RSS 1.0Instrumentation and Methods for Astrophysics (astro-ph.IM)
Browse by
Recent Submissions
-
The BlackGEM Telescope Array. I. OverviewThe main science aim of the BlackGEM array is to detect optical counterparts to gravitational wave mergers. Additionally, the array will perform a set of synoptic surveys to detect Local Universe transients and short timescale variability in stars and binaries, as well as a six-filter all-sky survey down to ∼22nd mag. The BlackGEM Phase-I array consists of three optical wide-field unit telescopes. Each unit uses an f/5.5 modified Dall-Kirkham (Harmer-Wynne) design with a triplet corrector lens, and a 65 cm primary mirror, coupled with a 110Mpix CCD detector, that provides an instantaneous field-of-view of 2.7 square degrees, sampled at 0.″564 pixel<SUP>‑1</SUP>. The total field-of-view for the array is 8.2 square degrees. Each telescope is equipped with a six-slot filter wheel containing an optimised Sloan set (BG-u, BG-g, BG-r, BG-i, BG-z) and a wider-band 440–720 nm (BG-q) filter. Each unit telescope is independent from the others. Cloud-based data processing is done in real time, and includes a transient-detection routine as well as a full-source optimal-photometry module. BlackGEM has been installed at the ESO La Silla observatory as of 2019 October. After a prolonged COVID-19 hiatus, science operations started on 2023 April 1 and will run for five years. Aside from its core scientific program, BlackGEM will give rise to a multitude of additional science cases in multi-colour time-domain astronomy, to the benefit of a variety of topics in astrophysics, such as infant supernovae, luminous red novae, asteroseismology of post-main-sequence objects, (ultracompact) binary stars, and the relation between gravitational wave counterparts and other classes of transients.
-
GERry: A code to optimise the hunt for the electromagnetic counter-parts to gravitational wave eventsThe search for the electromagnetic counterparts to Gravitational Wave (GW) events has been rapidly gathering pace in recent years thanks to the increasing number and capabilities of both gravitational wave detectors and wide field survey telescopes. Difficulties remain, however, in detecting these counterparts due to their inherent scarcity, faintness and rapidly evolving nature. To find these counterparts, it is important that one optimizes the observing strategy for their recovery. This can be difficult due to the large number of potential variables at play. Such follow-up campaigns are also capable of detecting hundreds or potentially thousands of unrelated transients, particularly for GW events with poor localization. Even if the observations are capable of detecting a counterpart, finding it among the numerous contaminants can prove challenging. Here we present the Gravitational wave Electromagnetic RecovRY code (GERRY) to perform detailed analysis and survey-agnostic quantification of observing campaigns attempting to recover electromagnetic counterparts. GERRY considers the campaign's spatial, temporal and wavelength coverage, in addition to Galactic extinction and the expected counterpart light curve evolution from the GW 3D localization volume. It returns quantified statistics that can be used to: determine the probability of having detected the counterpart, identified the most promising sources, and assessed and refine strategy. Here we demonstrate the code to look at the performance and parameter space probed by current and upcoming wide-field surveys such as GOTO and VRO.
-
The Gravitational-wave Optical Transient Observer (GOTO)The Gravitational-wave Optical Transient Observer (GOTO) is a project dedicated to identifying optical counterparts to gravitational-wave detections using a network of dedicated, wide-field telescopes. After almost a decade of design, construction, and commissioning work, the GOTO network is now fully operational with two antipodal sites: La Palma in the Canary Islands and Siding Spring in Australia. Both sites host two independent robotic mounts, each with a field-of-view of 44 square degrees formed by an array of eight 40cm telescopes, resulting in an instantaneous 88 square degree field-of-view per site. All four telescopes operate as a single integrated network, with the ultimate aim of surveying the entire sky every 2-3 days and allowing near-24-hour response to transient events within a minute of their detection. In the modern era of transient astronomy, automated telescopes like GOTO form a vital link between multi-messenger discovery facilities and in-depth follow-up by larger telescopes. GOTO is already producing a wide range of scientific results, assisted by an efficient discovery pipeline and a successful citizen science project: Kilonova Seekers.
-
Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Our GalaxyAs we learn more about the multi-scale interstellar medium (ISM) of our Galaxy, we develop a greater understanding for the complex relationships between the large-scale diffuse gas and dust in Giant Molecular Clouds (GMCs), how it moves, how it is affected by the nearby massive stars, and which portions of those GMCs eventually collapse into star forming regions. The complex interactions of those gas, dust and stellar populations form what has come to be known as the ecology of our Galaxy. Because we are deeply embedded in the plane of our Galaxy, it takes up a significant fraction of the sky, with complex dust lanes scattered throughout the optically recognizable bands of the Milky Way. These bands become bright at (sub-)millimetre wavelengths, where we can study dust thermal emission and the chemical and kinematic signatures of the gas. To properly study such large-scale environments, requires deep, large area surveys that are not possible with current facilities. Moreover, where stars form, so too do planetary systems, growing from the dust and gas in circumstellar discs, to planets and planetesimal belts. Understanding the evolution of these belts requires deep imaging capable of studying belts around young stellar objects to Kuiper belt analogues around the nearest stars. Here we present a plan for observing the Galactic Plane and circumstellar environments to quantify the physical structure, the magnetic fields, the dynamics, chemistry, star formation, and planetary system evolution of the galaxy in which we live with AtLAST; a concept for a new, 50m single-dish sub-mm telescope with a large field of view which is the only type of facility that will allow us to observe our Galaxy deeply and widely enough to make a leap forward in our understanding of our local ecology.
-
X-Shooting ULLYSES: Massive stars at low metallicity. II. DR1: Advanced optical data products for the Magellanic CloudsContext. The XShootU project aims to obtain ground-based optical to near-infrared spectroscopy of all targets observed by the Hubble Space Telescope (HST) under the Director's Discretionary program ULLYSES. Using the medium-resolution spectrograph X-shooter, spectra of 235 OB and Wolf-Rayet (WR) stars in subsolar metallicity environments have been secured. The bulk of the targets belong to the Large and Small Magellanic Clouds, with the exception of three stars in NGC 3109 and Sextans A. <BR /> Aims: This second paper in the series focuses on the optical observations of Magellanic Clouds targets. It describes the uniform reduction of the UVB (300-560 nm) and VIS (550-1020 nm) XShootU data as well as the preparation of advanced data products that are suitable for homogeneous scientific analyses. <BR /> Methods: The data reduction of the RAW data is based on the ESO CPL X-shooter pipeline. We paid particular attention to the determination of the response curves. This required equal flat-fielding of the science and flux standard star data and the derivation of improved flux standard models. The pipeline products were then processed with our own set of routines to produce a series of advanced data products. In particular, we implemented slit-loss correction, absolute flux calibration, (semi-)automatic rectification to the continuum, and a correction for telluric lines. The spectra of individual epochs were further corrected for the barycentric motion, re-sampled and co-added, and the spectra from the two arms were merged into a single flux-calibrated spectrum covering the entire optical range with maximum signal-to-noise ratio. <BR /> Results: We identify and describe an undocumented recurrent ghost visible on the RAW data. We present an improved flat-fielding strategy that limits artifacts when the SCIENCE and FLUX standard stars are observed on different nights. The improved FLUX standard models and the new grid of anchor points limit artifacts of the response curve correction, for example on the shape of the wings of the Balmer lines, from a couple of per cent of the continuum level to less than 0.5%. We confirm the presence of a radial velocity shift of about 3.5 km s<SUP>−1</SUP> between the UVB and the VIS arm of X-shooter and that there are no short term variations impacting the RV measurements. RV precision better than 1 km s<SUP>-1</SUP> can be obtained on sharp telluric lines while RV precision on the order of 2 to 3 km s<SUP>-1</SUP> is obtained on data with the best S/N. <BR /> Conclusions: For each target observed by XShootU, we provide three types of data products: (i) two-dimensional spectra for each UVB and VIS exposure before and after correction for the instrument response; (ii) one-dimensional UVB and VIS spectra as produced by the X-shooter pipeline before and after response-correction, and applying various processing, including absolute flux calibration, telluric removal, normalization and barycentric correction; and (iii) co-added flux-calibrated and rectified spectra over the full optical range, for which all available XShootU exposures were combined. For the large majority of the targets, the final signal-to-noise ratio per resolution element is above 200 in the UVB and in the VIS co-added spectra. The reduced data and advanced scientific data products are made available to the community. Together with the HST UV ULLYSES data, they should enable various science goals, from detailed stellar atmosphere and stellar wind studies, and empirical libraries for population synthesis, to the study of the local nebular environment and feedback of massive stars in subsolar metallicity environments. <P />Full Tables 1, 2 and C.1 are available at the CDS via anonymous ftp to <A href=https://cdsarc.cds.unistra.fr>cdsarc.cds.unistra.fr</A> (ftp://130.79.128.5) or via <A href=https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/688/A104>https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/688/A104</A> <P />The DR1 data and an accompanying release documentation are made available on Zenodo <A href=https://doi.org/10.5281/zenodo.11122188>https://doi.org/10.5281/zenodo.11122188</A> <P />Based on observations collected at the European Southern Observatory under ESO program ID 106.211Z.001.
-
X-Shooting ULLYSES: Massive stars at low metallicity: IV. Spectral analysis methods and exemplary results for O starsContext. The spectral analysis of hot, massive stars is a fundamental astrophysical method of determining their intrinsic properties and feedback. With their inherent, radiation-driven winds, the quantitative spectroscopy for hot, massive stars requires detailed numerical modeling of the atmosphere and an iterative treatment in order to obtain the best solution within a given framework. Aims. We present an overview of different techniques for the quantitative spectroscopy of hot stars employed within the X-Shooting ULLYSES collaboration, ranging from grid-based approaches to tailored spectral fits. By performing a blind test for selected targets, we gain an overview of the similarities and differences between the resulting stellar and wind parameters. Our study is not a systematic benchmark between different codes or methods; our aim is to provide an overview of the parameter spread caused by different approaches. Methods. For three different stars from the XShooting ULLYSES sample (SMC O5 star AzV 377, LMC O7 star Sk -69° 50, and LMC O9 star Sk-66° 171), we employ different stellar atmosphere codes (CMFGEN, FASTWIND, PoWR) and different strategies to determine their best-fitting model solutions. For our analyses, UV and optical spectroscopy are used to derive the stellar and wind properties with some methods relying purely on optical data for comparison. To determine the overall spectral energy distribution, we further employ additional photometry from the literature. Results. The effective temperatures found for each of the three different sample stars agree within 3 kK, while the differences in log g can be up to 0.2 dex. Luminosity differences of up to 0.1 dex result from different reddening assumptions, which seem to be systematically larger for the methods employing a genetic algorithm. All sample stars are found to be enriched in nitrogen. The terminal wind velocities are surprisingly similar and do not strictly follow the u<SUB>∞</SUB>‑T<SUB>eff</SUB> relation. Conclusions. We find reasonable agreement in terms of the derived stellar and wind parameters between the different methods. Tailored fitting methods tend to be able to minimize or avoid discrepancies obtained with coarser or increasingly automatized treatments. The inclusion of UV spectral data is essential for the determination of realistic wind parameters. For one target (Sk -69° 50), we find clear indications of an evolved status.
-
Kilonova Seekers: the GOTO project for real-time citizen science in time-domain astrophysicsTime-domain astrophysics continues to grow rapidly, with the inception of new surveys drastically increasing data volumes. Democratized, distributed approaches to training sets for machine learning classifiers are crucial to make the most of this torrent of discovery - with citizen science approaches proving effective at meeting these requirements. In this paper, we describe the creation of and the initial results from the Kilonova Seekers citizen science project, built to find transient phenomena from the GOTO telescopes in near real-time. Kilonova Seekers launched in 2023 July and received over 600 000 classifications from approximately 2000 volunteers over the course of the LIGO-Virgo-KAGRA O4a observing run. During this time, the project has yielded 20 discoveries, generated a 'gold-standard' training set of 17 682 detections for augmenting deep-learned classifiers, and measured the performance and biases of Zooniverse volunteers on real-bogus classification. This project will continue throughout the lifetime of GOTO, pushing candidates at ever-greater cadence, and directly facilitate the next-generation classification algorithms currently in development.
-
Feasibility of meteor surveying from a Venus orbiterMeteor and bolide phenomena caused by the atmospheric ablation of incoming meteoroids are predicted to occur at the planet Venus. Their systematic observation would allow to measure and compare the sub-mm to m meteoroid flux at different locations in the solar system. Using a physical model of atmospheric ablation, we demonstrate that Venus meteors would be brighter, shorter-lived, and appear higher in the atmosphere than Earth meteors. To investigate the feasibility of meteor detection at Venus from an orbiter, we apply the SWARMS survey simulator tool to sets of plausible meteoroid population parameters, atmospheric models and instrument designs suited to the task, such as the Mini-EUSO camera operational on the ISS since 2019. We find that such instrumentation would detect meteors at Venus with a 1.5× to 2.5× higher rate than at Earth. The estimated Venus–Earth detection ratio remains insensitive to variations in the chosen observation orbit and detector characteristics, implying that a meteor survey from Venus orbit is feasible, though contingent on the availability of suitable algorithms and methods for efficient on-board processing and downlinking of the meteor data to Earth. We further show that a hypothetical camera onboard the upcoming EnVision mission to Venus similar to the ISS instrument should detect many times more meteors than needed for an initial characterisation of the large meteoroid population at 0.7 au from the Sun.
-
X-Shooting ULLYSES: Massive Stars at Low MetallicityThe Hubble Space Telescope has devoted 500 orbits to observing 250 massive stars with low metallicity in the ultraviolet (UV) range within the framework of the ULLYSES program. The X-Shooting ULLYSES (XShootU) project enhances the legacy value of this UV dataset by providing high-quality optical and near-infrared spectra, which are acquired using the wide-wavelength- coverage X-shooter spectrograph at ESO's Very Large Telescope. XShootU emphasises the importance of combining UV with optical spectra for the consistent determination of key stellar parameters such as effective temperature, surface gravity, luminosity, abundances, and wind characteristics including mass-loss rates as a function of metallicity. Since uncertainties in these parameters have implications across various branches of astrophysics, the data and modelling generated by the XShootU project are poised to significantly advance our understanding of massive stars at low metallicity. This is particularly crucial for confidently interpreting James Webb Space Telescope (JWST) data of the earliest stellar generations, making XShootU a unique resource for comprehending individual spectra of low-metallicity stars.
-
The wide-field, multiplexed, spectroscopic facility WEAVE: Survey design, overview, and simulated implementationWEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, saw first light in late 2022. WEAVE comprises a new 2-deg field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable 'mini' integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366-959 nm at R ~ 5000, or two shorter ranges at $R\sim 20\, 000$. After summarizing the design and implementation of WEAVE and its data systems, we present the organization, science drivers, and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy's origins by completing Gaia's phase-space information, providing metallicities to its limiting magnitude for ~3 million stars and detailed abundances for ~1.5 million brighter field and open-cluster stars; (ii) survey ~0.4 million Galactic-plane OBA stars, young stellar objects, and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey ~400 neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionized gas in z < 0.5 cluster galaxies; (vi) survey stellar populations and kinematics in ${\sim} 25\, 000$ field galaxies at 0.3 ≲ z ≲ 0.7; (vii) study the cosmic evolution of accretion and star formation using >1 million spectra of LOFAR-selected radio sources; and (viii) trace structures using intergalactic/circumgalactic gas at z > 2. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator.
-
The Gravitational-wave Optical Transient Observer (GOTO)The Gravitational-wave Optical Transient Observer (GOTO) is a wide-field telescope project focused on detecting optical counterparts to gravitational-wave sources. GOTO uses arrays of 40 cm unit telescopes (UTs) on a shared robotic mount, which scales to provide large fields of view in a cost-effective manner. A complete GOTO mount uses 8 unit telescopes to give an overall field of view of 40 square degrees, and can reach a depth of 20th magnitude in three minutes. The GOTO-4 prototype was inaugurated with 4 unit telescopes in 2017 on La Palma, and was upgraded to a full 8-telescope array in 2020. A second 8-UT mount will be installed on La Palma in early 2021, and another GOTO node with two more mount systems is planned for a southern site in Australia. When complete, each mount will be networked to form a robotic, dual-hemisphere observatory, which will survey the entire visible sky every few nights and enable rapid follow-up detections of transient sources.
-
The Gravitational-wave Optical Transient Observer (GOTO)The Gravitational-wave Optical Transient Observer (GOTO) is a wide-field telescope project focused on detecting optical counterparts to gravitational-wave sources. Each GOTO robotic mount holds eight 40 cm telescopes, giving an overall field of view of 40 square degrees. As of 2022 the first two GOTO mounts have been commissioned at the Roque de los Muchachos Observatory on La Palma, Canary Islands, and construction of the second node with two additional 8-telescope mounts has begin at Siding Spring Observatory in New South Wales, Australia. Once fully operational each GOTO mount will be networked to form a robotic, multi-site observatory, which will survey the entire visible sky every two nights and enable rapid follow-up detections of transient sources.
-
Observations of meteors in the Earth's atmosphere: Reducing data from dedicated double-station wide-angle camerasMeteoroids entering the Earth's atmosphere can be observed as meteors, thereby providing useful information on their formation and hence on their parent bodies. We developed a data reduction software package for double station meteor data from the SPOSH camera, which includes event detection, image geometric and radiometric calibration, radiant and speed estimates, trajectory and orbit determination, and meteor light curve recovery. The software package is designed to fully utilise the high photometric quality of SPOSH images. This will facilitate the detection of meteor streams and studies of their trajectories. We have run simulations to assess the performance of the software by estimating the radiants, speeds, and magnitudes of synthetic meteors and comparing them with the a priori values. The estimated uncertainties in radiant location had a zero mean with a median deviation between 0.03<SUP>∘</SUP> and 0.11<SUP>∘</SUP> for the right ascension and 0.02<SUP>∘</SUP> and 0.07<SUP>∘</SUP> for the declination. The estimated uncertainties for the speeds had a median deviation between 0.40 and 0.45 km s<SUP>-1</SUP>. The brightness of synthetic meteors was estimated to within +0.01 m. We have applied the software package to 177 real meteors acquired by the SPOSH camera. The median propagated uncertainties in geocentric right ascension and declination were found to be of 0.64<SUP>∘</SUP> and 0.29<SUP>∘</SUP>, while the median propagated error in geocentric speed was 1.21 km s<SUP>-1</SUP>.
-
Polarimetry as a Tool to Study Multi-Dimensional Winds and DisksI start with a discussion of spherical winds and small-scale clumping, before continuing with various theories that have been proposed to predict how mass loss depends on stellar rotation - both in terms of wind strength, as well as the latitudinal dependence of the wind. This very issue is crucial for our general understanding of angular momentum evolution in massive stars, and the B[e] phenomenon in particular. I then discuss the tool of linear polarimetry that allows us to probe the difference between polar and equatorial mass loss, allowing us to test B[e] and related disk formation theories.
-
Scientific Goals of the Kunlun Infrared Sky Survey (KISS)The high Antarctic plateau provides exceptional conditions for infrared observations on account of the cold, dry and stable atmosphere above the ice surface. This paper describes the scientific goals behind the first program to examine the time-varying universe in the infrared from Antarctica - the Kunlun Infrared Sky Survey (KISS). This will employ a 50cm telescope to monitor the southern skies in the 2.4μmK <SUB>dark</SUB> window from China's Kunlun station at Dome A, on the summit of the Antarctic plateau, through the uninterrupted 4-month period of winter darkness. An earlier paper discussed optimisation of the K <SUB>dark</SUB> filter for sensitivity (Li et al. 2016). This paper examines the scientific program for KISS. We calculate the sensitivity of the camera for the extrema of observing conditions that will be encountered. We present the parameters for sample surveys that could then be carried out for a range of cadences and sensitivities. We then discuss several science programs that could be conducted with these capabilities, involving star formation, brown dwarfs and hot Jupiters, exoplanets around M dwarfs, the terminal phases of stellar evolution, fast transients, embedded supernova searches, reverberation mapping of AGN, gamma ray bursts and the detection of the cosmic infrared background.
-
The cloudbow of planet Earth observed in polarisationContext. Scattering processes in the atmospheres of planets cause characteristic features that can be particularly well observed in polarisation. For planet Earth, both molecular scattering (Rayleigh) and scattering by small particles (Mie) imprint specific signatures in its phase curve. Polarised phase curves allow us to infer physical and chemical properties of the atmosphere like the composition of the gaseous and liquid components, droplet sizes, and refraction indices. <BR /> Aims: An unequivocal prediction of a liquid-water-loaded atmosphere is the existence of a rainbow feature at a scattering angle of around 138-144°. Earthshine allows us to observe the primary rainbow in linear polarisation. <BR /> Methods: We observed polarisation spectra of Earthshine using FORS2 at the Very Large Telescope for phase angles from 33° to 65° (Sun-Earth-Moon angle). The spectra were used to derive the degree of polarisation in the B, V, R, and I passbands and the phase curve from 33° to 136°. The new observations extend to the smallest phases that can be observed from the ground. <BR /> Results: The degree of polarisation of planet Earth is increasing for decreasing phase angles downwards of 45° in the B, V, R, and I passbands. From comparison of the phase curve observed with models of an Earth-type atmosphere we are able to determine the refractive index of water and to constrain the mean water droplet sizes to 6-7μm. Furthermore, we can retrieve the mean cloud fraction of liquid water clouds to 0.3, and the mean optical depth of the water clouds to values between 10 and 20. <BR /> Conclusions: Our observations allow us to discern two fundamentally different scattering mechanisms of the atmosphere of planet Earth: molecular and particle scattering. The physical and chemical properties can be retrieved with high fidelity through suitable inversion of the phase curve. Observations of polarimetric phase curves of planets beyond the Solar System shall be extremely valuable for a thorough characterisation of their atmospheres.
-
Aliphatic hydrocarbon content of interstellar dustThere is considerable uncertainty as to the amount of carbon incorporated in interstellar dust. The aliphatic component of the carbonaceous dust is of particular interest because it produces a significant 3.4 μm absorption feature when viewed against a background radiation source. The optical depth of the 3.4 μm absorption feature is related to the number of aliphatic carbon C-H bonds along the line of sight. It is possible to estimate the column density of carbon locked up in the aliphatic hydrocarbon component of interstellar dust from quantitative analysis of the 3.4 μm interstellar absorption feature provided that the absorption coefficient of aliphatic hydrocarbons incorporated in the interstellar dust is known. We report laboratory analogues of interstellar dust by experimentally mimicking interstellar/circumstellar conditions. The resultant spectra of these dust analogues closely match those from astronomical observations. Measurements of the absorption coefficient of aliphatic hydrocarbons incorporated in the analogues were carried out by a procedure combining FTIR and <SUP>13</SUP>C NMR spectroscopies. The absorption coefficients obtained for both interstellar analogues were found to be in close agreement [4.76(8) × 10<SUP>-18</SUP> cm group<SUP>-1</SUP> and 4.69(14) × 10<SUP>-18</SUP> cm group<SUP>-1</SUP>], less than half those obtained in studies using small aliphatic molecules. The results thus obtained permit direct calibration of the astronomical observations, providing rigorous estimates of the amount of aliphatic carbon in the interstellar medium.
-
A method for mapping the aliphatic hydrocarbon content of interstellar dust towards the Galactic CentreIn the interstellar medium, the cosmic elemental carbon abundance includes the total carbon in both gas and solid phases. The aim of the study was to trial a new method for measuring the amount and distribution of aliphatic carbon within interstellar dust over wide fields of view of our Galaxy. This method is based on the measurement of the 3.4-μm absorption feature from aliphatic carbonaceous matter. This can readily be achieved for single sources using infrared (IR) spectrometers. However, making such measurements over wide fields requires an imaging IR camera, equipped with narrow-band filters that are able to sample the spectrum. While this cannot produce as good a determination of the spectra, the technique can be applied to potentially tens to hundreds of sources simultaneously, over the field of view of the camera. We examined this method for a field in the centre of the Galaxy, and produced a map showing the variation of 3.4-μm optical depth across it.
-
Method to observe Jupiter's radio emissions at high resolution using multiple LOFAR stations: a first case study of the Io-decametric emission using the Irish IE613, French FR606, and German DE604 stationsThe Low Frequency Array (LOFAR) is an international radio telescope array, consisting of 38 stations in the Netherlands and 14 international stations spread over Europe. Here, we present an observation method to study the Jovian decametric radio emissions from several LOFAR stations (here Birr Castle in Ireland, Nançay in France, and Postdam in Germany), at high temporal and spectral resolution. This method is based on prediction tools, such as radio emission simulations and probability maps, and data processing. We report an observation of Io-induced decametric emission from 2021 June, and a first case study of the substructures that compose the macroscopic emissions (called millisecond bursts). The study of these bursts makes it possible to determine the electron populations at the origin of these emissions. We then present several possible future avenues for study based on these observations. The methodology and study perspectives described in this paper can be applied to new observations of Jovian radio emissions induced by Io, but also by Ganymede or Europa, or Jovian auroral radio emissions.
-
Ultraviolet spectropolarimetry: conservative and nonconservative mass transfer in OB interacting binariesThe current consensus is that at least half of the OB stars are formed in binary or multiple star systems. The evolution of OB stars is greatly influenced by whether the stars begin as close binaries, and the evolution of the binary systems depend on whether the mass transfer is conservative or nonconservative. FUV/NUV spectropolarimetry is poised to answer the latter question. This paper discusses how the Polstar spectropolarimetry mission can characterize the degree of nonconservative mass transfer that occurs at various stages of binary evolution, from the initial mass reversal to the late Algol phase, and quantify its amount. The proposed instrument combines spectroscopic and polarimetric capabilities, where the spectroscopy can resolve Doppler shifts in UV resonance lines with 10 km/s precision, and polarimetry can resolve linear polarization with 10<SUP>−3</SUP> precision or better. The spectroscopy will identify absorption by mass streams and other plasmas seen in projection against the stellar disk as a function of orbital phase, as well as scattering from extended splash structures, including jets. The polarimetry tracks the light coming from material not seen against the stellar disk, allowing the geometry of the scattering to be tracked, resolving ambiguities left by the spectroscopy and light-curve information. For example, nonconservative mass streams ejected in the polar direction will produce polarization of the opposite sign from conservative transfer accreting in the orbital plane. Time domain coverage over a range of phases of the binary orbit are well supported by the Polstar observing strategy. Special attention will be given to the epochs of enhanced systemic mass loss that have been identified from IUE observations (pre-mass reversal and tangential gas stream impact). We show how the history of systemic mass and angular momentum loss/gain episodes can be inferred via ensemble evolution through the r-q diagram. Combining the above elements will significantly improve our understanding of the mass transfer process and the amount of mass that can escape from the system, an important channel for changing the final mass and ultimate supernova of a large number of massive stars found in binaries at close enough separation to undergo interaction.
