24 research outputs found
Measured performance of a 230 GHz prototype focal-plane feedhorn array made by direct drilling of smooth-walled horns
We present the first, complete 230 GHz feedhorn array manufactured by direct drilling of smooth–walled horns into a single plate of aluminium. The horn design process, based on a genetic algorithm, is described and the fabrication process, via direct drilling using shaped drill bits, is presented. We present cross coupling and beam pattern measurements of a close–packed pair of the smooth–walled horns fabricated in a single block of aluminium. We also present a prototype 37 horn array, again fabricated by drilling into a single block. Our measurements show that our designs and fabrication techniques will be robust when applied to large focal arrays of horns consisting of hundreds or thousands of feedhorns. We expect our smooth–walled horn designs and novel manufacturing techniques will offer an attractive, low-cost alternate to traditional horn arrays consisting of electroformed corrugated horns
Optimizing exoplanet atmosphere retrieval using unsupervised machine-learning classification
One of the principal bottlenecks to atmosphere characterisation in the era of
all-sky surveys is the availability of fast, autonomous and robust atmospheric
retrieval methods. We present a new approach using unsupervised machine
learning to generate informed priors for retrieval of exoplanetary atmosphere
parameters from transmission spectra. We use principal component analysis (PCA)
to efficiently compress the information content of a library of transmission
spectra forward models generated using the PLATON package. We then apply a
-means clustering algorithm in PCA space to segregate the library into
discrete classes. We show that our classifier is almost always able to
instantaneously place a previously unseen spectrum into the correct class, for
low-to-moderate spectral resolutions, , in the range and noise
levels up to ~per~cent of the peak-to-trough spectrum amplitude. The
distribution of physical parameters for all members of the class therefore
provides an informed prior for standard retrieval methods such as nested
sampling. We benchmark our informed-prior approach against a standard
uniform-prior nested sampler, finding that our approach is up to a factor two
faster, with negligible reduction in accuracy. We demonstrate the application
of this method to existing and near-future observatories, and show that it is
suitable for real-world application. Our general approach is not specific to
transmission spectroscopy and should be more widely applicable to cases that
involve repetitive fitting of trusted high-dimensional models to large data
catalogues, including beyond exoplanetary science.Comment: Accepted for publication in MNRA
TransitFit: an exoplanet transit fitting package for multi-telescope datasets and its application to WASP-127~b, WASP-91~b, and WASP-126~b
We present TransitFit, an open-source Python~3 package designed to fit
exoplanetary transit light-curves for transmission spectroscopy studies
(Available at https://github.com/joshjchayes/TransitFit and
https://github.com/spearnet/TransitFit, with documentation at
https://transitfit.readthedocs.io/). TransitFit employs nested sampling to
offer efficient and robust multi-epoch, multi-wavelength fitting of transit
data obtained from one or more telescopes. TransitFit allows per-telescope
detrending to be performed simultaneously with parameter fitting, including the
use of user-supplied detrending alogorithms. Host limb darkening can be fitted
either independently ("uncoupled") for each filter or combined ("coupled")
using prior conditioning from the PHOENIX stellar atmosphere models. For this
TransitFit uses the Limb Darkening Toolkit (LDTk) together with filter
profiles, including user-supplied filter profiles. We demonstrate the
application of TransitFit in three different contexts. First, we model SPEARNET
broadband optical data of the low-density hot-Neptune WASP-127~b. The data were
obtained from a globally-distributed network of 0.5m--2.4m telescopes. We find
clear improvement in our broadband results using the coupled mode over
uncoupled mode, when compared against the higher spectral resolution GTC/OSIRIS
transmission spectrum obtained by Chen et al. (2018). Using TransitFit, we fit
26 transit observations by TESS to recover improved ephemerides of the
hot-Jupiter WASP-91~b and a transit depth determined to a precision of 170~ppm.
Finally, we use TransitFit to conduct an investigation into the contested
presence of TTV signatures in WASP-126~b using 126 transits observed by TESS,
concluding that there is no statistically significant evidence for such
signatures from observations spanning 31 TESS sectors.Comment: 14 pages, 5 figures, 5 tables, submitted to MNRAS. Temporary data
address at https://cdsarc.u-strasbg.fr/ftp/vizier.submit/wasp-127b/ (Final
address to be included in accepted paper
TransitFit:an exoplanet transit fitting package for multi-telescope datasets and its application to WASP-127~b, WASP-91~b, and WASP-126~b
TransitFit: combined multi-instrument exoplanet transit fitting for JWST, HST, and ground-based transmission spectroscopy studies
We present TRANSITFIT1, a package designed to fit exoplanetary transit light curves. TRANSITFIT offers multi-epoch, multi-wavelength fitting of multi-telescope transit data. TRANSITFIT allows per-telescope detrending to be performed simultaneously with transit parameter fitting, including custom detrending. Host limb darkening can be fitted using prior conditioning from stellar atmosphere models. We demonstrate TRANSITFIT in a number of contexts. We model multi-telescope broad-band optical data from the ground-based SPEARNET survey of the low-density hot-Neptune WASP-127b and compare results to a previously published higher spectral resolution GTC/OSIRIS transmission spectrum. Using TRANSITFIT, we fit 26 transit epochs by TESS to recover improved ephemeris of the hot-Jupiter WASP-91b and a transit depth determined to a precision of 111 ppm. We use TRANSITFIT to conduct an investigation into the contested presence of TTV signatures in WASP-126b using 180 transits observed by TESS, concluding that there is no statistically significant evidence for such signatures from observations spanning 27 TESS sectors. We fit HST observations of WASP-43 b, demonstrating how TRANSITFIT can use custom detrending algorithms to remove complex baseline systematics. Lastly, we present a transmission spectrum of the atmosphere of WASP-96b constructed from simultaneous fitting of JWST NIRISS Early Release Observations and archive HST WFC3 transit data. The transmission spectrum shows generally good correspondence between spectral features present in both data sets, despite very different detrending requirements
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TransitFit: combined multi-instrument exoplanet transit fitting for JWST, HST and ground-based transmission spectroscopy studies
We present TRANSITFIT†, a package designed to fit exoplanetary transit light-curves. TRANSITFIT offers multi-epoch, multi-wavelength fitting of multi-telescope transit data. TRANSITFIT allows per-telescope detrending to be performed simultaneously with transit parameter fitting, including custom detrending. Host limb darkening can be fitted using prior conditioning from stellar atmosphere models. We demonstrate TRANSITFIT in a number of contexts. We model multi-telescope broadband optical data from the ground-based SPEARNET survey of the low-density hot-Neptune WASP-127 b and compare results to a previously published higher spectral resolution GTC/OSIRIS transmission spectrum. Using TRANSITFIT, we fit 26 transit epochs by TESS to recover improved ephemeris of the hot-Jupiter WASP-91 b and a transit depth determined to a precision of 111 ppm. We use TRANSITFIT to conduct an investigation into the contested presence of TTV signatures in WASP-126 b using 180 transits observed by TESS, concluding that there is no statistically significant evidence for such signatures from observations spanning 27 TESS sectors. We fit HST observations of WASP-43 b, demonstrating how TRANSITFIT can use custom detrending algorithms to remove complex baseline systematics. Lastly, we present a transmission spectrum of the atmosphere of WASP-96 b constructed from simultaneous fitting of JWST NIRISS Early Release Observations and archive HST WFC3 transit data. The transmission spectrum shows generally good correspondence between spectral features present in both datasets, despite very different detrending requirements
Theoretical and numerical analysis of very high harmonic superconducting tunnel junction mixers
We describe a procedure for modeling the nonlinear, quantum-mechanical behavior of very high harmonic superconductor-insulator-superconductor (SIS) mixers. A typical mixer is pumped by a strong microwave source at 10-15 GHz, which causes high-harmonic (20-40) currents to flow, any one of which can be used as a local oscillator to downconvert a submillimeter-wave signal to a low microwave frequency, 1-8 GHz. This mode of operation is attractive for measuring the beam patterns of conventional SIS mixers, because only a single submillimeter-wave source is needed. We conducted simulations using the 20th harmonic of a 13.5 GHz microwave source, downconverting a 271.4 GHz signal to a 1.4 GHz intermediate frequency. These simulations clearly show that linear downconversion can be achieved even for relatively high levels of rf signal power; although, care is needed when choosing the operating point. The patterns of behavior seen in the simulations are in remarkable agreement with recently published experimental results. © 2007 American Institute of Physics
Non-linear two-frequency analysis of SIS mixers through harmonic balance
We present a numerical procedure for simulating the non-linear behaviour of Superconductor-InsulatorSuperconductor (SIS) tunnel junction mixers. Mixers of this kind are used extensively in high-performance submillimetre-wave astronomical receivers. The procedure is complete in that both the signal and local-oscillator voltages can be at high levels, with significant amounts of harmonic content; also, the full quantum mechanical behaviour of the tunnel junction is taken into account. The initial simulations show that multi-tone analysis can be carried out in a numerically efficient manner, and that saturation, and the attendant generation of IF harmonics, can be modelled rigorously. This work constitutes the first full non-linear model of an SIS mixer, and the theoretical and numerical procedures described, will be of great importance when designing the next generation of heterodyne astronomical receivers
Multitone quantum simulations of saturating tunnel junction mixers
A theoretical technique was developed for simulating the quantum-mechanical multitone behavior of superconducting tunnel junction circuits. The procedure was based on a full quantum-mechanical description of photon-assisted tunneling. It was expected to be used to model saturation in submillimeter-wave SIS mixers. SIS mixers were used extensively in submillimeter-wave astronomy
Non-linear two-frequency analysis of SIS mixers through harmonic balance
We present a numerical procedure for simulating the non-linear behaviour of Superconductor-Insulator-Superconductor (SIS) tunnel-junction mixers. Mixers of this kind are used extensively in high-performance submillimetre-wave astronomical receivers. The procedure is complete in that both the signal and local-oscillator voltages can be at high levels, with significant amounts of harmonic content; also, the full quantum mechanical behaviour of the tunnel junction is taken into account. The initial simulations show that multi-tone analysis can be carried out in a numerically efficient manner, and that saturation, and the attendant generation of IF harmonics, can be modelled rigorously. This work constitutes the first full non-linear model of an SIS mixer, and the theoretical and numerical procedures described, will be of great importance when designing the next generation of heterodyne astronomical receivers