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L'aurora in una stanza
Get PDFAsteroidi, stelle cadenti, aurore e satelliti in realtà aumentata. L’app di Sorvegliati Spaziali mostra meraviglie e pericoli dello spazio
TOI-757 b: an eccentric transiting mini-Neptune on a 17.5-d orbit
Get PDFWe report the spectroscopic confirmation and fundamental properties of TOI757 b, a miniNeptune on a 17.5d orbit transiting a bright star ( mag) discovered by the TESS mission. We acquired highprecision radial velocity measurements with the HARPS, ESPRESSO, and PFS spectrographs to confirm the planet detection and determine its mass. We also acquired spaceborne transit photometry with the CHEOPS space telescope to place stronger constraints on the planet radius, supported with groundbased LCOGT photometry. WASP and KELT photometry were used to help constrain the stellar rotation period. We also determined the fundamental parameters of the host star. We find that TOI757 b has a radius of and a mass of , implying a bulk density of g cm. Our internal composition modelling was unable to constrain the composition of TOI757 b, highlighting the importance of atmospheric observations for the system. We also find the planet to be highly eccentric with e = 0.39, making it one of the very few highly eccentric planets among precisely characterized miniNeptunes. Based on comparisons to other similar eccentric systems, we find a likely scenario for TOI757 b's formation to be high eccentricity migration due to a distant outer companion. We additionally propose the possibility of a more intrinsic explanation for the high eccentricity due to starstar interactions during the earlier epoch of the Galactic disc formation, given the low metallicity and older age of TOI757
Discovery of two warm mini-Neptunes with contrasting densities orbiting the young K3V star TOI-815
Get PDFWe present the discovery and characterization of two warm mini-Neptunes transiting the K3V star TOI-815 in a K-M binary system. Analysis of its spectra and rotation period reveal the star to be young, with an age of 200−200+400 Myr. TOI-8l5b has a 11.2-day period and a radius of 2.94 ± 0.05 R⊕ with transits observed by TESS, CHEOPS, ASTEP, and LCOGT. The outer planet, TOI-8l5c, has a radius of 2.62 ± 0.10 R⊕, based on observations of three nonconsecutive transits with TESS; targeted CHEOPS photometry and radial velocity follow-up with ESPRESSO were required to confirm the 35-day period. ESPRESSO confirmed the planetary nature of both planets and measured masses of 7.6 ± 1.5 M⊕ (ρP = 1.64−0.31+0.33 g cm−3) and 23.5 ± 2.4 M⊕ (ρP = 7.2−1.0+1.1 g cm−3), respectively. Thus, the planets have very different masses, which is unusual for compact multi-planet systems. Moreover, our statistical analysis of mini-Neptunes orbiting FGK stars suggests that weakly irradiated planets tend to have higher bulk densities compared to those undergoing strong irradiation. This could be ascribed to their cooler atmospheres, which are more compressed and denser. Internal structure modeling of TOI-815b suggests it likely has a H-He atmosphere that constitutes a few percent of the total planet mass, or higher if the planet is assumed to have no water. In contrast, the measured mass and radius of TOI-815c can be explained without invoking any atmosphere, challenging planetary formation theories. Finally, we infer from our measurements that the star is viewed close to pole-on, which implies a spin-orbit misalignment at the 3σ level. This emphasizes the peculiarity of the system's orbital architecture, and probably hints at an eventful dynamical history. The photometric and radial velocity data are available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/685/A5 This study uses TESS data, CHEOPS data observed as part of guaranteed time observation programs CH_PR10031 and CH_PR10048, and ESPRESSO data collected with the ESO 3.6 m telescope under programs 105.20P7.001, 109.23DX.001, and 110.2481.001 (PI: Bouchy)
The GAPS programme at TNG. XLIX. TOI-5398, the youngest compact multi-planet system composed of an inner sub-Neptune and an outer warm Saturn
Get PDFContext. Short-period giant planets (P ≲ 10 days, Mp >0.1 MJ) are frequently found to be solitary compared to other classes of exo-planets. Small inner companions to giant planets with P ≲ 15 days are known only in five compact systems: WASP-47, Kepler-730, WASP-132, TOI-1130, and TOI-2000. Here, we report the confirmation of TOI-5398, the youngest known compact multi-planet system composed of a hot sub-Neptune (TOI-5398 c, Pc = 4.77271 days) orbiting interior to a short-period Saturn (TOI-5398 b, Pb = 10.590547 days) planet, both transiting around a 650 ± 150 Myr G-type star. Aims: As part of the Global Architecture of Planetary Systems (GAPS) Young Object project, we confirmed and characterised this compact system, measuring the radius and mass of both planets, thus constraining their bulk composition. Methods: Using multi-dimensional Gaussian processes, we simultaneously modelled stellar activity and planetary signals from the Transiting Exoplanet Survey Satellite (TESS) Sector 48 light curve and our High Accuracy Radial velocity Planet Searcher (HARPS-N) radial velocity (RV) time series. We confirmed the planetary nature of both planets, TOI-5398 b and TOI-5398 c, and obtained a precise estimation of their stellar parameters. Results: Through the use of astrometric, photometric, and spectroscopic observations, our findings indicate that TOI-5398 is a young, active G dwarf star (650 ± 150 Myr) with a rotational period of Prot = 7.34 days. The transit photometry and RV measurements enabled us to measure both the radius and mass of planets b, Rb = 10.30 ± 0.40 R⊕, Mb = 58.7 ± 5.7 M⊕, and c, Rc = 3.52 ± 0.19 R⊕, Mc = 11.8 ± 4.8 M⊕. TESS observed TOI-5398 during sector 48 and no further observations are planned in the current Extended Mission, making our ground-based light curves crucial for improvement of the ephemeris. With a transmission spectroscopy metric (TSM) value of around 300, TOI-5398 b is the most amenable warm giant (10 Table A.1 is available at the CDS ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/682/A129 Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated by the Fundación Galileo Galilei (FGG) of the Istituto Nazionale di Astrofisica (INAF) at the Observatorio del Roque de los Muchachos (La Palma, Canary Islands, Spain). Flatiron Research Fellow. NASA Sagan Fellow
In situ observations of large-amplitude Alfvén waves heating and accelerating the solar wind
Get PDFAfter leaving the Sun's corona, the solar wind continues to accelerate and cools, but more slowly than expected for a freely expanding adiabatic gas. Alfvén waves are perturbations of the interplanetary magnetic field that transport energy. We use in situ measurements from the Parker Solar Probe and Solar Orbiter spacecraft to investigate a stream of solar wind as it traverses the inner heliosphere. The observations show heating and acceleration of the plasma between the outer edge of the corona and near the orbit of Venus, along with the presence of large-amplitude Alfvén waves. We calculate that the damping and mechanical work performed by the Alfvén waves are sufficient to power the heating and acceleration of the fast solar wind in the inner heliosphere
First Solar Orbiter observation of a dark halo in the solar atmosphere
Get PDFSolar Orbiter is a space mission of international collaboration between ESA and NASA, operated by ESA. The EUI instrument was built by CSL, IAS, MPS, MSSL/UCL, PMOD/WRC, ROB, LCF/IO with funding from the Belgian Federal Science Policy Office (BELSPO/PRODEX PEA 4000134088); the Centre National d’Etudes Spatiales (CNES); the UK Space Agency (UKSA); the Bundesministerium für Wirtschaft und Energie (BMWi) through the Deutsches Zentrum fúr Luftund Raumfahrt (DLR); and the Swiss Space Office (SSO).The development of SPICE has been funded by ESA member states and ESA. It was built and is operated by a multi-
national consortium of research institutes supported by their respective funding agencies: STFC RAL (UKSA, hardware lead), IAS (CNES, operations lead), GSFC (NASA), MPS (DLR), PMOD/WRC (Swiss Space Office),
SwRI (NASA), UiO (Norwegian Space Agency). The German contribution to SO/PHI is funded by the Bundesministerium für Wirtschaft und Technologie through Deutsches Zentrum für Luftund Raumfahrt e.V. (DLR), Grants No. 50 OT 1001/1201/1901 as well as 50 OT 0801/1003/1203/1703, and by the President of the Max Planck Society (MPG). The Spanish contribution is funded by AEI/MCIN/10.13039/501100011033/(RTI2018-096886-C5, PID2021-125325OB-C5, PCI2022-135009-2) and ERDF “A way of making
Europe”; “Center of Excellence Severo Ochoa” awards to IAA-CSIC (SEV-2017-0709, CEX2021-001131-S); and a Ramón y Cajal fellowship awarded to DOS. The French contribution is funded by the Centre National d’Etudes
Spatiales. Part of this work was supported by the Italian agreement ASI-INAF 2021-12-HH.0 “Missione Solar-C EUVST–Supporto scientifico di Fase B/C/D; Addendum N. 2021-12-HH.1-2024”. D.B. is funded under Solar Orbiter EUI Operations grant No. ST/X002012/1 and Hinode Ops Continuation 2022-25 grant No. ST/X002063/1. SML thanks Marco Stangalini, Gherardo Valori and Nawin Ngampoopun for useful discussion and suggestions that improved the manuscript. The authors acknowledge important suggestions from the anonymous referee who helped to improve the manuscript. This study has made use of SAO/NASA Astrophysics Data System’s bibliographic services.Solar active regions (ARs) are often surrounded by dark large areas of
reduced emission compared to the quiet Sun, observed at various wavelengths
corresponding to chromosphere, transition region (TR) and corona, and known as
Dark Halos (DHs). DHs have been insufficiently studied, and the mechanisms
behind their darker emission remain unclear. This study aims to investigate for
the first time the fine structure of a DH observed by the EUV High Resolution
Imager (HRI) onboard the ESA's Solar Orbiter (SO) mission and its
appearance in the TR. We utilized the extensive 1-hour dataset from SO on 19
March 2022, which includes high-resolution observations of NOAA 12967 and part
of the surrounding DH. We analyzed the dynamics of the HRI DH fine
structure and its appearance in the HRI image and the Spectral
Imaging of the Coronal Environment (SPICE) Ly, C III, N VI, O VI and Ne
VIII lines, which sample the TR in the logT (K) 4.0 - 5.8 range. This
analysis was complemented with a simultaneous B magnetogram taken by
the High Resolution Telescope (HRT). We report the presence of a peculiar fine
structure which is not observed in the quiet Sun, characterized by combined
bright EUV bundles and dark regions, arranged and interconnected in such a way
that they cannot be clearly separated. They form a spatial continuum extending
approximately radially from the AR core, suggesting a deep connection between
the DH and the AR. Additionally, we find that the bright EUV bundles are
observed in all the SPICE TR lines and the HRI band and present
photospheric B footprints in the HRT magnetogram. This spatial
correlation indicates that the origin of the 174 \r{A} DH may lie in the low
atmosphere, i.e. photosphere/chromosphere
Fundamental physics measurements with Galileo FOC satellites and the Galileo for science project. II. A box wing for modeling direct solar radiation pressure and preliminaries orbit determinations
Get PDFThis paper concerns the development of a first simplified model to take into account the perturbations produced by the nongravitational forces acting on the satellites of the Galileo FOC constellation and the corresponding first orbital determinations within the G4S_2.0 project. G4S_2.0 has a series of objectives in verifying the gravitational interaction in the weak field limit of the theory of general relativity, exploiting in particular the eccentricity of the orbits of some Galileo FOC satellites and the precise measurements that can be derived from the atomic clocks on board these satellites. The study focused on the model for the acceleration produced by direct solar radiation pressure on the satellites. This is the largest of all nongravitational perturbations. It is therefore necessary to build a sufficiently accurate model for it before being able to seriously consider smaller perturbation effects, such as those related to terrestrial radiation and thermal thrust effects. The work presents new aspects in the literature of navigation satellites. One of these is the determination of the effects in the Keplerian elements produced by the direct solar acceleration obtained from a box-wing model of the satellite. A second aspect is the comparison of these predictions in the orbital elements with the corresponding orbital residuals achieved from an orbit determination of the satellite. The study therefore highlights even more the importance of being able to improve the model of the perturbation originating from solar radiation in the field of global navigation satellite systems. This is very important if one wants to extract gravitational measurements from the orbit and clock-bias measurements of these satellites to verify the predictions of general relativity and compare them with those of alternative theories of gravitation
Euclid: High-precision imaging astrometry and photometry from Early Release Observations: I. Internal kinematics of NGC6397 by combining Euclid and Gaia data
Get PDFThe instruments at the focus of the Euclid space observatory offer superb, diffraction-limited imaging over an unprecedented (from space) wide field of view of 0.57 deg2. This exquisite image quality has the potential to produce high-precision astrometry for point sources once the undersampling of Euclid's cameras is taken into account by means of accurate, effective point spread function (ePSF) modelling. We present a complex, detailed workflow to simultaneously solve for the geometric distortion (GD) and model the undersampled ePSFs of the Euclid detectors. Our procedure was successfully developed and tested with data from the Early Release Observations (ERO) programme focused on the nearby globular cluster NGC 6397. Our final one-dimensional astrometric precision for a well-measured star just below saturation is 0.7 mas (0.007 pixel) for the Visible Instrument (VIS) and 3 mas (0.01 pixel) for the Near-Infrared Spectrometer and Photometer (NISP). Finally, we present a specific scientific application of this high-precision astrometry: the combination of Euclid and Gaia data to compute proper motions and study the internal kinematics of NGC 6397. Future work, when more data become available, will allow for a better characterisation of the ePSFs and GD corrections that are derived here, along with assessment of their temporal stability, and their dependencies on the spectral energy distribution of the sources as seen through the wide-band filters of Euclid
Seasonal Thaws under Mid- to Low-pressure Atmospheres on Early Mars
Get PDFDespite decades of scientific research on the subject, the climate of the first 1.5 Gyr of Mars' history has not been fully understood yet. Especially challenging is the need to reconcile the presence of liquid water for extended periods of time on the Martian surface with the comparatively low insolation received by the planet, a problem which is known as the Faint Young Sun paradox. In this paper, we use the Earth-like planet surface-temperature model (or ESTM), a latitudinal energy-balance model with enhanced prescriptions for meridional heat diffusion, and the radiative-transfer code EOS to investigate how seasonal variations of temperature can give rise to local conditions which are conducive to liquid-water runoffs. We include the effects of the Martian dichotomy, a northern ocean with either 150 or 550 m of global equivalent layer, and simplified CO2 or H2O clouds. We find that 1.3–2.0 bar CO2-dominated atmospheres can produce seasonal thaws due to inefficient heat redistribution, provided that the eccentricity and the obliquity of the planet are sufficiently different from zero. We also studied the impact of different values for the argument of perihelion. When local favorable conditions exist, they nearly always persist for >15% of the Martian year. These results are obtained without the need for additional greenhouse gases (e.g., H2, CH4) or transient heat-injecting phenomena (e.g., asteroid impacts, volcanic eruptions). A moderate amount (0.1%–1%) of CH4 significantly widens the parameter space region in which seasonal thaws are possible