Time-dependent spectral-feature variations of stars displaying the B[e] phenomenon; I. V2028 Cyg

We present results of nearly six years of spectroscopic observations of the B[e] star V2028 Cyg. The presence of the cold-type absorption lines combined with a hot-type spectrum indicate the binarity of this object. Since B[e] stars are embedded in an extended envelope, the usage of common stellar atmosphere models for the analysis is quite inappropriate. Therefore, we focus on the analysis of the long-term spectral line variations in order to determine the nature of this object. We present the time dependences of the equivalent width and radial velocities of the H alpha line, [O I] 6300 A, Fe II 6427, 6433, and 6456 A lines. The bisector variations and line intensities are shown for the H alpha line. The radial velocities are also measured for the absorption lines of the K component. No periodic variation is found. The observed data show correlations between the measured quantities, which can be used in future modelling

Generalizations of Poisson Structures Related to Rational Gaudin Model

The Poisson structure arising in the Hamiltonian approach to the rational Gaudin model looks very similar to the so-called modified Reflection Equation Algebra.  Motivated by this analogy, we realize a braiding of the mentioned Poisson structure, i.e. we introduce a ”braided Poisson” algebra associated with an involutive solution to the quantum Yang-Baxter equation. Also, we exhibit another generalization of the Gaudin type Poisson structure by replacing the first derivative in the current parameter, entering the so-called local form of this structure, by a higher order derivative.  Finally, we introduce a structure, which combines both generalizations.  Some commutative families in the corresponding braided Poisson algebra are found

Time-dependent spectral-feature variations of stars displaying the B[e] phenomenon III. HD 50138

We analyse spectroscopic observations of the B[e] star HD 50138 (MWC 158, V743 Mon, or IRAS 06491-0654), a member of the FS CMa group, obtained over the last twenty years. Four different epochs are identified in the observational data, where the variability of the spectral features is substantially different. Additionally, two long periods of (3 000 +/- 500) and (5 000 +/- 1000) days are found in the variations of the equivalent widths of the H alpha and [OI] 6300 A lines and radial velocities of the H alpha line violet peak. Modest signatures of a regular period of ~34 days in the radial velocities of the H alpha red peak and H beta central depression are found in the season 2013/2014. The H alpha V/R changes indicate a periodicity of ~50 days. The correlations between individual spectral features significantly restricts the model of the object and suggest that it is most likely a binary system with a highly distorted disc with spiral arms around the primary component. At the same time, no obvious signs of the secondary component has been found in the object's spectrum

Heisenberg double versus deformed derivatives

Two approaches to the tangent space of a noncommutative space whose coordinate algebra is the enveloping algebra of a Lie algebra are known: the Heisenberg double construction and the approach via deformed derivatives, usually defined by procedures involving orderings among noncommutative coordinates or equivalently involving realizations via formal differential operators. In an earlier work, we rephrased the deformed derivative approach introducing certain smash product algebra twisting a semicompleted Weyl algebra. We show here that the Heisenberg double in the Lie algebra case, is isomorphic to that product in a nontrivial way, involving a datum $\phi$ parametrizing the orderings or realizations in other approaches. This way, we show that the two different formalisms, used by different communities, for introducing the noncommutative phase space for the Lie algebra type noncommutative spaces are mathematically equivalent

Spectra disentangling applied to the Hyades binary Theta^2 Tau AB: new orbit, orbital parallax and component properties

Theta^2 Tauri is a detached and single-lined interferometric-spectroscopic binary as well as the most massive binary system of the Hyades cluster. The system revolves in an eccentric orbit with a periodicity of 140.7 days. The secondary has a similar temperature but is less evolved and fainter than the primary. It is also rotating more rapidly. Since the composite spectra are heavily blended, the direct extraction of radial velocities over the orbit of component B was hitherto unsuccessful. Using high-resolution spectroscopic data recently obtained with the Elodie (OHP, France) and Hermes (ORM, La Palma, Spain) spectrographs, and applying a spectra disentangling algorithm to three independent data sets including spectra from the Oak Ridge Observatory (USA), we derived an improved spectroscopic orbit and refined the solution by performing a combined astrometric-spectroscopic analysis based on the new spectroscopy and the long-baseline data from the Mark III optical interferometer. As a result, the velocity amplitude of the fainter component is obtained in a direct and objective way. Major progress based on this new determination includes an improved computation of the orbital parallax. Our mass ratio is in good agreement with the older estimates of Peterson et al. (1991, 1993), but the mass of the primary is 15-25% higher than the more recent estimates by Torres et al. (1997) and Armstrong et al. (2006). Due to the strategic position of the components in the turnoff region of the cluster, these new determinations imply stricter constraints for the age and the metallicity of the Hyades cluster. The location of component B can be explained by current evolutionary models, but the location of the more evolved component A is not trivially explained and requires a detailed abundance analysis of its disentangled spectrum.Comment: in press, 13 pages, 10 Postscript figures, 5 tables. Table~4 is available as online material. Keywords: astrometry - techniques: high angular resolution - stars: binaries: visual - stars: binaries: spectroscopic - stars: fundamental parameter

Coherent states for Hopf algebras

Families of Perelomov coherent states are defined axiomatically in the context of unitary representations of Hopf algebras possessing a Haar integral. A global geometric picture involving locally trivial noncommutative fibre bundles is involved in the construction. A noncommutative resolution of identity formula is proved in that setup. Examples come from quantum groups.Comment: 19 pages, uses kluwer.cls; the exposition much improved; an example of deriving the resolution of identity via coherent states for SUq(2) added; the result differs from the proposals in literatur

Properties and nature of Be stars 31. The binary nature, light variability, physical elements, and emission-line changes of HD~81357

Reliable determination of the basic physical properties of hot emission-line binaries with Roche-lobe filling secondaries is important for developing the theory of mass exchange in binaries. It is not easy, however, due to the presence of circumstellar matter. Here, we report the first detailed investigation of a new representative of this class of binaries, HD~81357, based on the analysis of spectra and photometry from several observatories. HD~81357 was found to be a double-lined spectroscopic binary and an ellipsoidal variable seen under an intermediate orbital inclination of $\sim(63\pm5)^\circ$, having an orbital period of 33\fd77445(41) and a~circular orbit. From an automated comparison of the observed and synthetic spectra, we estimate the component's effective temperatures to be 12930(540)~K and 4260(24)~K. The combined light-curve and orbital solutions, also constrained by a very accurate Gaia Data Release 2 parallax, give the following values of the basic physical properties: masses $3.36\pm0.15$ and $0.34\pm0.04$~\Mnom, radii $3.9\pm0.2$ and 13.97\pm0.05~\Rnom, and a~mass ratio 10.0\pm0.5$. Evolutionary modelling of the system including the phase of mass transfer between the components indicated that HD~81357 is a~system observed in the final slow phase of the mass exchange after the mass-ratio reversal. Contrary to what has been seen for similar binaries like AU~Mon, no cyclic light variations were found on a~time scale an~order of magnitude longer than the orbital period. 243,1 15%Comment: 16 pages, 9 figures; accepted for publication in Astronomy and Astrophysic

Knowledge Graphs for the Life Sciences: Recent Developments, Challenges and Opportunities

The term life sciences refers to the disciplines that study living organisms and life processes, and include chemistry, biology, medicine, and a range of other related disciplines. Research efforts in life sciences are heavily data-driven, as they produce and consume vast amounts of scientific data, much of which is intrinsically relational and graphstructured. The volume of data and the complexity of scientific concepts and relations referred to therein promote the application of advanced knowledgedriven technologies for managing and interpreting data, with the ultimate aim to advance scientific discovery. In this survey and position paper, we discuss recent developments and advances in the use of graph-based technologies in life sciences and set out a vision for how these technologies will impact these fields into the future. We focus on three broad topics: the construction and management of Knowledge Graphs (KGs), the use of KGs and associated technologies in the discovery of new knowledge, and the use of KGs in artificial intelligence applications to support explanations (explainable AI). We select a few exemplary use cases for each topic, discuss the challenges and open research questions within these topics, and conclude with a perspective and outlook that summarizes the overarching challenges and their potential solutions as a guide for future research

Spectroscopic analysis of the B/Be visual binary HR 1847

We studied both components of a slightly overlooked visual binary HR 1847 spectroscopically to determine its basic physical and orbital parameters. Basic stellar parameters were determined by comparing synthetic spectra to the observed echelle spectra, which cover both the optical and near-IR regions. New observations of this system used the Ond\v{r}ejov and Rozhen 2-m telescopes and their coud\'e spectrographs. Radial velocities from individual spectra were measured and then analysed with the code {\FOTEL} to determine orbital parameters. The spectroscopic orbit of HR 1847A is presented for the first time. It is a single-lined spectroscopic binary with a B-type primary, a period of 719.79 days, and a highly eccentric orbit with e=0.7. We confirmed that HR 1847B is a Be star. Its H\alpha emission significantly decreased from 2003 to 2008. Both components have a spectral type B7-8 and luminosity class IV-V.Comment: Astronomy and Astrophysics, accepte