How drifting and evaporating pebbles shape giant planets III: The formation of WASP-77A b and τ\tau Bo\"otis b

Atmospheric abundances are thought to constrain the planet formation pathway, because different species evaporate at different temperatures leaving distinct signatures in the accreted atmosphere. The planetary C/O ratio is thought to constrain the planet formation pathway, because of the condensation sequence of H$_2$O, CO$_2$, CH$_4$, and CO, resulting in an increase of the gas phase C/O ratio with increasing distance. Here we use a disc evolution model including pebble growth, drift and evaporation coupled with a planet formation model that includes pebble and gas accretion as well as planet migration to compute the atmospheric compositions of giant planets. We compare our results to the recent observations of the hot Jupiters WASP-77A b and $\tau$ Bo\"otis b, which feature sub-solar and super-solar C/H and O/H values, respectively. Our simulations reproduce these measurements and show that giants like WASP-77A b should start to form beyond the CO$_2$ evaporation front, while giants like $\tau$ Bo\"otis b should originate from beyond the H$_2$O line. Our model allows the formation of sub- and super-solar atmospheric compositions. However simulations without pebble evaporation can not reproduce the super-solar C/H and O/H ratios of $\tau$ Bo\"otis b's atmosphere without additional accretion of solids. We identify the $\alpha$ viscosity parameter of the disc as a key ingredient, because the viscosity drives the inward motion of volatile enriched vapor, responsible for the accretion of gaseous C and O. Depending on the planet's migration history order-of-magnitude differences in atmospheric C/H and O/H are expected. Our simulations also predict super-solar N/H for $\tau$ Bo\"otis b and solar N/H for WASP-77A b. We conclude that pebble evaporation is a key ingredient to explain the variety of exoplanet atmospheres, because it can explain both, sub- and super-solar atmospheric abundances.Comment: Accepted by A&A, 7 pages, 4 figure

Photodissociation and induced chemical asymmetries on ultra-hot gas giants. A case study of HCN on WASP-76 b

Recent observations have resulted in the detection of chemical gradients on ultra-hot gas giants. Notwithstanding their high temperature, chemical reactions in ultra-hot atmospheres may occur in disequilibrium, due to vigorous day-night circulation and intense UV radiation from their stellar hosts. The goal of this work is to explore whether photochemistry is affecting the composition of ultra-hot giant planets, and if it can introduce horizontal chemical gradients. In particular, we focus on hydrogen cyanide (HCN) on WASP-76 b, as it is a photochemically active molecule with a reported detection on only one side of this planet. We use a pseudo-2D chemical kinetics code to model the chemical composition of WASP-76 b along its equator. Our approach improves on chemical equilibrium models by computing vertical mixing, horizontal advection, and photochemistry. We find that production of HCN is initiated through thermal and photochemical dissociation of CO and N2 on the day side of WASP-76 b, which are subsequently transported to the night side via the equatorial jet stream. This process results in an HCN gradient with a maximal abundance on the planet's morning limb. We verified that photochemical dissociation is a necessary condition for this mechanism, as thermal dissociation alone proves insufficient. Other species produced via night-side disequilibrium chemistry are SO2 and S2. Our model acts as a proof of concept for chemical gradients on ultra-hot exoplanets. We demonstrate that even ultra-hot planets can exhibit disequilibrium chemistry and recommend that future studies do not neglect photochemistry in their analyses of ultra-hot planets.Comment: 15 pages, 9 figure

WASP-39b: exo-Saturn with patchy cloud composition, moderate metallicity, and underdepleted S/O

WASP-39b is one of the first extrasolar giant gas planets that has been observed within the JWST ERS program. Fundamental properties that may enable the link to exoplanet formation differ amongst retrieval methods, for example metallicity and mineral ratios. In this work, the formation of clouds in the atmosphere of WASP-39b is explored to investigate how inhomogeneous cloud properties (particle sizes, material composition, opacity) may be for this intermediately warm gaseous exoplanet. WASP-39b's atmosphere has a comparable day-night temperature median with sufficiently low temperatures that clouds may form globally. The presence of clouds on WASP-39b can explain observations without resorting to a high (> 100x solar) metallicity atmosphere for a reduced vertical mixing efficiency. The assessment of mineral ratios shows an under-depletion of S/O due to condensation compared to C/O, Mg/O, Si/O, Fe/O ratios. Vertical patchiness due to heterogeneous cloud composition challenges simple cloud models. An equal mixture of silicates and metal oxides is expected to characterise the cloud top. Further, optical properties of Fe and Mg silicates in the mid-infrared differ significantly which will impact the interpretation of JWST observations. We conclude that WASP-39b's atmosphere contains clouds and the underdepletion of S/O by atmospheric condensation processes suggest the use of sulphur gas species as a possible link to primordial element abundances. Over-simplified cloud models do not capture the complex nature of mixed-condensate clouds in exoplanet atmospheres. The clouds in the observable upper atmosphere of WASP-39b are a mixture of different silicates and metal oxides. The use of constant particles sizes and/or one-material cloud particles alone to interpret spectra may not be sufficient to capture the full complexity available through JWST observations.Comment: 21 pages, 18 figures, submitted to A&A on 22. November 2022, in review since 8. December 202

Harnessing machine learning for accurate treatment of overlapping opacity species in GCMs

peer reviewedTo understand high precision observations of exoplanets and brown dwarfs, we need detailed and complex general circulation models (GCMs) that incorporate hydrodynamics, chemistry, and radiation. In this study, we specifically examine the coupling between chemistry and radiation in GCMs and compare different methods for mixing opacities of different chemical species in the correlated-k assumption, when equilibrium chemistry cannot be assumed. We propose a fast machine learning method based on DeepSets (DS), which effectively combines individual correlated-k opacities (k-tables). We evaluate the DS method alongside other published methods like adaptive equivalent extinction (AEE) and random overlap with rebinning and resorting (RORR). We integrate these mixing methods into our GCM (expeRT/MITgcm) and assess their accuracy and performance for the example of the hot Jupiter HD~209458 b. Our findings indicate that the DS method is both accurate and efficient for GCM usage, whereas RORR is too slow. Additionally, we observe that the accuracy of AEE depends on its specific implementation and may introduce numerical issues in achieving radiative transfer solution convergence. We then apply the DS mixing method in a simplified chemical disequilibrium situation, where we model the rainout of TiO and VO, and confirm that the rainout of TiO and VO would hinder the formation of a stratosphere. To further expedite the development of consistent disequilibrium chemistry calculations in GCMs, we provide documentation and code for coupling the DS mixing method with correlated-k radiative transfer solvers. The DS method has been extensively tested to be accurate enough for GCMs, however, other methods might be needed for accelerating atmospheric retrievals

The SWELLS Survey. I. A large spectroscopically selected sample of edge-on late-type lens galaxies

The relative contribution of baryons and dark matter to the inner regions of spiral galaxies provides critical clues to their formation and evolution, but it is generally difficult to determine. For spiral galaxies that are strong gravitational lenses, however, the combination of lensing and kinematic observations can be used to break the disk-halo degeneracy. In turn, such data constrain fundamental parameters such as i) the mass density profile slope and axis ratio of the dark matter halo, and by comparison with dark matter-only numerical simulations the modifications imposed by baryons; ii) the mass in stars and therefore the overall star formation efficiency, and the amount of feedback; iii) by comparison with stellar population synthesis models, the normalization of the stellar initial mass function. In this first paper of a series, we present a sample of 16 secure, 1 probable, and 6 possible strong lensing spiral galaxies, for which multi-band high-resolution images and rotation curves were obtained using the Hubble Space Telescope and Keck-II Telescope as part of the Sloan WFC Edge-on Late-type Lens Survey (SWELLS). The sample includes 8 newly discovered secure systems. [abridged] We find that the SWELLS sample of secure lenses spans a broad range of morphologies (from lenticular to late-type spiral), spectral types (quantified by Halpha emission), and bulge to total stellar mass ratio (0.22-0.85), while being limited to M_*>10^{10.5} M_sun. The SWELLS sample is thus well-suited for exploring the relationship between dark and luminous matter in a broad range of galaxies. We find that the deflector galaxies obey the same size-mass relation as that of a comparison sample of elongated non-lens galaxies selected from the SDSS survey. We conclude that the SWELLS sample is consistent with being representative of the overall population of high-mass high-inclination disky galaxies.Comment: 21 pages, 6 figures, MNRAS, in pres

Total Synthesis of (±)-Phomoidride D

Described herein is a synthetic strategy for the total synthesis of (±)‐phomoidride D. This highly efficient and stereoselective approach provides rapid assembly of the carbocyclic core by way of a tandem phenolic oxidation/intramolecular Diels–Alder cycloaddition. A subsequent SmI2‐mediated cyclization cascade delivers an isotwistane intermediate poised for a Wharton fragmentation that unveils the requisite bicyclo[4.3.1]decene skeleton and sets the stage for synthesis completion

Short-Term Forecasting and Detection of Explosions During the 2016–2017 Eruption of Bogoslof Volcano, Alaska

We describe a multidisciplinary approach to forecast, rapidly detect, and characterize explosive events during the 2016–2017 eruption of Bogoslof volcano, a back-arc shallow submarine volcano in Alaska’s Aleutian arc. The eruptive sequence began in December 2016 and included about 70 discrete explosive events. Because the volcano has no local monitoring stations, we used distant stations on the nearest volcanoes, Okmok (54 km) and Makushin (72 km), combined with regional infrasound sensors and lightning detection from the Worldwide Lightning Location Network (WWLLN). Pre-eruptive seismicity was detected for 12 events during the first half of the eruption; for all other events co-eruptive signals allowed for detection only. Monitoring of activity used a combination of scheduled checks combined with automated alarms. Alarms triggered on real-time data included real-time seismic amplitude measurement (RSAM); infrasound from several arrays, the closest being on Okmok; and lightning strokes detected from WWLLN within a 20-km radius of the volcano. During periods of unrest, a multidisciplinary response team of four people fulfilled specific roles to evaluate geophysical and remote-sensing data, run event-specific ash-cloud dispersion models, ensure interagency coordination, and develop and distribute of formalized warning products. Using this approach, for events that produced ash clouds ≥7.5 km above sea level, Alaska Volcano Observatory (AVO) called emergency response partners 15 min, and issued written notices 30 min, after event onset (mean times). Factors that affect timeliness of written warnings include event size and number of data streams available; bigger events and more data both decrease uncertainty and allow for faster warnings. In remote areas where airborne ash is the primary hazard, the approach used at Bogoslof is an effective strategy for hazard mitigation

LSST: from Science Drivers to Reference Design and Anticipated Data Products

(Abridged) We describe here the most ambitious survey currently planned in the optical, the Large Synoptic Survey Telescope (LSST). A vast array of science will be enabled by a single wide-deep-fast sky survey, and LSST will have unique survey capability in the faint time domain. The LSST design is driven by four main science themes: probing dark energy and dark matter, taking an inventory of the Solar System, exploring the transient optical sky, and mapping the Milky Way. LSST will be a wide-field ground-based system sited at Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m effective) primary mirror, a 9.6 deg$^2$ field of view, and a 3.2 Gigapixel camera. The standard observing sequence will consist of pairs of 15-second exposures in a given field, with two such visits in each pointing in a given night. With these repeats, the LSST system is capable of imaging about 10,000 square degrees of sky in a single filter in three nights. The typical 5$\sigma$ point-source depth in a single visit in $r$ will be $\sim 24.5$ (AB). The project is in the construction phase and will begin regular survey operations by 2022. The survey area will be contained within 30,000 deg$^2$ with $\delta<+34.5^\circ$, and will be imaged multiple times in six bands, $ugrizy$, covering the wavelength range 320--1050 nm. About 90\% of the observing time will be devoted to a deep-wide-fast survey mode which will uniformly observe a 18,000 deg$^2$ region about 800 times (summed over all six bands) during the anticipated 10 years of operations, and yield a coadded map to $r\sim27.5$. The remaining 10\% of the observing time will be allocated to projects such as a Very Deep and Fast time domain survey. The goal is to make LSST data products, including a relational database of about 32 trillion observations of 40 billion objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures available from https://www.lsst.org/overvie

Catching Element Formation In The Act

Gamma-ray astronomy explores the most energetic photons in nature to address some of the most pressing puzzles in contemporary astrophysics. It encompasses a wide range of objects and phenomena: stars, supernovae, novae, neutron stars, stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays and relativistic-particle acceleration, and the evolution of galaxies. MeV gamma-rays provide a unique probe of nuclear processes in astronomy, directly measuring radioactive decay, nuclear de-excitation, and positron annihilation. The substantial information carried by gamma-ray photons allows us to see deeper into these objects, the bulk of the power is often emitted at gamma-ray energies, and radioactivity provides a natural physical clock that adds unique information. New science will be driven by time-domain population studies at gamma-ray energies. This science is enabled by next-generation gamma-ray instruments with one to two orders of magnitude better sensitivity, larger sky coverage, and faster cadence than all previous gamma-ray instruments. This transformative capability permits: (a) the accurate identification of the gamma-ray emitting objects and correlations with observations taken at other wavelengths and with other messengers; (b) construction of new gamma-ray maps of the Milky Way and other nearby galaxies where extended regions are distinguished from point sources; and (c) considerable serendipitous science of scarce events -- nearby neutron star mergers, for example. Advances in technology push the performance of new gamma-ray instruments to address a wide set of astrophysical questions.Comment: 14 pages including 3 figure