Letteratura scientifica selezionata sul tema "FUV photochemistry"

Abstract Variability in the far-ultraviolet (FUV) emission produced by stellar activity affects photochemistry and heating in orbiting planetary atmospheres. We present a comprehensive analysis of the FUV variability of GJ 436, a field-age M2.5V star (P rot ≈ 44 days) that is orbited by a warm Neptune-sized planet (M ≈ 25 M ⊕, R ≈ 4.1 M ⊕, P orb ≈ 2.6 days). Observations at three epochs from 2012 to 2018 span nearly a full activity cycle, sample two rotations of the star and two orbital periods of the planet, and reveal a multitude of brief flares. From 2012 to 2018, the star’s 7.75 ± 0.10 yr activity cycle produced the largest observed variations, 38% ± 3% in the summed flux of the major FUV emission lines. In 2018, the variability due to rotation was 8% ± 2%. An additional 11% ± 1% scatter at a cadence of 10 minutes, which is treated as white noise in the fits, likely has both instrumental and astrophysical origins. Flares increased time-averaged emission by 15% over the 0.88 days of cumulative exposure, peaking as high as 25× quiescence. We interpret these flare values as lower limits given that flares too weak or too infrequent to have been observed likely exist. GJ 436’s flare frequency distribution at FUV wavelengths is unusual compared to other field-age M dwarfs, exhibiting a statistically significant dearth of high-energy (>4 × 1028 erg) events, which we hypothesize to be the result of a magnetic star–planet interaction (SPI) triggering premature flares. If an SPI is present, GJ 436 b’s magnetic field strength must be ≲100 G to explain the statistically insignificant increase in the orbit-phased FUV emission.

Abstract Characterizing rocky exoplanet atmospheres is a key goal of exoplanet science, but interpreting such observations will require understanding the stellar ultraviolet (UV) irradiation incident on the planet from its host star. Stellar UV mediates atmospheric escape, photochemistry, and planetary habitability, and observations of rocky exoplanets can only be understood in the context of the UV spectral energy distribution (SED) of their host stars. Particularly important are SEDs from observationally favorable but poorly understood low-mass M-dwarf stars, which are the only plausible targets for rocky planet atmospheric characterization for the next 1–2 decades. In this work, we explore the utility of AstroSat UltraViolet Imaging Telescope (UVIT) for the characterization of the UV SEDs of low-mass stars. We present observations of the nearby M0 star HIP 23309 in the far-UV (FUV) and near-UV (NUV) gratings of UVIT. Our FUV spectra are consistent with contemporaneous Hubble Space Telescope (HST) data and our NUV spectra are stable between orbits, suggesting UVIT is a viable tool for the characterization of the SEDs of low-mass stars. We apply our measured spectra to simulations of photochemistry and habitability for a hypothetical rocky planet orbiting HIP 23309 and elucidate the utility and limitations of UVIT in deriving UV SEDs of M-dwarf exoplanet hosts. Our work validates UVIT as a tool to complement HST in the characterization of exoplanet host stars and carries implications for its successor missions like INSIST.

Abstract Far-ultraviolet (FUV) emission lines from dwarf stars are important driving sources of photochemistry in planetary atmospheres. Properly interpreting spectral features of planetary atmospheres critically depends on the emission of its host star. While the spectral energy distributions (SEDs) of K- and M-type stars have been extensively characterized by previous observational programs, the full X-ray to infrared SED of F-type stars has not been assembled to support atmospheric modeling. On the second flight of the Suborbital Imaging Spectrograph for Transition-region Irradiance from Nearby Exoplanet host stars (SISTINE-2) rocket-borne spectrograph, we successfully captured the FUV spectrum of Procyon A (F5 IV-V) and made the first simultaneous observation of several emission features across the FUV bandpass (1010–1270 and 1300–1565 Å) of any cool star. We combine flight data with stellar models and archival observations to develop the first SED of a mid-F star. We model the response of a modern Earth-like exoplanet’s upper atmosphere to the heightened X-ray and extreme UV radiation within the habitable zone of Procyon A. These models indicate that this planet would not experience significant atmospheric escape. We simulate observations of the Lyα transit signal of this exoplanet with the Hubble Space Telescope (HST) and the Habitable Worlds Observatory (HWO). While marginally detectable with HST, we find that H i Lyα transits of potentially habitable exoplanets orbiting high radial velocity F-type stars could be observed with HWO for targets up to 150 pc away.

Context. Infrared and (sub-)millimeter observations of disks around T Tauri and Herbig Ae/Be stars point to a chemical differentiation, with a lower detection rate of molecules in disks around hotter stars. Aims. We aim to investigate the underlying causes of the chemical differentiation indicated by observations and perform a comparative study of the chemistry of T Tauri and Herbig Ae/Be disks. This is one of the first studies to compare the chemistry in the outer regions of these two types of disk. Methods. We developed a model to compute the chemical composition of a generic protoplanetary disk, with particular attention to the photochemistry, and applied it to a T Tauri and a Herbig Ae/Be disk. We compiled cross sections and computed photodissociation and photoionization rates at each location in the disk by solving the far-ultraviolet (FUV) radiative transfer in a 1+1D approach using the Meudon PDR code and adopting observed stellar spectra. Results. The warmer disk temperatures and higher ultraviolet flux of Herbig stars compared to T Tauri stars induce some differences in the disk chemistry. In the hot inner regions, H2O, and simple organic molecules like C2H2, HCN, and CH4 are predicted to be very abundant in T Tauri disks and even more in Herbig Ae/Be disks, in contrast with infrared observations that find a much lower detection rate of water and simple organics toward disks around hotter stars. In the outer regions, the model indicates that the molecules typically observed in disks, like HCN, CN, C2H, H2CO, CS, SO, and HCO+, do not have drastic abundance differences between T Tauri and Herbig Ae disks. Some species produced under the action of photochemistry, like C2H and CN, are predicted to have slightly lower abundances around Herbig Ae stars due to a narrowing of the photochemically active layer. Observations indeed suggest that these radicals are somewhat less abundant in Herbig Ae disks, although in any case, the inferred abundance differences are small, of a factor of a few at most. A clear chemical differentiation between both types of disks concerns ices. Owing to the warmer temperatures of Herbig Ae disks, one expects snow lines lying farther away from the star and a lower mass of ices compared to T Tauri disks. Conclusions. The global chemical behavior of T Tauri and Herbig Ae/Be disks is quite similar. The main differences are driven by the warmer temperatures of the latter, which result in a larger reservoir or water and simple organics in the inner regions and a lower mass of ices in the outer disk.

ABSTRACT Large ground- and space-based telescopes will be able to observe Earth-like planets in the near future. We explore how different planetary surfaces can strongly influence the climate, atmospheric composition, and remotely detectable spectra of terrestrial rocky exoplanets in the habitable zone depending on the host star’s incident irradiation spectrum for a range of Sun-like host stars from F0V to K7V. We update a well-tested 1D climate-photochemistry model to explore the changes of a planetary environment for different surfaces for different host stars. Our results show that using a wavelength-dependent surface albedo is critical for modelling potentially habitable rocky exoplanets.

Photochemistry and gas exchange in cold conditions in Zn-deficient red cabbage (Brassica oleraceaL. var.capitataf.rubra) plantsThe responses of red cabbage (Brassica oleraceaL. var.capitataf.rubra) plants to a low Zn supply and cold conditions (10°/7°C day/night temperature) were investigated in a hydroponic growing medium. A low Zn supply caused a significant reduction of shoot and root dry weight - up to 55% and 45% for the control and 62% and 52% for cold-treated plants, respectively. The total soluble carbohydrates and starch declined in Zn-deficient plants. Exposure to low temperatures, however, led to a decline in starch but an increase in soluble sugars. In Zn-sufficient plants, low temperatures increased the excitation capture efficiency of open photosystem II (PS II) reaction centres (RCs) (F'v/F'm), the quantum yield of PS II (ΦPSII), the electron transport rate (ETR) and the proportion of active chlorophyll associated with the RCs of PS II (Fv/F0). Low temperatures did not affect net CO2uptake in Zn-sufficient plants, though a reduction of stomatal conductance occurred. The results demonstrated that although cold-treated plants were slightly more susceptible to Zn deficiency, cold treatment caused greater shoot biomass (up to 32%) in plants supplied with adequate Zn. The adaptation of red cabbage plants to cold conditions is attributable to improved photochemical events in the leaves, a maintenance of the net CO2assimilation rate, lower water loss and the accumulation of anthocyanins as antioxidants.

Abstract High-sensitivity hypothesis-free subcellular proteomics is challenging due to the limited sensitivity of mass spectrometry and the lack of amplification tools for proteins. Without such technology, it is not possible to discover proteins at specific locations of interest in cells or tissue samples. Here, we introduce a total-sync ultra-content microscopic system termed MicroscoopTM that integrates microscopy, optics, FPGA-based mechatronics, photochemistry, and deep learning or computer vision to enable high-content in situ photolabeling. MicroscoopTM photolabels proteins at user defined regions of interests (ROIs) under a microscope utilizing directed photochemistry in one field of view (FOV) at a time for tens of thousands of FOVs with similar morphological features. With this platform, we are able to photolabel proteins with biotin probes in cellular organelles, granules or cell-cell contact surfaces with a high precision at nanoscale resolution, and obtain sufficient amount of biotinylated proteins for mass spectrometry. We made a robust demonstration in the proteome mapping of human cellular nucleus from single-shot experiment to >1000 nuclear protein identification with > 90% specificity. Further data analysis revealed identification of a hundred of low protein copy number proteins and a high coverage of nuclear complexes. In proteome mapping of the nucleolus, we ranked proteins by order of abundance and revealed that 97 out of the top 100 proteins were annotated as nucleolar proteins. Unexpectedly, in mapping the stress granule (SG) proteome, a relatively low SG specificity (74%) were found in the top 50 abundant proteins, therefore we further characterize the proteins that have no prior SG annotation by immunostaining. Nine out of the thirteen unexplored proteins including PDLIM7, EIF3CL, YWHAE, RPSA, UGDH, DDX17, ANLN, PSMA6, and MCM2 were found to have SG patterns and co-localized with SG marker (G3BP1), raising our top 50 SG specificity to up to 92%. Together, our total-sync ultra-content microscopic platform enables hypothesis-free, de novo subcellular proteome mapping at user defined ROIs with high sensitivity and specificity, thereby broadly benefits the cell biology field in finding novel proteins or biomarkers. Citation Format: Jung-Chi Liao, Chih-Wei Chang, Yi-De Chen, Chantal Hoi Yin Cheung, Chia-Wen Chung, Hsiao-Jen Chang, Yong-Da Sie, You-Pi Liu, Yu-Chih Lin, Hsiang-Ju Kai, Weng Man Chong, Hsin-Yi Wu. Total-sync ultra-content microscopic opto-biotinylation enables high-sensitivity hypothesis-free subcellular protein discovery. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5638.

Cette thèse porte sur l’étude de l’évolution photochimique des aérosols présents dans la stratosphère de Titan. Au début de la saison automnale au pôle sud, la stratosphère, atteinte par des rayonnements FUV solaires, s’est refroidie et particulièrement enrichie en matériaux organiques : en aérosols, ainsi qu’en benzène (C6H6) et cyanure hydrogène (HCN), formés à haute altitude, qui ont été à l’origine de la formation de nuages de glace saisonniers. Expérimentalement, la photochimie de ces glaces, induite par des rayonnements UV similaires à ceux parvenant dans la basse stratosphère (l > 230 nm), conduit à la formation d’une phase volatile et d’une phase réfractaire qui représente en laboratoire un analogue des aérosols de la stratosphère de Titan formés par photo-polymérisation de glaces organiques. Nos résultats permettent de montrer que les propriétés spectroscopiques des analogues d’aérosols issus de la photolyse de glaces résultant de la condensation simultanée du benzène et du cyanure d’hydrogène sont similaires à celles des aérosols présents dans la stratosphère, d’après les données collectées par les spectromètres Cassini/VIMS et CIRS, à l’inverse des analogues produits par l’irradiation des glaces de benzène pur qui eux se différencient significativement des aérosols de la stratosphère
This thesis deals with the study of the photochemical evolution of aerosols in Titan's stratosphere. At the beginning of the autumn season at the South Pole, the stratosphere, reached by FUV solar radiations, cooled and was particularly enriched in organic materials: aerosols as well as benzene (C6H6) and hydrogen cyanide (HCN), formed at high altitudes, and were responsible for the formation of seasonal ice clouds. Experimentally, the photochemistry of these systems, induced by UV radiations similar to those reaching the lower stratosphere (l > 230 nm), leads to the formation of a volatile phase and a refractory phase that represents experimentally an analogue of Titan stratospheric aerosols formed by polymerization of organic ice. Our results show that the spectroscopic properties of aerosols from the polymerization of ices of benzene mixed with hydrogen cyanide are more similar to aerosols present in the stratosphere, according to the data collected by the Cassini/VIMS and CIRS spectrometers, than those of aerosols produced by the irradiation of pure benzene ices