722 research outputs found
Ground-based NIR emission spectroscopy of HD189733b
We investigate the K and L band dayside emission of the hot-Jupiter HD
189733b with three nights of secondary eclipse data obtained with the SpeX
instrument on the NASA IRTF. The observations for each of these three nights
use equivalent instrument settings and the data from one of the nights has
previously reported by Swain et al (2010). We describe an improved data
analysis method that, in conjunction with the multi-night data set, allows
increased spectral resolution (R~175) leading to high-confidence identification
of spectral features. We confirm the previously reported strong emission at
~3.3 microns and, by assuming a 5% vibrational temperature excess for methane,
we show that non-LTE emission from the methane nu3 branch is a physically
plausible source of this emission. We consider two possible energy sources that
could power non-LTE emission and additional modelling is needed to obtain a
detailed understanding of the physics of the emission mechanism. The validity
of the data analysis method and the presence of strong 3.3 microns emission is
independently confirmed by simultaneous, long-slit, L band spectroscopy of HD
189733b and a comparison star.Comment: ApJ accepte
Scientific goals for the observation of Venus by VIRTIS on ESA/Venus Express mission
The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board the ESA/Venus Express mission has technical specifications well suited for many science objectives of Venus exploration. VIRTIS will both comprehensively explore a plethora of atmospheric properties and processes and map optical properties of the surface through its three channels, VIRTIS-M-vis (imaging spectrometer in the 0.3–1 micron range), VIRTIS-M-IR (imaging spectrometer in the 1–5 micron range) and VIRTIS-H (aperture highresolution spectrometer in the 2–5 micron range). The atmospheric composition below the clouds will be repeatedly measured in the night side infrared windows over a wide range of latitudes and longitudes, thereby providing information on Venus’s chemical cycles. In particular, CO, H2O, OCS and SO2 can be studied. The cloud structure will be repeatedly mapped from the brightness contrasts in the
near-infrared night side windows, providing new insights into Venusian meteorology. The global circulation and local dynamics of Venus will be extensively studied from infrared and visible spectral images. The thermal structure above the clouds will be retrieved in the night side using the 4.3 micron fundamental band of CO2. The surface of Venus is detectable in the short-wave infrared windows on the night side at 1.01, 1.10 and 1.18 micron, providing constraints on surface properties and the extent of active volcanism. Many more tentative studies are
also possible, such as lightning detection, the composition of volcanic emissions, and mesospheric wave propagation
The Spectrum of the Brown Dwarf Gliese 229B
We present a spectrum of the cool (T_eff = 900 K) brown dwarf Gliese 229B.
This spectrum, with a relatively high signal-to-noise ratio per spectral
resolution element (> 30), spans the wavelength range from 0.837 microns to 5.0
microns. We identify a total of four different major methane absorption
features, including the fundamental band at 3.3 microns, at least four steam
bands, and two neutral cesium features. We confirm the recent detection of
carbon monoxide (CO) in excess of what is predicted by thermochemical
equilibrium calculations. Carbon is primarily involved in a chemical balance
between methane and CO at the temperatures and pressures present in the outer
parts of a brown dwarf. At lower temperatures, the balance favors methane,
while in the deeper, hotter regions, the reaction reverses to convert methane
into CO. The presence of CO in the observable part of the atmosphere is
therefore a sensitive indicator of vertical flows. The high signal-to-noise
ratio in the 1 to 2.5 microns region permits us to place constraints on the
quantity of dust in the atmosphere of the brown dwarf. We are unable to
reconcile the observed spectrum with synthetic spectra that include the
presences of dust. The presence of CO but lack of dust may be a clue to the
location of the boundaries of the outer convective region of the atmosphere:
The lack of dust may mean that it is not being conveyed into the photosphere by
convection, or that it exists in patchy clouds. If the dust is not in clouds,
but rather sits below the outer convective region, we estimate that the
boundary between outer convective and inner radiative layers is between 1250 K
and 1600 K, in agreement with recent models.Comment: 15 pages, 8 figure
Significance Tests for Periodogram Peaks
We discuss methods currently in use for determining the significance of peaks
in the periodograms of time series. We discuss some general methods for
constructing significance tests, false alarm probability functions, and the
role played in these by independent random variables and by empirical and
theoretical cumulative distribution functions. We also discuss the concept of
"independent frequencies" in periodogram analysis. We propose a practical
method for estimating the significance of periodogram peaks, applicable to all
time series irrespective of the spacing of the data. This method, based on
Monte Carlo simulations, produces significance tests that are tailor-made for
any given astronomical time series.Comment: 22 pages, 11 Encapsulated Postscript figures, AAS LaTeX v5.2
Submitted to Ap
Recovery of surface reflectance spectra and evaluation of the optical depth of aerosols in the near-IR using a Monte-Carlo approach: Application to the OMEGA observations of high latitude regions of Mars
We present a model of radiative transfer through atmospheric particles based
on Monte Carlo methods. This model can be used to analyze and remove the
contribution of aerosols in remote sensing observations. We have developed a
method to quantify the contribution of atmospheric dust in near-IR spectra of
the Martian surface obtained by the OMEGA imaging spectrometer on board Mars
Express. Using observations in the nadir pointing mode with significant
differences in solar incidence angles, we can infer the optical depth of
atmospheric dust, and we can retrieve the surface reflectance spectra free of
aerosol contribution. Martian airborne dust properties are discussed and
constrained from previous studies and OMEGA data. We have tested our method on
a region at 90{\deg}E and 77{\deg}N extensively covered by OMEGA, where
significant variations of the albedo of ice patches in the visible have been
reported. The consistency between reflectance spectra of ice-covered and
ice-free regions recovered at different incidence angles validates our
approach. The optical depth of aerosols varies by a factor 3 in this region
during the summer of Martian year 27. The observed brightening of ice patches
does not result from frost deposition but from a decrease in the dust
contamination of surface ice and (to a lower extent) from a decrease in the
optical thickness of atmospheric dust. Our Monte Carlo-based model can be
applied to recover the spectral reflectance characteristics of the surface from
OMEGA spectral imaging data when the optical thickness of aerosols can be
evaluated. It could prove useful for processing image cubes from the Compact
Reconnaissance Imaging Spectrometer for Mars (CRISM) on board the Mars
Reconnaissance Orbiter (MRO)
Participation of women scientists in ESA solar system missions: A historical trend
We analyzed the participation of women scientists in 10 ESA (European Space Agency) Solar System missions over a period of 38 years. Being part of a spacecraft mission science team can be considered a proxy to measure the "success"in the field. Participation of women in PI (Principal Investigators) teams varied between 4% and 25 %, with several missions with no women as PI. The percentage of female scientists as Co-I (Co-Investigators) is always less than 16 %. This number is lower than the percentage of women in the International Astronomical Union from all ESA's Member State (24 %), which can give us an indication of the percentage of women in the field. We encountered many difficulties to gather the data for this study. The list of team members were not always easily accessible. An additional difficulty was to determine the percentage of female scientists in planetary science in Europe. We would like to encourage the planetary community as a whole, as well as international organizations, universities and societies to continuously gather statistics over many years. Detailed statistics are only the first step to closely monitor the development of achievement gaps and initiate measures to tackle potential causes of inequity, leading to gender inequalities in STEM careers
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