Exoplanet detections have revolutionized astronomy, offering new insights into solar system architecture and planet demographics. While nearly 1,900 exoplanets have now been discovered and confirmed, ...none are still in the process of formation. Transition disks, protoplanetary disks with inner clearings best explained by the influence of accreting planets, are natural laboratories for the study of planet formation. Some transition disks show evidence for the presence of young planets in the form of disk asymmetries or infrared sources detected within their clearings, as in the case of LkCa 15 (refs 8, 9). Attempts to observe directly signatures of accretion onto protoplanets have hitherto proven unsuccessful. Here we report adaptive optics observations of LkCa 15 that probe within the disk clearing. With accurate source positions over multiple epochs spanning 2009-2015, we infer the presence of multiple companions on Keplerian orbits. We directly detect Hα emission from the innermost companion, LkCa 15 b, evincing hot (about 10,000 kelvin) gas falling deep into the potential well of an accreting protoplanet.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Herbig Ae/Be stars represent the early outcomes of star formation and the initial stages of planet formation at intermediate stellar masses. Understanding both of these processes requires ...detailed characterization of their disk structures and companion frequencies. We present new 3.7 μm imaging of the Herbig Be star MWC 297 from nonredundant masking observations on the phase-controlled, 23 m Large Binocular Telescope Interferometer. The images reveal complex disk structure on the scales of several au, as well as a companion candidate. We discuss physical interpretations for these features and demonstrate that the imaging results are independent of choices such as priors, regularization hyperparameters, and error-bar estimates. With an angular resolution of ∼17 mas, these data provide the first robust Extremely Large Telescope–resolution view of a distant young star.
Context.
In recent decades, thousands of substellar companions have been discovered with both indirect and direct methods of detection. While the majority of the sample is populated by objects ...discovered using radial velocity and transit techniques, an increasing number have been directly imaged. These planets and brown dwarfs are extraordinary sources of information that help in rounding out our understanding of planetary systems.
Aims.
In this paper, we focus our attention on substellar companions detected with the latter technique, with the primary goal of investigating their close surroundings and looking for additional companions and satellites, as well as disks and rings. Any such discovery would shed light on many unresolved questions, particularly with regard to their possible formation mechanisms.
Methods.
To reveal bound features of directly imaged companions, whether for point-like or extended sources, we need to suppress the contribution from the source itself. Therefore, we developed a method based on the negative fake companion technique that first estimates the position in the field of view (FoV) and the flux of the imaged companion with high precision, then subtracts a rescaled model point spread function (PSF) from the imaged companion, using either an image of the central star or another PSF in the FoV. Next it performs techniques, such as angular differential imaging, to further remove quasi-static patterns of the star (i.e., speckle contaminants) that affect the residuals of close-in companions.
Results.
After testing our tools on simulated companions and disks and on systems that were chosen ad hoc, we applied the method to the sample of substellar objects observed with SPHERE during the SHINE GTO survey. Among the 27 planets and brown dwarfs we analyzed, most objects did not show remarkable features, which was as expected, with the possible exception of a point source close to DH Tau B. This candidate companion was detected in four different SPHERE observations, with an estimated mass of ~1
M
Jup
, and a mass ratio with respect to the brown dwarf of 1∕10. This binary system, if confirmed, would be the first of its kind, opening up interesting questions for the formation mechanism, evolution, and frequency of such pairs. In order to address the latter, the residuals and contrasts reached for 25 companions in the sample of substellar objects observed with SPHERE were derived. If the DH Tau Bb companion is real, the binary fraction obtained is ~7%, which is in good agreement with the results obtained for field brown dwarfs.
Conclusions.
While there may currently be many limitations affecting the exploration of bound features to directly imaged exoplanets and brown dwarfs, next-generation instruments from the ground and space (i.e., JWST, ELT, and LUVOIR) will be able to image fainter objects and, thus, drive the application of this technique in upcoming searches for exo-moons and circumplanetary disks.
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In the absence of a firm link between individual meteorites and their asteroidal parent bodies, asteroids are typically characterized only by their light reflection properties, and grouped ...accordingly into classes. On 6 October 2008, a small asteroid was discovered with a flat reflectance spectrum in the 554-995nm wavelength range, and designated 2008 TC3 (refs 4-6). It subsequently hit the Earth. Because it exploded at 37km altitude, no macroscopic fragments were expected to survive. Here we report that a dedicated search along the approach trajectory recovered 47 meteorites, fragments of a single body named Almahata Sitta, with a total mass of 3.95kg. Analysis of one of these meteorites shows it to be an achondrite, a polymict ureilite, anomalous in its class: ultra-fine-grained and porous, with large carbonaceous grains. The combined asteroid and meteorite reflectance spectra identify the asteroid as F class, now firmly linked to dark carbon-rich anomalous ureilites, a material so fragile it was not previously represented in meteorite collections.
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Abstract
The Large Binocular Telescope (LBT) has two 8.4 m primary mirrors that produce beams that can be combined coherently in a “Fizeau” interferometric mode. In principle, the Fizeau point-spread ...function (PSF) enables the probing of structure at a resolution up to three times better than that of the adaptive-optics-corrected PSF of a single 8.4 m telescope. In this work, we examined the nearby star Altair (5.13 pc, type A7V, hundreds of Myr to ≈1.4 Gyr) in the Fizeau mode with the LBT at Br
α
(4.05
μ
m) and carried out angular differential imaging to search for companions. This work presents the first filled-aperture LBT Fizeau science data set to benefit from a correcting mirror that provides active phase control. In the analysis of the
λ
/
D
angular regime, the sensitivity of the data set is down to ≈0.5
M
⊙
at 1″ for a 1.0 Gyr system. This sensitivity remains limited by the small amount of integration time, which is in turn limited by the instability of the Fizeau PSF. However, in the Fizeau fringe regime we attain sensitivities of Δ
m
≈ 5 at 0.″2 and put constraints on companions of 1.3
M
⊙
down to an inner angle of ≈0.″15, closer than any previously published direct imaging of Altair. This analysis is a pathfinder for future data sets of this type, and represents some of the first steps to unlocking the potential of the first Extremely Large Telescope. Fizeau observations will be able to reach dimmer targets with upgrades to the instrument, in particular the phase detector.
Sea-level rise is anticipated to alter hydrologic and salinity regimes of coastal wetlands. We conducted a mesocosm experiment to determine species-level responses to 12 sea-level rise scenarios. ...Both hydrologic regime (-10, +5, and +20 cm flooding depth) and salinity level (fresh, 2‰, 4‰, and 6‰) were interactively manipulated. Within these various sea-level rise scenarios, we sought to determine the effects of hydrologic regime, salinity level, and the interaction of these two stresses on the productivity of Panicum hemitomon, Sagittaria lancifolia, and Spartina patens, which are dominant macrophytes of fresh, intermediate, and brackish marsh types, respectively, in coastal Louisiana and the southeastern coastal plain. We found that altered hydrologic regimes and increased salinity levels differentially affected edaphic conditions and species-level productivity. Increases in flooding depth were most detrimental to S. patens. Salinity levels greater than 4‰ resulted in mortality of P. hemitomon, and salinity levels of 6‰ resulted in reduced growth and eventual death of S. lancifolia. The effects of elevated salinity levels on P. hemitomon and S. lancifolia were exacerbated when coupled with increased flooding levels. Although soil organic matter was shown to increase in all vegetative conditions, increases were dependent upon the productivity of the species under the different hydrologic regimes and salinity levels with P. hemitomon displaying tremendous potential to increase soil organic matter under fresh conditions, especially when coupled with moderate flooding. The results of this study indicate that as plant communities are subjected to long-term changes in hydrology and salinity levels, community productivity and sustainability ultimately will be determined by species-level tolerances in conjunction with species interactions.
Asteroids with diameters smaller than ∼50-100 m that collide with the Earth usually do not hit the ground as a single body; rather, they detonate in the atmosphere. These small objects can still ...cause considerable damage, such as occurred near Tunguska, Siberia, in 1908. The flux of small bodies is poorly constrained, however, in part because ground-based observational searches pursue strategies that lead them preferentially to find larger objects. A Tunguska-class event-the energy of which we take to be equivalent to 10 megatons of TNT-was previously estimated to occur every 200-300 years, with the largest annual airburst calculated to be ∼20 kilotons (kton) TNT equivalent (ref. 4). Here we report satellite records of bolide detonations in the atmosphere over the past 8.5 years. We find that the flux of objects in the 1-10-m size range has the same power-law distribution as bodies with diameters >50 m. From this we estimate that the Earth is hit on average annually by an object with ∼5 kton equivalent energy, and that Tunguska-like events occur about once every 1,000 years.
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ABSTRACT The Large Binocular Telescope Interferometer (LBTI) is a versatile instrument designed for high angular resolution and high-contrast infrared imaging (1.5-13 m). In this paper, we focus on ...the mid-infrared (8-13 m) nulling mode and present its theory of operation, data reduction, and on-sky performance as of the end of the commissioning phase in 2015 March. With an interferometric baseline of 14.4 m, the LBTI nuller is specifically tuned to resolve the habitable zone of nearby main-sequence stars, where warm exozodiacal dust emission peaks. Measuring the exozodi luminosity function of nearby main-sequence stars is a key milestone to prepare for future exo-Earth direct imaging instruments. Thanks to recent progress in wavefront control and phase stabilization, as well as in data reduction techniques, the LBTI demonstrated in 2015 February a calibrated null accuracy of 0.05% over a 3 hr long observing sequence on the bright nearby A3V star β Leo. This is equivalent to an exozodiacal disk density of 15-30 zodi for a Sun-like star located at 10 pc, depending on the adopted disk model. This result sets a new record for high-contrast mid-infrared interferometric imaging and opens a new window on the study of planetary systems.
Illuminating topics in plant photobiology Spalding, E.P; Folta, K.M
Plant, cell & environment/Plant, cell and environment,
January 2005, Volume:
28, Issue:
1
Journal Article
Peer reviewed
Open access
Light signals acting through photoreceptors and signal transduction chains shape plant growth, development, physiology and metabolism to best suit the organism to the prevailing conditions. Genetic, ...biochemical and molecular studies, particularly in the model system Arabidopsis thaliana, have produced highly detailed descriptions of many light responses so that now molecular pathways are coming into view. In this review the current state of research in several diverse areas within the field of plant photomorphogenesis is discussed. The topics include phytochrome localization and interactions with signalling elements, cryptochrome function, phototropin photochemistry and physiology, the role of proteolysis in light signalling, the plant circadian clock, and the transition to flowering.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Summary
Blue light (BL) rapidly and strongly inhibits hypocotyl elongation during the photomorphogenic response known as de‐etiolation, the transformation of a dark‐grown seedling into a pigmented, ...photoautotrophic organism. In Arabidopsis thaliana, high‐resolution studies of hypocotyl growth accomplished by computer‐assisted electronic image capture and analysis revealed that inhibition occurs in two genetically independent phases, the first beginning within 30 sec of illumination. The present work demonstrates that phototropin (nph1), the photoreceptor responsible for phototropism, is largely responsible for the initial, rapid inhibition. Signaling from phototropin during the curvature response is dependent upon interaction with NPH3, but the results presented here demonstrate that NPH3 is not necessary for phototropin‐dependent growth inhibition. Activation of anion channels, which transiently depolarizes the plasma membrane within seconds of BL, is an early event in the cryptochrome signaling pathway leading to a phase of growth inhibition that replaces the transient phototropin‐dependent phase after approximately 30 min of BL. Surprisingly, cry1 and cry2 were found to contribute equally and non‐redundantly to anion‐channel activation and to growth inhibition between 30 and 120 min of BL. Inspection of the inhibition kinetics displayed by nph1 and nph1cry1 mutants revealed that the cryptochrome phase of inhibition is delayed in seedlings lacking phototropin. This result indicates that BL‐activation of phototropin influences cryptochrome signaling leading to growth inhibition. Mutations in the NPQ1 gene, which inhibit BL‐induced stomatal opening, do not affect any aspect of the growth inhibition within the first 120 min examined here, and NPQ1 does not affect the activation of anion channels.
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