We present a catalogue of 73¿221 white dwarf candidates extracted from the astrometric and photometric data of the recently published Gaia-DR2 catalogue. White dwarfs were selected from the Gaia ...Hertzsprung–Russell diagram with the aid of the most updated population synthesis simulator. Our analysis shows that Gaia has virtually identified all white dwarfs within 100¿pc from the Sun. Hence, our sub-population of 8555 white dwarfs within this distance limit and the colour range considered, -0.52<(GBP-GRP)<0.80¿, is the largest and most complete volume-limited sample of such objects to date. From this sub-sample, we identified 8343 CO-core and 212 ONe-core white dwarf candidates and derived a white dwarf space density of 4.9±0.4×10-3pc-3¿. A bifurcation in the Hertzsprung–Russell diagram for these sources, which our models do not predict, is clearly visible. We used the Virtual Observatory SED Analyzer tool to derive effective temperatures and luminosities for our sources by fitting their spectral energy distributions, that we built from the ultraviolet to the near-infrared using publicly available photometry through the Virtual Observatory. From these parameters, we derived the white dwarf radii. Interpolating the radii and effective temperatures in hydrogen-rich white dwarf cooling sequences, we derived the surface gravities and masses. The Gaia 100¿pc white dwarf population is clearly dominated by cool (~8000¿K) objects and reveals a significant population of massive (¿M~0.8M¿¿) white dwarfs, of which no more than ~30--40 per cent can be attributed to hydrogen-deficient atmospheres, and whose origin remains uncertain.
Peer Reviewed
ABSTRACT
Gaia-DR2 has provided an unprecedented number of white dwarf candidates of our Galaxy. In particular, it is estimated that Gaia-DR2 has observed nearly 400 000 of these objects and close to ...18 000 up to 100 pc from the Sun. This large quantity of data requires a thorough analysis in order to uncover their main Galactic population properties, in particular the thin and thick disc and halo components. Taking advantage of recent developments in artificial intelligence techniques, we make use of a detailed Random Forest algorithm to analyse an 8D space (equatorial coordinates, parallax, proper motion components, and photometric magnitudes) of accurate data provided by Gaia-DR2 within 100 pc from the Sun. With the aid of a thorough and robust population synthesis code, we simulated the different components of the Galactic white dwarf population to optimize the information extracted from the algorithm for disentangling the different population components. The algorithm is first tested in a known simulated sample achieving an accuracy of 85.3 per cent. Our methodology is thoroughly compared to standard methods based on kinematic criteria demonstrating that our algorithm substantially improves previous approaches. Once trained, the algorithm is then applied to the Gaia-DR2 100 pc white dwarf sample, identifying 12 227 thin disc, 1410 thick disc, and 95 halo white dwarf candidates, which represent a proportion of 74:25:1, respectively. Hence, the numerical spatial densities are $(3.6\pm 0.4)\times 10^{-3}\, {\rm pc^{-3}}$, $(1.2\pm 0.4)\times 10^{-3}\, {\rm pc^{-3}}$, and $(4.8\pm 0.4)\times 10^{-5}\, {\rm pc^{-3}}$ for the thin disc, thick disc, and halo components, respectively. The populations thus obtained represent the most complete and volume-limited samples to date of the different components of the Galactic white dwarf population.
The kinetics of leaching of Karelian shungites (types I–III) with water at pH in the interval 1–12 was studied. Changes in the chemical composition and structure of the shungite substance were ...revealed by X-ray fluorescence analysis and scanning electron microscopy. The catalytic properties of shungite were studied in relation to the presence of oxygen in water. The optimum design of a shungite–carbonate installation for potable water treatment was substantiated.
Yields of the products of the microwave plasmoid treatment of liquid n-hexane, n-heptane, or chloroform and their mixtures have been measured using the gas chromatography—mass spectrometry technique.
Unmanned aerial systems (UAS) are becoming a common tool for aerial sensing applications. Nevertheless, sensed data need further processing before becoming useful information. This processing ...requires large computing power and time before delivery. In this paper, we present a parallel architecture that includes an unmanned aerial vehicle (UAV), a small embedded computer on board, a communication link to the Internet, and a cloud service with the aim to provide useful real-time information directly to the end-users. The potential of parallelism as a solution in remote sensing has not been addressed for a distributed architecture that includes the UAV processors. The architecture is demonstrated for a specific problem: the counting of olive trees in a crop field where the trees are regularly spaced from each other. During the flight, the embedded computer is able to process individual images on board the UAV and provide the total count. The tree counting algorithm obtains an F 1 score of 99.09 % for a sequence of ten images with 332 olive trees. The detected trees are geolocated and can be visualized on the Internet seconds after the take-off of the flight, with no further processing required. This is a use case to demonstrate near real-time results obtained from UAS usage. Other more complex UAS applications, such as tree inventories, search and rescue, fire detection, or stock breeding, can potentially benefit from this architecture and obtain faster outcomes, accessible while the UAV is still on flight.
Enthalpy of formation of gaseous CF, CF
2
, CF
3
, CF
4
, C
2
F
2
, and C
2
F
4
molecules in the ground state have been simulated via the ab initio method in the CCSD(T) approximation with ...extrapolation to full basis and correlation energy. Equilibrium geometry, frequency of normal vibrations, and other parameters of these molecules have been determined; their thermodynamic functions at 0–2000 K were calculated from these data. Constants of the C
2
F
6
←
→
2CF
3
, C
2
F
2
←
→
2CF, C
2
F
4
←
→
2CF
2
, CF
4
←
→
CF
3
+ F, CF
4
←
→
CF
2
+ F
2
, and CF
3
←
→
CF
2
+ F equilibriums have been calculated, and the data on the rate constants in the high-pressure limit have been obtained.
The efficiency of zone freezing for potable water treatment to remove inorganic impurities was examined. The content of impurities in model solutions before and after zone freezing was evaluated by ...neutron activation analysis with the formation of
56
Mn,
116
m
In, and
198
Au radionuclides. The zone freezing procedure is the most efficient at low ice front velocities (no greater than 0.15 cm h
−1
).
Of the two existing radiochemical procedures for determining the isotope composition and specific activities of radionuclides in potable water (the first procedure was developed at the Center for ...Examining Water Quality and the second, at the Ramzaev Research Institute of Radiation Hygiene), the second procedure is more reliable. It was used for total radiochemical analysis of water from a series of underground artesian wells of north-western regions of Leningrad oblast.
A mathematical apparatus for describing the kinetics of chemical reactions accompanied by phase transitions is suggested. The phenomenon of stimulated precipitation is singled out. Together with ...spontaneous precipitation-solution, it allows periodic sedimentation (Liesegang rings) to be correctly described and the concept of solubility product to be corrected and generalized.
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