Centaurs, distinguished by their volatile-rich compositions, play a pivotal
role in understanding the formation and evolution of the early solar system, as
they represent remnants of the primordial ...material that populated the outer
regions. Stellar occultations offer a means to investigate their physical
properties, including shape, rotational state, or the potential presence of
satellites and rings.
This work aims to conduct a detailed study of the centaur (54598) Bienor
through stellar occultations and rotational light curves from photometric data
collected during recent years.
We successfully predicted three stellar occultations by Bienor, which were
observed from Japan, Eastern Europe, and the USA. In addition, we organized
observational campaigns from Spain to obtain rotational light curves. At the
same time, we develop software to generate synthetic light curves from
three-dimensional shape models, enabling us to validate the outcomes through
computer simulations.
We resolve Bienor's projected ellipse for December 26, 2022, determine a
prograde sense of rotation, and confirm an asymmetric rotational light curve.
We also retrieve the axes of its triaxial ellipsoid shape as a = (127 $\pm$ 5)
km, b = (55 $\pm$ 4) km, and c = (45 $\pm$ 4) km. Moreover, we refine the
rotation period to 9.1736 $\pm$ 0.0002 hours and determine a geometric albedo
of (6.5 $\pm$ 0.5) %, higher than previously determined by other methods.
Finally, by comparing our findings with previous results and simulated
rotational light curves, we analyze whether an irregular or contact-binary
shape, the presence of an additional element such as a satellite, or
significant albedo variations on Bienor's surface, may be present.
We could accurately predict the shadow path and successfully observe an occultation of a bright star by Chiron on 2022 December 15. The Kottamia Astronomical Observatory in Egypt did not detect the ...occultation by the solid body, but we detected three extinction features in the light curve that had symmetrical counterparts with respect to the central time of the occultation. One of the features is broad and shallow, whereas the other two features are sharper with a maximum extinction of \(\sim\)25\(\%\) at the achieved spatial resolution of 19 km per data point. From the Wise observatory in Israel, we detected the occultation caused by the main body and several extinction features surrounding the body. When all the secondary features are plotted in the sky plane we find that they can be caused by a broad \(\sim\)580 km disk with concentrations at radii of 325 \pm 16 km and 423 \pm 11 km surrounding Chiron. At least one of these structures appears to be outside the Roche limit. The ecliptic coordinates of the pole of the disk are \(\lambda\) = 151\(^\circ~\pm\) 8\(^\circ\) and \(\beta\) = 18\(^\circ~\pm\) 11\(^\circ\), in agreement with previous results. We also show our long-term photometry indicating that Chiron had suffered a brightness outburst of at least 0.6 mag between March and September 2021 and that Chiron was still somewhat brighter at the occultation date than at its nominal pre-outburst phase. The outermost extinction features might be consistent with a bound or temporarily bound structure associated with the brightness increase. However, the nature of the brightness outburst is unclear, and it is also unclear whether the dust or ice released in the outburst could be feeding a putative ring structure or if it emanated from it.
After the discovery of rings around the largest known Centaur object, (10199) Chariklo, we carried out observation campaigns of stellar occultations produced by the second-largest known Centaur ...object, (2060) Chiron, to better characterize its physical properties and presence of material on its surroundings. We predicted and successfully observed two stellar occultations by Chiron. These observations were used to constrain its size and shape by fitting elliptical limbs with equivalent surface radii in agreement with radiometric measurements. Constraints on the (2060) Chiron shape are reported for the first time. Assuming an equivalent radius of R\(_{equiv}\) = 105\(^{+6}_{-7}\) km, we obtained a semi-major axis of a = 126 \(\pm\) 22 km. Considering Chiron's true rotational light curve amplitude and assuming it has a Jacobi equilibrium shape, we were able to derive a 3D shape with a semi-axis of a = 126 \(\pm\) 22 km, b = 109 \(\pm\) 19 km, and c = 68 \(\pm\) 13 km, implying in a volume-equivalent radius of R\(_{vol}\) = 98 \(\pm\) 17 km, implying a density of 1119 \(\pm\) 4 kg m\(^{-3}\). We determined the physical properties of the 2011 secondary events around Chiron, which may then be directly compared with those of Chariklo rings, as the same method was used. Data obtained from SAAO in 2018 do not show unambiguous evidence of the proposed rings, mainly due to the large sampling time. Meanwhile, we discarded the possible presence of a permanent ring similar to (10199) Chariklo's C1R in optical depth and extension. Using the first multi-chord stellar occultation by (2060) Chiron and considering it to have a Jacobi equilibrium shape, we derived its 3D shape. New observations of a stellar occultation by (2060) Chiron are needed to further investigate the material's properties around Chiron, such as the occultation predicted for September 10, 2023.
On 12 December 2023, the star \(\alpha\) Orionis (Betelgeuse) will be occulted by the asteroid (319) Leona. This represents an extraordinary and unique opportunity to analyze the diameter and ...brightness distribution of Betelgeuse's photosphere with extreme angular resolution by studying the light curve as the asteroid occults the star from different points on Earth and at different wavelengths. Here we present observations of another occultation by Leona on 13 September 2023 to determine its projected shape and size in preparation for the December 12th event. The occultation observation campaign was highly successful. The effective diameter in projected area derived from the positive detections at 17 sites turned out to be 66 km \(\pm\) 2 km using an elliptical fit to the instantaneous limb. The body is highly elongated, with dimensions of 79.6 \(\pm\) 2.2 km x 54.8 \(\pm\) 1.3 km in its long and short axis, respectively, at the occultation time. Also, an accurate position coming from the occultation, to improve the orbit determination of Leona for December 12 is provided.
Quaoar is a classical Trans-Neptunian Object (TNO) with an area equivalent diameter of 1,100 km and an orbital semi-major axis of 43.3 astronomical units. Based on stellar occultations observed ...between 2018 and 2021, an inhomogeneous ring (Q1R, Quaoar's first ring) was detected around this body. Aims. A new stellar occultation by Quaoar was observed on August 9th, 2022 aiming to improve Quaoar's shape models and the physical parameters of Q1R while searching for additional material around the body. Methods. The occultation provided nine effective chords across Quaoar, pinning down its size, shape, and astrometric position. Large facilities, such as Gemini North and the Canada-France-Hawaii Telescope (CFHT), were used to obtain high acquisition rates and signal-to-noise ratios. The light curves were also used to characterize the Q1R ring (radial profiles and orbital elements). Results. Quaoar's elliptical fit to the occultation chords yields the limb with an apparent semi-major axis of \(579.5\pm4.0\) km, apparent oblateness of \(0.12\pm0.01\), and area-equivalent radius of \(543\pm2\) km. Quaoar's limb orientation is consistent with Q1R and Weywot orbiting in Quaoar's equatorial plane. The orbital radius of Q1R is refined to a value of \(4,057\pm6\) km. The radial opacity profile of the more opaque ring profile follows a Lorentzian shape that extends over 60 km, with a full width at half maximum (FWHM) of \(\sim5\) km and a peak normal optical depth of 0.4. Besides the secondary events related to the already reported rings, new secondary events detected during the August 2022 occultation in three different data sets are consistent with another ring around Quaoar with a radius of \(2,520\pm20\) km, assuming the ring is circular and co-planar with Q1R. This new ring has a typical width of 10 km and a normal optical depth of \(\sim\)0.004. Like Q1R, it also lies outside Quaoar's classical Roche limit.
Within our program of physical characterization of trans-Neptunian objects and centaurs, we predicted a stellar occultation by the centaur (54598) Bienor to occur on January 11, 2019, with good ...observability potential. We obtained high accuracy astrometric data to refine the prediction, resulting in a shadow path favorable for the Iberian Peninsula. This encouraged us to carry out an occultation observation campaign that resulted in five positive detections from four observing sites. This is the fourth centaur for which a multichord (more than two chords) stellar occultation has been observed so far, the other three being (2060) Chiron, (10199) Chariklo, and (95626) 2002 GZ\(_{32}\). From the analysis of the occultation chords, combined with the rotational light curve obtained shortly after the occultation, we determined that Bienor has an area-equivalent diameter of \(150\pm20\) km. This diameter is \(\sim30\) km smaller than the one obtained from thermal measurements. The position angle of the short axis of the best fitting ellipse obtained through the analysis of the stellar occultation does not match that of the spin axis derived from long-term photometric models. We also detected a strong irregularity in one of the minima of the rotational light curve that is present no matter the aspect angle at which the observations were done. We present different scenarios to reconcile the results from the different techniques. We did not detect secondary drops related to potential rings or satellites. Nonetheless, similar rings in size to that of Chariklo's cannot be discarded due to low data accuracy.
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.
Longitudinal, remote monitoring of motor symptoms in Parkinson's disease (PD) could enable more precise treatment decisions. We developed the Motor fluctuations Monitor for Parkinson's Disease ...(MM4PD), an ambulatory monitoring system that used smartwatch inertial sensors to continuously track fluctuations in resting tremor and dyskinesia. We designed and validated MM4PD in 343 participants with PD, including a longitudinal study of up to 6 months in a 225-subject cohort. MM4PD measurements correlated to clinical evaluations of tremor severity (ρ = 0.80) and mapped to expert ratings of dyskinesia presence (
< 0.001) during in-clinic tasks. MM4PD captured symptom changes in response to treatment that matched the clinician's expectations in 94% of evaluated subjects. In the remaining 6% of cases, symptom data from MM4PD identified opportunities to make improvements in pharmacologic strategy. These results demonstrate the promise of MM4PD as a tool to support patient-clinician communication, medication titration, and clinical trial design.
The dose effect of dual delivery of vascular endothelial growth factor (VEGF) and bone morphogenetic protein-2 (BMP-2) on bone regeneration was investigated in a rat cranial critical-size defect ...(CSD). It was hypothesized that decreasing amounts of BMP-2 would result in a dose-dependent decrease in bone formation, and that this reduction in bone formation could be reversed by adding increasing amounts of VEGF. In vitro release kinetics of VEGF or BMP-2 were examined over 28 days. Next, scaffolds were implanted within a rat cranial CSD containing different combinations of both BMP-2 and VEGF. At 12 weeks, samples were analyzed using microcomputed tomography and histology. In vitro, VEGF and BMP-2 exhibited burst release in the first 24 h followed by a significant decrease in release rate over 27 days. Overall, BMP-2 had a more sustained release versus VEGF. An in vivo dose-dependent decrease in percentage of bone fill (PBF) was observed for BMP-2. The addition of VEGF was unable to reverse this decrease in PBF, although improvements in the number of bridged defects did occur in some groups. This suggests that for this particular model simultaneous release of BMP-2 and VEGF does not increase bone formation over BMP-2 alone at 12 weeks.
Elevated brain iron content, which has been observed in late-stage human Alzheimer's disease, is a potential target for early diagnosis. However, the time course for iron accumulation is currently ...unclear. Using the PSAPP mouse model of amyloid plaque formation, we conducted a time course study of metal ion content and distribution iron (Fe), copper (Cu), and zinc (Zn) in the cortex and hippocampus using X-ray fluorescence microscopy (XFM). We found that iron in the cortex was 34% higher than age-matched controls at an early stage, corresponding to the commencement of plaque formation. The elevated iron was not associated with the amyloid plaques. Interestingly, none of the metal ions were elevated in the amyloid plaques until the latest time point (56weeks), where only the Zn content was significantly elevated by 38%. Since neuropathological changes in human Alzheimer's disease are presumed to occur years before the first cognitive symptoms appear, quantification of brain iron content could be a powerful marker for early diagnosis of Alzheimer's disease.
► Brain metal content is a potential target for early diagnosis and treatment of AD. ► In the PSAPP mouse, iron was elevated in the cortex at the onset of plaque formation. ► The elevated iron was not associated with the amyloid plaques. ► Iron, copper, and zinc were not elevated in PSAPP plaques at time points up to 56weeks. ► Only the zinc content was elevated at 56weeks, representing a marker of late-stage AD.
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