577 research outputs found
CO on Titan: More Evidence for a Well-Mixed Vertical Profile
We report new interferometric observations of the CO (2-1) rotational
transition on Titan. We find that the spectrum is best fit by a uniform profile
of 52 ppm, with estimated errors of 6 ppm (40 to 200 km) and 12 ppm (200 to 300
km).Comment: Submitted to as a Note to Icarus. Uses emulateapj.sty under Latex, 6
text pages, 2 figs (includes with psfig
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
Adapting and expanding interferometric arrays
We outline here a simple yet efficient method for finding optimized
configurations of the elements of radio-astronomical interferometers with fixed
pad locations. The method can be successfully applied, as we demonstrate, to
define new configurations when changes to the array take place. This may
include the addition of new pads or new antennas, or the loss of pads or
antennas. Our method is based on identifying which placement of elements
provides the most appropriate uv plane sampling for astronomical imaging.Comment: Accepted for publication in ApJ
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&
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