A5075607587- Stellar, planetary, and galactic studies
- Astro and Planetary Science
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- Astrophysical Phenomena and Observations
- Planetary Science and Exploration
- History and Developments in Astronomy
- Space Exploration and Technology
- High-pressure geophysics and materials
- Adaptive optics and wavefront sensing
- Geological and Geochemical Analysis
- Spacecraft and Cryogenic Technologies
- Scientific Research and Discoveries
- Calibration and Measurement Techniques
- Paleontology and Stratigraphy of Fossils
- Pulsars and Gravitational Waves Research
- Marine animal studies overview
- Advanced ceramic materials synthesis
- ICT in Developing Communities
- Space Satellite Systems and Control
- Global Energy and Sustainability Research
- CCD and CMOS Imaging Sensors
- Galaxies: Formation, Evolution, Phenomena
University College London
2015-2024
Max Planck Institute for Radio Astronomy
2016
Max Planck Society
2016
Rutherford + Chekene
2016
University of Cambridge
2013-2014
University of Leicester
2008-2013
Queen's University Belfast
2011
Australian Astronomical Observatory
2011
University of Warwick
2011
Gemini North Observatory
2005-2009
Abstract The DESI Legacy Imaging Surveys ( http://legacysurvey.org/ ) are a combination of three public projects (the Dark Energy Camera Survey, the Beijing–Arizona Sky and Mayall z -band Survey) that will jointly image ≈14,000 deg 2 extragalactic sky visible from northern hemisphere in optical bands g , r using telescopes at Kitt Peak National Observatory Cerro Tololo Inter-American Observatory. combined survey footprint is split into two contiguous areas by Galactic plane. imaging...
(Abridged) We present the results of first unbiased survey for metal pollution among H-atmosphere (DA) white dwarfs with cooling ages 20-200 Myr and 17000K < Teff 27000K, using HST COS in far UV between 1130 1435 A. The atmospheric parameters element abundances are determined theoretical models, which include effects stratification due to gravitational settling radiative levitation. find 48 85 DA studied, or 56% show traces metals. In 25 stars, elements can be explained by levitation alone,...
Variable X-ray and gamma-ray emission is characteristic of the most extreme physical processes in Universe, studying sources these energetic photons has been a major driver astronomy for past 50 years. Here we present multiwavelength observations unique selected transient, discovered by Swift, which was accompanied bright across electromagnetic spectrum, whose properties are unlike any previously observed source. We pinpoint event to center small, star-forming galaxy at redshift z=0.3534....
We present Hubble Space Telescope (HST) ultraviolet spectroscopy of the white dwarfs PG 0843+516, 1015+161, SDSS 1228+1040, and GALEX 1931+0117, which accrete circumstellar planetary debris formed from destruction asteroids. Combined with optical data, a minimum five maximum 11 different metals are detected in their photospheres. With metal sinking time-scales only few days, these stars accretion/diffusion equilibrium, photospheric abundances closely reflect those material. find C/Si ratios...
Spitzer Space Observatory IRAC and MIPS photometric observations are presented for 20 white dwarfs with Teff ≲ 20, 000 K metal-contaminated photospheres. A warm circumstellar disk is detected at GD 16 likely PG 1457−086, while the remaining targets fail to reveal mid-infrared excess typical of dust disks, including a number heavily polluted stars. Extending previous studies, over 50% all single implied metal-accretion rates dM/dt≳ 3 × 108 g s−1 display infrared from orbiting dust; result...
This paper presents results of a near-infrared imaging survey for low-mass stellar and substellar companions to white dwarfs. A wide-field proper-motion 261 dwarfs was capable directly detecting at orbital separations between ~100 5000 AU with masses as low 0.05 M☉, while deep near-field search 86 ~50 1100 0.02 M☉. Additionally, all dwarf targets were examined excess emission, technique arbitrarily close down No brown candidates detected, which implies companion fraction <0.5% In contrast,...
The existence of water in extrasolar planetary systems is great interest as it constrains the potential for habitable planets and life. Here, we report identification a circumstellar disk that resulted from destruction water-rich rocky, minor planet. parent body formed evolved around star somewhat more massive than Sun, debris now closely orbits white dwarf remnant star. stellar atmosphere polluted with metals accreted disk, including oxygen excess expected oxide minerals, indicating was...
<i>Context. <i/>High contrast and high angular resolution imaging is the optimal search technique for substellar companions to nearby stars at physical separations larger than typically 10 AU. Two distinct populations of companions, brown dwarfs planets, can be probed characterized. As a result, fossile traces processes formation evolution revealed by orbital properties, both individual systems as an ensemble.<i>Aims. <i/>Since November 2002, we have conducted large, deep imaging, survey...
We report Spitzer Space Telescope photometry of 11 externally polluted white dwarfs. Of the nine stars for which we have IRAC photometry, find that GD 40, 133, and PG 1015+161 each has an infrared excess can be understood as arising from a flat, opaque, dusty disk. 56 also characteristic circumstellar dust, but flat-disk model cannot reproduce data unless there are grains warm 1700 K perhaps not even then. Our support previous suggestion metals in atmosphere 40 result accretion tidally...
Spitzer IRAC observations of 15 metal-polluted white dwarfs reveal infrared excesses in the spectral energy distributions HE 0110-5630, GD 61, and 1349-2305. All three these stars have helium-dominated atmospheres, their emissions are consistent with warm dust produced by tidal destruction (minor) planetary bodies. This study brings number metal-polluted, helium hydrogen atmosphere surveyed to 53 38 respectively. It also nearly doubles helium-rich found closely orbiting Spitzer. From...
The calcium and hydrogen abundances, Galactic positions kinematics of 146 DZ white dwarfs from the Sloan Digital Sky Survey are analysed to constrain possible origin their externally polluted atmospheres. There no correlations found between accreted abundances spatial–kinematical distributions relative interstellar material. Furthermore, two thirds stars currently located above gas dust layer, indicate multi-Myr residences in this region where material is virtually absent.
Spitzer Space Telescope IRAC 3-8 micron and AKARI IRC 2-4 photometry are reported for ten white dwarfs with photospheric heavy elements; nine relatively cool stars calcium, one hotter star a peculiar high carbon abundance. A substantial infrared excess is detected at HE 2221-1630, while modest emissions identified 0106-3253 0307+0746, implying these latter two have narrow (Delta r < 0.1 Rsol) rings of circumstellar dust. likely 7.9 found PG 1225-079 may represent, together G166-58, sub-class...
White dwarfs whose atmospheres are polluted by terrestrial-like planetary debris have become a powerful and unique tool to study evolved systems. This paper presents results for an unbiased Spitzer IRAC search circumstellar dust orbiting homogeneous well-defined sample of 134 single white dwarfs. The stars were selected without regard atmospheric metal content but chosen 1) hydrogen rich atmospheres, 2) 17 000 K < T_eff 25 correspondingly young post main-sequence ages 15-270Myr, 3)...
This paper explores how the stochastic accretion of planetesimals onto white dwarfs would be manifested in observations their atmospheric pollution. Archival pollution levels for unbiased samples DA and non-DA are used to derive distribution rates, confirming that rates become systematically lower as sinking time is decreased, with no discernable dependence on cooling age. The expected from all same mass (ie, a mono-mass distribution) explored both analytically using Monte Carlo model,...
The cool white dwarf SDSS J124231.07+522626.6 exhibits photospheric absorption lines of eight distinct heavy elements in medium resolution optical spectra, notably including oxygen. Teff = 13 000 K atmosphere is helium-dominated, but the convection zone contains significant amounts hydrogen and four most common rock-forming (O, Mg, Si, Fe) account for almost all accreted mass, totalling at least 1.2 × 1024 g, similar to mass Ceres. time-averaged accretion rate 2 1010 g s−1, one highest rates...
Observations of atmospheric metals and dust discs around white dwarfs provide important clues to the fate terrestrial planetary systems intermediate mass stars. We present Spitzer IRAC observations 15 metal polluted investigate occurrence physical properties circumstellar created by disruption bodies. find subtle infrared excess emission consistent with warm KUV 15519+1730 HS 2132+0941, weaker DZ dwarf G245-58, which, if real, makes it coolest known exhibit a 3.6 micron first star bright...
A low-mass planet around a white dwarf Numerous exoplanets have been detected Sun-like stars. These stars end their lives as dwarfs, which should inherit any surviving planetary systems. Manser et al. found periodic shifts in emission lines from disc of gas orbiting (see the Perspective by Fossati). They used numerical simulations to show that most likely explanation for spectral is within disc. The must be unusually small and dense avoid being ripped apart tidal forces. authors speculate it...
This paper presents combined ${\it Spitzer}$ IRAC and Hubble}$ COS results for a double-blind survey of 195 single 22 wide binary white dwarfs infrared excesses atmospheric metals. The selection criteria include cooling ages in the range 9 to 300 Myr, hydrogen-rich atmospheres so that presence metals can be confidently linked ongoing accretion from circumstellar disc. entire sample has photometry, whereas 168 targets have corresponding ultraviolet spectra. Three stars with due debris discs...
Eighteen years after an infrared excess was discovered associated with the white dwarf G29-38, we report ground-based measurements (JHKsKL'N') millijansky-level sensitivity of GD 362 that show it to be a second single excess. As first approximation, around 362, which amounts ~3% total stellar luminosity, can explained by emission from passive, flat, opaque dust disk lies within Roche radius dwarf. The may have been produced tidal disruption large parent body such as asteroid. Accretion this...
This paper reports follow-up photometric and spectroscopic observations, including warm Spitzer IRAC photometry of seven white dwarfs from the SDSS with apparent excess flux in UKIDSS K-band observations. Six science targets were selected 16,785 DA star candidates identified either spectroscopically or photometrically within DR7, spatially cross-correlated HK detections DR8. Thus selection criteria are completely independent stellar mass, effective temperature above 8000 K, presence (or...
We present optical and infrared characterization of the polluted DAZ white dwarf GALEX J193156.8+011745. Imaging spectroscopy from ultraviolet to thermal indicate that this hosts excess emission consistent with presence an orbiting dusty debris disk. In addition five elements previously identified, our echelle reveals chromium manganese enables restrictive upper limits on several other elements. Synthesis all detections suggests J193156.8+011745 has accreted a differentiated parent body....
Spitzer observations reveal the presence of warm debris from a tidally destroyed rocky and possibly icy planetary body orbiting white dwarf GD 61. Ultraviolet optical spectroscopy metal-contaminated stellar photosphere traces hydrogen, oxygen, magnesium, silicon, iron, calcium. The nominal ratios these elements indicate an excess oxygen relative to that expected rock-forming metal oxides, thus it is possible water was accreted together with terrestrial-like debris. Iron found be deficient...