7 research outputs found
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
Solar Magnetic Polarity Effect on Neutron Monitor Count Rates: Comparing Latitude Surveys and Antarctic Stations
The Galactic cosmic ray spectrum manifests pronounced variations over the
11-year sunspot cycle and more subtle variations over the 22-year solar
magnetic cycle. An important tool to study these variations is repeated
latitude surveys with neutron monitors (NMs) onboard icebreakers in conjunction
with land-based references. We revisit 13 annual latitude surveys from 1994 to
2007 using reference data from the Mawson NM instead of McMurdo NM (which
closed in 2017). We then consider two more latitude surveys (2018 and 2019)
with a monitor similar to the 3NM64 in the previous surveys but without lead
rings around the central tube, a so-called ``semi-leaded neutron monitor.'' The
new surveys extend the linear relationship among data taken at different cutoff
rigidity ranges. They also confirm the ``crossover'' measured near solar minima
during epochs of opposite solar magnetic polarity and the absence of a
crossover for epochs having the same solar magnetic polarity.Comment: Accepted for publication in Astrophys.
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
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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
KELT-24b: A 5M\u3csub\u3eJ\u3c/sub\u3e Planet on a 5.6 day Well-aligned Orbit around the Young V = 8.3 F-star HD 93148
We present the discovery of KELT-24 b, a massive hot Jupiter orbiting a bright (V = 8.3 mag, K = 7.2 mag) young F-star with a period of 5.6 days. The host star, KELT-24 (HD 93148), has a T eff = K, a mass of M * = M ⊙, a radius of R * = 1.506 ± 0.022 R ⊙, and an age of Gyr. Its planetary companion (KELT-24 b) has a radius of R P = 1.272 ± 0.021 R J and a mass of M P = M J, and from Doppler tomographic observations, we find that the planet\u27s orbit is well-aligned to its host star\u27s projected spin axis (). The young age estimated for KELT-24 suggests that it only recently started to evolve from the zero-age main sequence. KELT-24 is the brightest star known to host a transiting giant planet with a period between 5 and 10 days. Although the circularization timescale is much longer than the age of the system, we do not detect a large eccentricity or significant misalignment that is expected from dynamical migration. The brightness of its host star and its moderate surface gravity make KELT-24b an intriguing target for detailed atmospheric characterization through spectroscopic emission measurements since it would bridge the current literature results that have primarily focused on lower mass hot Jupiters and a few brown dwarfs