Publications


Spatial and seasonal variations in C<inf>3</inf>H<inf>x</inf>hydrocarbon abundance in Titan's stratosphere from Cassini CIRS observations

Icarus 317 (2019) 454-469

NA Lombardo, CA Nixon, RK Achterberg, A Jolly, K Sung, PGJ Irwin, FM Flasar

© 2018 Of the C3Hxhydrocarbons, propane (C3H8) and propyne (methylacetylene, CH3C2H) were first detected in Titan's atmosphere during the Voyager 1 flyby in 1980. Propene (propylene, C3H6) was first detected in 2013 with data from the Composite InfraRed Spectrometer (CIRS) instrument on Cassini. We present the first measured abundance profiles of propene on Titan from radiative transfer modeling, and compare our measurements to predictions derived from several photochemical models. Near the equator, propene is observed to have a peak abundance of 10 ppbv at a pressure of 0.2 mbar. Several photochemical models predict the amount at this pressure to be in the range 0.3–1 ppbv and also show a local minimum near 0.2 mbar which we do not see in our measurements. We also see that propene follows a different latitudinal trend than the other C3molecules. While propane and propyne concentrate near the winter pole, transported via a global convective cell, propene is most abundant above the equator. We retrieve vertical abundances profiles between 125 km and 375 km for these gases for latitude averages between 60°S–20°S, 20°S–20°N, and 20°N–60°N over two time periods, 2004 through 2009 representing Titan's atmosphere before the 2009 equinox, and 2012 through 2015 representing time after the equinox. Additionally, using newly corrected line data, we determined an updated upper limit for allene (propadiene, CH2CCH2, the isomer of propyne). We claim a 3-σ upper limit mixing ratio of 2.5 × 10−9 within 30° of the equator. The measurements we present will further constrain photochemical models by refining reaction rates and the transport of these gases throughout Titan's atmosphere.


Neptune's carbon monoxide profile and phosphine upper limits from Herschel/SPIRE: Implications for interior structure and formation

Icarus 319 (2019) 86-98

NA Teanby, PGJ Irwin, JI Moses

© 2018 On Neptune, carbon monoxide and phosphine are disequilibrium species, and their abundance profiles can provide insights into interior processes and the external space environment. Here we use Herschel/SPIRE (Spectral and Photometric Imaging REceiver) observations from 14.9–51.5 cm-1to obtain abundances from multiple CO and PH3spectral features. For CO, we find that nine CO bands can be simultaneously fitted using a step profile with a 0.22 ppm tropospheric abundance, a 1.03 ppm stratospheric abundance, and a step transition pressure of 0.11 bar near the tropopause. This is in broad agreement with previous studies. However, we also find that the CO spectral features could be fitted, to well within measurement errors, with a profile that contains no tropospheric CO for pressure levels deeper than 0.5 bar, which is our preferred interpretation. This differs from previous studies that have assumed CO is well mixed throughout the troposphere, which would require an internal CO source to explain and a high O/H enrichment. Our interpretation removes the requirement for extreme interior O/H enrichment in thermochemical models and can finally reconcile D/H and CO measurements. If true, the lack of lower tropospheric CO would imply a decrease in Neptune's interior water content, favouring a silicate-rich instead of an ice-rich interior. This would be consistent with a protoplanetary ice source with a similar D/H ratio to the current solar system comet population. The upper tropospheric and stratospheric CO at pressures less than 0.5 bar could then be entirely externally sourced from a giant impact as suggested by Lellouch et al.(2005). We also derive a 3-σ upper limit for PH3of 1.1 ppb at 0.4–0.8 bar. This is the most stringent upper limit to-date and is entirely consistent with predictions from a simple photochemical model.


Assessing the long-term variability of acetylene and ethane in the stratosphere of Jupiter

ICARUS 305 (2018) 301-313

H Melin, LN Fletcher, PT Donnelly, TK Greathouse, JH Lacy, GS Orton, RS Giles, JA Sinclair, PGJ Irwin


Haze and cloud structure of Saturn's North Pole and Hexagon Wave from Cassini/ISS imaging

Icarus (2018)

JF Sanz-Requena, S Pérez-Hoyos, A Sánchez-Lavega, A Antuñano, PGJ Irwin

© 2017 Elsevier Inc. In this paper we present a study of the vertical haze and cloud structure in the upper two bars of Saturn's Northern Polar atmosphere using the Imaging Science Subsystem (ISS) instrument onboard the Cassini spacecraft. We focus on the characterization of latitudes from 53° to 90° N. The observations were taken during June 2013 with five different filters (VIO, BL1, MT2, CB2 and MT3) covering spectral range from the 420 nm to 890 nm (in a deep methane absorption band). Absolute reflectivity measurements of seven selected regions at all wavelengths and several illumination and observation geometries are compared with the values produced by a radiative transfer model. The changes in reflectivity at these latitudes are mostly attributed to changes in the tropospheric haze. This includes the haze base height (from 600 ± 200 mbar at the lowest latitudes to 1000 ± 300 mbar in the pole), its particle number density (from 20 ± 2 particles/cm 3 to 2 ± 0.5 particles/cm 3 at the haze base) and its scale height (from 18 ± 0.1 km to 50 ± 0.1 km). We also report variability in the retrieved particle size distribution and refractive indices. We find that the Hexagonal Wave dichotomizes the studied stratospheric and tropospheric hazes between the outer, equatorward regions and the inner, Polar Regions. This suggests that the wave or the jet isolates the particle distribution at least at tropospheric levels.


Spatial variations in Titan's atmospheric temperature: ALMA and Cassini comparisons from 2012 to 2015

Icarus (2018)

AE Thelen, CA Nixon, NJ Chanover, EM Molter, MA Cordiner, RK Achterberg, J Serigano, PGJ Irwin, N Teanby, SB Charnley

© 2017 Elsevier Inc. Submillimeter emission lines of carbon monoxide (CO) in Titan's atmosphere provide excellent probes of atmospheric temperature due to the molecule's long chemical lifetime and stable, well constrained volume mixing ratio. Here we present the analysis of 4 datasets obtained with the Atacama Large Millimeter/Submillimeter Array (ALMA) in 2012, 2013, 2014, and 2015 that contain strong CO rotational transitions. Utilizing ALMA's high spatial resolution in the 2012, 2014, and 2015 observations, we extract spectra from 3 separate regions on Titan's disk using datasets with beam sizes ranging from 0.35 × 0.28'' to 0.39 × 0.34''. Temperature profiles retrieved by the NEMESIS radiative transfer code are compared to Cassini Composite Infrared Spectrometer (CIRS) and radio occultation science results from similar latitude regions. Disk-averaged temperature profiles stay relatively constant from year to year, while small seasonal variations in atmospheric temperature are present from 2012 to 2015 in the stratosphere and mesosphere (~100-500 km) of spatially resolved regions. We measure the stratopause (320 km) to increase in temperature by 5 K in northern latitudes from 2012 to 2015, while temperatures rise throughout the stratosphere at lower latitudes. We observe generally cooler temperatures in the lower stratosphere (~100 km) than those obtained through Cassini radio occultation measurements, with the notable exception of warming in the northern latitudes and the absence of previous instabilities; both of these results are indicators that Titan's lower atmosphere responds to seasonal effects, particularly at higher latitudes. While retrieved temperature profiles cover a range of latitudes in these observations, deviations from CIRS nadir maps and radio occultation measurements convolved with the ALMA beam-footprint are not found to be statistically significant, and discrepancies are often found to be less than 5 K throughout the atmosphere. ALMA's excellent sensitivity in the lower stratosphere (60-300 km) provides a highly complementary dataset to contemporary CIRS and radio science observations, including altitude regions where both of those measurement sets contain large uncertainties. The demonstrated utility of CO emission lines in the submillimeter as a tracer of Titan's atmospheric temperature lays the groundwork for future studies of other molecular species - particularly those that exhibit strong polar abundance enhancements or are pressure-broadened in the lower atmosphere, as temperature profiles are found to consistently vary with latitude in all three years by up to 15 K.


Late metal–silicate separation on the IAB parent asteroid: Constraints from combined W and Pt isotopes and thermal modelling

Earth and Planetary Science Letters 482 (2018) C

AC Hunt, DL Cook, T Lichtenberg, PM Reger, M Ek, GJ Golabek, M Schönbächler


A Chorus of the WindsOn Saturn!

JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS 123 (2018) 1007-1011

PL Read


The TRAPPIST-1 system: orbital evolution, tidal dissipation, formation and habitability

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 476 (2018) 5032-5056

JCB Papaloizou, E Szuszkiewicz, C Terquem


Dynamical models to explain observations with SPHERE in planetary systems with double debris belts

ASTRONOMY & ASTROPHYSICS 611 (2018) ARTN A43

C Lazzoni, S Desidera, F Marzari, A Boccaletti, M Langlois, D Mesa, R Gratton, Q Kral, N Pawellek, J Olofsson, M Bonnefoy, G Chauvin, AM Lagrange, A Vigan, E Sissa, J Antichi, H Avenhaus, A Baruffolo, JL Baudino, A Bazzon, JL Beuzit, B Biller, M Bonavita, W Brandner, P Bruno, E Buenzli, F Cantalloube, E Cascone, A Cheetham, RU Claudi, M Cudel, S Daemgen, V De Caprio, P Delorme, D Fantinel, G Farisato, M Feldt, R Galicher, C Ginski, J Girard, E Giro, M Janson, J Hagelberg, T Henning, S Incorvaia, M Kasper, T Kopytova, J Lannier, H LeCoroller, L Lessio, R Ligi, AL Maire, F Menard, M Meyer, J Milli, D Mouillet, S Peretti, C Perrot, D Rouan, M Samland, B Salasnich, G Salter, T Schmidt, S Scuderi, E Sezestre, M Turatto, S Udry, F Wildi, A Zurlo


The Atmospheric Chemistry Suite (ACS) of Three Spectrometers for the ExoMars 2016 Trace Gas Orbiter

SPACE SCIENCE REVIEWS 214 (2018) UNSP 7

O Korablev, F Montmessin, A Trokhimovskiy, AA Fedorova, AV Shakun, AV Grigoriev, BE Moshkin, NI Ignatiev, F Forget, F Lefevre, K Anufreychik, I Dzuban, YS Ivanov, YK Kalinnikov, TO Kozlova, A Kungurov, V Makarov, F Martynovich, I Maslov, D Merzlyakov, PP Moiseev, Y Nikolskiy, A Patrakeev, D Patsaev, A Santos-Skripko, O Sazonov, N Semena, A Semenov, V Shashkin, A Sidorov, AV Stepanov, I Stupin, D Timonin, AY Titov, A Viktorov, A Zharkov, F Altieri, G Arnold, DA Belyaev, JL Bertaux, DS Betsis, N Duxbury, T Encrenaz, T Fouchet, J-C Gerard, D Grass, S Guerlet, P Hartogh, Y Kasaba, I Khatuntsev, VA Krasnopolsky, RO Kuzmin, E Lellouch, MA Lopez-Valverde, M Luginin, A Maattanen, E Marcq, J Martin Torres, AS Medvedev, E Millour, KS Olsen, MR Patel, C Quantin-Nataf, AV Rodin, VI Shematovich, I Thomas, N Thomas, L Vazquez, M Vincendon, V Wilquet, CF Wilson, LV Zasova, LM Zelenyi, MP Zorzano


Analysis of gaseous ammonia (NH3) absorption in the visible spectrum of Jupiter

ICARUS 302 (2018) 426-436

PGJ Irwin, N Bowles, AS Braude, R Garland, S Calcutt


New spectro-photometric characterization of the substellar object HR2562B using SPHERE

ASTRONOMY & ASTROPHYSICS 612 (2018) ARTN A92

D Mesa, J-L Baudino, B Charnay, V D'Orazi, S Desidera, A Boccaletti, R Gratton, M Bonnefoy, P Delorme, M Langlois, A Vigan, A Zurlo, A-L Maire, M Janson, J Antichi, A Baruffolo, P Bruno, E Cascone, G Chauvin, RU Claudi, V De Caprio, D Fantinel, G Farisato, M Feldt, E Giro, J Hagelberg, S Incorvaia, E Lagadec, A-M Lagrange, C Lazzoni, L Lessio, B Salasnich, S Scuderi, E Sissa, M Turatto


Simulating the detection and classification of high-redshift supernovae with HARMONI on the ELT

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 478 (2018) 3189-3198

S Bounissou, N Thatte, S Zieleniewski, RCW Houghton, M Tecza, I Hook, B Neichel, T Fusco


Investigations of the Mars Upper Atmosphere with ExoMars Trace Gas Orbiter

SPACE SCIENCE REVIEWS 214 (2018) UNSP 29

MA Lopez-Valverde, J-C Gerard, F Gonzalez-Galindo, A-C Vandaele, I Thomas, O Korablev, N Ignatiev, A Fedorova, F Montmessin, A Maattanen, S Guilbon, F Lefevre, MR Patel, S Jimenez-Monferrer, M Garcia-Comas, A Cardesin, CF Wilson, RT Clancy, A Kleinboehl, DJ McCleese, DM Kass, NM Schneider, MS Chaffin, JJ Lopez-Moreno, J Rodriguez


The K2 M67 Study: Establishing the Limits of Stellar Rotation Period Measurements in M67 with K2 Campaign 5 Data

ASTROPHYSICAL JOURNAL 859 (2018) ARTN 167

R Esselstein, S Aigrain, A Vanderburg, JC Smith, S Meibom, J Van Saders, R Mathieu


A hexagon in Saturn's northern stratosphere surrounding the emerging summertime polar vortex.

Nature communications 9 (2018) 3564-

LN Fletcher, GS Orton, JA Sinclair, S Guerlet, PL Read, A Antuñano, RK Achterberg, FM Flasar, PGJ Irwin, GL Bjoraker, J Hurley, BE Hesman, M Segura, N Gorius, A Mamoutkine, SB Calcutt

Saturn's polar stratosphere exhibits the seasonal growth and dissipation of broad, warm vortices poleward of ~75° latitude, which are strongest in the summer and absent in winter. The longevity of the exploration of the Saturn system by Cassini allows the use of infrared spectroscopy to trace the formation of the North Polar Stratospheric Vortex (NPSV), a region of enhanced temperatures and elevated hydrocarbon abundances at millibar pressures. We constrain the timescales of stratospheric vortex formation and dissipation in both hemispheres. Although the NPSV formed during late northern spring, by the end of Cassini's reconnaissance (shortly after northern summer solstice), it still did not display the contrasts in temperature and composition that were evident at the south pole during southern summer. The newly formed NPSV was bounded by a strengthening stratospheric thermal gradient near 78°N. The emergent boundary was hexagonal, suggesting that the Rossby wave responsible for Saturn's long-lived polar hexagon-which was previously expected to be trapped in the troposphere-can influence the stratospheric temperatures some 300 km above Saturn's clouds.


Detectability of Biosignatures in Anoxic Atmospheres with the James Webb Space Telescope: A TRAPPIST-1e Case Study

ASTRONOMICAL JOURNAL 156 (2018) ARTN 114

J Krissansen-Totton, R Garland, P Irwin, DC Catling


Seasonal evolution of C2N2, C3H4, and C4H2 abundances in Titan's lower stratosphere

ASTRONOMY & ASTROPHYSICS 609 (2018) ARTN A64

M Sylvestre, NA Teanby, S Vinatier, S Lebonnois, PGJ Irwin


Uranus's Northern Polar Cap in 2014

GEOPHYSICAL RESEARCH LETTERS 45 (2018) 5329-5335

D Toledo, PGJ Irwin, NA Teanby, AA Simon, MH Wong, GS Orton


ELT HARMONI: Image slicer preliminary design

Proceedings of SPIE - The International Society for Optical Engineering 10702 (2018)

F Laurent, D Boudon, J Kosmalski, M Loupias, G Raffault, A Remillieux, N Thatte, I Bryson, H Schnetler, F Clarke, M Tecza

© 2018 SPIE. Harmoni is the ELT's first light visible and near-infrared integral field spectrograph. It will provide four different spatial scales, ranging from coarse spaxels of 60 × 30 mas best suited for seeing limited observations, to 4 mas spaxels that Nyquist sample the diffraction limited point spread function of the ELT at near-infrared wavelengths. Each spaxel scale may be combined with eleven spectral settings, that provide a range of spectral resolving powers from R 3500 to R 20000 and instantaneous wavelength coverage spanning the 0.47 - 2.45 μm wavelength range of the instrument. The consortium consists of several institutes in Europe under leadership of Oxford University. Harmoni is starting its Final Design Phase after a Preliminary Design Phase in November, 2017. The CRAL has the responsibility of the Integral Field Unit design linking the Preoptics to the 4 Spectrographs. It is composed of a field splitter associated with a relay system and an image slicer that create from a rectangular Field of View a very long (540mm) output slit for each spectrograph. In this paper, the preliminary design and performances of Harmoni Image Slicer will be presented including image quality, pupil distortion and slit geometry. It has been designed by CRAL for Harmoni PDR in November, 2017. Special emphases will be put on straylight analysis and slice diffraction. The optimisation of the manufacturing and slit geometry will also be reported.

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