Surprising variations in the rotation of the chemically peculiar stars CU Virginis and V901 Orionis

CU Vir and V901 Ori belong among these few magnetic chemically peculiar stars whose rotation periods vary on timescales of decades. We aim to study the stability of the periods in CU Vir and V901 Ori using all accessible observational data containing phase information. We collected all available relevant archived observations supplemented with our new measurements of these stars and analysed the period variations of the stars using a novel method that allows for the combination of data of diverse sorts. We found that the shapes of their phase curves were constant, while the periods were changing. Both stars exhibit alternating intervals of rotational braking and acceleration. The rotation period of CU Vir was gradually shortening until the year 1968, when it reached its local minimum of 0.52067198 d. The period then started increasing, reaching its local maximum of 0.5207163 d in the year 2005. Since that time the rotation has begun to accelerate again. We also found much smaller period changes in CU Vir on a timescale of several years. The rotation period of V901 Ori was increasing for the past quarter-century, reaching a maximum of 1.538771 d in the year 2003, when the rotation period began to decrease. A theoretically unexpected alternating variability of rotation periods in these stars would remove the spin-down time paradox and brings a new insight into structure and evolution of magnetic upper-main-sequence stars.Comment: 5 pages, 3 figure

Observations of radio pulses from CU Virginis

The magnetic chemically peculiar star CU Virginis is a unique astrophysical laboratory for stellar magnetospheres and coherent emission processes. It is the only known main sequence star to emit a radio pulse every rotation period. Here we report on new observations of the CU Virginis pulse profile in the 13 and 20\,cm radio bands. The profile is known to be characterised by two peaks of 100$\%$ circularly polarised emission that are thought to arise in an electron-cyclotron maser mechanism. We find that the trailing peak is stable at both 13 and 20\,cm, whereas the leading peak is intermittent at 13\,cm. Our measured pulse arrival times confirm the discrepancy previously reported between the putative stellar rotation rates measured with optical data and with radio observations. We suggest that this period discrepancy might be caused by an unknown companion or by instabilities in the emission region. Regular long-term pulse timing and simultaneous multi-wavelength observations are essential to clarify the behaviour of this emerging class of transient radio source.Comment: Accepted by MNRAS Letters; 5 pages, 2 figures, 3 table

Symmetry Breaking of Relativistic Multiconfiguration Methods in the Nonrelativistic Limit

The multiconfiguration Dirac-Fock method allows to calculate the state of relativistic electrons in atoms or molecules. This method has been known for a long time to provide certain wrong predictions in the nonrelativistic limit. We study in full mathematical details the nonlinear model obtained in the nonrelativistic limit for Be-like atoms. We show that the method with sp+pd configurations in the J=1 sector leads to a symmetry breaking phenomenon in the sense that the ground state is never an eigenvector of L^2 or S^2. We thereby complement and clarify some previous studies.Comment: Final version, to appear in Nonlinearity. Nonlinearity (2010) in pres

A Tight Upper Limit on Oscillations in the Ap star Epsilon Ursae Majoris from WIRE Photometry

Observations of Epsilon UMa obtained with the star tracker on the Wide Field Infrared Explorer (WIRE) satellite during a month in mid-2000 are analyzed. This is one of the most precise photometry of an Ap star. The amplitude spectrum is used to set an upper limit of 75 parts per million for the amplitude of stellar pulsations in this star unless it accidentally oscillates with a single mode at the satellite orbit, its harmonics or their one day aliases. This is the tightest limit put on the amplitude of oscillations in an Ap star. As the rotation period of Epsilon UMa is relatively short (5.1 d), it cannot be argued that the observations were made at a wrong rotational phase. Our results thus support the idea that some Ap stars do not pulsate at all.Comment: 4 pages, 4 figures, 2 style files, accepted for publication in ApJ

Correlation effects in MgO and CaO: Cohesive energies and lattice constants

A recently proposed computational scheme based on local increments has been applied to the calculation of correlation contributions to the cohesive energy of the CaO crystal. Using ab-initio quantum chemical methods for evaluating individual increments, we obtain 80% of the difference between the experimental and Hartree-Fock cohesive energies. Lattice constants corrected for correlation effects deviate by less than 1% from experimental values, in the case of MgO and CaO.Comment: LaTeX, 4 figure

Metal Oxide Semiconductor Materials for Photo-oxidation of Water and Organic Amine Groups.

With environmental decline due to increasing carbon dioxide and pollution levels, sustainability and ecofriendly improvements are necessary to maintain quality of life. In order to move in this direction, new sources of energy must be identified and sustainable methods must be realized. The overarching themes of sustainable energy addressed in this thesis are developing clean fuel, advancing energy efficiency, and advancing clean energy. These themes lend toward removal of our current reliance on unclean sources like oil and coal, and useless nonrenewables, toxic substances, and chemical waste. The future energy source we chose to focus on is hydrogen by photoelectrochemical water splitting using metal oxide semiconductors and visible sunlight. To advance clean energy we have chosen to focus on a greener approach to organic oxidations, specifically amine oxidation, by use of a semiconductor metal oxide and visible sunlight. With a Z-scheme approach for water splitting the central material focused on this work is copper tungstate, an n-type visible- light absorbing semiconductor, for the water oxidation half reaction. An emphasis is also placed on the use of copper tungstate to provide sustainable pathways for organic amine oxidation reactions. Another n-type material from the tungstate family, alpha tin tungstate, was also synthesized and explored for sustainable water oxidation. Copper tungstate was evaluated for mechanistic insight into water oxidation under visible-light illumination using electrochemical impedance spectroscopy (EIS). A mid-gap energy state (rather than the valence band) was identified as the carrier source in the water oxidation reaction on the surface of polycrystalline sol-gel copper tungstate electrodes. This state is likely composed of Cu(3d) character. The best way to improve materials for water oxidation is to identify more in depth information on how the reaction takes place on the material surface. These EIS studies on copper tungstate have provided us with chemical information to improve the reactivity of copper tungstate. It has also expanded the scope to a subset of organic reactions potentially catalyzed by these Cu 2+ sites with orbital energies within the band gap. Copper tungstate performs benzylamine oxidation to benzylidenebenzylimine with 89% Faradic efficiency, which was confirmed by gas chromatography.PHDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113412/1/kpyper_1.pd

Revisiting the Rigidly Rotating Magnetosphere model for sigma Ori E. I. Observations and Data Analysis

We have obtained 18 new high-resolution spectropolarimetric observations of the B2Vp star sigma Ori E with both the Narval and ESPaDOnS spectropolarimeters. The aim of these observations is to test, with modern data, the assumptions of the Rigidly Rotating Magnetosphere (RRM) model of Townsend & Owocki (2005), applied to the specific case of sigma Ori E by Townsend et al. (2005). This model includes a substantially offset dipole magnetic field configuration, and approximately reproduces previous observational variations in longitudinal field strength, photometric brightness, and Halpha emission. We analyze new spectroscopy, including H I, He I, C II, Si III and Fe III lines, confirming the diversity of variability in photospheric lines, as well as the double S-wave variation of circumstellar hydrogen. Using the multiline analysis method of Least-Squares Deconvolution (LSD), new, more precise longitudinal magnetic field measurements reveal a substantial variance between the shapes of the observed and RRM model time-varying field. The phase resolved Stokes V profiles of He I 5876 A and 6678 A lines are fit poorly by synthetic profiles computed from the magnetic topology assumed by Townsend et al. (2005). These results challenge the offset dipole field configuration assumed in the application of the RRM model to sigma Ori E, and indicate that future models of its magnetic field should also include complex, higher-order components.Comment: 13 pages, 8 figures. Accepted for publication in MNRA

Modelling the light variability of the Ap star epsilon Ursae Majoris

We simulate the light variability of the Ap star epsUMa using the observed surface distributions of Fe, Cr, Ca, Mn, Mg, Sr and Ti obtained with the help of Doppler Imaging technique. Using all photometric data available we specified light variations of epsUMa modulated by its rotation from far UV to IR. We employed the LLmodels stellar model atmosphere code to predict the light variability in different photometric systems. The rotational period of epsUMa is refined to 5d088631(18). It is shown that the observed light variability can be explained as a result of the redistribution of radiative flux from the UV spectral region to the visual caused by the inhomogeneous surface distribution of chemical elements. Among seven mapped elements, only Fe and Cr significantly contribute to the amplitude of the observed light variability. In general, we find a very good agreement between theory and observations. We confirm the important role of Fe and Cr to the magnitude of the well-known depression around 5200 \AA\ through the analysis of the peculiar $a$-parameter. Finally, we show that the abundance spots of considered elements cannot explain the observed variability in near UV and $\beta$ index which are likely due to some other causes. The inhomogeneous surface distribution of chemical elements can explain most of the observed light variability of the A-type CP star epsUMa.Comment: Accepted in A&A, 10 pages, 9 figures, 3 table

The facilitators of interagency working in the context of European service reform

This article provides an overview of key lessons, informed by European research projects, about the governance and leadership of interagency working in multi-level contexts. The article is based on interviews with local and national leaders across Europe. This topic is timely given the complexity of European public sector governance which demands leadership, co-production, and styles of collaboration which promote partnership-working within local contexts. This is a reflection of a pattern of principles related to the idea that localism will produce better outcomes for service users. We highlight that localism is central but this still requires national political leadership for localism to be managed and delivered effectively. In other words, empowerment-heavy models of governance, without top-down support, risks interagency ineffectiveness or even failure. We argue that leadership at macro, meso and micro levels of the governance system is required in order for successful interagency working to be delivered. We find that removing the barriers to interagency working requires the identification of an interagency leader (and to even enshrined this within statute), clear roles and lines of accountability for professionals, a breakdown of disciplinary silos, non-tokenistic bottom-up approaches, national public service leadership which promotes capacity building, and the dovetailing of planning and evaluation. The article concludes by proposing strategies for developing effective multi-level interagency working