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There is evidence that the young Sun emitted a high flux of energetic (⩾10 MeV) particles. The collisions of these particles with the material at the inner edge of the Protosolar Nebula disk induced spallation reactions that formed short-lived radionuclei, like ¹⁰Be, whose trace is now visible in some meteorites. However, it is poorly known exactly when this happened, and whether and how it affected the solar system. Here, we present indirect evidence for an ejection of energetic particles in the young protostar, OMC-2 FIR 4, similar to that experienced by the young solar system. In this case, the energetic particles collide with the material in the protostellar envelope, enhancing the abundance of two molecular ions, HCO⁺ and N₂H⁺, whose presence is detected via Herschel observations. The flux of energetic particles at a distance of 1 AU from the emitting source, estimated from the measured abundance ratio of HCO⁺ and N₂H⁺, can easily account for the irradiation required by meteoritic observations. These new observations demonstrate that the ejection of ⩾10 MeV particles is a phenomenon occurring very early in the life of a protostar, before the disappearance of the envelope from which the future star accretes. The whole envelope is affected by the event, which sets constraints on the magnetic field geometry in the source and opens up the possibility that the spallation reactions are not limited to the inner edge of the Protosolar Nebula disk.

There is intense interest in determining the precise contribution of Alfvénic waves propagating along solar structures to the problems of coronal heating and solar wind acceleration. Since the launch of SDO/AIA, it has been possible to resolve transverse oscillations in off-limb solar polar plumes and recently McIntosh et al. concluded that such waves are energetic enough to play a role in heating the corona and accelerating the fast solar wind. However, this result is based on comparisons to Monte Carlo simulations and confirmation via direct measurements is still outstanding. Thus, this Letter reports on the first direct measurements of transverse wave motions in solar polar plumes. Over a four hour period, we measure the transverse displacements, periods, and velocity amplitudes of 596 distinct oscillations observed in the 171 Å channel of SDO/AIA. We find a broad range of non-uniformly distributed parameter values which are well described by log-normal distributions with peaks at 234 km, 121 s, and 8 km s⁻¹, and mean and standard deviations of 407 ± 297 km, 173 ± 118 s, and 14 ± 10 km s⁻¹. Within standard deviations, our direct measurements are broadly consistent with previous results. However, accounting for the whole of our observed non-uniform parameter distribution we calculate an energy flux of 9–24 W m⁻², which is 4–10 times below the energy requirement for solar wind acceleration. Hence, our results indicate that transverse magnetohydrodynamic waves as resolved by SDO/AIA cannot be the dominant energy source for fast solar wind acceleration in the open-field corona.

Short-duration gamma-ray bursts (sGRBs) are widely believed to result from the mergers of compact binaries. This model predicts an afterglow that bears the characteristic signatures of a constant, low-density medium, including a smooth prompt-afterglow transition, and a simple temporal evolution. However, these expectations are in conflict with observations for a non-negligible fraction of sGRB afterglows. In particular, the onset of the afterglow phase for some of these events appears to be delayed and, in addition, a few of them exhibit late-time rapid fading in their light curves. We show that these peculiar observations can be explained independently of ongoing central engine activity if some sGRB progenitors are compact binaries hosting at least one pulsar. The Poynting flux emanating from the pulsar companion can excavate a bow-shock cavity surrounding the binary. If this cavity is larger than the shock deceleration length scale in the undisturbed interstellar medium, then the onset of the afterglow will be delayed. Should the deceleration occur entirely within the swept-up thin shell, a rapid fade in the light curve will ensue. We identify two types of pulsar that can achieve the conditions necessary for altering the afterglow: low-field, long-lived pulsars, and high-field pulsars. We find that a sizable fraction (≈20%–50%) of low-field pulsars are likely to reside in neutron star binaries based on observations, while their high-field counterparts are not. Hydrodynamical calculations motivated by this model are shown to be in good agreement with observations of sGRB afterglow light curves.

We found that a surge consists of multiple shock features. In our high-spatiotemporal spectroscopic observation of the surge, each shock is identified with the sudden appearance of an absorption feature at the blue wings of the Ca ii 8542 Å line and Hα line that gradually shifts to the red wings. The shock features overlap with one another with the time interval of 110 s, which is much shorter than the duration of each shock feature, 300–400 s. This finding suggests that the multiple shocks might not have originated from a train of sinusoidal waves generated by oscillations and flows in the photosphere. As we found the signature of the magnetic flux cancelations at the base of the surge, we conclude that the multiple shock waves in charge of the surge were generated by the magnetic reconnection that occurred in the low atmosphere in association with the flux cancelation.

We report on the discovery of the most distant Milky Way (MW) stars known to date: ULAS J001535.72+015549.6 and ULAS J074417.48+253233.0. These stars were selected as M giant candidates based on their infrared and optical colors and lack of proper motions. We spectroscopically confirmed them as outer halo giants using the MMT/Red Channel spectrograph. Both stars have large estimated distances, with ULAS J001535.72+015549.6 at 274 ± 74 kpc and ULAS J074417.48+253233.0 at 238 ± 64 kpc, making them the first MW stars discovered beyond 200 kpc. ULAS J001535.72+015549.6 and ULAS J074417.48+253233.0 are both moving away from the Galactic center at 52 ± 10 km s⁻¹ and 24 ± 10 km s⁻¹, respectively. Using their distances and kinematics, we considered possible origins such as: tidal stripping from a dwarf galaxy, ejection from the MW's disk, or membership in an undetected dwarf galaxy. These M giants, along with two inner halo giants that were also confirmed during this campaign, are the first to map largely unexplored regions of our Galaxy's outer halo.

We present an analysis of the fast coronal mass ejection (CME) of 2012  March 7, which was imaged by both STEREO spacecraft and observed in situ by MESSENGER, Venus Express, Wind, and Mars Express. Based on detected arrivals at four different positions in interplanetary space, it was possible to strongly constrain the kinematics and the shape of the ejection. Using the white-light heliospheric imagery from STEREO-A and B, we derived two different kinematical profiles for the CME by applying the novel constrained self-similar expansion method. In addition, we used a drag-based model to investigate the influence of the ambient solar wind on the CME's propagation. We found that two preceding CMEs heading in different directions disturbed the overall shape of the CME and influenced its propagation behavior. While the Venus-directed segment underwent a gradual deceleration (from ∼2700 km s⁻¹ at 15 R_☉ to ∼1500 km s⁻¹ at 154 R_☉), the Earth-directed part showed an abrupt retardation below 35 R_☉ (from ∼1700 to ∼900 km s⁻¹). After that, it was propagating with a quasi-constant speed in the wake of a preceding event. Our results highlight the importance of studies concerning the unequal evolution of CMEs. Forecasting can only be improved if conditions in the solar wind are properly taken into account and if attention is also paid to large events preceding the one being studied.

Sharp chemical discontinuities can occur in protoplanetary disks, particularly at "snow lines" where a gas-phase species freezes out to form ice grains. Such sharp discontinuities will diffuse out due to the turbulence suspected to drive angular momentum transport in accretion disks. We demonstrate that the concentration gradient—in the vicinity of the snow line—of a species present outside a snow line but destroyed inside is strongly sensitive to the level of turbulent diffusion (provided the chemical and transport timescales are decoupled) and provides a direct measurement of the radial "Schmidt number" (the ratio of the angular momentum transport to radial turbulent diffusion). Taking as an example the tracer species N₂H⁺, which is expected to be destroyed inside the CO snow line (as recently observed in TW Hya) we show that ALMA observations possess significant angular resolution to constrain the Schmidt number. Since different turbulent driving mechanisms predict different Schmidt numbers, a direct measurement of the Schmidt number in accretion disks would allow inferences to be made about the nature of the turbulence.

As new large-scale astronomical surveys greatly increase the number of objects targeted and discoveries made, the requirement for efficient follow-up observations is crucial. Adaptive optics imaging, which compensates for the image-blurring effects of Earth's turbulent atmosphere, is essential for these surveys, but the scarcity, complexity and high demand of current systems limit their availability for following up large numbers of targets. To address this need, we have engineered and implemented Robo-AO, a fully autonomous laser adaptive optics and imaging system that routinely images over 200 objects per night with an acuity 10 times sharper at visible wavelengths than typically possible from the ground. By greatly improving the angular resolution, sensitivity, and efficiency of 1–3 m class telescopes, we have eliminated a major obstacle in the follow-up of the discoveries from current and future large astronomical surveys.

We conduct simulations of turbulent mixing in the presence of a magnetic field, grown by the small-scale dynamo. We show that the scalar gradient field, ∇C, which must be large for diffusion to operate, is strongly biased perpendicular to the magnetic field, B. This is true both early on, when the magnetic field is negligible, and at late times, when the field is strong enough to back react on the flow. This occurs because ∇C increases within the plane of a compressive motion, but B increases perpendicular to it. At late times, the magnetic field resists compression, making it harder for scalar gradients to grow and likely slowing mixing.

Using photometry from Data Release 10 of the northern footprint of the Sloan Digital Sky Survey, we detect two new stellar streams with lengths of between 25° and 50°. The streams, which we designate Hermus and Hyllus, are at distances of between 15 and 23 kpc from the Sun and pass primarily through Hercules and Corona Borealis. Stars in the streams appear to be metal-poor, with [Fe/H]   ∼   − 2.3, though we cannot rule out metallicities as high as [Fe/H] = −1.2. While Hermus passes within 1° (in projection) of the globular cluster NGC 6229, a roughly one magnitude difference in distance modulus, combined with no signs of connecting with NGC 6229's Roche lobe, argue against any physical association between the two. Though the two streams almost certainly had different progenitors, similarities in preliminary orbit estimates suggest that those progenitors may themselves have been a product of a single accretion event.

Stellar activity can produce large amounts of high-energy radiation, which is absorbed by the planetary atmosphere leading to irradiation-driven mass loss. We present the detection and an investigation of high-energy emission in a transiting super-Earth host system, GJ 1214, based on XMM-Newton observations. We derive an X-ray luminosity of L_X = 7.4 × 10²⁵ erg s⁻¹ and a corresponding activity level of log (L_X/L_bol) ∼ −5.3. Further, we determine a coronal temperature of about ∼3.5 MK, which is typical for coronal emission of moderately active low-mass stars. We estimate that GJ 1214 b evaporates at a rate of 1.3× 10¹⁰ g s⁻¹ and has lost a total of ≈2–5.6 M_⊕.

Using statistically significant data at 1 AU, it has recently been shown (Bale et al.) that in the solar wind, when the Knudsen number K_T (the ratio between the electron mean free path and the electron temperature scale height) drops below about 0.3, the electron heat flux q intensity rapidly approaches the classical collisional Spitzer–Härm limit. Using a fully kinetic model including the effect of Coulomb collisions and the expansion of the solar wind with heliocentric distance, we observe that the heat flux strength does indeed approach the collisional value for Knudsen numbers smaller than about 0.3 in very good agreement with the observations. However, closer inspection of the heat flux properties, such as its variation with the heliocentric distance and its dependence on the plasma parameters, shows that for Knudsen numbers between 0.02 and 0.3 the heat flux is not conveniently described by the Spitzer–Härm formula. We conclude that even though observations at 1 AU seem to indicate that the electron heat flux intensity approaches the collisional limit when the Knudsen drops below ∼0.3, the collisional limit is not a generally valid closure for a Knudsen larger than 0.01. Moreover, the good agreement between the heat flux from our model and the heat flux from solar wind measurements in the high-Knudsen number regime seems to indicate that the heat flux at 1 AU is not constrained by electromagnetic instabilities as both wave–particle and wave–wave interactions are neglected in our calculations.

We present a study of the 2014 January 6 solar energetic particle event which produced a small ground level enhancement (GLE), making it the second GLE of this unusual solar cycle 24. This event was primarily observed by the South Pole neutron monitors (increase of ∼2.5%) while a few other neutron monitors recorded smaller increases. The associated coronal mass ejection (CME) originated behind the western limb and had a speed of 1960 km s⁻¹. The height of the CME at the start of the associated metric type II radio burst, which indicates the formation of a strong shock, was measured to be 1.61 Rs using a direct image from STEREO-A/EUVI. The CME height at the time of the GLE particle release (determined using the South Pole neutron monitor data) was directly measured as 2.96 Rs based on STEREO-A/COR1 white-light observations. These CME heights are consistent with those obtained for GLE71, the only other GLE of the current cycle, as well as cycle-23 GLEs derived using back-extrapolation. GLE72 is of special interest because it is one of only two GLEs of cycle 24, one of two behind-the-limb GLEs, and one of the two smallest GLEs of cycles 23 and 24.

We investigate the shock acceleration of particles in massive galaxy mergers or collisions, and show that cosmic rays (CRs) can be accelerated up to the second knee energy ∼0.1–1 EeV and possibly beyond, with a hard spectral index of Γ ≈ 2. Such CRs lose their energy via hadronuclear interactions within a dynamical timescale of the merger shock, producing gamma rays and neutrinos as a by-product. If ∼10% of the shock dissipated energy goes into CR acceleration, some local merging galaxies will produce gamma-ray counterparts detectable by the Cherenkov Telescope Array. Also, based on the concordance cosmology, where a good fraction of the massive galaxies experience a major merger in a cosmological timescale, the neutrino counterparts can constitute ∼20%–60% of the isotropic background detected by IceCube.