1,721,056 research outputs found
Alfnoor: assessing the information content of Ariel's low resolution spectra with planetary population studies.
No full textDetecting molecules in Ariel low resolution transmission spectra
Full text linkThe Ariel Space Mission aims to observe a diverse sample of exoplanet atmospheres across a wide wavelength range of 0.5 to 7.8 microns. The observations are organized into four Tiers, with Tier 1 being a reconnaissance survey. This Tier is designed to achieve a sufficient signal-to-noise ratio (S/N) at low spectral resolution in order to identify featureless spectra or detect key molecular species without necessarily constraining their abundances with high confidence. We introduce a P-statistic that uses the abundance posteriors from a spectral retrieval to infer the probability of a molecule’s presence in a given planet’s atmosphere in Tier 1. We find that this method predicts probabilities that correlate well with the input abundances, indicating considerable predictive power when retrieval models have comparable or higher complexity compared to the data. However, we also demonstrate that the P-statistic loses representativity when the retrieval model has lower complexity, expressed as the inclusion of fewer than the expected molecules. The reliability and predictive power of the P-statistic are assessed on a simulated population of exoplanets with H2
-He dominated atmospheres, and forecasting biases are studied and found not to adversely affect the classification of the survey
Alfnoor: Assessing the Information Content of Ariel's Low-resolution Spectra with Planetary Population Studies
Full text linkThe Ariel Space Telescope will provide a large and diverse sample of exoplanet spectra, performing spectroscopic observations of about 1000 exoplanets in the wavelength range 0.5–7.8 μm. In this paper, we investigate the information content of Ariel's Reconnaissance Survey low-resolution transmission spectra. Among the goals of the Ariel Reconnaissance Survey is also to identify planets without molecular features in their atmosphere. In this work, (1) we present a strategy that will allow us to select candidate planets to be reobserved in Ariel's higher-resolution tier, (2) we propose a metric to preliminary classify exoplanets by their atmospheric composition without performing an atmospheric retrieval, and (3) we introduce the possibility to find other methods to better exploit the data scientific content
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Estimation of the energy losses from shading and orientation issues: A large scale study on solar panels data.
No full textImperial Users onl
Next generation techniques to characterise exoplanetary atmospheres
Full text linkIn the past decade, more than 4000 exoplanets have been discovered using a host of detection techniques. However, as of today, only a fraction of these planets have been studied in great detail. For about 60 planets, we start to have preliminary information about their atmospheric properties. Despite these successes, the spectroscopic analysis of exoatmospheres is still in its infancy and with the arrival of better performing instrumentation from space and the ground, it is now necessary to upgrade our modelling tools to maximise the science return of said future facilities. Currently, spectral retrieval models represent the most successful tools to extract the chemical, thermal and dynamical properties of extrasolar atmospheres. In this thesis, a full re-design of the well-established retrieval code TauREx is presented along with new feature extraction models, such as a state-of-the-art phase curve retrieval method. New tools, such as the Alfnoor algorithm, were also developed and used to enable the simultaneous study of a large population of objects, as opposed to individual planets. These new methods were used, in concert with other dedicated tools, to analyse and interpret current data of exoplanetary atmospheres recorded with the Hubble and Spitzer Space Telescopes. While providing new insights into exoplanets’ atmospheric properties, these analyses also demonstrate the limitations of current instruments. Next generation space telescopes, such as Ariel and JWST, will be revolutionary in providing thousands of high-quality exoplanetary spectra. The dramatic improvement of the data provided by these facilities will undoubtedly cause big challenges in the interpretation. This thesis addresses some of the expected challenges and paves the way to the design of future techniques, valid for the study of large atmospheric samples
On spectroscopic phase-curve retrievals: H2 dissociation and thermal inversion in the atmosphere of the ultra-hot Jupiter WASP-103 b
Full text linkThis work presents a re-analysis of the spectroscopic phase-curve
observations of the ultra hot Jupiter WASP-103 b obtained by the Hubble Space
Telescope (HST) and the Spitzer Telescope. Traditional 1D and unified 1.5D
spectral retrieval techniques are employed, allowing to map the thermal
structure and the abundances of trace gases in this planet as a function of
longitude. On the day-side, the atmosphere is found to have a strong thermal
inversion, with indications of thermal dissociation traced by continuum H-
opacity. Water vapor is found across the entire atmosphere but with depleted
abundances of around 1e-5, consistent with the thermal dissociation of this
molecule. Regarding metal oxide and hydrides, FeH is detected on the hot-spot
and the day-side of WASP-103 b, but TiO and VO are not present in detectable
quantities. Carbon-bearing species such as CO and CH4 are also found, but since
their detection is reliant on the combination of HST and Spizer, the retrieved
abundances should be interpreted with caution. Free and Equilibrium chemistry
retrievals are overall consistent, allowing to recover robust constraints on
the metallicity and C/O ratio for this planet. The analyzed phase-curve data
indicates that the atmosphere of WASP-103 b is consistent with solar elemental
ratios
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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