Eclipse Research Articles

The state of Pluto’s atmosphere in 2012–2013

We observed two stellar occultations on UT 4 May 2013 and UT 9 September 2012, with the aim of measuring Pluto’s atmospheric parameters. Both of these events were observed by world-wide collaborations of many observers, and both occurred within 1month of Pluto’s stationary points. The PC20120909 event was observed at the McDonald Observatory (MONET 1.2-m), and Olin Observatory (the Ortega 0.8-m); the P20130504 event was observed at the Las Campanas Observatory (du Pont 2.5-m), the Cerro Tololo Inter-American Observatory (SMARTS 1-m), and the Cerro Calán National Astronomical Observatory (Goto 0.45-m). Analysis of the data indicates an atmospheric state similar to that in June 2011. The shadow radius for the event is unchanged from recent events, indicating an atmosphere that is holding stable and not in the midst of global collapse. We discuss the advantages and disadvantages of comparing various atmospheric parameters across events (the shadow radius vs. the pressure at a particular radius). These analyses suggest that Pluto will still have an atmosphere when the New Horizons spacecraft arrives in July 2015.

Project Report ECLIPSE: European Citizenship Learning Program for Secondary Education

This paper reports on a European project, the Comenius ECLIPSE project (European Citizenship Learning in a Programme for Secondary Education) developed by six European partners coordinated by the University of Trento in the years 2011-2014. ECLIPSE (co-financed by the EACEA - Education, Audiovisual and Culture Executive Agency) aims at developing, testing, and implementing a Programme of European Citizenship, in order to improve citizenship competence and responsibility and to strengthen the sense of belonging and European identity of 8th grade pupils. These goals are reachable thanks to a number of measures in formal, non-formal and informal fields. The project partners created teaching and monitoring tools for pupils: seven ECMs (European Citizenship Modules), knowledge tests, pupils’ portfolio, and suggestions for teachers, especially a portfolio for ECLIPSE educators. The ECLIPSE teaching/ testing materials were implemented in several schools of the partner’s countries in order to make sure that it is useful for European pupils of different school systems. It can be used in a flexible way keeping in mind different learning needs in each school system, with a view to improving transversal competencies like learning to learn, as well as initiative and active involvement in improving the chances for young people in citizenship and work worlds. Dieses Papier beschreibt ein europaisches Projekt: das Comenius Projekt ECLIPSE (European Citizenship Learning in einem Programm fur Secondary Education), das von sechs europaischen Partnern entwickelt und von der Universitat Trient in den Jahren 2011-2014 koordiniert wurde. ECLIPSE wurde von der EACEA (Education, Audiovisual and Culture Executive Agency) kofinanziert; es zielt auf die Entwicklung, Uberprufung und Implementierung eines Programms zur Entwicklung eines europaischen Burgersinns, um Kompetenzen als Staatsburger und zugleich einer europaischen Identitat und Verantwortung bei Schulerinnen und Schulern der 8. Klasse. Diese Ziele werden durch eine Reihe von Masnahmen im formalen, nicht formalen und informellen Bereich angestrebt. Die Projektpartner entwickelten Lehr-und Monitoring Materialien fur SchulerInnen, sieben ECM (European Citizenship Modules), Wissenstests, Portfolio fur Schuler und Hinweise fur Lehrer und speziell ein Portfolio fur den Lehrkorper. Die ECLIPSE Lehr / Testmaterialien wurden in mehreren Schulen und Schultypen der Partnerlander getestet. Es kann in flexibler Weise verwendet werden unter Berucksichtigung unterschiedlicher Lernbedurfnisse in jedem Schulsystem, um auch Querschnittskompetenzen wie Lernkompetenz und Eigeninitiative und aktive Mitarbeit zu fordern um die Chancen junger Menschen auf politische Partizipation und auf dem Arbeitsmarkt zu verbessern.

Exploring the spatial, temporal, and vertical distribution of methane in Pluto’s atmosphere

High-resolution spectra of Pluto in the 1.66μm region, recorded with the VLT/CRIRES instrument in 2008 (2 spectra) and 2012 (5 spectra), are analyzed to constrain the spatial and vertical distribution of methane in Pluto’s atmosphere and to search for mid-term (4year) variability. A sensitivity study to model assumptions (temperature structure, surface pressure, Pluto’s radius) is performed. Results indicate that (i) no variation of the CH4 atmospheric content (column-density or mixing ratio) with Pluto rotational phase is present in excess of 20%, (ii) CH4 column densities show at most marginal variations between 2008 and 2012, with a best guess estimate of a ∼20% decrease over this time frame. As stellar occultations indicate that Pluto’s surface pressure has continued to increase over this period, this implies a concomitant decrease of the methane mixing ratio (iii) the data do not show evidence for an altitude-varying methane distribution; in particular, they imply a roughly uniform mixing ratio in at least the first 22–27km of the atmosphere, and high concentrations of low-temperature methane near the surface can be ruled out. Our results are also best consistent with a relatively large (>1180km) Pluto radius. Comparison with predictions from a recently developed global climate model indicates that these features are best explained if the source of methane occurs in regional-scale CH4 ice deposits, including both low latitudes and high Northern latitudes, evidence for which is present from the rotational and secular evolution of the near-IR features due to CH4 ice. Our “best guess” predictions for the New Horizons encounter in 2015 are: a 1184km radius, a 17μbar surface pressure, and a 0.44% CH4 mixing ratio with negligible longitudinal variations.

Evidence that Pluto’s atmosphere does not collapse from occultations including the 2013 May 04 event

Combining stellar occultation observations probing Pluto’s atmosphere from 1988 to 2013, and models of energy balance between Pluto’s surface and atmosphere, we find the preferred models are consistent with Pluto retaining a collisional atmosphere throughout its 248-year orbit. The occultation results show an increasing atmospheric pressure with time in the current epoch, a trend present only in models with a high thermal inertia and a permanent N2 ice cap at Pluto’s north rotational pole.

Pluto’s climate modeled with new observational constraints

Pluto has a nitrogen atmosphere in vapor pressure equilibrium with surface ice. N2 is mobile and is transported seasonally even at Pluto’s cold temperatures in the outer Solar System. A thermal model developed by Hansen and Paige in 1996 to model Pluto’s climate has been re-deployed in response to new data and in anticipation of the New Horizons flyby of Pluto in 2015. A number of stellar occultations have been observed in the last 11years as Pluto has crossed the galactic plane. New Hubble Space Telescope images show a variegated surface. These recent observations allow us to model Pluto’s climate with much tighter constraints. Our findings suggest that Pluto’s atmosphere will not collapse prior to the arrival of New Horizons although pressure will be dropping as N2 condenses on the south polar cap. This finding is in contrast to the Olkin et al. (Olkin et al. [2013]. arXiv1309.0841O) prediction that permanent volatiles in the northern hemisphere maintain Pluto’s atmospheric pressure throughout its orbit. The range of surface pressures predicted for 2015 for nine cases with very good matches to observables is 0.3–3.2Pa. The best match predicts that New Horizons will detect an atmospheric pressure of 2.4Pa.

Ring in the new

Planets are no longer the only Solar System bodies sporting ring systems. Two dense rings have been detected encircling a Centaur object — a relatively small, icy interloper from the distant reaches of the Solar System. See Letter p.72 Observations of a stellar occultation by (10199) Chariklo, a Centaur-class outer-system asteroid orbiting between Saturn and Uranus, reveal that it has a ring system, a feature previously observed only for the four giant planets. Chariklo, with a diameter of about 250 km, has two narrow and dense rings separated by a small gap, probably due to the presence of a (yet-to-be-found) kilometre-sized satellite. The discovery of these rings raises questions about the formation and dynamical evolution of planetary rings. For one thing, it seems likely that planetary rings are much more common than previously thought.

A ring system detected around the Centaur (10199) Chariklo

Hitherto, rings have been found exclusively around the four giant planets in the Solar System. Rings are natural laboratories in which to study dynamical processes analogous to those that take place during the formation of planetary systems and galaxies. Their presence also tells us about the origin and evolution of the body they encircle. Here we report observations of a multichord stellar occultation that revealed the presence of a ring system around (10199) Chariklo, which is a Centaur--that is, one of a class of small objects orbiting primarily between Jupiter and Neptune--with an equivalent radius of 124 ± 9 kilometres (ref. 2). There are two dense rings, with respective widths of about 7 and 3 kilometres, optical depths of 0.4 and 0.06, and orbital radii of 391 and 405 kilometres. The present orientation of the ring is consistent with an edge-on geometry in 2008, which provides a simple explanation for the dimming of the Chariklo system between 1997 and 2008, and for the gradual disappearance of ice and other absorption features in its spectrum over the same period. This implies that the rings are partly composed of water ice. They may be the remnants of a debris disk, possibly confined by embedded, kilometre-sized satellites.

Transient atmospheres on Charon and water–ice covered KBOs resulting from comet impacts

Evidence from stellar occultation datasets and Charon’s H2O–ice dominated surface composition has long suggested a lack of any current atmosphere around this satellite planet. However, impacts from both Kuiper Belt and Oort Cloud comets must from time to time import N2, CH4, and other cometary super-volatiles that can create temporary atmospheres around Charon. Here we estimate the frequency of such cometary impacts on Charon and the imported mass of super-volatiles from each such impact. We then examine the characteristics of such transient atmospheric events, including their column densities, mean molecular weights, scale heights, and loss timescales. We then report on the detectability of such a transient atmosphere by New Horizons, and discuss the generalized case of cometary impact-created transient atmospheres on other satellites of Pluto and water–ice covered KBOs across the Kuiper Belt.

Self‐Sorting of Cyclic Peptide Homodimers into a Heterodimeric Assembly Featuring an Efficient Photoinduced Intramolecular Electron‐Transfer Process

We describe the thermodynamic characterisation of the self-sorting process experienced by two homodimers assembled by hydrogen-bonding interactions through their cyclopeptide scaffolds and decorated with Zn-porphyrin and fullerene units into a heterodimeric assembly that contains one electron-donor (Zn–porphyrin) and one electron-acceptor group (fullerene). The fluorescence of the Zn-porphyrin unit is strongly quenched upon heterodimer formation. This phenomenon is demonstrated to be the result of an efficient photoinduced electron-transfer (PET) process occurring between the Zn-porphyrin and the fullerene units of the heterodimeric system. The recombination lifetime of the charge-separated state of the heterodimer complex is in the order of 180 ns. In solution, both homo- and heterodimers are present as a mixture of three regioisomers: two staggered and one eclipsed. At the concentration used for this study, the high stability constant determined for the heterodimer suggests that the eclipsed conformer is the main component in solution. The application of the bound-state scenario allowed us to calculate that the heterodimer exists mainly as the eclipsed regioisomer (75-90 %). The attractive interaction that exists between the donor and acceptor chromophores in the heterodimeric assembly favours their arrangement in close contact. This is confirmed by the presence of charge-transfer bands centred at 720 nm in the absorption spectrum of the heterodimer. PET occurs in approximately 75% of the chromophores after excitation of both Zn-porphyrin and fullerene chromophores. Conversely, analogous systems, reported previously, decorated with extended tetrathiafulvalene and fullerene units showed a PET process in a significantly reduced extent (33%). We conclude that the strength (stability constant (K) x effective molarity (EM)) of the intramolecular interaction established between the two chromophores in the Zn-porphyrin/fullerene cyclopeptide-based heterodimers controls the regioisomeric distribution and regulates the high extent to which the PET process takes place in this system.

FINAL BINARY STAR RESULTS FROM THE ESO VLT LUNAR OCCULTATIONS PROGRAM

We report on 13 sub-arcsecond binaries, detected by means of lunar occultations in the near-infrared at the ESO Very Large Telescope. They are all first-time detections, except for the visual binary HD~158122 which we resolved for the first time in the near infrared. The primaries have magnitudes in the range $K$=4.5 to 10.0, and the companions in the range $K$=6.8 to 11.1. The magnitude differences have a median value of 2.4, with the largest being 4.6. The projected separations are in the range 4 to 168 milliarcseconds with a median of 13 milliarcseconds. We discuss and compare our results with the available literature. With this paper, we conclude the mining for binary star detections in the volume of 1226 occultations recorded at the VLT with the ISAAC instrument. We expect that the majority of these binaries may be unresolvable by adaptive optics on current telescopes, and they might be challenging for long-baseline interferometry. However they constitute an interesting sample for future larger telescopes and for astrometric missions such as GAIA.

Arts: Eclipse of power

Arts: Eclipse of power

An investigation of the temperature variations in Neptune’s upper stratosphere including a July 2008 stellar occultation event

We extracted physical atmospheric parameters from a 23 July 2008 single-chord stellar occultation of the star USNO-B1.0 0759-0739128 (I-band magnitude of 12.60) by Neptune using a light curve model fitting technique. We observed the occultation using the Agile CCD camera mounted on the Astrophysical Research Consortium 3.5m telescope at Apache Point Observatory. We found isothermal temperatures of 116.5± 12.0K and 154.0±13.0K for the immersion and emersion light curve profiles, respectively. We compare the stratospheric temperatures derived from the 2008 occultation to published temperatures of Neptune at similar atmospheric pressures derived from previous stellar occultations observed in the 1980s, and from long-term photometric measurements made routinely since the 1983–1990 occultation campaign. No obvious long-term temporal variation in stratospheric isothermal temperature is present. Fluctuations in the fitted isothermal temperature values, on the order of 20K, is evident. We explore several hypotheses to explain the observed temperature variability of Neptune’s stratosphere, including seasonal variability, variations in the Lyman-α flux received at Neptune due to the 11-year solar cycle, diurnal variations, varying insolation due to heliocentric variability, IR and UV heating by hydrocarbons, aerosol precipitation, inertia-gravity wave dissipation, and effects due to atmospheric tidal perturbations by Triton. We investigate the effects of these mechanisms on the gradual temporal changes of Neptune’s stratospheric temperature and conclude that local variations in stratospheric temperature during each event, on the order of 20K, are dominated by viscous dissipation of inertia-gravity waves.

An exploration of Pluto’s environment through stellar occultations

Context. Pluto has five known satellites with diameters ranging from ~1200 km down to ~40 km, a possible outcome of a collisional origin. Smaller objects probably exist and may maintain tenuous rings, thus representing hazards during the New Horizons flyby of July 2015. Aims. The goal is to provide an upper limit for the numbers of unseen small bodies and/or equivalent widths of putative Pluto rings. Methods. We use a Pluto stellar appulse on April 10, 2006, and a stellar occultation by the dwarf planet on June 14, 2007, to scan Pluto’s surroundings. Results. Our best data set places a 3σ upper limit of 0.3 km for the radius of isolated moonlets that we can detect. In the absence of detection, we derive an upper limit of 15 000 for the number of such bodies at distances smaller than ~70 000 km from Pluto’s system barycenter. We place a 3σ upper limit of typically 30−100 m for the equivalent width of ring material at barycentric distances ranging from 13 000 to 70 000 km. This limit applies for narrow rings only, i.e. less than about 10 km in width

A 3-D Shape Model of (704) Interamnia from Its Occultations and Lightcurves

A 3-D shape model of the sixth largest of the main belt asteroids, (704) Interamnia, is presented. The model is reproduced from its two stellar occultation observations and six lightcurves between 1969 and 2011. The first stellar occultation was the occultation of TYC 234500183 on 1996 December 17 observed from 13 sites in the USA. An elliptical cross section of (344.6 ± 9.6 km) × (306.2 ± 9.1 km), for position angle P = 73.4 ± 12.5° was fitted. The lightcurve around the occultation shows that the peak-to-peak amplitude was 0.04 mag. and the occultation phase was just before the minimum. The second stellar occultation was the occultation of HIP 036189 on 2003 March 23 observed from 39 sites in Japan and Hawaii. An elliptical cross section of (349.8 ± 0.9 km) × (303.7 ± 1.7 km), for position angle P = 86.0 ± 1.1° was fitted. A companion of 8.5 mag. of the occulted star was discovered whose separation is 12 ± 2 mas (milli-arcseconds), P = 148 ± 11°. A combined analysis of rotational lightcurves and occultation chords can return more information than can be obtained with either technique alone. From follow-up photometric observations of the asteroid between 2003 and 2011, its rotation period is determined to be 8.728967167 ± 0.00000007 hours, which is accurate enough to fix the rotation phases at other occultation events. The derived north pole is λ2000 = 259 ± 8°, β2000 = -50 ± 5° (retrograde rotation); the lengths of the three principal axes are 2a = 361.8 ± 2.8 km, 2b = 324.4 ± 5.0 km, 2c = 297.3 ± 3.5 km, and the mean diameter is D = 326.8 ± 3.0 km. Supposing the mass of Interamnia as (3.5 ± 0.9) × 10-11 solar masses, the density is then ρ = 3.8 ± 1.0 g·cm-3.

Conformation of hydroxyborane encapsulated within nanotubes

Nanotubes are known to influence the physicochemical parameters of the encapsulated molecules; properties of the latter may significantly differ from those of the free molecules [1–3]. In particular, it has been demonstrated recently that the eclipsed conformation is the favorable one in the case of ethane molecule inside the carbon nanotube, in contrast to the free ethane molecule with the favorable staggered conformation [4]. In this work, the PBE/3z DFT method (PRIRODA package [5]) was applied to study the barrier of internal rotation around the В–О bond in hydroxyborane H2BOH encapsulated within model single-wall nanotubes: С48Н12 (7.1 A long and 4.6 A in diameter, I) and С72Н12 (6.6 A long and 8.4 A in diameter, II) (see Schemes 1–3).

First principles calculations of solid phase transition of nitromethane

The solid phase transition in crystals prepared from molecular energetic materials under extreme conditions is important for understanding the detonation mechanisms. By applying the first principles density functional calculations, a detailed theoretical study of the lattice parameters and molecular structures, equations of state, densities of state for solid nitromethane is reported. By analyzing the pressure dependence of lattice parameters, a sudden change of the lattice parameters occurs between 10-12 GPa, implying that a transition has taken place. It is also found that the maximum dihedral angle of H-C-N-O has increased from 155.3° to 177.5°, indicating that a rotation of the methyl group from a staggered to an eclipsed conformation occurs in the pressure range 11–12 GPa. Before the phase transition, the intramolecular O … H–C interactions are mainly of hydrogen bonds. After the phase transition, the intramolecular and intermolecular O … H interactions are mainly of the hydrogen bonds. Phase transition also affects the reduced ratio of band gap and the density of state near the Fermi level.

Monnaie : quand la dette occulte le partage

L’article relève l’occultation du partage dans La Monnaie souveraine (1998) et les travaux qui s’en sont inspirés. Le néolibéralisme a rendu hégémonique une approche par la circulation de la monnaie et plus généralement de l’ensemble des faits sociaux. Or cette vision catallactique que des critiques de l’économie orthodoxe ont pu eux-mêmes soutenir, a éclipsé l’institution d’une hiérarchie de droits d’usage de biens communs au sein d’une société humaine.

Potassium trinickel(II) orthophosphate diphosphate, KNi3(PO4)P2O7

The structure of the title compound is characterized by the presence of two different anions, (PO4)3− and (P2O7)4− with an eclipsed conformation. The crystal structure consists of edge-sharing [NiO6] octa­hedra forming an [Ni3O14] chain running parallel to [001]. Adjacent chains are connected through edges and apices to PO4 and P2O7 groups in such a way as to build a three-dimensional host lattice. The resulting framework presents inter­secting tunnels running along [010] and [101] in which the 11-coordinated potassium cation is located. The crystal structure of this new phosphate probably represents a new structural type.

Candidate stellar occultations by Centaurs and trans-Neptunian objects up to 2014

Context. We study trans-Neptunian objects (TNOs) from stellar occultations.Aims. We predict stellar occultations from 2012.5 to the end of 2014 by 5 Centaurs and 34 TNOs.Methods. These predictions were achieved in two ways: first, we built catalogues with precise astrometric positions of the stellar content around the paths on the sky of these targets, as seen by a ground-based observer; second, the observed positions of the targets were determined with the help of these same catalogues so that we could improve their ephemerides and the reliability of the predictions. The reference system is the International Celestial Reference System (ICRS) as realised by the Fourth US Naval Observatory CCD Astrograph Catalog (UCAC4). All the sky paths as well as the selected targets were observed from Oct. 2011 to May 2013 with the ESO/MPG 2.2 m telescope equipped with the Wide Field Imager (WFI). All astrometric results were obtained with the platform for reduction of astronomical images automatically (PRAIA) after correcting the images for overscan, bias, and flatfield.Results. The catalogues with the stellar content around the sky path of each selected target are complete down to magnitude R = 19 and have an average positional accuracy of about 50 milliarcseconds. This same average accuracy also holds for the observed positions of the targets. In the catalogues from the sky paths, stellar proper motions for non-UCAC4 objects were derived from the combination of the current epoch WFI observations with either the 2MASS or the USNO-B1 catalogues. The offsets between the observed and (JPL) ephemeris positions of the targets frequently reach absolute values of some hundreds of milliarcseconds.Conclusions. We present here stellar occultation predictions for the selected 5 Centaurs and 34 TNOs from 2012.5 to the end of 2014. This work is also an extension of two previous prediction works by us, the first one for Pluto, Charon, Nix, and Hydra, and the second for ten other large TNOs. The use of catalogues from the observations of the sky paths in the astrometry of the TNOs and Centaurs enhanced the coherence between their positions and those of the respective occulted candidate stars. New observations of these TNOs and Centaurs are continuously used to redetermine their ephemerides.

First astronomical reference meridian in Norway

The first geodetic reference frame in Norway was established by triangulation 1779–1799. In 1785 the formal decision was made to establish the reference meridian in Trondheim. Latitude determinations had already been made in 1782–83 by observing meridian transits of the sun and stars with a geographical circle. Additional instruments were added to equip a small observatory. Time determinations were made with a transit instrument and pendulum clock. Lunar occultations and eclipses of the sun, moon, and Jovian satellites were observed with a Dollond refractor for longitude determination. This activity continued till 1791 when the instruments were transferred to Bergen to establish a control meridian there. We have searched archives in Denmark and Norway to recover original observations, correspondence, and other documents. This allows us to trace the history and to reanalyse observational data to determine statistical uncertainties and gain insight into systematic effects. Observing sites have been identified and allow comparison between historical results and modern GPS measurements.