Plastic pollution of South Africa's marine environment is widespread, yet limited research exists on the distribution, accumulation and transport of plastic debris around South Africa. In this paper, ...numerical modelling is used to provide a first approximation of the pathways and accumulation of marine micro-plastics around South Africa. To account for a range of plastic classes, particles with two different densities are considered. Low-density (LD) particles represent low- and high-density polyethylene while high-density (HD) particles are representative of Polyethylene terephthalate and Polyvinyl chloride. While the majority of micro-plastic particles that enter the ocean from the five major coastal urban-industrialised centers beach along the coastline of South Africa, a third is exported to the open ocean. LD and HD particles are primarily exported to the South Atlantic and South Indian Ocean, respectively. Particles that beach along South Africa's coastline tend to accumulate in close proximity to the coastal urban-industrialised centers.
•Low-density particles are primarily exported to the South Atlantic Ocean.•High-density particles are mainly exported to the South Indian Ocean.•Particles mainly beach close to urban centers along the South African coastline.•Beached particles accumulate close to urban centers along South AfricaŠs coastline.
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. The T
eff = 13 ...000 K atmosphere is helium-dominated, but the convection zone contains significant amounts of hydrogen and oxygen. The four most common rock-forming elements (O, Mg, Si, and Fe) account for almost all the accreted mass, totalling at least 1.2 × 1024 g, similar to the mass of Ceres. The time-averaged accretion rate is 2 × 1010 g s−1, one of the highest rates inferred among all known metal-polluted white dwarfs. We note a large oxygen excess, with respect to the most common metal oxides, suggesting that the white dwarf accreted planetary debris with a water content of ≈38 per cent by mass. This star, together with GD 61, GD 16, and GD 362, form a small group of outliers from the known population of evolved planetary systems accreting predominantly dry, rocky debris. This result strengthens the hypothesis that, integrated over the cooling ages of white dwarfs, accretion of water-rich debris from disrupted planetesimals may significantly contribute to the build-up of trace hydrogen observed in a large fraction of helium-dominated white dwarf atmospheres.
Propionibacterium acnes induction of inflammatory responses is a major etiological factor contributing to the pathogenesis of acne vulgaris. In particular, the IL-1 family of cytokines has a critical ...role in both initiation of acne lesions and in the inflammatory response in acne. In this study, we demonstrated that human monocytes respond to P. acnes and secrete mature IL-1β partially via the NLRP3-mediated pathway. When monocytes were stimulated with live P. acnes, caspase-1 and caspase-5 gene expression was upregulated; however, IL-1β secretion required only caspase-1 activity. P. acnes induced key inflammasome genes including NLRP1 and NLPR3. Moreover, silencing of NLRP3, but not NLRP1, expression by small interfering RNA attenuated P. acnes-induced IL-1β secretion. The mechanism of P. acnes-induced NLRP3 activation and subsequent IL-1β secretion was found to involve potassium efflux. Finally, in acne lesions, mature caspase-1 and NLRP3 were detected around the pilosebaceous follicles and colocalized with tissue macrophages. Taken together, our results indicate that P. acnes triggers a key inflammatory mediator, IL-1β, via NLRP3 and caspase-1 activation, suggesting a role for inflammasome-mediated inflammation in acne pathogenesis.
We present the final sample of 98 detached double white dwarf (WD) binaries found in the Extremely Low Mass (ELM) Survey, a spectroscopic survey targeting <0.3 M He-core WDs completed in the Sloan ...Digital Sky Survey footprint. Over the course of the survey we observed ancillary low-mass WD candidates like GD 278, which we show is a P = 0.19 day double WD binary, as well as candidates that turn out to be field blue straggler/subdwarf A-type stars with luminosities too high to be WDs given their Gaia parallaxes. Here, we define a clean sample of ELM WDs that is complete within our target selection and magnitude range 15 < g0 < 20 mag. The measurements are consistent with 100% of ELM WDs being 0.0089 < P < 1.5 day double WD binaries, 35% of which belong to the Galactic halo. We infer that these are mostly He+CO WD binaries given the measurement constraints. The merger rate of the observed He+CO WD binaries exceeds the formation rate of stable mass-transfer AM CVn binaries by a factor of 25, and so the majority of He+CO WD binaries must experience unstable mass transfer and merge. The systems with the shortest periods, such as J0651+2844, are signature LISA verification binaries that can be studied with gravitational waves and light.
Abstract
The distribution of white dwarf rotation periods provides a means for constraining angular momentum evolution during the late stages of stellar evolution, as well as insight into the physics ...and remnants of double degenerate mergers. Although the rotational distribution of low-mass white dwarfs is relatively well constrained via asteroseismology, that of high-mass white dwarfs, which can arise from either intermediate-mass stellar evolution or white dwarf mergers, is not. Photometric variability in white dwarfs due to rotation of a spotted star is rapidly increasing the sample size of high-mass white dwarfs with measured rotation periods. We present the discovery of 22.4 minute photometric variability in the light curve of EGGR 156, a strongly magnetic, ultramassive white dwarf. We interpret this variability as rapid rotation, and our data suggest that EGGR 156 is the remnant of a double degenerate merger. Finally, we calculate the rate of period change in rapidly-rotating, massive, magnetic WDs due to magnetic dipole radiation. In many cases, including EGGR 156, the period change is not currently detectable over reasonable timescales, indicating that these WDs could be very precise clocks. For the most highly-magnetic, rapidly-rotating massive WDs, such as ZTF J1901+1450 and RE J0317−853, the period change should be detectable and may help constrain the structure and evolution of these exotic white dwarfs.
White dwarfs are stellar embers depleted of nuclear energy sources that cool over billions of years
. These stars, which are supported by electron degeneracy pressure, reach densities of 10
grams per ...cubic centimetre in their cores
. It has been predicted that a first-order phase transition occurs during white-dwarf cooling, leading to the crystallization of the non-degenerate carbon and oxygen ions in the core, which releases a considerable amount of latent heat and delays the cooling process by about one billion years
. However, no direct observational evidence of this effect has been reported so far. Here we report the presence of a pile-up in the cooling sequence of evolving white dwarfs within 100 parsecs of the Sun, determined using photometry and parallax data from the Gaia satellite
. Using modelling, we infer that this pile-up arises from the release of latent heat as the cores of the white dwarfs crystallize. In addition to the release of latent heat, we find strong evidence that cooling is further slowed by the liberation of gravitational energy from element sedimentation in the crystallizing cores
. Our results describe the energy released by crystallization in strongly coupled Coulomb plasmas
, and the measured cooling delays could help to improve the accuracy of methods used to determine the age of stellar populations from white dwarfs
.
Acne vulgaris is the most common skin disorder affecting millions of people worldwide and inflammation resulting from the immune response targeting Propionibacterium acnes has a significant role in ...its pathogenesis. In this study, we have demonstrated that P. acnes is a potent inducer of T helper 17 (Th17) and Th1, but not Th2 responses in human peripheral blood mononuclear cells (PBMCs). P. acnes stimulated expression of key Th17-related genes, including IL-17A, RORα, RORc, IL-17RA, and IL-17RC, and triggered IL-17 secretion from CD4+, but not from CD8+ T cells. Supernatants from P. acnes–stimulated PBMCs were sufficient to promote the differentiation of naive CD4+CD45RA T cells into Th17 cells. Furthermore, we found that the combination of IL-1β, IL-6, and transforming growth factor-β-neutralizing antibodies completely inhibited P. acnes–induced IL-17 production. Importantly, we showed that IL-17-expressing cells were present in skin biopsies from acne patients but not from normal donors. Finally, vitamin A (all-trans retinoic acid) and vitamin D (1,25-dihydroxyvitamin D3) inhibited P. acnes–induced Th17 differentiation. Together, our data demonstrate that IL-17 is induced by P. acnes and expressed in acne lesions and that both vitamin A and D could be effective tools to modulate Th17-mediated diseases such as acne.
Observations 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 evolution of post-main-sequence exoplanetary systems. Emission lines from the gaseous debris in the accretion disks of some of these systems show variations on timescales of decades, and have been interpreted as the general relativistic precession of a recently formed, elliptical disk. Here we present a comprehensive spectroscopic monitoring campaign of the calcium infrared triplet emission in one system, HE 1349-2305, which shows morphological emission profile variations suggestive of a precessing, asymmetric intensity pattern. The emission profiles are shown to vary on a timescale of one to two years, which is an order of magnitude shorter than what has been observed in other similar systems. We demonstrate that this timescale is likely incompatible with general relativistic precession, and consider alternative explanations for the rapid evolution, including the propagation of density waves within the gaseous debris. We conclude with recommendations for follow-up observations, and discuss how the rapid evolution of the gaseous debris in HE 1349-2305 could be leveraged to test theories of exoplanetary debris disk evolution around white dwarf stars.
The scatter of the M dwarf mass–radius relationship Parsons, S G; Gänsicke, B T; Marsh, T R ...
Monthly notices of the Royal Astronomical Society,
11/2018, Letnik:
481, Številka:
1
Journal Article, Publication
Recenzirano
Odprti dostop
M 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 tempera-
tures, which facilitate the ...detection of temperate, rocky planets in orbit around them.
However, the fundamental properties of M dwarfs are difficult to constrain, often lim-
iting our ability to characterise the planets they host. Here we test several theoretical
relationships for M dwarfs by measuring 23 high precision, model-independent masses
and radii for M dwarfs in binaries with white dwarfs. We find a large scatter in the
radii of these low-mass stars, with 25 per cent having radii consistent with theoret-
ical models while the rest are up to 12 per cent over-inflated. This scatter is seen
in both partially- and fully-convective M dwarfs. No clear trend is seen between the
over-inflation and age or metallicity, but there are indications that the radii of slowly
rotating M dwarfs are more consistent with predictions, albeit with a similar amount of
scatter in the measurements compared to more rapidly rotating M dwarfs. The sample
of M dwarfs in close binaries with white dwarfs appears indistinguishable from other
M dwarf samples, implying that common envelope evolution has a negligible impact on
their structure. We conclude that theoretical and empirical mass-radius relationships
lack the precision and accuracy required to measure the fundamental parameters of
M dwarfs well enough to determine the internal structure and bulk composition of the
planets they host.
Peer Reviewed
Abstract
We 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 atmospheres enriched with remarkably similar amounts of nuclear ashes of partial O- and Si-burning. Kinematic evidence is consistent with ejection from a binary supernova progenitor; at least two stars have rest-frame velocities indicating they are unbound to the Galaxy. With masses and radii ranging between 0.20 and 0.28 M$\odot$ and between 0.16 and 0.60 R$\odot$, respectively, we speculate these inflated white dwarfs are the partly burnt remnants of either peculiar Type Iax or electron-capture supernovae. Adopting supernova rates from the literature, we estimate that ∼20 LP 40−365 stars brighter than 19 mag should be detectable within 2 kpc from the Sun at the end of the Gaia mission. We suggest that as they cool, these stars will evolve in their spectroscopic appearance, and eventually become peculiar O-rich white dwarfs. Finally, we stress that the discovery of new LP 40−365 stars will be useful to further constrain their evolution, supplying key boundary conditions to the modelling of explosion mechanisms, supernova rates, and nucleosynthetic yields of peculiar thermonuclear explosions.
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