Evidence for mass accretion driven by spiral shocks onto the white dwarf in SDSS J123813.73–033933.0

We present high-time-resolution photometry and phase-resolved spectroscopy of the short-period (⁠Porb=80.52min⁠) cataclysmic variable SDSS J123813.73–033933.0, observed with the Hubble Space Telescope (HST), the Kepler/K2 mission, and the Very Large Telescope (VLT). We also report observations of the first detected superoutburst. SDSS J1238–0339 shows two types of variability: quasi-regular brightenings recurring every ≃8.5  h during which the system increases in brightness by ≃0.5mag, and a double-hump quasi-sinusoidal modulation at the orbital period. The detailed K2 light curve reveals that the amplitude of the double-humps increases during the brightenings and that their phase undergoes a ≃90° phase shift with respect to the quiescent intervals. The HST  data unambiguously demonstrate that these phenomena both arise from the heating and cooling of two relatively large regions on the white dwarf. We suggest that the double-hump modulation is related to spiral shocks in the accretion disc resulting in an enhanced accretion rate heating two localized regions on the white dwarf, with the structure of the shocks fixed in the binary frame explaining the period of the double humps. The physical origin of the 8.5  h brightenings is less clear. However, the correlation between the observed variations of the amplitude and phase of the double-humps with the occurrence of the brightenings is supportive of an origin in thermal instabilities in the accretion disc

Exploiting Redundancy: Separable Group Convolutional Networks on Lie Groups

Group convolutional neural networks (G-CNNs) have been shown to increase parameter efficiency and model accuracy by incorporating geometric inductive biases. In this work, we investigate the properties of representations learned by regular G-CNNs, and show considerable parameter redundancy in group convolution kernels. This finding motivates further weight-tying by sharing convolution kernels over subgroups. To this end, we introduce convolution kernels that are separable over the subgroup and channel dimensions. In order to obtain equivariance to arbitrary affine Lie groups we provide a continuous parameterisation of separable convolution kernels. We evaluate our approach across several vision datasets, and show that our weight sharing leads to improved performance and computational efficiency. In many settings, separable G-CNNs outperform their non-separable counterpart, while only using a fraction of their training time. In addition, thanks to the increase in computational efficiency, we are able to implement G-CNNs equivariant to the $\mathrm{Sim(2)}$ group; the group of dilations, rotations and translations. $\mathrm{Sim(2)}$-equivariance further improves performance on all tasks considered

Mixed methods and visual representation of data with CAQDAS: empirical study

Mixed Methods increasingly progress and help research to evolve, combining quantitative and qualitative perspectives and helping the researcher to interpret and represent the studied reality with a holistic approach. In order to exemplify the research process from the methodological complementarity, a contextualized study was carried out in the city of Valladolid (Spain) through a mixed approach with the objective of identifying the socio-labour actions implemented by third sector entities that work with people at risk and socially excluded, including women. For this purpose, semi-structured interviews were conducted with workers from the participating entities, and information was also collected in other formats such as roadmaps and reports from the centres. From the categorization, the codification of the speeches and the results of the quantitative scales we proceeded to the triangulation of the data, with the support of digital supports, CAQDAS. Nvivo 12 and webQDA were used. The node map, project map, coding matrices, dendrogram, word trees and word clouds were made. This made it possible to respond to the objective and the research question, concluding that each entity developed different degrees of socio-labour attention based on its degree of available resources. The study was an example of the representation of reality from the convergence of the quantitative perspective and the qualitative perspective.publishe

An anticorrelation between X-ray luminosity and H? equivalent width in X-ray binaries

We report an anticorrelation between continuum luminosity and the equivalent width (EW) of the H? emission line in X-ray binary systems. The effect is evident both in a universal monotonic increase in H? EW with time following outbursts, as systems fade, and in a comparison between measured EWs and contemporaneous X-ray measurements. The effect is most clear for black hole binaries in the low/hard X-ray state, which is prevalent at X-ray luminosities below ?1 per cent of the Eddington luminosity. We do not find strong evidence for significant changes in line profiles across accretion state changes, but this is hampered by a lack of good data at such times. The observed anticorrelation, highly significant for black hole binaries, is only marginally so for neutron star systems, for which there are far less data. Comparison with previously established correlations between optical and X-ray luminosity suggests that the line luminosity is falling as the X-ray and optical luminosities drop, but not as fast, approximately, as LH??L?0.4X?L?0.7opt . We briefly discuss possible origins for such an effect, including the optical depth, form of the irradiating spectrum and geometry of the accretion flow. Further refinement of the relation in the future may allow measurements of H? EW to be used to estimate the luminosity of, and hence the distance to, X-ray binary systems. Beyond this, further progress will require a better sample of spectrophotometric data

Ultraviolet studies of interacting binaries

Interacting Binaries consist of a variety of stellar objects in different stages of evolution and those containing accreting compact objects still represent a major challenge to our understanding of not only close binary evolution but also of the chemical evolution of the Galaxy. These end-points of binary star evolution are ideal laboratories for the study of accretion and outflow processes, and provide insight on matter under extreme physical conditions. One of the key-questions of fundamental relevance is the nature of SN Ia progenitors. The study of accreting compact binary systems relies on observations over the entire electromagnetic spectrum and we outline here those unresolved questions for which access to the ultraviolet range is vital, as they cannot be addressed by observations in any other spectral region