M. Williams
A5012236841- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Galaxies: Formation, Evolution, Phenomena
- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- Astro and Planetary Science
- Astrophysical Phenomena and Observations
- Immune Cell Function and Interaction
- Solar and Space Plasma Dynamics
- SARS-CoV-2 and COVID-19 Research
- Cold Atom Physics and Bose-Einstein Condensates
- Respiratory viral infections research
- T-cell and B-cell Immunology
- History and Developments in Astronomy
- Adaptive optics and wavefront sensing
- Quantum Mechanics and Applications
- Influenza Virus Research Studies
- History of Science and Medicine
- Dark Matter and Cosmic Phenomena
- Single-cell and spatial transcriptomics
- Immune responses and vaccinations
- Computer Graphics and Visualization Techniques
- Atomic and Molecular Physics
- vaccines and immunoinformatics approaches
Emory University
2023-2025
Pennsylvania State University
2024
University of Georgia
2022
Leibniz Institute for Astrophysics Potsdam
2008-2020
Leibniz Association
2013
University of Ljubljana
2010
Australian National University
2008-2009
Mount Stromlo Observatory
2006-2009
Centre de Recherches Historiques
2005
University of Auckland
2003
We report the final redshift release of 6dF Galaxy Survey, a combined and peculiar velocity survey over southern sky (|b|>10 deg). Its 136,304 spectra have yielded 110,256 new extragalactic redshifts catalogue 125,071 galaxies making near-complete samples with (K, H, J, r_F, b_J) <= (12.65, 12.95, 13.75, 15.60, 16.75). The median is 0.053. Survey data, including images, spectra, photometry redshifts, are available through an online database. describe changes to information in database since...
We present the first data release of Radial Velocity Experiment (RAVE), an ambitious spectroscopic survey to measure radial velocities and stellar atmosphere parameters (temperature, metallicity, surface gravity) up one million stars using Six Degree Field multiobject spectrograph on 1.2 m UK Schmidt Telescope Anglo-Australian Observatory. The RAVE program started in 2003, obtaining medium-resolution spectra (median R = 7500) Ca-triplet region (8410-8795 Å) for southern hemisphere drawn from...
We present the stellar atmospheric parameters (effective temperature, surface gravity, overall metallicity), radial velocities, individual abundances, and distances determined for 425,561 stars, which constitute fourth public data release of RAdial Velocity Experiment (RAVE). The are computed using a new pipeline, based on algorithms MATISSE DEGAS. spectral degeneracies Two Micron All Sky Survey photometric information now better taken into consideration, improving parameter determination...
We made new estimates of the Galactic escape speed at various Galactocentric radii using latest data release RAdial Velocity Experiment (RAVE DR4). Compared to previous studies we have a database that is larger by factor 10, as well reliable distance for almost all stars. Our analysis based on statistical rigorously selected sample 90 high-velocity halo stars from RAVE and previously published set. calibrated extensively tested our method suite cosmological simulations formation Milky...
The RAdial Velocity Experiment survey, combined with proper motions and distance estimates, can be used to study in detail stellar kinematics the extended solar neighbourhood (solar suburb). Using 72 365 red-clump stars, we examine mean velocity components 3D between 6 < R 10 kpc −2 Z 2 kpc, concentrating on north–south differences. Simple parametric fits (R, Z) trends for Vϕ dispersions are presented. We confirm recently discovered gradient Galactocentric radial velocity, VR, finding that...
We present the second data release of Radial Velocity Experiment (RAVE), an ambitious spectroscopic survey to measure radial velocities and stellar atmosphere parameters (temperature, metallicity, surface gravity, rotational velocity) up one million stars using 6 dF multi-object spectrograph on 1.2 m UK Schmidt Telescope Anglo-Australian Observatory (AAO). The RAVE program started in 2003, obtaining medium resolution spectra (median R = 7500) Ca-triplet region (8410–8795 Å) for southern...
The 4MOST consortium is currently halfway through a Conceptual Design study for ESO with the aim to develop wide-field (>3 square degree, goal >5 degree), high-multiplex (>1500 fibres, 3000 fibres) spectroscopic survey facility an 4m-class telescope (VISTA). will run permanently on perform 5 year public yielding more than 20 million spectra at resolution R~5000 ({\lambda}=390-1000 nm) and 2 R~20,000 (395-456.5 nm & 587-673 nm). design especially intended complement three key all-sky,...
We present the third data release of RAdial Velocity Experiment (RAVE) which is first milestone RAVE project, releasing full pilot survey. The catalog contains 83,072 radial velocity measurements for 77,461 stars in southern celestial hemisphere, as well stellar parameters 39,833 stars. This paper describes content new release, processing pipeline, an updated calibration metallicity based upon observation additional standard Spectra will be made available a future release. can accessed via...
We investigate the kinematic parameters of Milky Way disc using RAVE and GCS stellar surveys. do this by fitting a model to data taking selection function into account. For stars in we use all phase-space coordinates, but for only $(l,b,v_{\rm los})$. Using MCMC technique, full posterior distributions given data. `age-velocity dispersion' relation three components ($\sigma_R,\sigma_{\phi},\sigma_z$), radial dependence velocity dispersions, Solar peculiar motion ($U_{\odot},V_{\odot},...
We perform numerical simulations of a stellar galactic disk with initial conditions chosen to represent an unrelaxed population which might have been left following merger. Stars are unevenly distributed in radial action angle, though the is axisymmetric. The velocity distribution simulated Solar neighborhood exhibits waves traveling direction positive v, where u,v and tangential components. As system relaxes structure wraps phase space, features seen uv-plane move closer together. show that...
We have undertaken the study of elemental abundances and kinematic properties a metal-poor sample candidate thick-disk stars selected from Radial Velocity Experiment spectroscopic survey bright to differentiate among present scenarios formation thick disk. In this paper, we report on 214 red giant branch, 31 clump/horizontal 74 main-sequence/sub-giant branch stars, which serves augment our previous only stars. find that disk [α/Fe] ratios are enhanced little variation (<0.1 dex), in...
Probability density functions are determined from new stellar parameters for the distance moduli of stars which RAdial Velocity Experiment (RAVE) has obtained spectra with S/N>=10. Single-Gaussian fits to pdf in modulus suffice roughly half stars, most other having satisfactory two-Gaussian representations. As expected, early-type rarely require more than one Gaussian. The expectation value is larger implied by modulus; latter itself parallax. Our parallaxes Hipparcos agree well values...
We analyse the kinematics of ~400000 RAVE stars. split sample into hot and cold dwarfs, red-clump non-clump giants. The clump giants are consistent with being identical those fit Gaussian velocity ellipsoids to meridional-plane components each star class give formulae from which shape orientation ellipsoid can be determined at any location. data cool dwarfs sharing same ellipsoids; sigma_z rises 21 kms in plane sim 55 |z|=2 kpc, while sigma_r 37 82 kms. At (R,z) longest axis one these is...
Using a sample of 213,713 stars from the Radial Velocity Experiment (RAVE) survey, limited to distance 2 kpc Sun and |z|<1 kpc, we report detection velocity gradient disc in fourth quadrant, directed radially Galactic centre. In direction centre, apply simple method independent stellar proper motions parameters assess existence this RAVE data. This corresponds |K+C| < 3 km/s/kpc, where K C are Oort constants measuring local divergence radial shear field, respectively. order illustrate...
The velocity dispersions of stars near the Sun are known to increase with stellar age, but age can be difficult determine so a proxy like abundance alpha elements (e.g., Mg) respect iron, [alpha/Fe], is used. Here we report an unexpected behavior found in dispersion sample giant from RAdial Velocity Experiment (RAVE) survey high quality chemical and kinematical information, that it decreases strongly for [Mg/Fe] > 0.4 dex (i.e., those formed first Gyr Galaxy's life). These findings explained...
Using the RAVE survey, we recently brought to light a gradient in mean galactocentric radial velocity of stars extended solar neighbourhood. This likely originates from non-axisymmetric perturbations potential, among which perturbation by spiral arms is possible explanation. Here, apply traditional density wave theory and analytically model component two-dimensional field. Provided that caused relatively long-lived can affect substantially above plane, this analytic provides new independent...
We present a measure of the inclination velocity ellipsoid at 1 kpc below Galactic plane using sample red clump giants from RAdial Velocity Experiment (RAVE) Data Release 2. find that is tilted towards with an . compare this value to computed inclinations for two mass models Milky Way. our measurement consistent short scalelength stellar disc (Rd≃ 2 kpc) if dark halo oblate or long 3 prolate. Once combined independent constraints on flattening halo, suggests approximately halfway between...
The RAdial Velocity Experiment (RAVE) is a spectroscopic survey of the Milky Way which already collected over 400000 spectra ~330000 different stars. We use subsample with spectroscopically determined values stellar parameters to determine distances these list currently contains 235064 high quality show no peculiarities and belong 210872 numbers will grow as RAVE progresses. public version catalog be made available through CDS services along ongoing data releases.
We present chemical elemental abundances for 36,561 stars observed by the RAdial Velocity Experiment (RAVE), an ambitious spectroscopic survey of our Galaxy at Galactic latitudes |b| > 25° and with magnitudes in range 9 <IDENIS <13. RAVE spectra cover Ca-triplet region 8410–8795 Å resolving power R ∼ 7500. This first data release catalog is complementary to third radial velocities stellar parameters, it contains elements Mg, Al, Si, Ca, Ti, Fe, Ni, a mean error ∼0.2 dex, as judged from...
We report the discovery of eight lithium-rich field giants found in a high resolution spectroscopic sample over 700 metal-poor stars ([Fe/H]<-0.5) selected from RAVE survey. The majority Li-rich our are very ([Fe/H]<-1.9), and have Li abundance (in form 7Li), A(Li)=log(n(Li)/n(H))+12, between 2.30 3.63, well above typical upper red giant branch limit, A(Li)<0.5, while two stars, with A(Li)~1.7-1.8, show similar lithium abundances to normal at same gravity. further included metal-poor,...
Aims. We aim at measuring the chemical gradients of elements Mg, Al, Si, and Fe along Galactic radius to provide new constraints on evolution models Galaxy such as Besançon model. Thanks large number stars our RAVE sample we can study how vary function distance from plane.
The diffuse interstellar bands (DIBs) are absorption lines observed in visual and near-infrared spectra of stars. Understanding their origin the medium is one oldest problems astronomical spectroscopy, as DIBs have been known since 1922. In a completely new approach to understanding DIBs, we combined information from nearly 500,000 stellar obtained by massive spectroscopic survey RAVE (Radial Velocity Experiment) produce first pseudo-three-dimensional map strength DIB at 8620 angstroms...
Abstract Antigen-experienced memory B-cells (MBC) are endowed with enhanced functional properties compared to naïve B cells and play an important role in the humoral response. However, epigenetic enzymes programs that govern their rapid differentiation incompletely understood. Here, of histone H3 lysine 27 methyltransferase EZH2 formation MBC response influenza infection was determined Mus musculus. expressed all postactivated B-cell subsets, including antibody-secreting (ASC), maximal...
We have searched for in-falling stellar streams on to the local Milky Way disc in CORAVEL and RAVE surveys. The survey consists of dwarf stars (Nordstrom et al. Geneva-Copenhagen survey) Famaey giant stars. select with radial velocities that are sensitive Galactic vertical space velocity (Galactic latitude b < -45 deg). Kuiper statistics been employed test symmetry distribution functions these samples evidence a net flow could be associated (tidal?) stream vertically coherent kinematics....