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.
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.
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.
•Six exoplanets with 82 transit light curves of ETD were studied in this paper.•Parameters of transit were extracted along with uncertainties in these measurements.•AIJ analysis results are in ...relatively good match with those residing in the NEA.•Small aperture optics can provide accurate parameters for follow-up observations.
Photometric observations of exoplanet transits can be used to derive the orbital and physical parameters of an exoplanet. We analyzed several transit light curves of exoplanets that are suitable for ground-based observations whose complete information is available on the Exoplanet Transit Database (ETD). We analyzed transit data of planets including HAT-P-8 b, HAT-P-16 b, HAT-P-21 b, HAT-P-22 b, HAT-P-28 b and HAT-P-30 b using the AstroImageJ (AIJ) software package. In this paper, we investigated 82 transit light curves from ETD, deriving their physical parameters as well as computing their mid-transit times for future Transit Timing Variation (TTV) analyses. The Precise values of the parameters show that using AIJ as a fitting tool for follow-up observations can lead to results comparable to the values at the NASA Exoplanet Archive (the NEA). Such information will be invaluable considering the numbers of future discoveries from ground and space-based exoplanet surveys.
•Monitored replicated experiment with 2 cultivars of barley and 3 irrigation treatments.•Detailed surface temperature and water balance measurements over crops lifecycle.•Wide range of ...evapotranspiration flux and surface temperature measured.•Model developed using surface temperature and NDVI to estimate evapotranspiration.•Enables sub-paddock mapping of evapotranspiration using remote measurements.
The availability of affordable instruments that measure surface radiative temperature and canopy cover have made it possible, in principle, to extend and improve existing methods of estimating potential evapotranspiration (ET) to predictions where assumptions of ‘full cover’ and ‘well-watered’ are violated. The aim of this study was to develop a model for ET whose input data requirements were not large, and would make use of surface temperature and cover measurements to predict ET in both potential and sub-potential conditions. A randomised experiment was conducted with two cultivars of barley (‘Dash’ and ‘Omaka’, erect and prostrate leaved, respectively) in combination with three irrigation treatments (High, Mid and Low) in a rain-out shelter. The treatments produced a wide range of surface temperature, cover and ET. Water fluxes in the soil were measured by methods sensitive enough to detect changes on the timescale of hours. Meteorological variables, short wave radiation albedo, ground heat flux density and surface temperature were logged on a sub-hour timescale. The Priestley and Taylor potential ET equation is modified and additional equations are derived to allow the inclusion of a crop coefficient to account for incomplete cover and to vary the alpha coefficient based on surface temperature to account for soil drying. Equations were also derived for estimating short-wave radiation, albedo and soil heat flux from canopy cover and meteorological variables. The resulting equations were able to quantify a wide range of ET values measured by detailed water balance in barley crops that often had incomplete canopy cover and encountered differing degrees of water stress. We conclude the approach presented has promise but requires broader testing. The successful integration of canopy measurements with an ET model will enable the production of ET maps which will have broad applications in research and irrigation management applications.
•Surface temperature measurement enabled accurate estimates of ET for variable soils•Plants growing in irrigated shallow soils encounter water stress, reducing ET and yield•Variable rate irrigation ...based on ET measurements reduced irrigation by 13-28%•Yields were maintained and drainage reduced under this variable rate irrigation•ET measurement approach could have wide application in irrigation management
An experiment was conducted to assess a modified Priestley and Taylor calculation (developed in a companion paper) that utilises surface temperature (Ts) to estimate evapotranspiration (ETMPT) and to assess the benefits of variable rate irrigation (VRI) based on ETMPT measurements. A ryegrass seed field with Low, Mid and High available water capacity soil zones was used. Four replicates of two irrigation treatments were established in each zone; uniform rate irrigation (URI) where the same amount of irrigation was applied to all three zones based on neutrone probe measurements; and VRI where ETMPT was measured and different amounts of irrigation applied to each zone to replace this. TS was measured continiously in each plot using stationary infrared radiometers, normalised difference vegetation index measured twice weekly with a hand-held instrument and meteorological variables were recorded in the field. Neutron probe access tubes were installed to 1.6m depth in all plots and monitored weekly to provide alternative evapotranspiration estimates (ETNP). The ETMPT decreased from 333mm in the high zone to 282 mm in the low zone. This in combination with faster canopy senescence and lower seed yields showed the low zone encountered water stress even though irrigated weekly. There was good agreement between ETMPT and ETNP in the VRI treatments and the High zone of the URI treatment. The higher values of ETNP in the Low and Med zones of the URI treatment were attributed to drainage. The URI treatment had 254.2 mm of irrigation applied to all zones during the season whereas VRI treatment had 183.4, 210.2 and 220.2 mm applied to the Low, Mid and High Zones, respectively. There, were no differences in ryegrass seed yield between the two irrigaiton treatments and less drainage from the VRI treatments. From this we conclude that VRI based on ETMPT is effective and field application of ETMPT is worth further development.
To determine the prevalence and extent of impairments impacting health-related quality of life among survivors of COVID-19 who required mechanical ventilation, 6 months after hospital discharge.
...Multicenter, prospective cohort study, enrolling adults 18 years old or older with laboratory-confirmed severe acute respiratory syndrome coronavirus 2 infection who received mechanical ventilation for 48 hours or more and survived to hospital discharge. Eligible patients were contacted 6 months after discharge for telephone-based interviews from March 2020 to December 2020. Assessments included: Montreal Cognitive Assessment-Blind, Hospital Anxiety and Depression Scale, Impact of Event Scale-6, EuroQOL 5 domain quality-of-life questionnaire, and components of the Multidimensional Dyspnea Profile.
Two tertiary academic health systems.
Of 173 eligible survivors, a random sample of 63 were contacted and 60 consented and completed interviews.
None.
Mean age was 57 + 13 years and mean duration of invasive mechanical ventilation was 14 + 8.2 days. Six months post-discharge, 48 patients (80%; 95% CI, 68-88%) met criteria for post-intensive care syndrome (PICS), with one or more domains impaired. Among patients with PICS, 28 (47%; 95% CI, 35-59%) were impaired in at least 2 domains, and 12 (20%; 95% CI, 12-32%) impaired in all three domains. Significant symptoms of post-traumatic stress were present in 20 patients (33%; 95% CI, 23-46%), anxiety in 23 (38%; 95% CI, 27-51%), and depression in 25 (42%; 95% CI, 30-54%). Thirty-three patients (55%; 95% CI, 42-67%) had impairments in physical activity; 25 patients (42%; 95% CI, 30-54%) demonstrated cognitive impairment.
Eighty percent of COVID-19 survivors who required mechanical ventilation demonstrated PICS 6 months after hospital discharge. Patients were commonly impaired in multiple PICS domains as well as coexisting mental health domains.
Background. Organ donors supported by extracorporeal membrane oxygenation (ECMO) have historically been considered high-risk and are judiciously utilized. This study examines transplant outcomes ...using renal allografts from donors supported on ECMO for nondonation purposes. Methods. Retrospective review of the Gift of Life (Pennsylvania, New Jersey, Delaware) organ procurement organization database, cross-referenced to the Organ Procurement and Transplantation Network database, assessed kidney transplants using donors supported on venoarterial (VA) and venovenous (VV) ECMO for nondonation purposes. Transplants using VA- and VV-ECMO donors were compared with Kidney Donor Profile Index (KDPI)-stratified non-ECMO donors. Regression modeling of the entire ECMO and non-ECMO populations assessed ECMO as predictive of graft survival. Additional regression of the ECMO population alone assessed for donor features associated with graft survival. Results. Seventy-eight ECMO donors yielded 128 kidney transplants (VA: 80, VV: 48). Comparing outcomes using these donors to kidney transplants using organs from KDPI-stratified non-ECMO donors, VA- and VV-ECMO donor grafts conferred similar rates of delayed graft function and posttransplant renal function to KDPI-matched non-ECMO counterparts. VA-ECMO kidneys demonstrated superior graft survival compared with the lowest-quality (KDPI 86%–100%) non-ECMO kidneys and similar graft survival to KDPI <85% non-ECMO kidneys. VV-ECMO showed inferior graft survival to all but the lowest-quality (KDPI 86%–100%) non-ECMO kidneys. VV-ECMO, but not VA-ECMO, was associated with increased risk of graft loss on multivariable regression (hazard ratios—VA: 1.02, VV: 2.18). Higher KDPI, advanced age, increased body mass index, hypertension, and diabetes were identified as high-risk features of ECMO donors. Conclusions. Kidney transplantation using appropriately selected ECMO donors can safely expand the donor pool. Ongoing studies are necessary to determine best practice patterns using kidneys from these donors.
To study the concordance of diurnal intraocular pressure (IOP) between fellow eyes in primary open-angle glaucoma (POAG).
Retrospective chart review.
Ninety-three POAG patients.
Patients who met the ...definition of POAG and underwent diurnal curve measurement were included. Subjects were excluded if there was a history of surgery, trauma, ocular vascular disease, incomplete diurnal curve, or asymmetric ocular medication use. Patients on symmetric ocular medication were included and analyzed separately. Goldmann applanation tonometry was performed at 10 am, 1 pm, 4 pm, 7 pm, 10 pm, and 7 am (the next day). The following statistical analyses were performed: (1) average Pearson correlation coefficient (r) from individual correlations of right and left eye IOP over the 6 time points for each subject; (2) linear mixed model analysis for repeated measures, with eye (right and left) and time as the within-subject fixed effects, and (3) absolute difference in change in IOP between fellow eyes over each time interval and probability that the difference was within 2 or 3 mmHg.
The concordance of the IOP between fellow eyes as measured by absolute difference in change in IOP between fellow eyes and probability of the difference being within 2 or 3 mmHg.
Thirty-seven patients were untreated and 56 were treated on symmetric IOP-lowering medications. The diurnal curves of fellow eyes exhibited parallel profiles according to the linear mixed model. The average difference in the change of IOP between fellow eyes over given time intervals ranged from 1.6 to 2.0 mmHg. The estimated probability that the absolute change in IOP between fellow eyes was within 2 mmHg was 68% to 90%, and within 3 mmHg was 78% to 95% for all time intervals.
The diurnal variation of IOP in POAG is largely concordant between fellow eyes. For any given time interval, the fellow eye IOPs may fluctuate asymmetrically a minority of the time. Clinicians who utilize the uniocular trial should be aware of the limit of the IOP concordance.
A new generation of communications satellites orbiting the Earth is presenting amateur astronomers and the general public with an exciting new experience—the ability to view objects that at times ...will be brighter than the brightest star or planet in the sky! Named the Iridium satellite constellation, this collection of artificial satellites circles the Earth 14 times daily. Each one is physically about the size of an automobile. Originally planned as a way for persons with portable telephones to communicate anywhere in the world using space-based technology, an unexpected feature of the design has caused the visual appearance of these spacecraft to reflect the light of the Sun like a giant mirror. While one might argue that the relative sameness of the night sky is rarely punctuated by anything dramatic, the Iridium satellites are about to change that view.
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