Results for "J. Grebel"

total 182338took 0.15s
Andromeda IX: Properties of the Smallest M 31 Dwarf Satellite GalaxyJan 20 2005We present WIYN observations of the recently discovered And IX dwarf spheroidal (dSph) satellite galaxy of M 31. Our data, obtained at a natural seeing of 0.5'' and just reaching the horizontal branch level, confirm And IX as a dSph galaxy with a distance ... More
Electrochemical Cells with Intermediate Capacitor ElementsAug 25 2015Our goal is to electronically regulate electrochemical cells. For this, we introduced a third element, called the gate, which was placed between the cathode and the anode electrodes of the cell. Voltage applied to this element controlled the local potential ... More
Detailed chemical abundances of distant RR Lyrae stars in the Virgo Stellar StreamMar 23 2016We present the first detailed chemical abundances for distant RR Lyrae stars members of the Virgo Stellar Stream (VSS), derived from X-Shooter medium-resolution spectra. Sixteen elements from carbon to barium have been measured in six VSS RR Lyrae stars, ... More
Local disc model in view of Gaia DR1 and RAVE dataOct 01 2018We test the performance of the semi-analytic self-consistent Just-Jahrei{\ss} disc model (JJ model) with the astrometric data from the Tycho-Gaia Astrometric Solution (TGAS) sub-catalogue of the first Gaia data release (Gaia DR1), as well as the radial ... More
Optical CagesJul 16 2018Dec 06 2018We examine array of metal-mesh frameworks for their wide-band absorption. These take the form of quasi-crystal optical cages. An array of cages tends to focus the incoming radiation within each framework. An array of cage-within-cage funnels the radiation ... More
Differences in the fractions of Be stars in galaxiesApr 01 1999The number ratios Be/(B+Be) of Be to B-type stars in young, well studied clusters of the Galaxy, the LMC and SMC are examined. In order to disentangle age and metallicity effects we choose clusters in the same age interval and for which reliable photometric ... More
Thick disk kinematics from RAVE and the solar motionSep 03 2012Radial velocity surveys such as the Radial Velocity Experiment (RAVE) provide us with measurements of hundreds of thousands of nearby stars most of which belong to the Galactic thin, thick disk or halo. Ideally, to study the Galactic disks (both thin ... More
Life-time and line-width of individual quantum dots interfaced with grapheneDec 26 2017We report on the luminescence's life-time and line-width from an array of individual quantum dots; these were interfaced with graphene surface guides or dispersed on a metal film. Our results are consistent with screening by charge carriers. Fluorescence ... More
Unidirectional Distributed Acoustic Reflection Transducers for Quantum ApplicationsMay 08 2019Recent significant advances in coupling superconducting qubits to acoustic wave resonators has led to demonstrations of quantum control of surface and bulk acoustic resonant modes as well Wigner tomography of quantum states in these modes. These advances ... More
Mass segregation in the outer halo globular cluster Palomar 14Jul 10 2014We present evidence for mass segregation in the outer-halo globular cluster Palomar 14, which is intuitively unexpected since its present-day two-body relaxation time significantly exceeds the Hubble time. Based on archival Hubble Space Telescope imaging, ... More
Red Runaways: Hypervelocity Stars, Hills Ejecta and Other Outliers in the F-M Star RegimeJun 10 2015In this paper we analyze a sample of metal-rich (>-0.8 dex) main sequence stars in the extended solar neighborhood, investigating kinematic outliers from the background population. The data, which are taken from the Sloan Digital Sky Survey, are kinematically ... More
Mass segregation in the diffuse outer-halo globular cluster Palomar 14Jan 21 2013We present an analysis of the radial dependence of the stellar mass function in the diffuse outer-halo globular cluster Palomar 14. Using archival HST/WFPC2 data of the cluster's central 39 pc (corresponding to ~0.85*r_h) we find that the mass function ... More
Identifying Blue Horizontal Branch Stars Using the z FilterJan 22 2012In this paper we present a new method for selecting blue horizontal branch (BHB) candidates based on color-color photometry. We make use of the Sloan Digital Sky Survey z band as a surface gravity indicator and show its value for selecting BHB stars from ... More
A Global Correction to PPMXL Proper MotionsFeb 29 2016In this paper we notice that extragalactic sources seem to have non-zero proper motions in the PPMXL proper motion catalog. We collect a large, all-sky sample of extragalactic objects and fit their reported PPMXL proper motions to an ensemble of spherical ... More
Logic Gates with Ion TransistorsNov 15 2016Electronic logic gates are the basic building blocks of every computing and micro controlling system. Logic gates are made of switches, such as diodes and transistors. Ion-selective, ionic switches may emulate electronic switches [1-8]. If we ever want ... More
A Search for Ionized Gas in the Draco and Ursa Minor Dwarf Spheroidal GalaxiesJan 13 2003The Wisconsin H Alpha Mapper has been used to set the first deep upper limits on the intensity of diffuse H alpha emission from warm ionized gas in the Local Group dwarf spheroidal galaxies (dSphs) Draco and Ursa Minor. Assuming a velocity dispersion ... More
CN Variations in NGC 7006Aug 01 2003Rotationally induced mixing with subsequent dredge-up of nucleosynthesized material is discussed as a second parameter of the horizontal branch morphology in globular clusters. CNO abundances have been proposed as tracers of the dredge up of processed ... More
ATHOS: On-the-fly stellar parameter determination of FGK stars based on flux ratios from optical spectraSep 05 2018Tools for the spectroscopic determination of fundamental stellar parameters should not only comprise customized solutions for one particular survey or instrument, but, in order to enable cross-survey comparability, they should also be capable of dealing ... More
Cold, old and metal-poor: New stellar substructures in the Milky Way's dwarf spheroidalsApr 23 2019Dwarf spheroidal galaxies (dSph) orbiting the Milky Way are complex objects often with complicated star formation histories and internal dynamics. In this work, we search for stellar substructures in four of the classical dSph satellites of the Milky ... More
Interstellar Medium Oxygen Abundances of Dwarf Irregular Galaxies in Centaurus A and Nearby GroupsJan 10 2007We present results of optical spectroscopy of 35 H II regions from eight dwarf galaxies in the Centaurus A group. [O III]4363 A is detected in ESO272-G025 and ESO324-G024, and direct oxygen abundances of 12+log(O/H) = 7.76 +/- 0.09 and 7.94 +/- 0.11 are ... More
Climbing the cosmic ladder with stellar twins in RAVE with GaiaMay 31 2017Jul 23 2017We apply the twin method to determine parallaxes to 232,545 stars of the RAVE survey using the parallaxes of Gaia DR1 as a reference. To search for twins in this large dataset, we apply the t-stochastic neighbour embedding t-SNE projection which distributes ... More
The properties of the local spiral arms from RAVE data: two-dimensional density wave approachJul 02 2012Using the RAVE survey, we recently brought to light a gradient in the mean galactocentric radial velocity of stars in the extended solar neighbourhood. This gradient likely originates from non-axisymmetric perturbations of the potential, among which a ... More
4MOST Consortium Survey 2: The Milky Way Halo High-Resolution SurveyMar 06 2019Apr 01 2019We will study the formation history of the Milky Way, and the earliest phases of its chemical enrichment, with a sample of more than 1.5 million stars at high galactic latitude. Elemental abundances of up to 20 elements with a precision of better than ... More
4MOST Consortium Survey 2: The Milky Way Halo High-Resolution SurveyMar 06 2019We will study the formation history of the Milky Way, and the earliest phases of its chemical enrichment, with a sample of more than 1.5 million stars at high galactic latitude. Elemental abundances of up to 20 elements with a precision of better than ... More
Kinematic groups beyond the Solar neighbourhood with RAVEMay 02 2012Sep 11 2013We analyse the kinematics of disc stars observed by the RAVE survey in and beyond the Solar neighbourhood.We detect significant overdensities in the velocity distributions using a technique based on the wavelet transform.We find that the main local kinematic ... More
Exploring the Morphology of RAVE Stellar SpectraApr 29 2012The RAdial Velocity Experiment (RAVE) is a medium resolution R~7500 spectroscopic survey of the Milky Way which already obtained over half a million stellar spectra. They present a randomly selected magnitude-limited sample, so it is important to use ... More
A calibration map for Wide Field Imager photometryOct 10 2003We present a prescription to correct large-scale intensity variations affecting imaging data taken with the Wide Field Imager (WFI) at the MPG/ESO 2.2 m telescope at the European Southern Observatory at La Silla in Chile. Such smoothly varying, large-scale ... More
Mass Segregation in the Globular Cluster Palomar 5 and its Tidal TailsAug 11 2004We present the stellar main sequence luminosity function (LF) of the disrupted, low-mass, low-concentration globular cluster Palomar 5 and its well-defined tidal tails, which emanate from the cluster as a result of its tidal interaction with the Milky ... More
A Catalog of Edge-on Disk Galaxies: From Galaxies with a Bulge to Superthin GalaxiesSep 12 2005The formation and evolution of disk-dominated galaxies is difficult to explain, yet these objects exist. We therefore embarked on a study aimed at a better understanding of these enigmatic objects. We used data from the SDSS DR1 in order to identify edge-on ... More
CIV absorption from hot gas inside supergiant shell LMC4 observed with HST and IUEJul 04 1996High resolution ultraviolet spectra with HST-GHRS of two stars in the direction of the supergiant shell LMC4 unambiguously show absorption by substantial quantities of CIV gas at velocities near the the systemic velocity of the LMC. In combination with ... More
Blazhko modulation in the infraredJan 10 2018We present first direct evidence of modulation in the $K$-band of Blazhko-type RR Lyrae stars that are identified by their secular modulations in the I-band data of OGLE-IV. A method has been developed to decompose the $K$-band light variation into two ... More
Exploring the IMF of star clusters: a joint SLUG and LEGUS effortMay 08 2017We present the implementation of a Bayesian formalism within the Stochastically Lighting Up Galaxies (SLUG) stellar population synthesis code, which is designed to investigate variations in the initial mass function (IMF) of star clusters. By comparing ... More
Low-mass star formation in CG1: a diffraction limited search for pre-main sequence stars next to NX PupSep 08 1995Using adaptive optics at the ESO 3.6m telescope, we obtained diffraction limited JHK-images of the region around the Herbig AeBe star NX Pup. We clearly resolved the close companion (sep. 0.128") to NX Pup -- originally discovered by HST -- and measured ... More
Velocity and abundance precisions for future high-resolution spectroscopic surveys: a study for 4MOSTNov 06 2012In preparation for future, large-scale, multi-object, high-resolution spectroscopic surveys of the Galaxy, we present a series of tests of the precision in radial velocity and chemical abundances that any such project can achieve at a 4m class telescope. ... More
Detection of new variable stars in the SMC cluster NGC 121Jan 17 2008Jan 18 2008New candidate variable stars have been identified in the Small Magellanic Cloud cluster NGC121, by applying both the image subtraction technique (ISIS, Alard 2000) and the Welch & Stetson (1993) detection method to HST WFPC2 archive and ACS proprietary ... More
Coma Berenices: first evidence for incomplete vertical phase-mixing in local velocity space with RAVE - confirmed with Gaia DR2Apr 20 2018May 08 2018Before the publication of the Gaia DR2 we confirmed with RAVE and TGAS an observation recently made with the GALAH survey by Quillen ey al. concerning the Coma Berenices moving group in the Solar neighbourhood, namely that it is only present at negative ... More
Breaks in surface brightness profiles and radial abundance gradients in the discs of spiral galaxiesSep 02 2017We examine the relation between breaks in the surface brightness profiles and radial abundance gradients within the optical radius in the discs of 134 spiral galaxies from the CALIFA survey. The distribution of the radial abundance (in logarithmic scale) ... More
Spatially Resolved Kinematics of an Ultra-Compact Dwarf GalaxyApr 13 2011We present the internal kinematics of UCD3, the brightest known ultra-compact dwarf galaxy (UCD) in the Fornax cluster, making this the first UCD with spatially resolved spectroscopy. Our study is based on seeing-limited observations obtained with the ... More
Relations between abundance characteristics and rotation velocity for star-forming MaNGA galaxiesJan 30 2019We derive rotation curves, surface brightness profiles, and oxygen abundance distributions for 147 late-type galaxies using the publicly available spectroscopy obtained by the MaNGA survey. Changes of the central oxygen abundance (O/H)_0, the abundance ... More
First Results for the Solar Neighborhood of the Asiago Red Clump SurveyNov 16 2011The Asiago Red Clump Spectroscopic Survey (ARCS) is an ongoing survey that provides atmospheric parameters, distances and space velocities of a well selected sample of Red Clump stars distributed along the celestial equator. We used the ARCS catalog for ... More
Dark Matter Subhalos in the Ursa Minor Dwarf GalaxyJul 24 2012Through numerical simulations, we study the dissolution timescale of the Ursa Minor cold stellar clump, due to the combination of phase-mixing and gravitational encounters with compact dark substructures in the halo of Ursa Minor. We compare two scenarios; ... More
Spiral arms in CALIFA galaxies traced by non-circular velocities, abundances, and extinctionsOct 27 2017Nov 01 2017We derive maps of the observed velocity of ionized gas, the oxygen abundance, and the extinction (Balmer decrement) across the area of the four spiral galaxies NGC36, NGC180, NGC6063, and NGC7653 from integral field spectroscopy obtained by the Calar ... More
Oxygen abundance maps of CALIFA galaxiesJul 25 2016We construct maps of the oxygen abundance distribution across the disks of 88 galaxies using CALIFA data release 2 (DR2) spectra. The position of the center of a galaxy (coordinates on the plate) were also taken from the CALIFA DR2. The galaxy inclination, ... More
On the mass of ultra-light bosonic dark matter from galactic dynamicsOct 12 2011Jan 26 2012We consider the hypothesis that galactic dark matter is composed of ultra-light scalar particles and use internal properties of dwarf spheroidal galaxies to establish a preferred range for the mass m of these bosonic particles. We re-investigate the problem ... More
The luminosity function of Palomar 5 and its tidal tailsJul 29 2003We present the main sequence luminosity function of the tidally disrupted globular cluster Palomar 5 and its tidal tails. For this work we analyzed imaging data obtained with the Wide Field Camera at the INT (La Palma) and data from the Wide Field Imager ... More
Sextans' cold substructures as a dynamical judge: Core, Cusp or MOND?Sep 06 2013The cold dark matter model predicts cuspy dark matter halos. However, it has been found that, in some low-mass galaxies, cored dark halos provide a better description of their internal dynamics. Here we give constraints on the dark halo profile in the ... More
Kinematically Cold Populations at Large Radii in the Draco and Ursa Minor Dwarf SpheroidalsJun 23 2004We present projected velocity dispersion profiles for the Draco and Ursa Minor (UMi) dwarf spheroidal galaxies based on 207 and 162 discrete stellar velocities, respectively. Both profiles show a sharp decline in the velocity dispersion outside ~30 arcmin ... More
The Local GroupAug 16 2000Local Group galaxies such as the Milky Way, the Magellanic Clouds, and M31 are being used by a number of international collaborations to search for microlensing events. Type and number of detections place constraints on dark matter and the stellar populations ... More
Local Group(s)May 22 2006The properties of the galaxies of the Local Group are reviewed, followed by a brief discussion of nearby groups. The galaxy groups in our vicinity - the M81 group, the Cen A group, and the IC 342/Maffei group - are in many respects Local Group analogs: ... More
4MOST Consortium Survey 3: Milky Way Disc and Bulge Low-Resolution Survey (4MIDABLE-LR)Mar 06 2019The mechanisms of the formation and evolution of the Milky Way are encoded in the orbits, chemistry and ages of its stars. With the 4MOST MIlky way Disk And BuLgE Low-Resolution Survey (4MIDABLE-LR) we aim to study kinematic and chemical substructures ... More
Dwarf Galaxies in the Local Group and in the Local VolumeJul 11 2001After summarizing the characteristics of different types of dwarf galaxies I briefly review our current state of knowledge of dwarf galaxy evolution in the Local Group, for which we now have a fairly detailed although by no means comprehensive picture. ... More
A Map of the Northern Sky: The Sloan Digital Sky Survey in Its First YearMay 09 2001The Sloan Digital Sky Survey (SDSS) is the largest and most ambitious optical CCD survey undertaken to date. It will ultimately map out one quarter of the sky with precision photometry in five bands, high-quality astrometry, and spectra of all galaxies ... More
Evolutionary Histories of Dwarf Galaxies in the Local GroupDec 24 1998The star formation histories of Local Group (LG) dwarf galaxies and more distant potential LG members are reviewed. Problems in defining the spatial extent of the LG and membership are briefly discussed. The morphological types found in the LG are presented, ... More
On the C and N Abundances of 47 Tucanae Main Sequence StarsDec 11 2003Dec 15 2003We report the results of an analysis of CN and CH band strengths among a large sample of 47 Tucanae main-sequence and turn-off stars presented earlier by Harbeck et al. The resulting C and N abundances derived from synthetic spectra demonstrate: 1) A ... More
Observational Comparison of Star Formation in Different Galaxy TypesSep 07 2010Galaxies cover a wide range of masses and star formation histories. In this review, I summarize some of the evolutionary key features of common galaxy types. At the high-mass end, very rapid, efficient early star formation is observed, accompanied by ... More
Mean age gradient and asymmetry in the star formation history of the Small Magellanic CloudAug 06 2013Sep 20 2013We derive the star formation history in four regions of the Small Magellanic Cloud (SMC) using the deepest VI color-magnitude diagrams (CMDs) ever obtained for this galaxy. The images were obtained with the Advanced Camera for Surveys onboard the Hubble ... More
Probing the boundary between star clusters and dwarf galaxies: A MUSE view on the dynamics of Crater/Laevens IApr 22 2016We present MUSE observations of the debated ultra faint stellar system Crater. We spectroscopically confirm 26 member stars of this system via radial velocity measurements. We derive the systematic instrumental velocity uncertainty of MUSE spectra to ... More
Star Formation History in two fields of the Small Magellanic Cloud BarJun 04 2012The Bar is the most productive region of the Small Magellanic Cloud in terms of star formation but also the least studied one. In this paper we investigate the star formation history of two fields located in the SW and in the NE portion of the Bar using ... More
LAMOST DR1: Stellar parameters and chemical abundances with SP_AceMar 06 2018We present a new analysis of the LAMOST DR1 survey spectral database performed with the code SP_Ace, which provides the derived stellar parameters T$_{\rm eff}$, log (g), [Fe/H], and [$\alpha$/Fe] for 1,097,231 stellar objects. We tested the reliability ... More
Does rotation of B stars depend on metallicity? preliminary results from GIRAFFE spectraMar 01 2006We show the vsini distribution of main sequence B stars in sites of various metallicities, in the absolute magnitude range -3.34 < Mv < -2.17. These include Galactic stars in the field measured by Abt et al. (2002), members of the h & chi Per open clusters ... More
Star Formation Histories of Nearby Dwarf GalaxiesNov 02 2000Properties of nearby dwarf galaxies are briefly discussed. Dwarf galaxies vary widely in their star formation histories, the ages of their subpopulations, and in their enrichment history. Furthermore, many dwarf galaxies show evidence for spatial variations ... More
Be star surveys with CCD photometry. II. NGC 1818 and its neighbouring cluster in the LMCJun 19 1996As part of an ongoing photometric survey of young Magellanic Cloud clusters we identified Be stars in NGC 1818 and a nearby smaller cluster in the Large Magellanic Cloud. The neighbouring cluster does not contain evolved stars, and its sparsely populated ... More
Star Formation Histories of Local Group Dwarf GalaxiesJun 14 1998Jun 16 199840 galaxies are currently known as, or suspected to be Local Group members within a radius of 1.8 Mpc. 37 of these galaxies are dwarf galaxies with M_B > -18.5 mag. I present a compilation of the star formation histories of dwarf irregulars, dwarf ellipticals, ... More
Graphene channels interfaced with an array of individual quantum dotsMay 16 2017Surface graphene guides were interfaced with an array of individual semiconductor quantum dots, whose position was commensurate with the optical guide modes. The surface guide served as a channel for a Field Effect Transistor (FET) while the dots were ... More
Satellites in the Local Group and Other Nearby GroupsMar 31 2011In recent years the census of known satellites in our own Local Group and in nearby galaxy groups has increased substantially due to sensitive wide-area surveys. In the Local Group these surveys have more than doubled its known galaxy content and extended ... More
Stellar Populations in the Local Group of GalaxiesAug 04 2005The characteristics and properties of the stellar populations and evolutionary histories of Local Group galaxies are summarized and compared to predictions of cosmological models. No clear signature of the re-ionization epoch is observed; in particular, ... More
The Star Formation History of the Local GroupMay 14 2000The star formation histories of Local Group galaxies are summarized. The three large spirals are discussed individually, whereas the discussion of the Local Group dwarfs concentrates on differences and commonalities. While Local Group galaxies exhibit ... More
Negative differential resistance with graphene channels, interfacing distributed quantum dots in Field-Effect TransistorsJul 25 2013Field effect transistors with channels made of graphene layer(s) were explored. The graphene layer(s) contacted a distributed array of well-separated semiconductor quantum dots (QDs). The dots were embedded in nano-structured hole-array; each filled hole ... More
Nonlinear behavior of vibrating molecules on suspended graphene waveguidesJun 18 2012Suspended graphene waveguides were deposited on micron-scale periodic metal (plasmonic) structures. Raman scattering of test molecules (B. Megaterium), deposited on the waveguides' surface, exhibited azimuthal cycles upon rotation: at these micron scales, ... More
Tracing the tidal streams of the Sagittarius dSph, and halo Milky Way features, with carbon-rich long-period variablesJul 24 2015We assemble 121 spectroscopically-confirmed halo carbon stars, drawn from the literature, exhibiting measurable variability in the Catalina Surveys. We present their periods and amplitudes, which are used to estimate distances from period-luminosity relationships. ... More
Observed Properties of Dark Matter: dynamical studies of dSph galaxiesAug 24 2006The Milky Way satellite dwarf spheroidal (dSph) galaxies are the smallest dark matter dominated systems in the universe. We have underway dynamical studies of the dSph to quantify the shortest scale lengths on which Dark Matter is distributed, the range ... More
Near-Field Cosmology with Local Group Dwarf SpheroidalsSep 06 2005The Local Group offers an excellent laboratory for near-field cosmology by permitting us to use the resolved stellar content of its constituent galaxies as probes of galaxy formation and evolution, which in turn is an important means for testing cosmological ... More
The Evolutionary History of Local Group Irregular GalaxiesMar 09 2004Irregular (Irr) galaxies are gas-rich objects with recent or ongoing star formation. In absence of spiral density waves, star formation occurs largely stochastically. The scattered star-forming regions tend to be long-lived and migrate slowly. Older populations ... More
Interstellar Media in the Magellanic Clouds and other Local Group Dwarf GalaxiesOct 21 2001I review the properties of the interstellar medium in the Magellanic Clouds and Local Group dwarf galaxies. The more massive, star-forming galaxies show a complex, multi-phase ISM full of shells and holes ranging from very cold phases (a few 10 K) to ... More
Star Clusters in Local Group GalaxiesDec 28 1999Dec 30 1999In about 40% of the Local Group galaxies star clusters have been detected so far, but the census is still incomplete. The properties of these clusters are briefly reviewed, and the impact of galaxy environment on the evolution and survival of star clusters ... More
Metal-poor Galaxies in the Local UniverseAug 14 2012A galaxy's mean metallicity is usually closely correlated with its luminosity and mass. Consequently the most metal-poor galaxies in the local universe are dwarf galaxies. Blue compact dwarfs and tidal dwarfs tend to deviate from the metallicity-luminosity ... More
The faint outer regions of the Pegasus Dwarf Irregular galaxy: a much larger and undisturbed galaxyAug 25 2009We investigate the spatial extent and structure of the Pegasus dwarf irregular galaxy using deep, wide-field, multicolour CCD photometry from the Sloan Digital Sky Survey (SDSS) and new deep HI observations. We study an area of ~0.6 square degrees centred ... More
A Curious New Milky Way Satellite in Ursa MajorJun 26 2006Jul 04 2006In this Letter, we study a localized stellar overdensity in the constellation of Ursa Major, first identified in Sloan Digital Sky Survey (SDSS) data and subsequently followed up with Subaru imaging. Its color-magnitude diagram (CMD) shows a well-defined ... More
A Faint New Milky Way Satellite in BootesApr 17 2006Jun 29 2006In this Letter, we announce the discovery of a new satellite of the Milky Way in the constellation of Bootes at a distance of 60 kpc. It was found in a systematic search for stellar overdensities in the North Galactic Cap using Sloan Digital Sky Survey ... More
A new low mass for the Hercules dSph: the end of a common mass scale for the dwarfs?Oct 07 2009We present a new mass estimate for the Hercules dwarf spheroidal galaxy (dSph), based on the revised velocity dispersion obtained by Aden et al. (2009, arXiv:0908.3489). The removal of a significant foreground contamination using newly acquired Stromgren ... More
Discovery of a new Galactic bona fide luminous blue variable with SpitzerAug 26 2014We report the discovery of a circular mid-infrared shell around the emission-line star Wray 16-137 using archival data of the Spitzer Space Telescope. Follow-up optical spectroscopy of Wray 16-137 with the Southern African Large Telescope revealed a rich ... More
The Age-Metallicity Relation of the SMCJul 04 2006The Small Magellanic Cloud (SMC) is the only dwarf galaxy in the Local Group known to have formed and preserved populous star clusters continuously over the past 12 Gyr. These clusters provide a unique, closely spaced set of single-age, single-metallicity ... More
Newly Discovered RR Lyrae Stars in the SDSSXPanXSTARRS1XCatalina FootprintApr 17 2014We present the detection of 6,371 RR Lyrae (RRL) stars distributed across ~14,000 deg^2 of the sky from the combined data of the Sloan Digital Sky Survey (SDSS), the Panoramic Survey Telescope and Rapid Response System 1 (PS1), and the second photometric ... More
Studies of binary star cluster candidates in the bar of the LMC. IIApr 14 2000Binary clusters account for more than 10 % of the cluster population in the Magellanic Clouds. Statistically fewer than 50 % of the found pairs are expected to be chance superpositions. We estimated the cluster encounter rate and suggest that tidal capture ... More
The cluster pair SL 538/ NGC 2006 (SL 537)Sep 24 1998We studied in detail the binary cluster candidates SL 538 and NGC 2006 in the Large Magellanic Cloud (LMC). This cluster pair is located in the northwestern part of the large OB association LH 77 in supergiant shell LMC 4. A third star cluster, KMHK 1019, ... More
Search for Extratidal Features Around 17 Globular Clusters in the Sloan Digital Sky SurveyAug 17 2010The dynamical evolution of a single globular cluster and also of the entire Galactic globular cluster system has been studied theoretically in detail. In particular, simulations show how the 'lost' stars are distributed in tidal tails emerging from the ... More
The Type Ia Supernova 1998bu in M96 and the Hubble ConstantJun 12 1999We present optical and near-infrared photometry and spectroscopy of the type Ia SN 1998bu in the Leo I Group galaxy M96 (NGC 3368). The data set consists of 356 photometric measurements and 29 spectra of SN 1998bu between UT 1998 May 11 and July 15. The ... More
The blue supergiant MN18 and its bipolar circumstellar nebulaAug 25 2015We report the results of spectrophotometric observations of the massive star MN18 revealed via discovery of a bipolar nebula around it with the Spitzer Space Telescope. Using the optical spectrum obtained with the Southern African Large Telescope, we ... More
The internal kinematics of dwarf spheroidal galaxiesFeb 08 2006The status of kinematic observations in Local Group dwarf spheroidal galaxies (dSphs) is reviewed. Various approaches to the dynamical modelling of these data are discussed and some general features of dSph dark matter haloes based on simple mass models ... More
The Anisotropic Distribution of M 31 Satellite Galaxies: A Polar Great Plane of Early-Type CompanionsSep 09 2005Nov 09 2005The highly anisotropic distribution and apparent alignment of the Galactic satellites in polar great planes begs the question how common such distributions are. The satellite system of M31 is the only nearby system for which we currently have sufficiently ... More
The tidal perturbation of the low-mass globular cluster NGC 5466Jul 28 2003The distribution of stars in the outer part of the sparse globular cluster NGC 5466 provides evidence for possible tidal mass loss after a recent disk-shock near the solar circle.
SP_Ace: a new code to derive stellar parameters and elemental abundancesDec 04 2015Aims: We developed a new method of estimating the stellar parameters Teff, log g, [M/H], and elemental abundances. This method was implemented in a new code, SP_Ace (Stellar Parameters And Chemical abundances Estimator). This is a highly automated code ... More
Ion-liquid based super-capacitors with inner gate diode-like separatorsJan 09 2019We demonstrate that the capacitance of ionic-liquid filled supercapacitors is substantially increased by placing a diode-like structure on the separator membrane. We call the structured separator: gate, and demonstrate that the order of a p-n layout with ... More
The extended tails of Palomar 5: A ten degree arc of globular cluster tidal debrisJul 25 2003Using wide-field photometric data from the Sloan Digital Sky Survey (SDSS) we recently showed that the Galactic globular cluster Palomar 5 is in the process of being tidally disrupted. Its tidal tails were initially detected in a 2.5 degree wide band ... More
A comprehensive model for the Monoceros tidal streamOct 19 2004We have compiled an extensive dataset on potential parts of the Monoceros tidal stream and performed an exhaustive survey of dwarf galaxy semi-analytic orbits in order to constrain its orbital properties. The best-fit orbits are subsequently realized ... More
Electrically tuned super-capacitorsDec 25 2015Aug 18 2018We show how to increase the capacitance of super-capacitors by modifying the otherwise passive separator layer and turn it into an active diode-like structure. We demonstrate 15% capacitance increase for a diode-like separators without a bias. Additional ... More
Observing the dark matter density profile of isolated galaxiesJan 17 2003Using the Sloan Digital Sky Survey (SDSS), we probe the halo mass distribution by studying the velocities of satellites orbiting isolated galaxies. In a subsample that covers 2500 sq. degrees on the sky, we detect about 3000 satellites with absolute blue ... More
On the origin of the radial mass density profile of the Galactic halo Globular Cluster SystemFeb 22 2005We investigate what may be the origin of the presently observed spatial distribution of the mass of the Galactic Old Halo globular cluster system. We propose its radial mass density profile to be a relic of the distribution of the cold baryonic material ... More
Complexity on Small Scales II: Metallicities and Ages in the Leo II Dwarf Spheroidal GalaxySep 26 2006We present metallicities and ages for 52 red giants in the remote Galactic dwarf spheroidal (dSph) galaxy Leo II. These stars cover the entire surface area of Leo II and are radial velocity members. We obtained medium-resolution multi-fiber spectroscopy ... More
Complexity on Small Scales III: Iron and alpha Element Abundances in the Carina Dwarf Spheroidal GalaxyFeb 14 2008We have obtained high-resolution spectroscopy of ten red giants in the Carina dwarf spheroidal (dSph) with UVES at the ESO/VLT. Here we present the abundances of O,Na,Mg,Si,Ca,Ti and Fe. By comparing the iron abundances [Fe/H] with calcium triplet (CaT) ... More