Colorado Ultraviolet Transit Experiment Data Simulator

The Colorado Ultraviolet Transit Experiment (CUTE) is a 6U NASA CubeSat carrying on-board a low-resolution (R~2000--3000), near-ultraviolet (2500--3300 {\AA}) spectrograph. It has a rectangular primary Cassegrain telescope to maximize the collecting area. CUTE, which is planned for launch in Spring 2020, is designed to monitor transiting extra-solar planets orbiting bright, nearby stars aiming at improving our understanding of planet atmospheric escape and star-planet interaction processes. We present here the CUTE data simulator, which we complemented with a basic data reduction pipeline. This pipeline will be then updated once the final CUTE data reduction pipeline is developed. We show here the application of the simulator to the HD209458 system and a first estimate of the precision on the measurement of the transit depth as a function of temperature and magnitude of the host star. We also present estimates of the effect of spacecraft jitter on the final spectral resolution. The simulator has been developed considering also scalability and adaptability to other missions carrying on-board a long-slit spectrograph. The data simulator will be used to inform the CUTE target selection, choose the spacecraft and instrument settings for each observation, and construct synthetic CUTE wavelength-dependent transit light curves on which to develop the CUTE data reduction pipeline.Comment: Accepted for publication in the Journal of Astronomical Telescopes, Instruments and System

Non-Local Thermodynamic Equilibrium Transmission Spectrum Modelling of HD209458b

Context - Exoplanetary upper atmospheres are low density environments where radiative processes can compete with collisional ones and introduce non-local thermodynamic equilibrium (NLTE) effects into transmission spectra. Aims - We develop a NLTE radiative transfer framework capable of modelling exoplanetary transmission spectra over a wide range of planetary properties. Methods - We adapt the NLTE spectral synthesis code Cloudy to produce an atmospheric structure and atomic transmission spectrum in both NLTE and local thermodynamic equilibrium (LTE) for the hot Jupiter HD209458b, given a published T-P profile and assuming solar metallicity. Selected spectral features, including H$\alpha$, Na I D, He I $\lambda$10830, Fe I & II ultra-violet (UV) bands, and C, O and Si UV lines, are compared with literature observations and models where available. The strength of NLTE effects are measured for individual spectral lines to identify which features are most strongly affected. Results - The developed modelling framework computing NLTE synthetic spectra reproduces literature results for the He I $\lambda$10830 triplet, the Na I D lines, and the forest of Fe I lines in the optical. Individual spectral lines in the NLTE spectrum exhibit up to 40 % stronger absorption relative to the LTE spectrum.Comment: Accepted for publication in A&A, 15 pages, 13 figure

New benzene absorption cross sections in the VUV, relevance for Titan’s upper atmosphere

This is a pre-print (pre-peer review) manuscript. It is moderately different from the accepted manuscript and from the published article. Citation of published article: Fernando J. Capalbo, Yves Bénilan, Nicolas Fray, Martin Schwell, Norbert Champion, Et-touhami Es-sebbar, Tommi T. Koskinen, Ivan Lehocki, Roger V. Yelle. Icarus, vol. 265, p. 95 - 109. February 2016. doi: 10.1016/j.icarus.2015.10.006.International audienceBenzene is an important molecule in Titan’s atmosphere because it is a potential link between the gas phase and the organic solid phase. We measured photoabsorption in the ultraviolet by benzene gas at temperatures covering the range from room temperature to 215 K. We derived benzene absorption cross sections and analyzed them in terms of the transitions observed. No significant variation with measurement temperature was observed. We discuss the implications of our measurements for the derivation of benzene abundance profiles in Titan’s thermosphere, by the Cassini/Ultraviolet Imaging Spectrograph (UVIS). The use of absorption cross sections at low temperature is recommended to avoid small systematic uncertainties in the profiles. We used our measurements, together with absorption cross sections from other molecules, to analyze four stellar occultations by Titan, measured by UVIS during flybys T21, T41, T41_II, and T53. We derived and compared benzene abundance profiles in Titan’s thermosphere between approximately 530 and 1000 km, for different dates and geographical locations. The comparisons of our benzene profiles with each other, and with profiles from models of the upper atmosphere, point to a complex behavior that is not explained by current photochemical models

Joint effects of alcohol use, smoking and body mass index as an explanation for the alcohol harm paradox : causal mediation analysis of eight cohort studies

Background and aims Lower socio-economic status (SES) is associated with higher alcohol-related harm despite lower levels of alcohol use. Differential vulnerability due to joint effects of behavioural risk factors is one potential explanation for this 'alcohol harm paradox'. We analysed to what extent socio-economic inequalities in alcohol-mortality are mediated by alcohol, smoking and body mass index (BMI), and their joint effects with each other and with SES. DesignCohort study of eight health examination surveys (1978-2007) linked to mortality data. Setting Finland.ParticipantsA total of 53 632 Finnish residents aged 25+ years.MeasurementsThe primary outcome was alcohol-attributable mortality. We used income as an indicator of SES. We assessed the joint effects between income and mediators (alcohol use, smoking and BMI) and between the mediators, adjusting for socio-demographic indicators. We used causal mediation analysis to calculate the total, direct, indirect and mediated interactive effects using Aalen's additive hazards models. Findings During 1 085 839 person-years of follow-up, we identified 865 alcohol-attributable deaths. We found joint effects for income and alcohol use and income and smoking, resulting in 46.8 and 11.4 extra deaths due to the interaction per 10 000 person-years. No interactions were observed for income and BMI or between alcohol and other mediators. The lowest compared with the highest income quintile was associated with 5.5 additional alcohol deaths per 10 000 person-years (95% confidence interval = 3.7, 7.3) after adjusting for confounders. The proportion mediated by alcohol use was negative (-69.3%), consistent with the alcohol harm paradox. The proportion mediated by smoking and BMI and their additive interactions with income explained 18.1% of the total effect of income on alcohol-attributable mortality. Conclusions People of lower socio-economic status appear to be more vulnerable to the effects of alcohol use and smoking on alcohol-attributable mortality. Behavioural risk factors and their joint effects with income may explain part of the alcohol harm paradox.Peer reviewe

Saturn's atmospheric response to the large influx of ring material inferred from Cassini INMS measurements

During the Grand Finale stage of the Cassini mission, organic-rich ring material was discovered to be flowing into Saturn's equatorial upper atmosphere at a surprisingly large rate. Through a series of photochemical models, we have examined the consequences of this ring material on the chemistry of Saturn's neutral and ionized atmosphere. We find that if a substantial fraction of this material enters the atmosphere as vapor or becomes vaporized as the solid ring particles ablate upon atmospheric entry, then the ring-derived vapor would strongly affect the composition of Saturn's ionosphere and neutral stratosphere. Our surveys of Cassini infrared and ultraviolet remote-sensing data from the final few years of the mission, however, reveal none of these predicted chemical consequences. We therefore conclude that either (1) the inferred ring influx represents an anomalous, transient situation that was triggered by some recent dynamical event in the ring system that occurred a few months to a few tens of years before the 2017 end of the Cassini mission, or (2) a large fraction of the incoming material must have been entering the atmosphere as small dust particles less than ~100 nm in radius, rather than as vapor or as large particles that are likely to ablate. Future observations or upper limits for stratospheric neutral species such as HC$_3$N, HCN, and CO$_2$ at infrared wavelengths could shed light on the origin, timing, magnitude, and nature of a possible vapor-rich ring-inflow event.Comment: accepted in Icaru

Colorado Ultraviolet Transit Experiment: a dedicated CubeSat mission to study exoplanetary mass loss and magnetic fields

The Colorado Ultraviolet Transit Experiment (CUTE) is a near-UV (2550 to 3300  Å) 6U CubeSat mission designed to monitor transiting hot Jupiters to quantify their atmospheric mass loss and magnetic fields. CUTE will probe both atomic (Mg and Fe) and molecular (OH) lines for evidence of enhanced transit absorption, and to search for evidence of early ingress due to bow shocks ahead of the planet’s orbital motion. As a dedicated mission, CUTE will observe ≳100 spectroscopic transits of hot Jupiters over a nominal 7-month mission. This represents the equivalent of <700 orbits of the only other instrument capable of these measurements, the Hubble Space Telescope. CUTE efficiently utilizes the available CubeSat volume by means of an innovative optical design to achieve a projected effective area of ∼28  cm^2, low instrumental background, and a spectral resolving power of R∼3000 over the primary science bandpass. These performance characteristics enable CUTE to discern transit depths between 0.1% and 1% in individual spectral absorption lines. We present the CUTE optical and mechanical design, a summary of the science motivation and expected results, and an overview of the projected fabrication, calibration, and launch timeline