Abstract
PSR J0740+6620 has a gravitational mass of 2.08 ± 0.07
M
⊙
, which is the highest reliably determined mass of any neutron star. As a result, a measurement of its radius will provide unique ...insight into the properties of neutron star core matter at high densities. Here we report a radius measurement based on fits of rotating hot spot patterns to Neutron Star Interior Composition Explorer (NICER) and X-ray Multi-Mirror (XMM-Newton) X-ray observations. We find that the equatorial circumferential radius of PSR J0740+6620 is
13.7
−
1.5
+
2.6
km (68%). We apply our measurement, combined with the previous NICER mass and radius measurement of PSR J0030+0451, the masses of two other ∼2
M
⊙
pulsars, and the tidal deformability constraints from two gravitational wave events, to three different frameworks for equation-of-state modeling, and find consistent results at ∼1.5–5 times nuclear saturation density. For a given framework, when all measurements are included, the radius of a 1.4
M
⊙
neutron star is known to ±4% (68% credibility) and the radius of a 2.08
M
⊙
neutron star is known to ±5%. The full radius range that spans the ±1
σ
credible intervals of all the radius estimates in the three frameworks is 12.45 ± 0.65 km for a 1.4
M
⊙
neutron star and 12.35 ± 0.75 km for a 2.08
M
⊙
neutron star.
Neutron stars are not only of astrophysical interest, but are also of great interest to nuclear physicists because their attributes can be used to determine the properties of the dense matter in ...their cores. One of the most informative approaches for determining the equation of state (EoS) of this dense matter is to measure both a star's equatorial circumferential radius Re and its gravitational mass M. Here we report estimates of the mass and radius of the isolated 205.53 Hz millisecond pulsar PSR J0030+0451 obtained using a Bayesian inference approach to analyze its energy-dependent thermal X-ray waveform, which was observed using the Neutron Star Interior Composition Explorer (NICER). This approach is thought to be less subject to systematic errors than other approaches for estimating neutron star radii. We explored a variety of emission patterns on the stellar surface. Our best-fit model has three oval, uniform-temperature emitting spots and provides an excellent description of the pulse waveform observed using NICER. The radius and mass estimates given by this model are km and (68%). The independent analysis reported in the companion paper by Riley et al. explores different emitting spot models, but finds spot shapes and locations and estimates of Re and M that are consistent with those found in this work. We show that our measurements of Re and M for PSR J0030+0451 improve the astrophysical constraints on the EoS of cold, catalyzed matter above nuclear saturation density.
We present the first spectroscopic study of the host environments of Type Ibc supernovae (SNe Ibc) discovered exclusively by untargeted SN searches. Past studies of SN Ibc host environments have been ...biased toward high-mass, high-metallicity galaxies by focusing on SNe discovered in galaxy-targeted SN searches. Our new observations more than double the total number of spectroscopic stellar population age and metallicity measurements published for untargeted SN Ibc host environments. We discuss the path forward for making progress on SN Ibc progenitor studies in the Large Synoptic Survey Telescope era. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.
Methane (CH4) production is a ubiquitous, apparently unavoidable side effect of fermentative fibre digestion by symbiotic microbiota in mammalian herbivores. Here, a data compilation is presented of ...in vivo CH4 measurements in individuals of 37 mammalian herbivore species fed forage-only diets, from the literature and from hitherto unpublished measurements. In contrast to previous claims, absolute CH4 emissions scaled linearly to DM intake, and CH4 yields (per DM or gross energy intake) did not vary significantly with body mass. CH4 physiology hence cannot be construed to represent an intrinsic ruminant or herbivore body size limitation. The dataset does not support traditional dichotomies of CH4 emission intensity between ruminants and nonruminants, or between foregut and hindgut fermenters. Several rodent hindgut fermenters and nonruminant foregut fermenters emit CH4 of a magnitude as high as ruminants of similar size, intake level, digesta retention or gut capacity. By contrast, equids, macropods (kangaroos) and rabbits produce few CH4 and have low CH4 : CO2 ratios for their size, intake level, digesta retention or gut capacity, ruling out these factors as explanation for interspecific variation. These findings lead to the conclusion that still unidentified host-specific factors other than digesta retention characteristics, or the presence of rumination or a foregut, influence CH4 production. Measurements of CH4 yield per digested fibre indicate that the amount of CH4 produced during fibre digestion varies not only across but also within species, possibly pointing towards variation in microbiota functionality. Recent findings on the genetic control of microbiome composition, including methanogens, raise the question about the benefits methanogens provide for many (but apparently not to the same extent for all) species, which possibly prevented the evolution of the hosting of low-methanogenic microbiota across mammals.
Variationally consistent phase-field methods have been shown to be able to predict complex three-dimensional crack patterns. However, current computational methodologies in the context of large ...deformations lack the necessary numerical stability to ensure robustness in different loading scenarios. In this work, we present a novel formulation for finite strain polyconvex elasticity by introducing a new anisotropic split based on the principal invariants of the right Cauchy–Green tensor, which always ensures polyconvexity of the resulting strain energy function. The presented phase-field approach is embedded in a sophisticated isogeometrical framework with hierarchical refinement for three-dimensional problems using a fourth order Cahn–Hilliard crack density functional with higher-order convergence rates for fracture problems. Additionally, we introduce for the first time a Hu–Washizu mixed variational formulation in the context of phase-field problems, which permits the novel introduction of a variationally consistent stress-driven split. The new polyconvex phase-field fracture formulation guarantees numerical stability for the full range of deformations and for arbitrary hyperelastic materials.
Estuaries in rainfall poor regions are highly susceptible to climatic and hydrological changes. The Coorong, a Ramsar-listed estuarine-coastal lagoon at the end of the Murray-Darling Basin ...(Australia), has experienced declining ecological health over recent decades. Twenty years of environmental data were analysed to assess patterns and drivers of water quality changes. Large areas of the Coorong are now persistently hyper-saline (salinity >80 psu) and hypereutrophic (total nitrogen, TN > 4 mg L−1, total phosphorus, TP > 0.2 mg L−1, chlorophyll a > 50 μg L−1) which coincided with reduced flushing due to diminished freshwater inflows and increasing evapo-concentration. Sediment quality also was related to flushing, with higher concentrations of organic carbon, TN, TP and sulfides as salinity increased. While total nutrient levels are very high, dissolved inorganic nutrients are generally low. Increased lagoonal flushing would be beneficial to reduce the hypersalinisation and hypereutrophication and improve ecosystem health.
Display omitted
•The Ramsar-listed Coorong estuary is experiencing declining ecological health.•Extreme eutrophication has intensified with persistent hypersalinity.•Nutrients increase with salinity increase in both water and sediment.•Loss of aquatic plants and macroinvertebrates has exacerbated eutrophication.•Increased flushing would be beneficial to improve water quality and ecosystem health.
ABSTRACT In the summer of 2012, during a Pulsar Search Collaboratory workshop, two high-school students discovered J1930-1852, a pulsar in a double neutron star (DNS) system. Most DNS systems are ...characterized by short orbital periods, rapid spin periods, and eccentric orbits. However, J1930-1852 has the longest spin period ( 185 ms) and orbital period ( 45 days) yet measured among known, recycled pulsars in DNS systems, implying a shorter than average and/or inefficient recycling period before its companion went supernova. We measure the relativistic advance of periastron for J1930-1852, (4) deg yr−1, which implies a total mass ( (4) ) consistent with other DNS systems. The constraints on place limits on the pulsar and companion masses ( and respectively). J1930-1852's spin and orbital parameters challenge current DNS population models and make J1930-1852 an important system for further investigation.
•Direct reactive sputtering of crystalline V2O3 thin films can generate polymorphism.•A bixbyite-type V2O3 phase can be obtained by a physical deposition method.•Amorphous V 3+ oxides are only found ...in combination with other valencies.•Polycrystalline films present up to four different electrical transport types.•Pure crystalline (nearly stoichiometric) corundum-type V2O3 is formed at 600 °C.
This comprehensive work investigates a technologically appealing synthesis of V2O3 oxide thin films for electronic applications by the use of direct reactive sputtering with a heavily diluted gas mixture on a conducting platinum electrode. Morphological characterization was performed by Scanning Electron Microscopy, Atomic Force Microscopy, X-Ray Diffraction and X-Ray Reflectometry. Vanadium valence states were investigated by X-Ray Photoelectron Spectroscopy and crystalline phases were checked by X-Ray Grazing Incidence measurements. Low temperature electrical transport characteristics were determined by 2-point probe measurements. Only amorphous V2O3 was found to exist in a mixed-valence phase in the investigated parameter range. Deposition temperatures between 400 °C and 550 °C enable formation of mixtures between crystallographic phases of corundum- and bixbyite-type V2O3 polymorphs. Depending on temperature and sputtering power, morphology and stoichiometry can be tuned to generate four distinct type of electrical transport characteristics. Most promising electrical properties of corundum V2O3 with a resistance ratio of up to four orders of magnitude (during the low temperature insulator-to-metal transition) have been obtained for a moderate sputtering power of 50 W (on a 1″ target) at a deposition temperature of 600 °C. Reactive sputtering thus enables direct control of structural and electrical parameters for polycrystalline V2O3 thin film phases on a conducting substrate.
Context. The extrasolar planet HAT-P-8 b was thought to be one of the more inflated transiting hot Jupiters. Aims. By using new and existing photometric data, we computed precise estimates of the ...physical properties of the system. Methods. We present photometric observations comprising eleven light curves covering six transit events, obtained using five medium-class telescopes and telescope-defocussing technique. One transit was simultaneously obtained through four optical filters, and two transits were followed contemporaneously from two observatories. We modelled these and seven published datasets using the jktebop code. The physical parameters of the system were obtained from these results and from published spectroscopic measurements. In addition, we investigated the theoretically-predicted variation of the apparent planetary radius as a function of wavelength, covering the range 330–960 nm. Results. We find that HAT-P-8 b has a significantly lower radius (1.321 ± 0.037 RJup) and mass (1.275 ± 0.053 MJup) compared to previous estimates (\hbox{$1.50_{-0.06}^{+0.08} \, R_{\mathrm{Jup}}$}1.50-0.06+0.08 RJup and \hbox{$1.52_{-0.16}^{+0.18} \, M_{\mathrm{Jup}}$}1.52-0.16+0.18 MJup respectively). We also detect a radius variation in the optical bands that, when compared with synthetic spectra of the planet, may indicate the presence of a strong optical absorber, perhaps TiO and VO gases, near the terminator of HAT-P-8 b. Conclusions. These new results imply that HAT-P-8 b is not significantly inflated, and that its position in the planetary mass-radius diagram is congruent with those of many other transiting extrasolar planets.
We present new photometric and spectroscopic observations for 2M 1533+3759 (= NSVS 07826147), the seventh eclipsing subdwarf B star + M dwarf (sdB+dM) binary ever found. It has an orbital period of ...0.16177042 days, or ~3.88 hr, significantly longer than the 2.3-3.0 hr periods of the other known eclipsing sdB+dM systems. Spectroscopic analysis of the hot primary yields T eff = 29230 +/- 125 K, log g = 5.58 +/- 0.03, and log N(He)/N(H) = -2.37 +/- 0.05. The sdB velocity amplitude is K 1 = 71.1 +/- 1.0 km s-1. The only detectable light contribution from the secondary is due to the surprisingly strong reflection effect, whose peak-to-peak BVRI amplitudes are 0.1,0.1,0.15, and 0.19 mag, respectively. Light-curve modeling produced several solutions corresponding to different values of the system mass ratio, q (M 2/M 1), but only one is consistent with a core helium burning star, q = 0.301. The orbital inclination is 866. The sdB primary mass is M 1 = 0.376 +/- 0.055 M and its radius is R 1 = 0.166 +/- 0.007 R. 2M 1533+3759 joins PG 0911+456 (and possibly also HS 2333+3927) in having an unusually low mass for an sdB star. SdB stars with masses significantly lower than the canonical value of 0.48 M, down to as low as 0.30 M, were theoretically predicted by Han et al., but observational evidence has only recently begun to confirm the existence of such stars. The existence of core helium burning stars with masses lower than 0.40-0.43 M implies that at least some sdB progenitors have initial main-sequence masses of 1.8-2.0 M or more, i.e., they are at least main-sequence A stars. The orbital separation in 2M 1533+3759 is a = 0.98 +/- 0.04R. The secondary has M 2 = 0.113 +/- 0.017 M, R 2 = 0.152 +/- 0.005R, and K, consistent with a main-sequence M5 star. If 2M 1533+3759 becomes a cataclysmic variable (CV), its orbital period will be 1.6 hr, below the CV period gap.
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