bluuebunny/crossref_metadata_2025_split huggingface dataset:
A comment on the properties of the matter flow through the first Langrangian point
Authors: Ziółkowski Janusz , Zdziarski Andrzej A 
Published: September 2021

Abstract
We analyse properties of the mass outflow from the Roche lobe filling component of a semi-detached binary system. We follow the approaches published by Paczyński & Sienkiewicz and by Lubow & Shu, which we compare with other simplified approaches. We find that the density of the flow at L1 is orders of magnitude lower than the density on the same equipotential but away from L1. Furthermore, the effective cross-section of the flow, after averaging over its profile of the momentum density, is much lower than some published estimates done without accounting for the averaging. Thus, the use of some simplified formulae for the density and the flow cross-section can lead to overestimates of the accretion rate and of the mass contained in the L1 regions by very large factors unless they are supported by simultaneous integrations of the equations of stellar structure for the outer layers of the donor.
Nucleosynthesis signatures of neutrino-driven winds from proto-neutron stars: a perspective from chemical evolution models
Authors: Vincenzo Fiorenzo , Thompson Todd A , Weinberg David H , Griffith Emily J , Johnson James W , Johnson Jennifer A 
Published: September 2021

ABSTRACT
We test the hypothesis that the observed first-peak (Sr, Y, Zr) and second-peak (Ba) s-process elemental abundances in low-metallicity Milky Way stars, and the abundances of the elements Mo and Ru, can be explained by a pervasive r-process contribution originating in neutrino-driven winds from highly magnetic and rapidly rotating proto-neutron stars (proto-NSs). We construct chemical evolution models that incorporate recent calculations of proto-NS yields in addition to contributions from asymptotic giant branch stars, Type Ia supernovae, and two alternative sets of yields for massive star winds and core-collapse supernovae. For non-rotating massive star yields from either set, models without proto-NS winds underpredict the observed s-process peak abundances by 0.3–$1\, \text{dex}$ at low metallicity, and they severely underpredict Mo and Ru at all metallicities. Models incorporating wind yields from proto-NSs with spin periods P ∼ 2–$5\, \text{ms}$ fit the observed trends for all these elements well. Alternatively, models omitting proto-NS winds but adopting yields of rapidly rotating massive stars, with vrot between 150 and $300\, \text{km}\, \text{s}^{-1}$, can explain the observed abundance levels reasonably well for [Fe/H] &lt; −2. These models overpredict [Sr/Fe] and [Mo/Fe] at higher metallicities, but with a tuned dependence of vrot on stellar metallicity they might achieve an acceptable fit at all [Fe/H]. If many proto-NSs are born with strong magnetic fields and short spin periods, then their neutrino-driven winds provide a natural source for Sr, Y, Zr, Mo, Ru, and Ba in low-metallicity stellar populations. Conversely, spherical winds from unmagnetized proto-NSs overproduce the observed Sr, Y, and Zr abundances by a large factor.
Diffusivity in force-free simulations of global magnetospheres
Authors: Mahlmann J F , Aloy M A 
Published: September 2021

ABSTRACT
Assuming that the numerical diffusivity triggered by violations of the force-free electrodynamics constraints is a proxy for the physical resistivity, we examine its impact on the overall dynamics of force-free aligned pulsar magnetospheres endowed with an equatorial current sheet (ECS). We assess the constraint violations as a diffusivity source. The effects of modifications on electric fields used to restore force-free conditions are not confined to the ECS, but modify the magnetospheric dynamics on time-scales shorter than the pulsar rotational period. These corrections propagate especially via a channel that was unexplored, namely, changes induced to the electric charge density, ρ. We quantify the global consequences of diffusivity by comparing different techniques to model ρ. By default, we combine a conservative ρ-evolution with hyperbolic/parabolic cleaning of inaccuracies in the Maxwell equations. As an alternative, we enforce a constrained evolution, where ρ is directly computed as the electric field divergence. The conservative approach reduces the Poynting flux dissipated in the ECS by an order of magnitude, along with an increase of the pulsar luminosity driven by a shift of the Y-point location. The luminosity changes according to LY ∝ α0.11, where α is the ratio of diffusion to advection time-scales, controlling the amount of (numerical) diffusivity. Our models suggest interpreting the luminosity dependence on the Y-point location as differences in resistivities encountered at the ECS. Alternatively, they could be interpreted in terms of the pair formation multiplicity, κ, smaller diffusion being consistent with κ ≫ 1.
M dwarf spectral indices at moderate resolution: accurate Teff and [Fe/H] for 178 southern stars
Authors: Costa-Almeida Ellen , de Mello Gustavo F Porto , Giribaldi Riano E , Lorenzo-Oliveira Diego , Ubaldo-Melo Maria L 
Published: September 2021

ABSTRACT
We present a spectroscopic and photometric calibration to derive effective temperatures Teff and metallicities [Fe/H] for M dwarfs, based on a principal component analysis (PCA) of 147 spectral indices measured off moderate resolution (R∼11 000), high S/N (&gt;100) spectra in the λλ 8390–8834 region, plus the J−H colour. Internal uncertainties, estimated by the residuals, are 81 K and 0.12 dex, respectively, for Teff and [Fe/H], the calibrations being valid for 3050 K &lt; T$_\text{eff}\, \lt $ 4100 K and −0.45 &lt; [Fe/H] $\lt \, +$0.50 dex. The PCA calibration is a competitive model-independent method to derive Teff and [Fe/H] for large samples of M dwarfs, well suited to the available database of far-red spectra. The median uncertainties are 105 K and 0.23 dex for Teff and [Fe/H], respectively, estimated by Monte Carlo simulations. We compare our values to other works based on photometric and spectroscopic techniques and find median differences 75 ± 273 K and 0.02 ± 0.31 dex for Teff and [Fe/H], respectively, achieving good accuracy but relatively low precision. We find considerable disagreement in the literature between atmospheric parameters for stars in common. We use the new calibration to derive Teff and [Fe/H] for 178 K7-M5 dwarfs, many previously unstudied. Our metallicity distribution function for nearby M dwarfs peaks at [Fe/H]∼−0.10 dex, in good agreement with the RAVE distribution for GK dwarfs. We present radial velocities (internal precision 1.4 km s−1) for 99 objects without previous measurements. The kinematics of the sample shows it to be fully dominated by thin/thick disc stars, excepting the well-known high-velocity Kapteyn’s star.
Bayesian analysis of quasar light curves with a running optimal average: new time delay measurements of COSMOGRAIL gravitationally lensed quasars
Authors: Donnan Fergus R , Horne Keith , Hernández Santisteban Juan V 
Published: September 2021

ABSTRACT
We present a new method of modelling time-series data based on the running optimal average (ROA). By identifying the effective number of parameters for the ROA model, in terms of the shape and width of its window function and the times and accuracies of the data, we enable a Bayesian analysis, optimizing the ROA width, along with other model parameters, by minimizing the Bayesian information criterion (BIC) and sampling joint posterior parameter distributions using MCMC methods. For analysis of quasar light curves, our implementation of ROA modelling can measure time delays among light curves at different wavelengths or from different images of a lensed quasar and, in future work, be used to inter-calibrate light-curve data from different telescopes and estimate the shape and thus the power-density spectrum of the light curve. Our noise model implements a robust treatment of outliers and error-bar adjustments to account for additional variance or poorly quantified uncertainties. Tests with simulated data validate the parameter uncertainty estimates. We compare ROA delay measurements with results from cross-correlation and from javelin, which models light curves with a prior on the power-density spectrum. We analyse published COSMOGRAIL light curves of multilensed quasar light curves and present the resulting measurements of the inter-image time delays and detection of microlensing effects.
Broad-band time-resolved spectroscopy of thermonuclear X-ray bursts from 4U 1636−536 using AstroSat
Authors: Kashyap Unnati , Ram Biki , Güver Tolga , Chakraborty Manoneeta 
Published: September 2021

ABSTRACT
Broad-band spectral studies of type I X-ray bursts can put strong constraints on the physics of burst spectra as well as their interaction with the environment. We present the results obtained from the broad-band time-resolved spectroscopy of 15 thermonuclear bursts detected simultaneously from the neutron star atoll source 4U 1636−536 using the Large Area X-ray Proportional Counter (LAXPC) and Soft X-ray Telescope (SXT) onboard AstroSat. During the observations with AstroSat, the low-mass X-ray binary 4U 1636−536 is observed to show a modest spectral evolution within the island state. The broad-band burst spectra are observed to show an excess in addition to the thermal emission from the neutron star surface near the peak of the bursts. We investigate the interpretation of the excess observed near the peak of the burst as re-emission/reprocessing of the photons by the accretion disc/corona or scattering of the photons in the neutron star atmosphere or the enhanced persistent emission due to the Poynting–Robertson drag. This is the first reported broad-band simultaneous study of type I bursts using LAXPC and SXT onboard AstroSat. This kind of study may provide a better understanding of the burst–accretion interaction and how the bursts influence the overall accretion process contributed by the accretion disc as well as the corona.
Detection of periodic signals in AGN red noise light curves: empirical tests on the Auto-Correlation Function and Phase Dispersion Minimization
Authors: Krishnan S , Markowitz A G , Schwarzenberg-Czerny A , Middleton M J 
Published: September 2021

ABSTRACT
Active galactic nucleus (AGN) emission is dominated by stochastic, aperiodic variability which overwhelms any periodic/quasi-periodic signal (QPO) if one is present. The Auto-Correlation Function (ACF) and Phase Dispersion Minimization (PDM) techniques have been used previously to claim detections of QPOs in AGN light curves. In this paper, we perform Monte Carlo simulations to empirically test QPO detection feasibility in the presence of red noise. Given the community’s access to large data bases of monitoring light curves via large-area monitoring programmes, our goal is to provide guidance to those searching for QPOs via data trawls. We simulate evenly sampled pure red noise light curves to estimate false alarm probabilities; false positives in both tools tend to occur towards time-scales longer than (very roughly) one-third of the light-curve duration. We simulate QPOs mixed with pure red noise and determine the true-positive detection sensitivity; in both tools, it depends strongly on the relative strength of the QPO against the red noise and on the steepness of the red noise PSD slope. We find that extremely large values of peak QPO power relative to red noise (typically ∼104−5) are needed for a 99.7 per cent true-positive detection rate. Given that the true-positive detections using the ACF or PDM are generally rare to obtain, we conclude that period searches based on the ACF or PDM must be treated with extreme caution when the data quality is not good. We consider the feasibility of QPO detection in the context of highly inclined, periodically self-lensing supermassive black hole binaries.
The ultra-steep diffuse radio emission observed in the cool-core cluster RX J1720.1+2638 with LOFAR at 54 MHz
Authors: Biava N , de Gasperin F , Bonafede A , Edler H W , Giacintucci S , Mazzotta P , Brunetti G , Botteon A , Brüggen M , Cassano R , Drabent A , Edge A C , Enßlin T , Gastaldello F , Riseley C J , Rossetti M , Rottgering H J A , Shimwell T W , Tasse C , van Weeren R J 
Published: September 2021

ABSTRACT
Diffuse radio emission at the centre of galaxy clusters has been observed both in merging clusters on scales of Mpc, called giant radio haloes, and in relaxed systems with a cool-core on smaller scales, named mini haloes. Giant radio haloes and mini haloes are thought to be distinct classes of sources. However, recent observations have revealed the presence of diffuse radio emission on Mpc scales in clusters that do not show strong dynamical activity. RX J1720.1+2638 is a cool-core cluster, presenting both a bright central mini halo and a fainter diffuse, steep-spectrum emission extending beyond the cluster core that resembles giant radio halo emission. In this paper, we present new observations performed with the LOw Frequency ARray Low Band Antennas (LBA) at 54 MHz. These observations, combined with data at higher frequencies, allow us to constrain the spectral properties of the radio emission. The large-scale emission presents an ultrasteep spectrum with $\alpha _{54}^{144}\sim 3.2$. The radio emission inside and outside the cluster core have strictly different properties, as there is a net change in spectral index and they follow different radio-X-ray surface brightness correlations. We argue that the large-scale diffuse emission is generated by particles re-acceleration after a minor merger. While for the central mini halo, we suggest that it could be generated by secondary electrons and positrons from hadronic interactions of relativistic nuclei with the dense cool-core gas, as an alternative to re-acceleration models.
Radiatively driven, time dependent bipolar outflows
Authors: Joshi Raj Kishor , Chattopadhyay Indranil , Yadav Lallan 
Published: September 2021

ABSTRACT
We study the radiatively driven fluid jets around a non-rotating black hole. The radiation arising from the inner compact corona and outer sub-Keplerian part of the disc accelerates the jets. We obtain the steady state, semi-analytical, radiatively driven outflow solutions. The thermodynamics of the outflow is described by a variable adiabatic index equation of state. We develop a total variation diminishing (TVD) routine to investigate the time dependent behaviour of the radiatively driven bipolar outflow. We inject with flow variables from the steady state outflow solutions in the TVD code and allow the code to settle into steady state and match the numerical results with the steady state solution. The radiation arising out of the accretion disc can provide a wide range of jet solutions, depending upon parameters like the intensity of disc, location of the inner corona etc. We induce the time dependence of the radiation field by inducing oscillation of the inner corona of the accretion disc. The radiation field then makes the bipolar outflow time dependent. We show that a non-steady radiation field arising out of disc oscillations can generate the internal shocks closer to the jet base. Depending on the disc geometry, there might be transient shocks in the jet and there might be multiple non-stationary shocks in the jet, which are of much interest in jet physics.
The Pristine survey – XIV. Chemical analysis of two ultra-metal-poor stars
Authors: Lardo C , Mashonkina L , Jablonka P , Bonifacio P , Caffau E , Aguado D S , González Hernández J I , Sestito F , Kielty C L , Venn K A , Hill V , Starkenburg E , Martin N F , Sitnova T , Arentsen A , Carlberg R G , Navarro J F , Kordopatis G 
Published: September 2021

ABSTRACT
Elemental abundances of the most metal-poor stars reflect the conditions in the early Galaxy and the properties of the first stars. We present a spectroscopic follow-up of two ultra-metal-poor stars ([Fe/H] &lt; −4.0) identified by the survey Pristine: Pristine 221.8781+9.7844 and Pristine 237.8588+12.5660 (hereafter Pr 221 and Pr 237, respectively). Combining data with earlier observations, we find a radial velocity of −149.25 ± 0.27 and −3.18 ± 0.19 km s−1 for Pr 221 and Pr 237, respectively, with no evidence of variability between 2018 and 2020. From a one-dimensional (1D) local thermodynamic equilibrium (LTE) analysis, we measure [Fe/H]LTE = −4.79 ± 0.14 for Pr 221 and −4.22 ± 0.12 for Pr 237, in good agreement with previous studies. Abundances of Li, Na, Mg, Al, Si, Ca, Ti, Fe, and Sr were derived based on the non-LTE (NLTE) line formation calculations. When NLTE effects are included, we measure slightly higher metallicities: [Fe/H]NLTE = −4.40 ± 0.13 and −3.93 ± 0.12, for Pr 221 and Pr 237, respectively. Analysis of the G band yields [C/Fe]1D-LTE ≤ +2.3 and [C/Fe]1D-LTE ≤ +2.0 for Pr 221 and Pr 237. Both stars belong to the low-carbon band. Upper limits on nitrogen abundances are also derived. Abundances for other elements exhibit good agreement with those of stars with similar parameters. Finally, to get insight into the properties of their progenitors, we compare NLTE abundances to theoretical yields of zero-metallicity supernovae (SNe). This suggests that the SNe progenitors had masses ranging from 10.6 to 14.4 M⊙ and low-energy explosions with (0.3–1.2) × 1051 erg.
A timing-based estimate of the spin of the black hole in MAXI J1820+070
Authors: Bhargava Yash , Belloni Tomaso , Bhattacharya Dipankar , Motta Sara , Ponti. Gabriele 
Published: September 2021

ABSTRACT
MAXI J1820+070 (ASSASN-18ey) is a black hole (BH) X-ray binary discovered in 2018. The brightness of the source triggered multi-wavelength campaigns of this source from different observatories. We analyse the power density spectra (PDS) obtained from NICER high cadence observations of the source in the hard state. We obtain the evolution of the characteristic frequencies by modelling the PDS. We interpret the characteristic frequencies of various PDS components (both QPOs and broad-band noise components) as variability occurring at a particular radius, and explain them in the context of the Relativistic Precession Model (RPM). We estimate the dimensionless spin of the BH at $0.799^{+0.016}_{-0.015}$ by fitting the RPM.
Dynamical modelling of the twisted galaxy PGC 046832
Authors: den Brok Mark , Krajnović Davor , Emsellem Eric , Brinchmann Jarle , Maseda Michael 
Published: September 2021

ABSTRACT
We analyse VLT/MUSE observations of PGC 046832, the brightest cluster galaxy of Abell 3556. The velocity structure of this galaxy is startling and shows two reversals in sign along the minor axis, and one along the major axis. We use triaxial Schwarzschild models to infer the intrinsic shape, central black hole mass, and orbit distribution of this galaxy. The shape determination suggests that the galaxy is highly triaxial in the centre (almost prolate) but has a low triaxiality (almost oblate) in the outer parts. The orbit distribution of the best-fitting Schwarzschild model shows that the kinematic reversal along the projected minor axis is driven by a slight asymmetry in the distribution and amount of long axis tubes in the inner parts. The kinematic reversals along the projected major axis are driven by a high fraction of counter-rotating orbits at intermediate radii in the galaxy. Using chemical tagging of orbits in the Schwarzschild model, we do not find evidence for any association of these orbits with specific stellar population parameters. Although the inner part of the galaxy almost certainty formed through one or more dry mergers producing the prolate shape, the outer parts are consistent with both accretion and in situ formation. While axisymmetric models suggests the presence of a supermassive black hole with mass ∼6 × 109 and ∼1010 M⊙(with Schwarzschild and Jeans modelling, respectively), triaxial Schwarzschild models provide only an upper limit of ∼2 × 109  M⊙.
Vertical settling of pebbles in turbulent circumbinary discs and the in situ formation of circumbinary planets
Authors: Pierens Arnaud , Nelson Richard P , McNally Colin P 
Published: September 2021

ABSTRACT
The inner-most regions of circumbinary discs are unstable to a parametric instability whose non-linear evolution is hydrodynamical turbulence. This results in significant particle stirring, impacting on planetary growth processes such as the streaming instability or pebble accretion. In this paper, we present the results of three-dimensional, inviscid global hydrodynamical simulations of circumbinary discs with embedded particles of 1 cm size. Hydrodynamical turbulence develops in the disc, and we examine the effect of the particle back-reaction on vertical dust. We find that higher solid-to-gas ratios lead to smaller gas vertical velocity fluctuations, and therefore to smaller dust scale heights. For a metallicity Z = 0.1, the dust scale height near the edge of the tidally truncated cavity is $\sim 80{{\ \rm per\ cent}}$ of the gas scale height, such that growing a Ceres-mass object to a 10 M⊕ core via pebble accretion would take longer than the disc lifetime. Collision velocities for small particles are also higher than the critical velocity for fragmentation, which precludes grain growth and the possibility of forming a massive planetesimal seed for pebble accretion. At larger distances from the binary, turbulence is weak enough to enable not only efficient pebble accretion but also grain growth to sizes required to trigger the streaming instability. In these regions, an in situ formation scenario of circumbinary planets involving the streaming instability to form a massive planetesimal followed by pebble accretion on to this core is viable. In that case, planetary migration has to be invoked to explain the presence of circumbinary planets at their observed locations.
Cleaning foregrounds from single-dish 21 cm intensity maps with Kernel principal component analysis
Authors: Irfan Melis O , Bull Philip 
Published: September 2021

ABSTRACT
The high dynamic range between contaminating foreground emission and the fluctuating 21 cm brightness temperature field is one of the most problematic characteristics of 21 cm intensity mapping data. While these components would ordinarily have distinctive frequency spectra, making it relatively easy to separate them, instrumental effects and calibration errors further complicate matters by modulating and mixing them together. A popular class of foreground cleaning method are unsupervised techniques related to principal component analysis (PCA), which exploit the different shapes and amplitudes of each component’s contribution to the covariance of the data in order to segregate the signals. These methods have been shown to be effective at removing foregrounds, while also unavoidably filtering out some of the 21 cm signal too. In this paper we examine, for the first time in the context of 21 cm intensity mapping, a generalized method called Kernel PCA, which instead operates on the covariance of non-linear transformations of the data. This allows more flexible functional bases to be constructed, in principle allowing a cleaner separation between foregrounds and the 21 cm signal to be found. We show that Kernel PCA is effective when applied to simulated single-dish (auto-correlation) 21 cm data under a variety of assumptions about foregrounds models, instrumental effects etc. It presents a different set of behaviours to PCA, e.g. in terms of sensitivity to the data resolution and smoothing scale, outperforming it on intermediate to large scales in most scenarios.