Abstract
We develop a shape model of asteroid 16 Psyche using observations acquired in a wide range of wavelengths: Arecibo
S
-band delay-Doppler imaging, Atacama Large Millimeter Array (ALMA) ...plane-of-sky imaging, adaptive optics (AO) images from Keck and the Very Large Telescope (VLT), and a recent stellar occultation. Our shape model has dimensions 278 (−4/+8 km) × 238(−4/+6 km) × 171 km (−1/+5 km), an effective spherical diameter
D
eff
= 222-1/+4 km, and a spin axis (ecliptic lon, lat) of (36°, −8°) ± 2°. We survey all the features previously reported to exist, tentatively identify several new features, and produce a global map of Psyche. Using 30 calibrated radar echoes, we find Psyche’s overall radar albedo to be 0.34 ± 0.08 suggesting that the upper meter of regolith has a significant metal (i.e., Fe–Ni) content. We find four regions of enhanced or complex radar albedo, one of which correlates well with a previously identified feature on Psyche, and all of which appear to correlate with patches of relatively high optical albedo. Based on these findings, we cannot rule out a model of Psyche as a remnant core, but our preferred interpretation is that Psyche is a differentiated world with a regolith composition analogous to enstatite or CH/CB chondrites and peppered with localized regions of high metal concentrations. The most credible formation mechanism for these regions is ferrovolcanism as proposed by Johnson et al. (2020).
Fast-rotating asteroids (FRAs) are considered to be small bodies having a rotation period (P) faster than the spin barrier of about 2.3 h, starting at diameters of less than 300 m. We selected the 20 ...fastest Arecibo radar-observed targets, with P<0.13 h (∼8 min). Some key measurements and calculations obtained from radar observations include: the Doppler bandwidth, the circular polarization ratio, radar astrometry, and (with enough signal-to-noise ratio) delay-Doppler images of the object. Rotation period data available from the Light Curve Database for the selected objects combined with the radar observations allow us to constrain the possible diameters and confirm the periods. Of the objects in this sample, the median absolute magnitude (H) is 24.9, and the median calculated diameter is 32 meters.
The apparent rotation period indicated by the bandwidth can appear slower than the object’s true rotation, but not faster, providing an upper limit to the true rotation period. Asteroid cohesion required to prevent rotational disruption depends on rotation rate, density, and diameter; we performed calculations for the minimum values for cohesion via the Drucker–Prager (D–P) cohesion criterion. Most of these objects need a few to a few hundred pascals of cohesion; however four cases stand out: 2014 TV, 2015 RF36, 2015 GS2 and 2017 EK, needing a minimum cohesion on the order of a few kilopascals. These are comparable to very weak Earth rocks, and are larger than previously reported values for NEAs.
•Analysis of fastest-rotating near-Earth asteroids observed from Arecibo Observatory.•Comparing radar- and lightcurve-derived rotation period, diameter, and cohesion.•We show the orbit determination for small NEAs is significantly improved when radar observations are available.•A few objects need cohesion on the order of a few kilopascals to prevent disruption.
Abstract
We conducted radar observations of near-Earth asteroid 2019 OK on 2019 July 25 using the Arecibo Observatory S-band (2380 MHz, 12.6 cm) planetary radar system. Based on Arecibo and optical ...observations the apparent diameter is between 70 and 130 m. Combined with an absolute magnitude of
H
= 23.3 ± 0.3, the optical albedo of 2019 OK is likely between 0.05 and 0.17. Our measured radar circular polarization ratio of
μ
C
= 0.33 ± 0.03 indicates 2019 OK is likely not a V- or E-type asteroid and is most likely a C- or S-type. The measured radar echo bandwidth of 39 ± 2 Hz restricts the apparent rotation period to be approximately between 3 minutes (0.049 hr, D = 70 m) and 5 minutes (0.091 h, D = 130 m). Together, the apparent diameter and rotation period suggest that 2019 OK is likely not a rubble-pile body bound only by gravity. 2019 OK is one of a growing number of fast-rotating near-Earth asteroids that require some internal strength to keep them from breaking apart.
Objetivo: Describir un caso de rabdomiolisis asociada a uso de quetiapina y lamotrigina en adolescente tratado por trastorno afectivo bipolar. Método: Descripción del caso clínico, análisis de los ...factores asociados y revisión no sistemática de la literatura relevante. Resultados: Mujer joven con trastorno afectivo bipolar, tratado farmacológicamente con quetiapina y lamotrigina, que presento mialgias y artralgias con manejo instaurado por psiquiatría. La quetiapina y el ejercicio se han asociado a rabdomiolisis. No se ha encontrado el mecanismo que media tal asociación, si bien se plantea disfunción neuromuscular e incremento en la permeabilidad sarcomérica. Conclusiones: Este caso clínico permite observar la interacción compleja de los psicofármacos y la actividad física en un paciente psiquiátrico adolescente, y la aparición de una complicación médica potencialmente letal.
We develop a shape model of asteroid 16 Psyche using observations acquired in a wide range of wavelengths: Arecibo S-band delay-Doppler imaging, Atacama Large Millimeter Array (ALMA) plane-of-sky ...imaging, adaptive optics (AO) images from Keck and the Very Large Telescope (VLT), and a recent stellar occultation. Our shape model has dimensions 278 (-4/+8) km x 238 (-4/+6) km x 171 (-1/+5) km, an effective spherical diameter Deff = 222 -1/+4 km, and a spin axis (ecliptic lon, lat) of (36 deg, -8 deg) +/- 2 deg. We survey all the features previously reported to exist, tentatively identify several new features, and produce a global map of Psyche. Using 30 calibrated radar echoes, we find Psyche's overall radar albedo to be 0.34 +/- 0.08 suggesting that the upper meter of regolith has a significant metal (i.e., Fe-Ni) content. We find four regions of enhanced or complex radar albedo, one of which correlates well with a previously identified feature on Psyche, and all of which appear to correlate with patches of relatively high optical albedo. Based on these findings, we cannot rule out a model of Psyche as a remnant core, but our preferred interpretation is that Psyche is a differentiated world with a regolith composition analogous to enstatite or CH/CB chondrites and peppered with localized regions of high metal concentrations. The most credible formation mechanism for these regions is ferrovolcanism as proposed by Johnson et al. (Nature Astronomy vol 4, January 2020, 41-44).
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