ABSTRACT
2021 was the year of Jupiter’s equinox, that is the Sun and the Earth passed through the equatorial plane of the planet and therefore the orbital planes of its main satellites. This ...occurrence made it possible to observe mutual occultations and eclipses between the satellites. Our former experience shows that observations of such events provide accurate astrometric data that can be used to obtain new information on the dynamics of the Galilean satellites. The observations are a series of photometric measurements of a satellite which are carried out through the organization of a world wide campaign of observations thus maximizing the number and the quality of the data obtained. This work focuses on processing the photometric observations of the mutual occultations and eclipses of the Galilean satellites of Jupiter made during the international campaign in 2021. The final goal is to derive new accurate astrometric data. We used an accurate photometric model of mutual events in conjunction with the accuracy of observation. We obtained and processed the 84 light curves obtained during the campaign. As compared with the current best ephemerides, the rms of ‘O–C’ residuals are equal to 49 and 48 mas in right ascension and declination, respectively.
Context.
We present results from the first recorded stellar occultation by the large trans-Neptunian object (174567) Varda that was observed on September 10, 2018. Varda belongs to the ...high-inclination dynamically excited population, and has a satellite, Ilmarë, which is half the size of Varda.
Aims.
We determine the size and albedo of Varda and constrain its 3D shape and density.
Methods.
Thirteen different sites in the USA monitored the event, five of which detected an occultation by the main body. A best-fitting ellipse to the occultation chords provides the instantaneous limb of the body, from which the geometric albedo is computed. The size and shape of Varda are evaluated, and its bulk density is constrained using Varda’s mass as is known from previous works.
Results.
The best-fitting elliptical limb has semi-major (equatorial) axis of (383 ± 3) km and an apparent oblateness of 0.066 ± 0.047, corresponding to an apparent area-equivalent radius
R
′
equiv
= (370±7) km and geometric albedo
p
v
= 0.099 ± 0.002 assuming a visual absolute magnitude
H
V
= 3.81 ± 0.01. Using three possible rotational periods for the body (4.76, 5.91, and 7.87 h), we derive corresponding MacLaurin solutions. Furthermore, given the low-amplitude (0.06 ± 0.01) mag of the single-peaked rotational light-curve for the aforementioned periods, we consider the double periods. For the 5.91 h period (the most probable) and its double (11.82 h), we find bulk densities and true oblateness of
ρ
= (1.78 ± 0.06) g cm
−3
,
ɛ
= 0.235 ± 0.050, and
ρ
= (1.23 ± 0.04) g cm
−3
,
ɛ
= 0.080 ± 0.049. However, it must be noted that the other solutions cannot be excluded just yet.
There are numerous potential applications for superconducting tapes based on YBa(2)Cu(3)O(7-x) (YBCO) films coated onto metallic substrates. A long-established goal of more than 15 years has been to ...understand the magnetic-flux pinning mechanisms that allow films to maintain high current densities out to high magnetic fields. In fact, films carry one to two orders of magnitude higher current densities than any other form of the material. For this reason, the idea of further improving pinning has received little attention. Now that commercialization of YBCO-tape conductors is much closer, an important goal for both better performance and lower fabrication costs is to achieve enhanced pinning in a practical way. In this work, we demonstrate a simple and industrially scaleable route that yields a 1.5-5-fold improvement in the in-magnetic-field current densities of conductors that are already of high quality.
We report the results of two multichord stellar occultations by the dwarf planet (1) Ceres that were observed from Brazil on 2010 August 17, and from the USA on 2013 October 25. Four positive ...detections were obtained for the 2010 occultation, and nine for the 2013 occultation. Elliptical models were adjusted to the observed chords to obtain Ceres’ size and shape. Two limb-fitting solutions were studied for each event. The first one is a nominal solution with an indeterminate polar aspect angle. The second one was constrained by the pole coordinates as given by Drummond et al. Assuming a Maclaurin spheroid, we determine an equatorial diameter of 972 ± 6 km and an apparent oblateness of 0.08 ± 0.03 as our best solution. These results are compared to all available size and shape determinations for Ceres made so far, and shall be confirmed by the NASA's Dawn space mission.
Abstract
A stellar occultation occurs when a Solar System object passes in front of a star for an observer. This technique allows the sizes and shapes of the occulting body to be determined with ...kilometer precision. In addition, this technique constrains the occulting body’s positions, albedos, densities, and so on. In the context of the Galilean moons, these events can provide their best ground-based astrometry, with uncertainties in the order of 1 mas (∼3 km at Jupiter’s distance during opposition). We organized campaigns and successfully observed a stellar occultation by Io (JI) in 2021, one by Ganymede (JIII) in 2020, and one by Europa (JII) in 2019, with stations in North and South America. We also re-analyzed two previously published events: one by Europa in 2016 and another by Ganymede in 2017. We then fit the known 3D shape of the occulting satellite and determine its center of figure. This resulted in astrometric positions with uncertainties in the milliarcsecond level. The positions obtained from these stellar occultations can be used together with dynamical models to ensure highly accurate orbits of the Galilean moons. These orbits can help when planning future space probes aiming at the Jovian system, such as JUICE by ESA and Europa Clipper by NASA. They also allow more efficient planning of flyby maneuvers.
ABSTRACT
We report the results of the stellar occultation by (UII) Umbriel on 2020 September 21. The shadow crossed the USA and Canada, and 19 positive chords were obtained. A limb parameter ...accounted for putative topographic features in the limb fittings. Ellipse fittings were not robust – only upper limits were derived for the true size/shape of a putative Umbriel ellipsoid. The adopted spherical solution gives radius = 582.4 ± 0.8 km, smaller/close to 584.7 ± 2.8 km from Voyager II. The apparent ellipse fit results in a true semi-major axis of 584.9 ± 3.8 km, semi-minor axis of 582.3 ± 0.6 km, and true oblateness of 0.004 ± 0.008 for a putative ellipsoid. The geometric albedo was pV = 0.26 ± 0.01. The density was ρ = 1.54 ± 0.04 g cm−3. The surface gravity was 0.251 ± 0.006 m s−2 and the escape velocity was 0.541 ± 0.006 km s−1. Upper limits of 13 and 72 nbar (at 1σ and 3σ levels, respectively) were obtained for the surface pressure of a putative isothermal CO2 atmosphere at T = 70 K. A milliarcsecond precision position was derived: α = 02h30m28${_{.}^{\rm s}}$84556 ± 0.1 mas, δ = 14o19′36″.5836 ± 0.2 mas. A large limb parameter of 4.2 km was obtained, in striking agreement with opposite Southern hemisphere measurements by Voyager II in 1986. Occultation and Voyager results indicate that the same strong topography variation in the surface of Umbriel is present on both hemispheres.
We present a software architecture and framework that can be used to facilitate the development of data processing applications for High Energy Physics experiments. The development strategy follows ...an architecture-centric approach as a way of creating a resilient software framework that can withstand changes in requirements and technology over the long lifetimes of experiments. The software architecture, called GAUDI, supports event data processing applications that run in different processing environments, from the high level triggers in the on-line system to the final physics analysis. We present our major architectural design choices and outline the arguments that led to these choices. Several iterations of a software framework based on this architecture have been released and the framework is now being used by the physicists of the collaboration to facilitate the development of data processing algorithms. Object oriented technologies have been used throughout.
Interlayer tunneling resistivity is used to probe the low-energy density-of-states (DOS) depletion due to the pseudogap in the normal state of Bi2Sr2CaCu2O8+y. Measurements up to 60 T reveal that a ...field that restores DOS to its ungapped state shows strikingly different temperature and doping dependencies from the characteristic fields of the superconducting state. The pseudogap closing field and the pseudogap temperature T small star, filled evaluated independently are related through a simple Zeeman energy scaling. These findings indicate a predominant role of spins over the orbital effects in the formation of the pseudogap.
PDF
