2,286 research outputs found
Advanced infrared astronomy
This task supports the application of infrared heterodyne and Fourier transform spectroscopy to ultra-high resolution studies of molecular constituents of planetary astomspheres and cometary comae. High spectral and spatial resolutions are especially useful for detection and study of localized, non-thermal phenomena in low temperature and low density regions, for detection of trace constituents and for measurement of winds and dynamical phenomena such as thermal tides. Measurement and analysis of individual spectial lines permits retrieval of atmospheric molecular abundances and temperatures and thus, information on local photochemical processes. Determination of absolute line positions to better than 10 to the minus eighth power permits direct measurements of gas velocity to a few meters/sec. Observations are made from ground based heterodyne spectrometers at the Kitt Peak McMath solar telescope and from the NASA infrared Telescope Facility on Mauna Kea, Hawaii. Wind velocities at 110km altitude on Venus were extracted approximately 1 m/sec from measurements of non-thermal emission cores of 10.3 micron CO2 lines. Results indicate a subsolar to antisolar circulationwith a small zonal retrograde component
Marginalising instrument systematics in HST WFC3 transit lightcurves
Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) infrared observations
at 1.1-1.7m probe primarily the HO absorption band at 1.4m, and
has provided low resolution transmission spectra for a wide range of
exoplanets. We present the application of marginalisation based on Gibson
(2014) to analyse exoplanet transit lightcurves obtained from HST WFC3, to
better determine important transit parameters such as R/R, important
for accurate detections of HO. We approximate the evidence, often referred
to as the marginal likelihood, for a grid of systematic models using the Akaike
Information Criterion (AIC). We then calculate the evidence-based weight
assigned to each systematic model and use the information from all tested
models to calculate the final marginalised transit parameters for both the
band-integrated, and spectroscopic lightcurves to construct the transmission
spectrum. We find that a majority of the highest weight models contain a
correction for a linear trend in time, as well as corrections related to HST
orbital phase. We additionally test the dependence on the shift in spectral
wavelength position over the course of the observations and find that
spectroscopic wavelength shifts , best describe the
associated systematic in the spectroscopic lightcurves for most targets, while
fast scan rate observations of bright targets require an additional level of
processing to produce a robust transmission spectrum. The use of
marginalisation allows for transparent interpretation and understanding of the
instrument and the impact of each systematic evaluated statistically for each
dataset, expanding the ability to make true and comprehensive comparisons
between exoplanet atmospheres.Comment: 19 pages, 13 figures, 8 tables, Accepted to Ap
Observations of the 10 micrometer natural laser emission from the mesospheres of Mars and Venus
Observations of the total flux and center to limb dependence of the nonthermal emission occurring in the cores of the 9.4 and 10.4 micrometers CO2 bands on Mars are compared to a theoretical model based on this mechanism. The model successfully reproduces the observed center to limb dependence of this emission, to within the limits imposed by the spatial resolution of the observations of Mars and Venus. The observed flux from Mars agrees closely with the prediction of the model; the flux observed from Venus is 74% of the flux predicted by the model. This emission is used to obtain the kinetic temperatures of the Martian and Venusian mesospheres. For Mars near 70 km altitude, a rotational temperature analysis using five lines gives T = 135 + or - 20 K. The frequency width of the emission is also analyzed to derive a temperature of 126 + or - 6 K. In the case of the Venusian mesosphere near 109 km, the frequency width of the emission gives T = 204 + or - 10 K
The role of bacteria in the turnover of organic carbon in deep-sea sediments
The cycling of organic carbon in the deep sea was inferred from measurements of sediment trap and box core samples taken on the Biscay and Demerara abyssal plains of the North Atlantic. Of the input of organic carbon to the bottom, less than 10% was buried, i.e., not consumed biologically. Based on laboratory measurements of bacterial activity in the sediment samples, incubated under in situ temperature and pressure, it was possible to attribute at least 13 to 30% of the total inferred biological consumption of organic carbon to microbial utilization. The complementarity of results from these biochemical and microbiological measurements implies that the decompression of cold abyssal samples during retrieval efforts does not prevent meaningful experiments on the microbial inhabitants, once returned to in situ pressure
Thermal bifurcation in the upper solar photosphere inferred from heterodyne spectroscopy of OH rotational lines
Low noise high spectral resolution observations of two pure rotation transitions of OH from the solar photosphere were obtained. The observations were obtained using the technique of optically null-balanced infrared heterodyne spectroscopy, and consist of center-to-limb line profiles of a v=1 and a v=0 transition near 12 microns. These lines should be formed in local thermodynamic equilibrium (LTE), and are diagnostics of the thermal structure of the upper photosphere. The v=0 R22 (24.5)e line strengthens at the solar limb, in contradiction to the predictions of current one dimensional photospheric models. Data for this line support a two dimensional model in which horizontal thermal fluctuations of order + or - 800K occur in the region Tau (sub 5000) approximately .001 to .01. This thermal bifurcation may be maintained by the presence of magnetic flux tubes, and may be related to the solar limb extensions observed in the 30 to 200 micron region
Detection of Planetary Emission from the Exoplanet TrES-2 using Spitzer /IRAC
We present here the results of our observations of TrES-2 using the Infrared
Array Camera on Spitzer. We monitored this transiting system during two
secondary eclipses, when the planetary emission is blocked by the star. The
resulting decrease in flux is 0.127%+-0.021%, 0.230%+-0.024%, 0.199%+-0.054%,
and 0.359%+-0.060%, at 3.6 microns, 4.5 microns, 5.8 microns, and 8.0 microns,
respectively. We show that three of these flux contrasts are well fit by a
black body spectrum with T_{eff}=1500 K, as well as by a more detailed model
spectrum of a planetary atmosphere. The observed planet-to-star flux ratios in
all four IRAC channels can be explained by models with and without a thermal
inversion in the atmosphere of TrES-2, although with different atmospheric
chemistry. Based on the assumption of thermochemical equilibrium, the chemical
composition of the inversion model seems more plausible, making it a more
favorable scenario. TrES-2 also falls in the category of highly irradiated
planets which have been theoretically predicted to exhibit thermal inversions.
However, more observations at infrared and visible wavelengths would be needed
to confirm a thermal inversion in this system. Furthermore, we find that the
times of the secondary eclipses are consistent with previously published times
of transit and the expectation from a circular orbit. This implies that TrES-2
most likely has a circular orbit, and thus does not obtain additional thermal
energy from tidal dissipation of a non-zero orbital eccentricity, a proposed
explanation for the large radius of this planet.Comment: 8 pages, 4 figures, 2 tables. Accepted for publication in the
Astrophysical Journal. V2: New figure added ; other minor changes throughou
Thermal Phase Variations of WASP-12b: Defying Predictions
[Abridged] We report Warm Spitzer full-orbit phase observations of WASP-12b
at 3.6 and 4.5 micron. We are able to measure the transit depths, eclipse
depths, thermal and ellipsoidal phase variations at both wavelengths. The large
amplitude phase variations, combined with the planet's previously-measured
day-side spectral energy distribution, is indicative of non-zero Bond albedo
and very poor day-night heat redistribution. The transit depths in the
mid-infrared indicate that the atmospheric opacity is greater at 3.6 than at
4.5 micron, in disagreement with model predictions, irrespective of C/O ratio.
The secondary eclipse depths are consistent with previous studies. We do not
detect ellipsoidal variations at 3.6 micron, but our parameter uncertainties
-estimated via prayer-bead Monte Carlo- keep this non-detection consistent with
model predictions. At 4.5 micron, on the other hand, we detect ellipsoidal
variations that are much stronger than predicted. If interpreted as a geometric
effect due to the planet's elongated shape, these variations imply a 3:2 ratio
for the planet's longest:shortest axes and a relatively bright day-night
terminator. If we instead presume that the 4.5 micron ellipsoidal variations
are due to uncorrected systematic noise and we fix the amplitude of the
variations to zero, the best fit 4.5 micron transit depth becomes commensurate
with the 3.6 micron depth, within the uncertainties. The relative transit
depths are then consistent with a Solar composition and short scale height at
the terminator. Assuming zero ellipsoidal variations also yields a much deeper
4.5 micron eclipse depth, consistent with a Solar composition and modest
temperature inversion. We suggest future observations that could distinguish
between these two scenarios.Comment: 19 pages, 10 figures, ApJ in press. Improved discussion of gravity
brightenin
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