Extreme UV Radiation Research Articles

Hydrogen-dominated upper atmosphere of an exoplanet: Heating by stellar radiation from soft X-rays to extreme ultraviolet

A study is presented of how the upper atmosphere of a planet is heated by extreme radiation from the parent star, depending on the distribution of the radiation flux in the soft X-ray and extreme ultraviolet (EUV) ranges. Calculations are performed to find the efficiency of heating by stellar X-ray to EUV radiation in a hydrogen-dominated upper atmosphere for the extrasolar gas giant HD 209458b. It is shown that heating efficiency by extreme stellar UV radiation in a hydrogen-dominated upper atmosphere does not exceed 20–25% at the main thermospheric heights given that the calculation takes into account the photoelectron impact. It is found that an increase in the X-ray flux by several orders of magnitude leads to a slight decrease in the heating efficiency.

Generation of bright phase-matched circularly-polarized extreme ultraviolet high harmonics

Circularly-polarized extreme UV and X-ray radiation provides valuable access to the structural, electronic and magnetic properties of materials. To date, this capability was available only at large-scale X-ray facilities such as synchrotrons. Here we demonstrate the first bright, phase-matched, extreme UV circularly-polarized high harmonics and use this new light source for magnetic circular dichroism measurements at the M-shell absorption edges of Co. We show that phase matching of circularly-polarized harmonics is unique and robust, producing a photon flux comparable to the linearly polarized high harmonic sources that have been used very successfully for ultrafast element-selective magneto-optic experiments. This work thus represents a critical advance that makes possible element-specific imaging and spectroscopy of multiple elements simultaneously in magnetic and other chiral media with very high spatial and temporal resolution, using tabletop-scale setups.

Measurement of the Wigner distribution function of non-separable laser beams employing a toroidal mirror

We present a new experimental approach to determine the Wigner distribution function of non-separable laser beams. A rotatable toroidal mirror is employed to focus an IR laser beam at a wavelength of . For different rotation angles of the mirror, intensity profiles of the reflected beam are captured. The resulting data suffices to fully reconstruct the four-dimensional Wigner distribution from which the global degree of coherence is derived. A comparison to theoretical expectations reveals validity of the applied formalism. Since the setup dispenses with any transmissive optics it can be applied to a broad spectral range, especially to extreme UV and soft x-ray radiation.

Effects of X-ray and extreme UV radiation on circumbinary planets

Several circumbinary planets have recently been discovered. The orbit of a planet around a binary stellar system poses several dynamic constraints. The effects that radiation from the host stars may have on the planet atmospheres must be considered. Because of the configuration of a close binary system, these stars have a high rotation rate, which causes a permanent state of high stellar activity and copious XUV radiation. The accumulated effects are stronger than for exoplanets around single stars, and cause a faster evaporation of their atmospheres. We evaluate the effects that stellar radiation has on the evaporation of exoplanets around binary systems and on the survival of these planets. We considered the XUV spectral range to account for the photons that are easily absorbed by a planet atmosphere that is mainly composed of hydrogen. A more complex atmospheric composition is expected to absorb this radiation more efficiently. We used direct X-ray observations to evaluate the energy in the X-rays range and coronal models to calculate the (nondetectable) EUV part of the spectrum. The simulations show that exoplanets in a close orbit will suffer strong photoevaporation that may cause a total loss of atmosphere in a short time. A binary system of two solar-like stars will be highly efficient in evaporating the atmosphere of the planet. These systems will be difficult to find, even if they are dynamically stable. Still, planets may orbit around binary systems of low mass stars for wider orbits. Currently known circumbinary planets are not substantially affected by thermal photoevaporation processes, unless Kepler-47 b has an inflated atmosphere. The distribution of the orbital periods of circumbinary planets is shifted to much longer periods than the average of Kepler planets, which supports a scenario of strong photoevaporation in close-in circumbinary planets.

Ionization fraction in the thermosphere of the exoplanet HD 209458b

Dissociation and ionization of hydrogen molecules and ionization of hydrogen atoms due to extreme UV radiation from the parent star are accompanied by the formation of a concurrent photoelectron flux with excess kinetic energy. These dissociation and ionization processes are the main source of atomic and molecular ions in the thermospheres of extrasolar planets, such as the “hot Jupiter” HD 209458b. The ionization processes are the most important part of contemporary aeronomic models of planetary atmospheres in the Solar System and extrasolar systems (Johnson et al., 2008; Yelle et al., 2008).

SOLAR PHOTOIONIZATION RATES FOR INTERSTELLAR NEUTRALS IN THE INNER HELIOSPHERE: H, He, O, AND Ne

Extreme UV (EUV) spectra from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)/Solar EUV Experiment are used to infer photoionization rates in the inner heliosphere. Relating these rates to various proxies describing the solar EUV radiation, we construct a multi-linear model which allows us to extrapolate ionization rates back to periods when no routine measurements of the solar EUV spectral distribution have been available. Such information is important, e.g., for comparing conditions of the interstellar neutral particles in the inner heliosphere at the time of Ulysses/GAS observations with conditions during the more recent observations of the Interstellar Boundary Explorer. From a period of 11 yr when detailed spectra from both TIMED and three proxies—Solar and Heliospheric Observatory/CELIAS/SEM-rates, F10.7 radio flux, and Mg II core-to-wing indices—have been available, we conclude that the simple model is able to reproduce the photoionization rates with an uncertainty of typically 5%.

Comets as solar probes

By rapidly evaporating as they fly through the Sun’s hot outer atmosphere, sungrazing comets reveal an otherwise invisible magnetic field that shapes the very beginnings of the solar wind.

Rosácea: puesta al día

Rosacea is a chronic inflammatory disease. Its frequency is higher in pale-skinned people and women over 30 years. Disease mechanisms include: abnormalities in innate immunity, inflammatory reactions to microorganisms, ultraviolet radiation damage, and vascular dysfunction. There are four clinical subtypes: erythematotelangiectatic, pustular papules, phymatous and ocular rosacea. Patients may present one or more characteristics of each subtypes. Injuries are classically located in midface area. Extreme temperatures, UV radiation, hot beberages, spicy foods, alcohol, exercise, topical irritants, psychological symptoms and drugs are associated to exacerbations. Clinical evaluation of the patient is usually enough for diagnosis. Nonpharmacologic interventions are essential for treatment. These include avoiding use of cosmetic, and triggers, skin care, and broad-spectrum sun protection. Patients with no response to general measures can respond to pharmacological agents. Topical metronidazole and azelaic acid are considered
 first-line treatments in mild to moderate disease. Oral tetracycline, have been used for many years for the treatment of papulopustular rosacea. Isotretinoin is useful in refractory disease. Treatment must be continous to maintain the response.

Limitation of the accuracy of F2-layer critical frequency predictions due to variations in the flux of the Sun’s extreme UV radiation

The accuracy limitations of critical frequency predictions in the ionospheric F2 layer are considered, which arise due to random variations in the Sun’s extreme UV radiation during the month. An analysis of δf (relative values of monthly rms scatters of the F2-layer critical frequencies) and the appropriate δu values (monthly rms scatters of extreme UV radiation) has shown their dependence on the solar activity level. A conclusion is drawn that when prognostic models of monthly medians are used for forecasting foF2 for a particular date, the error can hardly be less than ∼7% at low solar activity and ∼15% at a higher solar activity level.

Isolation of UVC-Tolerant Bacteria from the Hyperarid Atacama Desert, Chile

Martian surface microbial inhabitants would be challenged by a constant and unimpeded flux of UV radiation, and the study of analog model terrestrial environments may be of help to understand how such life forms could survive under this stressful condition. One of these environments is the Atacama Desert (Chile), a well-known Mars analog due to its extreme dryness and intense solar UV radiation. Here, we report the microbial diversity at five locations across this desert and the isolation of UVC-tolerant microbial strains found in these sites. Denaturing gradient gel electrophoresis (DGGE) of 16S rDNA sequences obtained from these sites showed banding patterns that suggest distinct and complex microbial communities. Analysis of 16S rDNA sequences obtained from UV-tolerant strains isolated from these sites revealed species related to the Bacillus and Pseudomonas genera. Vegetative cells of one of these isolates, Bacillus S3.300-2, showed the highest UV tolerance profile (LD(10) = 318 J m(2)), tenfold higher than a wild-type strain of Escherichia coli. Thus, our results show that the Atacama Desert harbors a noteworthy microbial community that may be considered for future astrobiological-related research in terms of UV tolerance.

Compression zone of a magnetoplasma compressor as a source of extreme UV radiation

Results from experimental studies of extreme UV (EUV) radiation from the compression zone of a magnetoplasma compressor (MPC) operating with xenon are presented. Two MPC operating modes that differ in the method of xenon injection into the discharge were studied. It is shown that EUV radiation in the wavelength range of 5–80 nm is emitted from the compression zone. In the MPC operating mode with local xenon injection directly into the compression zone surrounded by helium plasma, the radiation power reaches it peak value of 16–18 kW in the wavelength range of 12.2–15.8 nm.

He II λ4686 IN η CARINAE: COLLAPSE OF THE WIND-WIND COLLISION REGION DURING PERIASTRON PASSAGE

The periodic spectroscopic events in eta Carinae are now well established and occur near the periastron passage of two massive stars in a very eccentric orbit. Several mechanisms have been proposed to explain the variations of different spectral features, such as an eclipse by the wind-wind collision boundary, a shell ejection from the primary star or accretion of its wind onto the secondary. All of them have problems explaining all the observed phenomena. To better understand the nature of the cyclic events, we performed a dense monitoring of eta Carinae with 5 Southern telescopes during the 2009 low excitation event, resulting in a set of data of unprecedented quality and sampling. The intrinsic luminosity of the He II 4686 emission line (L~310 Lsun) just before periastron reveals the presence of a very luminous transient source of extreme UV radiation emitted in the wind-wind collision (WWC) region. Clumps in the primary's wind probably explain the flare-like behavior of both the X-ray and He II 4686 light-curves. After a short-lived minimum, He II 4686 emission rises again to a ne

Infrared suppression by hybrid EUV multilayer—IR etalon structures

We have developed a multilayer mirror for extreme UV (EUV) radiation (13.5 nm), which has near-zero reflectance for IR line radiation (10.6 μm). The EUV reflecting multilayer is based on alternating B4C and Si layers. Substantial transparency of these materials with respect to the IR radiation allowed the integration of the multilayer coating in a resonant quarter-wave structure for 10.6 μm. Samples were manufactured using magnetron sputtering deposition technique and demonstrated suppression of the IR radiation by up to 3 orders of magnitude. The EUV peak reflectance amounts 45% at 13.5 nm, with a bandwidth at FWHM being 0.284 nm. Therefore such a mirror could replace conventional multilayer mirrors to suppress undesired spectral components in monochromatic imaging applications, including EUV photolithography.

Sunlight-Exposed Biofilm Microbial Communities Are Naturally Resistant to Chernobyl Ionizing-Radiation Levels

BackgroundThe Chernobyl accident represents a long-term experiment on the effects of exposure to ionizing radiation at the ecosystem level. Though studies of these effects on plants and animals are abundant, the study of how Chernobyl radiation levels affect prokaryotic and eukaryotic microbial communities is practically non-existent, except for a few reports on human pathogens or soil microorganisms. Environments enduring extreme desiccation and UV radiation, such as sunlight exposed biofilms could in principle select for organisms highly resistant to ionizing radiation as well.Methodology/Principal FindingsTo test this hypothesis, we explored the diversity of microorganisms belonging to the three domains of life by cultivation-independent approaches in biofilms developing on concrete walls or pillars in the Chernobyl area exposed to different levels of radiation, and we compared them with a similar biofilm from a non-irradiated site in Northern Ireland. Actinobacteria, Alphaproteobacteria, Bacteroidetes, Acidobacteria and Deinococcales were the most consistently detected bacterial groups, whereas green algae (Chlorophyta) and ascomycete fungi (Ascomycota) dominated within the eukaryotes. Close relatives to the most radio-resistant organisms known, including Rubrobacter species, Deinococcales and melanized ascomycete fungi were always detected. The diversity of bacteria and eukaryotes found in the most highly irradiated samples was comparable to that of less irradiated Chernobyl sites and Northern Ireland. However, the study of mutation frequencies in non-coding ITS regions versus SSU rRNA genes in members of a same actinobacterial operational taxonomic unit (OTU) present in Chernobyl samples and Northern Ireland showed a positive correlation between increased radiation and mutation rates.Conclusions/SignificanceOur results show that biofilm microbial communities in the most irradiated samples are comparable to non-irradiated samples in terms of general diversity patterns, despite increased mutation levels at the single-OTU level. Therefore, biofilm communities growing in sunlight exposed substrates are capable of coping with increased mutation rates and appear pre-adapted to levels of ionizing radiation in Chernobyl due to their natural adaptation to periodical desiccation and ambient UV radiation.

Secondary electron emission in extreme-UV detectors: Application to diamond based devices

A study on the effect of secondary electron emission, which strongly affects the detection of extreme-UV radiation, was performed on diamond detectors. Two different structures were compared: interdigitated contacts and a transverse Schottky diode configuration. Both devices were electrically characterized by I-V measurements and their responsivity was measured in the extreme UV spectral region (20–120 nm) by using He-Ne gas discharge radiation sources and a toroidal grating vacuum monochromator. Through an ad-hoc measurement configuration, the contributions of the internal photocurrent and of the photoemission current have been analyzed and separately evaluated. The results showed that secondary electron emission, which clearly depends on the experimental conditions (e.g., external electric field, pressure, etc.), is one of the most relevant processes affecting the spectral responsivity in the extreme UV band. In particular, for interdigitated devices, extreme care must be taken in order to obtain an absolute value of their responsivity, while detectors in the transverse configuration can be shielded in such a way to avoid secondary electron current contribution and therefore provide a more correct and reliable response.

PHOKA experiment: Description of the equipment and first results

The CORONAS-PHOTON Russian satellite intended to study the Sun was successfully launched into orbit on January 30, 2009. Scientific equipment of the satellite includes the PHOKA radiometer of soft X-ray and extreme UV radiation. The PHOKA instrument is intended to measure the absolute flux of solar electromagnetic radiation in the spectral windows of 0.5–7 nm, 0.5–11 nm, 27–37 nm, and 116–125 nm. When leaving and entering the Earth’s shadow, the instrument aboard the spacecraft measures absorption of radiation by various layers of the Earth’s atmosphere. Before the launch, photodiodes of the instrument had been calibrated using a synchrotron radiation source. In-flight stability of sensitivity of main channels is controlled using calibration channels. The paper describes the PHOKA instrument and presents its capabilities and main characteristics, as well as some results of its operation in orbit.

Focus on cryogenics and vacuum

Focus on cryogenics and vacuum

Boris Peter Stoicheff

Boris Peter Stoicheff

Adaptation ofBacillus subtilisCells to Archean-Like UV Climate: Relevant Hints of Microbial Evolution to Remarkably Increased Radiation Resistance

In a precursory study for the space experiment ADAPT ("Molecular adaptation strategies of microorganisms to different space and planetary UV climate conditions"), cells of Bacillus subtilis 168 were continuously cultured for 700 generations under periodic polychromatic UV irradiation (200-400 nm) to model the suggested UV radiation environment on early Earth at the origin of the first microbial ecosystem during the Archean eon when Earth lacked a significant ozone layer. Populations that evolved under UV stress were about 3-fold more resistant than the ancestral and non-UV-evolved populations. UV-evolved cells were 7-fold more resistant to ionizing radiation than their non-UV-exposed evolved relatives and ancestor. In addition to the acquired increased UV resistance, further changes in microbial stress response to hydrogen peroxide, increased salinity, and desiccation were observed in UV-evolved cells. This indicates that UV-sensitive ancestral cells are capable of adapting to periodically applied UV stress via the evolution of cells with an increased UV resistance level and further enhanced responses to other environmental stressors, which thereby allows them to survive and reproduce under extreme UV radiation as a selection pressure.

Sub-70 nm resolution tabletop microscopy at 138 nm using a compact laser–plasma EUV source

We report the first (to our knowledge) demonstration of a tabletop, extreme UV (EUV) transmission microscope at 13.8 nm wavelength with a spatial (half-pitch) resolution of 69 nm. In the experiment, a compact laser-plasma EUV source based on a gas puff target is applied to illuminate an object. A multilayer ellipsoidal mirror is used to focus quasi-monochromatic EUV radiation onto the object, while a Fresnel zone plate objective forms the image. The experiment and the spatial resolution measurements, based on a knife-edge test, are described. The results might be useful for the realization of a compact high-resolution tabletop imaging systems for actinic defect characterization.