Psrd he ds-vesta

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Sérgio Sacani

Technology

Overview: Scientists are primed with geochemical data from HED meteorites
for Dawn's encounter with asteroid 4 Vesta

Reference: Usui, T. and McSween, Jr., H. Y. (2007) Geochemistry of 4 Vesta
based on HED meteorites: Prospective study for interpretation of gamma ray
and neutron spectra for the Dawn mission. v. 42, Meteoritics and Planetary
Science, v. 42, p. 255-269.

Abstract: The howardite-eucrite-diogenite class of meteorites (called the
HEDs) are rocks formed from basaltic magmas. What makes them special is
that the HEDs have reflectance spectra in the visible and near-infrared that
match spectra from asteroid 4 Vesta, implying Vesta is their parent body. We
will soon have new data from Vesta from NASA's Dawn orbiting spacecraft,
which carries a gamma ray and neutron detector, dubbed the GRaND
instrument. GRaND will orbit asteroid 4 Vesta and dwarf planet Ceres and
map the near-surface abundances of major and minor elements, and volatiles
found in ices (in the case of Ceres) such as hydrogen, carbon, nitrogen, and
oxygen. Tomohiro Usui and Harry Y. (Hap) McSween, Jr. (University of
Tennessee) have proposed a way to interpret the upcoming GRaND data from
Vesta based on well-analyzed samples of HED meteorites and a mixing model

1

GRaND uses 21 sensors to measure the energy from gamma rays and
neutrons that are reflected or emitted by the different elements on the target
body's surface and down to a depth of one meter. Scientists will make a global
elemental map of Vesta to show where elements exist and in what
abundances. They are particularly interested in mapping major elements (Si,
Fe, Ti, Mg, Al, Ca) and minor elements (K, Th, U) on Vesta. The beauty of the
minor elements is that they track the melting that led to the formation of the
crust of the body during differentiation.

Because of GRaND's coarse spatial resolution, its data is expected to mimic
the mixing of HED meteorites.

An interesting aspect of this approach by Usui and McSween is that the mixing
relations of the three end-member rock types can be plotted in an appropriate
two-dimensional diagram.

2

The dashed line represents perfect agreement between measured and
calculated concentrations. Elements are not labeled to avoid cluttering the
diagram.

3

Usui and McSween show their mixing model can accurately estimate the
abundances of all the major elements that can be measured by GRaND as
well as predict abundances of minor elements (Na, Cr, and Mn) not analyzed
by the instrument.
The use of the vast amount of data on HED meteorites to devise a mixing
model to understand data from a spacecraft orbiting Vesta shows the value of
an integrated approach to solar system exploration.

Both laboratory analysis of samples like that funded by the Cosmochemistry
Program and remote sensing data like that to be radioed back by the Dawn
mission are crucial bits of information about the igneous histories of the
building blocks of the planets.

In neutron activation analysis, rock samples are irradiated by neutrons in a
research nuclear reactor (like the one shown on this slide from the University
of Missouri, Columbia). Nuclear interactions take place, producing radioactive
isotopes. When the isotopes decay, they produce gamma rays with energies
characteristic of the isotope, giving a measurement of the abundance of an
element. The samples are placed into shielded detectors for gamma ray
measurements. Typically, the abundances of 25 to 30 elements are

4

What's hot

A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos. Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper. O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo. Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.

Evidence for a_distant_giant_planet_in_the_solar_system

Sérgio Sacani

Teletransportacion marcikic2003

Asesor De Tesis Doctorados

We describe the discovery of a satellite in orbit about the dwarf planet (136472) Makemake. This satellite, provisionally designated S/2015 (136472) 1, was detected in imaging data collected with the Hubble Space Telescope’s Wide Field Camera 3 on UTC April 27, 2015 at 7.80±0.04 magnitudes fainter than Makemake. It likely evaded detection in previous satellite searches due to a nearly edgeon orbital configuration, placing it deep within the glare of Makemake during a substantial fraction of its orbital period. This configuration would place Makemake and its satellite near a mutual event season. Insufficient orbital motion was detected to make a detailed characterization of its orbital properties, prohibiting a measurement of the system mass with the discovery data alone. Preliminary analysis indicates that if the orbit is circular, its orbital period must be longer than 12.4 days, and must have a semi-major axis &21,000 km. We find that the properties of Makemake’s moon suggest that the majority of the dark material detected in the system by thermal observations may not reside on the surface of Makemake, but may instead be attributable to S/2015 (136472) 1 having a uniform dark surface. This “dark moon hypothesis” can be directly tested with future JWST observations. We discuss the implications of this discovery for the spin state, figure, and thermal properties of Makemake and the apparent ubiquity of trans-Neptunian dwarf planet satellites.

Discovery of a_makemakean_moon

Sérgio Sacani

Desde 1974, observações feitas com o chamado Long Baseline Interferometry, ou VLBI, combinaram sinais de um objeto cósmico recebidos em diferentes rádio telescópios espalhados pelo globo para criar uma antena com o tamanho equivalente à maior separação entre elas. Isso fez com que fosse possível fazer imagens com uma nitidez sem precedentes, com uma resolução 1000 vezes melhor do que Hubble consegue na luz visível. Agora, uma equipe internacional de astrônomos quebrou todos os recordes combinando 15 rádio telescópios na Terra e a antena de rádio da missão RadioAstron, da agência espacial russa, na órbita da Terra. O trabalho, liderado pelo Instituto de Astrofísica de Andalucía, o IAA-CSIC, forneceu novas ideias sobre a natureza das galáxias ativas, onde um buraco negro extremamente massivo engole a matéria ao redor enquanto simultaneamente emite um par de jatos de partículas de alta energia e campos magnéticos a velocidades próximas da velocidade da luz. Observações feitas no comprimento de onda das micro-ondas são essenciais para explorar esses jatos, já que os elétrons de alta energia se movendo em campos magnéticos são mais proficientes em produzir micro-ondas. Mas a maioria das galáxias ativas com jatos brilhantes estão a bilhões de anos-luz de distância da Terra, de modo que esses jatos são minúsculos no céu. Desse modo a alta resolução é essencial para observar esses jatos em ação e então revelar fenômenos como as ondas de choque e a turbulência que controla o quanto de luz é produzida num dado tempo. “Combinando pela primeira vez rádio telescópios na Terra com rádio telescópios no espaço, operando na máxima resolução, tem permitido que a nossa equipe crie uma antena que tem um tamanho equivalente a 8 vezes o diâmetro da Terra, correspondendo a 20 micro arcos de segundo”, disse José L; Gómez, o líder da equipe no Instituto de Astrofísica de Andalucía, IAA-CSIC.

Probing the innermost_regions_of_agn_jets_and_their_magnetic_fields_with_radi...

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Further analysis of the References- part 2. Some further analyses about directional recoil, cross sections, galaxy Physics and experiment-optimizations techniques. VIA Forum Astroparticle Physics Forum COSMOVIA Author: O.M. Lecian. Title: LHAASO Further references- part2. 28/03/2020 http://viavca.in2p3.fr/2010c_o_s_m_o_v_i_a__forum_sd24fsdf4zerfzef4ze5f4dsq34sdteerui45788789745rt7yr68t4y54865h45g4hfg56h45df4h86d48h48t7uertujirjtiorjhuiofgrdsqgxcvfghfg5h40yhuyir/viewtopic.php?f=73&t=3705&sid=c56cbf76f87536fc4c3ff216d9edaba2

O.M. Lecian LHAASO Further references: part 2.

Orchidea Maria Lecian

We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts of the stellar disk of the LMC (r < 10 degrees from the center). These data have higher resolution than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in the northern periphery, with no comparable counterparts in the South. We compare these data to detailed simulations of the LMC disk outskirts, following interactions with its low mass companion, the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field. The simulations are used to assess the origin of the northern structures, including also the low density stellar arc recently identified in the DES data by Mackey et al. (2015) at ∼ 15 degrees. We conclude that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to constrain the LMC’s interaction history with and impact parameter of the SMC. More generally, we find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for 1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are driven by dwarf-dwarf interactions.

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Unit Pre Assessment

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Presentation

HIOTELIS IOANNIS

Cassini vims hyperspectral_observations_of_the_huygens _landing_site_on_titan

Sérgio Sacani

We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%. The bulk of this improvement comes from new, near-infrared observations of Cepheid variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All 19 hosts as well as the megamaser system NGC4258 have been observed with WFC3 in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the relative distance estimates from Cepheids. Other noteworthy improvements include a 33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW) Cepheids.

A 2 4_determination_of_the_local_value_of_the_hubble_constant

Sérgio Sacani

The event horizon_of_m87

Sérgio Sacani

Progress in a group of investigations designed to discover some of the structural details in individual galaxies and in the Metagalaxy is reported in the following pages. (a) The first section is concerned with the distribution of cluster-type Cepheids in high galactic latitude. To the 169 already known in latitudes, greater than or equal to ± 20o , the systematic variable star programme carried on at Harvard has added 312, mostly fainter than magnitude 13-0. With allowance for absorption and for uncertainties yet remaining in the mean absolute magnitude of these stars, the thickness of the Milky Way, so far as this type of star is concerned, is not less than twenty-five kiloparsecs ; he extent of the Milky Way in its own plane, by the same criterion, is more than thirty kiloparsecs, perhaps much more. (b) The extent of the Milky Way in the anti-centre quadrant is considered on the basis of classical and cluster-type Cepheids ; provisionally it is found that the galactic system reaches to a distance of at least ten kiloparsecs in longitude 150o . (r) More than six hundred new variables have been found in the Large Magellanic Cloud and measured for position, ranges and median magnitudes ; the frequency of periods is not unlike that for the classical Cepheids in the galactic system ; the light curves also are comparable in all details. The Magellanic Cepheids, like the galactic classical Cepheids, are concentrated in regions of high star-density. (d) Further study of the period-luminosity relation in the Large Magellanic Cloud permits its revision and strengthening for the Cepheids of highest absolute magnitude. An observed deviation from the relation that had previously been found for the Small Cloud is probably to be attributed to scale error in the magnitude system. No seriously disturbing

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Gj 832c a_super_earth_in_the_habitable_zone

Sérgio Sacani

We produce the first concrete evidence that violation of the weak cosmic censorship conjecture can occur in asymptotically flat spaces of five dimensions by numerically evolving perturbed black rings. For certain thin rings, we identify a new, elastic-type instability dominating the evolution, causing the system to settle to a spherical black hole. However, for sufficiently thin rings the Gregory-Laflamme mode is dominant, and the instability unfolds similarly to that of black strings, where the horizon develops a structure of bulges connected by necks which become ever thinner over time.

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Sérgio Sacani

Supermassive black holes in galaxy centres can grow by the accretion of gas, liberating enormous amounts of energy that might regulate star formation on galaxy-wide scales1–3 . The nature of gaseous fuel reservoirs that power black hole growth is nevertheless largely unconstrained by observations, and is instead routinely simplified as a smooth, spherical inflow of very hot gas in accordance with the Bondi solution4 . Recent theory5–7 and simulations8–10 instead predict that accretion can be dominated by a stochastic, clumpy distribution of very cold molecular clouds, though unambiguous observational support for this prediction remains elusive. Here we show observational evidence for a cold, clumpy accretion flow toward a supermassive black hole fuel reservoir in the nucleus of the Abell 2597 Brightest Cluster Galaxy (BCG), a nearby (z = 0.0821) giant elliptical galaxy surrounded by a dense halo of hot plasma11–13. Under the right conditions, thermal instabilities can precipitate from this hot gas, producing a rain of cold clouds that fall toward the galaxy’s centre14, sustaining star formation amid a kiloparsec-scale molecular nebula that inhabits its core15. New interferometric sub-millimetre observations show that these cold clouds also fuel black hole accretion, revealing “shadows” cast by molecular clouds as they move inward at ∼ 300 km s−1 toward the active supermassive black hole in the galaxy centre, which serves as a bright backlight. Corroborating evidence from prior observations16 of warmer atomic gas at extremely high spatial resolution17, along with simple arguments based on geometry and probability, indicates that these clouds are within the innermost hundred parsecs of the black hole, and falling closer toward it

Cold clumpy accretion_toward_an_active_supermasive_black_hole

Sérgio Sacani

6.2 Forces of attraction

mrrayner

The familiar axisymmetric zones and belts that characterize Jupiter’s weather system at lower latitudes give way to pervasive cyclonic activity at higher latitudes1 . Two-dimensional turbulence in combination with the Coriolis β-effect (that is, the large meridionally varying Coriolis force on the giant planets of the Solar System) produces alternating zonal flows2 . The zonal flows weaken with rising latitude so that a transition between equatorial jets and polar turbulence on Jupiter can occur3,4 . Simulations with shallowwater models of giant planets support this transition by producing both alternating flows near the equator and circumpolar cyclones near the poles5–9. Jovian polar regions are not visible from Earth owing to Jupiter’s low axial tilt, and were poorly characterized by previous missions because the trajectories of these missions did not venture far from Jupiter’s equatorial plane. Here we report that visible and infrared images obtained from above each pole by the Juno spacecraft during its first five orbits reveal persistent polygonal patterns of large cyclones. In the north, eight circumpolar cyclones are observed about a single polar cyclone; in the south, one polar cyclone is encircled by five circumpolar cyclones. Cyclonic circulation is established via time-lapse imagery obtained over intervals ranging from 20 minutes to 4 hours. Although migration of cyclones towards the pole might be expected as a consequence of the Coriolis β-effect, by which cyclonic vortices naturally drift towards the rotational pole, the configuration of the cyclones is without precedent on other planets (including Saturn’s polar hexagonal features). The manner in which the cyclones persist without merging and the process by which they evolve to their current configuration are unknown.

Clusters of cyclones encircling Jupiter’s poles

Sérgio Sacani

Photometry of Giant Propellers in Saturn's Rings

JakaylaRobinson

Binary black hole (BH) central engine description for the unique blazar OJ 287 predicted that the next secondary BH impact-induced bremsstrahlung flare should peak on 2019 July 31. This prediction was based on detailed general relativistic modeling of the secondary BH trajectory around the primary BH and its accretion disk. The expected flare was termed the Eddington flare to commemorate the centennial celebrations of now-famous solar eclipse observations to test general relativity by Sir Arthur Corresponding author: Lankeswar Dey lankeswar.dey@tifr.res.in arXiv:2004.13392v1 [astro-ph.HE] 28 Apr 2020 2 Laine et al. Eddington. We analyze the multi-epoch Spitzer observations of the expected flare between 2019 July 31 and 2019 September 6, as well as baseline observations during 2019 February–March. Observed Spitzer flux density variations during the predicted outburst time display a strong similarity with the observed optical pericenter flare from OJ 287 during 2007 September. The predicted flare appears comparable to the 2007 flare after subtracting the expected higher base-level Spitzer flux densities at 3.55 and 4.49 µm compared to the optical R-band. Comparing the 2019 and 2007 outburst lightcurves and the previously calculated predictions, we find that the Eddington flare arrived within 4 hours of the predicted time. Our Spitzer observations are well consistent with the presence of a nano-Hertz gravitational wave emitting spinning massive binary BH that inspirals along a general relativistic eccentric orbit in OJ 287. These multi-epoch Spitzer observations provide a parametric constraint on the celebrated BH no-hair theorem.

Spitzer Observations of the Predicted Eddington Flare from Blazar OJ 287

Sérgio Sacani

What's hot (20)

Evidence for a_distant_giant_planet_in_the_solar_system

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Probing the innermost_regions_of_agn_jets_and_their_magnetic_fields_with_radi...

O.M. Lecian LHAASO Further references: part 2.

Low surface brightness_imaging_of_the_magellanic_system_imprints_of_tidal_int...

Unit Pre Assessment

Presentation

Cassini vims hyperspectral_observations_of_the_huygens _landing_site_on_titan

A 2 4_determination_of_the_local_value_of_the_hubble_constant

The event horizon_of_m87

On some structural_features_of_the_metagalaxy

Astronomy: Stars

Gj 832c a_super_earth_in_the_habitable_zone

End point of_black_ring_instabilities_and_the_weak_cosmic_censorship_conjecture

Cold clumpy accretion_toward_an_active_supermasive_black_hole

6.2 Forces of attraction

Clusters of cyclones encircling Jupiter’s poles

Photometry of Giant Propellers in Saturn's Rings

Spitzer Observations of the Predicted Eddington Flare from Blazar OJ 287

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Eso1134b

Sérgio Sacani

The metal abundance of the hot plasma that permeates galaxy clusters represents the accumulation of heavy elements produced by billions of supernovae1. Therefore, X-ray spectroscopy of the intracluster medium provides an opportunity to investigate the nature of supernova explosions integrated over cosmic time. In particular, the abundance of the iron-peak elements (chromium, manganese, iron and nickel) is key to understanding how the progenitors of typical type Ia supernovae evolve and explode2–6. Recent X-ray studies of the intracluster medium found that the abundance ratios of these elements differ substantially from those seen in the Sun7–11, suggesting differences between the nature of type Ia supernovae in the clusters and in the Milky Way. However, because the K-shell transition lines of chromium and manganese are weak and those of iron and nickel are very close in photon energy, highresolution spectroscopy is required for an accurate determination of the abundances of these elements. Here we report observations of the Perseus cluster, with statistically significant detections of the resonance emission from chromium, manganese and nickel. Our measurements, combined with the latest atomic models, reveal that these elements have near-solar abundance ratios with respect to iron, in contrast to previous claims. Comparison between our results and modern nucleosynthesis calculations12–14 disfavours the hypothesis that type Ia supernova progenitors are exclusively white dwarfs with masses well below the Chandrasekhar limit (about 1.4 times the mass of the Sun). The observed abundance pattern of the iron-peak elements can be explained by taking into account a combination of near- and sub-Chandrasekhar-mass type Ia supernova systems, adding to the mounting evidence that both progenitor types make a substantial contribution to cosmic chemical enrichment5,15,16.

Solar abundance ratios of the iron-peak elements in the Perseus cluster

Sérgio Sacani

Mineralogy of a_mudstone_at_yellowknife_bay_gale_crater_mars

Sérgio Sacani

One tenth solar_abundances_along_the_body_of-the_stream

Sérgio Sacani

9805153v1

Sérgio Sacani

Auroral hot spots are observed across the Universe at different scales1 and mark the coupling between a surrounding plasma environment and an atmosphere. Within our own Solar System, Jupiter possesses the only resolvable example of this large-scale energy transfer. Jupiter’s northern X-ray aurora is concentrated into a hot spot, which is located at the most poleward regions of the planet’s aurora and pulses either periodically2,3 or irregularly4,5 . X-ray emission line spectra demonstrate that Jupiter’s northern hot spot is produced by high charge-state oxygen, sulfur and/or carbon ions with an energy of tens of MeV (refs 4–6) that are undergoing charge exchange. Observations instead failed to reveal a similar feature in the south2,3,7,8. Here, we report the existence of a persistent southern X-ray hot spot. Surprisingly, this largescale southern auroral structure behaves independently of its northern counterpart. Using XMM-Newton and Chandra X-ray campaigns, performed in May–June 2016 and March 2007, we show that Jupiter’s northern and southern spots each exhibit different characteristics, such as different periodic pulsations and uncorrelated changes in brightness. These observations imply that highly energetic, non-conjugate magnetospheric processes sometimes drive the polar regions of Jupiter’s dayside magnetosphere. This is in contrast to current models of X-ray generation for Jupiter9,10. Understanding the behaviour and drivers of Jupiter’s pair of hot spots is critical to the use of X-rays as diagnostics of the wide range of rapidly rotating celestial bodies that exhibit these auroral phenomena.

The independent pulsations of Jupiter’s northern and southern X-ray auroras

Sérgio Sacani

We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part of the Survey of H I in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength study of galaxies with H I masses in the range of 106-107:2 M discovered by the ALFALFA survey. We have obtained spectra of the lone H II region in AGC 198691 with the new high-throughput KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the temperature-sensitive [O III]4363 line and hence the determination of a \direct" oxygen abundance for AGC 198691. We nd this system to be an extremely metal-decient (XMD) system with an oxygen abundance of 12+log(O/H) = 7.02 0.03, making AGC 198691 the lowest-abundance starforming galaxy known in the local universe. Two of the ve lowest-abundance galaxies known have been discovered by the ALFALFA blind H I survey; this high yield of XMD galaxies represents a paradigm shift in the search for extremely metal-poor galaxies.

Alfalfa discovery of_the_most_metal_poor_gas_rich_galaxy_known_agc_198691

Sérgio Sacani

Most magnetized planetsare known to possess radiation belts, wherehigh-energy charged particles are trapped inlarge numbers. The possibility that a radiationbelt could exist also in the confined regionbetween Saturn and its main rings has beenproposed on the basis of remote sensing obser-vations and simulations. It was not until thefinal 5 months of the Cassini mission that in situmeasurements were obtained from this regionwith the Magnetosphere Imaging Instrument(MIMI). This paper provides an overview ofthese measurements andtheir interpretation.

A radiation belt of energetic protonslocated between Saturn and its rings

Sérgio Sacani

The effects of_the_target_material_properties_and layering_on_the_crater_chro...

Sérgio Sacani

The Sparkler: Evolved High-redshift Globular Cluster Candidates Captured by JWST

Sérgio Sacani

Theoriesofplanetformationpredictthatlow-massstarsshouldrarelyhostexoplanetswithmassesexceedingthatofNeptune.WeusedradialvelocityobservationstodetectaNeptune-massexoplanetorbitingLHS3154,astarthatisninetimeslessmassivethantheSun.Theexoplanet’sorbitalperiodis3.7days,anditsminimummassis13.2Earthmasses.Weusedsimulationstoshowthatthehighplanet-to-starmassratio(>3.5×10−4)isnotanexpectedoutcomeofeitherthecoreaccretionorgravitationalinstabilitytheoriesofplanetformation.Inthecore-accretionsimulations,weshowthatclose-inNeptune-massplanetsareonlyformedifthedustmassoftheprotoplanetarydiskisanorderofmagnitudegreaterthantypicallyobservedaroundverylow-massstars

A Neptune-mass exoplanet in close orbit around avery low-mass star challenges...

Sérgio Sacani

Similar to Psrd he ds-vesta (20)

Evidence of rocky_planetesimals_orbiting_two_hyades_stars

Observational constraints on mergers creating magnetism in massive stars

Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...

Deep nearinfrared survey_carina_nebula

AAS_Richard_poster1_final

Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03

Spirals and clumps in V960 Mon: signs of planet formation via gravitational i...

A Chandra X-ray study of millisecond pulsars in the globular cluster Omega Ce...

LHS 475 b: A Venus-sized Planet Orbiting a Nearby M Dwarf

Eso1134b

Solar abundance ratios of the iron-peak elements in the Perseus cluster

Mineralogy of a_mudstone_at_yellowknife_bay_gale_crater_mars

One tenth solar_abundances_along_the_body_of-the_stream

9805153v1

The independent pulsations of Jupiter’s northern and southern X-ray auroras

Alfalfa discovery of_the_most_metal_poor_gas_rich_galaxy_known_agc_198691

A radiation belt of energetic protonslocated between Saturn and its rings

The effects of_the_target_material_properties_and layering_on_the_crater_chro...

The Sparkler: Evolved High-redshift Globular Cluster Candidates Captured by JWST

A Neptune-mass exoplanet in close orbit around avery low-mass star challenges...

More from Sérgio Sacani

Theoretical predictions and observational data indicate a class of sub-Neptune exoplanets may have water-rich interiors covered by hydrogen-dominated atmospheres. Provided suitable climate conditions, such planets could host surface liquid oceans. Motivated by recent JWST observations of K2-18 b, we self-consistently model the photochemistry and potential detectability of biogenic sulfur gases in the atmospheres of temperate sub-Neptune waterworlds for the first time. On Earth today, organic sulfur compounds produced by marine biota are rapidly destroyed by photochemical processes before they can accumulate to significant levels. Domagal-Goldman et al. suggest that detectable biogenic sulfur signatures could emerge in Archean-like atmospheres with higher biological production or low UV flux. In this study, we explore biogenic sulfur across a wide range of biological fluxes and stellar UV environments. Critically, the main photochemical sinks are absent on the nightside of tidally locked planets. To address this, we further perform experiments with a 3D general circulation model and a 2D photochemical model (VULCAN 2D) to simulate the global distribution of biogenic gases to investigate their terminator concentrations as seen via transmission spectroscopy. Our models indicate that biogenic sulfur gases can rise to potentially detectable levels on hydrogen-rich water worlds, but only for enhanced global biosulfur flux (20 times modern Earth’s flux). We find that it is challenging to identify DMS at 3.4 μm where it strongly overlaps with CH4, whereas it is more plausible to detect DMS and companion byproducts, ethylene (C2H4) and ethane (C2H6), in the mid-infrared between 9 and 13 μm. Unified Astronomy Thesaurus concepts: Exoplanet atmospheres (487); Exoplanet

Biogenic Sulfur Gases as Biosignatures on Temperate Sub-Neptune Waterworlds

Sérgio Sacani

Context. WASP-76 b has been a recurrent subject of study since the detection of a signature in high-resolution transit spectroscopy data indicating an asymmetry between the two limbs of the planet. The existence of this asymmetric signature has been confirmed by multiple studies, but its physical origin is still under debate. In addition, it contrasts with the absence of asymmetry reported in the infrared (IR) phase curve. Aims. We provide a more comprehensive dataset of WASP-76 b with the goal of drawing a complete view of the physical processes at work in this atmosphere. In particular, we attempt to reconcile visible high-resolution transit spectroscopy data and IR broadband phase curves. Methods. We gathered 3 phase curves, 20 occultations, and 6 transits for WASP-76 b in the visible with the CHEOPS space telescope. We also report the analysis of three unpublished sectors observed by the TESS space telescope (also in the visible), which represents 34 phase curves. Results. WASP-76 b displays an occultation of 260±11 and 152±10 ppm in TESS and CHEOPS bandpasses respectively. Depending on the composition assumed for the atmosphere and the data reduction used for the IR data, we derived geometric albedo estimates that range from 0.05 ± 0.023 to 0.146 ± 0.013 and from <0.13 to 0.189 ± 0.017 in the CHEOPS and TESS bandpasses, respectively. As expected from the IR phase curves, a low-order model of the phase curves does not yield any detectable asymmetry in the visible either. However, an empirical model allowing for sharper phase curve variations offers a hint of a flux excess before the occultation, with an amplitude of ∼40 ppm, an orbital offset of ∼−30◦ , and a width of ∼20◦ . We also constrained the orbital eccentricity of WASP-76 b to a value lower than 0.0067, with a 99.7% confidence level. This result contradicts earlier proposed scenarios aimed at explaining the asymmetry observed in high-resolution transit spectroscopy. Conclusions. In light of these findings, we hypothesise that WASP-76 b could have night-side clouds that extend predominantly towards its eastern limb. At this limb, the clouds would be associated with spherical droplets or spherically shaped aerosols of an unknown species, which would be responsible for a glory effect in the visible phase curves.

Asymmetry in the atmosphere of the ultra-hot Jupiter WASP-76 b

Sérgio Sacani

Understanding circumstellar disks is of prime importance in astrophysics, however, their birth process remains poorly constrained due to observational and numerical challenges. Recent numerical works have shown that the small-scale physics, often wrapped into a sub-grid model, play a crucial role in disk formation and evolution. This calls for a combined approach in which both the protostar and circumstellar disk are studied in concert. Aims. We aim to elucidate the small scale physics and constrain sub-grid parameters commonly chosen in the literature by resolving the star-disk interaction. Methods. We carry out a set of very high resolution 3D radiative-hydrodynamics simulations that self-consistently describe the collapse of a turbulent dense molecular cloud core to stellar densities. We study the birth of the protostar, the circumstellar disk, and its early evolution (< 6 yr after protostellar formation). Results. Following the second gravitational collapse, the nascent protostar quickly reaches breakup velocity and sheds its surface material, thus forming a hot (∼ 103 K), dense, and highly flared circumstellar disk. The protostar is embedded within the disk, such that material can flow without crossing any shock fronts. The circumstellar disk mass quickly exceeds that of the protostar, and its kinematics are dominated by self-gravity. Accretion onto the disk is highly anisotropic, and accretion onto the protostar mainly occurs through material that slides on the disk surface. The polar mass flux is negligible in comparison. The radiative behavior also displays a strong anisotropy, as the polar accretion shock is shown to be supercritical whereas its equatorial counterpart is subcritical. We also f ind a remarkable convergence of our results with respect to initial conditions. Conclusions. These results reveal the structure and kinematics in the smallest spatial scales relevant to protostellar and circumstellar disk evolution. They can be used to describe accretion onto regions commonly described by sub-grid models in simulations studying larger scale physics.

Formation of low mass protostars and their circumstellar disks

Sérgio Sacani

HotJupiters are amongthebest-studied exoplanets, but it is still poorly understood how their chemical composition and cloud properties vary with longitude. Theoretical models predict that clouds may condense on the nightside and that molecular abundances can be driven out of equilibrium by zonal winds. Here we report a phase-resolved emission spectrum of the hot Jupiter WASP-43b measured from 5–12µ 5–12µ 5–12µm with JWST’s Mid-Infrared Instrument (MIRI). 1524 ±35 1524 ±35 and 863±23 The spectra reveal a large day–night temperature contrast (with average brightness temperatures of 1524 ± 35 863 ±23 863 ±23Kelvin, respectively) and evidence for water absorption at all orbital phases. Comparisons with three-dimensional atmospheric models show that both the phase curve shape and emission spectra strongly suggest the presence of nightside clouds which become optically thick to thermal emission at pressures greater than ∼100mbar. The dayside is consistent with a cloudless atmosphere above the mid-infrared photosphere. Con3trary to expectations from equilibrium chemistry but consistent with disequilibrium kinetics models, methane is not detected on the nightside (2σ upper limit of 1–6 parts per million, depending on model assumptions).

Nightside clouds and disequilibrium chemistry on the hot Jupiter WASP-43b

Sérgio Sacani

Wepresent Atacama Large Millimeter/submillimeter Array 12-m, 7-m, and Total Power Array observations of the FUOrionis outbursting system, covering spatial scales ranging from 160 to 25,000 au. The high-resolution interferometric data reveal an elongated 12CO(2–1) feature previously observed at lower resolution in 12CO(3–2). Kinematic modeling indicates that this feature can be interpreted as an accretion streamer feeding the binary system. The mass infall rate provided by the streamer is significantly lower than the typical stellar accretion rates (even in quiescent states), suggesting that this streamer alone is not massive enough to sustain the enhanced accretion rates characteristic of the outbursting class prototype. The observed streamer may not be directly linked to the current outburst, but rather a remnant of a previous, more massive streamer that may have contributed enough to the disk mass to render it unstable and trigger the FU Orionis outburst. The new data detect, for the first time, a vast, slow-moving carbon monoxide molecular outflow emerging from this object. To accurately assess the outflow properties (mass, momentum, and kinetic energy), we employ 13CO(2–1) data to correct for optical depth effects. The analysis indicates that the outflow corresponds to swept-up material not associated with the current outburst, similar to the slow molecular outflows observed around other FUor and Class I protostellar objects.

Discovery of an Accretion Streamer and a Slow Wide-angle Outflow around FUOri...

Sérgio Sacani

We explore different scenarios to explain the chemical difference found in the remarkable giant-giant binary system HD138202+CD−3012303. For the first time, we suggest how to distinguish these scenarios by taking advantage of the extensive convective envelopes of giant stars. Methods. We carried out a high-precision determination of stellar parameters and abundances by applying a full line-by-line differential analysis on GHOST high-resolution spectra. We used the FUNDPAR program with ATLAS12 model atmospheres and specific opacities calculated for an arbitrary composition through a doubly iterated method. Physical parameters were estimated with the isochrones package and evolutionary tracks were calculated via MIST models. Results. We found a significant chemical difference between the two stars (∆[Fe/H]∼0.08dex), which is largely unexpected considering the insensitivity of giant stars to planetary ingestion and diffusion effects. We tested the possibility of engulfment events by using several different combinations of stellar mass, ingested mass, metallicity of the engulfed object and different convective envelopes. However, the planetary ingestion scenario does not seem to explain the observed differences. For the first time, we distinguished the source of chemical differences using a giant-giant binary system. By ruling out other possible scenarios such as planet formation and evolutionary effects between the two stars, we suggest that primordial inhomogeneities might explain the observed differences. This remarkable result implies that the metallicity differences that were observed in at least some main-sequence binary systems might be related to primordial inhomogeneities rather than engulfment events. We also discuss the important implications of finding primordial inhomogeneities, which affect chemical tagging and other fields such as planet formation. We strongly encourage the use of giantgiant pairs. They are a relevant complement to main-sequence pairs for determining the origin of the observed chemical differences in multiple systems.

Disentangling the origin of chemical differences using GHOST

Sérgio Sacani

On 26 January 2023, a military pilot reported four potential unidentified anomalous phenomena (UAP) while operating in the Eglin Air Force Base training range off the coast of Florida. Through the onboard radar system, the pilot initially observed that the four objects were aloft between 16,000 – 18,000 feet and appeared to be flying in formation. However the pilot observed only one of the four objects visually and captured two images of the single object via the aircraft’s electro-optical/infrared (EO/IR) sensor (see Figures 1A and 1B). The pilot could not record video of the event because the aircraft’s video recording equipment was inoperable prior to and during the aircraft’s flight. The pilot observed this single object aloft at 16,000 feet. The following case information is based on the pilot’s initial report and a subsequent discussion that AARO held with the pilot to seek additional details about the pilot’s observation of the reported object.

All-domain Anomaly Resolution Office U.S. Department of Defense (U) Case: “Eg...

Sérgio Sacani

RecoveringancientrecordsofEarth'smagneticfieldisessentialfordeterminingtheroleofthemagnetosphereinprotectingearlyEarthfromcosmicradiationandatmosphericescape.WepresentpaleomagneticfieldtestshintingthatarecordofEarth's3.7‐billion‐year(Ga)oldmagneticfieldmaybepreservedinthenortheasternIsuaSupracrustalBeltasachemicalremanentmagnetizationacquiredduringamphibolite‐grademetamorphisminthebandedironformation.MultiplepetrologicalandgeochronologicallinesofevidenceindicatethatthenorthernmostpartofIsuahasnotexperiencedmetamorphictemperaturesexceeding380°CsincetheEoarchean,suggestingtherockshavenotbeensignificantlyheatedsincemagnetizationwasacquired.Weuse“pseudo”bakedcontacttests(intrusionsemplaced3.26–3.5Gaago)andafoldtest(folding3.6Gaago)todemonstratethatsomesamplespreserveaca.3.7Garecordofthemagneticfield.Werecoverafieldstrengthof>15μT.ThissuggeststhatEarth'smagneticfieldmayhavebeenweakenoughtoenhanceatmosphericescapeduringtheArchean

PossibleEoarcheanRecordsoftheGeomagneticFieldPreservedintheIsuaSupracrustalBe...

Sérgio Sacani

Jupiter’s moon Io hosts extensive volcanism, driven by tidal heating. The isotopic composition of Io's inventory of volatile chemical elements, including sulfur and chlorine, reflects its outgassing and mass loss history, and thus records information about its evolution. We used millimeter observations of Io’s atmosphere to measure sulfur isotopes in gaseous SO2 and SO, and chlorine isotopes in gaseous NaCl and KCl. We find 34S/32S = 0.0595 ± 0.0038 (equivalent to δ34S = +347 ± 86‰), which is highly enriched compared to average Solar System values and indicates that Io has lost 94 to 99% of its available sulfur. Our measurement of 37Cl/35Cl = 0.403 ± 0.028 (δ37Cl = +263 ± 88‰) shows that chlorine is similarly enriched. These results indicate that Io has been volcanically active for most (or all) of its history, with potentially higher outgassing and mass-loss rates at earlier times.

Isotopic evidence of long-lived volcanism on Io

Sérgio Sacani

Context. Determining the size distribution of asteroids is key to understanding the collisional history and evolution of the inner Solar System. Aims. We aim to improve our knowledge of the size distribution of small asteroids in the main belt by determining the parallaxes of newly detected asteroids in the Hubble Space Telescope (HST) archive and subsequently their absolute magnitudes and sizes. Methods. Asteroids appear as curved trails in HST images because of the parallax induced by the fast orbital motion of the spacecraft. Taking into account the trajectory of this latter, the parallax effect can be computed to obtain the distance to the asteroids by fitting simulated trajectories to the observed trails. Using distance, we can obtain the absolute magnitude of an object and an estimation of its size assuming an albedo value, along with some boundaries for its orbital parameters. Results. In this work, we analyse a set of 632 serendipitously imaged asteroids found in the ESA HST archive. Images were captured with the ACS/WFC and WFC3/UVIS instruments. A machine learning algorithm (trained with the results of a citizen science project) was used to detect objects in these images as part of a previous study. Our raw data consist of 1031 asteroid trails from unknown objects, not matching any entries in the Minor Planet Center (MPC) database using their coordinates and imaging time. We also found 670 trails from known objects (objects featuring matching entries in the MPC). After an accuracy assessment and filtering process, our analysed HST asteroid set consists of 454 unknown objects and 178 known objects. We obtain a sample dominated by potential main belt objects featuring absolute magnitudes (H) mostly between 15 and 22 mag. The absolute magnitude cumulative distribution logN(H > H0) ∝ αlog(H0) confirms the previously reported slope change for 15 < H < 18, from α ≈ 0.56 to α ≈ 0.26, maintained in our case down to absolute magnitudes of around H ≈ 20, and therefore expanding the previous result by approximately two magnitudes. Conclusions. HST archival observations can be used as an asteroid survey because the telescope pointings are statistically randomly oriented in the sky and cover long periods of time. They allow us to expand the current best samples of astronomical objects at no extra cost in regard to telescope time.

Hubble Asteroid Hunter III. Physical properties of newly found asteroids

Sérgio Sacani

We report the observation of a coalescing compact binary with component masses 2.5–4.5 M⊙ and 1.2–2.0 M⊙ (all measurements quoted at the 90% credible level). The gravitational-wave signal GW230529 181500 was observed during the fourth observing run of the LIGO–Virgo–KAGRA detector network on 2023 May 29 by the LIGO Livingston observatory. The primary component of the source has a mass less than 5 M⊙ at 99% credibility. We cannot definitively determine from gravitational-wave data alone whether either component of the source is a neutron star or a black hole. However, given existing estimates of the maximum neutron star mass, we find the most probable interpretation of the source to be the coalescence of a neutron star with a black hole that has a mass between the most massive neutron stars and the least massive black holes observed in the Galaxy. We estimate a merger rate density of 55+127 −47 Gpc−3yr−1 for compact binary coalescences with properties similar to the source of GW230529 181500; assuming that the source is a neutron star–black hole merger, GW230529 181500-like sources constitute about 60% of the total merger rate inferred for neutron star–black hole coalescences. The discovery of this system implies an increase in the expected rate of neutron star–black hole mergers with electromagnetic counterparts and provides further evidence for compact objects existing within the purported lower mass gap.

Observation of Gravitational Waves from the Coalescence of a 2.5–4.5 M⊙ Compa...

Sérgio Sacani

We use the SAMI Galaxy Surv e y to examine the drivers of galaxy spin, λR e , in a multidimensional parameter space including stellar mass, stellar population age (or specific star formation rate), and various environmental metrics (local density, halo mass, satellite versus central). Using a partial correlation analysis, we consistently find that age or specific star formation rate is the primary parameter correlating with spin. Light-weighted age and specific star formation rate are more strongly correlated with spin than mass-weighted age. In fact, across our sample, once the relation between light-weighted age and spin is accounted for, there is no significant residual correlation between spin and mass, or spin and environment. This result is strongly suggestive that the present-day environment only indirectly influences spin, via the removal of gas and star formation quenching. That is, environment affects age, then age affects spin. Older galaxies then have lower spin, either due to stars being born dynamically hotter at high redshift, or due to secular heating. Our results appear to rule out environmentally dependent dynamical heating (e.g. g alaxy–g alaxy interactions) being important, at least within 1 R e where our kinematic measurements are made. The picture is more complex when we only consider high-mass galaxies ( M ∗ ≳ 10 11 M ). While the age-spin relation is still strong for these high-mass galaxies, there is a residual environmental trend with central galaxies preferentially having lower spin, compared to satellites of the same age and mass. We argue that this trend is likely due to central galaxies being a preferred location for mergers.

The SAMI Galaxy Sur v ey: galaxy spin is more strongly correlated with stella...

Sérgio Sacani

The evolved stages of massive stars are poorly understood, but invaluable constraints can be derived from spatially resolved observations of nearby red supergiants, such as Betelgeuse. Atacama Large Millimeter/submillimeter Array (ALMA) observations of Betelgeuse showing a dipolar velocity field have been interpreted as evidence for a projected rotation rate of about 5 km s−1. This is 2 orders of magnitude larger than predicted by single-star evolution, which led to suggestions that Betelgeuse is a binary merger. We propose instead that large-scale convective motions can mimic rotation, especially if they are only partially resolved. We support this claim with 3D CO5BOLDsimulations of nonrotating red supergiants that we postprocessed to predict ALMA images and SiO spectra. We show that our synthetic radial velocity maps have a 90% chance of being falsely interpreted as evidence for a projected rotation rate of 2 km s−1 or larger for our fiducial simulation. We conclude that we need at least another ALMA observation to firmly establish whether Betelgeuse is indeed rapidly rotating. Such observations would also provide insight into the role of angular momentum and binary interaction in the late evolutionary stages. The data will further probe the structure and complex physical processes in the atmospheres of red supergiants, which are immediate progenitors of supernovae and are believed to be essential in the formation of gravitational-wave sources.

Is Betelgeuse Really Rotating? Synthetic ALMA Observations of Large-scale Con...

Sérgio Sacani

We present a comprehensive analysis aimed at proving the hypothesis that a train of small-scale features observed by the Wide-field Imager (WISPR) onboard the Parker Solar Probe (PSP) are the signature of a Kelvin–Helmholtz instability (KHI). These features were seen near the flank of a Coronal Mass Ejection (CME) wake between 7.5 Re and 9.5Re, lasting for about 30 minutes. The CME was a slow event, associated with a streamer blowout. We analyzed the size of the eddies and found growth during their evolution while maintaining separation distances and alignment typical of Kelvin–Helmholtz vortexes. We then assessed the magnetic field conditions that would make the observation of such an instability plausible. Two methods were used to cross-check our findings. The measured thickness of the boundary layer supports KHI candidacy, and the estimated linear growth rate suggests nonlinear saturation within the expected timescale. We conclude that a KHI is a plausible explanation for the observed features, and therefore that such instabilities might exist in the low and middle solar corona (within ∼15 Re) and can be detected in white light observations. Their observation, however, might be rare due to stringent conditions like the observer’s proximity, suitable viewing circumstances, magnetic field topology, and flow properties. This study highlights the unique capability of PSP/WISPR in observing such phenomena, especially as PSP perihelia reach closer distances to the Sun.

First Direct Imaging of a Kelvin–Helmholtz Instability by PSP/WISPR

Sérgio Sacani

Rapidly rotating fluids have a rotation profile that depends only on the distance from the rotation axis, in accor-dance with the Taylor- Proudman theorem. Although the Sun was expected to be such a body, helioseismology showed that the rotation rate in the convection zone is closer to constant on radii. It has been postulated that this deviation is due to the poles being warmer than the equator by a few degrees. Using numerical simulations, we show that the pole- to-equator temperature difference cannot exceed 7 kelvin as a result of the back- reaction of the high- latitude baroclinically unstable inertial modes. The observed amplitudes of the modes further indicate that this maximum temperature difference is reached in the Sun. We conclude that the Sun’s latitudinal differential rotation reaches its maximum allowed value

The Sun’s differential rotation is controlled by high- latitude baroclinicall...

Sérgio Sacani

We present the analysis of multiepoch observations of a set of 12 variable, Compton-thin, local (z<0.1) active galactic nuclei (AGN) selected from the 100-month BAT catalog. We analyze all available X-ray data from Chandra, XMMNewton, and NuSTAR, adding up to a total of 53 individual observations. This corresponds to between 3 and 7 observations per source, probing variability timescales between a few days and ∼ 20 yr. All sources have at least one NuSTAR observation, ensuring high-energy coverage, which allows us to disentangle the line-of-sight and reflection components in the X-ray spectra. For each source, we model all available spectra simultaneously, using the physical torus models MYTorus, borus02, and UXCLUMPY. The simultaneous fitting, along with the high-energy coverage, allows us to place tight constraints on torus parameters such as the torus covering factor, inclination angle, and torus average column density. We also estimate the line-of-sight column density (NH) for each individual observation. Within the 12 sources, we detect clear line-of-sight NH variability in 5, non-variability in 5, and for 2 of them it is not possible to fully disentangle intrinsic-luminosity and NH variability. We observe large differences between the average values of line-ofsight NH (or NH of the obscurer) and the average NH of the torus (or NH of the reflector), for each source, by a factor between ∼ 2 to > 100. This behavior, which suggests a physical disconnect between the absorber and the reflector, is more extreme in sources that present NH variability. NH-variable AGN also tend to present larger obscuration and broader cloud distributions than their non-variable counterparts. We observe that large changes in obscuration only occur at long timescales, and use this to place tentative lower limits on torus cloud sizes.

Hydrogen Column Density Variability in a Sample of Local Compton-Thin AGN

Sérgio Sacani

Titã, que é a maior lua de Saturno e envolta em mistério, possui uma atmosfera densa repleta de vários compostos orgânicos, alguns dos quais poderiam servir como indicadores de vida se fossem encontrados em nosso próprio planeta. Surge a questão intrigante sobre os mecanismos subjacentes à formação desses compostos em Titã e se eles são a chave para desvendar os mistérios que cercam as origens da vida na Terra, o que leva a uma busca por respostas que entrelaçam os dois corpos celestes. A sonda Huygens da Agência Espacial Européia (ESA), que fez sua chegada histórica a Titã no ano de 2005, é um instrumento fundamental pronto para esclarecer esses processos enigmáticos. Ao mesmo tempo, observatórios terrestres equipados com capacidades telescópicas avançadas contribuem significativamente para esse empreendimento científico, auxiliando no planejamento estratégico para determinar o local preciso de pouso da Huygens, contemplando a dicotomia entre solo sólido e um oceano envolto em metano como possíveis zonas de pouso.

Huygens - Exploring Titan A Mysterious World

Sérgio Sacani

Our Sun lies within 300 parsecs of the 2.7-kiloparsecs-long sinusoidal chain of dense gas clouds known as the Radclife Wave1 . The structure’s wave-like shape was discovered using three-dimensional dust mapping, but initial kinematic searches for oscillatory motion were inconclusive2–7 . Here we present evidence that the Radclife Wave is oscillating through the Galactic plane while also drifting radially away from the Galactic Centre. We use measurements of line-of-sight velocity8 for 12CO and threedimensional velocities of young stellar clusters to show that the most massive star-forming regions spatially associated with the Radclife Wave (including Orion, Cepheus, North America and Cygnus X) move as though they are part of an oscillating wave driven by the gravitational acceleration of the Galactic potential. By treating the Radclife Wave as a coherently oscillating structure, we can derive its motion independently of the local Galactic mass distribution, and directly measure local properties of the Galactic potential as well as the Sun’s vertical oscillation period. In addition, the measured drift of the Radclife Wave radially outwards from the Galactic Centre suggests that the cluster whose supernovae ultimately created today’s expanding Local Bubble9 may have been born in the Radclife Wave.

The Radcliffe Wave Of Milk Way is oscillating

Sérgio Sacani

Relativistic jets are observed from accreting and cataclysmic transients throughout the Universe, and have a profound impact on their surroundings1,2 . Despite their importance, their launch mechanism is not known. For accreting neutron stars, the speed of their compact jets can reveal whether the jets are powered by magnetic felds anchored in the accretion fow3 or in the star itself 4,5 , but so far no such measurements exist. These objects can show bright explosions on their surface due to unstable thermonuclear burning of recently accreted material, called type-I X-ray bursts6 , during which the mass-accretion rate increases7–9 . Here, we report on bright fares in the jet emission for a few minutes after each X-ray burst, attributed to the increased accretion rate. With these fares, we measure the speed of a neutron star compact jet to be v c = 0.38−0.08 +0.11 , much slower than those from black holes at similar luminosities. This discovery provides a powerful new tool in which we can determine the role that individual system properties have on the jet speed, revealing the dominant jet launching mechanism.

Thermonuclear explosions on neutron stars reveal the speed of their jets

Sérgio Sacani

Superclusters are the largest massive structures in the cosmic web, on tens to hundreds of megaparsec scales. They are the largest assembly of galaxy clusters in the Universe. Apart from a few detailed studies of such structures, their evolutionary mechanism is still an open question. In order to address and answer the relevant questions, a statistically significant, large catalog of superclusters covering a wide range of redshifts and sky areas is essential. Here, we present a large catalog of 662 superclusters identified using a modified friends-of-friends algorithm applied on the WHL (Wen–Han–Liu) cluster catalog within a redshift range of 0.05 z 0.42. We name the most massive supercluster at z ∼ 0.25 as the Einasto Supercluster. We find that the median mass of superclusters is ∼5.8 × 10 15 Me and the median size ∼65 Mpc. We find that the supercluster environment slightly affects the growth of clusters. We compare the properties of the observed superclusters with the mock superclusters extracted from the Horizon Run 4 cosmological simulation. The properties of the superclusters in the mocks and observations are in broad agreement. We find that the density contrast of a supercluster is correlated with its maximum extent with a power-law index, α ∼ −2. The phase-space distribution of mock superclusters shows that, on average, ∼90% of part of a supercluster has a gravitational influence on its constituents. We also show the mock halos’ average number density and peculiar velocity profiles in and around the superclusters.

Identification of Superclusters and Their Properties in the Sloan Digital Sky...

Sérgio Sacani

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