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The most powerful explosions on the Sun – in the form of bright flares, intense storms of solar energetic particles (SEPs), and fast coronal mass ejections (CMEs) – drive the most severe space‐weather storms. Proxy records of flare energies based on SEPs in principle may offer the longest time base to study infrequent large events. We conclude that one suggested proxy, nitrate concentrations in polar ice cores, does not map reliably to SEP events. Concentrations of select radionuclides measured in natural archives may prove useful in extending the time interval of direct observations up to ten millennia, but as their calibration to solar flare fluences depends on multiple poorly known properties and processes, these proxies cannot presently be used to help determine the flare energy frequency distribution. Being thus limited to the use of direct flare observations, we evaluate the probabilities of large‐energy solar events by combining solar flare observations with an ensemble of stellar flare observations. We conclude that solar flare energies form a relatively smooth distribution from small events to large flares, while flares on magnetically active, young Sun‐like stars have energies and frequencies markedly in excess of strong solar flares, even after an empirical scaling with the mean coronal activity level of these stars. In order to empirically quantify the frequency of uncommonly large solar flares extensive surveys of stars of near‐solar age need to be obtained, such as is feasible with the Kepler satellite. Because the likelihood of flares larger than approximately X30 remains empirically unconstrained, we present indirect arguments, based on records of sunspots and on statistical arguments, that solar flares in the past four centuries have likely not substantially exceeded the level of the largest flares observed in the space era, and that there is at most about a 10% chance of a flare larger than about X30 in the next 30 years. Key Points Solar, stellar, lunar, and terrestrial data need to be combined Radionuclide data and ice cores do not tell us much about largest solar flares We argue for an upper limit for the largest solar flares of about X30

Radio detections of stellar systems provide a window onto stellar magnetic activity and the space weather conditions of extrasolar planets — information that is difficult to obtain at other wavelengths. The maturation of low-frequency radio instruments and the plethora of wide-field radio surveys have driven recent advances in observing auroral emissions from radio-bright low-mass stars and exoplanets. To guide us in putting these recent results in context, we introduce the foremost local analogues for the field: solar bursts and the aurorae found on Jupiter. We detail how radio bursts associated with stellar flares are foundational to the study of stellar coronae, and time-resolved radio dynamic spectra offer one of the best prospects for detecting and characterizing coronal mass ejections from other stars. We highlight the possibility of directly detecting coherent radio emission from exoplanetary magnetospheres, as well as early tentative results. We bridge this discussion with the field of brown dwarf radio emission — the larger and stronger magnetospheres of these stars are amenable to detailed study with current instruments. Bright, coherent radio emission is also predicted from magnetic interactions between stars and close-in planets. We discuss the underlying physics of these interactions and the implications of recent provisional detections for exoplanet characterization. We conclude with an overview of outstanding questions in the theory of stellar, star–planet interaction and exoplanet radio emission and the potential of future facilities to answer them. The maturation of low-frequency radio astronomy instruments has further opened the magnetic environment of stars to investigation, yielding indications of star–planet interactions and coronal mass ejections in stellar systems other than our own.

The heating mechanism at high densities during M-dwarf flares is poorly understood. Spectra of M-dwarf flares in the optical and near-ultraviolet wavelength regimes have revealed three continuum components during the impulsive phase: 1) an energetically dominant blackbody component with a color temperature of T ≈ 10 4 K in the blue-optical, 2) a smaller amount of Balmer continuum emission in the near-ultraviolet at λ ≤ 3 646  Å, and 3) an apparent pseudo-continuum of blended high-order Balmer lines between λ = 3 646  Å and λ ≈ 3 900  Å. These properties are not reproduced by models that employ a typical “solar-type” flare heating level of ≤ 10 11 erg cm − 2 s − 1 in nonthermal electrons, and therefore our understanding of these spectra is limited to a phenomenological three-component interpretation. We present a new 1D radiative-hydrodynamic model of an M-dwarf flare from precipitating nonthermal electrons with a high energy flux of 10 13 erg cm − 2 s − 1 . The simulation produces bright near-ultraviolet and optical continuum emission from a dense ( n > 10 15 cm − 3 ), hot ( T ≈ 12 000 – 13 500 K ) chromospheric condensation. For the first time, the observed color temperature and Balmer jump ratio are produced self-consistently in a radiative-hydrodynamic flare model. We find that a T ≈ 10 4 K blackbody-like continuum component and a low Balmer jump ratio result from optically thick Balmer ( ∞ → n = 2 ) and Paschen recombination ( ∞ → n = 3 ) radiation, and thus the properties of the flux spectrum are caused by blue ( λ ≈ 4 300  Å) light escaping over a larger physical depth range than by red ( λ ≈ 6 700  Å) and near-ultraviolet ( λ ≈ 3 500  Å) light. To model the near-ultraviolet pseudo-continuum previously attributed to overlapping Balmer lines, we include the extra Balmer continuum opacity from Landau–Zener transitions that result from merged, high-order energy levels of hydrogen in a dense, partially ionized atmosphere. This reveals a new diagnostic of ambient charge density in the densest regions of the atmosphere that are heated during dMe and solar flares.

The search for life in the Universe is a fundamental problem of astrobiology and modern science. The current progress in the detection of terrestrial-type exoplanets has opened a new avenue in the characterization of exoplanetary atmospheres and in the search for biosignatures of life with the upcoming ground-based and space missions. To specify the conditions favourable for the origin, development and sustainment of life as we know it in other worlds, we need to understand the nature of global (astrospheric), and local (atmospheric and surface) environments of exoplanets in the habitable zones (HZs) around G-K-M dwarf stars including our young Sun. Global environment is formed by propagated disturbances from the planet-hosting stars in the form of stellar flares, coronal mass ejections, energetic particles and winds collectively known as astrospheric space weather. Its characterization will help in understanding how an exoplanetary ecosystem interacts with its host star, as well as in the specification of the physical, chemical and biochemical conditions that can create favourable and/or detrimental conditions for planetary climate and habitability along with evolution of planetary internal dynamics over geological timescales. A key linkage of (astro)physical, chemical and geological processes can only be understood in the framework of interdisciplinary studies with the incorporation of progress in heliophysics, astrophysics, planetary and Earth sciences. The assessment of the impacts of host stars on the climate and habitability of terrestrial (exo)planets will significantly expand the current definition of the HZ to the biogenic zone and provide new observational strategies for searching for signatures of life. The major goal of this paper is to describe and discuss the current status and recent progress in this interdisciplinary field in light of presentations and discussions during the NASA Nexus for Exoplanetary System Science funded workshop ‘Exoplanetary Space Weather, Climate and Habitability’ and to provide a new roadmap for the future development of the emerging field of exoplanetary science and astrobiology.

The Cosmic Origins Spectrograph (COS) was installed in the Hubble Space Telescope in May, 2009 as part of Servicing Mission 4 to provide high sensitivity, medium and low resolution spectroscopy at far- and near-ultraviolet wavelengths (FUV, NUV). COS is the most sensitive FUV/NUV spectrograph flown to date, spanning the wavelength range from 900 Å to 3200 Å with peak effective area approaching 3000 cm 2 . This paper describes instrument design, the results of the Servicing Mission Orbital Verification (SMOV), and the ongoing performance monitoring program.

Solar coronal dimmings have been observed extensively in the past two decades and are believed to have close association with coronal mass ejections (CMEs). Recent study found that coronal dimming is the only signature that could differentiate powerful flares that have CMEs from those that do not. Therefore, dimming might be one of the best candidates to observe the stellar CMEs on distant Sun-like stars. In this study, we investigate the possibility of using coronal dimming as a proxy to diagnose stellar CMEs. By simulating a realistic solar CME event and corresponding coronal dimming using a global magnetohydrodynamics model (AWSoM: Alfvén-wave Solar Model), we first demonstrate the capability of the model to reproduce solar observations. We then extend the model for simulating stellar CMEs by modifying the input magnetic flux density as well as the initial magnetic energy of the CME flux rope. Our result suggests that with improved instrument sensitivity, it is possible to detect the coronal dimming signals induced by the stellar CMEs.

Background: Internationally, the roles of Community Health Workers, also known as Community Health Navigators (CHNs), have been developed as an intervention to improve the transition of people to their homes following a hospital admission. Generally, CHNs are trusted members of the communities they serve. This trusting relationship enables them to serve as a link between health services, social services and the community to facilitate access and improve the quality and cultural competence of service delivery. Research has found that CHNs can reduce barriers to access for marginalised communities, identify emerging needs, and can make health services more responsive. The CHN’s are employed by the Sydney Local Health District and are embedded within the Planned Care team under the governance of the Aged Health Rehabilitation and Chronic Care Clinical Stream. This trial aims to evaluate the impact of CHNs who support people with chronic conditions to transition from hospital to their homes. The CHNs are employed by a Local Health District and embedded within the health service. The trial, which is currently underway, will evaluate the impact of a CHN intervention’s on 60-day unplanned hospital readmission, medication adherence, health literacy, quality of life, experience of health care and health service use, compared to usual care. Implementation of the navigator role will also be qualitatively appraised, incorporating data from patients, health professionals and the navigators themselves. Trial population: Patients aged over 40 years and living with chronic health conditions in a Local Health District in Sydney, Australia.   Engagement: This trial is underpinned and guided by a multi-stakeholder partnership of health planners, primary healthcare providers, and consumers. These stakeholders have joined in co-designing this study to evaluate the effectiveness and cost of CHN follow-up of patients after discharge as a key strategy in preventing re-hospitalisation, and to develop the CHN roles and functions. What we are doing: This parallel group, pragmatic RCT design will randomly allocate patients after hospital discharge to the CHN intervention or usual care arm. Comparison of outcomes will be made between intervention and control groups. Results: This RCT is currently underway. Interviews with 27 health staff and a co-design process with 18 participants have informed the development of the CHN roles and the implementation of the trial. Codesign participants were generally enthusiastic about the potential of the CHNs, but there were concerns about how these roles could fit within existing services and supervision arrangements, and the CHNs’ competence to fulfil their roles. A detailed CHN training program was developed with emphases on communication, rapport-building, services that can be referred to, and supervision arrangements. Three CHNs are currently employed. Lessons: This study includes an intervention embedded in a real-world healthcare setting. The co-design process enabled the CHN roles to be well-described and to have the potential to meet the needs of the study population and to be responsive to service stakeholders. The CHN are integrated into existing health service structures and processes, and are embedded in an established outreach team. Next steps: Reporting on study.

The Very Large Array Sky Survey (VLASS) is a synoptic, all-sky radio sky survey with a unique combination of high angular resolution ( 2 5), sensitivity (a 1 goal of 70 Jy/beam in the coadded data), full linear Stokes polarimetry, time domain coverage, and wide bandwidth (2-4 GHz). The first observations began in 2017 September, and observing for the survey will finish in 2024. VLASS will use approximately 5500 hr of time on the Karl G. Jansky Very Large Array (VLA) to cover the whole sky visible to the VLA (decl. > −40°), a total of 33 885 deg 2 . The data will be taken in three epochs to allow the discovery of variable and transient radio sources. The survey is designed to engage radio astronomy experts, multi-wavelength astronomers, and citizen scientists alike. By utilizing an \"on the fly\" interferometry mode, the observing overheads are much reduced compared to a conventional pointed survey. In this paper, we present the science case and observational strategy for the survey, and also results from early survey observations.

We aim at advancing our understanding of magnetic activity and the underlying dynamo mechanism at the end of the main-sequence. To this end, we collected simultaneous X-ray and radio observations for a sample of M7-L0 dwarfs using XMM-Newton jointly with the JVLA and the ATCA. We also included data from the all-sky surveys of eROSITA on board the Russian Spektrum-Roentgen-Gamma mission (SRG) and rotation periods from TESS together with an archival compilation of X-ray and radio data for UCDs from the literature. We limit the sample to objects with rotation period <1d, focusing on the study of a transition in magnetic behavior suggested by a drastic change in the radio detection rate at vsini 38 km/s. We compiled the most up-to-date radio/X-ray luminosity relation for 26 UCDs with rotation periods lower than 1d, finding that rapid rotators lie the furthest away from the Güdel-Benz relation previously studied for earlier-type stars. Radio bursts are mainly experienced by very fast UCDs, while X-ray flares are seen along the whole range of rotation. We examined the L_ x/L_ bol vs P_ rot relation, finding no evident relation between the X-ray emission and rotation, reinforcing previous speculations on a bimodal dynamo across late-type dwarfs. One radio-detected object has a rotation period consistent with the range of auroral bursting sources; while it displays moderately circularly polarized emission. A radio flare from this object is interpreted as gyrosynchrotron emission, and it displays X-ray and optical flares. We also found a slowly rotating apparent auroral emitter, that is also one of the X-ray brightest radio-detected UCDs. We speculate that this UCD is experiencing a transition of its magnetic behavior since it produces signatures expected from higher mass M dwarfs along with emerging evidence of auroral emission.

New data acquired on the active, cool binary CC Eri ranged across the spectrum from Chandra X-ray to broadband photometry and microwave observations using the VLA and ATCA. Also, high-dispersion spectropolarimetry using the AAT enabled Zeeman-Doppler imaging to be performed. Our interpretations infer strong localised concentrations of the stellar magnetic field, manifested by surface activity and related large coronal plasma structures. Comprehensive matching of the modelling parameters awaits more detailed investigation. This brief interim review includes consideration of the ATCA data. Microwave radio emission is usually low level ('quiescent'), but occasionally flares of several mJy peak intensity are observed. We associate the emission, generally, with wave-like mechanisms, expanding through the outer atmosphere. Related characteristics of this emission are discussed.