Field Of Astrophysics Research Articles

Хранитель найбільшого у світі радіотелескопа (інтерв’ю до 70-річчя академіка НАН України О.О. Коноваленка)

February 27 marks the 70th anniversary of the famous scientist in the field of radio astronomy and astrophysics, laureate of the State Prize of Ukraine in Science and Technology (2018), laureate of the USSR State Prize (1988), Honored Worker of Science and Technology of Ukraine (2001), laureate of the NAS of Ukraine Prizes named after S.Ya. Braude (2008) and M.K. Yangel (2013), Head of the Department of Low-Frequency Radio Astronomy, Deputy Director of the Radio Astronomical Institute of the NAS of Ukraine (since 2007), Doctor of Physics and Mathematics (1984), Academician of the NAS of Ukraine (2003) Olexander O. Konovalenko. Taking the opportunity, the editorial board of the Visnyk of the National Academy of Sciences of Ukraine interviewed Academician O.O. Konovalenko and asked about his path in science, his greatest achievements and plans for the future.

STARFORGE: the effects of protostellar outflows on the IMF

ABSTRACT The initial mass function (IMF) of stars is a key quantity affecting almost every field of astrophysics, yet it remains unclear what physical mechanisms determine it. We present the first runs of the STAR FORmation in Gaseous Environments project, using a new numerical framework to follow the formation of individual stars in giant molecular clouds (GMCs) using the gizmo code. Our suite includes runs with increasingly complex physics, starting with isothermal ideal magnetohydrodynamics (MHD) and then adding non-isothermal thermodynamics and protostellar outflows. We show that without protostellar outflows the resulting stellar masses are an order of magnitude too high, similar to the result in the base isothermal MHD run. Outflows disrupt the accretion flow around the protostar, allowing gas to fragment and additional stars to form, thereby lowering the mean stellar mass to a value similar to that observed. The effect of jets upon global cloud evolution is most pronounced for lower mass GMCs and dense clumps, so while jets can disrupt low-mass clouds, they are unable to regulate star formation in massive GMCs, as they would turn an order unity fraction of the mass into stars before unbinding the cloud. Jets are also unable to stop the runaway accretion of massive stars, which could ultimately lead to the formation of stars with masses ${\gt}500\, \mathrm{M}_{\rm \odot }$. Although we find that the mass scale set by jets is insensitive to most cloud parameters (i.e. surface density, virial parameter), it is strongly dependent on the momentum loading of the jets (which is poorly constrained by observations) as well as the temperature of the parent cloud, which predicts slightly larger IMF variations than observed. We conclude that protostellar jets play a vital role in setting the mass scale of stars, but additional physics are necessary to reproduce the observed IMF.

Electromagnetic counterparts of compact binary mergers

The first detection of a binary neutron star merger through gravitational waves and photons marked the dawn of multimessenger astronomy with gravitational waves, and it greatly increased our insight in different fields of astrophysics and fundamental physics. However, many open questions on the physical process involved in a compact binary merger still remain and many of these processes concern plasma physics. With the second generation of gravitational wave interferometers approaching their design sensitivity, the new generation under design study and new X-ray detectors under development, the high energy universe will become more and more a unique laboratory for our understanding of plasma in extreme conditions. In this review, we discuss the main electromagnetic signals expected to follow the merger of two compact objects highlighting the main physical processes involved and some of the most important open problems in the field.

A dearth of young and bright massive stars in the Small Magellanic Cloud

Context. Massive star evolution at low metallicity is closely connected to many fields in high-redshift astrophysics, but is poorly understood so far. Because of its metallicity of ∼0.2 Z⊙, its proximity, and because it is currently forming stars, the Small Magellanic Cloud (SMC) is a unique laboratory in which to study metal-poor massive stars. Aims. We seek to improve the understanding of this topic using available SMC data and a comparison to stellar evolution predictions. Methods. We used a recent catalog of spectral types in combination with Gaia magnitudes to calculate temperatures and luminosities of bright SMC stars. By comparing these with literature studies, we tested the validity of our method, and using Gaia data, we estimated the completeness of stars in the catalog as a function of luminosity. This allowed us to obtain a nearly complete view of the most luminous stars in the SMC. We also calculated the extinction distribution, the ionizing photon production rate, and the star formation rate. Results. Our results imply that the SMS hosts only ∼30 very luminous main-sequence stars (M ≥ 40 M⊙; L ≳ 3 ⋅ 105 L⊙), which are far fewer than expected from the number of stars in the luminosity range 3 ⋅ 104 < L/L⊙ < 3 ⋅ 105 and from the typically quoted star formation rate in the SMC. Even more striking, we find that for masses above M ≳ 20 M⊙, stars in the first half of their hydrogen-burning phase are almost absent. This mirrors a qualitatively similar peculiarity that is known for the Milky Way and Large Magellanic Cloud. This amounts to a lack of hydrogen-burning counterparts of helium-burning stars, which is more pronounced for higher luminosities. We derived the H I ionizing photon production rate of the current massive star population. It agrees with the H α luminosity of the SMC. Conclusions. We argue that a declining star formation rate or a steep initial mass function are unlikely to be the sole explanations for the dearth of young bright stars. Instead, many of these stars might be embedded in their birth clouds, although observational evidence for this is weak. We discuss implications for the role that massive stars played in cosmic reionization, and for the top end of the initial mass function.

The research progress of Si-based blocked-impurity-band infrared detecting materials and detectors

<p indent=0mm>Infrared detection possesses a significantly application prospect in the field of astrophysics. Due to the special natures of deep-space exploring objects, the performance of infrared detector is very demanding. Blocked-impurity-band (BIB) infrared detectors, with advantages of wide spectrum coverage, low noise, high sensitivity, good resistance to cosmic particle radiation etc., have become the state-of-the-art choice for astronomical application internationally. The response of BIB detectors ranges from mid-infrared to far-infrared waveband, and the widespread use of BIB detectors help human beings obtain a series of important scientific achievements in the field of deep-space exploration. The research on BIB infrared detector in China started rather late. Even though big progress has been achieved in recent years, it still lags far behind the advanced level globally. This article reviews the research progress for BIB infrared detectors of China in the past <sc>5 years.</sc> The preparation technology, physical property characterization, photoelectric response characteristics of BIB infrared detection material and corresponding devices, and the control of surface plasmon polaritons on the photoelectric response of the detectors are introduced detailly. These provide references and experimental bases for the development of BIB infrared detector in China.

JaSTA-3: Light scattering simulations for heterogeneous aggregate

JaSTA-3: Light scattering simulations for heterogeneous aggregate

Influence of operating parameters on discharge mode of parallel-rail accelerator

Electromagnetic plasma accelerators which can generate hypervelocity and high density plasma jets have been widely used in the fields of nuclear physics and astrophysics. In this paper, an experimental platform of parallel-rail accelerator electromagnetically driven plasma is established, and the discharge modes under different discharge currents and gas injection conditions are studied through using magnetic probes, a spectrometer and an ICCD. A fast gas valve is used to inject argon into the rail electrode area. The time delay between the fast valve discharge and the parallel-rail accelerator discharge is fixed to be 450 μs. The waveform of power supply of the parallel-rail accelerator is a sinusoidal wave. The total capacitance is 120 μF, the total inductance is about 400 nH, and the maximum current is 170 kA. The fast valve current waveform is a double exponential waveform with a maximum current of 2.5 kA. When the discharge current is 40 kA, a current sheet with a certain thickness is generated, and the current sheet moves through different detection positions along the rail electrode at a certain velocity. Therefore, the working mode of the parallel-rail accelerator is the snowplow mode. As the discharge current increases, the trailing edge of the current channel is fixed during the current rising phase, and starts to move to the end of the rail during the current falling phase. A diffuse distributed current channel is formed, and the parallel-rail accelerator operates in a deflagration mode. As the gas injection mass increases, the current channel front velocity decreases to form a more concentrated distributed current channel, and the discharge mode turns into the snowplow mode. The stationary current channel in the deflagration mode is maintained mainly by ablating the electrode. The operating parameters mainly affect the rail voltage, which in turn affects the discharge mode of the parallel-rail accelerator. The rail voltage increases when the discharge current or the current rate of change increases. If the rail gap behind the current channel cannot withstand the high rail voltage under large discharge current or large current rate of change, the breakdown occurs, which results in the deflagration mode discharge.

The latest developments in computer science and their impact on space exploration

In the paper, the important role of tools and distributed IT resources in the dynamic development of astrophysics, astronomy, and space exploration are discussed. New possibilities and approaches to conducting research in the field of astronomy and astrophysics with the use of cloud computing and advanced data visualization techniques are also presented. Finally, some examples of the use of digital sky survey databases in scientific research are shown.

Cloud storage capable to select events upon user request for medium-sized astrophysical experiments

We present a cloud storage for collaborations of small and medium-sized experiments in the field of particle astrophysics. This storage provides a unified interface for accessing data from different experiments. In this article, we will focus on the capabilities of the storage for processing user requests for data, as well as on some technical details of the implementation of data selection. We have deployed a working prototype of the storage. Currently the prototype integrates data from such astrophysical experiments as TAIGA and KASCADE. As a result, users of the respective collaborations have the opportunity to collect scientific data from different experiments seamlessly within one request to conduct joint data analysis.

The Effect of the Axisymmetric and Non-Axisymmetric Ambient Field on the Magnetic Field of Planets

At least a minority of planets, moons and other bodies exist within significant external astrophysical fields. The ambient field problem is more relevant to these bodies than the classical dynamo problem, but remains relatively little studied. This paper will concern with the effect of axisymmetric and non-axi- symmetric ambient field on a spherical, axisymmetric dynamo model, through nonlinear calculations with α-quenching feedback. Ambient fields of varying strengths are imposed in the model. The effect of these fields on the generation process is considered, with particular focus on the equatorial symmetry and the time dependence of the solutions.

APPLICATION OF TWO-CLUSTER MICROSCOPIC MODEL TO STUDY PROCESSES ASSOCIATED WITH THE COSMOLOGICAL LITHIUM PROBLEM

This paper presents the results of studies of long-lived resonance states of the 6Li nucleus and the radiative capture reaction leading to the synthesis of 6Li. In connection with the importance of the lithium problem for the fields of nuclear physics and nuclear astrophysics, the reactions of primary nucleosynthesis are of great interest for studies and consideration using new calculation methods. Cluster models are a powerful tool for theoretical analysis and solution of this problem. One of these models is the microscopic cluster model, or a method known as the algebraic version of the resonant group method (AVRGM), which will allow us to investigate this problem from a new angle and obtain data on resonance states. For this task, a modified Hasegawa-Nagata potential was chosen, which has its own unique characteristics and exchange parameters. The obtained data were compared with experimental data and it was shown that they showed good agreement, and the applicability of this technique to the description of similar reactions that originate in the first three minutes after the birth of the universe.

Synthesis of radioactive elements in novae and supernovae and their use as a diagnostic tool

Novae and supernovae play a key role in many fields of Astrophysics and Cosmology. Despite their importance, an accurate description of which objects explode and why and how they explode is still lacking. One of the main characteristics of such explosions is that they are the main suppliers of newly synthesized chemical elements in the Galaxy. Since some of these isotopes are radioactive, it is possible to use the corresponding gamma-rays as a diagnostic tool of the explosion thanks to their independence on the thermal state of the debris. The drawback is the poor sensitivity of detectors in the MeV energy domain. As a consequence, the radioactive lines have only been detected in one core collapse supernova (SN 1987A), one Type Ia supernova (SN 2014J), and one supernova remnant (Cas A). Nevertheless these observations have provided and are providing important information about the explosion mechanisms. Unfortunately, novae are still eluding detection. These results emphasize the necessity to place as soon as possible a new instrument in orbit with enough sensitivity to noticeably enlarge the sample of detected events.

PENGIRAAN JARAK KE DINDING LANGIT PERTAMA BERDASARKAN ISYARAT-ISYARAT DARI AL-QURAN DAN HADIS

The distance from the earth to the cliffs or walls of the universe is a study made by many scientists, especially from the astrophysics field. Among the latest studies is a team study led by Professor Mihran Vardayan at Oxford University in 2011. Their study found that the size of the universe is at least 267 times larger than the ‘Hubble volume’ measurement by the NASA Hubble Space Telescope. At that time the Planck satellite was able to detect a distance of 13.8 billion light-years. This means the study about the distance to the walls of the universe was 3.68 trillion light-years. The most recent study by Professor Eithan Siegal of the University of Florida, USA found that the distance to the walls of the universe was 11.6 trillion lights. Our study is a calculation of the distance to the walls of the universe based on the sign of the Qur'an and hadith. The results of our study are compared with those studies and distance reviews based on the perimeter of time from the israk mikraj event.

The RAdial Velocity Experiment (RAVE): Parameterisation of RAVE spectra based on convolutional neural networks

Context. Data-driven methods play an increasingly important role in the field of astrophysics. In the context of large spectroscopic surveys of stars, data-driven methods are key in deducing physical parameters for millions of spectra in a short time. Convolutional neural networks (CNNs) enable us to connect observables (e.g. spectra, stellar magnitudes) to physical properties (atmospheric parameters, chemical abundances, or labels in general). Aims. We test whether it is possible to transfer the labels derived from a high-resolution stellar survey to intermediate-resolution spectra of another survey by using a CNN. Methods. We trained a CNN, adopting stellar atmospheric parameters and chemical abundances from APOGEE DR16 (resolution R = 22 500) data as training set labels. As input, we used parts of the intermediate-resolution RAVE DR6 spectra (R ∼ 7500) overlapping with the APOGEE DR16 data as well as broad-band ALL_WISE and 2MASS photometry, together with Gaia DR2 photometry and parallaxes. Results. We derived precise atmospheric parameters Teff, log(g), and [M/H], along with the chemical abundances of [Fe/H], [α/M], [Mg/Fe], [Si/Fe], [Al/Fe], and [Ni/Fe] for 420 165 RAVE spectra. The precision typically amounts to 60 K in Teff, 0.06 in log(g) and 0.02−0.04 dex for individual chemical abundances. Incorporating photometry and astrometry as additional constraints substantially improves the results in terms of the accuracy and precision of the derived labels, as long as we operate in those parts of the parameter space that are well-covered by the training sample. Scientific validation confirms the robustness of the CNN results. We provide a catalogue of CNN-trained atmospheric parameters and abundances along with their uncertainties for 420 165 stars in the RAVE survey. Conclusions. CNN-based methods provide a powerful way to combine spectroscopic, photometric, and astrometric data without the need to apply any priors in the form of stellar evolutionary models. The developed procedure can extend the scientific output of RAVE spectra beyond DR6 to ongoing and planned surveys such as Gaia RVS, 4MOST, and WEAVE. We call on the community to place a particular collective emphasis and on efforts to create unbiased training samples for such future spectroscopic surveys.

The Catalogue for Astrophysical Turbulence Simulations (CATS)

Abstract Turbulence is a key process in many fields of astrophysics. Advances in numerical simulations of fluids over the last several decades have revolutionized our understanding of turbulence and related processes such as star formation and cosmic ray propagation. However, data from numerical simulations of astrophysical turbulence are often not made public. We introduce a new simulation-oriented database for the astronomical community: the Catalogue for Astrophysical Turbulence Simulations (CATS), located at www.mhdturbulence.com. CATS includes magnetohydrodynamic (MHD) turbulent box simulation data products generated by the public codes athena++, arepo, enzo, and flash. CATS also includes several synthetic observational data sets, such as turbulent HI data cubes. We also include measured power spectra and three-point correlation functions from some of these data. We discuss the importance of open-source statistical and visualization tools for the analysis of turbulence simulations such as those found in CATS.

First-principles equation of state of liquid hydrogen and dissociative transition

The properties of dense hot hydrogen, in particular the phase transition between the molecular insulating and atomic conductive states, are important in the fields of astrophysics and high-pressure physics. Previous ab initio calculations suggested the metallization in liquid hydrogen, accompanied by dissociation, is a first-order phase transition and ends at a critical point in temperature range between 1500 and 2000 K and pressure close to 100 GPa. Using density functional theoretical molecular dynamics simulations, we report a first-principles equation of state of hydrogen that covers dissociation transition conditions at densities ranging from 0.20 to 1.00 g/cc and temperatures of 600–9000 K. Our results clearly indicate that a drop in pressure and a sharp structural change still occur as the system transforms from a diatomic to monoatomic phase at temperatures above 2000 K, and support the first-order phase transition in liquid hydrogen would end in the temperature about 4500 K.

The Impact of Nuclear Physics Uncertainties on Galactic Chemical Evolution Predictions

Modeling the evolution of the elements in the Milky Way is a multidisciplinary and challenging task. In addition to simulating the ∽ 13 billion years evolution of our Galaxy, chemical evolution simulations must keep track of the elements synthesized and ejected from every astrophysical site of interest (e.g., supernova, compact binary merger). The elemental abundances of such ejecta, which are a fundamental input for chemical evolution codes, are usually taken from theoretical nucleosynthesis calculations performed by the nuclear astrophysics community. Therefore, almost all chemical evolution predictions rely on the nuclear physics behind those calculations. In this proceedings article, we highlight the impact of nuclear physics uncertainties on galactic chemical evolution predictions. We demonstrate that nuclear physics and galactic evolution uncertainties both have a significant impact on interpreting the origin of neutron-capture elements in our Solar System. Those results serve as a motivation to create and maintain collaborations between the fields of nuclear astrophysics and galaxy evolution.

Dark Matter: Candidates and Searches

Dark matter is an unknown field in astrophysics and cosmology. Various experiments to detect dark matter have already been done around the world since the hypothesis of dark matter was first proposed. In this article, several prevalent dark matter candidate theories have been reviewed, which will make contributions to the understanding of these theories, especially for beginners. The detections and methods, such as Weakly Interacting Massive Particles (WIMPs), have also been included.

Experimental and extraction procedure for the electrical characterisation of silicon photomultiplier detectors

Silicon photomultipliers (SiPMs), owing to their low-level photon counting capabilities, have increased in popularity in the field of high energy astrophysics, particle physics and medical imaging. It is crucial to accurately characterise SiPMs so they can be optimised for a particular application such as the Compact High Energy Camera (CHEC-S) for Imaging Atmospheric Cherenkov Telescopes (IACT). Extraction techniques, applied to SiPMs, can quantify opto-electrical parameters such as gain, quenching resistance, junction, parasitic and grid capacitance, rise time constant and slow and fast fall time constants. Various authors have applied and compared different extraction techniques to SiPMs, usually based on the Laplace Transform in the s-domain of the equivalent circuit model. These techniques typically utilise the pulse tail, and therefore only parameterise the recharge phase of the pulse. We will improve upon existing methods by utilising the discharge phase of an SiPM pulse in our transfer function model. In this paper, we have also applied this method to present the electrical characterisation of a novel SiPM detector: Hamamatsu LVR3 S14520-6075. The paper also details a method by which an accurate, average pulse shape, uncontaminated by after-pulsing or dark noise, can be obtained. This is a prerequisite for our analysis method, which fits the pulse shape derived from the transfer function of the SiPM model to the experimental data.

The GAPS Programme at TNG

Context. The detailed chemical composition of stars is important in many astrophysical fields, among which is the characterisation of exoplanetary systems. Previous studies seem to indicate an anomalous chemical pattern of the youngest stellar population in the solar vicinity that has sub-solar metal content. This can influence various observational relations linking the properties of exoplanets to the characteristics of the host stars, for example the giant planet-metallicity relation. Aims. In this framework, we aim to expand our knowledge of the chemical composition of intermediate-age stars and understand whether these peculiarities are real or related to spectroscopic analysis techniques. Methods. We analysed high-resolution optical and near-infrared spectra of intermediate-age stars (&lt;700 Myr) that have been observed simultaneously with HARPS-N and GIANO-B spectrographs in GIARPS mode. To overcome issues related to the young ages of the stars, we applied a new spectroscopic method that uses titanium lines to derive the atmospheric parameters, in particular surface gravities and microturbulence velocity parameter. We derived abundances of C I, Na I, Mg I, Al I, Si I, Ca I, Ti I, Ti II, Cr I, Cr II, Fe I, Fe II, Ni I, and Zn I. Results. The lack of systematic trends between elemental abundances and effective temperatures validates our methods. However, we observed that the coolest stars in the sample, where Teff &lt; 5400 K, display higher abundances for the ionised species, in particular Cr II, and for high-excitation potential C I lines. Conclusions. We found a positive correlation between the higher abundances measured of C I and Cr II and the activity index log RHK′. Instead, we found no correlations between the C abundances obtained from CH molecular band at 4300 Å and both effective temperatures and activity. Thus, we suggest that these are better estimates for C abundances in young and cool stars. Finally, we found an indication of an increasing abundance ratio [X/H] with the condensation temperature for HD 167389, indicating possible episodes of planet engulfment.