182 research outputs found
Molecular Detectability in Exoplanetary Emission Spectra
Of the many recently discovered worlds orbiting distant stars, very little is
yet known of their chemical composition. With the arrival of new transit
spectroscopy and direct imaging facilities, the question of molecular
detectability as a function of signal-to-noise (SNR), spectral resolving power
and type of planets has become critical. In this paper, we study the
detectability of key molecules in the atmospheres of a range of planet types,
and report on the minimum detectable abundances at fixed spectral resolving
power and SNR. The planet types considered - hot Jupiters, hot super-Earths,
warm Neptunes, temperate Jupiters and temperate super-Earths - cover most of
the exoplanets characterisable today or in the near future. We focus on key
atmospheric molecules, such as CH4, CO, CO2, NH3, H2O, C2H2, C2H6, HCN, H2S and
PH3. We use two methods to assess the detectability of these molecules: a
simple measurement of the deviation of the signal from the continuum, and an
estimate of the level of confidence of a detection through the use of the
likelihood ratio test over the whole spectrum (from 1 to 16). We find
that for most planetary cases, SNR=5 at resolution R=300 ()
and R=30 () is enough to detect the very strongest spectral
features for the most abundant molecules, whereas an SNR comprised between 10
and 20 can reveal most molecules with abundances 10^-6 or lower, often at
multiple wavelengths. We test the robustness of our results by exploring
sensitivity to parameters such as vertical thermal profile, mean molecular
weight of the atmosphere and relative water abundances. We find that our main
conclusions remain valid except for the most extreme cases. Our analysis shows
that the detectability of key molecules in the atmospheres of a variety of
exoplanet cases is within realistic reach, even with low SNR and spectral
resolving power.Comment: ICARUS Accepte
Small Bodies Science with Twinkle
Twinkle is an upcoming 0.45m space-based telescope equipped with a visible
and two near-infrared spectrometers covering the spectral range 0.4 to
4.5{\mu}m with a resolving power R~250 ({\lambda}<2.42{\mu}m) and R~60
({\lambda}>2.42{\mu}m). We explore Twinkle's capabilities for small bodies
science and find that, given Twinkle's sensitivity, pointing stability, and
spectral range, the mission can observe a large number of small bodies. The
sensitivity of Twinkle is calculated and compared to the flux from an object of
a given visible magnitude. The number, and brightness, of asteroids and comets
that enter Twinkle's field of regard is studied over three time periods of up
to a decade. We find that, over a decade, several thousand asteroids enter
Twinkle's field of regard with a brightness and non-sidereal rate that will
allow Twinkle to characterise them at the instrumentation's native resolution
with SNR > 100. Hundreds of comets can also be observed. Therefore, Twinkle
offers researchers the opportunity to contribute significantly to the field of
Solar System small bodies research.Comment: Published in JATI
Remote-sensing Characterisation of Major Solar System Bodies with the Twinkle Space Telescope
Remote-sensing observations of Solar System objects with a space telescope
offer a key method of understanding celestial bodies and contributing to
planetary formation and evolution theories. The capabilities of Twinkle, a
space telescope in a low Earth orbit with a 0.45m mirror, to acquire
spectroscopic data of Solar System targets in the visible and infrared are
assessed. Twinkle is a general observatory that provides on demand observations
of a wide variety of targets within wavelength ranges that are currently not
accessible using other space telescopes or that are accessible only to
oversubscribed observatories in the short-term future. We determine the periods
for which numerous Solar System objects could be observed and find that Solar
System objects are regularly observable. The photon flux of major bodies is
determined for comparison to the sensitivity and saturation limits of Twinkle's
instrumentation and we find that the satellite's capability varies across the
three spectral bands (0.4-1, 1.3-2.42, and 2.42-4.5{\mu}m). We find that for a
number of targets, including the outer planets, their large moons, and bright
asteroids, the model created predicts that with short exposure times,
high-resolution spectra (R~250, {\lambda}
2.42{\mu}m) could be obtained with signal-to-noise ratio (SNR) of >100 with
exposure times of <300s
Dual focus polarisation splitting lens
We have successfully designed and measured a unique polarisation splitting lens which focuses the orthogonal linear polarisations side-by-side in the lens focal plane. This concept can find application in situations where there is limited space for the beam splitters and focusing optics that are required for incoherent detectors
A Demonstration of Spectral and Spatial Interferometry at THz Frequencies
A laboratory prototype spectral/spatial interferometer has been constructed
to demonstrate the feasibility of the double Fourier technique at Far Infrared
(FIR) wavelengths (0.15 - 1 THz). It is planned to use this demonstrator to
investigate and validate important design features and data processing methods
for future astronomical FIR interferometer instruments. In building this
prototype we have had to address several key technologies to provide an end-end
system demonstration of this double Fourier interferometer. We report on the
first results taken when viewing single slit and double slit sources at the
focus of a large collimator used to simulate real sources at infinity. The
performance of the prototype instrument for these specific field geometries is
analyzed to compare with the observed interferometric fringes and to
demonstrate image reconstruction capabilities.Comment: Accepted for publication in Applied Optic
A Focusing Metamaterial Based Wollaston Prism
By using existing metal mesh technology we propose a new lens design that behaves in a similar way to a Wollaston Prism. That is, a device that separates out the two linear polarised states of the incident field and then focuses them separately on same focal plane. The design is an evolution of an existing GRIN lens based on the same technology. The proposed lens design has a diameter of 75mm while only being 2mm thick. This will focus two beams at a distance of 250mm with a separation of 10mm, over the frequency range of 100-200GHZ. Such a device would be useful where space and weight are an issue and would allow the use of incoherent detectors
Transmission Properties of Subwavelength Planar Fractals for THz Wavelengths
We investigate the transmission properties of planar H fractal structures in THz range. 3D EM simulations using HFSS are used to design the parameters of the fractals and to evaluate the optical properties. We observe the transmission spectra with pass bands and stop bands, which show the subwavelength transmission through the non-metallic gaps. This unique transmission property through subwavelength apertures makes it potentially useful frequency selective components in THz region. We experimentally demonstrate its behavior by designing and fabricating four prototype planar fractals in the range of 0-1.5THz and characterize using a polarizing Fourier transform spectrometer. We find good agreement between the models and measurements
Polypropylene Embedded Metal-Mesh Broadband Achromatic Half Wave Plate for Millimeter Wavelengths
We describe a novel multi-layered metal mesh achromatic half wave plate for
use in astronomical polarimetric instruments. The half wave plate is designed
to operate across the frequency range from 125-250 GHz. The wave plate is
manufactured from 12-layers of thin film metallic inductive and capacitive
grids patterned onto polypropylene sheets, which are then bonded together using
a hot pressing technique. Transmission line modelling and 3-D electromagnetic
simulations are used to optimize the parameters of the metal-mesh patterns and
to evaluate their optical properties. A prototype half wave plate has been
fabricated and its performance characterized in a polarizing Fourier transform
spectrometer. The device performance is consistent with the modelling although
the measured differential phase shift for two orthogonal polarizations is lower
than expected. This difference is likely to result from imperfect patterning of
individual layers and misalignment of the grids during manufacture.Comment: 14 pages, 13 Figures, 1 Tabl
Testicular degeneration and infertility following arbovirus infection
Arboviruses can cause a variety of clinical signs including febrile illness, arthritis, encephalitis and hemorrhagic fever. The recent Zika epidemic highlighted the possibility that arboviruses may also negatively affect the male reproductive tract. In this study, we focused on bluetongue virus (BTV), the causative agent of bluetongue and one of the major arboviruses of ruminants. We show that rams that recovered from bluetongue displayed signs of testicular degeneration and azoospermia up to 100 days after the initial infection. Importantly, testicular degeneration was induced in rams experimentally infected with either a high (BTV-1IT2006) or low (BTV-1IT2013) virulence strain of BTV. Rams infected with the low virulent BTV strain displayed testicular lesions in the absence of other major clinical signs. Testicular lesions in BTV-infected rams were due to viral replication in the endothelial cells of the peritubular areas of the testes, resulting in stimulation of a type-I IFN response, reduction of testosterone biosynthesis by Leydig cells, and destruction of Sertoli cells and the blood-testis barrier in more severe cases. Hence, BTV induces testicular degeneration and disruption of spermatogenesis by replicating solely in the endothelial cells of the peritubular areas unlike other gonadotropic viruses. This study shows that a naturally occurring arboviral disease can cause testicular degeneration and affect male fertility at least temporarily
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