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Deconvolving the complex structure of the asteroid beltThe asteroid belt is a unique source of information on some of the most important questions facing solar system science. These questions include the sizes, numbers, types and orbital distributions of the planetesimals that formed the planets, and the identification of those asteroids that are the sources of meteorites and near-Earth asteroids. Answering these questions requires an understanding of the dynamical evolution of the asteroid belt, but this evolution is governed by a complex interplay of mechanisms that include catastrophic disruption, orbital evolution driven by Yarkovsky radiation forces, and chaotic orbital evolution driven by gravitational forces. While the timescales of these loss mechanisms have been calculated using estimates of some critical parameters that include the thermal properties, strengths and mean densities of the asteroids, we argue here that the uncertainties in these parameters are so large that deconvolution of the structure of the asteroid belt must be guided primarily by observational constraints. We argue that observations of the inner asteroid belt indicate that the size-frequency distribution is not close to the equilibrium distribution postulated by Dohnanyi (<xref rid=ref10 ref-type=bibr>1969</xref>). We also discuss the correlations observed between the sizes and the orbital elements of the asteroids. While some of these correlations are significant and informative, others are spurious and may arise from the limitations of the Hierarchical Clustering Method that is currently used to define family membership.
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Evidence of Cosmic Impact at Abu Hureyra, Syria at the Younger Dryas Onset ( 12.8 ka): High-temperature melting at >2200 °CAt Abu Hureyra (AH), Syria, the 12,800-year-old Younger Dryas boundary layer (YDB) contains peak abundances in meltglass, nanodiamonds, microspherules, and charcoal. AH meltglass comprises 1.6 wt.% of bulk sediment, and crossed polarizers indicate that the meltglass is isotropic. High YDB concentrations of iridium, platinum, nickel, and cobalt suggest mixing of melted local sediment with small quantities of meteoritic material. Approximately 40% of AH glass display carbon-infused, siliceous plant imprints that laboratory experiments show formed at a minimum of 1200°-1300 °C; however, reflectance-inferred temperatures for the encapsulated carbon were lower by up to 1000 °C. Alternately, melted grains of quartz, chromferide, and magnetite in AH glass suggest exposure to minimum temperatures of 1720 °C ranging to >2200 °C. This argues against formation of AH meltglass in thatched hut fires at 1100°-1200 °C, and low values of remanent magnetism indicate the meltglass was not created by lightning. Low meltglass water content (0.02-0.05% H<SUB>2</SUB>O) is consistent with a formation process similar to that of tektites and inconsistent with volcanism and anthropogenesis. The wide range of evidence supports the hypothesis that a cosmic event occurred at Abu Hureyra ~12,800 years ago, coeval with impacts that deposited high-temperature meltglass, melted microspherules, and/or platinum at other YDB sites on four continents.
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A numerical study of near-Earth asteroid family orbital dispersionWe have studied the evolution of near-Earth asteroid (NEA) families and pairs to inform future searches. To do so, we integrated clusters of simulated NEAs with different initial conditions, namely the orbital inclination, ejection speed, and the effects of mean-motion resonances on the parent body prior to breakup while also varying the orbit, mass, and number of perturbing planetary bodies. We studied the orbital element dispersion rates of NEA family members and found a power-law increase in those families whose orbits brought them close to a planet. This allowed us to conclude that family dispersion is significantly affected by the Kozai-Lidov effect due to oscillations in the eccentricity, and that the rate of dispersion is slowest at high inclination relatively far from the nearest planet. In most cases, the ejection speed of the initial breakup does not affect the dispersion, except within weaker mean-motion resonances where more violent breakups will result in the ejection of a fraction of the asteroids, causing a large increase in dispersion. Within mean-motion resonances, where Kozai-Lidov oscillations are slowed, increases in the dispersion of a family are delayed, leading them to be identifiable for longer.
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The clumped winds of the most massive starsThe core of the cluster R136 in the Large Magellanic Cloud hosts the most massive stars known. The high mass-loss rates of these stars strongly impact their surroundings, as well as the evolution of the stars themselves. To quantify this impact accurate mass-loss rates are needed, however, uncertainty about the degree of inhomogeneity of the winds (`wind clumping'), makes mass-loss measurements uncertain. We combine optical and ultraviolet HST/STIS spectroscopy of 56 stars in the core of R136 in order to put constraints on the wind structure, improving the accuracy of the mass-loss rate measurements. We find that the winds are highly clumped, and use our measured mass-loss rates to test theoretical predictions. Furthermore we find, for the first time, tentative trends in the wind-structure parameters as a function of mass-loss rate, suggesting that the winds of stars with higher mass-loss rates are less clumped than those with lower mass-loss rates.
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Constraining physical processes in pre-supernovae massive star evolutionWhile we have growing numbers of massive star observations, it remains unclear how efficient the key physical processes such as mass loss, convection and rotation are, or indeed how they impact each other. We reconcile this with detailed stellar evolution models, yet these models have their own drawbacks with necessary assumptions for 3-dimensional processes like rotation which need to be adapted into 1-dimensional models. The implementation of empirical mass-loss prescriptions in stellar evolution codes can lead to the extrapolation of base rates to unconstrained evolutionary stages leading to a range of uncertain fates. In short, there remain many free parameters and physical processes which need to be calibrated in order to align our theory better with upcoming observations. We have tested various processes such as mass loss and internal mixing, including rotational mixing and convective overshooting, against multiple observational constraints such as using eclipsing binaries, the Humphreys-Davidson limit, and the final masses of Wolf-Rayet stars, across a range of metallicities. In fact, we developed a method of disentangling the effects of mixing and mass loss in the `Mass-Luminosity Plane' allowing direct calibration of these processes. In all cases, it is important to note that a combined appreciation for both stellar winds and internal mixing are important to reproduce observations.
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Predictions for the Maximum Masses of Black Holes below the PI BoundaryWhile the initial discovery of GW150914 resulted in the detection of black holes larger than initially expected, it was the GW190521 event which truly challenged astrophysical assumptions about stellar evolution and black hole progenitors, as the components of GW190521 were firmly within the traditional Pair-Instability (PI) mass-gap – a range of masses where no black holes were expected to be created due to PI supernovae (PISN). We investigate the possibility that this merger involved first generation black holes, and that the unexpectedly heavy 85 solar mass BH could be produced from fundamental stellar physics. We present the results of studies involving the stellar evolution code MESA, as we systematically vary several parameters of stellar physics (in particular mixing and mass loss) to test assumptions and build a population of potential black hole progenitors within the traditional PI gap.
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A resolved view of the impact of massive star formation in the atomic, molecular and ionized gas in the Carina NebulaThe Carina Nebula Complex (CNC) is a spectacular star-forming region located at 2.3 kpc, which is close enough to observe different size scales in detail. With more than 65 O-stars and more than 900 young stellar objects identified it is also the nearest analogue of more extreme star forming regions, such as 30 Doradus. In this talk I will present the results of a major effort to study the relationship between the different gas phases in the Carina region from 100 pc to 0.01 pc using the Australia Telescope Compact Array (ATCA), the Mopra telescope and ALMA. At large scales, CO image combined with far-infrared data from Herschel revealed the overall molecular mass and its distribution across the CNC (Rebolledo et al. 2016). An extremely detailed map of the HI 21-cm line across the whole nebula revealed a complex filamentary structure in the atomic gas, which allowed the identification of regions where phase transition between atomic and molecular gas is happening (Rebolledo et al. 2017). An ATCA 1-3 GHz radio continuum image across the whole Carina region revealed a complete and spectacular view of the ionized gas in the region (Rebolledo et al. 2021). At small scales, ALMA high spatial resolution observations of molecular line tracers and dust showed that the level of stellar feedback effectively influences the fragmentation process in clumps, and provides further evidence for a higher level of turbulence in the material with a higher level of massive stellar feedback (Rebolledo et al. 2020).
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Pre- and protostellar cores in the 200 brightest Planck compact sourcesThe Planck compact source catalogue provides excellent samples for studying the earliest phases of star formation. Covering all galactic longitudes and latitudes they can give an overview of how star formation varies throughout the Milky Way, enabling a better insight into star formation out of the Galactic plane, where our current understanding is restricted mostly to nearby clouds. We examined the 200 brightest Planck compact sources visible from the northern hemisphere using observations from the James Clerk Maxwell Telescope's SCUBA2 bolometer array. Its high resolution revealed diverse, mostly filamentary structures, and allowed the extraction of point sources from the maps. We classified more than 1500 of these point sources and compiled a catalogue with their positions, sizes, and physical parameters. In our statistical analysis, we investigate properties of star-forming regions at different latitudes, aiming to better understand the flow of interstellar matter in the Galaxy and thus refine our latest view of the Milky Way.
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How to make an 85 Solar Mass Black HoleWe present in-progress resolution test and parameter space studies for very massive stars using MESA, showcasing current MESA version convergence studies.
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On the Z-(in)dependence of the Humphreys-Davidson LimitThe temperature independent part of the Humphreys-Davidson (HD) limit sets the boundary for evolutionary channels of massive stars that either end their lives as red supergiants (RSGs) or as the hotter blue supergiants (BSGs) and Wolf-Rayet stars. Recent downward revision of most luminous RSGs the Galaxy below log(L / L<SUB>⊙</SUB>) ≈ 5.5, more in line with the Magellanic Clouds, might hint towards a metallicity (Z)-independent HD limit. We present MESA single star models in the 15-40 M<SUB>⊙</SUB> range and study the different Z-dependent processes that could potentially affect the location of the upper luminosity limit of RSGs.
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TOI-2447 b / NGTS-29 b: a 69-day Saturn around a Solar analogueDiscovering transiting exoplanets with relatively long orbital periods (>10 d) is crucial to facilitate the study of cool exoplanet atmospheres (T<SUB>eq</SUB> < 700 K) and to understand exoplanet formation and inward migration further out than typical transiting exoplanets. In order to discover these longer period transiting exoplanets, long-term photometric, and radial velocity campaigns are required. We report the discovery of TOI-2447 b (=NGTS-29 b), a Saturn-mass transiting exoplanet orbiting a bright (T = 10.0) Solar-type star (T<SUB>eff</SUB> = 5730 K). TOI-2447 b was identified as a transiting exoplanet candidate from a single transit event of 1.3 per cent depth and 7.29 h duration in TESS Sector 31 and a prior transit event from 2017 in NGTS data. Four further transit events were observed with NGTS photometry which revealed an orbital period of P = 69.34 d. The transit events establish a radius for TOI-2447 b of $0.865 \pm 0.010\, \rm R_{\rm J}$, while radial velocity measurements give a mass of $0.386 \pm 0.025\, \rm M_{\rm J}$. The equilibrium temperature of the planet is 414 K, making it much cooler than the majority of TESS planet discoveries. We also detect a transit signal in NGTS data not caused by TOI-2447 b, along with transit timing variations and evidence for a ~150 d signal in radial velocity measurements. It is likely that the system hosts additional planets, but further photometry and radial velocity campaigns will be needed to determine their parameters with confidence. TOI-2447 b/NGTS-29 b joins a small but growing population of cool giants that will provide crucial insights into giant planet composition and formation mechanisms.
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Mass loss implementation and temperature evolution of very massive starsVery massive stars (VMS) dominate the physics of young clusters due to their extreme stellar winds. The mass lost by these stars in their winds determine their evolution, chemical yields and their end fates. In this contribution we study the main-sequence evolution of VMS with a new mass-loss recipe that switches from optically-thin O star winds to optically-thick Wolf-Rayet type winds through the model independent transition mass loss.
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Decomposing the AIA 304 Å Channel into Its Cool and Hot ComponentsThe AIA 304 Å channel on board the Solar Dynamics Observatory (SDO) offers a unique view of ≈10<SUP>5</SUP> K plasma emitting in the He II 304 Å line. However, when observing off-limb, the emission of the (small) cool structures in the solar atmosphere (such as spicules, coronal rain and prominence material) can be of the same order as the surrounding hot coronal emission from other spectral lines included in the 304 Å passband, particularly over active regions. In this paper, we investigate three methods based on temperature and morphology that are able to distinguish the cool and hot emission within the 304 Å passband. The methods are based on the Differential Emission Measure (DEM), a linear decomposition of the AIA response functions (RFit) and the Blind Source Separation (BSS) technique. All three methods are found to produce satisfactory results in both quiescent and flaring conditions, largely removing the diffuse corona and leading to images with cool material off-limb in sharp contrast with the background. We compare our results with co-aligned data from the Interface Region Imaging Spectrograph (IRIS) in the SJI 1400 Å and 2796 Å channels, and find the RFit method to best match the quantity and evolution of the cool material detected with IRIS. Some differences can appear due to plasma emitting in the logT =5.1 -5.5 temperature range, particularly during the catastrophic cooling stage prior to rain appearance during flares. These methods are, in principle, applicable to any passband from any instrument suffering from similar cool and hot emission ambiguity, as long as there is good coverage of the high-temperature range.
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Coma and tail of Comet 67P/Churyumov-Gerasimenko during the 2021-2022 apparitionWe present results on the global activity of comet 67P/Churyumov-Gerasimenko (67P), the ROSETTA target, during its first perihelion passage after the mission and after an encounter with planet Jupiter. 67P was observed by broad-band filter imaging at 33 epochs during 2021 May 21 to 2022 June 1. The mean radial flux profiles suggest that 'equilibrium' conditions for the dust flow in the coma existed from around perihelion until about 100 d thereafter. We propose a scenario for the smaller and larger radial exponents, measured before and after the 'equilibrium' phase. Four coma fans with possible source regions at +40°, -10°, -50°, and -70° latitude on the nucleus are identified. The three fans at southern latitudes may be identical with fan sources seen during post-perihelion in 2015-2016. The rotation axis of 67P may not have changed at all or at least not much (<5°) from the orientation measured during the Rosetta mission at the comet. The dust streamers in the coma originated from observed coma fans, containing mostly dust emitted within days to weeks before observation. Two dust streamers, a long- and a short-lasting one, contained heavy dust grains from emission periods hundreds of days before perihelion. Similar emission periods are obtained for the dust seen in the tail region of the comet. Similarities and differences in the dust activity during the recent apparition with that of the Rosetta mission at the comet are found.
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Polarimetry of small bodies and satellites of our Solar SystemThe large majority of astronomical observations are based on intensity measurements as a function of either wavelength or time, or both. Polarimetry, a technique which measures the way in which the electromagnetic field associated to the radiation oscillates, does provide further information about the objects that have emitted or scattered the observed radiation. For instance, polarimetric measurements can provide important constraints to the characterisation of cosmic dust (be it of interstellar or cometary origin), of the surfaces of the atmosphereless bodies and of planetary atmospheres. This property has been exploited in solar system science to study asteroids, comets, rocky and giant gaseous planets, and their satellites. In this paper we present a review of the polarimetric studies of the small bodies of the Solar System.
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Diagnosing transient plasma status: from solar atmosphere to tokamak divertorThis work strongly exploits the interdisciplinary links between astrophysical (such as the solar upper atmosphere) and laboratory plasmas (such as tokamak devices) by sharing the development of a common modelling for time-dependent ionisation. This is applied to the interpretation of solar flare data observed by the UVSP (Ultraviolet Spectrometer and Polarimeter), on-board the Solar Maximum Mission and the IRIS (Interface Region Imaging Spectrograph), and also to data from B2-SOLPS (Scrape Off Layer Plasma Simulations) for MAST (Mega Ampère Spherical Tokamak) Super-X divertor upgrade. The derived atomic data, calculated in the framework of the ADAS (Atomic Data and Analysis Structure) project, allow equivalent prediction in non-stationary transport regimes and transients of both the solar atmosphere and tokamak divertors, except that the tokamak evolution is about one thousand times faster.
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HST spectroscopy of chemically peculiar hot subdwarfs: PG 0909+276 and UVO0512-08High-resolution ultraviolet spectroscopy of two chemically peculiar hot subdwarfs, PG 0909+276 and UVO0512-08, has been obtained using the Hubble Space Telescope. Chemical abundances in the stars' atmospheres were measured from previous optical spectra and from the new ultraviolet observations. Iron-group metals, including cobalt, copper and zinc, are highly enriched relative to typical subdwarf B (sdB) stars. Lead is also enriched, but with an abundance similar to other sdB stars. The surface chemistry of these two stars is quite distinct from both hydrogen-rich normal sdB stars and also from the intermediate helium-rich sdB stars which show heavy-element superabundances. A full explanation for exotic chemistries in hot subdwarfs remains elusive.
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New Intense Multiband Photometric Observations of the Hot Carbon Star V348 Sagittarii (Abstract)(Abstract only) V348 Sgr is one of four hot carbon-rich and hydrogen-deficient stars. It is also the central star of a planetary nebula with a strong stellar wind, an infrared dust excess, and a circumstellar dust shell. Since July 2014, near daily multi-band photometric observations have been obtained at the Remote Observatory Atacama Desert (ROAD) close to San Pedro de Atacama, Chile. Strong variations of the brightness of V348 Sgr have been observed, ranging from magnitude 19 to 11.2 in V band. No clear periodicity is discernible in the data. The observed light curve shows much more variation and on a much shorter time scale than that of R CrB, the prototype hydrogen deficient, carbon- and helium-rich star. The star becomes markedly redder during extinction phases as a consequence of obscuring dust. The particular challenge in this case is to understand what triggers the production of dust.
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A review of seismic observations of Kepler and K2-Observed sdBV starsThis paper reviews recent seismic findings from Kepler and K2 data. Using three years of short cadence Kepler (K1) data, it is possible to examine time evolution of pulsations in an unprecedented way. While K2 observations are shorter, only three months, they are important as they are finding more sdBV stars than K1 did. Most importantly, K2 is discovering more p-mode pulsators with coverage not possible to get from the ground.
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LS IV — 14°116 : A Time-Resolved Spectroscopic StudyLSIV-14 116 is a very unusual subdwarf B star. It pulsates non-radially with high-order g-modes, these pulsations are unexpected and unexplained, as the effective temperature is 6 000K hotter than the blue edge of the hot subdwarf g-mode instability strip. Its spectrum is enriched in helium which is not seen in either the V361 Hya (p-mode pulsators) or the V1093 Her stars (g-mode pulsators). Even more unusual is the 4 dex overabundance of zirconium, yttrium, and strontium. It is proposed that these over-abundances are a result of extreme chemical stratification driven by radiative levitation. We have over 20hrs of VLT/UVES spectroscopy from which we have obtained radial velocity curves for individual absorption lines. We are currently exploring ways in which to resolve the photospheric motion as a function of optical depth.
