Seabroke G.M.,University College London |
Seabroke G.M.,Open University Milton Keynes |
Prod'homme T.,European Space Agency |
Prod'homme T.,Leiden University |
And 6 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013
The European Space Agency (ESA) Gaia satellite has 106 CCD image sensors which will suffer from increased charge transfer inefficiency (CTI) as a result of radiation damage. To aid the mitigation at low signal levels, the CCD design includes supplementary buried channels (SBCs, otherwise known as 'notches') within each CCD column. We present the largest published sample of Gaia CCD SBC full well capacity (FWC) laboratory measurements and simulations based on 13 devices. We find that Gaia CCDs manufactured post-2004 have SBCs with FWCs in the upper half of each CCD that are systematically smaller by two orders of magnitude (<50 electrons) compared to those manufactured pre-2004 (thousands of electrons). Gaia's faint star (13 < G < 20 mag) astrometric performance predictions by Prod'homme et al. and Holl et al. use pre-2004 SBC FWCs as inputs to their simulations. However, all the CCDs already integrated on to the satellite for the 2013 launch are post-2004. SBC FWC measurements are not available for one of our five post-2004 CCDs but the fact that it meets Gaia's image location requirements suggests that it has SBC FWCs similar to pre-2004. It is too late to measure the SBC FWCs onboard the satellite and it is not possible to theoretically predict them. Gaia's faint star astrometric performance predictions depend on knowledge of the onboard SBC FWCs but as these are currently unavailable, it is not known how representative of the whole focal plane the current predictions are. Therefore, we suggest that Gaia's initial in-orbit calibrations should include measurement of the onboard SBC FWCs. We present a potential method to do this. Faint star astrometric performance predictions based on onboard SBC FWCs at the start of the mission would allow satellite operating conditions or CTI software mitigation to be further optimized to improve the scientific return of Gaia. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
Markiewicz W.J.,Max Planck Institute for Solar System Research |
Petrova E.,Space Research Institute |
Shalygina O.,Max Planck Institute for Solar System Research |
Almeida M.,ESA ESAC |
And 6 more authors.
Icarus | Year: 2014
We report on the implications of the observations of the glory phenomenon made recently by Venus Express orbiter. Glory is an optical phenomenon that poses stringent constraints on the cloud properties. These observations thus enable us to constrain two properties of the particles at the cloud tops (about 70 km altitude) which are responsible for a large fraction of the solar energy absorbed by Venus. Firstly we obtain a very accurate estimate of the cloud particles size to be 1.2 μm with a very narrow size distribution. We also find that for the two observations presented here the clouds are homogenous, as far as cloud particles sizes are concerned, on scale of at least 1200 km. This is in contrast to previous estimates that were either local, from entry probes data, or averaged over space and time from polarization data. Secondly we find that the refractive index for the data discussed here is higher than that of sulfuric acid previously proposed for the clouds composition (Hansen, J.E., Hovenier, J.W. . J. Atmos. Sci. 31, 1137-1160; Ragent, B. et al. . Adv. Space Res. 5, 85-115). Assuming that the species contributing to the increase of the refractive index is the same as the unknown UV absorber, we are able to constrain the list of candidates. We investigated several possibilities and argue that either small ferric chloride (FeCl3) cores inside sulfuric acid particles or elemental sulfur coating their surface are good explanations of the observation. Both ferric chloride and elemental sulfur have been suggested in the past as candidates for the as yet unknown UV absorber (Krasnopolsky, V.A. . Planet. Space Sci. 54, 1352-1359; Mills, F.P. et al. . In: Esposito, L.W., Stofan, E.R., Cravens, T.E. (Eds.), Exploring Venus as a Terrestrial Planet, vol. 176. AGU Monogr. Ser., Washington, DC, pp. 73-100). © 2014 Elsevier Inc.
Marchi S.,University of Nice Sophia Antipolis |
Massironi M.,University of Padua |
Vincent J.-B.,Max Planck Institute for Solar System Research |
Morbidelli A.,University of Nice Sophia Antipolis |
And 8 more authors.
Planetary and Space Science | Year: 2012
The European Space Agency's Rosetta spacecraft passed by the main belt asteroid (21) Lutetia on 10th July 2010. With its ∼100km size, Lutetia is one of the largest asteroids ever imaged by a spacecraft. During the flyby, the on-board OSIRIS imaging system acquired spectacular images of Lutetia's northern hemisphere revealing a complex surface scarred by numerous impact craters, reaching the maximum dimension of about 55 km. In this paper, we assess the cratering history of the asteroid. For this purpose, we apply current models describing the formation and evolution of main belt asteroids, that provide the rate and velocity distributions of impactors. These models, coupled with appropriate crater scaling laws, allow us to interpret the observed crater size-frequency distribution (SFD) and constrain the cratering history. Thanks to this approach, we derive the crater retention age of several regions on Lutetia, namely the time lapsed since their formation or global surface reset. We also investigate the influence of various factors - like Lutetia's bulk structure and crater obliteration - on the observed crater SFDs and the estimated surface ages. From our analysis, it emerges that Lutetia underwent a complex collisional evolution, involving major local resurfacing events till recent times. The difference in crater density between the youngest and oldest recognized units implies a difference in age of more than a factor of 10. The youngest unit (Beatica) has an estimated age of tens to hundreds of Myr, while the oldest one (Achaia) formed during a period when the bombardment of asteroids was more intense than the current one, presumably around 3.6 Gyr ago or older. © 2011 Elsevier Ltd.
Christou A.A.,Armagh Observatory |
Oberst J.,German Aerospace Center |
Oberst J.,TU Berlin |
Elgner S.,German Aerospace Center |
And 4 more authors.
Planetary and Space Science | Year: 2012
We investigate the expected performance of a wide-angle camera in Martian orbit, which, unlike previous cameras that have flown to Mars, is capable of recording meteor activity in that planets atmosphere. We show that, based on our current understanding of meteor physics and the interplanetary meteoroid population, several meteors will be detected by this instrument during a single nightside pass on a low Martian orbit. The instrument will also record the signatures of meteor showers expected to occur every Martian year (1.88 Earth years). The results of this investigation will test models of the flux of "large" (mm-cm) meteoroids at the orbit of Mars and their interaction with the Martian atmosphere. © 2011 Elsevier Ltd. All rights reserved.
Khatuntsev I.V.,Moscow Institute of Physics and Technology |
Patsaeva M.V.,Moscow Institute of Physics and Technology |
Titov D.V.,European Space Agency |
Titov D.V.,Max Planck Institute for Solar System Research |
And 7 more authors.
Icarus | Year: 2013
Six years of continuous monitoring of Venus by European Space Agency's Venus Express orbiter provides an opportunity to study dynamics of the atmosphere our neighbor planet. Venus Monitoring Camera (VMC) on-board the orbiter has acquired the longest and the most complete so far set of ultra violet images of Venus. These images enable a study the cloud level circulation by tracking motion of the cloud features. The highly elliptical polar orbit of Venus Express provides optimal conditions for observations of the Southern hemisphere at varying spatial resolution. Out of the 2300 orbits of Venus Express over which the images used in the study cover about 10 Venus years. Out of these, we tracked cloud features in images obtained in 127 orbits by a manual cloud tracking technique and by a digital correlation method in 576 orbits. Total number of wind vectors derived in this work is 45,600 for the manual tracking and 391,600 for the digital method. This allowed us to determine the mean circulation, its long-term and diurnal trends, orbit-to-orbit variations and periodicities. We also present the first results of tracking features in the VMC near-IR images. In low latitudes the mean zonal wind at cloud tops (67. ±. 2. km following: Rossow, W.B., Del Genio, A.T., Eichler, T. . J. Atmos. Sci. 47, 2053-2084) is about 90. m/s with a maximum of about 100. m/s at 40-50°S. Poleward of 50°S the average zonal wind speed decreases with latitude. The corresponding atmospheric rotation period at cloud tops has a maximum of about 5. days at equator, decreases to approximately 3. days in middle latitudes and stays almost constant poleward from 50°S. The mean poleward meridional wind slowly increases from zero value at the equator to about 10. m/s at 50°S and then decreases to zero at the pole. The error of an individual measurement is 7.5-30. m/s. Wind speeds of 70-80. m/s were derived from near-IR images at low latitudes. The VMC observations indicate a long term trend for the zonal wind speed at low latitudes to increase from 85. m/s in the beginning of the mission to 110. m/s by the middle of 2012. VMC UV observations also showed significant short term variations of the mean flow. The velocity difference between consecutive orbits in the region of mid-latitude jet could reach 30. m/s that likely indicates vacillation of the mean flow between jet-like regime and quasi-solid body rotation at mid-latitudes. Fourier analysis revealed periodicities in the zonal circulation at low latitudes. Within the equatorial region, up to 35°S, the zonal wind show an oscillation with a period of 4.1-5. days (4.83. days on average) that is close to the super-rotation period at the equator. The wave amplitude is 4-17. m/s and decreases with latitude, a feature of the Kelvin wave. The VMC observations showed a clear diurnal signature. A minimum in the zonal speed was found close to the noon (11-14. h) and maxima in the morning (8-9. h) and in the evening (16-17. h). The meridional component peaks in the early afternoon (13-15. h) at around 50°S latitude. The minimum of the meridional component is located at low latitudes in the morning (8-11. h). The horizontal divergence of the mean cloud motions associated with the diurnal pattern suggests upwelling motions in the morning at low latitudes and downwelling flow in the afternoon in the cold collar region. © 2013 Elsevier Inc.
Besse S.,European Space Agency |
Kuppers M.,ESA ESAC |
Barnouin O.S.,Johns Hopkins University |
Thomas N.,University of Bern |
Benkhoff J.,European Space Agency
Planetary and Space Science | Year: 2014
The European Space Agencys Rosetta spacecraft flew by asteroid (21) Lutetia on July 10, 2010. Observations through the OSIRIS camera have revealed many geological features. Lineaments are identified on the entire observed surface of the asteroid. Many of these features are concentric around the North Pole Crater Cluster (NPCC). As observed on (433) Eros and (4) Vesta, this analysis of Lutetia assesses whether or not some of the lineaments could be created orthogonally to observed impact craters. The results indicate that the orientation of lineaments on Lutetias surface could be explained by three impact craters: the Massilia and the NPCC craters observed in the northern hemisphere, and candidate crater Suspicio inferred to be in the southern hemisphere. The latter has not been observed during the Rosetta flyby. Of note, is that the inferred location of the Suspicio impact crater derived from lineaments matches locations where hydrated minerals have been detected from Earth-based observations in the southern hemisphere of Lutetia. Although the presence of these minerals has to be confirmed, this analysis shows that the topography may also have a significant contribution in the modification of the spectral shape and its interpretation. The cross-cutting relationships of craters with lineaments, or between lineaments themselves show that Massilia is the oldest of the three impact feature, the NPCC the youngest, and that the Suspicio impact crater is of intermediate age that is likely occurred closer in time to the Massilia event. © 2014 Elsevier Ltd.
Maiolino R.,University of Cambridge |
Gallerani S.,Normal School of Pisa |
Neri R.,Institute Of Radioastronomie Millimetrique Iram |
Cicone C.,University of Cambridge |
And 9 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012
Most theoretical models invoke quasar-driven outflows to quench star formation in massive galaxies, and this feedback mechanism is required to account for the population of old and passive galaxies observed in the local Universe. The discovery of massive, old and passive galaxies at z ~ 2 implies that such quasar feedback on to the host galaxy must have been at work very early on, close to the reionization epoch. We have observed the [C II] 158 μm transition in SDSS J114816.64+525150.3, which, at z = 6.4189, is one of the most distant quasars known. We detect broad wings of the line tracing a quasar-driven massive outflow. This is the most distant massive outflow ever detected and is likely tracing the long-sought quasar feedback, already at work in the early Universe. The outflow is marginally resolved on scales of ~ 16 kpc, implying that the outflow can really affect the whole galaxy, as required by quasar feedback models. The inferred outflow rate, M>3500 M ⊙yr -1, is the highest ever MTSY.-1.circledot found. At this rate, the outflow can clean the gas in the host galaxy, and therefore quench star formation, in a few million years. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.
Maquet L.,ESA ESAC |
Pierret F.,CNRS Time Space Reference Systems
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015
In recent work [L. Blanchet and J. Novak, Mon. Not. R. Astron. Soc. 412, 2530 (2011); L. Blanchet and J. Novak, Testing MOND in the Solar System (2011); and M. Milgrom, Mon. Not. R. Astron. Soc. 399, 474 (2009)], the authors showed that modified Newton dynamics (MOND) has a non-negligible secular perturbation effect on planets with large semimajor axes (gaseous planets) in the Solar System. Some comets also have a very eccentric orbit with a large semimajor axis (Halley family comets) going far away from the Sun (more than 15 AU) in a low acceleration regime where they would be subject to MOND perturbation. They also approach the Sun very closely (less than 3 AU) and are affected by the sublimation of ices from their nucleus, triggering so-called nongravitational forces. The main goal of this paper is to investigate the effect of MOND perturbation on three comets with various orbital elements (2P/Encke, 1P/Halley and 153P/Ikeya-Zhang) and then compare it to the nongravitational perturbations. It is motivated by the fact that when fitting an outgassing model for a comet, we have to take into account all of the small perturbing effects to avoid absorbing these effects into the nongravitational parameters. Otherwise, we could derive a completely wrong estimation of the outgassing. For this work, we use six different forms of MOND functions and compute the secular variations of the orbital elements due to MOND and nongravitational perturbations. We show that, for comets with large semimajor axis, the MONDian effects are not negligible compared to the nongravitational perturbations. © 2015 American Physical Society.
Aberasturi M.,CSIC - National Institute of Aerospace Technology |
Burgasser A.J.,University of California at San Diego |
Mora A.,ESA ESAC |
Solano E.,CSIC - National Institute of Aerospace Technology |
And 3 more authors.
Astronomical Journal | Year: 2014
We used Hubble Space Telescope/Wide Field Camera 3 (WFC3) observations of a sample of 26 nearby (≤20 pc) mid- to late T dwarfs to search for cooler companions and measure the multiplicity statistics of brown dwarfs (BDs). Tightly separated companions were searched for using a double point-spread-function-fitting algorithm. We also compared our detection limits based on simulations to other prior T5+ BD binary programs. No new wide or tight companions were identified, which is consistent with the number of known T5+ binary systems and the resolution limits of WFC3. We use our results to add new constraints to the binary fraction (BF) of T-type BDs. Modeling selection effects and adopting previously derived separation and mass ratio distributions, we find an upper limit total BF of <16% and <25% assuming power law and flat mass ratio distributions, respectively, which are consistent with previous results. We also characterize a handful of targets around the L/T transition. © 2014. The American Astronomical Society. All rights reserved.
Ponti G.,University Paris Diderot |
Ponti G.,University of Southampton |
Terrier R.,University Paris Diderot |
Goldwurm A.,University Paris Diderot |
And 4 more authors.
Astrophysical Journal | Year: 2010
We present the result of a study of the X-ray emission from the galactic center (GC) molecular clouds (MCs) within 15 arcmin from SgrA*. We use XMM-Newton data (about 1.2 Ms of observation time) spanning about eight years. The MC spectra show all the features characteristic of reflection: (1) intense Fe Kα, with equivalent width of about 0.7-1keV, and the associated Kβ line; (2) flat power-law continuum, and (3) a significant Fe K edge (τ ∼ 0.1-0.3). The diffuse low ionization Fe K emission follows the MC distribution, nevertheless not all MC are Fe K emitters. The long baseline monitoring allows the characterization of the temporal evolution of the MC emission. A complex pattern of variations is shown by the different MCs, with some having constant Fe K emission, some increasing, and some decreasing. In particular, we observe an apparent superluminal motion of a light front illuminating a molecular nebula. This might be due to a source outside the MC (such as SgrA* or a bright and long outburst of a X-ray binary), though it cannot be due to low energy cosmic rays or a source located inside the cloud. We also observe a decrease of the X-ray emission from G0.11-0.11, behavior similar to that of Sgr B2. The line intensities, clouds dimensions, columns densities, and positions with respect to SgrA* are consistent with being produced by the same SgrA* flare. The required high luminosity (about 1.5 × 1039 erg s-1) can hardly be produced by a binary system, while it is in agreement with a flare of SgrA* fading about 100 years ago. The low intensity of the Fe K emission coming from the 50 and the 20 km s-1 MC places an upper limit of 1036 erg s-1 to the mean luminosity of SgrA* in the last 60-90 years. The Fe K emission and variations from these MC might have been produced by a single flare of SgrA*. © 2010. The American Astronomical Society. All rights reserved.