A5007841663- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astronomical Observations and Instrumentation
- Gamma-ray bursts and supernovae
- Astro and Planetary Science
- Pulsars and Gravitational Waves Research
- Astrophysical Phenomena and Observations
- History and Developments in Astronomy
- Adaptive optics and wavefront sensing
- Geophysics and Gravity Measurements
- Spacecraft and Cryogenic Technologies
- High-pressure geophysics and materials
- Solar and Space Plasma Dynamics
- Superconducting Materials and Applications
- Political Systems and Governance
- Atomic and Molecular Physics
- European history and politics
- Calibration and Measurement Techniques
- Scientific Research and Discoveries
- Astrophysics and Cosmic Phenomena
- Nuclear physics research studies
- Geochemistry and Geologic Mapping
- Geophysics and Sensor Technology
- Magnetic confinement fusion research
Armagh Observatory & Planetarium
2016-2025
Harper Adams University
2024
University of Oklahoma Health Sciences Center
2024
University of Oklahoma
2023
Trinity College Dublin
2012-2021
University of Cambridge
2019
Tohoku University
2006-2016
Chinese Academy of Sciences
2015
Université Libre de Bruxelles
2010
Friedrich-Alexander-Universität Erlangen-Nürnberg
2010
Mass extinctions are recognized through the study of fossil groups across event horizons, and from analyses long-term trends in taxonomic richness diversity. Both approaches have inherent flaws, data that once seemed reliable can be readily superseded by discovery new fossils and/or application analytical techniques. Herein current state Cretaceous-Tertiary (K-T) biostratigraphical record is reviewed for most major clades, including: calcareous nannoplankton, dinoflagellates, diatoms,...
Recent surveys have demonstrated the existence of several short-period binary systems containing two white dwarfs. Following orbital decay by gravitational-wave radiation, such binaries are expected to merge at a rate or three per thousand years galaxy. The consequences merger depend on individual dwarf masses, but believed include helium-rich subdwarfs, R CrB stars, extreme helium stars and also AM CVn possibly Type Ia supernovae.
We have examined the evolution of merged low-mass double white dwarfs that become luminous helium stars. approximated merging process by rapid accretion matter, consisting mostly helium, on to a carbon–oxygen (CO) dwarf. After certain mass is accumulated, shell flash occurs, radius and luminosity increase star becomes yellow giant. Mass stopped artificially when total reaches pre-determined value. When above helium-burning small enough, evolves blueward almost horizontally in...
We have examined the evolution of merged low-mass double white dwarfs which become low-luminosity (or high-gravity) extreme helium stars. approximated merging process by rapid accretion matter, consisting mostly helium, on to a dwarf. After certain mass is accumulated, shell flash occurs, radius and luminosity increase star becomes yellow giant. Mass stopped artificially when total reaches pre-determined value. As helium-burning moves inwards with repeating flashes, effective temperature...
We present the first volume-limited sample of spectroscopically confirmed hot subluminous stars out to 500 pc, defined using accurate parallax measurements from Gaia space mission data release 3 (DR3). The comprises a total 397 members, with 305 (~77%) identified as subdwarf stars, including 83 newly discovered systems. Of these, we observe that 178 (~58%) are hydrogen-rich sdBs, 65 sdOBs (~21%), 32 sdOs (~11%), and 30 He-sdO/Bs (~10%). Among them, 48 (~16%) exhibit an infrared excess in...
We present an unbiased orbit solution and mass determination of the components eclipsing binary NY Vir as a critical test for formation scenarios subdwarf B stars. obtained high-resolution time series VLT/UVES spectra high-speed multicolour VLT/ULTRACAM photometric observations Vir, rapidly pulsating star in short period binary. Combining radial velocity curve from with lightcurves, we determined numerical orbital solutions this Due to large number free parameters their strong correlations,...
Using a detailed Galactic model in which we consider distinct contributions from the bulge, thin disc, thick and halo, population synthesis approach, determined birth rates, numbers, period distributions of double white dwarfs (DWDs) within each component. In Galaxy as whole, our predicts current rate DWDs to be 3.21x10^{-2} yr^{-1}, local density 2.2x10^{-4} pc^{-3} total number 2.76x10^{8}. Assuming SNIa are formed merger two CO dwarfs, should 0.0013 yr^{-1}. The frequency spectra DWD...
Helium-rich subdwarf B (He-sdB) stars represent a small group of low-mass hot with luminosities greater than those conventional sdB stars, and effective temperatures lower O (sdO) stars. By measuring their surface chemistry, we aim to explore the connection between He-sdB He-rich sdO normal LS IV−14°116 is relatively intermediate star, also known be photometric variable. High-resolution blue–optical spectroscopy was obtained Anglo-Australian Telescope. Analysis spectrum shows have...
The surface abundances of extreme helium (EHe) and R Coronae Borealis (RCB) stars are discussed in terms a model for their origin the merger carbon–oxygen white dwarf with dwarf. is expressed as linear mixture individual layers both constituent dwarfs, taking account specific evolution each star. In developing this recipe from previous versions, particular attention has been given to intershell asymptotic giant branch (AGB) star which evolved become Thus composition merged estimated function...
Orbital decay by gravitational-wave radiation will cause some close-binary white dwarfs (WDs) to merge within a Hubble time. The results from previous hydrodynamical WD-merger simulations have been used guide calculations of the post-merger evolution carbon–oxygen + helium (CO+He) WD binaries. Our models include formation hot corona in addition Keplerian disc. We introduce 'destroyed-disc' model simulate effect direct disc ingestion into expanding envelope. These indicate significant...
An MK (Morgan-Keenan)-like system of spectral classification for hot subdwarfs is presented. We find that a three-dimensional type, consisting "spectral" class, "luminosity" and "helium" necessary to classify the sdO (subdwarf O) sdB B) stars. In addition, helium-strong stars appear form two parallel sequences: one showing strong lines CII, CIII, or CIV, other with these same weak absent. also give preliminary calibration new types in terms effective temperature, surface gravity,...
A series of 59 moderate-resolution high signal-to-noise spectra the pulsating helium star V652 Her covering 1.06 pulsation cycles was obtained with William Herschel Telescope. These have been supplemented by archival ultraviolet and visual spectrophotometry used to make a time-dependent study properties throughout cycle. This includes following features: most precise radial velocity curve for measured so far, new software automatic measurement effective temperature, surface gravity projected...
The identification of non-radial g-mode oscillations as the cause variability in cool subdwarf B stars (PG1716 variables) has been frustrated by a 5 000 K discrepancy between observed and theoretical blue edge instability domain (Fontaine et al. 2003). A major component solution to this problem identified} (a) using updated OP instead OPAL opacities (b) considering an enhancement nickel, addition that iron, driving zone. reason for success is that, OP, ``Fe-bump'' contributions from iron...
Hot subdwarfs represent a group of low-mass helium-burning stars formed through binary-star interactions and include some the most chemically peculiar in Galaxy. Stellar evolution theory suggests that they should have helium-rich atmospheres but, because radiation causes hydrogen to diffuse upwards, majority are extremely helium poor. Questions posed include: when does atmosphere become stratified at what rate?
In this paper, we report on our analysis using Hubble Space Telescope astrometry and Keck-I HIRES spectroscopy of the central six stars Tycho's supernova remnant (SN 1572). With these data, measured proper motions, radial velocities, rotational chemical abundances objects. Regarding abundances, do not confirm unusually high [Ni/Fe] ratio previously reported for Tycho-G. Rather, find that all metrics in stars, none exhibit characteristics expected from traditional Type Ia...
UVO0825+15 is a hot bright helium-rich subdwarf which lies in {\it K2} Field 5 and sample of intermediate subdwarfs observed with Subaru/HDS}. The light curve shows low-amplitude variations, whilst the Subaru} spectrum Pb{\sc iv} absorption lines, indicative very high lead overabundance. also has proper motion kinematics typical for thick disk star. Analyses ultraviolet dispersion optical spectra rule out short-period binary companion, provide fundamental atmospheric parameters $T_{\rm...
Abstract The formation histories of lithium-rich and carbon-rich red giants are not yet understood. It has been proposed that the merger a helium-core white dwarf with giant branch (RGB) star might provide solution. We have computed an extended grid post-merger evolution models combined these predictions binary-star population synthesis. results strongly support proposal helium RGB can progenitors both clump stars early-R carbon stars. distribution in T eff , log g L surface abundances...
The UK's devolution reforms have been piecemeal, directed at specific territorial issues in one or other part of the UK, and poorly coordinated with another. While this piecemeal approach reflects a centuries-old to statecraft addition since 1999 democratic process and, more recently, partisan conflict between UK devolved government, has established strong centrifugal tendencies. article explores how policy variation, inter-regional spillovers, fusion central government institutions those...
We investigate the uncertainty in surface abundances and yields of asymptotic giant branch (AGB) stars. apply three different mass loss laws to a 1.5 solar star metallicity Z=0.008 at beginning thermally pulsing (TP-AGB) phase. Efficient third dredge-up is found even very low envelope mass, contrary previous simulations with other evolution codes. find that yield carbon uncertain by about 15% for most light elements level 20-80%. For iron group varies from around 30% more abundant species...