Eclipse Research Articles

New benzene absorption cross sections in the VUV, relevance for Titan’s upper atmosphere

Benzene is an important molecule in Titan’s atmosphere because it is a potential link between the gas phase and the organic solid phase. We measured photoabsorption in the ultraviolet by benzene gas at temperatures covering the range from room temperature to 215K. We derived benzene absorption cross sections and analyzed them in terms of the transitions observed. No significant variation with measurement temperature was observed. We discuss the implications of our measurements for the derivation of benzene abundance profiles in Titan’s thermosphere, by the Cassini/Ultraviolet Imaging Spectrograph (UVIS). The use of absorption cross sections at low temperature is recommended to avoid small systematic uncertainties in the profiles. We used our measurements, together with absorption cross sections from other molecules, to analyze four stellar occultations by Titan, measured by UVIS during flybys T21, T41, T41_II, and T53. We derived and compared benzene abundance profiles in Titan’s thermosphere between approximately 530 and 1000km, for different dates and geographical locations. The comparisons of our benzene profiles with each other, and with profiles from models of the upper atmosphere, point to a complex behavior that is not explained by current photochemical models.

PLUTO’s ATMOSPHERE FROM STELLAR OCCULTATIONS IN 2012 AND 2013

We analyze two multi-chord stellar occultations by Pluto observed on July 18th, 2012 and May 4th, 2013, and monitored respectively from five and six sites. They provide a total of fifteen light-curves, twelve of them being used for a simultaneous fit that uses a unique temperature profile, assuming a clear (no-haze) and pure N_2 atmosphere, but allowing for a possible pressure variation between the two dates. We find a solution that fits satisfactorily (i.e. within the noise level) all the twelve light-curves, providing atmospheric constraints between ~1,190 km (pressure ~ 11 \mubar) and ~ 1,450 km (pressure ~0.1 \mubar) from Pluto's center. Our main results are: (1) the best-fitting temperature profile shows a stratosphere with strong positive gradient between 1,190 km (at 36 K, 11 \mubar) and r = 1,215 km (6.0 \mubar), where a temperature maximum of 110 K is reached; above it is a mesosphere with negative thermal gradient of -0.2 K/km up to ~ 1,390 km (0.25 \mubar), where, the mesosphere connects itself to a more isothermal upper branch around 81 K; (2) the pressure shows a small (6 %) but significant increase (6-\sigma level) between the two dates; (3) without troposphere, Pluto's radius is found to be R_P = 1,190 +/- 5km. Allowing for a troposphere, R_P is constrained to lie between 1,168 and 1,195 km; (4) the currently measured CO abundance is too small to explain the mesospheric negative thermal gradient. Cooling by HCN is possible, but only if this species is largely saturated; Alternative explanations like zonal winds or vertical compositional variations of the atmosphere are unable to explain the observed mesospheric trend.

VLT/SPHERE- and ALMA-based shape reconstruction of asteroid (3) Juno

We use the recently released Atacama Large Millimeter Array (ALMA) and VLT/SPHERE science verification data, together with earlier adaptive-optics images, stellar occultation, and lightcurve data to model the 3D shape and spin of the large asteroid (3) Juno with the all-data asteroid modelling (ADAM) procedure. These data set limits on the plausible range of shape models, yielding reconstructions suggesting that, despite its large size, Juno has sizable unrounded features moulded by non-gravitational processes such as impacts.

GOMOS bright limb ozone data set

Abstract. We have created a daytime ozone profile data set from the measurements of the Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument on board the Envisat satellite. This so-called GOMOS bright limb (GBL) data set contains ∼ 358 000 stratospheric daytime ozone profiles measured by GOMOS in 2002–2012. The GBL data set complements the widely used GOMOS nighttime data based on stellar occultation measurements. The GBL data set is based on the GOMOS daytime occultations but instead of the transmitted star light we use limb-scattered solar light. The ozone profiles retrieved from these radiance spectra cover the 18–60 km altitude range and have approximately 2–3 km vertical resolution. We show that these profiles are generally in better than 10 % agreement with the NDACC (Network for the Detection of Atmospheric Composition Change) ozonesonde profiles and with the GOMOS nighttime, MLS (Microwave Limb Sounder), and OSIRIS (Optical Spectrograph and InfraRed Imager System) satellite measurements. However, there is a 10–13 % negative bias at 40 km altitude and a 10–50 % positive bias at 50 km for solar zenith angles > 75°. These biases are most likely caused by stray light which is difficult to characterize and to remove entirely from the measured spectra. Nevertheless, the GBL data set approximately doubles the amount of useful GOMOS ozone profiles and improves coverage of the summer pole.

“Genomical” Set to Eclipse “Astronomical”

Clinical OMICsVol. 2, No. 8 NEWS“Genomical” Set to Eclipse “Astronomical”Published Online:27 Oct 2015https://doi.org/10.1089/clinomi.02.08.03AboutSectionsView articleView Full TextPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail View articleFiguresReferencesRelatedDetails Volume 2Issue 8Aug 2015 InformationCopyright © GEN PublishingTo cite this article:“Genomical” Set to Eclipse “Astronomical”.Clinical OMICs.Aug 2015.7, 16.http://doi.org/10.1089/clinomi.02.08.03Published in Volume: 2 Issue 8: October 27, 2015PDF download

Astrometric positions for 18 irregular satellites of giant planets from 23 years of observations

The irregular satellites of the giant planets are believed to have been captured during the evolution of the solar system. Knowing their physical parameters, such as size, density, and albedo is important for constraining where they came from and how they were captured. The best way to obtain these parameters are observations in situ by spacecrafts or from stellar occultations by the objects. Both techniques demand that the orbits are well known. We aimed to obtain good astrometric positions of irregular satellites to improve their orbits and ephemeris. We identified and reduced observations of several irregular satellites from three databases containing more than 8000 images obtained between 1992 and 2014 at three sites (Observat\'orio do Pico dos Dias, Observatoire de Haute-Provence, and European Southern Observatory - La Silla). We used the software PRAIA (Platform for Reduction of Astronomical Images Automatically) to make the astrometric reduction of the CCD frames. The UCAC4 catalog represented the International Celestial Reference System in the reductions. Identification of the satellites in the frames was done through their ephemerides as determined from the SPICE/NAIF kernels. Some procedures were followed to overcome missing or incomplete information (coordinates, date), mostly for the older images. We managed to obtain more than 6000 positions for 18 irregular satellites: 12 of Jupiter, 4 of Saturn, 1 of Uranus (Sycorax), and 1 of Neptune (Nereid). For some satellites the number of obtained positions is more than 50\% of what was used in earlier orbital numerical integrations. Comparison of our positions with recent JPL ephemeris suggests there are systematic errors in the orbits for some of the irregular satellites. The most evident case was an error in the inclination of Carme.

Saturn’s variable thermosphere from Cassini/UVIS occultations

We retrieved the density and temperature profiles in Saturn’s thermosphere from 26 stellar occultations observed by the Cassini/UVIS instrument. These results expand upon and complement the previous analysis of 15 Cassini/UVIS solar occultations by Saturn’s upper thermosphere. We find that the exospheric temperatures based on the stellar occultations agree with the solar occultations and range from 380K to 590K. These temperatures are also consistent with the recent re-analysis of the Voyager/UVS occultations. The retrieved density profiles support our earlier inference that the shape of the atmosphere at low pressures is consistent with a meridional trend of increasing temperatures with absolute latitude. This implies a high-latitude heat source, such as auroral heating, although the existing circulation models that include auroral heating still underestimate the equatorial temperatures by overestimating the meridional temperature gradient. This suggests either that the circulation models are somehow incomplete or there is some other heat source at low to mid latitudes that is relatively less efficient than high-latitude heating. We also find evidence for the expansion of the exobase by about 500km between 2006 and 2011 near the equator, followed by possible contraction after 2011. The expansion appears to be caused by significant warming of the lower thermosphere that anti-correlates with solar activity and may be connected to changes in global circulation. Lastly, we note that our density profiles are in good general agreement with the Voyager/UVS data. In particular, the Voyager density profiles are most consistent with the Cassini/UVIS stellar occultations from late 2008 and early 2009 that roughly coincide in season with the Voyager flybys.

Results of two multichord stellar occultations by dwarf planet (1) Ceres

We report the results of two multi-chord 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 $\pm$ 6 km and an apparent oblateness of 0.08 $\pm$ 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.

Saturn’s upper atmosphere during the Voyager era: Reanalysis and modeling of the UVS occultations

The Voyager 1 and 2 Ultraviolet Spectrometer (UVS) solar and stellar occultation dataset represents one of the primary, pre-Cassini sources of information that we have on the neutral upper atmosphere of Saturn. Despite its importance, however, the full set of occultations has never received a consistent, nor complete, analysis, and the results derived from the initial analyses over thirty years ago left questions about the temperature and density profiles unanswered. We have reanalyzed all six of the UVS occultations (three solar and three stellar) to provide an up-to-date, pre-Cassini view of Saturn’s upper atmosphere. From the Voyager UVS data, we have determined vertical profiles for H2, H, CH4, C2H2, C2H4, and C2H6, as well as temperature. Our analysis also provides explanations for the two different thermospheric temperatures derived in earlier analyses (400–450K versus 800K) and for the unusual shape of the total density profile noted by Hubbard et al. (1997). Aside from inverting the occultation data to retrieve densities and temperatures, we have investigated the atmospheric structure through a series of photochemical models to infer the strength of atmospheric mixing and other physical and chemical properties of Saturn’s mesopause region during the Voyager flybys. We find that the data exhibit considerable variability in the vertical profiles for methane, suggesting variations in vertical winds or the eddy diffusion coefficient as a function of latitude and/or time in Saturn’s upper atmosphere. The results of our reanalysis will provide a useful baseline for interpreting new data from Cassini, particularly in the context of change over the past three decades.

Eclipsing Aestheticism: Western Landscape Photography After Ansel Adams

Bien que l’heritage photographique d’Ansel Adams (1902-84) reste incontestable dans la culture de masse, dans les musees et parmi les collectionneurs, la nature de cet heritage fait debat parmi les artistes contemporains, les chercheurs et les theoriciens de la photographie. Pour certains, a la fin du 20eme siecle, les paysages typiques de Adams representant l’Ouest americain au milieu du siecle designaient une connivence secrete avec l’expansion americaine vers l’ouest durant la guerre froide, meme si dans le meme temps, son nom etait associe a un type de photographie de paysage esthetisee et depolitisee. Pour leur part, les photographes contemporains sont attires par l’esthetique du paysage, si en plus ils sont animes de considerations politiques et environnementales. Cet article analyse certaines des failles qui se font jour dans l’heritage d’Ansel Adams dans le domaine de la photographie de paysage par des artistes qui prennent en compte les problemes politiques et environnementaux de l’Ouest global.

Refraction in planetary atmospheres: improved analytical expressions and comparison with a new ray-tracing algorithm

Atmospheric refraction affects to various degrees exoplanet transit, lunar eclipse, as well as stellar occultation observations. Exoplanet retrieval algorithms often use analytical expressions for the column abundance along a ray traversing the atmosphere as well as for the deflection of that ray, which are first-order approximations valid for low densities in a spherically symmetric homogeneous isothermal atmosphere. We derive new analytical formulae for both of these quantities, which are valid for higher densities, and use them to refine and validate a new ray-tracing algorithm which can be used for arbitrary atmospheric temperature–pressure profiles. We illustrate with simple isothermal atmospheric profiles the consequences of our model for different planets: temperate Earth-like and Jovian-like planets, as well as HD 189733b, and GJ1214b. We find that, for both hot exoplanets, our treatment of refraction does not make much of a difference to pressures as high as 10 atm, but that it is important to consider the variation of gravity with altitude for GJ1214b. However, we find that the temperate atmospheres have an apparent scaleheight significantly smaller than their actual density scaleheight at densities larger than 1 amagat, thus increasing the difficulty of detecting spectral features originating in these regions. These denser atmospheric regions form a refractive boundary layer where column abundances and ray deflection increases dramatically with decreasing impact parameter. This refractive boundary layer mimics a surface, and none of the techniques mentioned above can probe atmospheric regions denser than about 4 amagat on these temperate planets.

Computational studies of π–π interactions in dimers of heterosubstituted sumanenes

A computational study of dimers of heterosubstituted sumanenes has been carried out using a dispersion-corrected density functional theory method. In the heterosubstituted systems, the three bridging CH2 groups of sumanene have been replaced by O, NH, and S. For each dimer system, two motifs, staggered and eclipsed forms, were considered. The most stable geometry was the staggered stacked concave–convex motif where one monomer was rotated by 60° from the eclipsed configuration. The calculated binding energies and equilibrium distances of the staggered concave–convex dimers are predicted to be 20.1 kcal/mol and 3.7 A for the parent sumanene molecule, 17.4 kcal/mol and 3.8 A, 12.3 kcal/mol and 3.7 A, and 16.6 kcal/mol and 3.7 A for the NH-, O-, and S-substituted analogs, respectively. The binding energies of the dimers have been analyzed in terms of dipole–dipole contributions, dispersion contributions, and C–H···π interactions.

Eclipse proof of relativity

Eclipse proof of relativity

Celestial shadows: eclipses, transits, and occultations

Preface.- Part I. The Diversity of Eclipse Events.- Eclipse Phenomena.- The Waltz of the Planets.- The Performers.- Part II. A Transit Chronicle.- The Beginnings.- Scaling the Heavens.- A Century of Progress and Disappointment - and Completion.- Our Own Venus Transit - The June Flowers of 2004.- Part III. 2012 - Our Last Chance for a Venus Transit.- The 2012 Event.- Observing the 2012 Transit.- Mercury also Transits the Sun.- Transits Galore.- The Splendor of a Solar Eclipse.- The Beauty of a Lunar Eclipse.- Planetary Satellites.- Occultations - When Blocking the View is Helpful.- Appendices.- References.- Index.

Demonstration platform for collaborative design of space science missions

There are several problems during the demonstration process of collaborative design of space science missions,such as strong coupling between sub-system solutions,poor data consistency,difficulty in data modification,and associated relationship between data and demonstration process. In order to solve these problems,a multi-layer digital model for typical space missions was proposed. The demonstration process was graphically modeled,and the mapping between the process and data was established. The shared data pool was provided as the data collaboration mechanism for all users and all sub-system solutions. The message bus was adopted as the timely reminder to notify the changes of data. The design solution coupling matrix was used to describe the coupling relationship between sub-system solutions and to gain the system solution for the missions by the automatically merged method. The demonstration platform,as a distributed platform for the collaborative design of space science missions,uses the technology architecture of Eclipse RCP and Spring and integrates the middlewares of Hibernate and Activiti5. The platform can provide a unified portal and support multiuser,multi-mission,multi-solution and multi-version data management,and also support process monitor and data interactive collaboration. A space mission was used as an example to verify the efficacy of the platform.

Lunar occultation of the diffuse radio sky: LOFAR measurements between 35 and 80 MHz

We present radio observations of the Moon between $35$ and $80$ MHz to demonstrate a novel technique of interferometrically measuring large-scale diffuse emission extending far beyond the primary beam (global signal) for the first time. In particular, we show that (i) the Moon appears as a negative-flux source at frequencies $35<\nu<80$ MHz since it is `colder' than the diffuse Galactic background it occults, (ii) using the (negative) flux of the lunar disc, we can reconstruct the spectrum of the diffuse Galactic emission with the lunar thermal emission as a reference, and (iii) that reflected RFI (radio-frequency interference) is concentrated at the center of the lunar disc due to specular nature of reflection, and can be independently measured. Our RFI measurements show that (i) Moon-based Cosmic Dawn experiments must design for an Earth-isolation of better than $80$ dB to achieve an RFI temperature $<1$ mK, (ii) Moon-reflected RFI contributes to a dipole temperature less than $20$ mK for Earth-based Cosmic Dawn experiments, (iii) man-made satellite-reflected RFI temperature exceeds $20$ mK if the aggregate cross section of visible satellites exceeds $80$ m$^2$ at $800$ km height, or $5$ m$^2$ at $400$ km height. Currently, our diffuse background spectrum is limited by sidelobe confusion on short baselines (10-15% level). Further refinement of our technique may yield constraints on the redshifted global $21$-cm signal from Cosmic Dawn ($40>z>12$) and the Epoch of Reionization ($12>z>5$).

Long-term variability of CO2and O in the Mars upper atmosphere from MRO radio science data

We estimate the annual variability of CO2 and O partial density using approximately 6 years of Mars Reconnaissance Orbiter (MRO) radio science data from August 2006 to January 2012, which cover three full Martian years (from the northern hemisphere summer of 28 to the northern hemisphere summer of 31). These two elements are the dominant species at the MRO periapsis altitude, constituting about 70–80% of the total density. We report the recovered annual cycle of CO2 and the annual and seasonal cycle of O in the upper atmosphere. Although no other observations are available at those altitudes, our results are in good agreement with the density measurements of the Mars Express Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars, which uses stellar occultations between 60 and 130 km to determine the CO2 variability, and with the Mars Global Reference Atmospheric Model 2010 for the O annual and seasonal variabilities. Furthermore, the updated model provides more reasonable MRO drag coefficients (CD), which are estimated to absorb mismodeling in the atmospheric density prediction. The higher content of dust in the atmosphere due to dust storms increases the density, so the CDs should compensate for this effect. The correlation between the drag coefficient and the dust optical depth, measured by the Mars Odyssey Thermal Emission Imaging System (THEMIS) instrument, increases from 0.4 to 0.8 with the a priori and adjusted models, respectively. The trend of CDs not only confirms a substantial improvement in the prediction of the atmospheric density with the updated model but also provides useful information for local dust storms, near MRO periapsis, that cannot be measured by the opacity level since THEMIS does not always sample the southern hemisphere evenly.

Crystal structure of bis-[4-(1H-pyrrol-1-yl)phen-yl] ferrocene-1,1'-di-carboxyl-ate: a potential chemotherapeutic drug.

The title iron(II) complex, [Fe(C16H12NO2)2], crystallizes in the ortho-rhom-bic space group Pbca with the Fe(2+) cation positioned on an inversion center. The cyclo-penta-dienyl (Cp) rings adopt an anti conformation in contrast with other substituted ferrocenes in which the Cp rings appear in a nearly eclipsed conformation. The Cp and the aromatic rings are positioned out of the plane, with a twist angle of 70.20 (12)°, and the C(Cp)-C(CO) bond length is shorter than a typical C-C single bond, which suggests a partial double-bond character and delocalization with the Cp π system. The structure of the complex is compared to other functionalized ferrocenes synthesized in our laboratory.

First record of Coleopterophagus albini Haitlinger 1990 (Acari: Astigmata: Canestriniidae) from Estonia and Norway

The genus Coleopterophagus contains nine species: C. megnini (Berlese) known from Czech Republic, Croatia, England, Holland, Hungary, Italy, Poland, Serbia (Syrmia), Turkey and Ukraine, C. albini Haitlinger from Austria, Czech Republic, Germany, Poland, Romania and Ukraine, C. baali Haitlinger from Iran, C. belzebubi Haitlinger from China, Japan and Taiwan, C. dionizyi Haitlinger from Syria, C. donaldi Haitlinger from Italy and Ukraine, C. maroni Haitlinger from Romania, Syria and Ukraine and C. rudolfi Haitlinger from China. All these species are associated only with hosts belonging to the Protaetia Burmeister (Coleoptera, Scarabaeidae, Cetoniinae) (Berlese 1882, Cooreman 1954, Haitlinger 1988, 1990, 2002, 2012, Khaustov and Eidelberg 2001, Trach 2006, Trach and Khaustov 2011). Now, C. albini is found for the first time in Estonia and Norway. In Europe, only C. megnini and C. albini were noted in middle Europe in Germany and Poland. Localities of C. albini in Estonia and Norway placed farthest on north of Europe for species of the genus Coleopterophagus and in general for canestriniid mites. Flower beetles were collected during 8 July 1998 in Norway and 10 July 2009 in Estonia. Mites collected from Protartia (Potosia) metallica were mounted on microscopic slides in Berlese’s medium. Mites are studied using microscope NIKON Eclipse 50i. The terminology of idiosomal and leg chaetotaxy follow Grandjean (1939), Griffiths et al. (1990) and Norton (1998). Measurements are given in micrometers (μm).

High angular resolution stellar imaging with occultations from the Cassini spacecraft – II. Kronocyclic tomography

We present an advance in the use of Cassini observations of stellar occultations by the rings of Saturn for stellar studies. Stewart et al. (2013) demonstrated the potential use of such observations for measuring stellar angular diameters. Here, we use these same observations, and tomographic imaging reconstruction techniques, to produce two dimensional images of complex stellar systems. We detail the determination of the basic observational reference frame. A technique for recovering model-independent brightness profiles for data from each occulting edge is discussed, along with the tomographic combination of these profiles to build an image of the source star. Finally we demonstrate the technique with recovered images of the {\alpha} Centauri binary system and the circumstellar environment of the evolved late-type giant star, Mira.