Time filter

Source Type

Prieur J.-L.,University Of Toulouse Ups Omp Irap | Prieur J.-L.,French National Center for Scientific Research | Scardia M.,National institute for astrophysics | Pansecchi L.,National institute for astrophysics | And 3 more authors.
Astronomische Nachrichten | Year: 2014

We present relative astrometric measurements of visual binaries, made in 2012 with the speckle camera PISCO at the 102-cm Zeiss telescope of Brera Astronomical Observatory, in Merate. Our observing list contains orbital couples as well as binaries whose motion is still uncertain. We obtained 355 new measurements of 344 visual binary stars, with angular separations in the range 0'.14-6'.9, and an average accuracy of 0.'02. The mean error on the position angles is 0°.5. Most of the position angles were determined without the usual 180° ambiguity with the application of triple-correlation techniques and/or by inspection of the long integration files. We also present new revised orbits for ADS 10786 BC, 12144, 12515, 16314, and 16539, partly derived from PISCO observations. The corresponding estimated values for the masses of those systems are compatible with the spectral types. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Lannes A.,University Paris - Sud | Lannes A.,Supelec | Prieur J.-L.,University Of Toulouse Ups Omp Irap | Prieur J.-L.,French National Center for Scientific Research
Astronomische Nachrichten | Year: 2014

Recent theoretical developments in astronomical aperture synthesis have revealed the existence of integer-ambiguity prob-lems. Those problems, which appear in the self-calibration procedures of radio imaging, have been shown to be similar to the nearest-lattice point (NLP) problems encountered in high-precision geodetic positioning and in global navigation satellite systems. In this paper we analyse the theoretical aspects of the matter and propose new methods for solving those NLP problems. The related optimization aspects concern both the preconditioning stage, and the discrete-search stage in which the integer ambiguities are finally fixed. Our algorithms, which are described in an explicit manner, can easily be implemented. They lead to substantial gains in the processing time of both stages. Their efficiency was shown via intensive numerical tests. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Scardia M.,National institute for astrophysics | Prieur J.-L.,University Of Toulouse Ups Omp Irap | Prieur J.-L.,French National Center for Scientific Research | Pansecchi L.,National institute for astrophysics | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present relative astrometric measurements of visual binaries, made in 2011 with the Pupil Interferometry Speckle camera and COronagraph (PISCO) at the 102-cm Zeiss telescope of the Brera Astronomical Observatory in Merate (Italy). Our observing list contains orbital couples as well as binaries whose motion is still uncertain. We obtained new measurements of 469 objects, with angular separations in the range 0.14-8.1 arcsec, and an average accuracy of 0.02 arcsec. The mean error on the position angles is 0°.7. Most of the position angles were determined without the usual 180° ambiguity with the application of triple-correlation techniques and/or by inspection of the long integration files. Thanks to a newlow-magnification option included in PISCO, we have been able to observe fainter stars than previously. The limiting magnitude of our instrumentation on the Zeiss telescope is now close to mV = 10-12, which permits the observation of some red dwarfs. Finally, we present new revised orbits for ADS8739, 9182 Aa, Ab, 9626 Ba, Bb, 12880 and 14412, partly derived from those observations. The corresponding estimated values for the masses of those systems are compatible with the spectral types. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Scardia M.,National institute for astrophysics | Prieur J.-L.,University Of Toulouse Ups Omp Irap | Prieur J.-L.,French National Center for Scientific Research | Pansecchi L.,National institute for astrophysics | And 2 more authors.
Astronomische Nachrichten | Year: 2011

We present relative astrometric measurements of visual binaries, made in 2009 with the speckle camera PISCO at the 102 cm Zeiss telescope of Brera Astronomical Observatory, in Merate. Our observing list contains orbital couples as well as binaries whose motion is still uncertain. We obtained 345 new measurements of 259 objects, with angular separations in the range 0.″18-4.″6, and an average accuracy of 0.″011. The mean error on the position angles is 0.°6. Most of the position angles were determined without the usual 180° ambiguity with the application of triple-correlation techniques and/or by inspection of the long integration files. We have found a possible new close component for ADS 2377, which would be a new quadruple star system. We also present new revised orbits for ADS 8035, 9982, 11484, and MLR 198, partly derived from those observations, and infer estimated values for the masses of those systems that are compatible with the spectral types © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Lannes A.,University Paris - Sud | Prieur J.-L.,University Of Toulouse Ups Omp Irap
Journal of Geodesy | Year: 2013

In global navigation satellite systems (GNSS), the problem of retrieving clock-phase biases from network data has a basic rank defect. We analyse the different ways of removing this rank defect, and define a particular strategy for obtaining these phase biases in a standard form. The minimum-constrained problem to be solved in the least-squares (LS) sense depends on some integer vector which can be fixed in an arbitrary manner. We propose to solve the problem via an undifferenced approach based on the notion of closure ambiguity. We present a theoretical justification of this closure-ambiguity approach (CAA), and the main elements for a practical implementation. The links with other methods are also established. We analyse all those methods in a unified interpretative framework, and derive functional relations between the corresponding solutions and our CAA solution. This could be interesting for many GNSS applications like real-time kinematic PPP for instance. To compare the methods providing LS estimates of clock-phase biases, we define a particular solution playing the role of reference solution. For this solution, when a phase bias is estimated for the first time, its fractional part is confined to the one-cycle width interval centred on zero; the integer-ambiguity set is modified accordingly. Our theoretical study is illustrated with some simple and generic examples; it could have applications in data processing of most GNSS networks, and particularly global networks using GPS, Glonass, Galileo, or BeiDou/Compass satellites. © 2013 European Union.


PubMed | Southwest Research Institute, University of Michigan, Max Planck Institute for Solar System Research, Aix - Marseille University and 10 more.
Type: Journal Article | Journal: Nature | Year: 2015

The composition of the neutral gas comas of most comets is dominated by H2O, CO and CO2, typically comprising as much as 95 per cent of the total gas density. In addition, cometary comas have been found to contain a rich array of other molecules, including sulfuric compounds and complex hydrocarbons. Molecular oxygen (O2), however, despite its detection on other icy bodies such as the moons of Jupiter and Saturn, has remained undetected in cometary comas. Here we report in situ measurement of O2 in the coma of comet 67P/Churyumov-Gerasimenko, with local abundances ranging from one per cent to ten per cent relative to H2O and with a mean value of 3.80 0.85 per cent. Our observations indicate that the O2/H2O ratio is isotropic in the coma and does not change systematically with heliocentric distance. This suggests that primordial O2 was incorporated into the nucleus during the comets formation, which is unexpected given the low upper limits from remote sensing observations. Current Solar System formation models do not predict conditions that would allow this to occur.

Loading University Of Toulouse Ups Omp Irap collaborators
Loading University Of Toulouse Ups Omp Irap collaborators