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Mar 22, 20121 like268 views

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Das Dokument behandelt die Unternehmensziele und die Bedeutung einer durchdachten Content-Strategie im Kontext des Storytellings, um die Markenbekanntheit zu steigern und Kunden zu gewinnen. Es werden verschiedene Medientypen und Werkzeuge vorgestellt, um Geschichten effektiv zu kommunizieren und die Marke als Erlebnis darzustellen. Wichtig sind Authentizität, regelmäßige Interaktionen und die Positionierung relevanter Inhalte, um die Bindung zu Kunden zu stärken.

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First Frequency Phase Transfer from the 3mm to the 1mm Band on an Earth-sized...Sérgio Sacani

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Frequency phase transfer (FPT) is a technique designed to increase coherence and sensitivity in radio interferometry by making use of the nondispersive nature of the troposphere to calibrate high-frequency data using solutions derived at a lower frequency. While the Korean very long baseline interferometry (VLBI) network has pioneered the use of simultaneous multiband systems for routine FPT up to an observing frequency of 130 GHz, this technique remains largely untested in the (sub)millimeter regime. A recent effort has been made to outfit dualband systems at (sub)millimeter observatories participating in the Event Horizon Telescope (EHT) and to test the feasibility and performance of FPT up to the observing frequencies of the EHT. We present the results of simultaneous dual-frequency observations conducted in 2024 January on an Earth-sized baseline between the IRAM 30-m in Spain and the James Clerk Maxwell Telescope (JCMT) and Submillimeter Array (SMA) in Hawai‘i. We performed simultaneous observations at 86 and 215GHz on the bright sources J0958+6533 and OJ287, with strong detections obtained at both frequencies. We observe a strong correlation between the interferometric phases at the two frequencies, matching the trend expected for atmospheric fluctuations and demonstrating for the first time the viability of FPT for VLBI at a wavelength of ∼1 millimeter. We show that the application of FPT systematically increases the 215 GHz coherence on all averaging timescales. In addition, the use of the colocated JCMT and SMA as a single dual-frequency station demonstrates the feasibility of paired-antenna FPT for VLBI for the first time, with implications for future array capabilities (e.g., Atacama Large Millimeter/ submillimeter Array subarraying and ngVLA calibration strategies).

Water ice in the debris disk around HD 181327Sérgio Sacani

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Debris disks are exoplanetary systems that contain planets, minor bodies (asteroids, Kuiper belt objects, comets and so on) and micrometre-sized debris dust1. Because water ice is the most common frozen volatile, it plays an essential role in the formation of planets2,3 and minor bodies. Although water ice has been commonly found in Kuiper belt objects and comets in the Solar System4, no definitive evidence for water ice in debris disks has been obtained to date1. Here we report the discovery of water ice in the HD 181327 debris disk using the near-infrared spectrograph onboard the James Webb Space Telescope. We detected the solid-state broad absorption feature of water ice at 3 μm including a distinct Fresnel peak at 3.1 μm, which is indicative of large, crystalline water-ice particles. Gradients in the water-ice feature as a function of stellocentric distance reveal a dynamic environment in which water ice is destroyed and replenished. We estimated the water-ice mass fractions as ranging from 0.1% at approximately 85 au to 21% at approximately 113 au, indicating the presence of a water-ice reservoir in the HD 181327 disk beyond the snow line. The icy bodies that release water ice in HD 181327 are probably the extra-solar counterparts of water-icerich Kuiper belt objects in our Solar System.

The atmosphere of Titan in late northern summer from JWST and Keck observationsSérgio Sacani

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Saturn’s moon Titan undergoes a long annual cycle of 29.45 Earth years. Titan’s northern winter and spring were investigated in detail by the Cassini– Huygens spacecraft (2004–2017), but the northern summer season remains sparsely studied. Here we present new observations from the James Webb Space Telescope (JWST) and Keck II telescope made in 2022 and 2023 during Titan’s late northern summer. Using JWST’s mid-infrared instrument, we spectroscopically detected the methyl radical, the primary product of methane break-up and key to the formation of ethane and heavier molecules. Using the near-infrared spectrograph onboard JWST, we detected several non-local thermodynamic equilibrium CO and CO2 emission bands, which allowed us to measure these species over a wide altitude range. Lastly, using the near-infrared camera onboard JWST and Keck II, we imaged northern hemisphere tropospheric clouds evolving in altitude, which provided new insights and constraints on seasonal convection patterns. These observations pave the way for new observations and modelling of Titan’s climate and meteorology as it progresses through the northern fall equinox, when its atmosphere is expected to show notable seasonal changes.

Discovery of a dwarf planet candidate in an extremely wide orbit: 2017 OF201Sérgio Sacani

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We report the discovery of a dwarf planet candidate, 2017 OF201, currently located at a distance of 90.5 au. Its orbit is extremely wide and extends to the inner Oort cloud, with a semi-major axis of 838 au andaperihelion of 44.9 au precisely determined from 19 observations over seven years. Assuming a typical albedo of 0.15, we estimate a diameter ∼700 km, making it the second-largest known object in this dynamical population and a likely dwarf planet. Its high eccentricity suggests that it is part of a broader, unseen population of similar objects totaling ∼1% of Earth’s mass. Notably, the longitude of perihelion of 2017 OF201 lies well outside the clustering observed in extreme trans-Neptunian objects, which has been proposed as dynamical evidence for a distant, undetected planet.

Streaks on martian slopes are dry - No Water On MarsSérgio Sacani

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Slope streaks are dark albedo features on martian slopes that form spontaneously and fade over years to decades. Along with seasonally recurring slope lineae, streak formation has been attributed to aqueous processes, implying the presence of transient yet substantial amounts of liquid water or brines on Mars’ surface, with important implications for present-day Mars’ habitability. Here, we use a deep learning-enabled approach to create the first consistent, global catalog of half a million individual slope streaks. We show that slope streaks modify less than 0.1% of the martian surface, but transport several global storm equivalents of dust per Mars year, potentially playing a major role in the martian dust cycle. Our global geostatistical analysis challenges wet streak formation models and instead supports dry streak formation, driven by seasonal dust delivery and energetic triggers like wind and meteoritic impacts. We further identify a qualitative, spatiotemporal relation between recurring slope lineae formation, seasonal dust deposition, and dust devil activity. Our findings suggest that modern Mars’ slopes do not commonly experience transient flows of water or brines, implying that streak bearing terrain can be explored without raising planetary protection concerns.

The Link Between Subsurface Rheology and EjectaMobility: The Case of Small Ne...Sérgio Sacani

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The dynamics of crater ejecta are sensitive to the material properties of the target, much like thecrater size and morphology. We isolate and quantify the effect of target properties on the ejecta mobility (EM) ‐the maximum radial extent of ejecta scaled by the crater radius. We compile geologically motivated subsurfacestructures based on data gathered by orbiters and landers. Those structures arise from varying properties ofmaterials in single layers (strength, composition, porosity); the thickness of top regolith cover; and the sequenceand thicknesses of 3–4 stacked layers. We realize 2D simulations with the iSALE shock physics code whichresult in a 50 m diameter crater (an analog of new craters formed in the period of spacecraft observation). Wefind that varied subsurface rheologies result in EM numbers with a wide range of values between 7 and 19. Somesubsurface models can result in a similar EM, and some have distinct EMs, which shows potential for using thisquantity as a new diagnostic of target properties. We also show that ejecta dynamics are sensitive not only to thematerial in the excavation zone but also at much greater depths than commonly assumed (at least 1–2 craterradii). EM also depends on both material properties and layering: the impedance contrast governs the nature ofwave propagation, while the layer depth controls the timing of the shock wave reflection. Detailed studies of EMthus have promise for unveiling shallow subsurface rheologies on many Solar System bodies in the future.

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Liquid water was abundant on Mars during the Noachian and Hesperian periods but vanished as 17 the planet transitioned into the cold, dry environment we see today. It is hypothesized that much 18 of this water was either lost to space or stored in the crust. However, the extent of the water 19 reservoir within the crust remains poorly constrained due to a lack of observational evidence. 20 Here, we invert the shear wave velocity structure of the upper crust, identifying a significant 21 low-velocity layer at the base, between depths of 5.4 and 8 km. This zone is interpreted as a 22 high-porosity, water-saturated layer, and is estimated to hold a liquid water volume of 520–780 23 m of global equivalent layer (GEL). This estimate aligns well with the remaining liquid water 24 volume of 710–920 m GEL, after accounting for water loss to space, crustal hydration, and 25 modern water inventory.

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Black holes are assumed to decay via Hawking radiation. Recently we found evidence that spacetime curvature alone without the need for an event horizon leads to black hole evaporation. Here we investigate the evaporation rate and decay time of a non-rotating star of constant density due to spacetime curvature-induced pair production and apply this to compact stellar remnants such as neutron stars and white dwarfs. We calculate the creation of virtual pairs of massless scalar particles in spherically symmetric asymptotically flat curved spacetimes. This calculation is based on covariant perturbation theory with the quantum f ield representing, e.g., gravitons or photons. We find that in this picture the evaporation timescale, τ, of massive objects scales with the average mass density, ρ, as τ ∝ ρ−3/2. The maximum age of neutron stars, τ ∼ 1068yr, is comparable to that of low-mass stellar black holes. White dwarfs, supermassive black holes, and dark matter supercluster halos evaporate on longer, but also finite timescales. Neutron stars and white dwarfs decay similarly to black holes, ending in an explosive event when they become unstable. This sets a general upper limit for the lifetime of matter in the universe, which in general is much longer than the HubbleLemaˆ ıtre time, although primordial objects with densities above ρmax ≈ 3×1053 g/cm3 should have dissolved by now. As a consequence, fossil stellar remnants from a previous universe could be present in our current universe only if the recurrence time of star forming universes is smaller than about ∼ 1068years.

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One notable example of exoplanet diversity is the population of circumbinary planets, which orbit around both stars of a binary star system. There are so far only 16 known circumbinary exoplanets, all of which lie in the same orbital plane as the host binary. Suggestions exist that circumbinary planets could also exist on orbits highly inclined to the binary, close to 90◦, polar orbits. No such planets have been found yet but polar circumbinary gas and debris discs have been observed and if these were to form planets then those would be left on a polar orbit. We report strong evidence for a polar circumbinary exoplanet, which orbits a close pair of brown dwarfs which are on an eccentric orbit. We use radial-velocities to measure a retrograde apsidal precession for the binary, and show that this can only be attributed to the presence of a polar planet.

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Recent renewed interest regarding the possibility of life in the Venusian clouds has led to new studies on organicchemistry in concentrated sulfuric acid. However, life requires complex genetic polymers for biological function.Therefore, finding suitable candidates for genetic polymers stable in concentrated sulfuric acid is a necessary firststep to establish that biologically functional macromolecules can exist in this environment. We explore peptidenucleic acid (PNA) as a candidate for a genetic-like polymer in a hypothetical sulfuric acid biochemistry. PNA hex-amers undergo between 0.4 and 28.6% degradation in 98% (w/w) sulfuric acid at ~25°C, over the span of 14 days,depending on the sequence, but undergo complete solvolysis above 80°C. Our work is the first key step towardthe identification of a genetic-like polymer that is stable in this unique solvent and further establishes that con-centrated sulfuric acid can sustain a diverse range of organic chemistry that might be the basis of a form of lifedifferent from Earth’s

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Common features of sub-Neptune atmospheres observed to date include signatures of aerosols at moderate equilibrium temperatures (∼500–800 K) and a prevalence of high mean molecular weight atmospheres, perhaps indicating novel classes of planets such as water worlds. Here we present a 0.83–5μm JWST transmission spectrum of the sub-Neptune TOI-421 b. This planet is unique among previously observed counterparts in its high equilibrium temperature (Teq ≈ 920 K) and its Sun-like host star. We find marked differences between the atmosphere of TOI-421 b and those of sub-Neptunes previously characterized with JWST, which all orbit late K and M stars. Specifically, water features in the NIRISS/SOSS bandpass indicate a low mean molecular weight atmosphere consistent with solar metallicity and no appreciable aerosol coverage. Hints of SO2 and CO (but not CO2 or CH4) also exist in our NIRSpec/G395M observations, but not at sufficient signal-to-noise ratio to draw f irm conclusions. Our results support a picture in which sub-Neptunes hotter than ∼850K do not form hydrocarbon hazes owing to a lack of methane to photolyze. TOI-421 b additionally fits the paradigm of the radius valley for planets orbiting FGK stars being sculpted by mass-loss processes, which would leave behind primordial atmospheres overlying rock/iron interiors. Further observations of TOI-421 b and similar hot sub-Neptunes will confirm whether haze-free atmospheres and low mean molecular weights are universal characteristics of such objects.

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Direct Evidence for r-process Nucleosynthesis in Delayed MeV Emission from th...Sérgio Sacani

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The origin of heavy elements synthesized through the rapid neutron capture process (r-process) has been an enduring mystery for over half a century. J. Cehula et al. recently showed that magnetar giant flares, among the brightest transients ever observed, can shock heat and eject neutron star crustal material at high velocity, achieving the requisite conditions for an r-process.A. Patel et al. confirmed an r-process in these ejecta using detailed nucleosynthesis calculations. Radioactive decay of the freshly synthesized nuclei releases a forest of gamma-ray lines, Doppler broadened by the high ejecta velocities v  0.1c into a quasi-continuous spectrum peaking around 1 MeV. Here, we show that the predicted emission properties (light curve, fluence, and spectrum) match a previously unexplained hard gamma-ray signal seen in the aftermath of the famous 2004 December giant flare from the magnetar SGR 1806–20. This MeV emission component, rising to peak around 10 minutes after the initial spike before decaying away over the next few hours, is direct observational evidence for the synthesis of ∼10−6 Me of r-process elements. The discovery of magnetar giant flares as confirmed r-process sites, contributing at least ∼1%–10% of the total Galactic abundances, has implications for the Galactic chemical evolution, especially at the earliest epochs probed by low-metallicity stars. It also implicates magnetars as potentially dominant sources of heavy cosmic rays. Characterization of the r-process emission from giant flares by resolving decay line features offers a compelling science case for NASA’s forthcomingCOSI nuclear spectrometer, as well as next-generation MeV telescope missions.

OGLE-2011-BLG-0462: An Isolated Stellar-mass Black Hole Confirmed Using New H...Sérgio Sacani

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The long-duration Galactic-bulge microlensing event OGLE-2011-BLG-0462 produced relativistic astrometric deflections of the source star, which we measured using Hubble Space Telescope (HST) observations taken at eight epochs over ∼6yr. Analysis of the microlensing light curve and astrometry led our group (followed by other independent groups) to conclude that the lens is an isolated stellar-mass black hole (BH)—the first and only one unambiguously discovered to date. There have now been three additional epochs of HST observations, increasing the astrometric time baseline to 11 yr. Additionally, the ground-based OGLE data have been updated. We have reanalyzed the data, including the new HST astrometry, and photometry obtained with 16 different telescopes. The source lies only  0.4 from a bright neighbor, making it crucial to perform precise subtraction of its point-spread function (PSF) in the astrometric measurements of the source. Moreover, we show that it is essential to perform a separate PSF subtraction for each individual HST frame as part of the reductions. Our final solution yields a lens mass of 7.15±0.83Me. Combined with the lack of detected light from the lens at late HST epochs, the BH nature of the lens is conclusively verified. The BH lies at a distance of 1.52 ± 0.15kpc, and it is moving with a space velocity of 51.1 ± 7.5 kms−1 relative to the stars in the neighborhood. We compare our results with those of other studies and discuss reasons for the differences. We also searched for binary companions of the BH at a range of separations, but found no evidence for any.

Arecibo Wow! I: An Astrophysical Explanation for the Wow! SignalSérgio Sacani

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The Ohio State University Big Ear radio telescope detected in 1977 the Wow! Signal, one of the most famous and intriguing signals of extraterrestrial origin. Characterized by its strong relative intensity and narrow bandwidth near the 1420 MHz hydrogen line, its source has never been detected again despite numerous follow-up attempts. Arecibo Wow! is a new technosignature project using archived data from the Arecibo Observatory. Here we present our first results of drift scans made between February and May 2020 at 1420 MHz. The methods, frequency, and bandwidth of these observations are similar to those used to detect the Wow! Signal. However, our observations are more sensitive, have better temporal resolution, and include polarization measurements. We report the detection of narrowband signals (∆ν ≤ 10 kHz) near the hydrogen line similar to the Wow! Signal, although twoorders of magnitude less intense and in multiple locations. Despite the similarities, these signals are easily identifiable as small interstellar clouds of cold hydrogen (Hi) in the galaxy. We hypothesize that the Wow! Signal was caused by a sudden brightening of the hydrogen line in these clouds triggered by a strong transient radiation source, such as a magnetar flare or a soft gamma repeater (SGR). A maser f lare or superradiance mechanisms can produce stimulated emission consistent with the Wow! Signal. Our hypothesis explains all observed properties of the Wow! Signal, proposes a new source of false positives in technosignature searches, and suggests that the Wow! Signal could be the first recorded event of an astronomical maser-like flare in the hydrogen line.

Earth-like planet predictor: a machine learning approachSérgio Sacani

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Context. Searching for planets analogous to Earth in terms of mass and equilibrium temperature is currently the first step in the quest for habitable conditions outside our Solar System and, ultimately, the search for life in the universe. Future missions such as PLAnetary Transits and Oscillations of stars (PLATO) or Large Interferometer For Exoplanets (LIFE) will begin to detect and characterise these small, cold planets, dedicating significant observation time to them. Aims. The aim of this work is to predict which stars are most likely to host an Earth-like planet (ELP) to avoid blind searches, minimises detection times, and thus maximises the number of detections. Methods. Using a previous study on correlations between the presence of an ELP and the properties of its system, we trained a Random Forest to recognise and classify systems as ‘hosting an ELP’ or ‘not hosting an ELP’. The Random Forest was trained and tested on populations of synthetic planetary systems derived from the Bern model, and then applied to real observed systems. Results. The tests conducted on the machine learning (ML) model yield precision scores of up to 0.99, indicating that 99% of the systems identified by the model as having ELPs possess at least one. Among the few real observed systems that have been tested, eight have been selected as having a high probability of hosting an ELP, and a quick study of the stability of these systems confirms that the presence of an Earth-like planet within them would leave them stable. Conclusions. The excellent results obtained from the tests conducted on the ML model demonstrate its ability to recognise the typical architectures of systems with or without ELPs within populations derived from the Bern model. If we assume that the Bern model adequately describes the architecture of real systems, then such a tool can prove indispensable in the search for Earth-like planets. A similar approach could be applied to other planetary system formation models to validate those predictions.

Telescópio James Webb Revela Evidências de Buraco Negro no Coração da Galáxia...Sérgio Sacani

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Wereport the first detections of [Ne v] λ14.3 μm and [NeVI] λ7.7μm at high confidence (S/N 6) in the nuclear region of the nearby spiral galaxy M83. Emission-line maps of these high-ionization lines show several compact structures. Specifically, the [Ne VI] emission is located at 140 pc from the optical nucleus and appears as a point source of size 18pc (FWHM  0. 8). We investigate the possible source of this extreme emission through comparison with photoionization models and ancillary data. We find that photoionization models of fast radiative shocks are able to reproduce the observed high-excitation emission-line fluxes only for the lowest preshock density available in the library, n = 0.01 cm−3. Additionally, tailored active galactic nucleus (AGN) photoionization models assuming a two-zone structure are compatible with the observed high-ionization fluxes. Our simple AGN model shows that the emission at the location of the [Ne VI] source can be the result of a cloud being ionized by the radiation cone of an AGN. We stress, however, that to definitively confirm an AGN as the main source of the observed emission, more complex modeling accounting for different geometries is required. Previously known as a purely starburst system, these new findings of the nuclear region of M83 will require a reassessment of its nature and of objects similar to it, particularly now that we have access to the unparalleled infrared sensitivity and spatial resolution of the James Webb Space Telescope.

New Constraints on DMS and DMDS in the Atmosphere of K2-18 b from JWST MIRISérgio Sacani

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The sub-Neptune frontier has opened a new window into the rich diversity of planetary environments beyond the solar system. The possibility of hycean worlds, with planet-wide oceans and H2-rich atmospheres, significantly expands and accelerates the search for habitable environments elsewhere. Recent JWST transmission spectroscopy of the candidate hycean world K2-18 b in the near-infrared led to the first detections of the carbon-bearing molecules CH4 and CO2 in its atmosphere, with a composition consistent with predictions for hycean conditions. The observations also provided a tentative hint of dimethyl sulfide (DMS), a possible biosignature gas, but the inference was of low statistical significance. We report a mid-infrared transmission spectrum of K2-18 b obtained using the JWST MIRI LRS instrument in the ∼6–12μm range. The spectrum shows distinct features and is inconsistent with a featureless spectrum at 3.4σ significance compared to our canonical model. We find that the spectrum cannot be explained by most molecules predicted for K2-18 b, with the exception of DMS and dimethyl disulfide (DMDS), also a potential biosignature gas. We report new independent evidence for DMS and/or DMDS in the atmosphere at 3σ significance, with high abundance (10ppmv) of at least one of the two molecules. More observations are needed to increase the robustness of the findings and resolve the degeneracy between DMS and DMDS. The results also highlight the need for additional experimental and theoretical work to determine accurate cross sections of important biosignature gases and identify potential abiotic sources. We discuss the implications of the present findings for the possibility of biological activity on K2-18 b.

First Frequency Phase Transfer from the 3mm to the 1mm Band on an Earth-sized...Sérgio Sacani

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Water ice in the debris disk around HD 181327Sérgio Sacani

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The atmosphere of Titan in late northern summer from JWST and Keck observationsSérgio Sacani

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Discovery of a dwarf planet candidate in an extremely wide orbit: 2017 OF201Sérgio Sacani

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Streaks on martian slopes are dry - No Water On MarsSérgio Sacani

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The Link Between Subsurface Rheology and EjectaMobility: The Case of Small Ne...Sérgio Sacani

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Seismic evidence of liquid water at the base of Mars' upper crustSérgio Sacani

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A Massive Black Hole 0.8kpc from the Host Nucleus Revealed by the Offset Tida...Sérgio Sacani

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An upper limit to the lifetime of stellar remnants from gravitational pair pr...Sérgio Sacani

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Evidence for a polar circumbinary exoplanet orbiting a pair of eclipsing brow...Sérgio Sacani

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Astrobiological implications of the stability andreactivity of peptide nuclei...Sérgio Sacani

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TOI-421 b: A Hot Sub-Neptune with a Haze-free, Low Mean Molecular Weight Atmo...Sérgio Sacani

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Structure formation with primordial black holes: collisional dynamics, binari...Sérgio Sacani

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On the Lunar Origin of Near-Earth Asteroid 2024 PT5Sérgio Sacani

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Direct Evidence for r-process Nucleosynthesis in Delayed MeV Emission from th...Sérgio Sacani

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OGLE-2011-BLG-0462: An Isolated Stellar-mass Black Hole Confirmed Using New H...Sérgio Sacani

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Arecibo Wow! I: An Astrophysical Explanation for the Wow! SignalSérgio Sacani

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Earth-like planet predictor: a machine learning approachSérgio Sacani

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Telescópio James Webb Revela Evidências de Buraco Negro no Coração da Galáxia...Sérgio Sacani

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New Constraints on DMS and DMDS in the Atmosphere of K2-18 b from JWST MIRISérgio Sacani

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