174 research outputs found
First Disk-Resolved Millimeter Observations Of Io's Surface And SO2 Atmosphere
Aims. In spite of considerable progress in the last two decades, Io's atmosphere remains poorly understood. The goal of this work is to improve our understanding of its spatial distribution, temperature and dynamics. Methods. We present millimeter observations of Io's surface and SO2 atmosphere at 1.4 mm obtained with the IRAM Plateau de Bure Interferometer in January-February 2005. With a synthesized beam of 0.5 x 1.5 '', these observations resolve Io's similar to 1.0 '' disk in the longitudinal/local time direction, and sample the leading and trailing hemispheres of Io. Results. The measured continuum total flux and visibilities show that continuum radiation originates from a depth of at least 1 cm in Io's subsurface. On both the leading and trailing sides, emission in the SO2 216.643 GHz line appears spatially narrower than the continuum, and suggests that the atmosphere covers similar to 80% of the surface on the leading side and similar to 60% on the trailing. On the leading side, disk-resolved spectra yield Doppler shift measurements, indicating a beam-integrated limb-to-limb velocity difference of 330 +/-3 100 m/s in the prograde direction. Such a flow allows an improved fit of disk-averaged SO2 spectra, but its origin remains to be understood. Mean gas temperatures are in the range 130-180 K, in agreement with estimates from IR measurements, and with a tendency for higher trailing vs leading side gas temperatures. On the basis of realistic plume models, we find that the contribution of isolated volcanic plumes to the SO2 emission is small.Astronom
Exploring Io's atmospheric composition with APEX: first measurement of 34SO2 and tentative detection of KCl
The composition of Io's tenuous atmosphere is poorly constrained. Only the
major species SO2 and a handful of minor species have been positively
identified, but a variety of other molecular species should be present, based
on thermochemical equilibrium models of volcanic gas chemistry and the
composition of Io's environment. This paper focuses on the spectral search for
expected yet undetected molecular species (KCl, SiO, S2O) and isotopes (34SO2).
We analyze a disk-averaged spectrum of a potentially line-rich spectral window
around 345 GHz, obtained in 2010 at the APEX-12m antenna (Atacama Pathfinder
EXperiment). Using different models assuming either extended atmospheric
distributions or a purely volcanically-sustained atmosphere, we tentatively
measure the KCl relative abundance with respect to SO2 and derive a range of
4x10^{-4}-8x10^{-3}. We do not detect SiO or S2O and present new upper limits
on their abundances. We also present the first measurement of the 34S/32S
isotopic ratio in gas phase on Io, which appears to be twice as high as the
Earth and ISM reference values. Strong lines of SO2 and SO are also analyzed to
check for longitudinal variations of column density and relative abundance. Our
models show that, based on their predicted relative abundance with respect to
SO2 in volcanic plumes, both the tentative KCl detection and SiO upper limit
are compatible with a purely volcanic origin for these species.Comment: Accepted for publication in ApJ. 11 pages, 4 figure
Wind mapping in Venus' upper mesosphere with the IRAM-Plateau de Bure interferometer
The dynamics of the upper mesosphere of Venus (~85-115 km) have been
characterized as a combination of a retrograde superrotating zonal wind (RSZ)
with a subsolar-to-antisolar flow (SSAS). Numerous mm-wave single-dish
observations have been obtained and could directly measure mesospheric
line-of-sight winds by mapping Doppler-shifts on CO rotational lines, but their
limited spatial resolution makes their interpretation difficult. By using
interferometric facilities, one can obtain better resolution on Doppler-shifts
maps, allowing in particular to put firmer constraints on the respective
contributions of the SSAS and RSZ circulations to the global mesospheric wind
field. We report on interferometric observations of the CO(1-0) line obtained
with the IRAM-Plateau de Bure interferometer in November 2007 and June 2009,
that could map the upper mesosphere dynamics on the morning hemisphere with a
very good spatial resolution (3.5-5.5"). All the obtained measurements show,
with a remarkably good temporal stability, that the wind globally flows in the
(sky) East-West direction, corresponding in the observed geometry either to an
unexpected prograde zonal wind or a SSAS flow. A very localized inversion of
the wind direction, that could correspond to a RSZ wind, is also repeatedly
detected in the night hemisphere. The presence of significant meridional winds
is not evidenced. Using models with different combinations of zonal and SSAS
winds, we find that the data is best reproduced by a dominant SSAS flow with a
maximal velocity at the terminator of ~200 m/s, displaying large diurnal and
latitudinal asymmetries, combined with an equatorial RSZ wind of 70-100 m/s,
overall indicating a wind-field structure consistent with but much more complex
than the usual representation of the mesospheric dynamics.Comment: Accepted for publication in A&
Thermal Properties of the Icy Galilean Satellites from Millimeter ALMA Observations
We present spatially-resolved maps of the leading and trailing hemispheres of Europa, Ganymede, and Callisto from ALMA millimeter wavelength observations
PRIMA General Observer Science Book
PRIMA (The PRobe for-Infrared Mission for Astrophysics) is a concept for a
far-infrared (IR) observatory. PRIMA features a cryogenically cooled 1.8 m
diameter telescope and is designed to carry two science instruments enabling
ultra-high sensitivity imaging and spectroscopic studies in the 24 to 235
microns wavelength range. The resulting observatory is a powerful survey and
discovery machine, with mapping speeds better by 2 - 4 orders of magnitude with
respect to its far-IR predecessors. The bulk of the observing time on PRIMA
should be made available to the community through a General Observer (GO)
program offering 75% of the mission time over 5 years. In March 2023, the
international astronomy community was encouraged to prepare authored
contributions articulating scientific cases that are enabled by the telescope
massive sensitivity advance and broad spectral coverage, and that could be
performed within the context of GO program. This document, the PRIMA General
Observer Science Book, is the edited collection of the 76 received
contributions.Comment: A. Moullet, T. Kataria, D. Lis, S. Unwin, Y. Hasegawa, E. Mills, C.
Battersby, A. Roc, M. Meixner are the editors of the PRIMA General Observer
Science Book. The book compiles 76 authored contributions. 399 page
Detection of CO and HCN in Pluto's atmosphere with ALMA
Observations of the Pluto-Charon system, acquired with the ALMA
interferometer on June 12-13, 2015, have yielded a detection of the CO(3-2) and
HCN(4-3) rotational transitions from Pluto, providing a strong confirmation of
the presence of CO, and the first observation of HCN, in Pluto's atmosphere.
The CO and HCN lines probe Pluto's atmosphere up to ~450 km and ~900 km
altitude, respectively. The CO detection yields (i) a much improved
determination of the CO mole fraction, as 515+/-40 ppm for a 12 ubar surface
pressure (ii) clear evidence for a well-marked temperature decrease (i.e.,
mesosphere) above the 30-50 km stratopause and a best-determined temperature of
70+/-2 K at 300 km, in agreement with recent inferences from New Horizons /
Alice solar occultation data. The HCN line shape implies a high abundance of
this species in the upper atmosphere, with a mole fraction >1.5x10-5 above 450
km and a value of 4x10-5 near 800 km. The large HCN abundance and the cold
upper atmosphere imply supersaturation of HCN to a degree (7-8 orders of
magnitude) hitherto unseen in planetary atmospheres, probably due to the slow
kinetics of condensation at the low pressure and temperature conditions of
Pluto's upper atmosphere. HCN is also present in the bottom ~100 km of the
atmosphere, with a 10-8 - 10-7 mole fraction; this implies either HCN
saturation or undersaturation there, depending on the precise stratopause
temperature. The HCN column is (1.6+/-0.4)x10^14 cm-2, suggesting a
surface-referred net production rate of ~2x10^7 cm-2s-1. Although HCN
rotational line cooling affects Pluto's atmosphere heat budget, the amounts
determined in this study are insufficient to explain the well-marked mesosphere
and upper atmosphere's ~70 K temperature. We finally report an upper limit on
the HC3N column density (< 2x10^13 cm-2) and on the HC15N / HC14N ratio (<
1/125).Comment: Revised version. Icarus, in press, Oct. 11, 2016. 57 pages, including
13 figures and 4 table
Thermal expansion in small metal clusters and its impact on the electric polarizability
The thermal expansion coefficients of clusters with and , and
are obtained from {\it ab initio} Born-Oppenheimer LDA molecular dynamics.
Thermal expansion of small metal clusters is considerably larger than that in
the bulk and size-dependent. We demonstrate that the average static electric
dipole polarizability of Na clusters depends linearly on the mean interatomic
distance and only to a minor extent on the detailed ionic configuration when
the overall shape of the electron density is enforced by electronic shell
effects. The polarizability is thus a sensitive indicator for thermal
expansion. We show that taking this effect into account brings theoretical and
experimental polarizabilities into quantitative agreement.Comment: 4 pages, 2 figures, one table. Accepted for publication in Physical
Review Letters. References 10 and 23 update
Development and application of a 2-step methodology to select a reference society providing Dietary Reference Values for national implementation
Objective: To describe and discuss a 2-step methodology developed to select a reference society that provides Dietary Reference Values (DRVs) for national implementation and to illustrate its application in Switzerland with one macronutrient and one micronutrient.Design: During Step 1, we searched and compared DRVs and methodologies used to define DRVs from eight European societies for seven selected nutrients. We repeated this procedure during Step 2 for DRVs from two preselected societies for 44 nutrients.Setting: The 2-step methodology applied here for Switzerland may be used in other countriesParticipants: The research team commissioned six external experts from three linguistic regions of Switzerland, who provided their opinions through two online surveys, individual interviews, and a focus group.Results: After Step 1, we excluded five societies because of old publication dates, irrelevant publication languages for Switzerland, difficulty in accessing documents, or because their DRVs were mainly based on another society. After Step 2, the two societies were qualified based on the analysis of the values and methodologies used. The need for free and easily accessible scientific background information favored the European Food Safety Authority (EFSA). We chose alternative societies for nine nutrients for the overall population or subgroups, and for elderly.Conclusions: To manage heterogeneous and complex data from several societies, adopting a 2-step methodology including fewer nutrients and more societies during Step 1, and fewer societies but all nutrients in Step 2, was very helpful. With some exceptions, we selected EFSA as the main society to provide DRVs for Switzerland
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