Eclipse Research Articles

Introduction to the Techniques of Interferometry and Lunar Occultation in Radio Astronomy

Radio telescopes allow a 24 × 7 observation time window of those regions of the space which appear dark in the visible region. But, the major problem with a single radio telescope is its poor resolution. In this article, the method of interferometry in radio astronomy is discussed by citing the example of a two-element interferometer. Interferometry provides improved resolution.With a single telescope as well, the resolution can be improved for the radio sources along the ecliptic which are smaller in angular spread as compared to the Moon. The theoretical principle behind the technique of occultation is discussed using its optical analog of diffraction.

Limits on a Ring System at 2014 MU69 from Recent Stellar Occultations

Limits on a Ring System at 2014 MU69 from Recent Stellar Occultations

The SOFIA Focal Plane Imager: A Highly Sensitive and Fast Photometer for the Wavelength Range 0.4 to 1 Micron

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a heavily modified Boeing 747SP aircraft, accommodating a 2.7[Formula: see text]m infrared telescope. This airborne observation platform operates at flight altitudes of up to 13.7[Formula: see text]km (45,000[Formula: see text]ft) and therefore allows a nearly unobstructed view of the visible and infrared universe at wavelengths between 0.4[Formula: see text]μm and 1600[Formula: see text]μm. The Focal Plane Imager (FPI+) is SOFIA’s main tracking camera. It uses a commercial, off-the-shelf camera with a thermoelectrically cooled EMCCD. The back-illuminated sensor has a peak quantum efficiency greater than 95% at 550[Formula: see text]nm and the dark current is as low as 0.001 e-/pix/sec. Since 2015, the FPI[Formula: see text] has been available to the community as a Facility Science Instrument (FSI), and can be used as a high speed photometer for events in the visual wavelength range. This paper presents a detailed overview of the design and optical configuration of the FPI+. Different settings and specifications of the camera are explained and the focal plane sensor is described. The camera’s performance in regards to sensitivity and frame rate is shown. The operation of the instrument is described as well as the support for guest observers throughout the process from proposing to data analysis. To date, SOFIA has conducted multiple FPI+ observations of stellar occultations, e.g. occultations by Pluto in 2011 and 2015, the occultation by 2014MU69 in July 2017 and the occultation by Triton in October 2017. Additionally, multiple observations of exo-planet transits have been observed with the FPI+. Throughout these observations, the FPI+ has proven to be an excellent photometer for astronomical events that have challenging requirements for sensitivity and temporal resolution.

A Charge-Transfer Salt Based on Ferrocene/Ferrocenium Pairs and Keggin-Type Polyoxometalates.

A new hybrid inorganic-organometallic salt has been obtained from the reaction of the Keggin-type silicotungstate anion with ferrocene in a water/methanol mixture as a result of the partial oxidation of ferrocene molecules to ferrocenium cations. Single-crystal X-ray diffraction analysis reveals the presence of four ferrocenium (FeIII) cations and one ferrocene (FeII) molecule per plenary Keggin anion in the crystal structure of [FeIII (Cp)2]4[SiW12O40]·[FeII(Cp)2]·2CH3OH (1). Compound 1 thus constitutes the first example in the literature in which ferrocenium and ferrocene species coexist in the structure of a polyoxometalate-based salt. The two crystallographically independent ferrocenium species in the asymmetric unit of 1 exhibit different configurations: One displays an eclipsed conformation with ideal D5h symmetry, whereas the conformation in the other one is staggered D5d. The crystal packing of 1 can be best described as an organometallic sub-lattice of ferrocenium and ferrocene species linked by a network of π-π interactions that generates rectangular cavities of about 14 × 10 Å in which strings of Keggin anions and methanol molecules are hosted, further connected to each other via weak OPOM···CMeOH-OMeOH···OPOM type hydrogen bonds. The charge-transfer nature of the salt has been studied by solid-state diffuse reflectance UV-Vis spectroscopy and the presence of magnetically isolated FeIII/FeII centres has been confirmed by Mössbauer spectroscopy. A topological study carried out on all of the pristine ferrocenyl species deposited in the Cambridge Structural Database (CSD) has allowed two main conclusions to be drawn: (1) these species tend to adopt extreme conformations (either eclipsed or staggered) with less than a 15% of examples showing intermediate states and (2) the oxidation state of the iron centres can be unequivocally assigned on the basis of a close inspection of the Fe···Cp distances, which allows ferrocene neutral molecules and ferrocenium cations to be easily distinguished.

World of Technology:: Better or Blinding?

By sharing the technological eclipses that have shadowed many lives in multiple cultural contexts, in this paper, I attempt to explore the meaning of technology by revisiting Ferneding’ s quest to understand technology. I share how humanity, immersed in technoculture, in its ongoing pursuit for salvation through technological inventions, has in turn become a slave of technology. In an attempt to awaken our collective moral consciousness and break this technological cocoon, I join Grant in re(thinking): “What technology is”? For guidance, I turn to Heidegger who invites us to contemplate technology as an intellectual capacity. I hope to invite technology as a technoscience — a way of uncovering nature and illuminating life amid teaching, learning and living encounters of education that do not technicalize schooling to alienate our self from us, but call for love and belongingness as we engage in complicated conversations to understand curriculum.

TYC 9040-2855-1: A Possible Eclipsing Binary with a Red Giant Primary

TYC 9040-2855-1: A Possible Eclipsing Binary with a Red Giant Primary

A stellar occultation by Vanth, a satellite of (90482) Orcus

A stellar occultation by the large trans-Neptunian object (90482) Orcus was predicted to occur on 2017 March 07. Observations were made at five sites in North and South America: the 0.6-m Astronomical Telescope of the University of Stuttgart (ATUS) at Sierra Remote Observatories, California; Las Cumbres Observatory's 1-m telescope at McDonald Observatory, Fort Davis, Texas (ELP); NASA's 3-m InfraRed Telescope Facility (IRTF) on Mauna Kea, Hawai'i; the 0.6-m Southeastern Association for Research in Astronomy (SARA-CT) telescope at Cerro Tololo, Chile; and the 4.1-m Southern Astrophysical Research (SOAR) telescope on Cerro Pachón, Chile. High-speed, visible-wavelength images were taken at all sites, in addition to simultaneous K-band images at the IRTF. Solid-body occultations were observed from two sites. Post-event reconstruction suggested an occultation of two different stars observed from two different sites. Follow-up, speckle imaging revealed a second star, which verified that the occulting body in both cases was Orcus’ satellite, Vanth. The two single-chord detections, with an anomalously large timing delay in one chord, have lengths of 291 ± 125 km and 434.4 ± 2.4 km. The observations, combined with a non-detection at a nearby site, allow a tight constraint of 443 ± 10 km to be placed on Vanth's size (assuming it is spherical). A 3-σ upper limit of 1–4 μbar (depending on constituent) is found for a global Vanth atmosphere. The immersion and emersion profiles are slightly different, with atmospheric constraints 40% higher on immersion than on emersion. No rings or other material were detected within ten thousand kms of Vanth, and beyond 8010 km from Orcus, to the tightest optical depth limit of ∼0.1 at ∼5 km scale. The occultation probed as close as 5040 km from Orcus, placing an optical depth limit of ∼0.3 at ∼5 km scale on any encircling material at that distance.

Kronoseismology III: Waves in Saturn’s inner C ring

We investigate waves driven in Saturn’s rings by planetary normal modes, concentrating on the previously unexplored inner C ring. In this region, the known waves all have exceptionally short wavelengths, which has proven problematic for previous studies that depended on the accurate estimate of wave phases for wave identification. However, detailed study of over 200 stellar and radio occultations observed by Cassini, involving measurements of ∼ 65 circular ring features, has resulted in a radius scale for the rings which has absolute errors of ∼ 250 m and internal (relative) uncertainties of ∼ 150 m (French et al., 2017). This permits us to measure the phases of waves with wavelengths as short as ∼ 1 km, or even less, which has enabled the identification of additional waves in the inner C ring. Using a variety of wavelet-based approaches and employing stellar occultation data acquired by the Visual and Infrared Mapping Spectrometer (VIMS) instrument, we have identified three new Saturn-driven outer Lindblad resonance density waves: W76.02 (radius near 76020 km, wavenumber m=−9), W76.44 (m=−2), and W76.46 (m=−7). We also identify a new class of waves driven by Saturn’s internal oscillations: vertical (bending) waves W74.67 (m=−7), W74.93 (m=−4), W74.94 (m=−9), and W76.24 (m=−8). All of these identifications are based on the three observational parameters that can be derived from the wave profiles: their m-values (or number of spiral arms), their pattern speeds ΩP, and their directions of propagation. These results, when combined with previous identifications of Saturn-driven waves, provide significant constraints on Saturn’s internal structure.

On the accuracy of the SGP4 to predict stellar occultation events using ENVISAT/GOMOS data and recommendations for the ALTIUS mission

In preparation for the operations of the ALTIUS mission, research is carried out to assess the accuracy of the SGP4 orbital propagator in predicting stellar occultation events. The quantification of the accuracy and its consequent improvement will enable reliable measurement planning and, therefore, maximize the number of measurements. To this end, predictions are made for the timing of occultations for the GOMOS instrument on-board the ENVISAT, which are then compared to actual occultation occurrences. It is found that the error is substantial but follows a trend that can be interpolated. This enables devising a method for highly accurate predictions given a sufficient number of data points. Statistically significant results for the accuracy of the propagator and a calibration method are presented. Recommendations for a measurement planning procedure of ALTIUS are formulated.

A preliminary study of template library-based auto-planning of volume modulated arc therapy

Objective To explore the feasibility of the volume modulated arc therapy (VMAT) auto-planning based on template library (TL). Methods VMAT plans of 68 patients diagnosed with postoperative rectal cancer in Eclipse system were retrospectively selected. The prescription dose was 50 Gy/25F. In 19 patients, the feature values of target and organs at risk were extracted as the vectors. The final optimized restricted conditions were saved as the TL. Then, the plans of 15 rectal cancer patients (10 cases from TL and 5 outside TL) were automatically optimized. According to the multi-dimensional vector similarity principle, the similarity parameter αwas defined. The designed program automatically selected the optimal-object template in an in-house software developed with Matlab. The dosimetric parameters of the auto-optimized plans with the optimal-object template (ATP) and the clinical plan (CP) were compared by the paired t-test. The changes in the dosimetric parameters and similarity parameter α were statistically compared by Pearson′s correlation analysis. The linear fitting of the dosimetric parameters with α was used by least squares method to explore the tendency of the ATP dosimetric parameters relative to CP. Results The dosimetric parameters of ATP for 13 cases were slightly worse than those of CP. The conformal index (P=0.004), heterogeneous index (P=0.015), V40(P=0.003) and mean dose (P=0.022) of the intestine significantly differed. The α values of these 13 cases were 2.67, 2.60, 2.60, 2.49, 2.67, 2.74, 2.72, 2.48, 2.53, 2.86, 2.68, 2.56 and 2.63. The α value was significantly correlated with the V40 or mean dose of the bladder (r=0.649 and 0.603, P=0.016 and 0.029). Along with the increase of α value, V40 and mean dose of the intestine for ATP were gradually deteriorated than those of CP. The remaining dosimetric para-meters of ATP were close to or superior to those of CP. Conclusions The results of ATP are slightly worse than those of CP, whereas can satisfy the clinical requirements. The TL, the quality of TL and ATP remain to be further optimized. Key words: Radiotherapy; Template library; Auto-optimize; Volume modulated arc therapy plan

Reversible Olefin Addition to Extended Lattices of a Nickel–Selenium Framework

We performed density functional theory computations to study the structural and electronic properties as the basis of ethylene addition activity for [Ni(XC)4]n (X = Se, S)-extended lattices. We demonstrated that the mechanism of ethylene cycloaddition to a periodic [Ni(SeC)4]n two-dimensional (2D) network is analogous to that previously described for [Ni(SC)4]n 2D sheets and similar to the metal bis(dithiolene) molecular complexes [M(S2C2R2)2] (M = Ni, Pd, Pt, Co, Cu). These nanosheet materials avoid decomposition upon olefin addition, which is one of the main limitations of the molecular metal bis(dithiolene) complexes, as we find the decomposition processes to be thermodynamically unfavorable. Our calculations also suggest that the preferred conformation of the [Ni(SeC)4]n bilayer lattice is parallel displaced, with the Se atoms positioned above the Ni atoms, which is different from the eclipsed conformation found for [Ni(SC)4]n. We also managed to optimize an adduct of [Ni(SC)4]n in the bilayer form, w...

Measuring the global 21-cm signal with the MWA-I: improved measurements of the Galactic synchrotron background using lunar occultation

We present early results from a project to measure the sky-averaged (global), redshifted $21\,$cm signal from the Epoch of Reionisation (EoR), using the Murchison Widefield Array (MWA) telescope. Because interferometers are not sensitive to a spatially-invariant global average, they cannot be used to detect this signal using standard techniques. However, lunar occultation of the radio sky imprints a spatial structure on the global signal, allowing us to measure the average brightness temperature of the patch of sky immediately surrounding the Moon. In this paper we present one night of Moon observations with the MWA between 72 - 230 MHz and verify our techniques to extract the background sky temperature from measurements of the Moon's flux density. We improve upon previous work using the lunar occultation technique by using a more sophisticated model for reflected `earthshine' and by employing image differencing to remove imaging artefacts. We leave the Moon's (constant) radio brightness temperature as a free parameter in our fit to the data and as a result, measure $T_{\rm{moon}} = 180 \pm 12 $ K and a Galactic synchrotron spectral index of $-2.64\pm0.14$, at the position of the Moon. Finally, we evaluate the prospects of the lunar occultation technique for a global EoR detection and map out a way forward for future work with the MWA.

Crystal structure of [μ-1κ2C1,C4:2(1,2,3,4-η)-1,2,3,4-tetra-phenyl-buta-1,3-diene-1,4-di-yl]bis-(tri-carbonyl-osmium)(Os-Os).

In the title complex C34H20O6Os2 or (μ-η4-C4Ph4)Os2(CO)6, one Os atom is part of a metalla-cyclo-penta-diene ring, while the second Os atom is π-bonded to the organic portion of this ring. The distance of 2.7494 (2) Å between the two Os atoms is typical of an Os-Os single bond. Three carbonyl ligands are attached to each Os atom and these six carbonyls adopt an eclipsed conformation. There are no bridging or semibridging CO groups. Two carbonyl ligands and all four phenyl groups are disordered over two slightly different positions for which each atom in the minor components is displaced less than 1 Å from the corresponding atom in the major components. The refined occupancies of the major com-ponents of the carbonyl ligands are 0.568 (16) and 0.625 (13), while those for the phenyl rings are 0.50 (3), 0.510 (12), 0.519 (18), and 0.568 (12).

The Bible and the first recorded eclipse

The Bible and the first recorded eclipse

Geomagnetic Field Variations During Solar Eclipses and the Geographic Location of Observing Sites

Geomagnetic Field Variations During Solar Eclipses and the Geographic Location of Observing Sites

Ammonia Borane in Nanotubes: The Preference of Eclipsed Conformation

The DFT PBE/3ζ modeling of conformational transformations of an ammonia borane molecule BH3 ← NH3 in model single-layer carbon nanotubes indicates an unusual shift of conformational equilibrium to the eclipsed form. In cluster, the В ← N coordination bond demonstrates a noticeable decrease in length and an increase in its order. The increasing diameter of nanoobject weakens the observed effects and shifts conformation equilibrium to the staggered conformer.

Probing the Hill Sphere of (486958) 2014 MU69: HST FGS Observations during the 2017 July 17 Stellar Occultation

Abstract We observed the 2017 July 17 stellar occultation of HD 168233 by the Kuiper Belt Object (486958) 2014 MU69, the close flyby target of the extended New Horizons mission. Rather than capture a solid body occultation by the KBO itself, our program aimed to constrain the opacity of rings, moons, or other debris in the nearby environment. We used the Hubble Space Telescope Fine Guidance Sensors (HST FGS) instrument in TRANS F583W mode to collect 40 Hz time resolution photometry of the stellar occultation star for two HST orbits during this observation. We present the results of reduction and calibration of the HST FGS photometry, and set upper limits on rings or other dust opacity within the Hill sphere of (486958) 2014 MU69 at distances ranging from ∼20000 km to ∼75000 km from the main body.

Photoelectric Observations of the Lunar Occultation of the Star SAO 79361 during a Total Lunar Eclipse

The results of photoelectric observation of the occultation of the visual binary star SAO 79361 = ADS 6038 by the Moon during the total lunar eclipse of January 9, 1982 are presented. The upper limit of the angular diameter of the brighter component A is estimated to be dul ≃ 0.0011″ based on direct measurements, which is in agreement with indirect estimates. Accurate estimates for the magnitude difference between components A and B, their angular separation, p ≃ 3.2″, and the inclination of the Moon’s edge’s at the point of occultation to the mean lunar horizon, θ ≃ +25°, are obtained. The time of the geometrical occultation of the center of the stellar disk of component A is determined with an accuracy of 1 ms. The results obtained for this star are unique among observations worldwide.

High-precision Orbit Fitting and Uncertainty Analysis of (486958) 2014 MU69

Abstract NASA’s New Horizons spacecraft will conduct a close flyby of the cold-classical Kuiper Belt Object (KBO) designated (486958) 2014 MU69 on 2019 January 1. At a heliocentric distance of 44 au, “MU69” will be the most distant object ever visited by a spacecraft. To enable this flyby, we have developed an extremely high-precision orbit fitting and uncertainty processing pipeline, making maximal use of the Hubble Space Telescope’s Wide Field Camera 3 (WFC3) and pre-release versions of the ESA Gaia Data Release 2 (DR2) catalog. This pipeline also enabled successful predictions of a stellar occultation by MU69 in 2017 July. We describe how we process the WFC3 images to match the Gaia DR2 catalog, extract positional uncertainties for this extremely faint target (typically 140 photons per WFC3 exposure), and translate those uncertainties into probability distribution functions for MU69 at any given time. We also describe how we use these uncertainties to guide New Horizons, plan stellar occultions of MU69, and derive MU69's orbital evolution and long-term stability.

Determination of the body of the dwarf planet Haumea from observations of a stellar occultation and photometry data

Determination of the body of the dwarf planet Haumea from observations of a stellar occultation and photometry data