Field Of Astrophysics Research Articles

Progress in Global Helioseismology: A New Light on the Solar Modeling Problem and Its Implications for Solar-Like Stars

Since the first observations of solar oscillations in 1962, helioseismology has probably been one of the most successful fields of astrophysics. Data of unprecedented quality were obtained through the implementation of networks of ground-based observatories such as the GONG project or the BiSON network, coupled with space-based telescopes such as SOHO, Solar Orbiter and SDO missions. Besides the improvement of observational data, solar seismologists developed sophisticated techniques to infer the internal structure of the Sun from its eigenfrequencies. These methods, then already extensively used in the field of Geophysics, are called inversion techniques. They allowed to precisely determine the position of the solar convective envelope, the helium abundance in this region and the internal radial profiles of given thermodynamic quantities. Back in 1990s these comparisons showed a very high agreement between solar models and the Sun. However, the downward revision of the CNO surface abundances in the Sun in 2005, confirmed in 2009, induced a drastic reduction of this agreement leading to the so-called solar modelling problem. More than ten years later, in the era of the space-based photometry missions which have established asteroseismology of solar-like stars as a standard approach to obtain their masses, radii and ages, the solar modelling problem still awaits a solution. In this paper, we will present the results of new helioseismic inversions, discuss the current uncertainties of solar models as well as some possible solutions to the solar modelling problem. We will show how helioseismology can help us grasp what is amiss in our solar models. We will also show that, far from being an argument about details of solar models, the solar problem has significant implications for seismology of solar-like stars, on the main sequence and beyond, impacting asteroseismology as a whole as well as the fields requiring precise and accurate knowledge of stellar masses, radii and ages, such as Galactic archaeology and exoplanetology.

Analytical model of strange star in Durgapal spacetime

A new strange star model based on Durgapal IV metric (Durgapal 1982) is presented here.Here we have applied a specific method to study the inner physical properties of the compact objects 4U 1702-429, 2A 1822-371, PSR J1756-2251,PSR J1802-2124 and PSR J1713+0747.The main objective of our study is to determine central density ($\rho_{0}$), surface density ($\rho_{b}$), central pressure ($p_{0}$), surface redshift ($Z_{s}$), compactness and radius. Further we perform different tests to study the stability of our model and finally we are able to give an equation based on pressure and density i.e probable equation of state (EoS) which has an important significances in the field of Astrophysics.

Early galaxy formation and its large-scale effects

AbstractGalaxy formation in the first billion years mark a time of great upheaval in the history of the Universe: the first galaxies started both the ‘metal age’ as well as the era of cosmic reionization. I will start by reviewing the dust production mechanisms and dust masses for high-redshift galaxies which will be revolutionized in the ALMA era. I will then show how the JWST will be an invaluable experiment to shed light on the impact of reionization feedback on early galaxy formation. As we look forward towards the era of 21cm cosmology, I will highlight the crucial and urgent synergies required between 21cm facilities (such as the SKA) and galaxy experiments (JWST, E-ELT and Subaru to name a few) to understand the physics of the epoch of reionization that remains a crucial frontier in the field of astrophysics and physical cosmology. Time permitting, I will try to give a flavour of how the assembly of early galaxies, accessible with the forthcoming JWST, can provide a powerful testbed for Dark Matter models beyond ‘Cold Dark Matter’.

Experimental Investigation of radiative proton-capture reactions relevant to Nucleosynthesis

One of the primary objectives of the field of Nuclear Astrophysics is the study of the elemental and isotopic abundances in our solar system. Although a lot of progress has been made regarding a large number of nuclides, there is still a number of neutron-deficient nuclei, ie the p nuclei, which cannot be created via the s and r processes. These processes are responsible for the production of the bulk of heavy nuclides. The pre-explosive or explosive phases of massive stars are considered potential loci for p nuclides production via various combinations of photodisintegrations and nucleon captures, along with β+ decays and electron captures. For the study of the vast network of nuclear reactions (over 20'000) that are responsible for observed isotopic abundances, the statistical model of Hauser-Feshbach is employed. The model requires the knowledge of nuclear reaction cross sections, quantities that can be measured in the laboratory. In this work, we report on recent experimental attempts to measure such cross sections in radiative proton-capture reactions involving 107,109Ag near the astrophysically relevant energy window. Measurements have been performed at the Tandem Accelerator Laboratory of the N.S.C.R. “Demokritos”. The results are compared to various theoretical models, using the TALYS and EMPIRE codes, in an attempt to provide experimental input to astrophysical models.

Improved Visualisation of Patient-Specific Heart Structure Using Three-Dimensional Printing Coupled with Image-Processing Techniques Inspired by Astrophysical Methods

The aim of this study is to use image-processing techniques developed in the field of astrophysics as inspiration for a novel approach to the three-dimensional (3D) imaging of periprocedural medical data, with the intention of providing improved visualisation of patient-specific heart structure and thereby allowing for an improved quality of procedural planning with regards to individualized cardiovascular healthcare. Using anonymized patient DICOM data for a cardiac computed tomography (CT) angiography, two-dimensional slices of the patient's heart were processed using a series of software packages in order to produce an accurate 3D representation of the patient's heart tissue as a computer-generated stereolithography (STL) file, followed by the creation of a tactile 3D printout. We find that the models produced provide clear definition of heart structure, in particular in the left atrium, left ventricle and aorta. This level of clarity also allows for the aortic valve to be observed and 3D printed. This study provides a step-by-step blueprint of how this can be achieved using open source software, specifically Slicer 4.8.1, MeshLab and AutoDesk Netfabb. In addition, the implementation of astrophysical image-processing techniques shows an improvement in modelling of the heart based on the CT data, in particular in the case of small-scale features where echocardiography has previously been required for more reliable results.

J-PLUS: The Javalambre Photometric Local Universe Survey

The Javalambre Photometric Local Universe Survey (J-PLUS ) is an ongoing 12-band photometric optical survey, observing thousands of square degrees of the Northern Hemisphere from the dedicated JAST/T80 telescope at the Observatorio Astrofísico de Javalambre (OAJ). The T80Cam is a camera with a field of view of 2 deg2 mounted on a telescope with a diameter of 83 cm, and is equipped with a unique system of filters spanning the entire optical range (3500–10 000 Å). This filter system is a combination of broad-, medium-, and narrow-band filters, optimally designed to extract the rest-frame spectral features (the 3700–4000 Å Balmer break region, Hδ, Ca H+K, the G band, and the Mg b and Ca triplets) that are key to characterizing stellar types and delivering a low-resolution photospectrum for each pixel of the observed sky. With a typical depth of AB ∼21.25 mag per band, this filter set thus allows for an unbiased and accurate characterization of the stellar population in our Galaxy, it provides an unprecedented 2D photospectral information for all resolved galaxies in the local Universe, as well as accurate photo-z estimates (at the δ z/(1 + z)∼0.005–0.03 precision level) for moderately bright (up to r ∼ 20 mag) extragalactic sources. While some narrow-band filters are designed for the study of particular emission features ([O II]/λ3727, Hα/λ6563) up to z < 0.017, they also provide well-defined windows for the analysis of other emission lines at higher redshifts. As a result, J-PLUS has the potential to contribute to a wide range of fields in Astrophysics, both in the nearby Universe (Milky Way structure, globular clusters, 2D IFU-like studies, stellar populations of nearby and moderate-redshift galaxies, clusters of galaxies) and at high redshifts (emission-line galaxies at z ≈ 0.77, 2.2, and 4.4, quasi-stellar objects, etc.). With this paper, we release the first ∼1000 deg2 of J-PLUS data, containing about 4.3 million stars and 3.0 million galaxies at r < 21 mag. With a goal of 8500 deg2 for the total J-PLUS footprint, these numbers are expected to rise to about 35 million stars and 24 million galaxies by the end of the survey.

Core-Collapse Supernova neutrino detection prospects with the KM3NeT neutrino telescopes.

Core Collapse Supernovae (CCSN) are explosive phenomena that may occur at the end of the life of massive stars, releasing over 99% of the energy through neutrino emission with energies on the 10 MeV scale. While the explosion mechanism is not fully understood, neutrinos are believed to play an important role. The only detection as of today are the 24 neutrinos from supernova SN1987A. The observation of the next Galactic CCSN will lead to important breakthroughs across the fields of astrophysics, nuclear and particle physics. For a Galactic CCSN, the KM3NeT ORCA and ARCA detectors in the Mediterranean Sea will observe a significant number of neutrinos via the detection of Cherenkov light, mostly induced by Inverse Beta Decay (IBD) interactions in sea water. The detection of coincident photons by the 31 photomultipliers of the KM3NeT digital optical modules (DOMs) allows to separate the signal from the optical background sources. The KM3NeT detection sensitivity to a Galactic CCSN and the potential to resolve the neutrino light-curve have been estimated exploiting detailed Monte-Carlo simulations. Specific criteria are proposed for the online triggering and the participation in the SNEWS network.

The Galactic WC and WO stars

Wolf-Rayet stars of the carbon sequence (WC stars) are an important cornerstone in the late evolution of massive stars before their core collapse. As core-helium burning, hydrogen-free objects with huge mass-loss, they are likely the last observable stage before collapse and thus promising progenitor candidates for type Ib/c supernovae. Their strong mass-loss furthermore provides challenges and constraints to the theory of radiatively driven winds. Thus, the determination of the WC star parameters is of major importance for several astrophysical fields. With Gaia DR2, for the first time parallaxes for a large sample of Galactic WC stars are available, removing major uncertainties inherent to earlier studies. In this work, we re-examine a previously studied sample of WC stars to derive key properties of the Galactic WC population. All quantities depending on the distance are updated, while the underlying spectral analyzes remain untouched. Contrasting earlier assumptions, our study yields that WC stars of the same subtype can significantly vary in absolute magnitude. With Gaia DR2, the picture of the Galactic WC population becomes more complex: We obtain luminosities ranging from logL/L⊙ = 4.9–6.0 with one outlier (WR 119) having logL/L⊙ = 4.7. This indicates that the WC stars are likely formed from a broader initial mass range than previously assumed. We obtain mass-loss rates ranging between log Ṁ = −5.1 and −4.1, with Ṁ ∝ L0.68 and a linear scaling of the modified wind momentum with luminosity. We discuss the implications for stellar evolution, including unsolved issues regarding the need of envelope inflation to address the WR radius problem, and the open questions in regard to the connection of WR stars with Gamma-ray bursts. WC and WO stars are progenitors of massive black holes, collapsing either silently or in a supernova that most-likely has to be preceded by a WO stage.

Evolving from xSonify: a new digital platform for sonorization

In general, Space Sciences data exploration is thought to be suitable for people who do not have Neurological Disorders (ND) that may impair reading (RI), and are not blind or visually impaired (BVI). Data exploration methods used in these fields are generally visual, and do not provide the accessibility to allow full participation of blind and visually impaired individuals in the field. This has been the case even after evidence that sound increases the sensitivity to events in data that would otherwise be undetected. A set of tools that guarantees a thorough data inspection, and assures the access to the same amount and quality of information to all, is useful for everyone. The present project, devoted to design a new user centered software to produce audio-visual outputs from astrophysical data, integrates multidisciplinary and interdisciplinary astronomers, engineers, computer specialists, software designers, educators, disability specialists, bioengineers, neurobiologists, and sociologists, both blind and sighted, and addresses the topics of accessibility to astronomical data, The possibility of exploring the bibliographic databases (ADSABS, among others), creation of a new multimodal access prototype, creation of an accessible, user-centered (from back end to front end), human-computer interface suitable for collection, sonification and analysis of astrophysical data, and the efficiency, utility and effectiveness of the resource in different cultural environments and at different levels of expertise. In this contribution, we present the first results related to the creation and application of the techniques and tools proposed, taking into account that the focus of this research is on the knowledge in the field of physics and astrophysics, but can be scalable to other areas of human activity so that people with other learning styles can have "equal opportunities". Finally, this project is based on the premises of addressing the technical challenges in basic research to achieve the promised benefits of Big Data, which is of world-wide interest.

Development of position sensitive detector module using scintillator and Si photomultiplier for hard x-ray imaging and spectroscopy

We explore the use of scintillation detectors coupled with silicon photomultipliers (SiPMs) as position sensitive hard x-ray spectroscopic detectors for potential applications in the field of high-energy astrophysics. X-ray photons on interaction with scintillation crystals generate optical photons and the distribution of these scintillation light photons is captured with the array of SiPM pixels, providing the spectral and spatial information of the incident x-ray photons. As the position is estimated by fitting the distribution of optical photons, it should be possible to achieve spatial resolution lesser than the pixel size. Development of two detector modules with CsI (Tl) and CeBr3 scintillators coupled with different sets of array of SiPM pixels is presented here. Spectral and spatial resolutions of both detector modules are characterized with experiments using x-ray lines from laboratory radioactive sources. It is shown that a faster scintillator with an array of low-noise SiPM pixels provides better spectral and spatial resolution and it is possible to achieve subpixel spatial resolution with such a detector module.

An estimate of the antineutrino energy loss by beta decay on strongly screening iron group nuclei in presupernova

The research on supernovae explosions is one of the most exciting fields in astrophysics. Recent studies show that the electron capture and beta decay play key roles in supernovae explosions. In this paper, the half-lives of some iron group nuclei by β−-decay are investigated due to shell effect, pair effect, and the changes of the decay energy. We also discuss the influence of strong electron screening (SES) on the electron energy, beta decay threshold energy, and the antineutrino energy loss rates (AELR) in β− decay. The AELR increases, and the screening enhancement factor can get to 4.684 in SES due to Q-value correction, shell and pairing effect. The AELR can be suppressed at lower density and higher temperature environment (e.g., 0.1 < ρ7 < 800, T9 > 30). The screening enhancement factor decreases about 14.10% (e.g., for 56Ni).

The Arab Astronomical Society (ArAS): Developing Astrophysics Research in the Arab World

AbstractThe Arab Astronomical Society (ArAS) was officially created during the constitutional assembly held in Marrakech (Morocco) on November 30, 2016, and legally recognized on May 15, 2017. ArAS is composed of a group of Arab researchers and students in the field of astrophysics who aim to develop research in this field in the Arab world (22 countries). ArAS is working on bridging the gap between the Arab astrophysicists in the Arab world and those around the world by organizing collaborative workshops and international scientific meetings, offering scholarships and developing graduate programs in astrophysics. Presently, the Society is working on establishing personal and material scientific infrastructure in the Arab world by training advanced undergraduate and graduate students in astrophysics and stimulating the building of new telescopes on the best sites in the Arab world. This will be accomplished through the hosting of specialized schools and conferences in astrophysics, international collaborations, facilitation of students’ and post-docs’ training in international research centres and universities, the establishment of prizes in astronomy to honour leading Arab scientists in astronomy and to motivate junior researchers to present notable works in astronomy. In this work, we present the on-going ArAS activities as well as future projects. ArAS is a young but energetic organization which is welcoming collaborations and partnership with other groups.

GAMMA-400 Project

Extraterrestrial gamma-ray astronomy is now a source of a new knowledge in the fields of astrophysics, cosmic-ray physics, and the nature of dark matter. The next absolutely necessary step in the development of extraterrestrial high-energy gamma-ray astronomy is the improvement of the physical and technical characteristics of gamma-ray telescopes, especially their angular and energy resolutions. Such a new generation telescope will be GAMMA-400, currently under development. Together with an X-ray telescope, it will perform precise and detailed observations in the energy range of ~20 MeV to ~10 000 GeV and 3–30 keV the Galactic plane, especially, toward the Galactic Center, Fermi Bubbles, Crab, Cygnus, etc. The GAMMA-400 will operate in the highly elliptic orbit continuously for a long time with the unprecedented angular (~0.01◦ at Eγ = 100 GeV) and energy (~1% at Eγ = 100 GeV) resolutions, exceeding the Fermi-LAT as well as ground-based gamma-ray telescopes by a factor of 5–10. GAMMA-400 will permit resolving gamma rays from annihilation or decay of dark matter particles, identifyingmany discrete sources (many of which are variable), clarifying the structure of extended sources, specifying the data on the diffuse emission, as well as measuring electron + positron fluxes and specifying electron + positron spectrum in the energy range from 1 GeV to 10 000 GeV.

Large-Scale Compressibility in Rotating Flows of Astrophysical Plasma in the Shallow Water Approximation

Two systems of magnetohydrodynamic equations in the shallow water approximation are proposed as a basis for studies in the field of plasma astrophysics: the system of equations with a full allowance for the Coriolis force and the system of equations on the β-plane in which the changes of the Coriolis parameter are linear in coordinate. Both systems of equations take into account such fundamentally important phenomena in plasma astrophysics as the compressibility and external magnetic field effects, increasing significantly the potential for applying these equations to study astrophysical objects. Compressibility in plasma astrophysics is shown to change significantly the dispersion laws for magneto-Poincare, magnetostrophic, and magneto-Rossby waves. The same nonlinear interactions as those in the absence of compressibility have been found to be realized in the case of a compressible rotating plasma. Three-wave equations in the weak nonlinearity approximation, in which the interaction coefficients depend on plasma large-scale compressibility and thermodynamic characteristics, have been derived by the method of multiscale expansions. Expressions for the growth rates of the parametric instabilities of three-wave interactions with large-scale compressibility have been derived.

Searching for Subsecond Stellar Variability with Wide-field Star Trails and Deep Learning

Abstract We present a method that enables wide-field ground-based telescopes to scan the sky for subsecond stellar variability. The method has operational and image processing components. The operational component takes star trail images. Each trail serves as a light curve for its corresponding source and facilitates subexposure photometry. We train a deep neural network to identify stellar variability in wide-field star trail images. We use the Large Synoptic Survey Telescope Photon Simulator to generate simulated star trail images and include transient bursts as a proxy for variability. The network identifies transient bursts on timescales down to 10 ms. We argue that there are multiple fields of astrophysics that can be advanced by the unique combination of time resolution and observing throughput that our method offers.

Subdwarf B stars as possible surviving companions in Type Ia supernova remnants

Although type Ia supernovae (SNe Ia) are so important in many astrophysical fields, a debate on their progenitor model is still endless. Searching the surviving companion in a supernova remnant (SNR) may distinguish different progenitor models, since a companion still exists in the remnant for the single-degenerate (SD) model, but does not for the double degenerate (DD) model. However, some recent surveys do not discover the surviving companions in the remnant of SN 1006 and Kepler's supernova, which seems to disfavor the SD model. Such a result could be derived from an incorrect survey target. Here, based on the common-envelope wind SD model for SNe Ia, in which the initial binary system consists of a white dwarf (WD) and a main-sequence (MS) star, we found that the companion at the moment of supernova explosion may be a MS, red-giant (RG) or subdwarf B (sdB) star if a spin-down timescale of less than $10^{\rm 7}$ yr is assumed. We show the properties of the companions at the moment of supernova explosion, which are key clues to search the surviving companions in SNRs. Here, we suggest that the sdB star may be the surviving companion in some SNRs, even if the progenitor systems are the WD + MS systems. The SNe Ia with the sdB companions may contribute to all SNe Ia as much as 22\%.

The Laboratory Astrophysics Spectroscopy Programme at Imperial College London

Accurate atomic parameters, such as transition probabilities, wavelengths, and energy levels, are indispensable for the analysis of stellar spectra and the obtainment of chemical abundances. However, the quantity and quality of the existing data in many cases lie far from the current needs of astronomers, creating an acute need for laboratory measurements of matching accuracy and completeness to exploit the full potential of the very expensively acquired astrophysical spectra. The Fourier Transform Spectrometer at Imperial College London works in the vacuum ultraviolet-visible region with a resolution of 2,000,000 at 200 nm. We can acquire calibrated spectra of neutral, singly, and doubly ionized species. We collaborate with the National Institute of Standards and Technology (NIST) and the University of Lund to extend our measurements into the infrared region. The aim of this review is to explain the current capabilities of our experiment in an understandable way to bring the astronomy community closer to the field of laboratory astrophysics and encourage further dialogue between our laboratory and all those astronomers who need accurate atomic data. This exchange of ideas will help us to focus our efforts on the most urgently needed data.

Introduction

In the 1960s, novel and increasingly powerful observational techniques opened up the field of high-energy astrophysics. Cosmology started to become an empirical science, and there was a resurgence in the study of general relativity. Martin Rees became a ...Read More

PeV scale supersymmetry breaking and the IceCube neutrino flux

The observation of very high energy neutrino events at IceCube has grasped a lot of attention in the fields of both astrophysics and particle physics. It has been speculated that these high energy neutrinos might originate either from purely conventional astrophysical sources or from the late decay of a super heavy (PeV scale) dark matter (DM) particle. In order for decaying DM to be a dominant source of the IceCube high-energy neutrinos, it would require an unusually suppressed value of the coupling of DM to neutrinos. We attempt to explain this small coupling in the context of an R-parity conserving minimal supergravity model which has right-handed neutrino superfields. With the main assumptions of super-partner masses at the PeV scale and also a reheating temperature not much larger than the PeV scale, we find in our model several natural order-of-magnitude “miracles”, (i) the gravitino is produced via freeze-in as a DM candidate with the correct relic density (ii) the right-handed (RH) sneutrino makes up only a tiny fraction (10−6), of the present day energy density of the universe, yet its decay lifetime to the gravitino and neutrinos is such that it naturally predicts the right order-of-magnitude for the IceCube neutrino flux. The long lifetime of the RH sneutrino is explained by the existence of a global R-symmetry which is only broken due to supersymmetry breaking effects. Our model also predicts a flux of 100 TeV gamma rays from the decaying RH sneutrino which are within the current observational constraints.

A new model for strange stars

In the present work, we attempt to find a new class of solutions for the spherically symmetric perfect fluid sphere by employing the Homotopy Perturbation Method (HPM), a new tool via which the mass polynomial function facilitates to tackle the Einstein field equations. A set of interior solutions found on the basis of the simplest MIT bag model equation of state (EOS) in the form $p=\frac{1}{3}(\rho-4B)$ where $B$ is the bag constant. The proposed interior metric for the stellar system is consistent with the exterior Schwarzschild spacetime on the boundary. In addition, we also conduct a detailed study on different tests, viz. the energy conditions, TOV equation, adiabatic index, Buchdahl limit, etc., to verify the physical validity of the proposed model. The numerical value of the used parameters is predicted for different strange star candidates, for different chosen values of the bag constant. In a nutshell, by exploiting HPM technique first time ever in the field of relativistic astrophysics, we have predicted in the present literature a singularity-free and stable stellar model which is suitable to describe ultra-dense objects, like strange (quark) stars.