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Spectropolarimetic campaigns have established that large-scale magnetic fields are present at the surfaces of approximately 10% of massive dwarf stars. However, there is a dearth of magnetic field measurements for their deep interiors. Asteroseismology of gravity-mode pulsations combined with rotating magneto-hydrodynamical calculations of the early-B main-sequence star HD 43317 constrain its magnetic field strength to be approximately 5 × 105 G just outside its convective core. This proof-of-concept study for magneto-asteroseismology opens a new window into the observational characterisation of magnetic fields inside massive stars. [ABSTRACT FROM AUTHOR]

We present the results of a systematic search of the Transiting Exoplanet Survey Satellite (TESS) 2-min cadence data for new rapidly oscillating Ap (roAp) stars observed during the Cycle 2 phase of its mission. We find seven new roAp stars previously unreported as such and present the analysis of a further 25 roAp stars that are already known. Three of the new stars show multiperiodic pulsations, while all new members are rotationally variable stars, leading to almost 70 per cent (22) of the roAp stars presented being α2 CVn-type variable stars. We show that targeted observations of known chemically peculiar stars are likely to overlook many new roAp stars, and demonstrate that multiepoch observations are necessary to see pulsational behaviour changes. We find a lack of roAp stars close to the blue edge of the theoretical roAp instability strip, and reaffirm that mode instability is observed more frequently with precise, space-based observations. In addition to the Cycle 2 observations, we analyse TESS data for all-known roAp stars. This amounts to 18 further roAp stars observed by TESS. Finally, we list six known roAp stars that TESS is yet to observe. We deduce that the incidence of roAp stars amongst the Ap star population is just 5.5  per cent, raising fundamental questions about the conditions required to excite pulsations in Ap stars. This work, coupled with our previous work on roAp stars in Cycle 1 observations, presents the most comprehensive, homogeneous study of the roAp stars in the TESS nominal mission, with a collection of 112 confirmed roAp stars in total. [ABSTRACT FROM AUTHOR]

The ESA/KU Leuven CubeSpec mission is specifically designed to provide low-cost space-based high-resolution optical spectroscopy. Here we highlight the science requirements and capabilities of CubeSpec. The primary science goal is to perform pulsation mode identification from spectroscopic line profile variability and empower asteroseismology of massive stars. [ABSTRACT FROM AUTHOR]

A helium‐filled mylar balloon carrying a smartphone and infrasound sensors ascended to a stratospheric height of 35 km over the surface detonation of a chemical explosive, with a total acoustic propagation distance of 127 km. The smartphone was configured to collect multi‐modal data at high rates from internal sensors. Analysis of the data shows successful collection of the explosion signal by both the smartphone's microphone and its accelerometers, the first from an ascending balloon. Comparison of the acoustic signal with that collected by other infrasound sensors, both airborne and ground‐based, provides insight into the possibilities and limitations of collecting acoustic data from the stratosphere. Plain Language Summary: A surface chemical explosion was observed by pressure and acceleration sensors suspended from an ascending free‐floating balloon at a height of 35 km and a total propagation distance of 127 km from the blast. The balloon's sensor package included a smartphone collecting different types of data (including audio, acceleration, and position), as well as more traditional infrasound and location sensors. The explosion signal was observed by the airborne pressure and vertical accelerometer sensors, as well as by surface‐deployed traditional and smartphone pressure and acceleration sensors. The blast signatures recorded by the airborne and ground‐based stations are compared to provide insight into the present capabilities, limitations, and possible improvements to future balloon‐borne collections of seismo‐acoustic signatures on Earth and beyond. Key Points: Explosion signals were captured using acoustic sensors in an ascending balloon at a height of 35 km and a propagation distance of 127 kmThe signal was briefly trapped in the troposphere before escaping into the stratosphereAccelerometers can distinguish acoustic signals from wind noise on ascending balloons [ABSTRACT FROM AUTHOR]

The Sound Fixing and Ranging (SOFAR) channel in the ocean allows for low frequency sound to travel thousands of kilometers, making it particularly useful for detecting underwater nuclear explosions. Suggestions that an elevated SOFAR‐like channel should exist in the stratosphere date back over half a century and imply that sources within this region can be reliably sensed at vast distances. However, this theory has not been supported with evidence of direct observations from sound within this channel. Here we show that an infrasound sensor on a solar hot air balloon recorded the first infrasound detection of a ground truth airborne source while within this acoustic channel, which we refer to as the AtmoSOFAR channel. Our results support the existence of the AtmoSOFAR channel, demonstrate that acoustic signals can be recorded within it, and provide insight into the characteristics of recorded signals. Results also show a lack of detections on ground‐based stations, highlighting the advantages of using balloon‐borne infrasound sensors to detect impulsive sources at altitude. Plain Language Summary: A layer exists in the ocean that allows sound to travel great distances. Something like this could exist in our atmosphere, too, but until now no one had verified this. Low frequency sound, known as infrasound, travels efficiently through the atmosphere. Specialized instruments, called infrasound sensors, are microphones that can record low frequency sound. We attached an infrasound sensor to a solar hot air balloon to make the first recording of a known object within the theorized atmospheric layer. Our results show that this layer exists, sound can be recorded within it, and analysis can give us more information about what generated that sound. The rocket launch was not well recorded by infrasound sensors on the ground, highlighting the advantages of our method for detecting objects that travel through this region of the atmosphere. Key Points: First direct observation of an elevated acoustic duct using an airborne acoustic source and receiverDetections provide insight into the characteristics of signals from ascending and descending supersonic objectsLack of detections on ground‐based stations highlights the advantages of using balloon‐borne sensors to detect sources at altitude [ABSTRACT FROM AUTHOR]

It is difficult to demonstrate the soil water retention relationship and related concepts because the specialized equipment required for performing these measurements is unavailable in most classrooms. This article outlines a low-cost, easily visualized method by which these concepts can be demonstrated in most any classroom. Columns (62.5 cm tall) were constructed using 25, 2.5 cm tall sections of 7.62-cm (3-inch) i.d. polyvinyl chloride pipe, which were connected using transparent tape. Three different soil materials were packed to specified bulk densities in the columns, and saturated with water. These vertical columns were then allowed to drain into a simulated water table 2.5 cm above the bottom of the soil volume until drainage ceased. After drainage, columns were sectioned to determine water content distribution with depth along the column. It was assumed that matric potential was inversely related to height above the water table. Therefore, water content measurements and assumed potentials for each section provided data for a water retention curve with minimum potential of approximately -60 cm. During drainage, measurements of soil matric potential were taken at regular intervals using tensiometers installed within the column, validating assumptions about matric potential. Among soil materials tested, those with narrow particle-size distributions, [approximately]100% sand, gave the widest distribution of water contents in the observed matric potential ranges. This method, with proper explanation and execution, may be a valuable learning tool by which visual, auditory, and kinesthetic learners may be better able to understand the concepts pertaining to soil-water retention relationships. (Contains 1 table and 5 figures.)

Earth's ionosphere has long been targeted as a medium for remote sensing of explosive terrestrial events such as earthquakes, volcanic eruptions, and nuclear/conventional weapon detonations. Until now, the only confirmed ionospheric detections have been of very large events that were easily detectable through other traditional global sensor systems (e.g., seismic). We present the first clear, confirmed detections of relatively low yield 1‐ton TNT‐equivalent chemical explosions using pulsed Doppler radar observations of isodensity layers in the ionospheric E region. The shape and spectra of the detected waveforms closely match predictions from the acoustic ray tracing and weakly nonlinear waveform propagation models. The explosions were roughly three orders of magnitude lower yield than any previous confirmed ionospheric detection and represent the first conclusive evidence that explosions of this size can have clear impacts on the ionosphere. This technique could improve the remote detection of both anthropogenic and natural explosive events. Plain Language Summary: Explosions, even of modest yield, generate copious amounts of acoustic waves across a wide range of frequencies. While the high frequencies are quickly absorbed by the atmosphere, the lowest frequencies, in the sub‐audible infrasound part of the spectrum, are capable of traveling to great distances. Typically this infrasound is detected on the ground using highly sensitive listening equipment such as microbarometers. We present a different method, however, where we utilize the fact that the upper atmosphere is ionized (the ionosphere) and is therefore a good target for a radar. As the sound wave passes through the ionosphere it sloshes the bulk ions such that it shows up an oscillating radar target. We use this new technique to clearly detect explosions with yields of 1‐ton TNT equivalent. These detections are 500 times smaller than previous confirmed detections using the ionosphere as a sensor for explosions. Key Points: Infrasound from 1‐ton TNT‐equivalent chemical explosions are clearly detectable using pulsed Doppler radar of the ionosphereObservations match the modeled temporal and spectral predictions of infrasound propagationStrong azimuthal differences in waveform shape and strength could be caused by uneven terrain or complex wind fields [ABSTRACT FROM AUTHOR]

Context. Thanks to the high-precision photometry from space missions such as Kepler and TESS, tidal perturbations and tilting of pulsations have been detected in more than a dozen binary systems. However, only two of these were gravity-mode (g-mode) pulsators. Aims. We aim to detect tidally perturbed g modes in additional binary systems and characterise them observationally. Methods. We performed a custom data reduction of the available Kepler and TESS photometry of a well-studied, published sample of 35 binary systems with γ Doradus (γ Dor) pulsators. For each target, we modelled the binary signal using a sum of 100 sine waves with frequencies at orbital harmonics and measured significant pulsation frequencies in an iterative pre-whitening analysis of the residual light curve. Pulsations are labelled as tidally perturbed g modes if they are part of both period-spacing patterns and multiplets spaced by integer multiples of the orbital frequency. After visual inspection and confirmation, the properties of these targets and g modes were characterised. Results. We detect tidally perturbed g-mode pulsations for five short-period binaries that are circularised and (almost) synchronously rotating: KIC 3228863, KIC 3341457, KIC 4947528, KIC 9108579, and KIC 12785282. Tidally perturbed g modes that occur within the same star and have the same mode identification (k, m), are found to have near-identical relative amplitude and phase modulations, which are within their respective 1 − σ uncertainties and also identical for the Kepler and TESS photometric passbands. By contrast, pulsations with different mode identifications (k, m) are found to exhibit different modulations. Moreover, the observed amplitude and phase modulations are correlated, indicating that the binary tides primarily distort the g-mode amplitudes on the stellar surface. The phase modulations are then primarily a geometric effect of the integration of the stellar flux over the visible stellar surface. All selected binaries also exhibit signal that resembles rotational modulation in the Fourier domain. In the case of KIC 3228863, this is caused by the presence of the known tertiary component, and for the other systems we hypothesise that it is caused by temperature variations on the stellar surface. Alternatively, the signal can be made up of overstable convective modes in the stellar core or may belong to the non-pulsating companion. Conclusions. While g-mode pulsation periods are known to be a direct probe of the deep interior stellar structure, the binary tides that cause the pulsation modulations are dominant in the outer stellar layers. Hence, in the future, tidally perturbed g modes may allow us to carry out core-to-surface asteroseismic modelling of tidally distorted stars. [ABSTRACT FROM AUTHOR]

Since the end of 2018, the Transiting Exoplanet Survey Satellite (TESS) has provided stellar photometry to the astronomical community. We have used TESS data to study rotational modulation in the light curves of a sample of chemically peculiar stars with measured large-scale magnetic fields (mCP stars). In general, mCP stars show inhomogeneous distributions of elements in their atmospheres that lead to spectroscopic (line profile) and photometric (light curve) variations commensurate with the rotational period. We analyzed the available TESS data from 50 sectors for eight targets after post-processing them in order to minimize systematic instrumental trends. Analysis of the light curves allowed us to determine rotational periods for all eight of our targets. For each star, we provide a phase diagram calculated using the derived period from the light curves and from the available measurements of the disc-averaged longitudinal magnetic field 〈 B z〉. In most cases, the phased light curve and 〈 B z〉 measurements show consistent variability. Using our rotation periods, and global stellar parameters derived from fitting Balmer line profiles, and from Geneva and Strömgren–Crawford photometry, we determined the equatorial rotational velocities and calculated the respective critical rotational fractions v eq/ v crit. We have shown from our sample that the critical rotational fraction decreases with stellar age, at a rate consistent with the magnetic braking observed in the larger population of mCP stars. [ABSTRACT FROM AUTHOR]

Studies on the circumstellar structures around evolved stars provide vital information on the evolution of the parent star and the properties of the local interstellar medium. In this work, we present the discovery and characterization of an optical cocoon tail behind the star HD 185806. The cocoon apex emission is puzzling, as it is detected in the infrared but shows no signal in the optical wavelength. The H α and [O  iii ]  fluxes of the nebular structure vary from 2.7 to 8.5 × 10−12 erg s−1 cm−2 and from 0.9 to 7.0 × 10−13 erg s−1 cm−2, respectively. Through high-resolution spectroscopy, we derive the spectral type of the star, construct the position–velocity diagrams of the cocoon tail for the H α, [O  iii ], and [N  ii ] emission lines, and determine its velocity in the range of −100–40 km s−1. Furthermore, we use SED fitting and mesa evolutionary models adopting a distance of 900 pc, and classify HD 185806 as a 1.3 M⊙ star, in the transition phase between the RGB and early AGB stages. Finally, we study the morpho-kinematic structure of the cocoon tail using the astronomical software SHAPE. An ellipsoidal structure, with an inclination of ∼19° with respect to the plane of sky is found to better reproduce the observed cocoon tail of HD 185806. [ABSTRACT FROM AUTHOR]

We present the analysis of the optical variability of the early, nitrogen-rich Wolf–Rayet (WR) star WR 7. The analysis of multisector Transiting Exoplanet Survey Satellite (TESS) light curves and high-resolution spectroscopic observations confirm multiperiodic variability that is modulated on time-scales of years. We detect a dominant period of 2.6433 ± 0.0005 d in the TESS sectors 33 and 34 light curves in addition to the previously reported high-frequency features from sector 7. We discuss the plausible mechanisms that may be responsible for such variability in WR 7, including pulsations, binarity, co-rotating interaction regions (CIRs), and clumpy winds. Given the lack of strong evidence for the presence of a stellar or compact companion, we suggest that WR 7 may pulsate in quasi-coherent modes in addition to wind variability likely caused by CIRs on top of stochastic low-frequency variability. WR 7 is certainly a worthy target for future monitoring in both spectroscopy and photometry to sample both the short (≲1 d) and long (≳1000 d) variability time-scales. [ABSTRACT FROM AUTHOR]

When an acoustic wave strikes a topographic feature, some of its energy is scattered. Sensors on the ground cannot capture these scattered signals when they propagate at high angles. We report observations of upwardly‐scattered acoustic waves prior to refraction back to the ground, intercepting them with a set of balloon‐borne infrasound microbarometers in the lower stratosphere over northern Sweden. We show that these scattered waves generate a coda whose presence can be related to topography beneath balloons and low‐altitude acoustic ducts. The inclination of the coda signals changes systematically with time, as expected from waves arriving from scatterers successively closer to receivers. The codas are present when a temperature inversion channels infrasound from a set of ground chemical explosions along the ground, but are absent following the inversion's dissipation. Since scattering partitions energy away from the main arrival, these observations imply a mechanism of amplitude loss that had previously been inaccessible to measurement. As such, these data and results allow for a better comprehension of interactions between atmospheric infrasound propagation and the solid earth. Plain Language Summary: Sound is a useful tool in monitoring phenomena of both natural and manmade origins. Sound below the limits of human hearing, known as infrasound, can travel very long distances, making it particularly worthwhile for study. Infrasound is typically recorded at ground level. However, vantage points higher in the atmosphere will record sound that cannot be observed at the ground. As a result, experiments where infrasound is recorded on balloons have become more popular. In this study, explosions are recorded at several balloon‐based microphones. In some cases, the sound of the explosion at the microphones is followed by additional pulses of sound. We show that the timing of these pulses and the angle they approach the balloon from can be explained by sound bouncing off of the ground. Further, these pulses only occur in the morning, which can be explained by the differences in the atmosphere during the morning and afternoon. Key Points: Upwardly scattered infrasound is directly observed at high inclinationsAirborne sensors allow for observation prior to refraction back to ground‐levelNear‐surface temperature inversions enhance this effect [ABSTRACT FROM AUTHOR]

We present an experiment to detect one ton TNT‐equivalent chemical explosions using pulsed Doppler radar observations of isodensity layers in the ionospheric E region during two campaigns. The first campaign, conducted on 15 October 2019, produced potential detections of all three shots. The detections closely resemble the temporal and spectral properties predicted using the InfraGA ray tracing and weakly nonlinear waveform propagation model. Here the model predicts that within 6.5–7.25 min of each shot a waveform peaking between 0.9 and 0.4 Hz will impact the ionosphere at 100 km. As the waves pass through this region, they will imprint their signal on an isodensity layer, which is detectable using a Doppler radar operating at the plasma frequency of the isodensity. Within the time windows of each of the three shots in the first campaign, we detect enhanced wave activity peaking near 0.5 Hz. These waves were imprinted on the Doppler signal probing an isodensity layer at 2.785 MHz near 100 km altitude. Despite these detections, the method appears to be unreliable as none of the six shots from the second campaign, conducted on 10 July 2020 were detected. The observations from this campaign were characterized by an increased acoustic noise environment in the microbarom band and persistent scintillation on the radar returns. These effects obscured any detectable signal from these shots and the baseline noise was well above the detection levels of the first campaign. Plain Language Summary: Energetic events occurring near Earth's surface have long been known to produce detectable impacts in the ionosphere. As atmospheric waves propagate away from earthquakes, tsunamis, storms and explosions they eventually make it high enough to perturb ionospheric plasma. While large events have been shown to be detectable using radio signals from global navigation satellite systems, we show that smaller events, such as conventional (non‐nuclear) explosions, can be detected in the lower ionosphere using ground based radar systems. We present observations from two campaigns showing a potential positive detection as well as a non‐detection. The parameters of the positive detection match well with modeling. The non‐detection, however, was likely due to signal degradation caused by structures in the ionosphere and an increase in acoustic noise during the campaign. Key Points: Acoustic waves from one ton TNT‐equivalent explosions are detectable using pulsed Doppler radar of the ionosphereObservations roughly match the modeled temporal and spectral predictions of acoustic wave propagationThe acoustic noise environment and scintillation of the radar signal are main limitations on the technique [ABSTRACT FROM AUTHOR]