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The icy dwarf planet Makemake has projected axes of 1,430 ± 9 and 1,502 ± 45 km and a V-band geometric albedo larger than Pluto’s but smaller than Eris’s, with no global Pluto-like atmosphere. Makemake shapes up against Pluto and Eris Makemake is thought to be the third-largest dwarf planet in our Solar System, a little smaller than Pluto and Eris, but until now knowledge of its size and albedo were only approximate. This paper reports the results of observations of the occultation of a faint star known as NOMAD 1181-0235723 by Makemake on 23 April 2011. The data confirm that Makemake is smaller than Pluto and Eris, with axes of 1,430±9 km and 1,502±45 km. Makemake's mean geometric albedo — the ratio of light reflected to light received — is intermediate between that of Pluto and that of Eris. All three are icy, making them among the most reflective objects in the Solar System. And the occultation light curves rule out the presence of a global Pluto-like atmosphere on Makemake, although the presence of dark terrain might imply the presence of a localized atmosphere. Pluto and Eris are icy dwarf planets with nearly identical sizes, comparable densities and similar surface compositions as revealed by spectroscopic studies 1 , 2 . Pluto possesses an atmosphere whereas Eris does not; the difference probably arises from their differing distances from the Sun, and explains their different albedos 3 . Makemake is another icy dwarf planet with a spectrum similar to Eris and Pluto 4 , and is currently at a distance to the Sun intermediate between the two. Although Makemake’s size (1,420 ± 60 km) and albedo are roughly known 5 , 6 , there has been no constraint on its density and there were expectations that it could have a Pluto-like atmosphere 4 , 7 , 8 . Here we report the results from a stellar occultation by Makemake on 2011 April 23. Our preferred solution that fits the occultation chords corresponds to a body with projected axes of 1,430 ± 9 km (1 σ ) and 1,502 ± 45 km, implying a V-band geometric albedo p V = 0.77 ± 0.03. This albedo is larger than that of Pluto, but smaller than that of Eris. The disappearances and reappearances of the star were abrupt, showing that Makemake has no global Pluto-like atmosphere at an upper limit of 4–12 nanobar (1 σ ) for the surface pressure, although a localized atmosphere is possible. A density of 1.7 ± 0.3 g cm −3 is inferred from the data.

Observations of a stellar occultation by (10199) Chariklo, a minor body that orbits the Sun between Jupiter and Neptune, reveal that it has a ring system, a property previously observed only for the four giant planets of the Solar System. Tiny Chariklo has its own ring system Observations of a stellar occultation by (10199) Chariklo, a Centaur-class outer-system asteroid orbiting between Saturn and Uranus, reveal that it has a ring system, a feature previously observed only for the four giant planets. Chariklo, with a diameter of about 250 km, has two narrow and dense rings separated by a small gap, probably due to the presence of a (yet-to-be-found) kilometre-sized satellite. The discovery of these rings raises questions about the formation and dynamical evolution of planetary rings. For one thing, it seems likely that planetary rings are much more common than previously thought. Hitherto, rings have been found exclusively around the four giant planets in the Solar System 1 . Rings are natural laboratories in which to study dynamical processes analogous to those that take place during the formation of planetary systems and galaxies. Their presence also tells us about the origin and evolution of the body they encircle. Here we report observations of a multichord stellar occultation that revealed the presence of a ring system around (10199) Chariklo, which is a Centaur—that is, one of a class of small objects orbiting primarily between Jupiter and Neptune—with an equivalent radius of 124   9 kilometres (ref. 2 ). There are two dense rings, with respective widths of about 7 and 3 kilometres, optical depths of 0.4 and 0.06, and orbital radii of 391 and 405 kilometres. The present orientation of the ring is consistent with an edge-on geometry in 2008, which provides a simple explanation for the dimming 3 of the Chariklo system between 1997 and 2008, and for the gradual disappearance of ice and other absorption features in its spectrum over the same period 4 , 5 . This implies that the rings are partly composed of water ice. They may be the remnants of a debris disk, possibly confined by embedded, kilometre-sized satellites.

Wind erosion is an important soil degradation process in semiarid environments that can affect soil organic carbon (C) and nitrogen (N) dynamics. Wind erosion can decrease the proportion of easily erodable <0.84 mm (0.03 in) size fractions (aggregates + individual particles), and increase the non erodable. Tillage and rain can breakdown large aggregates increasing organic C and N losses by wind erosion, and can decrease the proportion of aggregates to sand in coarse size fractions. Therefore the variations of organic C and N in size fractions of 20 A-horizons of Haplustolls and Ustipsamments of the semiarid part of Argentina submitted to three management conditions with increasing tillage and wind erosion levels (VIRGIN < Eragrostis curvula PASTURE < AGRICULTURE) were analyzed. The <2, 2 to 50, 50 to 74, 74 to 100, and 100 to 2000 μm size fractions (aggregates + individual sand particles) were separated by wet sieving, and their content of organic C and N determined. The relative amount of aggregates and sand were analyzed together, in order to asses the effect of tillage on the proportion aggregates to sand within each size fraction and the selection caused by wind erosion. Results showed that AGRICULTURE decreased the 74 to 100 um and the 2 to 50 μm sized fractions in relation to VIRGIN soils. Decreases of 74 to 100 um fractions were attributed to the breakdown by tillage of the aggregates composing this size fraction; while decreases of 2 to 50 μm sized fractions (100 percent aggregates) were attributed to losses by wind erosion. PASTURES showed lower proportions of 2 to 50 μm sized fractions than VIRGIN soils, probably as a consequence of wind erosion events occurred before the Eragrostis curvula pasture plantation. The amount of aggregates of the 100 to 2000 um size fraction did not differ between management systems probably because they suffered a rapid turnover in AGRICULTURE soils. Nevertheless, the proportion of sand in relation to aggregates was higher in comparison to VIRGIN soils in this size fraction, which indicates that a relative accumulation of sand occurred. The 2 to 50 μm size fraction (aggregates) were positively correlated with contents of total organic matter (R 2 = 0.55, p<0.001) and silt + clay [R 2 = 0.39, p<0.01]. A multiple regression analysis demonstrated that both variables explained 77 percent of the aggregate variability. Organic C and N contents tend mainly to decrease from fine to coarse aggregates within each management type. This was attributed to the formation of organo-mineral complexes with fine sized particles in finer aggregates. Organic C and N contents of coarse fractions (>50 μm) were higher in VIRGIN than in both PASTURE and AGRICULTURE soils, indicating that cultivation promoted C and N losses in coarser fractions. AGRICULTURE promoted larger N than organic C losses in coarse fractions, indicating that nitrogenous compounds were more affected than C compounds. Organic C and N contents in < 50 sized fractions, (i.e. aggregates) did not differ between management systems, probably because of the higher stability of nitrogenous and C compounds accumulated in these fine fractions as organo-mineral complexes. C/N ratios remained unchanged in most cases, indicating homogeneous composition of organic matter with all management types. We concluded that VIRGIN soils converted to agriculture in the semiarid part of Argentina will decrease the proportion of coarse fractions, mainly by breakdown of their aggregates by tillage, and will increase the proportion of sand in these size fractions. The 2 to 50 μm sized aggregates generated by the breakdown of coarser aggregates will be eroded by wind. The concentration of organic C and N will be drastically decreased by cultivation in coarse size fractions but not in the fine ones. The Eragrostis curvula pasture is not effective in recovering soil aggregation nor increasing organic C or N levels in coarse fractions of degraded soils.

We present results from three world-wide campaigns that resulted in the detections of two single-chord and one multi-chord stellar occultations by the Plutino object (84922) 2003~VS\\(_2\\). From the single-chord occultations in 2013 and 2014 we obtained accurate astrometric positions for the object, while from the multi-chord occultation on November 7th, 2014, we obtained the parameters of the best-fitting ellipse to the limb of the body at the time of occultation. We also obtained short-term photometry data for the body in order to derive its rotational phase during the occultation. The rotational light curve present a peak-to-peak amplitude of 0.141 \\(\\pm\\) 0.009 mag. This allows us to reconstruct the three-dimensional shape of the body, with principal semi-axes \\(a = 313.8 \\pm 7.1\\) km, \\(b = 265.5^{+8.8}_{-9.8}\\) km, and \\(c = 247.3^{+26.6}_{-43.6}\\) km, which is not consistent with a Jacobi triaxial equilibrium figure. The derived spherical volume equivalent diameter of \\(548.3 ^{+29.5}_{-44.6}\\) km is about 5\\% larger than the radiometric diameter of 2003~VS\\(_2\\) derived from Herschel data of \\(523 \\pm 35\\) km, but still compatible with it within error bars. From those results we can also derive the geometric albedo (\\(0.123 ^{+0.015}_{-0.014}\\)) and, under the assumption that the object is a Maclaurin spheroid, the density \\(\\rho = 1400^{+1000}_{-300}\\) for the plutino. The disappearances and reappearances of the star during the occultations do not show any compelling evidence for a global atmosphere considering a pressure upper limit of about 1 microbar for a pure nitrogen atmosphere, nor secondary features (e.g. rings or satellite) around the main body.

Context. The so-called Barbarian asteroids share peculiar, but common polarimetric properties, probably related to both their shape and composition. They are named after (234) Barbara, the first on which such properties were identified. As has been suggested, large scale topographic features could play a role in the polarimetric response, if the shapes of Barbarians are particularly irregular and present a variety of scattering/incidence angles. This idea is supported by the shape of (234) Barbara, that appears to be deeply excavated by wide concave areas revealed by photometry and stellar occultations. Aims. With these motivations, we started an observation campaign to characterise the shape and rotation properties of Small Main- Belt Asteroid Spectroscopic Survey (SMASS) type L and Ld asteroids. As many of them show long rotation periods, we activated a worldwide network of observers to obtain a dense temporal coverage. Methods. We used light-curve inversion technique in order to determine the sidereal rotation periods of 15 asteroids and the con- vergence to a stable shape and pole coordinates for 8 of them. By using available data from occultations, we are able to scale some shapes to an absolute size. We also study the rotation periods of our sample looking for confirmation of the suspected abundance of asteroids with long rotation periods. Results. Our results show that the shape models of our sample do not seem to have peculiar properties with respect to asteroids with similar size, while an excess of slow rotators is most probably confirmed.

The Centaur (10199) Chariklo has the first rings system discovered around a small object. It was first observed using stellar occultation in 2013. Stellar occultations allow the determination of sizes and shapes with kilometre accuracy and obtain characteristics of the occulting object and its vicinity. Using stellar occultations observed between 2017 and 2020, we aim at constraining Chariklo's and its rings physical parameters. We also determine the rings' structure, and obtain precise astrometrical positions of Chariklo. We predicted and organised several observational campaigns of stellar occultations by Chariklo. Occultation light curves were measured from the data sets, from which ingress and egress times, and rings' width and opacity were obtained. These measurements, combined with results from previous works, allow us to obtain significant constraints on Chariklo's shape and rings' structure. We characterise Chariklo's ring system (C1R and C2R), and obtain radii and pole orientations that are consistent with, but more accurate than, results from previous occultations. We confirmed the detection of W-shaped structures within C1R and an evident variation of radial width. The observed width ranges between 4.8 and 9.1 km with a mean value of 6.5 km. One dual observation (visible and red) does not reveal any differences in the C1R opacity profiles, indicating ring particle's size larger than a few microns. The C1R ring eccentricity is found to be smaller than 0.022 (3-sigma), and its width variations may indicate an eccentricity higher than 0.005. We fit a tri-axial shape to Chariklo's detections over eleven occultations and determine that Chariklo is consistent with an ellipsoid with semi-axes of 143.8, 135.2 and 99.1 km. Ultimately, we provided seven astrometric positions at a milliarcseconds accuracy level, based on Gaia EDR3, and use it to improve Chariklo's ephemeris.

We present a comparison of several Difference Image Analysis (DIA) techniques, in combination with Machine Learning (ML) algorithms, applied to the identification of optical transients associated with gravitational wave events. Each technique is assessed based on the scoring metrics of Precision, Recall, and their harmonic mean F1, measured on the DIA results as standalone techniques, and also in the results after the application of ML algorithms, on transient source injections over simulated and real data. This simulations cover a wide range of instrumental configurations, as well as a variety of scenarios of observation conditions, by exploring a multi dimensional set of relevant parameters, allowing us to extract general conclusions related to the identification of transient astrophysical events. The newest subtraction techniques, and particularly the methodology published in Zackay et al. (2016) are implemented in an Open Source Python package, named properimage, suitable for many other astronomical image analyses. This together with the ML libraries we describe, provides an effective transient detection software pipeline. Here we study the effects of the different ML techniques, and the relative feature importances for classification of transient candidates, and propose an optimal combined strategy. This constitutes the basic elements of pipelines that could be applied in searches of electromagnetic counterparts to GW sources.

The Centaur (60558) Echeclus was discovered on March 03, 2000, orbiting between the orbits of Jupiter and Uranus. After exhibiting frequent outbursts, it also received a comet designation, 174P. If the ejected material can be a source of debris to form additional structures, studying the surroundings of an active body like Echeclus can provide clues about the formation scenarios of rings, jets, or dusty shells around small bodies. Stellar occultation is a handy technique for this kind of investigation, as it can, from Earth-based observations, detect small structures with low opacity around these objects. Stellar occultation by Echeclus was predicted and observed in 2019, 2020, and 2021. We obtain upper detection limits of rings with widths larger than 0.5 km and optical depth of \\(\\tau\\) = 0.02. These values are smaller than those of Chariklo's main ring; in other words, a Chariklo-like ring would have been detected. The occultation observed in 2020 provided two positive chords used to derive the triaxial dimensions of Echeclus based on a 3D model and pole orientation available in the literature. We obtained \\(a = 37.0\\pm0.6\\) km, \\(b = 28.4 \\pm 0.5\\) km, and \\(c= 24.9 \\pm 0.4\\) km, resulting in an area-equivalent radius of \\(30.0 \\pm 0.5\\) km. Using the projected limb at the occultation epoch and the available absolute magnitude (\\(\\rm{H}_{\\rm{v}} = 9.971 \\pm 0.031\\)), we calculate an albedo of \\(p_{\\rm{v}} = 0.050 \\pm 0.003\\). Constraints on the object's density and internal friction are also proposed.

With an estimated diameter in the 320 to 350 km range, (704) Interamnia is the fifth largest main belt asteroid and one of the few bodies that fills the gap in size between the four largest bodies with \\(D\\) > 400 km (Ceres, Vesta, Pallas and Hygiea) and the numerous smaller bodies with \\(D\\) \\(\\lesssim\\) 200 km. However, despite its large size, little is known about the shape and spin state of Interamnia and, therefore, about its bulk composition and past collisional evolution. We aimed to test at what size and mass the shape of a small body departs from a nearly ellipsoidal equilibrium shape (as observed in the case of the four largest asteroids) to an irregular shape as routinely observed in the case of smaller (\\(D\\) \\(\\lesssim\\) 200 km) bodies. We observed Interamnia as part of our ESO VLT/SPHERE large program (ID: 199.C-0074) at thirteen different epochs. In addition, several new optical lightcurves were recorded. These data, along with stellar occultation data from the literature, were fed to the All-Data Asteroid Modeling (ADAM) algorithm to reconstruct the 3D-shape model of Interamnia and to determine its spin state. Interamnia's volume-equivalent diameter of 332 \\(\\pm\\) 6 km implies a bulk density of \\(\\rho\\)=1.98 \\(\\pm\\) 0.68 gcm\\(^{-3}\\) , which suggests that Interamnia - like Ceres and Hygiea - contains a high fraction of water ice, consistent with the paucity of apparent craters. Our observations reveal a shape that can be well approximated by an ellipsoid, and that is compatible with a fluid hydrostatic equilibrium at the 2 \\(\\sigma\\) level. The rather regular shape of Interamnia implies that the size and mass limit, under which the shapes of minor bodies with a high amount of water ice in the subsurface become irregular, has to be searched among smaller (\\(D\\) \\(\\lesssim\\) 300km) less massive (\\(m\\) \\(\\lesssim\\) 3x10\\(^{19}\\) kg) bodies.

We present the results of prompt optical follow-up of the electromagnetic counterpart of the gravitational-wave event GW170817 by the Transient Optical Robotic Observatory of the South Collaboration (TOROS). We detected highly significant dimming in the light curves of the counterpart (Delta g=0.17+-0.03 mag, Delta r=0.14+-0.02 mag, Delta i=0.10 +- 0.03 mag) over the course of only 80 minutes of observations obtained ~35 hr after the trigger with the T80-South telescope. A second epoch of observations, obtained ~59 hr after the event with the EABA 1.5m telescope, confirms the fast fading nature of the transient. The observed colors of the counterpart suggest that this event was a \"blue kilonova\" relatively free of lanthanides.