Results for "J. J. Hermes"

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Limits on Mode Coherence Due to a Non-static Convection ZoneFeb 14 2019The standard theory of pulsations deals with the frequencies and growth rates of infinitesimal perturbations in a stellar model. Modes which are calculated to be linearly driven should increase their amplitudes exponentially with time; the fact that nearly ... More
A search for variable white dwarfs in large area time domain surveys: a pilot study in SDSS Stripe 82Oct 27 2015We present a method to reliably select variable white dwarfs from large area time domain surveys and apply this method in a pilot study to search for pulsating white dwarfs in the Sloan Digital Sky Survey Stripe 82. From a sample 400 high-confidence white ... More
PSR J1738+0333: The First Millisecond Pulsar + Pulsating White Dwarf BinaryOct 18 2014Oct 26 2014We report the discovery of the first millisecond pulsar with a pulsating white dwarf companion. Following the recent discoveries of pulsations in extremely low-mass (ELM, <0.3 Msol) white dwarfs (WDs), we targeted ELM WD companions to two millisecond ... More
Seven-Period Asteroseismic Fit of the Kepler DBVAug 19 2014We present a new, better-constrained asteroseismic analysis of the helium-atmosphere (DB) white dwarf discovered in the field of view of the original Kepler mission. Observations obtained over the course of two years yield at least seven independent modes, ... More
Deeply-Virtual Compton Scattering on Deuterium and Neon at HERMESDec 09 2002We report the first observation of azimuthal beam-spin asymmetries in hard electroproduction of real photons off nuclei. Attributed to the interference between the Bethe-Heitler process and the deeply-virtual Compton scattering process, the asymmetry ... More
Jamming and the onset of granulation in a model particle systemJul 29 2015Granulation is a ubiquitous process crucial for many products ranging from food and care products to pharmaceuticals. Granulation is the process in which a powder is mixed with a small amount of liquid (binder) to form solid agglomerates surrounded by ... More
Filament mechanics in a half-space via regularised Stokeslet segmentsApr 02 2019We present a generalisation of efficient numerical frameworks for modelling fluid-filament interactions via the discretisation of a recently-developed, non-local integral equation formulation to incorporate regularised Stokeslets with half-space boundary ... More
Tensor network techniques for the computation of dynamical observables in 1D quantum spin systemsApr 23 2012We analyze the recently developed folding algorithm [Phys. Rev. Lett. 102, 240603 (2009)] to simulate the dynamics of infinite quantum spin chains, and relate its performance to the kind of entanglement produced under the evolution of product states. ... More
Filament mechanics in a half-space via regularised Stokeslet segmentsApr 02 2019Apr 09 2019We present a generalisation of efficient numerical frameworks for modelling fluid-filament interactions via the discretisation of a recently-developed, non-local integral equation formulation to incorporate regularised Stokeslets with half-space boundary ... More
Spermatozoa scattering by a microchannel feature: an elastohydrodynamic modelOct 23 2014Feb 18 2015Sperm traverse their microenvironment through viscous fluid by propagating flagellar waves; the waveform emerges as a consequence of elastic structure, internal active moments, and low Reynolds number fluid dynamics. Engineered microchannels have recently ... More
A New Gravitational Wave Verification SourceJun 12 2014We report the discovery of a detached 20 min orbital period binary white dwarf. WD0931+444 (SDSS J093506.93+441106.9) was previously classified as a WD + M dwarf system based on its optical spectrum. Our time-resolved optical spectroscopy observations ... More
Seismology of an Ensemble of ZZ Ceti StarsNov 08 2016We combine all the reliably-measured eigenperiods for hot, short-period ZZ Ceti stars onto one diagram and show that it has the features expected from evolutionary and pulsation theory. To make a more detailed comparison with theory we concentrate on ... More
Detections and Constraints on White Dwarf Variability from Time-Series GALEX ObservationsDec 13 2018Dec 20 2018We search for photometric variability in more than 23,000 known and candidate white dwarfs, the largest ultraviolet survey compiled for a single study of white dwarfs. We use gPhoton, a publicly available calibration/reduction pipeline, to generate time-series ... More
A New Timescale for Period Change in the Pulsating DA White Dwarf WD 0111+0018Feb 07 2013We report the most rapid rate of period change measured to date for a pulsating DA (hydrogen atmosphere) white dwarf (WD), observed in the 292.9 s mode of WD 0111+0018. The observed period change, faster than 10^{-12} s/s, exceeds by more than two orders ... More
Two New Tidally Distorted White DwarfsFeb 20 2012We identify two new tidally distorted white dwarfs (WDs), SDSS J174140.49+652638.7 and J211921.96-001825.8 (hereafter J1741 and J2119). Both stars are extremely low mass (ELM, < 0.2 Msun) WDs in short-period, detached binary systems. High-speed photometric ... More
Searching for new white dwarf pulsators for TESS observations at Konkoly ObservatoryMay 25 2018We present the results of our survey searching for new white dwarf pulsators for observations by the TESS space telescope. We collected photometric time-series data on 14 white dwarf variable-candidates at Konkoly Observatory, and found two new bright ... More
Precise Atmospheric Parameters for the Shortest Period Binary White Dwarfs: Gravitational Waves, Metals, and PulsationsAug 13 2014Aug 16 2014We present a detailed spectroscopic analysis of 61 low mass white dwarfs and provide precise atmospheric parameters, masses, and updated binary system parameters based on our new model atmosphere grids and the most recent evolutionary model calculations. ... More
The seismic properties of low-mass He-core white dwarf starsSep 23 2012We present here a detailed pulsational study applied to low-mass He-core white dwarfs, based on full evolutionary models representative of these objects. The background stellar models on which our pulsational analysis was carried out were derived by taking ... More
A deep test of radial differential rotation in a helium-atmosphere white dwarf: I. Discovery of pulsations in PG 0112+104Dec 22 2016We present the detection of non-radial oscillations in a hot, helium-atmosphere white dwarf using 78.7 d of nearly uninterrupted photometry from the Kepler space telescope. With an effective temperature >30,000 K, PG 0112+104 becomes the hottest helium-atmosphere ... More
Likely detection of water-rich asteroid debris in a metal-polluted white dwarfMar 26 2015The cool white dwarf SDSS J124231.07+522626.6 exhibits photospheric absorption lines of 8 distinct heavy elements in medium resolution optical spectra, notably including oxygen. The Teff = 13000 K atmosphere is helium-dominated, but the convection zone ... More
Rapid Evolution of the Gaseous Exoplanetary Debris Around the White Dwarf Star HE 1349--2305Jan 16 2018Observations of heavy metal pollution in white dwarf stars indicate that metal-rich planetesimals are frequently scattered into star-grazing orbits, tidally disrupted, and accreted onto the white dwarf surface, offering direct insight into the dynamical ... More
Complex charge ordering in CeRuSnNov 24 2011At ambient temperatures, CeRuSn exhibits an extraordinary structure with a coexistence of two types of Ce ions in a metallic environment, namely trivalent Ce3+ and intermediate valent Ce(4-x)+. Charge ordering produces a doubling of the unit cell along ... More
Complete devil's staircase and crystal--superfluid transitions in a dipolar XXZ spin chain: A trapped ion quantum simulationAug 17 2010Dec 03 2010Systems with long-range interactions show a variety of intriguing properties: they typically accommodate many meta-stable states, they can give rise to spontaneous formation of supersolids, and they can lead to counterintuitive thermodynamic behavior. ... More
Testing the Wyart-Cates model for non-Brownian shear thickening using bidisperse suspensionsJan 07 2019There is a growing consensus that shear thickening of concentrated dispersions is driven by the formation of stress-induced frictional contacts. The Wyart-Cates (WC) model of this phenomenon, in which the microphysics of the contacts enters solely via ... More
SDSS J163030.58+423305.8: A 40 minute Orbital Period Detached White Dwarf BinarySep 28 2011We report the discovery of a new detached, double white dwarf system with an orbital period of 39.8 min. We targeted SDSS J163030.58+423305.8 (hereafter J1630) as part of our radial velocity program to search for companions around low-mass white dwarfs ... More
A 12 minute Orbital Period Detached White Dwarf Eclipsing BinaryJul 12 2011We have discovered a detached pair of white dwarfs (WDs) with a 12.75 min orbital period and a 1,315 km/s radial velocity amplitude. We measure the full orbital parameters of the system using its light curve, which shows ellipsoidal variations, Doppler ... More
SDSS J184037.78+642312.3: The First Pulsating Extremely Low Mass White DwarfApr 05 2012We report the discovery of the first pulsating extremely low mass (ELM) white dwarf (WD), SDSS J184037.78+642312.3 (hereafter J1840). This DA (hydrogen-atmosphere) WD is by far the coolest and the lowest-mass pulsating WD, with Teff = 9100 \pm 170 K and ... More
Anatomy of the hyper-runaway star LP 40-365 with GaiaApr 25 2018Jun 08 2018LP 40-365 (aka GD 492) is a nearby low-luminosity hyper-runaway star with an extremely unusual atmospheric composition, which has been proposed as the remnant of a white dwarf that survived a subluminous Type Ia supernova (SN Ia) in a single-degenerate ... More
KIC11911480: the second ZZ Ceti in the $Kepler$ fieldDec 16 2013We report the discovery of the second pulsating hydrogen-rich (DA) white dwarf in the $Kepler$ field, KIC11911480. It was selected from the $Kepler$-INT Survey (KIS) on the basis of its colours and its variable nature was confirmed using ground-based ... More
Further insight on the hypervelocity white dwarf, LP 40-365 (GD 492): a nearby emissary from a single-degenerate Type Ia supernovaMar 20 2018The recently discovered hypervelocity white dwarf LP 40-65 (aka GD 492) has been suggested as the outcome of the failed disruption of a white dwarf in a sub-luminous Type Ia supernova (SN Ia). We present new observations confirming GD 492 as a single ... More
3D Model Atmospheres for Extremely Low-Mass White DwarfsJul 07 2015We present an extended grid of mean three-dimensional (3D) spectra for low-mass, pure-hydrogen atmosphere DA white dwarfs (WDs). We use CO5BOLD radiation-hydrodynamics 3D simulations covering Teff = 6000-11,500 K and logg = 5-6.5 (cgs units) to derive ... More
The Shortest Period Detached Binary White Dwarf SystemMar 11 2011We identify SDSS J010657.39-100003.3 (hereafter J0106-1000) as the shortest period detached binary white dwarf (WD) system currently known. We targeted J0106-1000 as part of our radial velocity program to search for companions around known extremely low-mass ... More
Discovery of pulsations, including possible pressure modes, in two new extremely low mass, He-core white dwarfsNov 05 2012Jan 25 2013We report the discovery of the second and third pulsating extremely low mass white dwarfs (WDs), SDSS J111215.82+111745.0 (hereafter J1112) and SDSS J151826.68+065813.2 (hereafter J1518). Both have masses < 0.25 Msun and effective temperatures below 10,000 ... More
A new class of pulsating white dwarf of extremely low mass: the fourth and fifth membersSep 30 2013We report the discovery of two new pulsating extremely low-mass (ELM) white dwarfs (WDs), SDSS J161431.28+191219.4 (hereafter J1614) and SDSS J222859.93+362359.6 (hereafter J2228). Both WDs have masses <0.25 Msun and thus likely harbor helium cores. Spectral ... More
Creep and flow of glasses: strain response linked to the spatial distribution of dynamical heterogeneitiesJul 10 2015Mechanical properties are of central importance to materials sciences, in particular if they depend on external stimuli. Here we investigate the rheological response of amorphous solids, namely col- loidal glasses, to external forces. Using confocal microscopy ... More
Found: The Progenitors of AM CVn and Supernovae .IaOct 23 2013We present optical and X-ray observations of two tidally distorted, extremely low-mass white dwarfs (WDs) with massive companions. There is no evidence of neutron stars in our Chandra and XMM observations of these objects. SDSS J075141.18$-$014120.9 (J0751) ... More
A Dark Spot on a Massive White DwarfNov 23 2015We present the serendipitous discovery of eclipse-like events around the massive white dwarf SDSS J152934.98+292801.9 (hereafter J1529+2928). We selected J1529+2928 for time-series photometry based on its spectroscopic temperature and surface gravity, ... More
The First Six Outbursting Cool DA White Dwarf PulsatorsSep 28 2016Extensive observations from the Kepler spacecraft have recently revealed a new outburst phenomenon operating in cool pulsating DA (hydrogen atmosphere) white dwarfs (DAVs). With the introduction of two new outbursting DAVs from K2 Fields 7 (EPIC 229228364) ... More
SDSS J074511.56+194926.5: Discovery of a Metal-Rich and Tidally Distorted Extremely Low Mass White DwarfDec 05 2013Dec 16 2013We present the discovery of an unusual, tidally-distorted extremely low mass white dwarf (WD) with nearly solar metallicity. Radial velocity measurements confirm that this is a compact binary with an orbital period of 2.6975 hrs and a velocity semi-amplitude ... More
Rapid Orbital Decay in the 12.75-minute WD+WD Binary J0651+2844Aug 24 2012We report the detection of orbital decay in the 12.75-min, detached binary white dwarf (WD) SDSS J065133.338+284423.37 (hereafter J0651). Our photometric observations over a 13-month baseline constrain the orbital period to 765.206543(55) s and indicate ... More
A Refined Search for Pulsations in White Dwarf Companions to Millisecond PulsarsJun 10 2018We present optical high-speed photometry of three millisecond pulsars with low-mass ($< 0.3 M_{\odot}$) white dwarf companions, bringing the total number of such systems with follow-up time-series photometry to five. We confirm the detection of pulsations ... More
When flux standards go wild: white dwarfs in the age of KeplerMar 06 2017White dwarf stars have been used as flux standards for decades, thanks to their staid simplicity. We have empirically tested their photometric stability by analyzing the light curves of 398 high-probability candidates and spectroscopically confirmed white ... More
KIC 4552982: Outbursts and Asteroseismology from the Longest Pseudo-Continuous Light Curve of a ZZ CetiJun 25 2015We present the Kepler light curve of KIC 4552982, the first ZZ Ceti (hydrogen-atmosphere pulsating white dwarf star) discovered in the Kepler field of view. Our data span more than 1.5 years with a 86% duty cycle, making it the longest pseudo-continuous ... More
Discovery of an ultramassive pulsating white dwarfJun 17 2013We announce the discovery of the most massive pulsating hydrogen-atmosphere (DA) white dwarf (WD) ever discovered, GD 518. Model atmosphere fits to the optical spectrum of this star show it is a 12,030 +/- 210 K WD with a log(g) = 9.08 +/- 0.06, which ... More
Discovery of a ZZ Ceti in the Kepler Mission FieldSep 27 2011We report the discovery of the first identified pulsating DA white dwarf in the field of the Kepler mission, WD J1916+3938 (Kepler ID 4552982). This ZZ Ceti star was first identified through ground-based, time-series photometry, and follow-up spectroscopy ... More
Astro2020 Decadal Science White Paper: Gravitational Wave Survey of Galactic Ultra Compact BinariesMar 13 2019Ultra-compact binaries (UCBs) are systems containing compact or degenerate stars with orbital periods less than one hour. Tens of millions of UCBs are predicted to exist within theGalaxy emitting gravitational waves (GWs) at mHz frequencies. Combining ... More
Discovery of the first resolved triple white dwarfNov 19 2018We report the discovery of J1953-1019, the first resolved triple white dwarf system. The triplet consists of an inner white dwarf binary and a wider companion. Using Gaia DR2 photometry and astrometry combined with our follow-up spectroscopy, we derive ... More
A catalogue of white dwarf candidates in VST ATLASMar 28 2017The Sloan Digital Sky Survey (SDSS) has created a knowledge gap between the Northern and the Southern hemispheres which is very marked for white dwarfs: only $\simeq 15$% of the known white dwarfs are south of the equator. Here we make use of the VST ... More
Conching chocolate: A prototypical transition from frictionally jammed solid to flowable suspension with maximal solid contentFeb 01 2019The mixing of a powder of 10-50{\mu}m primary particles into a liquid to form a dispersion with the highest possible solid content is a common industrial operation. Building on recent advances in the rheology of such 'granular dispersions', we study a ... More
A second case of outbursts in a pulsating white dwarf observed by KeplerJul 22 2015We present observations of a new phenomenon in pulsating white dwarf stars: large-amplitude outbursts at timescales much longer than the pulsation periods. The cool (Teff = 11,010 K), hydrogen-atmosphere pulsating white dwarf PG 1149+057 was observed ... More
Local moments and symmetry breaking in metallic PrMnSbOJun 02 2010We report a combined experimental and theoretical investigation of the layered antimonide PrMnSbO which is isostructural to the parent phase of the iron pnictide superconductors. We find linear resistivity near room temperature and Fermi liquid-like T^{2} ... More
Detection of vertical muons with the HAWC water Cherenkov detectors and its application to gamma/hadron discriminationAug 30 2017The HAWC observatory reconstructs atmospheric showers induced by very high-energy primary cosmic- or gamma-rays. Cosmic-rays with hadronic nature are several orders of magnitude more frequent than primary gammas and therefore it is necessary to perform ... More
Conching chocolate: A prototypical transition from frictionally jammed solid to flowable suspension with maximal solid contentFeb 01 2019May 06 2019The mixing of a powder of 10-50{\mu}m primary particles into a liquid to form a dispersion with the highest possible solid content is a common industrial operation. Building on recent advances in the rheology of such 'granular dispersions', we study a ... More
Evidence from K2 for rapid rotation in the descendant of an intermediate-mass starApr 27 2017Using patterns in the oscillation frequencies of a white dwarf observed by K2, we have measured the fastest rotation rate, 1.13(02) hr, of any isolated pulsating white dwarf known to date. Balmer-line fits to follow-up spectroscopy from the SOAR telescope ... More
SDSS J105754.25+275947.5: a period-bounce eclipsing cataclysmic variable with the lowest-mass donor yet measuredJan 26 2017We present high-speed, multicolour photometry of the faint, eclipsing cataclysmic variable (CV) SDSS J105754.25+275947.5. The light from this system is dominated by the white dwarf. Nonetheless, averaging many eclipses reveals additional features from ... More
Radius constraints from high-speed photometry of 20 low-mass white dwarf binariesJul 14 2014We carry out high-speed photometry on 20 of the shortest-period, detached white dwarf binaries known and discover systems with eclipses, ellipsoidal variations (due to tidal deformations of the visible white dwarf), and Doppler beaming. All of the binaries ... More
The search for ZZ Ceti stars in the original Kepler missionJan 06 2016We report the discovery of 42 white dwarfs in the original Kepler mission field, including nine new confirmed pulsating hydrogen-atmosphere white dwarfs (ZZ Ceti stars). Guided by the Kepler-INT Survey (KIS), we selected white dwarf candidates on the ... More
HST and Optical Data Reveal White Dwarf Cooling, Spin and Periodicities in GW Librae 3-4 Years after OutburstMay 11 2012Since the large amplitude 2007 outburst which heated its accreting, pulsating white dwarf, the dwarf nova system GW Librae has been cooling to its quiescent temperature. Our Hubble Space Telescope ultraviolet spectra combined with ground-based optical ... More
Outbursts in two new cool pulsating DA white dwarfsJul 05 2016The unprecedented extent of coverage provided by Kepler observations recently revealed outbursts in two hydrogen-atmosphere pulsating white dwarfs (DAVs) that cause hours-long increases in the overall mean flux of up to 14%. We have identified two new ... More
Heavy metals in a light white dwarf: Abundances of the metal-rich, extremely low-mass GALEX J1717+6757Jul 29 2014Using the Hubble Space Telescope, we detail the first abundance analysis enabled by far-ultraviolet spectroscopy of a low-mass (~0.19 Msun) white dwarf (WD), GALEX J1717+6757, which is in a 5.9-hr binary with a fainter, more-massive companion. We see ... More
Single-spin azimuthal asymmetry in exclusive electroproduction of pi+ mesons on transversely polarized protonsJul 15 2009Exclusive electroproduction of pi+ mesons was studied by scattering 27.6 GeV positrons or electrons off a transversely polarized hydrogen target. The single-spin azimuthal asymmetry with respect to target polarization was measured as a function of the ... More
Using Gaussian processes to model light curves in the presence of flickering: the eclipsing cataclysmic variable ASASSN-14agSep 20 2016The majority of cataclysmic variable (CV) stars contain a stochastic noise component in their light curves, commonly referred to as flickering. This can significantly affect the morphology of CV eclipses and increases the difficulty in obtaining accurate ... More
The McDonald Observatory search for pulsating sdA stars: asteroseismic support for multiple populationsMay 28 2018Context. The nature of the recently identified "sdA" spectroscopic class of star is not well understood. The thousands of known sdAs have H-dominated spectra, spectroscopic surface gravities intermediate to main sequence stars and isolated white dwarfs, ... More
Minimal Model of Ginzburg AlgebrasJun 22 2014Oct 06 2015We compute the minimal model for Ginzburg algebras associated to acyclic quivers $Q$. In particular, we prove that there is a natural grading on the Ginzburg algebra making it formal and quasi-isomorphic to the preprojective algebra in non-Dynkin type, ... More
High-speed Photometric Observations of ZZ Ceti White Dwarf CandidatesFeb 18 2015We present high-speed photometric observations of ZZ Ceti white dwarf candidates drawn from the spectroscopic survey of bright DA stars from the Villanova White Dwarf Catalog by Gianninas et al., and from the recent spectroscopic survey of white dwarfs ... More
Compensated de Casteljau algorithm in $K$ times the working precisionAug 30 2018Aug 31 2018In computer aided geometric design a polynomial is usually represented in Bernstein form. This paper presents a family of compensated algorithms to accurately evaluate a polynomial in Bernstein form with floating point coefficients. The principle is to ... More
A Curious Case of Curbed ConditionJun 13 2018In computer aided geometric design a polynomial is usually represented in Bernstein form. The de Casteljau algorithm is the most well-known algorithm for evaluating a polynomial in this form. Evaluation via the de Casteljau algorithm has relative forward ... More
Two planets orbiting the recently formed post-common envelope binary NN SerpentisOct 18 2010Planets orbiting post-common envelope binaries provide fundamental information on planet formation and evolution. We searched for such planets in NN Ser ab, an eclipsing short-period binary that shows long-term eclipse time variations. Using published, ... More
A 2-Norm Condition Number for Bézier Curve IntersectionAug 18 2018We present a short note describing a condition number of the intersection of two B\'ezier curves.
Analysis of the first variation and a numerical gradient flow for integral Menger curvatureAug 27 2014In this thesis, we consider the knot energy "integral Menger curvature" which is the triple integral over the inverse of the classic circumradius of three distinct points on the given knot to the power $p\in [2,\infty)$. We prove the existence of the ... More
Using large spectroscopic surveys to test the double degenerate model for Type Ia supernovaeFeb 16 2017An observational constraint on the contribution of double degenerates to Type Ia supernovae requires multiple radial velocity measurements of ideally thousands of white dwarfs. This is because only a small fraction of the double degenerate population ... More
A large, long-lived structure near the trojan L5 point in the post common-envelope binary SDSS J1021+1744Nov 30 2015SDSS J1021+1744 is a detached, eclipsing white dwarf / M dwarf binary discovered in the Sloan Digital Sky Survey. Outside the primary eclipse, the light curves of such systems are usually smooth and characterised by low-level variations caused by tidal ... More
Photometric variability in a warm, strongly magnetic DQ white dwarf, SDSS J103655.39+652252.2Apr 10 2013We present the discovery of photometric variability in the DQ white dwarf SDSS J103655.39+652252.2 (SDSS J1036+6522). Time-series photometry reveals a coherent monoperiodic modulation at a period of 1115.64751(67) s with an amplitude of 0.442% +/- 0.024%; ... More
The first sub-70 minute non-interacting WD-BD system: EPIC212235321Jan 23 2018Feb 08 2018We present the discovery of the shortest-period, non-interacting, white dwarf-brown dwarf post-common-envelope binary known. The K2 light curve shows the system, EPIC 21223532 has a period of 68.2 min and is not eclipsing, but does show a large reflection ... More
The Planets around the Post-Common Envelope Binary NN SerpentisFeb 02 2011We have detected 2 circumbinary planets around the close binary system NN Serpentis using the orbital time delay effect measured via the sharp eclipses of the white dwarf primary. The present pre-cataclysmic binary was formed when the original - 2 M primary ... More
The first sub-70 minute non-interacting WD-BD system: EPIC212235321Jan 23 2018We present the discovery of the shortest-period, non-interacting, white dwarf-brown dwarf post-common-envelope binary known. The K2 light curve shows the system, EPIC 21223532 has a period of 68.2 min and is not eclipsing, but does show a large reflection ... More
Probing the structure of Kepler ZZ Ceti stars with full evolutionary models-based asteroseismologyNov 03 2017We present an asteroseismological analysis of four ZZ Ceti stars observed with \emph{Kepler}: GD 1212, SDSS J113655.17+040952.6, KIC 11911480 and KIC 4552982, based on a grid of full evolutionary models of DA white dwarf stars. We employ a grid of carbon-oxygen ... More
Multi-band photometry and spectroscopy of an all-sky sample of bright white dwarfsAug 30 2017The upcoming NASA Transiting Exoplanet Survey Satellite (TESS) will obtain space-based uninterrupted light curves for a large sample of bright white dwarfs distributed across the entire sky, providing a very rich resource for asteroseismological studies ... More
A 15.7-Minute AM CVn Binary Discovered in K2Apr 19 2018We present the discovery of SDSS J135154.46-064309.0, a short-period variable observed using 30-minute cadence photometry in K2 Campaign 6. Follow-up spectroscopy and high-speed photometry support a classification as a new member of the rare class of ... More
A search for white dwarfs in the Galactic plane: the field and the open cluster populationJan 08 2016Jan 12 2016We investigated the prospects for systematic searches of white dwarfs at low Galactic latitudes, using the VLT Survey Telescope (VST) H$\alpha$ Photometric Survey of the Galactic plane and Bulge (VPHAS+). We targeted 17 white dwarf candidates along sightlines ... More
A class of partly burnt runaway stellar remnants from peculiar thermonuclear supernovaeFeb 13 2019We report the discovery of three stars that, along with the prototype LP 40-365, form a distinct class of chemically peculiar runaway stars that are the survivors of thermonuclear explosions. Spectroscopy of the four confirmed LP 40-365 stars finds ONe-dominated ... More
Orbital properties of an unusually low-mass sdB star in a close binary system with a white dwarfMay 11 2012Jul 03 2012We have used 605 days of photometric data from the Kepler spacecraft to study KIC 6614501, a close binary system with an orbital period of 0.15749747(25) days (3.779939 hours), that consists of a low-mass subdwarf B (sdB) star and a white dwarf. As seen ... More
White Dwarf Rotation as a Function of Mass and a Dichotomy of Mode Linewidths: Kepler Observations of 27 Pulsating DA White Dwarfs Through K2 Campaign 8Sep 20 2017We present photometry and spectroscopy for 27 pulsating hydrogen-atmosphere white dwarfs (DAVs, a.k.a. ZZ Ceti stars) observed by the Kepler space telescope up to K2 Campaign 8, an extensive compilation of observations with unprecedented duration (>75 ... More
Insights into internal effects of common-envelope evolution using the extended Kepler missionMay 07 2015We present an analysis of the binary and physical parameters of a unique pulsating white dwarf with a main-sequence companion, SDSS J1136+0409, observed for more than 77 d during the first pointing of the extended Kepler mission: K2 Campaign 1. Using ... More
High-Speed Photometry of Gaia14aae: An Eclipsing AM CVn That Challenges Formation ModelsFeb 01 2018AM CVn-type systems are ultra-compact, hydrogen-deficient accreting binaries with degenerate or semi-degenerate donors. The evolutionary history of these systems can be explored by constraining the properties of their donor stars. We present high-speed ... More
Seismic evidence for non-synchronization in two close sdB+dM binaries from Kepler photometryFeb 16 2012We report on extended photometry of two pulsating sdB stars in close binaries. For both cases, we use rotational splitting of the pulsation frequencies to show that the sdB component rotates much too slowly to be in synchronous rotation. We use a theory ... More
Discovery of ZZ Cetis in detached white dwarf plus main-sequence binariesNov 18 2014We present the first results of a dedicated search for pulsating white dwarfs (WDs) in detached white dwarf plus main-sequence binaries. Candidate systems were selected from a catalogue of WD+MS binaries, based on the surface gravities and effective temperatures ... More
Long-term eclipse timing of white dwarf binaries: an observational hint of a magnetic mechanism at workJun 02 2016We present a long-term programme for timing the eclipses of white dwarfs in close binaries to measure apparent and/or real variations in their orbital periods. Our programme includes 67 close binaries, both detached and semi-detached and with M-dwarfs, ... More
Evidence for mass accretion driven by spiral shocks onto the white dwarf in SDSS J123813.73-033933.0Nov 14 2018Dec 12 2018We present high-time-resolution photometry and phase-resolved spectroscopy of the short-period ($P_\mathrm{orb} = 80.52\,\mathrm{min}$) cataclysmic variable SDSS J123813.73-033933.0, observed with the $\mathit{Hubble}$ $\mathit{Space}$ $\mathit{Telescope}$ ... More
Spin Density Matrix Elements in Exclusive rho^0 Electroproduction on 1H and 2H Targets at 27.5 GeV Beam EnergyJan 06 2009Jun 13 2009Spin Density Matrix Elements (SDMEs) describing the angular distribution of exclusive rho^0 electroproduction and decay are determined in the HERMES experiment with 27.6 GeV beam energy and unpolarized hydrogen and deuterium targets. Eight (fifteen) SDMEs ... More
Measurement of single-spin azimuthal asymmetries in semi-inclusive electroproduction of pions and kaons on a longitudinally polarised deuterium targetDec 16 2002Feb 21 2003Single-spin asymmetries have been measured for semi-inclusive electroproduction of $\pi^+$, $\pi^-$, $\pi^0$ and $K^+$ mesons in deep-inelastic scattering off a longitudinally polarised deuterium target. The asymmetries appear in the distribution of the ... More
Measurement of the z- and x-dependence of the Mean Transverse Momentum of Charged Hadrons, Charged Pions and K_s^0 at HERMESJul 02 2001The mean transverse momenta of hadrons, <P_{\bot}>, produced in e^+ N deep inelastic scattering was studied as a function of the hadron energy fraction z and the Bjorken variable x. The statistical accuracy of the HERMES data permitted to observe at high ... More
Longitudinal Spin Transfer to the $Λ$ Hyperon in Semi-Inclusive Deep-Inelastic ScatteringJul 03 2006Sep 18 2006The transfer of polarization from a high-energy positron to a \lam hyperon produced in semi-inclusive deep-inelastic scattering has been measured. The data have been obtained by the HERMES experiment at DESY using the 27.6 GeV longitudinally polarized ... More
The HERMES Polarized Hydrogen and Deuterium Gas Target in the HERA Electron Storage RingAug 31 2004Nov 10 2004The HERMES hydrogen and deuterium nuclear-polarized gas targets have been in use since 1996 with the polarized electron beam of HERA at DESY to study the spin structure of the nucleon. Polarized atoms from a Stern-Gerlach Atomic Beam Source are injected ... More
Single-spin Azimuthal Asymmetries in Electroproduction of Neutral Pions in Semi-inclusive Deep-inelastic ScatteringApr 02 2001Jun 07 2001A single-spin asymmetry in the azimuthal distribution of neutral pions relative to the lepton scattering plane has been measured for the first time in deep-inelastic scattering of positrons off longitudinally polarized protons. The analysing power in ... More
Nuclear Polarization of Molecular Hydrogen Recombined on a Non-metallic SurfaceAug 31 2004The nuclear polarization of $\mathrm{H}_2$ molecules formed by recombination of nuclear polarized H atoms on the surface of a storage cell initially coated with a silicon-based polymer has been measured by using the longitudinal double-spin asymmetry ... More
Beam-Spin Azimuthal Asymmetries in Pion Electroproduction at HERMESAug 01 2004Aug 06 2004We present the measurement of Single Beam-Spin Azimuthal Asymmetries in pion electroproduction off hydrogen in semi-inclusive deep inelastic scattering (SIDIS). The measurement was made using the HERMES spectrometer with an internal gas target and the ... More
Testing the white dwarf mass-radius relationship with eclipsing binariesJun 15 2017We present high precision, model independent, mass and radius measurements for 16 white dwarfs in detached eclipsing binaries and combine these with previously published data to test the theoretical white dwarf mass-radius relationship. We reach a mean ... More
The scatter of the M dwarf mass-radius relationshipAug 23 2018M dwarfs are prime targets in the hunt for habitable worlds around other stars. This is due to their abundance as well as their small radii and low masses and temperatures, which facilitate the detection of temperate, rocky planets in orbit around them. ... More
Higgs Couplings in an Effective Theory FrameworkJul 20 2015The study of the properties of the scalar boson recently discovered at the LHC (ATLAS and CMS experiments) may allow us to know whether it is well described by the Standard Model. In the case where deviations from SM predictions are present, this would ... More