ABSTRACT We present results of a stellar occultation by the Jupiter Trojan asteroid Patroclus and its nearly equal size moon, Menoetius. The geocentric mid-time of the event was 2013 October 21 ...06:43:02 UT. Eleven sites out of 36 successfully recorded an occultation. Seven chords across Patroclus yielded an elliptical limb fit of 124.6 by 98.2 km. There were six chords across Menoetius that yielded an elliptical limb fit of 117.2 by 93.0 km. There were three sites that got chords on both objects. At the time of the occultation we measured a separation of 664.6 km (0.247 arcsec) and a position angle for Menoetius of 265 7 measured eastward from J2000 north. Combining this occultation data with previous light curve data, the axial ratios of both objects are 1.3 : 1.21 : 1, indicative of a mostly oblate ellipsoid with a slight asymmetry in its equatorial projection. The oblate shape is not an equilibrium shape for the current rotation period, but would be if it were rotating with an ∼8 h period. This faster period is consistent with a pre-evolved state of the system with an orbital separation that is 50% smaller. Our best estimate of the system density is 0.88 g cm−3.
Abstract
We present the results from four stellar occultations by (486958) Arrokoth, the flyby target of the
New Horizons
extended mission. Three of the four efforts led to positive detections of the ...body, and all constrained the presence of rings and other debris, finding none. Twenty-five mobile stations were deployed for 2017 June 3 and augmented by fixed telescopes. There were no positive detections from this effort. The event on 2017 July 10 was observed by the Stratospheric Observatory for Infrared Astronomy with one very short chord. Twenty-four deployed stations on 2017 July 17 resulted in five chords that clearly showed a complicated shape consistent with a contact binary with rough dimensions of 20 by 30 km for the overall outline. A visible albedo of 10% was derived from these data. Twenty-two systems were deployed for the fourth event on 2018 August 4 and resulted in two chords. The combination of the occultation data and the flyby results provides a significant refinement of the rotation period, now estimated to be 15.9380 ± 0.0005 hr. The occultation data also provided high-precision astrometric constraints on the position of the object that were crucial for supporting the navigation for the
New Horizons
flyby. This work demonstrates an effective method for obtaining detailed size and shape information and probing for rings and dust on distant Kuiper Belt objects as well as being an important source of positional data that can aid in spacecraft navigation that is particularly useful for small and distant bodies.
Abstract
We present observations of five stellar occultations for (11351) Leucus and reports from two efforts on (21900) Orus. Both objects are prime mission candidate targets for the Lucy Discovery ...mission. Combined results for Leucus indicate a very dark surface with
p
V
= 0.037 ± 0.001, which is derived from the average of the multichord occultations. Our estimate of the triaxial ellipsoidal shape is for axial diameters of 63.8 × 36.6 × 29.6 km assuming that the spin pole is normal to the line of sight. The actual shape of the object is only roughly elliptical in profile at each epoch. Significant topography is seen with horizontal scales up to 30 km and vertical scales up to 5 km. The most significant feature is a large depression on the southern end of the object as seen from a terrestrial viewpoint. For this work we developed a method to correct for differential refraction, accounting for the difference in color between the target object and the reference stars for astrometry derived from ground-based images.
We present results derived from the first multi-chord stellar occultation by the trans-Neptunian object (229762) 2007 UK\(_{126}\), observed on 2014 November 15. The event was observed by the ...Research and Education Collaborative Occultation Network (RECON) project and International Occultation Timing Association (IOTA) collaborators throughout the United States. Use of two different data analysis methods obtain a satisfactory fit to seven chords, yelding an elliptical fit to the chords with an equatorial radius of \(R=338_{-10} ^{+15}\) km and equivalent radius of \(R_{eq}=319_{-7} ^{+14}\) km. A circular fit also gives a radius of \(R=324_{-23} ^{+30}\) km. Assuming that the object is a Maclaurin spheroid with indeterminate aspect angle, and using two published absolute magnitudes for the body, we derive possible ranges for geometric albedo between \(p_{V}=0.159_{-0.013} ^{+0.007}\) and \(p_{R}=0.189_{-0.015}^{+0.009}\), and for the body oblateness between \(\epsilon=0.105_{-0.040} ^{+0.050}\) and \(\epsilon=0.118_{-0.048} ^{+0.055}\). For a nominal rotational period of 11.05 h, an upper limit for density of \(\rho=1740\) kg~m\(^{-3}\) is estimated for the body.
Arctic sea-ice loss is emblematic of an amplified Arctic water cycle and has critical feedback implications for global climate. Stable isotopes (δ
18
O, δ
2
H,
d-excess
) are valuable tracers for ...constraining water cycle and climate processes through space and time. Yet, the paucity of well-resolved Arctic isotope data preclude an empirically derived understanding of the hydrologic changes occurring today, in the deep (geologic) past, and in the future. To address this knowledge gap, the Pan-Arctic Precipitation Isotope Network (PAPIN) was established in 2018 to coordinate precipitation sampling at 19 stations across key tundra, subarctic, maritime, and continental climate zones. Here, we present a first assessment of rainfall samples collected in summer 2018 (
n
= 281) and combine new isotope and meteorological data with sea ice observations, reanalysis data, and model simulations. Data collectively establish a summer Arctic Meteoric Water Line where δ
2
H = 7.6⋅δ
18
O–1.8 (
r
2
= 0.96,
p
< 0.01). Mean amount-weighted δ
18
O, δ
2
H, and
d-excess
values were −12.3, −93.5, and 4.9‰, respectively, with the lowest summer mean δ
18
O value observed in northwest Greenland (−19.9‰) and the highest in Iceland (−7.3‰). Southern Alaska recorded the lowest mean
d-excess
(−8.2%) and northern Russia the highest (9.9‰). We identify a range of δ
18
O-temperature coefficients from 0.31‰/°C (Alaska) to 0.93‰/°C (Russia). The steepest regression slopes (>0.75‰/°C) were observed at continental sites, while statistically significant temperature relations were generally absent at coastal stations. Model outputs indicate that 68% of the summer precipitating air masses were transported into the Arctic from mid-latitudes and were characterized by relatively high δ
18
O values. Yet 32% of precipitation events, characterized by lower δ
18
O and high
d-excess
values, derived from northerly air masses transported from the Arctic Ocean and/or its marginal seas, highlighting key emergent oceanic moisture sources as sea ice cover declines. Resolving these processes across broader spatial-temporal scales is an ongoing research priority, and will be key to quantifying the past, present, and future feedbacks of an amplified Arctic water cycle on the global climate system.
Groups of newborn rats were each subjected to a specific 10% simulated increase in body weight, ranging from 1.1G to 2.0G, to study changes in bone robusticity. (In this paper, “G” is the ...acceleration due to gravity.) Constant centrifugation was used. At 90 days of age, the rats were killed and the humerus, radius, ulna, femur, and tibia were removed, weighed, and measured. Bone robusticity was calculated using the ponderal index: bone length/\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt3{{{\rm bone}\,{\rm weight}}} $\end{document}. Tukey's Multiple Range Test was used. The data suggest that, for both males and females, bone robusticity is increased with simulated increases in body weight.
The purpose of this study was to subject groups of weanling male rats each to a specific 10% simulated increase in body weight, ranging from 1.1G–2.0G, using constant centrifugation. (In this paper, ...“G” is the acceleration due to gravity.) After 30 and 60 days, rats were killed and perfused with 10% buffered neutral formalin (B.N.F.). The humerus, radius, ulna, femur, and tibia were removed, cleared of all soft tissues, weighed, and the total length measured. Bone robusticity was calculated using the ponderal index: bone length/\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt3{{{\rm bone}\,{\rm weight}}} $\end{document}. Tukey's Multiple Range Test was used. The data suggest that the specific limb bone, G, and duration of centrifugation are each factors in the response of limb bones to simulated increases in body weight.
The purpose of this investigation was to subject separate male and female groups of weanling hypophysectomized rats each to a specific 10% simulated increase in body weight using constant ...centrifugation, ranging from 1.1G to 2.0G, to study changes in bone robusticity and bone mineral content. (In this paper, “G” is the acceleration due to gravity.) After 60 days of centrifugation at 24 rpm, the rats were killed and the humerus, radius, ulna, femur, and tibia were removed, cleared of soft tissues, weighed, measured, decalcified with EDTA, and reweighed. Bone robusticity was determined using the ponderal index: P.I. = bone length ÷ \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt3{{{\rm bone}\,{\rm weight}}} $\end{document}; and bone mineral content (BMC) was determined using the formula: BMC = (Wu – Wd) ÷ Wu × 100. Tukey's Studentized Multiple Range T Test was used. The data suggest that, for both male and female hypophysectomized rats, bone robusticity is decreased with simulated increases in body weight; also, for males, a bimodal curve describing the relationship between BMC and simulated increases in body weight is suggested.
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