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S Udry - One of the best experts on this subject based on the ideXlab platform.
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the High Energy Environment and atmospheric escape of the mini neptune k2 18 b
2020Co-Authors: Leonardo Dos A Santos, D Ehrenreich, V Bourrier, Nicola Astudillodefru, Xavier Bonfils, Francois Forget, Christophe Lovis, Francesco Pepe, S UdryAbstract:K2-18 b is a transiting mini-Neptune that orbits a nearby (38 pc) cool M3 dwarf and is located inside its region of temperate irradiation. We report on the search for hydrogen escape from the atmosphere K2-18 b using Lyman-$\alpha$ transit spectroscopy with the Space Telescope Imaging Spectrograph (STIS) instrument installed on the Hubble Space Telescope (HST). We analyzed the time-series of the fluxes of the stellar Lyman-$\alpha$ emission of K2-18 in both its blue- and redshifted wings. We found that the average blueshifted emission of K2-18 decreases by $67\% \pm 18\%$ during the transit of the planet compared to the pre-transit emission, tentatively indicating the presence of H atoms escaping vigorously and being blown away by radiation pressure. This interpretation is not definitive because it relies on one partial transit. Based on the reconstructed Lyman-$\alpha$ emission of K2-18, we estimate an EUV irradiation between $10^1-10^2$ erg s$^{-1}$ cm$^{-2}$ and a total escape rate in the order of $10^8$ g s$^{-1}$. The inferred escape rate suggests that the planet will lose only a small fraction (< 1%) of its mass and retain its volatile-rich atmosphere during its lifetime. More observations are needed to rule out stellar variability effects, confirm the in-transit absorption and better assess the atmospheric escape and High-Energy Environment of K2-18 b.
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High Energy Environment of super earth 55 cnc e i far uv chromospheric variability as a possible tracer of planet induced coronal rain
2018Co-Authors: V Bourrier, D Ehrenreich, Lecavelier Des A Etangs, T Louden, P J Wheatley, A Wyttenbach, A Vidalmadjar, B Lavie, F Pepe, S UdryAbstract:The irradiation of close-in planets by their star influences their evolution and might be responsible for a population of ultra-short period planets eroded to their bare core. In orbit around a bright, nearby G-type star, the super-Earth 55 Cnc e offers the possibility to address these issues through UV transit observations. We used the Hubble Space Telescope to observe the transit in the FUV over 3 epochs in Apr. 2016, Jan. 2017, and Feb. 2017. These observations reveal significant short- and long-term variability in 55 Cnc chromospheric emission lines. In the last 2 epochs, we detected a larger flux in the C III, Si III, and Si IV lines after the planet passed the approaching quadrature, followed by a flux decrease in the Si IV doublet. In the second epoch these variations are contemporaneous with flux decreases in the Si II and C II doublet. All epochs show flux decreases in the N V doublet as well, albeit at different orbital phases. These flux decreases are consistent with absorption from optically thin clouds of gas, are mostly localized at low and redshifted radial velocities in the star rest frame, and occur preferentially before and during the transit. These 3 points make it unlikely that the variations are purely stellar, yet we show that the occulting material is also unlikely to originate from the planet. We tentatively propose that the motion of 55 Cnc e at the fringes of the stellar corona leads to the formation of a cool coronal rain. The inhomogeneity and temporal evolution of the stellar corona would be responsible for the differences between the visits. Additional variations are detected in the C II doublet in the first epoch and in the O I triplet in all epochs with a different behavior that points toward intrinsic stellar variability. Further observations at FUV wavelengths are required to disentangle between star-planet interactions and the activity of the star
Hamed, Hamed Basher Osman - One of the best experts on this subject based on the ideXlab platform.
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Pleistozäne Riffe an der Küste des Roten Meeres, Sudan : Ablagerungsräume, fossile Korallen, Altersdatierung und Diagenese : Pleistozäne Riffe an der Küste des Roten Meeres, Sudan : Ablagerungsräume, fossile Korallen, Altersdatierung und Diagenese
2015Co-Authors: Hamed, Hamed Basher OsmanAbstract:In einem Streifen von etwa 3 km Breite sind entlang der sudanesischen Küste des Roten Meers pleistozäne Korallenriffe aufgeschlossen. In dieser Arbeit werden die Verbreitungsmuster der fossilen Korallen, die Sedimentfaziestypen, Diageneseerscheinungen sowie das Alter dieser Riffe untersucht. Insgesamt wurden 29 Steinkorallenarten bestimmt, die in 8 Familien und 16 Gattungen gehören. Drei Korallengemeinschaften werden unterschieden: eine distale, durch dicht gepackte, röhrenförmige Galaxea facicularis dominierte Gemeinschaft, eine mediale Gemeinschaft, die durch verzweigte Korallen der Art Porites sp. beherrscht wird, und eine durch massive, säulenförmige Porites columnaris dominierte proximale Gemeinschaft. Vier Hauptriffzonen und zehn Subfaziestypen werden differenziert. Als Hauptriffzonen sind 1) der Riffrand, 2) die Rifffront, 3) die Riffplattform und 4) das Rückriff ausgebildet. Der Riffrand besteht hauptsächlich aus coralgal-foraminifera bindstone, die Rifffront aus Porites/stony coral bindstone, die Riffplattform aus whole fossil wackestone/floatstone, Porites bafflestone, large bivalve floatstone und Porites framestone, und das Rückriff aus einem basalen rudstone, baumförmigen coral framestone und massiven, domförmigen Mikroriffen. Das Alter der pleistozänen Korallen wird über die Vertikalabfolge der Riffe im Gelände sowie mit Hilfe von δ18O-Untersuchungen bestimmt, vor allem von Proben aus der Rifffrontfazies. Außerdem werden die Einstufungen mit bereits bekannten Altern ähnlicher fossiler Riffkomplexe in der Roten Meer-Region verglichen. Die meisten Alter aus den hier vorgenommenen δ18O-Untersuchungen sind nicht aussagekräftig, was auf die geringe Zahl geeigneter Proben und insbesondere auf Kalzitgehalte in den Proben zurückzuführen ist. Allerdings lieferten zwei Porites-Korallen der Rifffront als zuverlässig eingeschätzte δ18O-Alter von 120 und 122 ky. Diese stimmen mit der Sauerstoff-Isotopenstufe MIS 5.5 überein. Auf diesen Altern und auf Geländebefunden basierend wurden die Riffplattformzone in MIS 9 und die Rückriffzone in MIS 7 eingestuft, sowie der Riffrand in MIS 5.1. Die Einstufung bestimmter Riffzonen in unterschiedliche Alter drückt vermutlich eine begünstigte Entwicklung dieser Faziesbereiche in den jeweiligen Bildungszeiträumen und/oder eine stärkere nachfolgende Erosion der anderen Zonen z.B. durch Welleneinwirkung aus. Die Vertikalabfolge in der Riffplattform (MIS 9) belegt eine Entwicklung von einer ruhigen Lagune hin zu einem mäßig- bis hoch-energetischen Bildungsmilieu. Im von starker Welleneinwirkung geschützten Rückriffbereich (MIS 7) dominierten Korallen der Arten Galaxea facicularis und Caulastrea connate. Die Rifffront (MIS 5.5) besteht weitgehend aus durch massige, säulenförmige Porites-Korallen aufgebauten Knollenriffen, deren Morphologie auf eine mäßige bis hohe Wellenenergie hindeutet. Die Riffrandfazies (MIS 5.1) weist dagegen auf ein hochenergetisches Milieu hin. Subrezent ist aus Schutt von fossilen Rifffront- und Riffrandzonen durch Zementation mit Aragonit Beachrock entstanden. Die Riffplattform (MIS 9) war intensiven meteorisch-phreatischen Diagenesevorgängen ausgesetzt, wobei im unteren Plattformbereich ein stagnierendes Milieu herrschte, und im mittleren und oberen Bereich ein aktives Milieu. Die Vertikalabfolge spiegelt möglicherweise einen Wechsel von einem semiariden zu einem humiden Paläoklima wieder. Die Rückriffzone (MIS 7), die Rifffrontzone (MIS 5.5), der Riffrand (MIS 5.1) und der Beachrock weisen dagegen Anzeiger einer marinen Frühdiagenese auf. Nur in den höchsten Bereichen dieser Riffzonen sind Indikatoren für eine meteorisch-vadose Diagenese vorhanden. Das hier vorgestellte Sedimentationsmodell unterscheidet sich von existierenden Modellen für die fossilen Riffe der Roten Meer-Region in der Bildung der Rückriffzone während MIS 7, wogegen frühere Untersuchungen diese Zone in MIS 9 einstufen. Eine hohe Diversität und die ungewöhnlich gute Erhaltung der Korallen in MIS 7 zeigen, dass diese in geschützten Bereichen landeinwärts der Riffplattform wuchsen.Pleistocene coral reefs are well exposed over a width of about 3 km parallel to the Red Sea coast in Sudan. Patterns of fossil corals, sedimentary facies, diagenetic features and age of the reefs were studied in order to construct a sedimentation model. A total of 29 scleractinian coral species that belong to 8 families and 16 genera were identified. Three coral communities were distinguished: distal communities predominated by pipe-like packed Galaxea facicularis, middle communities predominated by branched Porites sp. and proximal communities predominated by massive and columnar Porites columnaris. Four major reef zones and ten sub-facies were recognized. The major reef zones recognized are (1) rock-reef rim, (2) reef-front zone, (3) reef-flat zone, and (4) back-reef zone. Coralgal-foraminifera bindstone dominates the rock-reef rim, while Porites/stony coral framestone and coral framestone are typical for the reef-front zone. The reef-flat succession primarily consists of whole fossil wackestone/floatstone, Porites bafflestone, large bivalve floatstone and Porites framestone. The back-reef zone facies includes lower lag rudstone, arborescent coral framestone and massive domal microreef. δ18O analysis was conducted to estimate the age of the Pleistocene coral reefs. Results obtained were correlated to previous age dating of correlative reefs in Sudan and other parts of the Red Sea. Estimation of reef ages was mainly based on δ18O values of the reef-front zone and the observed sedimentary succession of the reefs. Most ages obtained were considered not reliable due to the limited number of analysed samples and their High content of calcite. However, δ18O values of two Porites coral samples from the reef-front zone strongly suggest equivalent ages of 120 and 122 ky that correspond to marine isotope stage MIS 5.5. Based on δ18O values and field relationship to the reef-front zone, ages of the reef-flat and back-reef zones could be assigned to MIS 9 and MIS 7 respectively. MIS 5.1 is suggested for the reef-rock rim. The relationship of the reef zones to individual MIS might relate to the predominance of a specific zone during a certain stage, while other facies were less well developed and/or later eroded by wave action. The vertical architecture of the reef-flat facies (MIS 9) suggests a change from an initial quiet water lagoon to a shallow reef Environment with moderate to High water Energy. The back-reef sediments (MIS 7) are dominated by Galaxea facicularis and Caulastrea connate that grew in an Environment largely protected from wave action. The reef-front zone (MIS 5.5) is formed by large reef knolls dominated by massive, columnar Porites corals. Its coral association and morphology suggests a moderate to High Energy Environment. The reef-rock rim (MIS 5.1) onlaps the bottom slope of the reef-front zone and formed during a minor sea-level rise. Its components and fabric indicate a High-Energy Environment. The sub-recent beach rock is formed by the reworking of reef debris from nearby reef-cliffs (reef-front zone) and reef-rock rim in the foreslope Environment and subjected to cementation by marine aragonite cement. The reef-flat succession (MIS 9) was exposed to intense freshwater dissolution, replacement and cementation. It shows evidence of stagnant freshwater phreatic diagenesis in the lower and active freshwater phreatic diagenesis in the middle and upper part. This pattern likely resulted to a change from a semi-arid to a more humid palaeoclimate. Back-reef zone (MIS 7), reef-front zone (MIS 5.5), reef-rock rim (5.1) and sub-recent beach rock exhibit features typical of early diagenesis within the marine diagenetic Environment. Features of freshwater vadose diagenesis characterize the upper part of most reef zones. The proposed sedimentation model differs, when compared to previous models in the Red Sea region, in the formation of the back-reef zone during MIS 7, while previous studies assigned it to MIS 9. High diversity and excellent preservation of corals in MIS 7 reefs reflect their growth in protected structural troughs landward of the reef-flat
Leonardo Dos A Santos - One of the best experts on this subject based on the ideXlab platform.
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the High Energy Environment and atmospheric escape of the mini neptune k2 18 b
2020Co-Authors: Leonardo Dos A Santos, D Ehrenreich, V Bourrier, Nicola Astudillodefru, Xavier Bonfils, Francois Forget, Christophe Lovis, Francesco Pepe, S UdryAbstract:K2-18 b is a transiting mini-Neptune that orbits a nearby (38 pc) cool M3 dwarf and is located inside its region of temperate irradiation. We report on the search for hydrogen escape from the atmosphere K2-18 b using Lyman-$\alpha$ transit spectroscopy with the Space Telescope Imaging Spectrograph (STIS) instrument installed on the Hubble Space Telescope (HST). We analyzed the time-series of the fluxes of the stellar Lyman-$\alpha$ emission of K2-18 in both its blue- and redshifted wings. We found that the average blueshifted emission of K2-18 decreases by $67\% \pm 18\%$ during the transit of the planet compared to the pre-transit emission, tentatively indicating the presence of H atoms escaping vigorously and being blown away by radiation pressure. This interpretation is not definitive because it relies on one partial transit. Based on the reconstructed Lyman-$\alpha$ emission of K2-18, we estimate an EUV irradiation between $10^1-10^2$ erg s$^{-1}$ cm$^{-2}$ and a total escape rate in the order of $10^8$ g s$^{-1}$. The inferred escape rate suggests that the planet will lose only a small fraction (< 1%) of its mass and retain its volatile-rich atmosphere during its lifetime. More observations are needed to rule out stellar variability effects, confirm the in-transit absorption and better assess the atmospheric escape and High-Energy Environment of K2-18 b.
D Ehrenreich - One of the best experts on this subject based on the ideXlab platform.
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the High Energy Environment and atmospheric escape of the mini neptune k2 18 b
2020Co-Authors: Leonardo Dos A Santos, D Ehrenreich, V Bourrier, Nicola Astudillodefru, Xavier Bonfils, Francois Forget, Christophe Lovis, Francesco Pepe, S UdryAbstract:K2-18 b is a transiting mini-Neptune that orbits a nearby (38 pc) cool M3 dwarf and is located inside its region of temperate irradiation. We report on the search for hydrogen escape from the atmosphere K2-18 b using Lyman-$\alpha$ transit spectroscopy with the Space Telescope Imaging Spectrograph (STIS) instrument installed on the Hubble Space Telescope (HST). We analyzed the time-series of the fluxes of the stellar Lyman-$\alpha$ emission of K2-18 in both its blue- and redshifted wings. We found that the average blueshifted emission of K2-18 decreases by $67\% \pm 18\%$ during the transit of the planet compared to the pre-transit emission, tentatively indicating the presence of H atoms escaping vigorously and being blown away by radiation pressure. This interpretation is not definitive because it relies on one partial transit. Based on the reconstructed Lyman-$\alpha$ emission of K2-18, we estimate an EUV irradiation between $10^1-10^2$ erg s$^{-1}$ cm$^{-2}$ and a total escape rate in the order of $10^8$ g s$^{-1}$. The inferred escape rate suggests that the planet will lose only a small fraction (< 1%) of its mass and retain its volatile-rich atmosphere during its lifetime. More observations are needed to rule out stellar variability effects, confirm the in-transit absorption and better assess the atmospheric escape and High-Energy Environment of K2-18 b.
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High Energy Environment of super earth 55 cnc e i far uv chromospheric variability as a possible tracer of planet induced coronal rain
2018Co-Authors: V Bourrier, D Ehrenreich, Lecavelier Des A Etangs, T Louden, P J Wheatley, A Wyttenbach, A Vidalmadjar, B Lavie, F Pepe, S UdryAbstract:The irradiation of close-in planets by their star influences their evolution and might be responsible for a population of ultra-short period planets eroded to their bare core. In orbit around a bright, nearby G-type star, the super-Earth 55 Cnc e offers the possibility to address these issues through UV transit observations. We used the Hubble Space Telescope to observe the transit in the FUV over 3 epochs in Apr. 2016, Jan. 2017, and Feb. 2017. These observations reveal significant short- and long-term variability in 55 Cnc chromospheric emission lines. In the last 2 epochs, we detected a larger flux in the C III, Si III, and Si IV lines after the planet passed the approaching quadrature, followed by a flux decrease in the Si IV doublet. In the second epoch these variations are contemporaneous with flux decreases in the Si II and C II doublet. All epochs show flux decreases in the N V doublet as well, albeit at different orbital phases. These flux decreases are consistent with absorption from optically thin clouds of gas, are mostly localized at low and redshifted radial velocities in the star rest frame, and occur preferentially before and during the transit. These 3 points make it unlikely that the variations are purely stellar, yet we show that the occulting material is also unlikely to originate from the planet. We tentatively propose that the motion of 55 Cnc e at the fringes of the stellar corona leads to the formation of a cool coronal rain. The inhomogeneity and temporal evolution of the stellar corona would be responsible for the differences between the visits. Additional variations are detected in the C II doublet in the first epoch and in the O I triplet in all epochs with a different behavior that points toward intrinsic stellar variability. Further observations at FUV wavelengths are required to disentangle between star-planet interactions and the activity of the star
V Bourrier - One of the best experts on this subject based on the ideXlab platform.
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the High Energy Environment and atmospheric escape of the mini neptune k2 18 b
2020Co-Authors: Leonardo Dos A Santos, D Ehrenreich, V Bourrier, Nicola Astudillodefru, Xavier Bonfils, Francois Forget, Christophe Lovis, Francesco Pepe, S UdryAbstract:K2-18 b is a transiting mini-Neptune that orbits a nearby (38 pc) cool M3 dwarf and is located inside its region of temperate irradiation. We report on the search for hydrogen escape from the atmosphere K2-18 b using Lyman-$\alpha$ transit spectroscopy with the Space Telescope Imaging Spectrograph (STIS) instrument installed on the Hubble Space Telescope (HST). We analyzed the time-series of the fluxes of the stellar Lyman-$\alpha$ emission of K2-18 in both its blue- and redshifted wings. We found that the average blueshifted emission of K2-18 decreases by $67\% \pm 18\%$ during the transit of the planet compared to the pre-transit emission, tentatively indicating the presence of H atoms escaping vigorously and being blown away by radiation pressure. This interpretation is not definitive because it relies on one partial transit. Based on the reconstructed Lyman-$\alpha$ emission of K2-18, we estimate an EUV irradiation between $10^1-10^2$ erg s$^{-1}$ cm$^{-2}$ and a total escape rate in the order of $10^8$ g s$^{-1}$. The inferred escape rate suggests that the planet will lose only a small fraction (< 1%) of its mass and retain its volatile-rich atmosphere during its lifetime. More observations are needed to rule out stellar variability effects, confirm the in-transit absorption and better assess the atmospheric escape and High-Energy Environment of K2-18 b.
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High Energy Environment of super earth 55 cnc e i far uv chromospheric variability as a possible tracer of planet induced coronal rain
2018Co-Authors: V Bourrier, D Ehrenreich, Lecavelier Des A Etangs, T Louden, P J Wheatley, A Wyttenbach, A Vidalmadjar, B Lavie, F Pepe, S UdryAbstract:The irradiation of close-in planets by their star influences their evolution and might be responsible for a population of ultra-short period planets eroded to their bare core. In orbit around a bright, nearby G-type star, the super-Earth 55 Cnc e offers the possibility to address these issues through UV transit observations. We used the Hubble Space Telescope to observe the transit in the FUV over 3 epochs in Apr. 2016, Jan. 2017, and Feb. 2017. These observations reveal significant short- and long-term variability in 55 Cnc chromospheric emission lines. In the last 2 epochs, we detected a larger flux in the C III, Si III, and Si IV lines after the planet passed the approaching quadrature, followed by a flux decrease in the Si IV doublet. In the second epoch these variations are contemporaneous with flux decreases in the Si II and C II doublet. All epochs show flux decreases in the N V doublet as well, albeit at different orbital phases. These flux decreases are consistent with absorption from optically thin clouds of gas, are mostly localized at low and redshifted radial velocities in the star rest frame, and occur preferentially before and during the transit. These 3 points make it unlikely that the variations are purely stellar, yet we show that the occulting material is also unlikely to originate from the planet. We tentatively propose that the motion of 55 Cnc e at the fringes of the stellar corona leads to the formation of a cool coronal rain. The inhomogeneity and temporal evolution of the stellar corona would be responsible for the differences between the visits. Additional variations are detected in the C II doublet in the first epoch and in the O I triplet in all epochs with a different behavior that points toward intrinsic stellar variability. Further observations at FUV wavelengths are required to disentangle between star-planet interactions and the activity of the star