OA@INAF - Istituto Nazionale di Astrofisica
Not a member yet
15494 research outputs found
Sort by
Salts and organics on Ganymede’s surface observed by the JIRAM spectrometer onboard Juno
Get PDFThe surface of Ganymede exhibits diversity in composition, interpreted as indicative of geological age differences between dark and bright terrains. Observations from Galileo and Earth-based telescopes have revealed the presence of both water ice and non-ice material, indicative of either endogenic or exogenic processes, or some combination. However, these observations attained a spatial resolution that was too coarse to reveal the surface composition at a local scale. Here we present the high-spatial-resolution infrared spectra of Ganymede observed with the Jovian InfraRed Auroral Mapper onboard the National Aeronautics and Space Administration’s Juno spacecraft during a close flyby that occurred on 7 June 2021. We found that at a pixel resolution <1 km, the surface of Ganymede exhibits signatures diagnostic of hydrated sodium chloride, ammonium chloride and sodium/ammonium carbonate, as well as organic compounds, possibly including aliphatic aldehydes. Carbon dioxide shows up mostly at trailing longitudes. The composition and spatial distribution of these salts and organics suggest that their origin is endogenic, resulting from the extrusion of subsurface brines, whose chemistry reflects the water–rock interaction inside Ganymede
Potential climates and habitability on Gl 514 b: a super-Earth exoplanet with high eccentricity
Get PDFThe recently discovered super-Earth Gl 514 b, orbiting a nearby M0.5-1.0 star at 7.6 pc, is one of the best benchmark exoplanets for understanding the potential climate states of eccentric planets. The elongated (e = 0.45) orbit of Gl 514 b, which only partially lies in the Conservative Habitable Zone, suggests a dynamically young system, where the spin-orbit tidal synchronization may not have yet occurred up to the present time. In the present work, we use a seasonal-latitudinal energy balance model, EOS-ESTM, to explore the potential impact of both constrained and unconstrained planetary, orbital, and atmospheric parameters on the Gl 514 b habitability, mapped in terms of surface temperature. We test three distinct CO2-dominated atmospheres by varying the CH4 concentration values (0 per cent, 0.1 per cent, and 1 per cent) and the total surface pressure. As a general trend, we find that habitable conditions are favoured by high-CH4 and high-pressure regimes. Habitability also increases for high-axis obliquities (at least until the appearance of an icebelt), long-rotation periods, and high-ocean fractional coverage. If the ocean fraction is low, then also the argument of periastron becomes relevant. Our results are robust against changes of the continental distribution. Thus, we conclude that Gl 514 b can potentially maintain temperate surface conditions with modest seasonal temperature variations under a wide variety of planetary, orbital, and atmospheric conditions. Despite no transit have been detected yet, the results found in this work should motivate the community to invest time in future observations
A SPectroscopic Survey of Biased Halos In the Reionization Era (ASPIRE): JWST Supports Earlier Reionization around [O III] Emitters
Get PDFUnderstanding when and how reionization happened is crucial for studying the early structure formation and the properties of the first galaxies in the Universe. At z > 5.5, the observed intergalactic medium (IGM) optical depth shows a significant scatter, indicating an inhomogeneous reionization process. However, the nature of the inhomogeneous reionization remains debated. A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE) is a JWST Cycle 1 program that has spectroscopically identified >400 [O III] emitters in 25 quasar fields at z > 6.5. Combined with deep ground-based optical spectroscopy of ASPIRE quasars, the ASPIRE program provides the current largest sample for IGM-galaxy connection studies during cosmic reionization. We present the first results of IGM effective optical depth measurements around [O III] emitters using 14 ASPIRE quasar fields. We find the IGM transmission is tightly related to reionization era galaxies to the extent that a significant excess of Lyα transmission exists around [O III] emitters. We measure the stacked IGM effective optical depth of IGM patches associated with [O III] emitters and find they reach the same IGM effective optical depth at least d z ∼ 0.1 ahead of those IGM patches where no [O III] emitters are detected, supporting earlier reionization around [O III] emitters. Our results indicate an enhancement in IGM Lyα transmission around [O III] emitters at scales beyond 25 h ‑1 cMpc, consistent with the predicted topology of reionization from fluctuating UV background models
Dramatic Drop in the X-Ray Polarization of Swift J1727.8–1613 in the Soft Spectral State
Get PDFBlack hole X-ray binaries exhibit different spectral and timing properties in different accretion states. The X-ray outburst of a recently discovered and extraordinarily bright source, Swift J1727.8–1613, has enabled the first investigation of how the X-ray polarization properties of a source evolve with spectral state. The 2–8 keV polarization degree was previously measured by the Imaging X-ray Polarimetry Explorer (IXPE) to be ≈4% in the hard and hard intermediate states. Here we present new IXPE results taken in the soft state, with the X-ray flux dominated by the thermal accretion disk emission. We find that the polarization degree has dropped dramatically to ≲1%. This result indicates that the measured X-ray polarization is largely sensitive to the accretion state and the polarization fraction is significantly higher in the hard state when the X-ray emission is dominated by upscattered radiation in the X-ray corona. The combined polarization measurements in the soft and hard states disfavor a very high or low inclination of the system
Leverage collaborative design techniques to develop a unified interface for the SKA central signal processor
Get PDFThe Square Kilometre Array (SKA) Central Signal Processor (CSP) is a real-time backend system that processes incoming astronomical signals to produce visibilities and detects and profiles pulsars. The CSP is composed of the Local Monitoring and Control (LMC), the Correlator and Beam-Former (CBF), and the Pulsar Search and Timing (PSS, PST) engines. Each subsystem is developed by a different team in the SKA control software domain following the Scaled Agile Framework (SAFe) to guarantee coherence in the development. The definition of an engineering User Interface (UI) for the CSP is challenging due to the variety of skills that are required to identify the most relevant design concepts and potential roadblocks to an effective representation and the fact that several teams are involved. For this reason, we chose to leverage a collaborative design approach that can easily fit SKA’s biweekly sprint cadence while involving experts from different fields in a “think outside the box” process. Sketches and wireframes undergo multiple refinement sessions that lead to the realisation of an engineering dashboard representing the current state of CSP implementation. User testing sessions constitute the means by which the success of the proposed UI is measured. Additional positive effects are alignment across different teams on the current capabilities of the system and its future development, as well as a way for continuously adapting the UI to the system’s evolution. In this paper, we describe the challenges we faced while coordinating the design across multiple teams, show how the process was implemented to fit the short agile iterations and overall SAFe framework and present the results of the work
The MICADO first light imager for the ELT: overview and current status
Get PDFMICADO is a first light instrument for the Extremely Large Telescope (ELT), set to start operating later this decade. It will provide diffraction limited imaging, astrometry, high contrast imaging, and long slit spectroscopy at near-infrared wavelengths. During the initial phase operations, adaptive optics (AO) correction will be provided by its own natural guide star wavefront sensor. In its final configuration, that AO system will be retained and complemented by the laser guide star multi-conjugate adaptive optics module MORFEO (formerly known as MAORY). Among many other things, MICADO will study exoplanets, distant galaxies and stars, and investigate black holes, such as Sagittarius A* at the centre of the Milky Way. After their final design phase, most components of MICADO have moved on to the manufacturing and assembly phase. Here we summarize the final design of the instrument and provide an overview about its current manufacturing status and the timeline. Some lessons learned from the final design review process will be presented in order to help future instrumentation projects to cope with the challenges arising from the substantial differences between projects for 8-10m class telescopes (e.g. ESO's VLT) and the next generation Extremely Large Telescopes (e.g. ESO's ELT). Finally, MICADO's expected performance will be discussed in the context of the current landscape of astronomical observatories and instruments. For instance, MICADO will have similar sensitivity as the James Webb Space Telescope (JWST), but with six times the spatial resolution
The accretion burst of the massive young stellar object G323.46 -0.08
No full textAccretion bursts from low-mass young stellar objects (YSOs) are known for
many decades. In recent years, the first accretion bursts of massive YSOs
(MYSOs) have been observed. These phases of intense protostellar growth are of
particular importance for studying massive star formation. Bursts of MYSOs are
accompanied by flares of Class II methanol masers (hereafter masers), caused by
an increase in exciting mid-infrared (MIR) emission. The G323.460.08
(hereafter G323) event extends the small sample of known MYSO bursts. Maser
observations of the MYSO G323 show evidence of a flare, which was presumed to
be caused by an accretion burst. This should be verified with IR data. We used
time-dependent radiative transfer (TDRT) to characterize the heating and
cooling timescales for eruptive MYSOs and to infer the main burst parameters.
The G323 accretion burst is confirmed. It reached its peak in late 2013/early
2014 with a Ks-band increase of 2.5mag. TDRT indicates that the duration of the
thermal afterglow in the far-infrared (FIR) can exceed the burst duration by
years. The latter was proved by SOFIA observations, which indicate a flux
increase of % at and % at m in 2022 (2 years after the burst end). A one-sided light echo emerged
that was propagating into the interstellar medium. The G323 burst is probably
the most energetic MYSO burst observed so far. Within , an
energy of was released. The
short timescale points to the accretion of a compact body, while the burst
energy corresponds to an accumulated mass of at least
and possibly even more if the protostar is bloated.
In this case, the accretion event might have triggered protostellar pulsations,
which give rise to the observed maser periodicity
The influence of accretion bursts on methanol and water in massive young stellar objects
No full textContext. The effect of accretion bursts on massive young stellar objects (MYSOs) represents a new research field in the study of young stars and their environment. The impact of such bursts on the disk and envelope has been observed and plays the role of a smoking gun providing information about the properties of the burst itself. Aims. We aim to investigate the impact of an accretion burst on massive disks with different types of envelopes and to study the effects of an accretion burst on the temperature structure and the chemistry of the disk. We focus on water and methanol as chemical species for this paper. Methods. The thermochemical code of ProDiMo (PROtoplanetary DIsk MOdel) is used to perform simulations of high-mass protoplanetary-disk models with different types of envelopes in the presence of an accretion burst. The models in question represent different evolutionary stages of protostellar objects. We calculated and show the chemical abundances in three phases of the simulation (pre-burst, burst, and post-burst). Results. More heavily embedded disks show higher temperatures. The impact of the accretion burst is mainly characterized by the desorption of chemical species present in the disk and envelope from the dust grains to the gas phase. When the post-burst phase starts, the sublimated species freeze out again. The degree of sublimation depends strongly on the type of envelope the disk is embedded in. An accretion burst in more massive envelopes produces stronger desorption of the chemical species. However, our models show that the timescale for the chemistry to reach the pre-burst state is independent of the type of envelope. Conclusions. The study shows that the disk s temperature increases with a more massive envelope enclosing it. Thus, the chemistry of MYSOs in earlier stages of their evolution reacts stronger to an accretion burst than at later stages where the envelope has lost most of its mass or has been dissipated. The study of the impact of accretion bursts could also provide helpful theoretical context to the observation of methanol masers in massive disks
Supermassive Black Hole Winds in X-rays: SUBWAYS: III. A population study on ultra-fast outflows
No full textThe detection of blueshifted absorption lines likely associated with ionized iron K-shell transitions in the X-ray spectra of many active galactic nuclei (AGNs) suggests the presence of a highly ionized gas outflowing with mildly relativistic velocities (0.03c-0.6c) named ultra-fast outflow (UFO). Within the SUBWAYS project, we characterized these winds starting from a sample of 22 radio-quiet quasars at an intermediate redshift (0.1 ≤ z ≤ 0.4) and compared the results with similar studies in the literature on samples of local Seyfert galaxies (i.e., 42 radio-quiet AGNs observed with XMM-Newton at z ≤ 0.1) and high redshift radio-quiet quasars (i.e., 14 AGNs observed with XMM-Newton and Chandra at z ≥ 1.4). The scope of our work is a statistical study of UFO parameters and incidence considering the key physical properties of the sources, such as supermassive black hole (SMBH) mass, bolometric luminosity, accretion rates, and spectral energy distribution (SED) with the aim of gaining new insights into the UFO launching mechanisms. We find indications that highly luminous AGNs with a steeper X-ray/UV ratio, αox, are more likely to host UFOs. The presence of UFOs is not significantly related to any other AGN property in our sample. These findings suggest that the UFO phenomenon may be transient. Focusing on AGNs with UFOs, other important findings from this work include: (1) faster UFOs have larger ionization parameters and column densities; (2) X-ray radiation plays a more crucial role in driving highly ionized winds compared to UV; (3) the correlation between outflow velocity and luminosity is significantly flatter than what is expected for radiatively driven winds; (4) more massive black holes experience higher wind mass losses, suppressing the accretion of matter onto the black hole; (5) the UFO launching radius is positively correlated with the Eddington ratio. Furthermore, our analysis suggests the involvement of multiple launching mechanisms, including radiation pressure and magneto-hydrodynamic processes, rather than pointing to a single, universally applicable mechanism
Cosmic rays: physics, chemistry, and computational challenges
Get PDFIn regions shielded from ultraviolet radiation, energetic charged particles, called cosmic rays, are the dominant drivers of ionization, dissociation, and excitation. This chapter discusses the basics of cosmic-ray transport and acceleration, their impact on the thermochemistry of molecular gas, and methods to include cosmic-ray processes into astrochemical models