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Three black holes (BHs) in wide binaries – Gaia BH1, BH2, and BH3 – were recently discovered. The likely progenitors of the BHs were massive stars that experienced a supergiant phase, reaching radii of |$\sim\!\! 1000 \ \mathrm{ R}_{\odot }$|⁠ , before collapsing to form the BH. Such radii are difficult to accommodate with the present-day orbits of BH1 and BH2 – with semimajor axes of 1.4 and 3.7 au, respectively. In this letter, we show that the maximal radii of the supergiants are not necessarily so large, and realistic stellar evolution models, with some assumed overshooting above the convective core into the radiative stellar envelope, produce substantially smaller maximal radii. The limited expansion of supergiants is consistent with the empirical Humphreys–Davidson limit – the absence of red supergiants above an upper luminosity limit, notably lower than the highest luminosity of main-sequence stars. We propose that the evolution that led to the formation of Gaia BH1 and BH2 simply did not involve an expansion to the cool supergiant phase. [ABSTRACT FROM AUTHOR]

This letter reports the first detection of a periodic light curve whose modulation is unambiguously due to rotation in a polluted white dwarf. TESS observations of WD 2138−332, at a distance of 16.1 pc, reveal a 0.39 per cent amplitude modulation with a 6.19 h period. While this rotation is relatively rapid for isolated white dwarfs, it falls within the range of spin periods common to those with detectable magnetic fields, where WD 2138−332 is notably both metal-rich and weakly magnetic. Within the local 20 pc volume of white dwarfs, multisector TESS data find no significant periodicities among the remaining 16 polluted objects (five of which are also magnetic), whereas six of 23 magnetic and metal-free targets have light curves consistent with rotation periods between 0.7 and 35 h (three of which are new discoveries). This indicates the variable light curve of WD 2138−332 is primarily a result of magnetism, as opposed to an inhomogeneous distribution of metals. From 13 magnetic and metallic degenerates with acceptable TESS data, a single detection of periodicity suggests that polluted white dwarfs are not rotating as rapidly as their magnetic counterparts, and planet ingestion is thus unlikely to be a significant channel for rapid rotation. [ABSTRACT FROM AUTHOR]

There is a common assumption in the particulate disc community that the pressure in particulate discs is essentially zero and that the disc streamlines follow Keplerian orbits, in the absence of self-gravity or external perturbations. It is also often assumed that the fluid description of particulate discs is not valid in the presence of crossing orbits (e.g. from non-zero free eccentricities). These stem from the misconception that fluid pressure arises due to the (typically rare) collisions between particles and that the velocity of particles in fluids are single-valued in space. In reality, pressure is a statistical property of the particle distribution function which arises precisely because there is a distribution of velocities at a given position. In this letter we demonstrate, with simple examples, that pressure in particulate discs is non-zero and is related to the inclination and free eccentricity distributions of the constituent particles in the discs. This means many common models of debris discs implicitly assume a non-zero, and potentially quite significant, dust pressure. We shall also demonstrate that the bulk motion of the dust is not the same as the particle motion and that the presence of pressure gradients can lead to strong departures from Keplerian motion. [ABSTRACT FROM AUTHOR]

This letter reports the first JWST spectroscopy of a white dwarf debris disc, giving a preliminary assessment of the salient features, and recommendations for future observations. The polluted and dusty star WD 0145+234 experienced a major collisional event in its circumstellar disc in 2018, accompanied by an infrared outburst, and subsequently a gradual decrease in thermal emission. Time-series NIRSpec observations demonstrate that the circumstellar disc is returning to a quiescent state with a T ≈ 1000 K infrared excess similar to the bulk of known dusty white dwarfs. MIRI spectroscopy reveals a 9–12  |$\mu$| m solid-state emission feature consistent with silicate minerals as seen in debris discs observed with Spitzer. The strength and morphology of the silicate feature appear unchanged relative to the continuum in spectra taken over a year apart, consistent with steady-state collisional evolution of the circumstellar debris. A tentative emission feature around 7  |$\mu$| m may be due to carbonates, and if confirmed would indicate aqueous alteration in the parent body. [ABSTRACT FROM AUTHOR]

We present Paper II of the Eccentric Debris Disc Morphologies series to explore the effects that significant free and forced eccentricities have on high-resolution millimetre-wavelength observations of debris discs, motivated by recent ALMA images of HD53143's disc. In this work, we explore the effects of free eccentricity, and by varying disc fractional widths and observational resolutions, show for a range of narrow eccentric discs, orbital overlaps result in dust emission distributions that have either one or two radial peaks at apocentre and/or pericentre. The narrowest discs contain two radial peaks, whereas the broadest discs contain just one radial peak. For fixed eccentricities, as fractional disc widths are increased, we show that these peaks merge first at apocentre (producing apocentre glow), and then at pericentre (producing pericentre glow). Our work thus demonstrates that apocentre/pericentre glows in models with constant free and forced eccentricities can be both width and resolution dependent at millimetre wavelengths, challenging the classical assertion that apocentre/pericentre glows are purely wavelength dependent. We discuss future high-resolution observations that can distinguish between competing interpretations of underlying debris disc eccentricity distributions. [ABSTRACT FROM AUTHOR]

Low- and intermediate-mass stars end their life dispersing their outer layers into the circumstellar medium, during the asymptotic and post-asymptotic giant branch phases. OH masers at 18 cm offer an effective way to probe their circumstellar environment. In this work, we present the discovery of seven OH maser sources likely associated with such evolved stars from the visual inspection of Australian SKA Pathfinder (ASKAP) continuum images. These seven sources do not emit real continuum emission, but the high sensitivity of our images allows us to detect their maser emission, resembling continuum sources. To confirm their nature, we carried out spectral-line observations with ATCA. All the sources showed the double-peaked spectra at 1612 MHz, typical of evolved stars. The detection of maser emission in continuum images can be a complementary and easy-to-use method to discover new maser sources with the large-area deep surveys conducted with the Square Kilometre Array (SKA) precursors. The implication for radio stars studies are remarkable since pure OH maser sources (i.e. with no continuum associated) represent, at a sensitivity of |$100\,\mu \mathrm{Jy\,beam}^{-1}$|⁠ , about 4 per cent of all Galactic sources and by far the most numerous stellar population. [ABSTRACT FROM AUTHOR]

The interaction between equilibrium tides and convection in stellar envelopes is often considered important for tidal evolution in close binary and extrasolar planetary systems. Its efficiency for fast tides has however long been controversial, when the tidal frequency exceeds the turnover frequency of convective eddies. Recent numerical simulations indicate that convection can act like an effective viscosity which decays quadratically with tidal frequency for fast tides, resulting in inefficient dissipation in many applications involving pre- and main-sequence stars and giant planets. A new idea was however recently proposed by Terquem (2021), who suggested Reynolds stresses involving correlations between tidal flow components dominate the interaction instead of correlations between convective flow components as usually assumed. They further showed that this can potentially significantly enhance tidal dissipation for fast tides in many applications. Motivated by the importance of this problem for tidal dissipation in stars and planets, we directly compute this new term using analytical arguments and global spherical simulations using Boussinesq and anelastic hydrodynamic models. We demonstrate that the new term proposed by Terquem vanishes identically for equilibrium tides interacting with convection in both Boussinesq and anelastic models; it is therefore unlikely to contribute to tidal dissipation in stars and planets. [ABSTRACT FROM AUTHOR]

Supernova (SN) properties in radio strongly depend on their circumstellar environment and they are an important probe to investigate the mass-loss of SN progenitors. Recently, core-collapse SN observations in radio have been assembled and the rise time and peak luminosity distribution of core-collapse SNe at 8.4 GHz has been estimated. In this paper, we constrain the mass-loss prescriptions for red supergiants (RSGs) by using the rise time and peak luminosity distribution of Type II SNe in radio. We take the de Jager and van Loon mass-loss rates for RSGs, calculate the rise time and peak luminosity distribution based on them, and compare the results with the observed distribution. We found that the de Jager mass-loss rate explains the widely spread radio rise time and peak luminosity distribution of Type II SNe well, while the van Loon mass-loss rate predicts a relatively narrow range for the rise time and peak luminosity. We conclude that the mass-loss prescriptions of RSGs should have strong dependence on the luminosity as in the de Jager mass-loss rate to reproduce the widely spread distribution of the rise time and peak luminosity in radio observed in Type II SNe. [ABSTRACT FROM AUTHOR]

We observed the K7 class III star NO Lup in an ALMA survey of the 1–3 Myr Lupus association and detected circumstellar dust and CO gas. Here we show that the J = 3–2 CO emission is both spectrally and spatially resolved, with a broad velocity width ∼19 km s−1 for its resolved size ∼1 arcsec (∼130 au). We model the gas emission as a Keplerian disc, finding consistency, but only with a central mass of ∼11M⊙, which is implausible given its spectral type and X-Shooter spectrum. A good fit to the data can also be found by modelling the CO emission as outflowing gas with a radial velocity ∼22 km s−1. We interpret NO Lup's CO emission as the first imaged class III circumstellar disc with outflowing gas. We conclude that the CO is continually replenished, but cannot say if this is from the breakup of icy planetesimals or from the last remnants of the protoplanetary disc. We suggest further work to explore the origin of this CO, and its higher than expected velocity in comparison to photoevaporative models. [ABSTRACT FROM AUTHOR]

We investigate the origin of close-in planets and related phenomena orbiting white dwarfs (WDs), which are thought to originate from orbits more distant from the star. We use the planetary architectures of the 75 multiple-planet systems (four, five, and six planets) detected orbiting main-sequence stars to build 750 dynamically analogous templates that we evolve to the WD phase. Our exploration of parameter space, although not exhaustive, is guided and restricted by observations and we find that the higher the multiplicity of the planetary system, the more likely it is to have a dynamical instability (losing planets, orbit crossing, and scattering), that eventually will send a planet (or small object) through a close periastron passage. Indeed, the fraction of unstable four- to six-planet simulations is comparable to the 25–50 |${{\ \rm per\ cent}}$| fraction of WDs having atmospheric pollution. Additionally, the onset of instability in the four- to six-planet configurations peaks in the first Gyr of the WD cooling time, decreasing thereafter. Planetary multiplicity is a natural condition to explain the presence of close-in planets to WDs, without having to invoke the specific architectures of the system or their migration through the von Zeipel–Lidov–Kozai effects from binary companions or their survival through the common envelope phase. [ABSTRACT FROM AUTHOR]

Planetary systems appear to form contemporaneously around young stars within young star-forming regions. Within these environments, the chances of survival, as well as the long-term evolution of these systems, are influenced by factors such as dynamical interactions with other stars and photoevaporation from massive stars. These interactions can also cause young stars to be ejected from their birth regions and become runaways. We present examples of such runaway stars in the vicinity of the Orion Nebula Cluster (ONC) found in Gaia DR2 data that have retained their discs during the ejection process. Once set on their path, these runaways usually do not encounter any other dense regions that could endanger the survival of their discs or young planetary systems. However, we show that it is possible for star–disc systems, presumably ejected from one dense star-forming region, to encounter a second dense region, in our case the ONC. While the interactions of the ejected star–disc systems in the second region are unlikely to be the same as in their birth region, a second encounter will increase the risk to the disc or planetary system from malign external effects. [ABSTRACT FROM AUTHOR]

Peter Pan discs are a recently discovered class of long-lived discs around low-mass stars that survive for an order of magnitude longer than typical discs. In this paper, we use disc evolutionary models to determine the required balance between initial conditions and the magnitude of dispersal processes for Peter Pan discs to be primordial. We find that we require low transport (α ∼ 10−4), extremely low external photoevaporation (⁠|${\le}10^{-9}\, {\rm M}_{\odot }\, {\rm yr^{-1}}$|⁠), and relatively high disc masses (>0.25 M *) to produce discs with ages and accretion rates consistent with Peter Pan discs. Higher transport (α = 10−3) results in disc lifetimes that are too short and even lower transport (α = 10−5) leads to accretion rates smaller than those observed. The required external photoevaporation rates are so low that primordial Peter Pan discs will have formed in rare environments on the periphery of low-mass star-forming regions, or deeply embedded, and as such have never subsequently been exposed to higher amounts of UV radiation. Given that such an external photoevaporation scenario is rare, the required disc parameters and accretion properties may reflect the initial conditions and accretion rates of a much larger fraction of the discs around low-mass stars. [ABSTRACT FROM AUTHOR]

RZ Psc is a young Sun-like star with a bright and warm infrared excess that is occasionally dimmed significantly by circumstellar dust structures. Optical depth arguments suggest that the dimming events do not probe a typical sightline through the circumstellar dust, and are instead caused by structures that appear above an optically thick mid-plane. This system may therefore be similar to systems where an outer disc is shadowed by material closer to the star. Here, we report the discovery that RZ Psc hosts a |$0.12\, \mathrm{ M}_\odot$| companion at a projected separation of 23 au. We conclude that the disc must orbit the primary star. While we do not detect orbital motion, comparison of the angle of linear polarization of the primary with the companion's on-sky position angle provides circumstantial evidence that the companion and disc may not share the same orbital plane. Whether the companion severely disrupts the disc, truncates it, or has little effect at all will require further observations of both the companion and disc. [ABSTRACT FROM AUTHOR]

A correlation between proto-planetary disc radii and sub-mm fluxes has been recently reported. In this letter, we show that the correlation is a sensitive probe of grain growth processes. Using models of grain growth and drift, we have shown in a companion paper that the observed disc radii trace where the dust grains are large enough to have a significant sub-mm opacity. We show that the observed correlation emerges naturally if the maximum grain size is set by radial drift, implying relatively low values of the viscous α parameter ≲0.001. In this case, the relation has an almost universal normalization, while if the grain size is set by fragmentation the flux at a given radius depends on the dust-to-gas ratio. We highlight two observational consequences of the fact that radial drift limits the grain size. The first is that the dust masses measured from the sub-mm could be overestimated by a factor of a few. The second is that the correlation should be present also at longer wavelengths (e.g. 3mm), with a normalization factor that scales as the square of the observing frequency as in the optically thick case. [ABSTRACT FROM AUTHOR]

Archival data from the WISE satellite reveal infrared flux variations of tens of per cent around numerous dusty white dwarfs. Data spanning more than 7 yr reveal more than half of known systems are varying in the 3.4  |${\mu}$| m band, while the 4.6  |${\mu}$| m data are challenging to interpret due to lower signal-to-noise ratios. The sparsely-sampled data limit interpretation, but the heterogeneous light curves suggest each source may be idiosyncratic, where there may be competing processes operating on different time-scales. Collisions are likely driving the observed decays in flux, and this finding suggests that dust production is operating more often than indicated by previous observations. The observed variation is at odds with the canonical flat disc model in isolation, and underscores the need for infrared monitoring of these evolved planetary systems to inform the next generation of theoretical models. [ABSTRACT FROM AUTHOR]

We report the first detection of circumstellar CO in a globular cluster. Observations with ALMA have detected the CO J  = 3–2 and SiO v  = 1 J  = 8 − 7 transitions at 345 and 344 GHz, respectively, around V3 in 47 Tucanae (NGC 104; [Fe/H]  = –0.72 dex), a star on the asymptotic giant branch. The CO line is detected at 7σ at a rest velocity v LSR  = –40.6 km s−1 and expansion velocity of 3.2 ± ∼0.4 km s−1. The brighter, asymmetric SiO line may indicate a circumstellar maser. The stellar wind is slow compared to similar Galactic stars, but the dust opacity remains similar to Galactic comparisons. We suggest that the mass-loss rate is set by the levitation of material into the circumstellar environment by pulsations, but that the terminal wind-expansion velocity is determined by radiation pressure on the dust: a pulsation-enhanced dust-driven wind. We suggest the metal-poor nature of the star decreases the grain size, slowing the wind and increasing its density and opacity. Metallic alloys at high altitudes above the photosphere could also provide an opacity increase. The CO line is weaker than expected from Galactic AGB stars, but its strength confirms a model that includes CO dissociation by the strong interstellar radiation field present inside globular clusters. [ABSTRACT FROM AUTHOR]

The presence of ultrahigh excitation (UHE) absorption lines (e.g. O VIII) in the optical spectra of several of the hottest white dwarfs poses a decades-long mystery and is something that has never been observed in any other astrophysical object. The occurrence of such features requires a dense environment with temperatures near 106 K, by far exceeding the stellar effective temperature. Here we report the discovery of a new hot wind white dwarf, GALEX J014636.8+323615. Astonishingly, we found for the first time rapid changes of the equivalent widths of the UHE features, which are correlated to the rotational period of the star (P  = 0.242035 d). We explain this with the presence of a wind-fed circumstellar magnetosphere in which magnetically confined wind shocks heat up the material to the high temperatures required for the creation of the UHE lines. The photometric and spectroscopic variability of GALEX J014636.8+323615 can then be understood as consequence of the obliquity of the magnetic axis with respect to the rotation axis of the white dwarf. This is the first time a wind-fed circumstellar magnetosphere around an apparently isolated white dwarf has been discovered and finally offers a plausible explanation of the ultrahot wind phenomenon. [ABSTRACT FROM AUTHOR]

Empirical evidence of planets in gas-rich circumstellar discs is required to constrain giant planet formation theories. Here we study the kinematic patterns which arise from planet–disc interactions and their observability in CO rotational emission lines. We perform 3D hydrodynamical simulations of single giant planets and predict the emergent intensity field with radiative transfer. Pressure gradients at planet-carved gaps, spiral wakes, and vortices bear strong kinematic counterparts. The isovelocity contours in the CO(2-1) line centroids |$v$| ○ reveal large-scale perturbations, corresponding to abrupt transitions from below sub -Keplerian to super -Keplerian rotation along with radial and vertical flows. The increase in line optical depth at the edge of the gap also modulates |$v$| ○, but this is a mild effect compared to the dynamical imprint of the planet–disc interaction. The large-scale deviations from the Keplerian rotation thus allow the planets to be indirectly detected via the first moment maps of molecular gas tracers, at Atacama Large Millimetre/submillimetre Array angular resolutions. The strength of these deviations depends on the mass of the perturber. This initial study paves the way to eventually determine the mass of the planet by comparison with more detailed models. [ABSTRACT FROM AUTHOR]

The rapidly evolving dust and gas extinction observed towards WD1145+017 has opened a real-time window on to the mechanisms for destruction-accretion of planetary bodies on to white dwarf stars, and has served to underline the importance of considering the dynamics of dust particles around such objects. Here it is argued that the interaction between (charged) dust grains and the stellar magnetic field is an important ingredient in understanding the physical distribution of infrared emitting particles in the vicinity of such white dwarfs. These ideas are used to suggest a possible model for WD1145+017 in which the unusual transit shapes are caused by opaque clouds of dust trapped in the stellar magnetosphere. The model can account for the observed transit periodicities if the stellar rotation is near 4.5 h, as the clouds of trapped dust are then located near or within the co-rotation radius. The model requires the surface magnetic field to be at least around some tens of kG. In contrast to the eccentric orbits expected for large planetesimals undergoing tidal disintegration, the orbits of magnetospherically-trapped dust clouds are essentially circular, consistent with the observations. [ABSTRACT FROM AUTHOR]

Recent Atacama Large Millimeter/submillimeter Array (ALMA) observations indicate that CW Leo, the closest carbon-rich asymptotic giant branch star to Sun, might have a low-mass stellar companion. We present archival ground-based astrometric measurements of CW Leo obtained within the context of the Torino Parallax Program and with >6 yr (1995-2001) of time baseline. The residuals to a single-star solution show significant curvature, and they are strongly correlated with the well-known I-band photometric variations due to stellar pulsations. We describe successfully the astrometry of CW Leo with a variability-induced motion (VIM) + acceleration model. We obtain proper motion and parallax of the centre-of-mass of the binary, the former in fair agreement with recent estimates, the latter at the near end of the range of inferred distances based on indirect methods. The VIM + acceleration model results allow us to derive a companion mass in agreement with that inferred by ALMA, they point towards a somewhat longer period than implied by ALMA, but are not compatible with much longer period estimates. These data will constitute a fundamental contribution towards the full understanding of the orbital architecture of the system when combined with Gaia astrometry, providing an ∼25 yr time baseline. [ABSTRACT FROM AUTHOR]

Type IIP supernova progenitors are often surrounded by dense circumstellar media that may result from mass-loss enhancement of the progenitors shortly before their explosions. Previous light-curve studies suggest that themass-loss rates are enhanced up to~0.1M☉ yr-1, assuming a constant wind velocity. However, the density of circumstellar media at the immediate stellar vicinity can be much higher than previously inferred for a given mass-loss rate if wind acceleration is taken into account. We show that the wind acceleration has a huge impact when we estimate mass-loss rates from early light curves of Type IIP supernovae by taking SN 2013fs as an example. We perform numerical calculations of the interaction between supernova ejecta and circumstellar media with a constant mass-loss rate but with a β-law wind velocity profile. We find that the mass-loss rate of the progenitor of SN 2013fs shortly before the explosion, which was inferred to be ~0.1M☉ yr-1 with a constant wind velocity of 10 km s-1 by a previous light-curve modelling, can be as low as~10-3M☉ yr-1 with the same terminal wind velocity of 10 km s-1 but with a wind velocity profile with β ≃ 5. In both cases, the mass of the circumstellar medium is similar (≃0.5M☉). Therefore, the beginning of the progenitor's mass-loss enhancement in our interpretation is ~100 yr before the explosion, not several years. Our result indicates that the immediate dense environment of Type II supernova progenitors may be significantly influenced by wind acceleration. [ABSTRACT FROM AUTHOR]

We present both archival and new high-spectral resolution visible observations of the δ Scuti/λ Boötis star HD 183324 recorded over the 2009-2013 timeframe. Previous observations of this A0V-type star have hinted at the presence of a circumstellar disc of gas surrounding the star. These new spectral data unequivocally show a remarkably high level of variable absorption activity, whose behaviour is typical of a stellar system in which gas is added to a circumstellar disc on a sporadic basis due to the evaporation of planetesimal-like objects (i.e. 'exocomets'). This planetesimal material most probably resides in an IR-emitting debris disc of dust and gas, similar to that of the β Pictoris exoplanet system that has recently been shown to harbor an exoplanet. [ABSTRACT FROM AUTHOR]

Whether BP Piscium (BP Psc) is either a pre-main sequence T Tauri star at d ≈ 80 pc, or a post-main sequence G giant at d ≈ 300 pc is still not clear. As a first-ascent giant, it is the first to be observed with a molecular and dust disc. Alternatively, BP Psc would be among the nearest T Tauri stars with a protoplanetary disc (PPD). We investigate whether the disc geometry resembles typical PPDs, by comparing polarimetric images with radiative transfer models. Our Very Large Telescope/Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE)/Zurich IMaging Polarimeter (ZIMPOL) observations allow us to perform polarimetric differential imaging, reference star differential imaging, and Richardson–Lucy deconvolution. We present the first visible light polarization and intensity images of the disc of BP Psc. Our deconvolution confirms the disc shape as detected before, mainly showing the southern side of the disc. In polarized intensity the disc is imaged at larger detail and also shows the northern side, giving it the typical shape of high-inclination flared discs. We explain the observed disc features by retrieving the large-scale geometry with mcmax radiative transfer modelling, which yields a strongly flared model, atypical for discs of T Tauri stars. [ABSTRACT FROM AUTHOR]

The luminosity of young giant planets can inform about their formation and accretion history. The directly imaged planets detected so far are consistent with the ‘hot-start’ scenario of high entropy and luminosity. If nebular gas passes through a shock front before being accreted into a protoplanet, the entropy can be substantially altered. To investigate this, we present high-resolution, three-dimensional radiative hydrodynamic simulations of accreting giant planets. The accreted gas is found to fall with supersonic speed in the gap from the circumstellar disc’s upper layers on to the surface of the circumplanetary disc and polar region of the protoplanet. There it shocks, creating an extended hot supercritical shock surface. This shock front is optically thick; therefore, it can conceal the planet’s intrinsic luminosity beneath. The gas in the vertical influx has high entropy which when passing through the shock front decreases significantly while the gas becomes part of the disc and protoplanet. This shows that circumplanetary discs play a key role in regulating a planet’s thermodynamic state. Our simulations furthermore indicate that around the shock surface extended regions of atomic – sometimes ionized – hydrogen develop. Therefore, circumplanetary disc shock surfaces could influence significantly the observational appearance of forming gas giants. [ABSTRACT FROM AUTHOR]

The BRITE (BRIght Target Explorer) constellation of nanosatellites performs seismology of bright stars via high-precision photometry. In this context, we initiated a high-resolution, high signal-to-noise, high-sensitivity, spectropolarimetric survey of all stars brighter than V = 4. The goal of this survey is to detect new bright magnetic stars and provide prime targets for both detailed magnetic studies and asteroseismology with BRITE. Circularly polarized spectra were acquired with Narval at TBL (Bernard Lyot Telescope, France) and HARPSpol at ESO (European Southern Observatory) in La Silla (Chile). We discovered two new magnetic B stars: the B3V star i Car and the B8V component of the binary star Atlas. Each star was observed twice to confirm the magnetic detections and check for variability. These bright magnetic B stars are prime targets for asteroseismology and for flux-demanding techniques, such as interferometry. [ABSTRACT FROM AUTHOR]

There is much evidence that planet formation is occurring in the disc around the Herbig Be star HD100546. To learn more about the processes occurring in this disc, we conducted high-resolution imaging at 43/45 GHz with the Australia Telescope Compact Array. Multiple array configurations were used, providing a best spatial resolution of ~0.15 arcsec, or 15 au at HD100546's distance of ~100 pc. Significant structure is revealed, but its precise form is dependent on the u - v plane sampling used for the image reconstruction. At a resolution of ≤30 au, we detected an inner gap in the disc with a radius of ~25 au and a position angle approximately along the known disc major axis. With different weighting, and an achieved resolution of ~15 au, emission appears at the centre and the disc takes on the shape of an incomplete ring, much like a horseshoe, again with a gap radius of ~25 au. The position angle of the disc major axis and its inclination from face-on are determined to be 140° ± 5° and 40° ± 5°, respectively. The ~25 au gap radius is confirmed by a null in the real part of the binned visibilities at 320 ± 10 kλ, whilst the non-axisymmetric nature is also confirmed through significant structure in the imaginary component. The emission mechanism at the central peak is most likely to be free-free emission from a stellar or disc wind. Overall our data support the picture of at least one, but probably several, giant planets orbiting HD100546 within 25 au. [ABSTRACT FROM AUTHOR]

We present high spectral resolution mid-IR observations of SiS towards the C-rich AGB star IRC+10216 carried out with the Texas Echelon-cross-Echelle Spectrograph mounted on the NASA Infrared Telescope Facility. We have identified 204 ro-vibrational lines of 28Si32S, 26 of 29Si32S, 20 of 28Si34S, and 15 of 30Si32S in the frequency range 720-790 cm-1. These lines belong to bands ν = 1-0, 2-1, 3-2, 4-3, and 5-4, and involve rotational levels with Jlow ≲ 90. About 30 per cent of these lines are unblended or weakly blended and can be partially or entirely fitted with a code developed to model the mid-IR emission of a spherically symmetric circumstellar envelope composed of expanding gas and dust. The observed lines trace the envelope at distances to the star ≲35R* (⋍0.7 arcsec). The fits are compatible with an expansion velocity of 1 + 2.5(r/R* - 1) km s-1 between 1 and 5R*, 11kms-1 between 5 and 20R*, and 14.5 kms-1 outwards. The derived abundance profile of 28Si32S with respect to H2 is 4.9 × 10-6 between the stellar photosphere and 5R*, decreasing linearly down to 1.6 × 10-6 at 20R* and to 1.3 × 10-6 at 50R*. 28Si32S seems to be rotationally under local thermodynamic equilibrium (LTE) in the region of the envelope probed with our observations and vibrationally out of LTE in most of it. There is a red-shifted emission excess in the 28Si32S lines of band ν = 1-0 that cannot be found in the lines of bands ν = 2-1, 3-2, 4-3, and 5-4. This excess could be explained by an enhancement of the vibrational temperature around 20R* behind the star. The derived isotopic ratios 28Si/29Si, and 32S/34S are 17 and 14, compatible with previous estimates. [ABSTRACT FROM AUTHOR]

We present a detailed study based on infrared (IR) photometry of all Galactic RV Tauri stars from the General Catalogue of Variable Stars (GCVS). RV Tauri stars are the brightest among the Population II Cepheids. They are thought to evolve away from the asymptotic giant branch (AGB) towards the white dwarf domain. IRAS detected several RV Tauri stars because of their large IR excesses and it was found that they occupy a specific region in the [12] - [25], [25] - [60] IRAS two-colour diagram. We used the all sky survey of Wide-field Infrared Survey Explorer to extend these studies and compare the IR properties of all RV Tauri stars in the GCVS with a selected sample of post-AGB objects with the goal to place the RV Tauri pulsators in the context of post-AGB evolution. Moreover, we correlated the IR properties of both the RV Tauri stars and the comparison sample with other observables like binarity and the presence of a photospheric chemical anomaly called depletion. We find that Galactic RV Tauri stars display a range of IR properties and we differentiate between disc sources, objects with no IR excess and objects for which the spectral energy distribution (SED) is uncertain. We obtain a clear correlation between disc sources and binarity. RV Tauri stars with a variable mean magnitude are exclusively found among the disc sources. We also find evidence for disc evolution among the binaries. Furthermore our studies show that the presence of a disc seems to be a necessary but not sufficient condition for the depletion process to become efficient. [ABSTRACT FROM AUTHOR]

Dust-Obscured Galaxies (DOGs) are bright 24 μm-selected sources with extreme obscuration at optical wavelengths. They are typically characterized by a rising power-law continuum of hot dust (TD ∼ 200-1000 K) in the near-IR indicating that their mid-IR luminosity is dominated by an active galactic nucleus (AGN). DOGs with a fainter 24 μm flux display a stellar bump in the near-IR and their mid-IR luminosity appears to be mainly powered by dusty star formation. Alternatively, it may be that the mid-IR emission arising from AGN activity is dominant but the torus is sufficiently opaque to make the near-IR emission from the AGN negligible with respect to the emission from the host component. In an effort to characterize the astrophysical nature of the processes responsible for the IR emission in DOGs, this paper exploits Herschel data (PACS + SPIRE) on a sample of 95 DOGs within the COSMOS field. We derive a wealth of far-IR properties (e.g. total IR luminosities; mid-to-far-IR colours; dust temperatures and masses) based on spectral energy distribution fitting. Of particular interest are the 24 μm-bright DOGs (F24 μm > 1 mJy). They present bluer far-IR/mid-IR colours than the rest of the sample, unveiling the potential presence of an AGN. The AGN contribution to the total 8-1000 μm flux increases as a function of the rest-frame 8 μm-luminosity irrespective of the redshift. This confirms that faint DOGs (L8 μm < 1012 L⊙) are dominated by star formation while brighter DOGs show a larger contribution from an AGN. [ABSTRACT FROM AUTHOR]

We investigate the formation and evolution of a first core, protostar, and circumstellar disc with a three-dimensional non-ideal (including both Ohmic and ambipolar diffusion) radiation magnetohydrodynamics simulation. We found that the magnetic flux is largely removed by magnetic diffusion in the first-core phase and that the plasma β of the centre of the first core becomes large, β > 104. Thus, proper treatment of first-core phase is crucial in investigating the formation of protostar and disc. On the other hand, in an ideal simulation, β ∼ 10 at the centre of the first core. The simulations with magnetic diffusion show that the circumstellar disc forms at almost the same time of protostar formation even with a relatively strong initial magnetic field (the value for the initial mass-to-flux ratio of the cloud core relative to the critical value is μ = 4). The disc has a radius of r ∼ 1 AU at the protostar formation epoch. We confirm that the disc is rotationally supported. We also show that the disc is massive (Q ∼ 1) and that gravitational instability may play an important role in the subsequent disc evolution. [ABSTRACT FROM AUTHOR]

The 13-Myr old star HD 106906 is orbited by a debris disc of at least 0.067MMoon with inner and outer radii of 20 and 120 au, respectively, and by a planet at a distance of 650 au. We use this curious combination of a close low-mass disc and a wide planet to motivate our simulations of this system. We study the parameter space of the initial conditions to quantify the mass loss from the debris disc and its lifetime under the influence of the planet. We find that when the planet orbits closer to the star than about 50 au and with low inclination relative to the disc (less than about 10°), more disc material is perturbed outside than inside the region constrained by observations on time-scales shorter than 1 Myr. Considering the age of the system, such a short lifetime of the disc is incompatible with the time-scale for planet-planet scattering, which is one of the scenarios suggested to explain the wide separation of the planet. For some configurations, when the planet orbit is inclined with respect to the disc, the latter will start to wobble. We argue that this wobbling is caused by a mechanism similar to Kozai- Lidov oscillations. We also observe various resonant structures (such as rings and spiral arms) induced in the disc by the planet. [ABSTRACT FROM AUTHOR]

ISO-Oph-50 is a young low-mass object in the ~1 Myr old Ophiuchus star-forming region undergoing dramatic changes in its optical/near/mid-infrared brightness by 2-4 mag. We present new multi-band photometry and near-infrared spectra, combined with a synopsis of the existing literature data. Based on the spectroscopy, the source is confirmed as a mid-M dwarf, with evidence for ongoing accretion. The near-infrared light curves showlarge-scale variations, with 2-4 mag amplitude in the bands IJHK, with the object generally being bluer when faint. Near its brightest state, the object shows colour changes consistent with variable extinction of ΔAV ~ 7 mag. High-cadence monitoring at 3.6 μm reveals quasi-periodic variations with a typical time-scale of 1-2 weeks. The best explanation for these characteristics is a lowmass star seen through circumstellar matter, whose complex variability is caused by changing inhomogeneities in the inner parts of the disc. When faint, the direct stellar emission is blocked; the near-infrared radiation is dominated by scattered light. When bright, the emission is consistent with a photosphere strongly reddened by circumstellar dust. Based on the available constraints, the inhomogeneities have to be located at or beyond ~0.1 au distance from the star. If this scenario turns out to be correct, a major portion of the inner disc has to be clumpy, structured, and/or in turmoil. In its observational characteristics, this object resembles other types of young stellar objects with variability caused in the inner disc. Compared to other objects, however, ISO-Oph-50 is clearly an extreme case, given the large amplitude of the brightness and colour changes combined with the erratic behaviour. ISO-Oph-50 has been near its brightest state since 2013; further monitoring is highly encouraged. [ABSTRACT FROM AUTHOR]

Observations of jets from young stellar objects reveal the asymmetric outflows from some sources. A large set of 2.5D magnetohydrodynamic simulations was carried out for axisym-metric viscous/diffusive disc accretion to rotating magnetized stars for the purpose of assessing the conditions where the outflows are asymmetric relative to the equatorial plane. We consider initial magnetic fields that are symmetric about the equatorial plane and consist of a radially distributed field threading the disc (disc field) and a stellar dipole field. (1) For pure disc-fields the symmetry or asymmetry of the outflows is affected by the mid-plane plasma β of the disc. For discs with small plasma β, outflows are symmetric to within 10 per cent over time-scales of hundreds of inner disc orbits. For higher β discs, the coupling of the upper and lower coronal plasmas is broken, and quasi-periodic field motion leads to asymmetric episodic outflows. (2) Accreting stars with a stellar dipole field and no disc-field exhibit episodic, two component outflows - a magnetospheric wind and an inner disc wind. Both are characterized by similar velocity profiles but the magnetospheric wind has densities ≳ 10 times that of the disc wind. (3) Adding a disc field parallel to the stellar dipole field enhances the magnetospheric winds but suppresses the disc wind. (4) Adding a disc field which is antiparallel to the stellar dipole field in the disc suppresses the magnetospheric and disc winds. Our simulations reproduce some key features of observations of asymmetric outflows of T Tauri stars. [ABSTRACT FROM AUTHOR]

M-dwarfs are emerging in the literature as promising targets for detecting low-mass, Earth-like planets. An important step in this process is to determine the stellar parameters of the M-dwarf host star as accurately as possible. Different well-tested stellar model atmosphere simulations from different groups are widely applied to undertake this task. This paper provides a comparison of different model atmosphere families to allow a better estimate of systematic errors on host-star stellar parameter introduced by the use of one specific model atmosphere family only. We present a comparison of the ATLAS9, MARCS, PHOENIX and DRIFT-PHOENIX model atmosphere families including the M-dwarf parameter space (Teff = 2500-4000 K, log(g) = 3.0-5.0, [M/H] = -2.5to0.5). We examine the differences in the (Tgas, pgas)-structures, in synthetic photometric fluxes and in colour indices. Model atmospheres results for higher log(g) deviate considerably less between different models families than those for lower log(g) for all Teff = 2500-4000 K examined. We compiled the broad-band synthetic photometric fluxes for all available model atmospheres (incl. M-dwarfs and brown dwarfs) for the UKIRT WFCAM ZYJHK, 2MASS JHKs and Johnson UBVRI filters, and calculated related colour indices. Synthetic colours in the IR wavelengths diverge by no more than 0.15 dex amongst all model families. For all spectral bands considered, model discrepancies in colour diminish for higher Teff atmosphere simulations. We notice differences in synthetic colours between all model families and observed example data (including Kepler 42 and GJ1214). [ABSTRACT FROM AUTHOR]

ABSTRACT Mass-loss rate, , is one of the key parameters affecting evolution and observational manifestations of massive stars and their impact on the ambient medium. Despite its importance, there is a factor of ∼100 discrepancy between empirical and theoretical of late-type O dwarfs, the so-called weak-wind problem. In this Letter, we propose a simple novel method to constrain of runaway massive stars through observation of their bow shocks and Strömgren spheres, which might be of decisive importance for resolving the weak-wind problem. Using this method, we found that of the well-known runaway O9.5 V star ζ Oph is more than an order of magnitude higher than that derived from ultraviolet (UV) line fitting and is by a factor of 6-7 lower than those based on the theoretical recipe by Vink et al. and the Hα line. The discrepancy between derived by our method and that based on UV lines would be even more severe if the stellar wind is clumpy. At the same time, our estimate of agrees with that predicted by the moving reversing layer theory by Lucy. [ABSTRACT FROM AUTHOR]

ABSTRACT LHA 115-S 18 is a very peculiar emission-line star exhibiting the B[e] phenomenon. Located in the Small Magellanic Cloud, its spectrum shows features of an extremely wide range of excitation and ionization stages, extending from highly ionized atomic lines (Si iv, C iv, He ii) in the ultraviolet and optical regions to molecular emission bands of CO and TiO in the optical and infrared regions. The most distinguishing spectral characteristic of LHA 115-S 18 is the high variability detected in the He iiλ4686 emission line, which can be a very conspicuous or completely invisible feature. In this work, we report on another peculiarity of LHA 115-S 18. From high-resolution optical spectra taken between 2000 and 2008, we discovered the appearance and strengthening of two emission features at λλ6825 and 7082 Å , which we have identified as Raman-scattered lines. This is the first time that these lines have been detected in the spectrum of a massive luminous B[e] star. As the classification of LHA 115-S 18 is highly controversial, we discuss how the discovery of the appearance of Raman-scattered lines in this peculiar star might help us to solve this puzzle. [ABSTRACT FROM AUTHOR]

ABSTRACT Molecular emission has been detected in several Magellanic Cloud B[e] supergiants. In this Letter, we report on the detection of CO band head emission in the B[e] supergiant LHA 115-S 65, and present a K-band near-infrared spectrum obtained with the Spectrograph for INtegral Field Observation in the Near-Infrared (SINFONI; R= 4500) on the ESO VLT UT4 telescope. The observed molecular band head emission in S65 is quite surprising in the light of a previous non-detection by McGregor, Hyland & McGinn, as well as a high-resolution ( R= 50 000) Gemini/Phoenix spectrum of this star taken nine months earlier showing no emission. Based on analysis of the optical spectrum by Kraus, Borges Fernandes & de Araújo, we suspect that the sudden appearance of molecular emission could be due to density build-up in an outflowing viscous disc, as seen for Be stars. This new discovery, combined with variability in two other similar evolved massive stars, indicates an evolutionary link between B[e] supergiants and luminous blue variables. [ABSTRACT FROM AUTHOR]

ABSTRACT We present Spitzer Space Telescope and Herschel Space Observatory infrared observations of the recurrent nova T Pyx during its 2011 eruption, complemented by ground-base optical-infrared photometry. We find that the eruption has heated dust in the pre-existing nebulosity associated with T Pyx. This is most likely interstellar dust swept up by T Pyx - either during previous eruptions or by a wind - rather than the accumulation of dust produced during eruptions. [ABSTRACT FROM AUTHOR]

ABSTRACT We present Spitzer Space Telescope and Herschel Space Observatory infrared observations of the recurrent nova T Pyx during its 2011 eruption, complemented by ground-base optical-infrared photometry. We find that the eruption has heated dust in the pre-existing nebulosity associated with T Pyx. This is most likely interstellar dust swept up by T Pyx - either during previous eruptions or by a wind - rather than the accumulation of dust produced during eruptions. [ABSTRACT FROM AUTHOR]

ABSTRACT Two luminous debris discs around 100 Myr old have been searched for 1 cm dust emission, to a depth three times greater than in any such previous study. Very low limits were set towards both HD 377 and HD 104860 (noise levels of 12-14 Jy), extending the spectral range from 70 m to 3 mm where cool dust has previously been sought. The almost-identical fluxes of the two systems were merged into an average spectral energy distribution, which was then fitted using a distribution of grain sizes. The canonical infinite collisional cascade, with numbers of particles n( D) ∝ D−3.5 for diameter D, overpredicts the 1-cm flux, which should have been detected at over 3σ for the merged system. Preferred solutions have truncated grain populations with largest particles around 1.5-4 mm in diameter, and slightly flatter distributions, up to n( D) ∝ D−3.1. The lack of cm-sized and larger particles is reminiscent of the similar deficit inferred around comets from spacecraft encounters. Such departures from simple power-law distributions of particles have been predicted in recent models where some size regimes are more readily broken up than others. A deficit of cm-scale particles can explain the fits we obtain, and reduces the total masses inferred for the comet belts of these stars. [ABSTRACT FROM AUTHOR]

ABSTRACT During the late stages of stellar evolution in massive stars (C fusion and later), the fusion luminosity in the core of the star exceeds the star's Eddington luminosity. This can drive vigorous convective motions which in turn excite internal gravity waves. The local wave energy flux excited by convection is itself well above Eddington during the last few years in the life of the star. We suggest that an interesting fraction of the energy in gravity waves can, in some cases, convert into sound waves as the gravity waves propagate (tunnel) towards the stellar surface. The subsequent dissipation of the sound waves can unbind up to several M⊙ of the stellar envelope. This wave-driven mass loss can explain the existence of extremely large stellar mass-loss rates just prior to core collapse, which are inferred via circumstellar interaction in some core-collapse supernovae (e.g. SNe 2006gy and PTF 09uj, and even Type IIn supernovae more generally). An outstanding question is understanding what stellar parameters (mass, rotation, metallicity and age) are the most susceptible to wave-driven mass loss. This depends on the precise internal structure of massive stars and the power spectrum of internal gravity waves excited by stellar convection. [ABSTRACT FROM AUTHOR]

ABSTRACT While the presence of discs around classical Be stars is well established, their origin is still uncertain. To understand what processes result in the creation of these discs and how angular momentum is transported within them, their physical properties must be constrained. This requires comparing high spatial and spectral resolution data with detailed radiative transfer modelling. We present a high spectral resolution, R∼ 80 000, sub-milliarcsecond precision, spectroastrometric study of the circumstellar disc around the Be star β CMi. The data are confronted with 3D, non-local thermodynamic equilibrium radiative transfer calculations to directly constrain the properties of the disc. Furthermore, we compare the data to disc models featuring two velocity laws: Keplerian, the prediction of the viscous disc model, and angular momentum conserving rotation. It is shown that the observations of β CMi can only be reproduced using Keplerian rotation. The agreement between the model and the observed spectral energy distribution, polarization and spectroastrometric signature of β CMi confirms that the discs around Be stars are well modelled as viscous decretion discs. [ABSTRACT FROM AUTHOR]

ABSTRACT While the presence of discs around classical Be stars is well established, their origin is still uncertain. To understand what processes result in the creation of these discs and how angular momentum is transported within them, their physical properties must be constrained. This requires comparing high spatial and spectral resolution data with detailed radiative transfer modelling. We present a high spectral resolution, R∼ 80 000, sub-milliarcsecond precision, spectroastrometric study of the circumstellar disc around the Be star β CMi. The data are confronted with 3D, non-local thermodynamic equilibrium radiative transfer calculations to directly constrain the properties of the disc. Furthermore, we compare the data to disc models featuring two velocity laws: Keplerian, the prediction of the viscous disc model, and angular momentum conserving rotation. It is shown that the observations of β CMi can only be reproduced using Keplerian rotation. The agreement between the model and the observed spectral energy distribution, polarization and spectroastrometric signature of β CMi confirms that the discs around Be stars are well modelled as viscous decretion discs. [ABSTRACT FROM AUTHOR]

ABSTRACT We present Herschel/SPIRE observations for the 2MASS 1207334−393254 (2M1207) system. Based on radiative transfer modelling of near-infrared to submillimetre data, we estimate a disc mass of 3 ± 2 MJup and an outer disc radius of 50-100 au for the 2M1207A disc. The relative disc mass for 2M1207A is similar to the T Tauri star TW Hya, which indicates that massive discs are not underabundant around substellar objects. In probing the various formation mechanisms for this system, we find that core accretion is highly uncertain mainly due to the large separation between the primary and the companion. Disc fragmentation could be a likely scenario based on analytical models, and if the disc initially was more massive than its current estimate. Considering that the TW Hydrae Association (TWA) is sparsely populated, this system could have formed via one of the known binary formation mechanisms (e.g. turbulent fragmentation of a core) and survived disruption at an early stage. [ABSTRACT FROM AUTHOR]

ABSTRACT We present Herschel/SPIRE observations for the 2MASS 1207334−393254 (2M1207) system. Based on radiative transfer modelling of near-infrared to submillimetre data, we estimate a disc mass of 3 ± 2 MJup and an outer disc radius of 50-100 au for the 2M1207A disc. The relative disc mass for 2M1207A is similar to the T Tauri star TW Hya, which indicates that massive discs are not underabundant around substellar objects. In probing the various formation mechanisms for this system, we find that core accretion is highly uncertain mainly due to the large separation between the primary and the companion. Disc fragmentation could be a likely scenario based on analytical models, and if the disc initially was more massive than its current estimate. Considering that the TW Hydrae Association (TWA) is sparsely populated, this system could have formed via one of the known binary formation mechanisms (e.g. turbulent fragmentation of a core) and survived disruption at an early stage. [ABSTRACT FROM AUTHOR]

ABSTRACT We present infrared spectra of the binary XX Oph obtained with the Infrared Spectrograph on the Spitzer Space Telescope. The data show some evidence for the presence of solid C60- the first detection of C60 in the solid phase - together with the well-known 'unidentified infrared' emission features. We suggest that, in the case of XX Oph, the C60 is located close to the hot component, and that in general it is preferentially excited by stars having effective temperatures in the range 15 000-30 000 K. C60 may be common in circumstellar environments, but unnoticed in the absence of a suitable exciting source. [ABSTRACT FROM AUTHOR]

ABSTRACT We present an analysis of the WISE photometric data for 829 stars in the Sco-Cen OB2 association, using the latest high-mass membership probabilities. We detect infrared excesses associated with 135 BAF-type stars, 99 of which are secure Sco-Cen members. There is a clear increase in excess fraction with membership probability, which can be fitted linearly. We infer that 41 ± 5 per cent of Sco-Cen OB2 BAF stars have excesses, while the field star excess fraction is consistent with zero. This is the first time that the probability of non-membership has been used in the calculation of excess fractions for young stars. We do not observe any significant change in excess fraction between the three subgroups. Within our sample, we have observed that B-type association members have a significantly smaller excess fraction than A- and F-type association members. [ABSTRACT FROM AUTHOR]

ABSTRACT We present K-band integral field observations of the circumstellar envelope of the evolved star OH 231.8+4.2. Spatial and spectral information was simultaneously acquired using the SINFONI integral field unit, with adaptive optics, on the Very Large Telescope. The observations reveal the discovery of H2 emission (1) around the centre of the nebula and (2) located in clumps along the western side of the northern lobe, presumably associated with the strong shocks that stimulate the previously reported Hα emission at the same location. An observed H2 1→0/2→1S(1) line ratio of 8.3 ± 1.9 was calculated for the central field, a value consistent with shock excitation. [ABSTRACT FROM AUTHOR]

ABSTRACT Debris discs are known to exist around many planet-host stars, but no debris dust has been found so far in systems with transiting planets. Using publicly available catalogues, we searched for infrared excesses in such systems. In the recently published Wide-field Infrared Survey Explorer catalogue, we found 52 stars with transiting planets. Two systems with one transiting 'hot Jupiter' each, TrES-2 and XO-5, exhibit small excesses both at 12 and at 22 μ m at a ≳3σ level. Provided that one or both of these detections are real, the frequency of warm excesses in systems with transiting planets of 2-4 per cent is comparable to that around solar-type stars probed at similar wavelengths with Spitzer's MIPS and IRS instruments. Modelling suggests that the observed excesses would stem from dust rings with radii of several au. The inferred amount of dust is close to the maximum expected theoretically from a collisional cascade in asteroid belt analogues. If confirmed, the presence of debris discs in systems with transiting planets may put important constraints on the scenario of formation and migration of hot Jupiters. [ABSTRACT FROM AUTHOR]