• A diffuse tidal dwarf galaxy destined to fade out as a "dark galaxy"

      Román, J.; Jones, M.G.; Montes, M.; Verdes-Montenegro, L.; Garrido, J.; Sánchez, S.; Steward Observatory, University of Arizona (EDP Sciences, 2021)
      We have explored the properties of a peculiar object detected in deep optical imaging and located at the tip of an H » I tail emerging from Hickson Compact Group 16. Using multiband photometry from infrared to ultraviolet, we were able to constrain its stellar age to 58-9+22 Myr with a rather high metallicity of [Fe/H] = -0.16-0.41+0.43 for its stellar mass of M- = 4.2 × 106 Mpdbl, a typical signature of tidal dwarf galaxies. The structural properties of this object are similar to those of diffuse galaxies, with a round and featureless morphology, a large effective radius (reff = 1.5 kpc), and a low surface brightness (μg-eff = 25.6 mag arcsec-2). Assuming that the object is dynamically stable and able to survive in the future, its fading in time via the aging of its stellar component will make it undetectable in optical observations in just ∼2 Gyr of evolution, even in the deepest current or future optical surveys. Its high H » I mass, M(HI) = 3.9 × 108 Mpdbl, and future undetectable stellar component will make the object match the observational properties of dark galaxies, that is, dark matter halos that failed to turn gas into stars. Our work presents further observational evidence of the feasibility of H » I tidal features becoming fake dark galaxies; it also shows the impact of stellar fading, particularly in high metallicity systems such as tidal dwarfs, in hiding aged stellar components beyond detection limits in optical observations. © ESO 2021.
    • A MUSE view of the asymmetric jet from HD 163296

      Xie, C.; Haffert, S.Y.; De Boer, J.; Kenworthy, M.A.; Brinchmann, J.; Girard, J.; Snellen, I.A.G.; Keller, C.U.; Steward Observatory, University of Arizona (EDP Sciences, 2021)
      Context. Jets and outflows are thought to play important roles in regulating star formation and disk evolution. An important question is how the jets are launched. HD 163296 is a well-studied Herbig Ae star that hosts proto-planet candidates, a protoplanetary disk, a protostellar jet, and a molecular outflow, which makes it an excellent laboratory for studying jets. Aims. We aim to characterize the jet at the inner regions and check if there are large differences with the features at large separations. A secondary objective is to demonstrate the performance of Multi Unit Spectroscopic Explorer (MUSE) in high-contrast imaging of extended line emission. Methods. MUSE in the narrow field mode (NFM) can provide observations at optical wavelengths with high spatial (∼75 mas) and medium spectral (R  ∼  2500) resolution. With the high-resolution spectral differential imaging technique, we can characterize the kinematic structures and physical conditions of jets down to 100 mas. Results. We detect multiple atomic lines in two new knots, B3 and A4, at distances of < 4 from the host star with MUSE. The derived M jet/M acc is about 0.08 and 0.06 for knots B3 and A4, respectively. The observed [Ca II]/[S II] ratios indicate that there is no sign of dust grains at distances of < 4. Assuming the A4 knot traced the streamline, we can estimate a jet radius at the origin by fitting the half width half maximum of the jet, which sets an upper limit of 2.2 au on the size of the launching region. Although MUSE has the ability to detect the velocity shifts caused by high- and low-velocity components, we found no significant evidence of velocity decrease transverse to the jet direction in our 500 s MUSE observation. Conclusions. Our work demonstrates the capability of using MUSE NFM observations for the detailed study of stellar jets in the optical down to 100 mas. The derived M jet/M acc, no dust grain, and jet radius at the star support the magneto-centrifugal models as a launching mechanism for the jet. © C. Xie et al. 2021.
    • A near-infrared interferometric survey of debris-disk stars: VII. The hot-to-warm dust connection

      Absil, O.; Marion, L.; Ertel, S.; Defrère, D.; Kennedy, G.M.; Romagnolo, A.; Le Bouquin, J.-B.; Christiaens, V.; Milli, J.; Bonsor, A.; et al. (EDP Sciences, 2021)
      Context. Hot exozodiacal dust has been shown to be present in the innermost regions of an increasing number of main sequence stars over the past 15 yr. However, the origin of hot exozodiacal dust and its connection with outer dust reservoirs remains unclear. Aims. We aim to explore the possible connection between hot exozodiacal dust and warm dust reservoirs (>100 K) in asteroid belts. Methods. We use precision near-infrared interferometry with VLTI/PIONIER to search for resolved emission at H-band around a selected sample of 62 nearby stars that show possible signs of warm dust populations. Results. Our observations reveal the presence of resolved near-infrared emission around 17 out of 52 stars with sufficient data quality. For four of these, the emission is shown to be due to a previously unknown stellar companion. The 13 other H-band excesses are thought to originate from the thermal emission of hot dust grains, close to their sublimation temperature. Taking into account earlier PIONIER observations, where some stars with warm dust were also observed, and after re-evaluating the warm dust content of all our PIONIER targets through spectral energy distribution modeling, we find a detection rate of 17:1+8:1-4:6% for H-band excess around main sequence stars hosting warm dust belts, which is statistically compatible with the occurrence rate of 14:6+4:3-2:8% found around stars showing no signs of warm dust. After correcting for the sensitivity loss due to partly unresolved hot disks, under the assumption that they are arranged in a thin ring around their sublimation radius, we find tentative evidence at the 3s level that H-band excesses around stars with outer dust reservoirs (warm or cold) could be statistically larger than H-band excesses around stars with no detectable outer dust. Conclusions. Our observations do not suggest a direct connection between warm and hot dust populations at the sensitivity level of the considered instruments, although they bring to light a possible correlation between the level of H-band excess and the presence of outer dust reservoirs in general. © 2021 ESO.
    • A new view of energetic particles from stream interaction regions observed by Parker Solar Probe

      Schwadron, N.A.; Joyce, C.J.; Aly, A.; Cohen, C.M.S.; Desai, M.I.; McComas, D.J.; Niehof, J.T.; Möbius, E.; Lee, M.; Bower, J.; et al. (EDP Sciences, 2021)
      Early observations from the first orbit of Parker Solar Probe (PSP) show recurrent stream interaction regions that form close to the Sun. Energetic particle enhancements were observed on the 320th-326th day of the year 2018, which corresponds to ~1-7 days after the passage of the stream interface between faster and slower solar wind. Energetic particles stream into the inner heliosphere to the PSP spacecraft near 0.33 au (71 solar radii) where they are measured by the Integrated Science Investigation of the Sun (IS⊙ IS). The large 6-day time interval over which energetic particles are observed after the stream passage provides a unique perspective on the development of stream interactions within the heliosphere. The long duration of energetic particle enhancements suggests that particles stream in through the inner heliosphere more directly along magnetic field lines that form a sub-Parker spiral structure due to magnetic footpoint motion at the Sun and shearing of the magnetic field in the rarefaction region behind the stream interface. The strong build-up of energetic particle fluxes in the first 3 days after the passage of the stream interface indicates that suprathermal populations are enhanced near the interaction region through compression or other acceleration processes in addition to being diffusively accelerated. The early increases in energetic particle fluxes (in the first 3 days) in the formation of these events allows for the characterization of the acceleration associated with these suprathermal seed populations. Thus, we show that the time history of energetic particle fluxes observed by IS⊙ IS provides a new view of particle acceleration at stream interaction regions throughout the inner heliosphere. © ESO 2021.
    • ALMA multiline survey of the ISM in two quasar host-companion galaxy pairs at z > 6

      Pensabene, A.; Decarli, R.; Bañados, E.; Venemans, B.; Walter, F.; Bertoldi, F.; Fan, X.; Farina, E.P.; Li, J.; Mazzucchelli, C.; et al. (EDP Sciences, 2021)
      We present a multiline survey of the interstellar medium (ISM) in two z > 6 quasar host galaxies, PJ231-20 (z = 6:59) and PJ308-21 (z = 6:23), and their two companion galaxies. Observations were carried out using the Atacama Large (sub-)Millimeter Array (ALMA). We targeted 11 transitions including atomic fine-structure lines (FSLs) and molecular lines: [NII]205μm, [CI]369μm, CO (Jup = 7; 10; 15; 16), H2O 312-221, 321-312, 303-212, and the OH163μm doublet. The underlying far-infrared (FIR) continuum samples the Rayleigh-Jeans tail of the respective dust emission. By combining this information with our earlier ALMA [CII]158μm observations, we explored the effects of star formation and black hole feedback on the ISM of the galaxies using the CLOUDY radiative transfer models. We estimated dust masses, spectral indexes, IR luminosities, and star-formation rates from the FIR continuum. The analysis of the FSLs indicates that the [CII]158μm and [CI]369μm emission arises predominantly from the neutral medium in photodissociation regions (PDRs). We find that line deficits agree with those of local luminous IR galaxies. The CO spectral line energy distributions (SLEDs) reveal significant high-J CO excitation in both quasar hosts. Our CO SLED modeling of the quasar PJ231-20 shows that PDRs dominate the molecular mass and CO luminosities for Jup ≤ 7, while the Jup ≥10 CO emission is likely driven by X-ray dissociation regions produced by the active galactic nucleus (AGN) at the very center of the quasar host. The Jup > 10 lines are undetected in the other galaxies in our study. The H2O 321-312 line detection in the same quasar places this object on the LH2O-LTIR relation found for low-z sources, thus suggesting that this water vapor transition is predominantly excited by IR pumping. Models of the H2O SLED and of the H2O-to-OH163μm ratio point to PDR contributions with high volume and column density (nH ∼ 0:8 × 105 cm-3, NH = 1024 cm-2) in an intense radiation field. Our analysis suggests a less highly excited medium in the companion galaxies. However, the current data do not allow us to definitively rule out an AGN in these sources, as suggested by previous studies of the same objects. This work demonstrates the power of multiline studies of FIR diagnostics in order to dissect the physical conditions in the first massive galaxies emerging from cosmic dawn. © 2021 EDP Sciences. All rights reserved.
    • Climate of an ultra hot Jupiter: Spectroscopic phase curve of WASP-18b with HST/WFC3

      Arcangeli, J.; Désert, J.-M.; Parmentier, V.; Stevenson, K.B.; Bean, J.L.; Line, M.R.; Kreidberg, L.; Fortney, J.J.; Showman, A.P.; Department of Planetary Sciences and Lunar and Planetary Laboratory, University of Arizona (EDP Sciences, 2019)
      We present the analysis of a full-orbit, spectroscopic phase curve of the ultra hot Jupiter (UHJ) WASP-18b, obtained with the Wide Field Camera 3 aboard the Hubble Space Telescope. We measured the normalised day-night contrast of the planet as >0.96 in luminosity: the disc-integrated dayside emission from the planet is at 964 ± 25 ppm, corresponding to 2894 ± 30 K, and we place an upper limit on the nightside emission of <32 ppm or 1430 K at the 3σ level. We also find that the peak of the phase curve exhibits a small, but significant offset in brightness of 4.5 ± 0.5° eastward. We compare the extracted phase curve and phase-resolved spectra to 3D global circulation models and find that broadly the data can be well reproduced by some of these models. We find from this comparison several constraints on the atmospheric properties of the planet. Firstly we find that we need efficient drag to explain the very inefficient day-night recirculation observed. We demonstrate that this drag could be due to Lorentz-force drag by a magnetic field as weak as 10 gauss. Secondly, we show that a high metallicity is not required to match the large day-night temperature contrast. In fact, the effect of metallicity on the phase curve is different from cooler gas-giant counterparts because of the high-temperature chemistry in the atmosphere of WASP-18b. Additionally, we compared the current UHJ spectroscopic phase curves, WASP-18b and WASP-103b, and show that these two planets provide a consistent picture with remarkable similarities in their measured and inferred properties. However, key differences in these properties, such as their brightness offsets and radius anomalies, suggest that UHJ could be used to separate between competing theories for the inflation of gas-giant planets. © ESO 2019.
    • Component properties and mutual orbit of binary main-belt comet 288P/(300163) 2006 VW139

      Agarwal, J.; Kim, Y.; Jewitt, D.; Mutchler, M.; Weaver, H.; Larson, S.; Lunar and Planetary Laboratory, University of Arizona (EDP Sciences, 2020-11-19)
      The binary asteroid 288P/(300163) is unusual both for its combination of wide-separation and high mass ratio and for its comet-like activity. It is not currently known whether there is a causal connection between the activity and the unusual orbit or if instead the activity helped to overcome a strong detection bias against such sub-arcsecond systems. Aims. We aim to find observational constraints discriminating between possible formation scenarios and to characterise the physical properties of the system components. Methods. We measured the component separation and brightness using point spread function fitting to high-resolution Hubble Space Telescope/Wide Field Camera 3 images from 25 epochs between 2011 and 2020.We constrained component sizes and shapes from the photometry, and we fitted a Keplerian orbit to the separation as a function of time. Results. Approximating the components A and B as prolate spheroids with semi-axis lengths a < b and assuming a geometric albedo of 0.07, we find aA 0.6 km, bA 1.4 km, aB 0.5 km, and bB 0.8 km.We find indications that the dust production may have concentrated around B and that the mutual orbital period may have changed by 1-2 days during the 2016 perihelion passage. Orbit solutions have semi-major axes in the range of (105-109) km, eccentricities between 0.41 and 0.51, and periods of (117.3-117.5) days preperihelion and (118.5-119.5) days post-perihelion, corresponding to system masses in the range of (6.67-7.23) 1012 kg. The mutual and heliocentric orbit planes are roughly aligned. Conclusions. Based on the orbit alignment, we infer that spin-up of the precursor by the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect led to the formation of the binary system. We disfavour (but cannot exclude) a scenario of very recent formation where activity was directly triggered by the break-up, because our data support a scenario with a single active component. © J. Agarwal et al. 2020.
    • A data-driven approach to constraining the atmospheric temperature structure of the ultra-hot Jupiter KELT-9b

      Fossati, L.; Shulyak, D.; Sreejith, A. G.; Koskinen, T.; Young, M. E.; Cubillos, P. E.; Lara, L. M.; France, K.; Rengel, M.; Cauley, P. W.; et al. (EDP Sciences, 2020-11-13)
      Context. Observationally constraining the atmospheric temperature-pressure (TP) profile of exoplanets is an important step forward for improving planetary atmosphere models, thus further enabling one to place the detection of spectral features and the measurement of atomic and molecular abundances through transmission and emission spectroscopy on solid ground. Aims. The aim is to constrain the TP profile of the ultra-hot Jupiter KELT-9b by fitting synthetic spectra to the observed Hα and Hβ lines and identify why self-consistent planetary TP models are unable to fit the observations. Methods. We constructed 126 one-dimensional TP profiles varying the lower and upper atmospheric temperatures, as well as the location and gradient of the temperature rise. For each TP profile, we computed the transmission spectra of the Hα and Hβ lines employing the Cloudy radiative transfer code, which self-consistently accounts for non-local thermodynamic equilibrium (NLTE) effects. Results. The TP profiles, leading to best fit the observations, are characterised by an upper atmospheric temperature of 10 000-11 000 K and by an inverted temperature profile at pressures higher than 10-4 bar. We find that the assumption of local thermodynamic equilibrium (LTE) leads one to overestimate the level population of excited hydrogen by several orders of magnitude and hence to significantly overestimate the strength of the Balmer lines. The chemical composition of the best fitting models indicate that the high upper atmospheric temperature is most likely driven by metal photoionisation and that FeII and FeIII have comparable abundances at pressures lower than 10-6 bar, possibly making the latter detectable. Conclusions. Modelling the atmospheres of ultra-hot Jupiters requires one to account for metal photoionisation. The high atmospheric mass-loss rate (>1011 g s-1), caused by the high temperature, may have consequences on the planetary atmospheric evolution. Other ultra-hot Jupiters orbiting early-type stars may be characterised by similarly high upper atmospheric temperatures and hence high mass-loss rates. This may have consequences on the basic properties of the observed planets orbiting hot stars. © ESO 2020.
    • Detection of small magnetic flux ropes from the third and fourth Parker Solar Probe encounters

      Zhao, L.-L.; Zank, G.P.; Hu, Q.; Telloni, D.; Chen, Y.; Adhikari, L.; Nakanotani, M.; Kasper, J.C.; Huang, J.; Bale, S.D.; et al. (EDP Sciences, 2021)
      Context. Aims. We systematically search for magnetic flux rope structures in the solar wind to within the closest distance to the Sun of ~0.13 AU, using data from the third and fourth orbits of the Parker Solar Probe. Methods. We extended our previous magnetic helicity-based technique of identifying magnetic flux rope structures. The method was improved upon to incorporate the azimuthal flow, which becomes larger as the spacecraft approaches the Sun. Results. A total of 21 and 34 magnetic flux ropes are identified during the third (21-day period) and fourth (17-day period) orbits of the Parker Solar Probe, respectively. We provide a statistical analysis of the identified structures, including their relation to the streamer belt and heliospheric current sheet crossing. © ESO 2021.
    • Detection of the hydrogen Balmer lines in the ultra-hot Jupiter WASP-33b

      Yan, F.; Wyttenbach, A.; Casasayas-Barris, N.; Reiners, A.; Pallé, E.; Henning, T.; Mollière, P.; Czesla, S.; Nortmann, L.; Molaverdikhani, K.; et al. (EDP Sciences, 2021)
      Ultra-hot Jupiters (UHJs) are highly irradiated giant exoplanets with extremely high day-side temperatures, which lead to thermal dissociation of most molecular species. It is expected that the neutral hydrogen atom is one of the main species in the upper atmospheres of UHJs. Neutral hydrogen has been detected in several UHJs by observing their Balmer line absorption. In this work, we report four transit observations of the UHJ WASP-33b, performed with the CARMENES and HARPS-North spectrographs, and the detection of the Hα, Hβ, and Hγ lines in the planetary transmission spectrum. The combined Hα transmission spectrum of the four transits has an absorption depth of 0.99 ± 0.05%, which corresponds to an effective radius of 1.31 ± 0.01 Rp. The strong Hα absorption indicates that the line probes the high-altitude thermosphere. We further fitted the three Balmer lines using the PAWN model, assuming that the atmosphere is hydrodynamic and in local thermodynamic equilibrium. We retrieved a thermosphere temperature 12 200-1000+1300 K and a mass-loss rate ? = 1011.8-0.5+0.6 g s-1. The retrieved high mass-loss rate is compatible with the "Balmer-driven"atmospheric escape scenario, in which the stellar Balmer continua radiation in the near-ultraviolet is substantially absorbed by excited hydrogen atoms in the planetary thermosphere. © ESO 2020.
    • Direct imaging and spectroscopy of exoplanets with the ELT/HARMONI high-contrast module

      Houllé, M.; Vigan, A.; Carlotti, A.; Choquet, É.; Cantalloube, F.; Phillips, M.W.; Sauvage, J.-F.; Schwartz, N.; Otten, G.P.P.L.; Baraffe, I.; et al. (EDP Sciences, 2021)
      Combining high-contrast imaging with medium-resolution spectroscopy has been shown to significantly boost the direct detection of exoplanets. HARMONI, one of the first-light instruments to be mounted on ESO's future extremely large telescope (ELT), will be equipped with a single-conjugated adaptive optics system to reach the diffraction limit of the ELT in the H and K bands, a high-contrast module dedicated to exoplanet imaging, and a medium-resolution (up to R = 17 000) optical and near-infrared integral field spectrograph. When combined, these systems will provide unprecedented contrast limits at separations between 50 and 400 mas. This paper is aimed at estimating the capabilities of the HARMONI high-contrast module for the direct detection of young giant exoplanets. We use an end-to-end model of the instrument to simulate high-contrast observations performed with HARMONI, based on realistic observing scenarios and conditions. We then analyze these data with the so-called "molecule mapping"technique combined with a matched-filter approach in order to disentangle companions from the host star and tellurics and to increase the signal-to-noise ratio (S/N) of the planetary signal. We detected planets above 5σ at contrasts up to 16 mag and separations down to 75 mas in several spectral configurations of the instrument. We show that molecule mapping allows for the detection of companions up to 2.5 mag fainter compared to state-of-the-art high-contrast imaging techniques based on angular differential imaging. We also demonstrate that the performance is not strongly affected by the spectral type of the host star and we show that we are able to reach close sensitivities for the best three quartiles of observing conditions at Armazones, which means that HARMONI could be used in near-critical observations during 60 to 70% of telescope time at the ELT. Finally, we simulated planets from population synthesis models to further explore the parameter space that HARMONI and its high-contrast module will open up and compare this to the current high-contrast instrumentation. © M. Houllé et al. 2021.
    • Effect of binary evolution on the inferred initial and final core masses of hydrogen-rich, Type II supernova progenitors

      Zapartas, E.; De Mink, S.E.; Justham, S.; Smith, N.; Renzo, M.; De Koter, A.; Steward Observatory, University of Arizona (EDP Sciences, 2021)
      The majority of massive stars, which are the progenitors of core-collapse supernovae (SNe), are found in close binary systems. In a previous work, we modeled the fraction of hydrogen-rich, Type II SN progenitors whose evolution is affected by mass exchange with their companion, finding this to be between ≈1/3 and 1/2 for most assumptions. Here we study in more depth the impact of this binary history of Type II SN progenitors on their final pre-SN core mass distribution, using population synthesis simulations. We find that binary star progenitors of Type II SNe typically end their life with a larger core mass than they would have had if they had lived in isolation because they gained mass or merged with a companion before their explosion. The combination of the diverse binary evolutionary paths typically leads to a marginally shallower final core mass distribution. In discussing our results in the context of the red supergiant problem, that is, the reported lack of detected high luminosity progenitors, we conclude that binary evolution does not seem to significantly affect the issue. This conclusion is quite robust against our variations in the assumptions of binary physics. We also predict that inferring the initial masses of Type II SN progenitors by "age-dating"their surrounding environment systematically yields lower masses compared to methods that probe the pre-SN core mass or luminosity. A robust discrepancy between the inferred initial masses of a SN progenitor from those different techniques could indicate an evolutionary history of binary mass accretion or merging. © ESO 2020.
    • Electron heat flux in the near-Sun environment

      Halekas, J.S.; Whittlesey, P.L.; Larson, D.E.; McGinnis, D.; Bale, S.D.; Berthomier, M.; Case, A.W.; Chandran, B.D.G.; Kasper, J.C.; Klein, K.G.; et al. (EDP Sciences, 2021)
      Aims. We survey the electron heat flux observed by the Parker Solar Probe (PSP) in the near-Sun environment at heliocentric distances of 0.125-0.25 AU. Methods. We utilized measurements from the Solar Wind Electrons Alphas and Protons and FIELDS experiments to compute the solar wind electron heat flux and its components and to place these in context. Results. The PSP observations reveal a number of trends in the electron heat flux signatures near the Sun. The magnitude of the heat flux is anticorrelated with solar wind speed, likely as a result of the lower saturation heat flux in the higher-speed wind. When divided by the saturation heat flux, the resulting normalized net heat flux is anticorrelated with plasma beta on all PSP orbits, which is consistent with the operation of collisionless heat flux regulation mechanisms. The net heat flux also decreases in very high beta regions in the vicinity of the heliospheric current sheet, but in most cases of this type the omnidirectional suprathermal electron flux remains at a comparable level or even increases, seemingly inconsistent with disconnection from the Sun. The measured heat flux values appear inconsistent with regulation primarily by collisional mechanisms near the Sun. Instead, the observed heat flux dependence on plasma beta and the distribution of suprathermal electron parameters are both consistent with theoretical instability thresholds associated with oblique whistler and magnetosonic modes. © ESO 2021.
    • Energetic particle behavior in near-Sun magnetic field switchbacks from PSP

      Bandyopadhyay, R.; Matthaeus, W.H.; McComas, D.J.; Joyce, C.J.; Szalay, J.R.; Christian, E.R.; Giacalone, J.; Schwadron, N.A.; Mitchell, D.G.; Hill, M.E.; et al. (EDP Sciences, 2021)
      Context. The observation of numerous magnetic switchbacks and associated plasma jets in Parker Solar Probe (PSP) during its first five orbits, particularly near the Sun, has attracted considerable attention. Switchbacks have been found to be systematically associated with correlated reversals in the direction of the propagation of Alfvénic fluctuations, as well as similar reversals of the electron strahl. Aims. Here we aim to see whether the energetic particles change direction at the magnetic field switchbacks. Methods. We use magnetic field data from the MAG suite's fluxgate magnetometer instrument to identify switchback regions. We examine the radial anisotropy of the energetic particles measured by the EPI-Lo instrument of the IS⊙ IS suite. Results. We find that energetic particles measured by EPI-Lo generally do not preferentially change their directionality from that of the background magnetic field to that of the switchbacks. Conclusions. A reasonable hypothesis is that particles with smaller gyroradii, such as strahl electrons, can reverse direction by following the magnetic field in switchbacks, but that larger gyroradii particles cannot. This provides the possibility of setting a constraint on the radius of the curvature of the magnetic field in switchbacks, a property not otherwise observed by PSP. We expect that particles at higher energies than those detectable by EPI-Lo will also not respond to switchbacks. The observed reversals of radial energetic particle flux are separate phenomena, likely associated with source locations or other propagation effects occurring at greater radial distances. © ESO 2021.
    • Energetic particle evolution during coronal mass ejection passage from 0.3 to 1 AU

      Joyce, C.J.; McComas, D.J.; Schwadron, N.A.; Vourlidas, A.; Christian, E.R.; McNutt, R.L.; Cohen, C.M.S.; Leske, R.A.; Mewaldt, R.A.; Stone, E.C.; et al. (EDP Sciences, 2021)
      We provide analysis of a coronal mass ejection (CME) that passed over Parker Solar Probe (PSP) on January 20, 2020 when the spacecraft was at just 0.32 AU. The Integrated Science Investigation of the Sun instrument suite measures energetic particle populations associated with the CME before, during, and after its passage over the spacecraft. We observe a complex evolution of energetic particles, including a brief ~2 h period where the energetic particle fluxes are enhanced and the nominal orientation of the energetic particle streaming outward from the Sun (from 30 to 100 keV nuc-1) abruptly reverses inward toward the Sun. This transient and punctuated evolution highlights the importance of magnetic field structures that connect the spacecraft to different acceleration sites, one of which is likely more distant from the Sun than PSP during the evolution of the CME. We discuss these characteristics and what they tell us about the source of the energetic particles. During this period, PSP was radially aligned with the Solar Terrestrial Relations Observatory A (STEREO-A), which measured the same CME when it passed 1 AU. The magnetic field measurements at both spacecraft are remarkably similar, indicating that the spacecraft are likely encountering the same portion of the magnetic structure that has not evolved significantly in transit. The energetic particle observations on the other hand, are quite different at STEREO-A, showing how transport effects have acted on the energetic particle populations and obscured the detailed properties present earlier in the development of the CME. This event provides a unique case study in how energetic particle populations evolve as CMEs propagate through the heliosphere. © ESO 2021.
    • Evaluation research using astronomy theatre suggests good promise for young Spanish-origin women to choose science majors

      Corbally, Christopher; Rappaport, Margaret Boone; Univ Arizona, Vatican Observ (EDP Sciences, 2019-02-01)
      We report evaluation findings and best practices from a morning of research with senior class students at an all-Spanish-origin, secondary school in the southwest United States. We found a jump in interest toward science for the women who self-identified as humanities students, and over the morning, surprisingly, this affected their remembrance of previous attitudes. Our results for this and other evaluations corroborate that experiential activities involving one-to-one or group activities are useful in attracting high school and college students to the sciences, especially young women. These results also pointed toward best practices.
    • Evidence for disequilibrium chemistry from vertical mixing in hot Jupiter atmospheres: A comprehensive survey of transiting close-in gas giant exoplanets with warm-Spitzer /IRAC

      Baxter, C.; Désert, J.-M.; Tsai, S.-M.; Todorov, K.O.; Bean, J.L.; Deming, D.; Parmentier, V.; Fortney, J.J.; Line, M.; Thorngren, D.; et al. (EDP Sciences, 2021)
      Aims. We present a large atmospheric study of 49 gas giant exoplanets using infrared transmission photometry with Spitzer/IRAC at 3.6 and 4.5 μm. Methods. We uniformly analyze 70 photometric light curves of 33 transiting planets using our custom pipeline, which implements pixel level decorrelation. Augmenting our sample with 16 previously published exoplanets leads to a total of 49. We use this survey to understand how infrared photometry traces changes in atmospheric chemical properties as a function of planetary temperature. We compare our measurements to a grid of 1D radiative-convective equilibrium forward atmospheric models which include disequilibrium chemistry. We explore various strengths of vertical mixing (Kzz = 0-1012 cm2 s-1) as well as two chemical compositions (1x and 30x solar). Results. We find that, on average, Spitzer probes a difference of 0.5 atmospheric scale heights between 3.6 and 4.5 μm, which is measured at 7.5σ level of significance. Changes in the opacities in the two Spitzer bandpasses are expected with increasing temperature due to the transition from methane-dominated to carbon-monoxide-dominated atmospheres at chemical equilibrium. Comparing the data with our model grids, we find that the coolest planets show a lack of methane compared to expectations, which has also been reported by previous studies of individual objects. We show that the sample of coolest planets rule out 1x solar composition with >3σ confidence while supporting low vertical mixing (Kzz = 108 cm2 s-1). On the other hand, we find that the hot planets are best explained by models with 1x solar metallicity and high vertical mixing (Kzz = 1012 cm2 s-1). We interpret this as the lofting of CH4 to the upper atmospheric layers. Changing the interior temperature changes the expectation for equilibrium chemistry in deep layers, hence the expectation of disequilibrium chemistry higher up. We also find a significant scatter in the transmission signatures of the mid-Temperate and ultra-hot planets, likely due to increased atmospheric diversity, without the need to invoke higher metallicities. Additionally, we compare Spitzer transmission with emission in the same bandpasses for the same planets and find no evidence for any correlation. Although more advanced modelling would test our conclusions further, our simple generic model grid points towards different amounts of vertical mixing occurring across the temperature range of hot Jupiters. This finding also agrees with the observed scatter with increasing planetary magnitude seen in Spitzer/IRAC color-magnitude diagrams for planets and brown dwarfs. © ESO 2021.
    • H-band discovery of additional second-generation stars in the Galactic bulge globular cluster NGC 6522 as observed by APOGEE and Gaia

      Cunha, K.; Univ Arizona, Steward Observ (EDP Sciences, 2019-07-22)
      We present an elemental abundance analysis of high-resolution spectra for five giant stars spatially located within the innermost regions of the bulge globular cluster NGC 6522 and derive Fe, Mg, Al, C, N, O, Si, and Ce abundances based on H-band spectra taken with the multi-object APOGEE-north spectrograph from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. Of the five cluster candidates, two previously unremarked stars are confirmed to have second-generation (SG) abundance patterns, with the basic pattern of depletion in C and Mg simultaneous with enrichment in N and Al as seen in other SG globular cluster populations at similar metallicity. In agreement with the most recent optical studies, the NGC 6522 stars analyzed exhibit (when available) only mild overabundances of the s-process element Ce, contradicting the idea that NGC 6522 stars are formed from gas enriched by spinstars and indicating that other stellar sources such as massive AGB stars could be the primary polluters of intra-cluster medium. The peculiar abundance signatures of SG stars have been observed in our data, confirming the presence of multiple generations of stars in NGC 6522.
    • High gas-to-dust size ratio indicating efficient radial drift in the mm-faint CX Tauri disk

      Facchini, S.; Van Dishoeck, E.F.; Manara, C.F.; Tazzari, M.; Maud, L.; Cazzoletti, P.; Rosotti, G.; Van Der Marel, N.; Pinilla, P.; Clarke, C.J.; et al. (EDP Sciences, 2019)
      The large majority of protoplanetary disks have very compact continuum emission (≲ 15 AU) at millimeter wavelengths. However, high angular resolution observations that resolve these small disks are still lacking, due to their intrinsically fainter emission compared with large bright disks. In this Letter we present 1.3 mm ALMA data of the faint disk (∼10 mJy) orbiting the TTauri star CX Tau at a resolution of ∼40 mas, ∼5 AU in diameter. The millimeter dust disk is compact, with a 68% enclosing flux radius of 14 AU, and the intensity profile exhibits a sharp drop between 10 and 20 AU, and a shallow tail between 20 and 40 AU. No clear signatures of substructure in the dust continuum are observed, down to the same sensitivity level of the DSHARP large program. However, the angular resolution does not allow us to detect substructures on the scale of the disk aspect ratio in the inner regions. The radial intensity profile closely resembles the inner regions of more extended disks imaged at the same resolution in DSHARP, but with no rings present in the outer disk. No inner cavity is detected, even though the disk has been classified as a transition disk from the spectral energy distribution in the near-infrared. The emission of 12CO is much more extended, with a 68% enclosing flux radius of 75 AU. The large difference of the millimeter dust and gas extents (> 5) strongly points to radial drift, and closely matches the predictions of theoretical models. © ESO 2019.
    • Indications for very high metallicity and absence of methane in the eccentric exo-Saturn WASP-117b

      Carone, L.; Mollière, P.; Zhou, Y.; Bouwman, J.; Yan, F.; Baeyens, R.; Apai, D.; Espinoza, N.; Rackham, B.V.; Jordán, A.; et al. (EDP Sciences, 2021)
      We investigate the atmospheric composition of the long-period (Porb = 10 days) eccentric exo-Saturn WASP-117b. WASP-117b could be similar in atmospheric temperature and chemistry to WASP-107b. In mass and radius, WASP-117b is similar to WASP-39b, which allows a comparative study of these planets. Methods. We analyzed a near-infrared transmission spectrum of WASP-117b taken with the Hubble Space Telescope (HST) WFC3 G141, which was reduced with two independent pipelines. High-resolution measurements were taken with VLT/ESPRESSO in the optical. Results. We report the robust (3-) detection of a water spectral feature. In a 1D atmosphere model with isothermal temperature, uniform cloud deck, and equilibrium chemistry, the Bayesian evidence of a retrieval analysis of the transmission spectrum indicates a preference for a high atmospheric metallicity [Fe=H] = 2:58+0:26 -0:37 and clear skies. The data are also consistent with a lower metallicity composition [Fe=H] > 1:75 and a cloud deck between 10-2:2 and 10-5:1 bar, but with weaker Bayesian preference. We retrieve a low CH4 abundance of >10-4 volume fraction within 1 and >2 10-1 volume fraction within 3. We cannot constrain the equilibrium temperature between theoretically imposed limits of 700 and 1000 K. Further observations are needed to confirm quenching of CH4 with Kzz 108 cm2 s-1.We report indications of Na and K in the VLT/ESPRESSO high-resolution spectrum with substantial Bayesian evidence in combination with HST data. © ESO 2021.