Stellar Systems Research Articles

New and robust gravitational-waveform model for high-mass-ratio binary neutron star systems with dynamical tidal effects

For the analysis of gravitational-wave signals, fast and accurate gravitational-waveform models are required. These enable us to obtain information on the system properties from compact binary mergers. In this article, we introduce the model, which contains a closed-form expression that describes tidal effects, focusing on the description of binary neutron star systems. The model improves upon previous versions by employing a larger set of numerical-relativity data for its calibration, by including high-mass ratio systems covering also a wider range of equations of state. It also takes into account dynamical tidal effects and the known post-Newtonian mass-ratio dependence of individual calibration parameters. We implemented the model in the publicly available uite software library by augmenting different binary black hole waveform models (, , and ). We test the validity of by comparing it with numerical-relativity waveforms, as well as other tidal models. Finally, we perform parameter estimation for GW170817 and GW190425 with the new tidal approximant and find overall consistent results with respect to previous studies. Published by the American Physical Society 2024

Measurements of visual double stars with PISCO2 at the Nice 76‐cm refractor in 2016–2017

AbstractWe present relative astrometric and photometric measurements of visual double stars made in 2016–2017, with PISCO2 installed at the 76‐cm refractor of Côte d'Azur Observatory in Nice (France). Our observing list contains orbital couples as well as double stars whose motion is still uncertain. Three different techniques were used for obtaining measurements: Lucky Imaging, Speckle Interferometry and the direct vector autocorrelation (DVA) method. From our observations of 1,510 multiple stars, we obtained 2,918 new measurements with angular separations in the range 0″.1–20″ and an average accuracy of . The mean error on the position angles is 1°.1. Most of the position angles were determined without the usual 180° ambiguity with the application of the DVA technique and/or by inspection of the Lucky images or the long integration files. We managed to routinely monitor faint systems () with large magnitude differences (up to ). We have thus been able to measure six systems containing red dwarf stars that had been poorly monitored since their discovery, from which we estimated the stellar masses thanks to Gaia measurements. We also measured the magnitude difference of the two components of 593 double stars with a mean error of 0.1 mag. Thanks to good seeing images and with the use of high‐contrast numerical filters, we have also been able to obtain 46 measurements with an angular separation smaller than the diffraction limit of our instrumentation. Except for a few objects that have been discussed, our measurements are in good agreement with the ephemerides computed with published orbital elements, even for the double stars whose separation is smaller than the diffraction limit. We also report the measurements of 205 new double stars that we found in the files obtained during the observations.

Acceleration and transport of relativistic electrons in the jets of the microquasar SS 433.

SS 433 is a microquasar, a stellar binary system that launches collimated relativistic jets. We observed SS 433 in gamma rays using the High Energy Stereoscopic System (H.E.S.S.) and found an energy-dependent shift in the apparent position of the gamma-ray emission from the parsec-scale jets. These observations trace the energetic electron population and indicate that inverse Compton scattering is the emission mechanism of the gamma rays. Our modeling of the energy-dependent gamma-ray morphology constrains the location of particle acceleration and requires an abrupt deceleration of the jet flow. We infer the presence of shocks on either side of the binary system, at distances of 25 to 30 parsecs, and that self-collimation of the precessing jets forms the shocks, which then efficiently accelerate electrons.

Behind the mask: can HARMONI@ELT detect biosignatures in the reflected light of Proxima b?

ABSTRACT Proxima b is a rocky exoplanet in the habitable zone of the nearest star system and a key test case in the search for extraterrestrial life. Here, we investigate the characterization of a potential Earth-like atmosphere around Proxima b in reflected light via molecule mapping, combining high-resolution spectroscopy (HRS) and high contrast imaging, using the first-generation integral field spectrograph, High Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph (HARMONI), on the 39-m Extremely Large Telescope (ELT). We simulate comprehensive observations of Proxima b at an assumed 45° inclination using HARMONI’s High Contrast Adaptive Optics mode, with spatial resolution $\sim 8 \,\rm mas$ ($3.88 \,\rm mas$ spaxel−1) and spectral resolving power R ≃ 17 000 between 1.538–$1.678\,\mathrm{\mu }\mathrm{m}$, containing the spectral features of water, carbon dioxide, and methane. Tellurics, stellar features, and additional noise sources are included, and removed using established molecule mapping techniques. We find that HARMONI’s current focal plane mask (FPM) is too large and obscures the orbit of Proxima b and thus explore smaller and offset FPMs to yield a detection. An $\rm {S/N}=5$ detection of Proxima b’s reflected light, suitable for atmospheric characterization, is possible with such modifications, requiring a minimum of 20 h, but ideally at least 30 h of integration time. We highlight that such detections do not scale with the photon noise, hence suitably detailed simulations of future instruments for the ELTs are needed to fully understand their ability to perform HRS observations of exoplanet atmospheres. Alterations to the HARMONI FPM design are feasible at this stage, but must be considered in context of other science cases.

Large dynamic range stellar radiation simulation optical system

For the current stellar spectral simulation can not realize the stellar color temperature information with large dynamic range simulation, this paper proposes a broad spectrum high-resolution subdivision and spatial beam zoning modulation combined with a large dynamic range of stellar radiation information simulation method, designed a kind of imaging and non-imaging stellar radiation information simulation optical system, using an optical system to achieve multi-color temperature spectrum and large dynamic range stellar simulation. The experimental results show that the designed system can simultaneously achieve the spectral simulation accuracy (single point evaluation) better than ± 7% in the range of spectral 450–1000 nm and color temperature 3000–11,000 K; on the premise of ensuring the spectral simulation accuracy, the magnitude simulation range reaches 0 to + 12 Mv, and the magnitude simulation accuracy is better than ± 0.05 Mv; Accurate simulation of stellar spectral information and energy large dynamic range tuning is realized, and the system is extended. The system function has been extended to realize the switching of broadband and narrowband modes, The half-peak width of the narrowband output beam is better than 4.1 nm, which extends the application of the spectral simulation technology and provides the theoretical and technical basis for the ground calibration of the development of the high-precision stellar radiation information ground simulation system.

Spatiotemporal dual-dimensional separation enables ultra-simple one-pot CRISPR-based molecular diagnostics

Recently, CRISPR/Cas-based technology has shown great promise for nucleic acid-based molecular diagnostics. However, most established strategies reported two-step operations to achieve high sensitivity but carry the risk of aerosol contamination. Herein, we developed a SpatioTemporal dual-dimensional sepAration-based CRISPR/Cas detection (STAR) system for simple and sensitive one-pot nucleic acid detection, taking advantage of the capillary forces of 3D-printed inner tube which dynamically connects the recombinase polymerase amplification (RPA, inner tube) and CRISPR/Cas12a derived detection (outer tube). With RPA reaction proceeding, the spontaneously defused amplicons will activate the CRISPR/Cas12a reaction, lighting up the inner tube with glamorous fluorescent signals. Benefiting from spatiotemporal dual-dimensional separation, the STAR system not only can address the carryover contamination and incompatibility between two reactions, but also does not require for additional operations once assembled. Our STAR system has exhibited high specificity and sensitivity for the detection of Salmonella typhimurium in both broth and spiked milk samples with detection limits of 100 CFU/mL. With the outstanding performance, the developed STAR system has shown great potential for the development of next-generation point-of-care molecular diagnostics.

Anisotropic energy injection from magnetar central engines in short GRBs

ABSTRACT A long-lived magnetar, potentially originating from a binary neutron star system, has been proposed to explain the extended emission observed in certain short-duration gamma-ray bursts (sGRBs), and is posited as a potential central engine to power the engine-fed kilonovae. Previously, the process by which energy is injected into the surrounding ejecta/jet was widely believed to be nearly isotropic. In this study, we employ special relativity magnetohydrodynamic (SRMHD) simulations to investigate the wind injection process from a magnetar central engine. We explore the dynamics and energy distribution within the system and found that the parameter α = uA/uMWN can be used to indicate the collimation of the magnetar wind energy injection, where uA is the local Alfven four-speed and uMWN is the four-speed of the magnetar wind nebular (MWN) formed from wind-ejecta collision. A significant portion of the injected energy from the magnetar spin-down wind will be channeled to the jet axis due to collimation within the MWN. Achieving isotropic energy injection requires a significantly small α that necessitates either an ultra-relativistic expanding MWN or an extremely low magnetization MWN, both of which are challenging to attain in sGRBs. Consequently, a considerably reduced energy budget (i.e. energy per solid angle reduced by a factor of up to 10 with respect to the value under isotropic assumption) is anticipated to be injected into the ejecta for engine-fed kilonovae. Engine-fed kilonovae would appear fainter than originally anticipated.

Observations of high-order multiplicity in a high-mass stellar protocluster

The dominant mechanism forming multiple stellar systems in the high-mass regime (M* ≳ 8 M⊙) remained unknown because direct imaging of multiple protostellar systems at early phases of high-mass star formation is very challenging. High-mass stars are expected to form in clustered environments containing binaries and higher-order multiplicity systems. So far only a few high-mass protobinary systems, and no definitive higher-order multiples, have been detected. Here we report the discovery of one quintuple, one quadruple, one triple and four binary protostellar systems simultaneously forming in a single high-mass protocluster, G333.23–0.06, using Atacama Large Millimeter/submillimeter Array high-resolution observations. We present a new example of a group of gravitationally bound binary and higher-order multiples during their early formation phases in a protocluster. This provides the clearest direct measurement of the initial configuration of primordial high-order multiple systems, with implications for the in situ multiplicity and its origin. We find that the binary and higher-order multiple systems, and their parent cores, show no obvious sign of disk-like kinematic structure. We conclude that the observed fragmentation into binary and higher-order multiple systems can be explained by core fragmentation, indicating its crucial role in establishing the multiplicity during high-mass star cluster formation.

Star-forming environments in smoothed particle magnetohydrodynamics simulations II: re-simulating isolated clumps to determine equivalence of extracted clumps and parent simulations

ABSTRACT What is the numerical reproducibility of a stellar system (including its discs) when evolving only a subset of (partially-evolved) smoothed particle hydrodynamics (SPH) particles? To investigate this, we modelled the evolution of 29 star-forming clumps that were extracted from our previous simulations that investigated the formation and early evolution of low-mass star clusters. These clumps were evolved using a three-dimensional smoothed particle radiation magnetohydrodynamics code, where we included or excluded non-ideal magnetohydrodynamics to match the cluster simulation. While star formation proceeded as expected, we were unable to identically reproduce any of the systems present at the end of the cluster simulations. However, the final distributions of stellar mass, stellar system mass, disc mass, and disc radii were reproduced statistically; unfortunately, the distribution of average magnetic field strengths in the discs was not reproduced statistically, but this may be a result of our updated algorithms governing the evolution of the magnetic field. Therefore, given that our clumps yield stellar masses that are statistically similar to those in the original low-mass star clusters, we have demonstrated that we can statistically reproduce systems (aside from their magnetic field strength) by evolving a subset of SPH particles. Therefore, clumps such as these can be used as initial conditions to investigate the formation of isolated stars from less-contrived initial environments.

Identification of birth places of high-velocity stars: CepOB2 association

We have searched high-velocity stars (runaway, walk-away, pulsars, HMXBs and LMXBs), which could have, most probably, originated in the complex CepOB2 association, i.e. in the cores (small clusters or multiple stellar systems) of it. With the trace-back motion study of them we found at least two pairs consisting of a runaway star and pulsar, which were within stellar groups in the Cep OB2 association ∼ 1.5-5.5 Myr ago.

Fermion Proca Stars: Vector-Dark-Matter-Admixed Neutron Stars

Dark matter could accumulate around neutron stars in sufficient amounts to affect their global properties. In this work, we study the effect of a specific model for dark matter—a massive and self-interacting vector (spin-1) field—on neutron stars. We describe the combined systems of neutron stars and vector dark matter using Einstein–Proca theory coupled to a nuclear matter term and find scaling relations between the field and metric components in the equations of motion. We construct equilibrium solutions of the combined systems, compute their masses and radii, and also analyze their stability and higher modes. The combined systems admit dark matter (DM) core and cloud solutions. Core solutions compactify the neutron star component and tend to decrease the total mass of the combined system. Cloud solutions have the inverse effect. Electromagnetic observations of certain cloud-like configurations would appear to violate the Buchdahl limit. This could make Buchdahl-limit-violating objects smoking gun signals for dark matter in neutron stars. The self-interaction strength is found to significantly affect both mass and radius. We also compare fermion Proca stars to objects where the dark matter is modeled using a complex scalar field. We find that fermion Proca stars tend to be more massive and geometrically larger than their scalar field counterparts for equal boson masses and self-interaction strengths. Both systems can produce degenerate masses and radii for different amounts of DM and DM particle masses.

Utilizing a control technique for orbital maintenance near [formula omitted] point and Lyapunov exponents

In present article, we have explored the orbit maintenance strategy around an artificial equilibrium point in the Sun–Jupiter system. Two control strategies, proportional control and proportional derivative control laws are discussed for orbit maintenance. The maximum Lyapunov exponent is used to check the chaotic behavior of planetary orbit. We anticipate that the recently established Lyapunov exponent criteria may be used to study motion of planets in generalized stellar binary systems. This research is being guided by the conclusions of recent observations as well as those that are expected from existing and upcoming planet search missions.

Karizma teorije

Against the background of the policing power of university discourse, the article discusses the prototypes and general roles of charismatic theorists from the 1960s to the present in the contexts of transformations of the university from its Humboldtian type based in the importance of national culture to its late-capitalist subjection to the neoliberal mercantilisation and globalisation of knowledge. Focused on the case study of the Slovenian literary theorist Dušan Pirjevec (1921–77) and the conditions of the communist policing of the university, the charisma of theory is explained as the theorist’s fascinating personal presence (working through the transfer with him/herself as the “subject who is supposed to know”) that imbues his/her texts with a quasi-metaphysical quality transgressing both the boundaries of any disciplinary knowledge and the “bureaucratised” position of average university teachers. In Pirjevec’s case, the charisma of theory is patterned on the figure of critical intellectuals, whereas in the neoliberal present, it is produced or reinforced within the global star system, driven mostly by US-American universities and transnational scholarly publishing.

Does Age Matter? Aging Masculinities in the Spanish Audiovisual Industry

The Spanish star system is witnessing the aging of its most acclaimed and awarded male actors from the 70s, 80s, 90s, and the first two decades of the 21st century: male actors belonging to the silent generation like José Sacristán (86), Emilio Gutiérrez Caba (81), Miguel Rellán (80), José María Pou (78), and Eusebio Poncela (76); actors belonging to the baby boomers such as Antonio Resines (69), Imanol Arias (67), José Coronado (66), Antonio Banderas (63), and Juan Echanove (62), to mention a few. Likewise, out of the 48 million people in Spain, 34.1% are individuals over 55, representing an important segment of Spanish society. Therefore, the aging of the star system mirrors the aging of Spanish moviegoers and TV spectators. Long-lasting TV series such as Cuéntame cómo pasó underscore the identification created across the years of the series between character, actor and viewer, and how they all experience and live time. This article also examines how aging Spanish male actors play, on the one hand, leading or secondary roles that do not deviate from the fit, tough, attractive, and sexually active profile often associated with the successful aging narrative in the American audiovisual industry of the geriaction subgenre, although in some instances they experience some sort of feminization attributed to aging, as is the case of the TV series Entrevías (2022) and El Príncipe (2014–2017). In these representations, the new roles assumed by aging masculinities when addressing social and family issues, ranging from the materiality of the body to moral obligations, are explored. On the other hand, series like Sentimos las molestias (Spain 2022) follow the path opened by The Kominsky Method (US 2018) by portraying aging as decline through the wide use of stereotypes.

“I want to be good:” morality, faith, and female spectatorial pleasure during World War I

ABSTRACT In this article, I draw on a handful of personal fan collections created in the first decade of the star system to examine how schoolgirls of faith engaged Hollywood cinema as a visual vernacular that helped them externalize ‘extreme states of personal being’, including grief, disgust, and arousal. Working through what I term ‘a cinephilia steeped in the distrust of pleasure’, I argue that some moviegoing girls turned to private scrapbooking and film reviewing to sort out embattled feelings arising while coming of age in the United States at a time of social upheaval, war, and epidemics.

Orbital Eccentricity of Celestial Motion—from Stars to Planets

The orbital eccentricity is one of the key parameters to describe the orbit of celestial bodies, which can provide important clues to reveal their dynamical evolution, and thus help to understand their formation and evolution processes along with the physical mechanisms behind them. The continuous improvement of observational technologies, enable us to explore the orbit of celestial bodies beyond the solar system, i.e., from stellar systems to planetary systems. Focusing on the orbital eccentricity of celestial bodies, this paper reviews the progress in stellar systems (including the main sequence stars, brown dwarfs, and compact stars) and planetary systems (including gas-giants, low-mass exoplanets such as “super-Earth” and “sub-Neptune”), and summarizes several similarities and issues among the investigations of orbital eccentricity under different scales. Finally, based on the ongoing and future astronomical facilities and missions, we discuss the future prospect on eccentricity studies of stellar systems, extra-solar planetary systems, and even extra-solar satellite systems.

The early evolution of young massive clusters

Context. Characterising the outcome of the star formation process is key to understand and predict the evolution of stellar populations. Especially the fraction of massive stars in young stellar clusters is of importance as they are the dominant sources of both mechanical and radiative feedback, strongly influencing the thermal and dynamical state of their birth environments, and beyond. Their supernovae may trigger the formation of new generations of stars in neighbouring regions. It turns out that a significant fraction of massive stars escape from their parent cluster via dynamical interactions of single stars and/or multiple stellar systems. Aims. M 17 is the nearest giant H II region hosting a very young and massive cluster: NGC 6618. Our aim is to identify stars brighter than G ≲ 21 mag that belong to NGC 6618, including the (massive) stars that may have escaped since its formation, and to determine the cluster distance and age. Methods. The Gaia DR3 database was used to identify members of NGC 6618 based on parallax and proper motion within 9′ from the cluster centre. We searched for nearby stars in a field of 5° around the cluster centre that may have originated from the cluster, and we determined their transverse velocity, kinematic age, and impact parameter. Results. We identified 42 members of NGC 6618 of which eight have a spectral type of O, with a mean distance of 1675−18+19 pc and a (transversal) velocity dispersion of about 3 km s−1, and a radial velocity dispersion of ∼6 km s−1. Another ten O stars are associated with NGC 6618, but they cannot be classified as members due to poor astrometry and/or high extinction. We have also identified six O star runaways. The relative transverse velocity of these runaways ranges from 10 to 70 km s−1 and their kinematic age ranges from about 100 to 750 kyr. Given the already established young age of NGC 6618 (≲1 Myr), this implies that massive stars are being ejected from the cluster already directly after (or during) the cluster formation process. Conclusions. When constructing the initial mass function, one has to take into account the massive stars that have already escaped from the cluster, that is, about 30% of the O stars of the original population of NGC 6618. The trajectories of the O runaways can be traced back to the central 0.2–0.3 pc region of NGC 6618. The good agreement between the evolutionary and kinematic age of the runaways implies that the latter provides an independent way to estimate (a lower limit to) the age of the cluster.

New KiDS in town

We report the discovery of a significant and compact over-density of old and metal-poor stars in the fourth data release of the KiDS survey (DR4). The discovery is confirmed by deeper HSC-SSP data revealing the old main sequence turn-off of a stellar system located at a distance from the sun of D⊙ = 145-13+14 kpc in the direction of the Sextans constellation. The system has an absolute integrated magnitude (MV = −3.9 ± 0.4), half-light radius (rh = 193-46+61 pc), and ellipticity (e = 0.46-0.15+0.11) values that are typical of ultra-faint dwarf galaxies (UFDs). The central surface brightness is near the lower limits of known local dwarf galaxies of a similar integrated luminosity, as expected for stellar systems that have escaped detection until now. The distance of the newly found system suggests that it is likely to be a satellite of our own Milky Way and we have thus tentatively named it Sextans II (KiDS-UFD-1).

MgAl burning chain in ω Centauri

In this study, we report the results of the analysis of Fe, Mg, Al, and Si abundances analysis for a sample of 439 stars in ω Centauri, using high-resolution spectra obtained with the VLT/FLAMES multi-object spectrograph. Our analysis reveals the presence of four distinct Fe populations, with the main peak occurring at a low metallicity, consistent with previous literature findings. We observe a discrete and pronounced Mg–Al anticorrelation, which exhibits variations in shape and extension as a function of metallicity. Specifically, this anticorrelation is present in stars with metallicities lower than approximately −1.3 dex, while it becomes less evident or absent for higher [Fe/H] values. Additionally, we detect (anti)correlations between Mg and Si, and between Al and Si, whose extensions also vary with metallicity, similar to the Mg–Al anticorrelation. These results suggest that the MgAl cycle plays a crucial role in the formation of multiple populations in ω Centauri, with the presence of all (anti)correlations at metallicities lower than –1.3 dex, providing evidence for the burning of Mg at very high temperatures (> 108 K), at least in the metal-poor regime. Furthermore, we observe a clear trend of stars with [Al/Fe] > +0.5 dex as a function of metallicity, confirming for the first time the existence of the two channels of Al production and destruction. This evidence can help to provide further constraints on the potential nature of the polluters responsible for the observed chemical anomalies in this stellar system. Finally, we find that the two most metal-poor populations identified in our sample are compatible with null or very small metallicity dispersion and we discuss how this result fits into a scenario where ω Centauri is the remnant of a disrupted nucleated dwarf galaxy.

A Study of Ultracompact H II Regions with Extended Emission: their Importance, Origin, and Evolution

Studies of ultracompact H II regions have shown that the Lyman-continuum photon (hereafter, Ly-photon) rates inferred from the radio emission and values based on the infrared emission are inconsistent with a rate estimated from radio being up to 90% lower. One possible solution to this inconsistency is the presence of extended radio emission associated with the ultracompact core, which is undetected by most interferometric arrays, due to the lack of very short baselines. Since such extended emission would require a significantly higher rate of Ly-photons to keep its ionization state compared to the compact core, its existence would also resolve the “age problem of the ultracompact H II regions: the number of ultracompact H II regions observed in the Galaxy is much larger than what is expected based on their dynamical age (sound crossing time)”, as there is no need to confine the ionized gas within the ultracompact core. To test this hypothesis, we conducted a study of eight ultracompact H II regions with extended emission using radio data from the upgraded Giant Metrewave Radio Telescope (1.25–1.45 GHz) and the GLOSTAR survey (4–8 GHz), and infrared data from the UKIDSS, 2MASS, MIPSGAL, and Hi-GAL surveys. From our study, we found that the Ly-photon rate inferred from the radio emission is consistent with that inferred from the total infrared luminosity to within 20–30% when we include the extended emission. Furthermore, we identified the candidate ionizing stars and observed that, in some cases, multiple stars were responsible for ionizing the neutral gas in an ultracompact H II region. Here, we present the key results for one region (G19.68–0.13) out of the entire list of our targets.