the fundamental mode was tentatively identified in one RRab star that might belong to a gravity mode. We determined the photometric [Fe/H] values for all fundamental-mode stars and provide the preliminary results of our efforts to fit the double-mode stars with non-linear hydrodynamic pulsation models. The results from this short test run indicate that the K2 mission will be, and has started to be, an ideal tool to expand our knowledge about RR Lyrae stars. As a by-product of the target search and analysis, we identified 165 bona fide double-mode RR Lyrae stars from the Catalina Sky Survey observations throughout the sky, 130 of which are new discoveries.

Description: The 2014 LoNNe (Loss of the Night Network) intercomparison campaign is the third of four campaigns planned during EU COST Action ES1204. This report provides a brief synopsis of the campaign and its preliminary outcomes. Section 2 describes the measurement locations, the activities of the participants, the instruments used, and the environmental conditions. Section 3 describes a public outreach event held during the campaign. Section 4 provides some preliminary results, outlines the ongoing analyses, and presents research questions for the next campaign to address. Section 5 provides recommendations for the final LoNNe intercomparison campaign in 2016. Section 6 concludes the report.

Description: The 2016 LoNNe (Loss of the Night Network) intercomparison campaign is the fourth of four campaigns planned during EU COST Action ES1204. The first campaign took place in 2013 in Lastovo, Croatia, the second in Madrid, Spain (Bará et al 2015), the third in Torniella and Florence, Italy (Kyba et al 2015a). The 2016 campaign took place at the Parc Astronòmic Montsec (PAM). The campaign was supported by the European Collective Awareness Platform for Social and Sustainable Innovation (CAPPSI) STARS4ALL, in which the activity is planned to become a continuous light pollution initiative (LPI). The financing of this campaign, which is listed as a milestone in the MoU of the COST Action ES1204, was unexpectedly waived by the EU-COST Office due to administrative complications and re-organization of the grant-periods. The campaign continued the strategy of taking measurements at multiple sites, this year with a main fixed site and then excursions to other sites. The goals of the campaigns included: ● Understanding the difference between extinction measurements made by DSLR photometry and classical astronomical (telescope) photometry, and also understanding the relation between extinction and sky brightness at these two sites. ● Examining the difference in radiance measured with the mosaic technique of the US National Parks Service camera compared to all-sky fisheye imagery ● Examining the relationships between all-sky and zenith radiance reported by different instruments ● Quantifying the sky brightness at the sites, including full zenith spectral radiance at selected locations ● Measuring the systematic uncertainty on handheld SQM observations due to unit-to-unit differences This report provides a brief synopsis of the campaign and its preliminary outcomes. Section 2 describes the measurement locations, the detailed activities of the participants, the instruments used, and the environmental conditions. Section 3 describes a meeting with local authorities that took place during the campaign. Section 4 provides some preliminary results, outlines the ongoing analyses, and presents research questions for the next campaign to address. Section 5 provides recommendations for future intercomparison campaigns. The Municipality of Balaguer coordinated with us regarding the time that architectural lamps were turned off, and the village of Àger allowed us to turn all street lighting off at a time of our choice.