273 research outputs found
Hdo And SO2 Thermal Mapping On Venus: Evidence For Strong SO2 Variability
We have been using the TEXES high-resolution imaging spectrometer at the NASA Infrared Telescope Facility to map sulfur dioxide and deuterated water over the disk of Venus. Observations took place on January 10-12, 2012. The diameter of Venus was 13 arcsec, with an illumination factor of 80%. Data were recorded in the 1344-1370 cm(-1) range (around 7.35 mu m) with a spectral resolving power of 80 000 and a spatial resolution of about 1.5 arcsec. In this spectral range, the emission of Venus comes from above the cloud top (z = 60-80 km). Four HDO lines and tens of SO2 lines have been identified in our spectra. Mixing ratios have been estimated from HDO/CO2 and SO2/CO2 line depth ratios, using weak neighboring transitions of comparable depths. The HDO maps, recorded on Jan. 10 and Jan. 12, are globally uniform with no significant variation between the two dates. A slight enhancement of the HDO mixing ratio toward the limb might be interpreted as a possible increase of the D/H ratio with height above the cloud level. The mean H2O mixing ratio is found to be 1.5 +/-0.75 ppm, assuming a D/H ratio of 0.0312 (i.e. 200 times the terrestrial value) over the cloud deck. The SO2 maps, recorded each night from Jan. 10 to Jan. 12, show strong variations over the disk of Venus, by a factor as high as 5 to 10. In addition, the position of the maximum SO2 mixing ratio strongly varies on a timescale of 24 h. The maximum SO2 mixing ratio ranges between 75 +/-25 ppb and 125 +/-50 ppb between Jan. 10 and Jan. 12. The high variability of sulfur dioxide is probably a consequence of its very short photochemical lifetime.NASA NNX-08AE38A, NNX08AW33G S03NSF AST-0607312, AST-0708074Astronom
Recommended from our members
HDO And SO2 Thermal Mapping On Venus II. The So2 Spatial Distribution Above And Within The Clouds
Sulfur dioxide and water vapor, two key species of Venus photochemistry, are known to exhibit significant spatial and temporal variations above the cloud top. In particular, ground-based thermal imaging spectroscopy at high spectral resolution, achieved on Venus in January 2012, has shown evidence for strong SO2 variations on timescales shorter than a day. We have continued our observing campaign using the TEXES high-resolution imaging spectrometer at the NASA InfraRed Telescope Facility to map sulfur dioxide over the disk of Venus at two different wavelengths, 7 mu m (already used in the previous study) and 19 mu m. The 7 mu m radiation probes the top of the H2SO4 cloud, while the 19 mu m radiation probes a few kilometers below within the cloud. Observations took place on October 4 and 5, 2012. Both HDO and SO2 lines are identified in our 7-mu m spectra and SO2 is also easily identified at 19 mu m. The CO2 lines at 7 and 19 mu m are used to infer the thermal structure. An isothermal/inversion layer is present at high latitudes (above 60 N and S) in the polar collars, which was not detected in October 2012. The enhancement of the polar collar in October 2012 is probably due to the fact that the morning terminator is observed, while the January data probed the evening terminator. As observed in our previous run, the HDO map is relatively uniform over the disk of Venus, with a mean mixing ratio of about 1 ppm. In contrast, the SO2 maps at 19 mu m show intensity variations by a factor of about 2 over the disk within the cloud, less patchy than observed at the cloud top at 7 mu m. In addition, the SO2 maps seem to indicate significant temporal changes within an hour. There is evidence for a cutoff in the SO2 vertical distribution above the cloud top, also previously observed by SPICAV/SOIR aboard Venus Express and predicted by photochemical models.NASA NNX-08AE38AIRTF AST-0607312, AST-0708074Astronom
STF Optimierung von single-bit CT ΣΔ Modulatoren basierend auf skalierten Filterkoeffizienten
Die vorliegende Arbeit beschäftigt sich mit dem Signalübertragungsverhalten von single-bit continuous-time (CT) ΣΔ Modulatoren. Dabei liegt der Fokus der Untersuchung auf dem Peaking der Signaltransferfunktion (STF). Dieser Effekt kann die Performance und die Stabilität des Gesamtsystems negativ beeinflussen, da bei auftretendem STF-Peaking Signale außerhalb des Signalbands verstärkt werden. In dieser Arbeit wird ein neuer Ansatz zur Reduktion des Peakings vorgestellt, der auf der Optimierung der Systemdynamik basiert. Dabei werden die Filterkoeffizienten des Modulators systematisch angepasst. Anhand eines Beispielsystems wird gezeigt, dass der Ansatz genutzt werden kann, um das Übertragungsverhalten des Modulators abhängig vom Ausgangssystem zu verändern. So kann entweder die Systemsperformance verbessert werden, ohne Peaking in der STF zu erzeugen, oder das STF-Peaking reduziert werden, ohne die Systemperformance stark zu beeinflussen.DF
Probing Rock Type, Fe Redox State, and Transition Metal Contents with Six-Window VNIR Spectroscopy Under Venus Conditions
VEM-window data are shown to distinguish among key rock types on Venus, and evaluate redox state and transition metal contents of Venus surface rocks
Sunlight refraction in the mesosphere of Venus during the transit on June 8th, 2004
Many observers in the past gave detailed descriptions of the telescopic
aspect of Venus during its extremely rare transits across the Solar disk. In
particular, at the ingress and egress, the portion of the planet's disk outside
the Solar photosphere has been repeatedly perceived as outlined by a thin,
bright arc ("aureole"). Those historical visual observations allowed inferring
the existence of Venus' atmosphere, the bright arc being correctly ascribed to
the refraction of light by the outer layers of a dense atmosphere. On June 8th,
2004, fast photometry based on electronic imaging devices allowed the first
quantitative analysis of the phenomenon. Several observers used a variety of
acquisition systems to image the event -- ranging from amateur-sized to
professional telescopes and cameras -- thus collecting for the first time a
large amount of quantitative information on this atmospheric phenomenon. In
this paper, after reviewing some elements brought by the historical records, we
give a detailed report of the ground based observations of the 2004 transit.
Besides confirming the historical descriptions, we perform the first
photometric analysis of the aureole using various acquisition systems. The
spatially resolved data provide measurements of the aureole flux as a function
of the planetocentric latitude along the limb. A new differential refraction
model of solar disk through the upper atmosphere allows us to relate the
variable photometry to the latitudinal dependency of scale-height with
temperature in the South polar region, as well as the latitudinal variation of
the cloud-top layer altitude. We compare our measurements to recent analysis of
the Venus Express VIRTIS-M, VMC and SPICAV/SOIR thermal field and aerosol
distribution. Our results can be used a starting point for new, more optimized
experiments during the 2012 transit event.Comment: Icarus, in pres
World-leading science with SPIRou - the nIR spectropolarimeter / high-precision velocimeter for CFHT
SPIRou is a near-infrared (nIR) spectropolarimeter / velocimeter proposed as
a new-generation instrument for CFHT. SPIRou aims in particular at becoming
world-leader on two forefront science topics, (i) the quest for habitable
Earth-like planets around very- low-mass stars, and (ii) the study of low-mass
star and planet formation in the presence of magnetic fields. In addition to
these two main goals, SPIRou will be able to tackle many key programs, from
weather patterns on brown dwarf to solar-system planet atmospheres, to dynamo
processes in fully-convective bodies and planet habitability. The science
programs that SPIRou proposes to tackle are forefront (identified as first
priorities by most research agencies worldwide), ambitious (competitive and
complementary with science programs carried out on much larger facilities, such
as ALMA and JWST) and timely (ideally phased with complementary space missions
like TESS and CHEOPS).
SPIRou is designed to carry out its science mission with maximum efficiency
and optimum precision. More specifically, SPIRou will be able to cover a very
wide single-shot nIR spectral domain (0.98-2.35 \mu m) at a resolving power of
73.5K, providing unpolarized and polarized spectra of low-mass stars with a
~15% average throughput and a radial velocity (RV) precision of 1 m/s.Comment: 12 pages, 5 figures, conference proceedings of the French Society of
Astronomy and Astrophysics meeting 201
Study of the plutino object (208996) 2003 AZ84 from stellar occultations: size, shape and topographic features
We present results derived from four stellar occultations by the plutino
object (208996) 2003~AZ, detected at January 8, 2011 (single-chord
event), February 3, 2012 (multi-chord), December 2, 2013 (single-chord) and
November 15, 2014 (multi-chord). Our observations rule out an oblate spheroid
solution for 2003~AZ's shape. Instead, assuming hydrostatic equilibrium,
we find that a Jacobi triaxial solution with semi axes ~km % axis ratios and
, can better account for all our occultation observations.
Combining these dimensions with the rotation period of the body (6.75~h) and
the amplitude of its rotation light curve, we derive a density ~g~cm a geometric albedo . A grazing chord
observed during the 2014 occultation reveals a topographic feature along
2003~AZ's limb, that can be interpreted as an abrupt chasm of width
~km and depth ~km or a smooth depression of width ~km
and depth ~km (or an intermediate feature between those two extremes)
Environmental response functions - relating eddy-covariance flux measurements to ecosystem drivers
Relation of Quantitative Histologic and Radiologic Breast Tissue Composition Metrics with Invasive Breast Cancer Risk
Transmission spectrum of Venus as a transiting exoplanet
On 5-6 June 2012, Venus will be transiting the Sun for the last time before
2117. This event is an unique opportunity to assess the feasibility of the
atmospheric characterisation of Earth-size exoplanets near the habitable zone
with the transmission spectroscopy technique and provide an invaluable proxy
for the atmosphere of such a planet. In this letter, we provide a theoretical
transmission spectrum of the atmosphere of Venus that could be tested with
spectroscopic observations during the 2012 transit. This is done using
radiative transfer across Venus' atmosphere, with inputs from in-situ missions
such as Venus Express and theoretical models. The transmission spectrum covers
a range of 0.1-5 {\mu}m and probes the limb between 70 and 150 km in altitude.
It is dominated in UV by carbon dioxide absorption producing a broad transit
signal of ~20 ppm as seen from Earth, and from 0.2 to 2.7 {\mu}m by Mie
extinction (~5 ppm at 0.8 {\mu}m) caused by droplets of sulfuric acid composing
an upper haze layer above the main deck of clouds. These features are not
expected for a terrestrial exoplanet and could help discriminating an
Earth-like habitable world from a cytherean planet.Comment: 4 pages, 3 figures, 1 table. Figure 3 and Table 1 will be only
available on-line. Table 1 will be fully available at the CDS. Accepted for
publication in Astronomy and Astrophysics (Letter
- …