UVES and X-Shooter spectroscopy of the emission line AM CVn systems GP Com and V396 Hya

We present time-resolved spectroscopy of the AM CVn-type binaries GP Com and V396 Hya obtained with VLT/X-Shooter and VLT/UVES. We fully resolve the narrow central components of the dominant helium lines and determine radial velocity semi-amplitudes of $K_{\rm spike} = 11.7\pm0.3$ km s$^{-1}$ for GP Com and $K_{\rm spike} = 5.8\pm0.3$ km s$^{-1}$ for V396 Hya. The mean velocities of the narrow central components show variations from line to line. Compared to calculated line profiles that include Stark broadening we are able to explain the displacements, and the appearance of forbidden helium lines, by additional Stark broadening of emission in a helium plasma with an electron density $n_e\simeq 5\times 10^{15}$ cm$^{-3}$. More than $30$ nitrogen and more than $10$ neon lines emission lines were detected in both systems. Additionally, $20$ nitrogen absorption lines are only seen in GP Com. The radial velocity variations of these lines show the same phase and velocity amplitude as the central helium emission components. The small semi-amplitude of the central helium emission component, the consistency of phase and amplitude with the absorption components in GP Com as well as the measured Stark effect shows that the central helium emission component, the so-called central-spike, is consistent with an origin on the accreting white dwarf. We use the dynamics of the bright spot and the central spike to constrain the binary parameters for both systems and find a donor mass of $9.6$ - $42.8$ M$_{\rm Jupiter}$ for GP Com and $6.1$ - $30.5$ M$_{\rm Jupiter}$ for V396 Hya. We find an upper limit for the rotational velocity of the accretor of $v_{\rm rot}<46$ km s$^{-1}$ for GP Com and $v_{\rm rot}<59$ km s$^{-1}$ for V396 Hya which excludes a fast rotating accretor in both systems.Comment: Accepted for publication in MNRAS, 15 pages, 14 figures, 5 table

KIC7668647: a 14 day beaming sdB+WD binary with a pulsating subdwarf

The recently discovered subdwarf B (sdB) pulsator KIC7668647 is one of the 18 pulsating sdB stars detected in the Kepler field. It features a rich g-mode frequency spectrum, with a few low-amplitude p-modes at short periods. We use new ground-based low-resolution spectroscopy, and the near-continuous 2.88 year Kepler lightcurve, to reveal that KIC7668647 consists of a subdwarf B star with an unseen white-dwarf companion with an orbital period of 14.2d. An orbit with a radial-velocity amplitude of 39km/s is consistently determined from the spectra, from the orbital Doppler beaming seen by Kepler at 163ppm, and from measuring the orbital light-travel delay of 27 by timing of the many pulsations seen in the Kepler lightcurve. The white dwarf has a minimum mass of 0.40 M_sun. We use our high signal-to-noise average spectra to study the atmospheric parameters of the sdB star, and find that nitrogen and iron have abundances close to solar values, while helium, carbon, oxygen and silicon are underabundant relative to the solar mixture. We use the full Kepler Q06--Q17 lightcurve to extract 132 significant pulsation frequencies. Period-spacing relations and multiplet splittings allow us to identify the modal degree L for the majority of the modes. Using the g-mode multiplet splittings we constrain the internal rotation period at the base of the envelope to 46-48d as a first seismic result for this star. The few p-mode splittings may point at a slightly longer rotation period further out in the envelope of the star. From mode-visibility considerations we derive that the inclination of the rotation axis of the sdB in KIC7668647 must be around ~60 degrees. Furthermore, we find strong evidence for a few multiplets indicative of degree 3 <= L <= 8, which is another novelty in sdB-star observations made possible by Kepler.Comment: arXiv admin note: text overlap with arXiv:1206.387

Electro-Mechanical Fredericks Effects in Nematic Gels

The solid nematic equivalent of the Fredericks transition is found to depend on a critical field rather than a critical voltage as in the classical case. This arises because director anchoring is principally to the solid rubbery matrix of the nematic gel rather than to the sample surfaces. Moreover, above the threshold field, we find a competition between quartic (soft) and conventional harmonic elasticity which dictates the director response. By including a small degree of initial director misorientation, the calculated field variation of optical anisotropy agrees well with the conoscopy measurements of Chang et al (Phys.Rev.E56, 595, 1997) of the electro-optical response of nematic gels.Comment: Latex (revtex style), 5 EPS figures, submitted to PRE, corrections to discussion of fig.3, cosmetic change

Aging and memory phenomena in magnetic and transport properties of vortex matter: a brief review

There is mounting experimental evidence that strong off-equilibrium phenomena, such as ``memory'' or ``aging'' effects, play a crucial role in the physics of vortices in type II superconductors. We give a short review, based on a recently introduced schematic vortex model, of current progresses in understanding out of equilibrium vortex behaviours. We develop a unified description of ``memory'' phenomena in magnetic and transport properties, such as magnetisation loops and their ``anomalous'' 2nd peak, logarithmic creep, ``anomalous'' finite creep rate in the limit of vanishing temperature, ``memory'' and ``irreversibility'' in I-V characteristics, time dependent critical currents, ``rejuvenation'' and ``aging'' of the system response.Comment: updated versio

Substellar companions and the formation of hot subdwarf stars

"Copyright 2011 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics."We give a brief review over the observational evidence for close substellar companions to hot subdwarf stars. The formation of these core helium-burning objects requires huge mass loss of their red giant progenitors. It has been suggested that besides stellar companions substellar objects in close orbits may be able to trigger this mass loss. Such objects can be easily detected around hot subdwarf stars by medium or high resolution spectroscopy with an RV accuracy at the km s(-1)-level. Eclipsing systems of Vir type stick out of transit surveys because of their characteristic light curves. The best evidence that substellar objects in close orbits around sdBs exist and that they are able to trigger the required mass loss is provided by the eclipsing system SDSS J0820+0008, which was found in the course of the MUCHFUSS project. Furthermore, several candidate systems have been discovered.Final Accepted Versio

Census of the Local Universe (CLU) Narrow-Band Survey I: Galaxy Catalogs from Preliminary Fields

We present the Census of the Local Universe (CLU) narrow-band survey to search for emission-line (\ha) galaxies. CLU-\ha~has imaged $\approx$3$\pi$ of the sky (26,470~deg$^2$) with 4 narrow-band filters that probe a distance out to 200~Mpc. We have obtained spectroscopic follow-up for galaxy candidates in 14 preliminary fields (101.6~deg$^2$) to characterize the limits and completeness of the survey. In these preliminary fields, CLU can identify emission lines down to an \ha~flux limit of $10^{-14}$~$\rm{erg~s^{-1}~cm^{-2}}$ at 90\% completeness, and recovers 83\% (67\%) of the \ha~flux from catalogued galaxies in our search volume at the $\Sigma$=2.5 ($\Sigma$=5) color excess levels. The contamination from galaxies with no emission lines is 61\% (12\%) for $\Sigma$=2.5 ($\Sigma$=5). Also, in the regions of overlap between our preliminary fields and previous emission-line surveys, we recover the majority of the galaxies found in previous surveys and identify an additional $\approx$300 galaxies. In total, we find 90 galaxies with no previous distance information, several of which are interesting objects: 7 blue compact dwarfs, 1 green pea, and a Seyfert galaxy; we also identified a known planetary nebula. These objects show that the CLU-\ha~survey can be a discovery machine for objects in our own Galaxy and extreme galaxies out to intermediate redshifts. However, the majority of the CLU-\ha~galaxies identified in this work show properties consistent with normal star-forming galaxies. CLU-\ha~galaxies with new redshifts will be added to existing galaxy catalogs to focus the search for the electromagnetic counterpart to gravitational wave events.Comment: 28 pages, 22 figures, 4 tables (Accepted to ApJ

Sifting for Sapphires: Systematic Selection of Tidal Disruption Events in iPTF

We present results from a systematic selection of tidal disruption events (TDEs) in a wide-area (4800~deg$^2$), $g+R$ band, Intermediate Palomar Transient Factory (iPTF) experiment. Our selection targets typical optically-selected TDEs: bright ($>$60\% flux increase) and blue transients residing in the center of red galaxies. Using photometric selection criteria to down-select from a total of 493 nuclear transients to a sample of 26 sources, we then use follow-up UV imaging with the Neil Gehrels Swift Telescope, ground-based optical spectroscopy, and light curve fitting to classify them as 14 Type Ia supernovae (SNe Ia), 9 highly variable active galactic nuclei (AGNs), 2 confirmed TDEs, and 1 potential core-collapse supernova. We find it possible to filter AGNs by employing a more stringent transient color cut ($g-r <$ $-$0.2 mag); further, UV imaging is the best discriminator for filtering SNe, since SNe Ia can appear as blue, optically, as TDEs in their early phases. However, when UV-optical color is unavailable, higher precision astrometry can also effectively reduce SNe contamination in the optical. Our most stringent optical photometric selection criteria yields a 4.5:1 contamination rate, allowing for a manageable number of TDE candidates for complete spectroscopic follow-up and real-time classification in the ZTF era. We measure a TDE per galaxy rate of 1.7$^{+2.9}_{-1.3}$ $\times$10$^{-4}$ gal$^{-1}$ yr$^{-1}$ (90\% CL in Poisson statistics). This does not account for TDEs outside our selection criteria, thus may not reflect the total TDE population, which is yet to be fully mapped.Comment: 24 pages, 21 figures. Accepted for publication in the Astrophysical Journal Supplement Serie

Highly Luminescent Transparent Cs2AgxNa1−xBiyIn1−yCl6 Perovskite Films Produced by Single-Source Vacuum Deposition

Thermal deposition of halide perovskites as a universal and scalable route to transparent thin films becomes highly challenging in the case of lead-free double perovskites, requiring the evaporation dynamics of multiple metal halide sources to be balanced or a single-phase precursor preliminary synthesized to achieve a reliable control over the composition and the phase of the final films. In the present Letter, the feasibility of the single-source vacuum deposition of microcrystalline Cs2AgxNa1-xBiyIn1-yCl6 double perovskites into corresponding transparent nanocrystalline films while preserving the bulk spectral and structural properties is shown. The perovskite films produced from the most emissive powders with x = 0.40 and y = 0.01 revealed a photoluminescence quantum yield of 85%, highlighting thermal evaporation as a promising approach to functional perovskite-based optical materials