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Now for a tool that is central to the topic of astrophysics—spectroscopy, and how it used to classify stellar spectra. This is an amazing subject; from just looking at the light from an object, we can tell how hot it is, how far away it is, in which direction it is moving, if it is rotating, and (from all this data) infer its age, its mass, how long it has left to live, etc. In fact, so important is this topic that it has been given its own chapter. From this point on in the book, a star will be referred to by its spectral classification.

In this article, we propose a bilevel segmentation framework with metacognitive learning (BS-McL) to detect power lines with an RGB camera mounted on an unmanned aerial vehicle (UAV) platform. The proposed framework consists of two levels based on spectral and spatial techniques. In the first level, spectral classification is carried out using the McL method, which is an evolving online learning neural network architecture. Due to similarities in spectral intensities, few nonpower line pixels are grouped along with power line pixels. The nonpower line pixels are removed by spatial segmentation in the second level. The second level includes morphological operations such as geometric features (shape and density indices), which are applied to detect the power lines. The processing steps of BS-McL are illustrated using a synthetic image of size 9 x 6 pixels. Also, two datasets consisting of 64 images with varying backgrounds, different locations, and dimensions of power lines are used to demonstrate the performance of the proposed BS-McL. The obtained results for BS-McL are compared with five commonly used methods. For both datasets, the efficiency of the BS-McL for power line extraction is better than for the methods used for comparison. Furthermore, the trained knowledge from our experimental set-up (Dataset 1: suburban scene) can be transferred to another dataset that is available publicly (Dataset 2: urban and mountain scenes) if the power line spectral values are in relevance with the distribution in the training dataset. The proposed approach BS-McL is based on online learning with a self-adaptive architecture, which provides improved generalization ability.

The near-Earth objects with low-Jovian Tisserand invariant (TJ) represent about 9 per cent of the known objects orbiting in the near-Earth space, being subject of numerous planetary encounters and large temperature variations. We aim to make a spectral characterization for a large sample of NEOs with TJ ≤ 3.1. Consequently, we can estimate the fraction of bodies with a cometary origin. We report new spectral observations for 26 low-TJ NEOs. The additional spectra, retrieved from different public data bases, allowed us to perform the analysis over a catalogue of 150 objects. We classified them with respect to Bus-DeMeo taxonomic system. The results are discussed regarding their orbital parameters. The taxonomic distribution of low-TJ NEOs differs from the entire NEOs population. Consequently, TJ ∼ 3 can act as a composition border too. We found that 56.2 per cent of low-TJ NEOs have comet-like spectra and they become abundant (79.7 per cent) for TJ ≤ 2.8. 16 D-type objects have been identified in this population, distributed on orbits with an average TJ = 2.65 ± 0.6. Using two dynamical criteria, together with the comet-like spectral classification as an identification method and by applying an observational bias correction, we estimate that the fraction of NEOs with a cometary nature and H ∈ (14, 21) mag has the lower and upper bounds (1.5 ± 0.15) and (10.4 ± 2.2) per cent. Additionally, our observations show that all extreme cases of low-perihelion asteroids (q ≤ 0.3 au) belong to S-complex.

Terahertz (THz) spectroscopy is now achieving increasing attention in security inspection owning to its non-destructiveness and deep penetrability of most packaging materials, such as leather, wood and wrapper. However, two major obstacles remain in spectral classification of liquid contraband: the complex components in some contraband and the spectral overlapping effect in similar types of contraband. In this paper, we establish two THz classification datasets and propose a real-time multi-class and multi-concentration liquid contraband spectral classification framework based on a convolutional neural network (CNN). The framework can not only identify contraband with complex components but also classify different concentrations of contraband. We also evaluate the robustness of the framework in different signal-to-noise ratio (SNR). Experimental results demonstrate that our algorithm (CNN) achieves the best performance compared with other deep learning and machine learning algorithms. It can be concluded that THz spectroscopy together with CNN is a promising technique for the classification of liquid contraband.

We perform a series of three-dimensional, magnetohydrodynamical (MHD) simulations of star cluster formation including gravity, turbulence, magnetic fields, stellar radiative heating and outflow feedback. We observe that the inclusion of protostellar outflows (1) reduces the star formation rate by a factor of $\sim2$, (2) increases fragmentation, and (3) shifts the initial mass function (IMF) to lower masses by a factor of $2.0\pm0.2$, without significantly affecting the overall shape of the IMF. The form of the sink particle (protostellar objects) mass distribution obtained from our simulations matches the observational IMFs reasonably well. We also show that turbulence-based theoretical models of the IMF agree well with our simulation IMF in the high-mass and low-mass regime, but do not predict any brown dwarfs, whereas our simulations produce a considerable number of sub-stellar objects, which are produced by dynamical interactions (ejections). We find that these dynamical interactions also play a key role for the binary separation distribution and stellar kinematics in general. Our numerical model of star cluster formation also reproduces the observed mass dependence of multiplicity. Our multiplicity fraction estimates generally concur with the observational estimates for different spectral types. We further calculate the specific angular momentum of all the sink particles and find that the average value of $1.5 \times 10^{19}\, \mathrm{cm^2\, s^{-1}}$ is consistent with observational data. The specific angular momentum of our sink particles lies in the range typical of protostellar envelopes and binaries. We conclude that the IMF is controlled by a combination of gravity, turbulence, magnetic fields, radiation and outflow feedback., Comment: 21 pages, 20 figures, 2 tables, accepted for publication in MNRAS, included brief discussions on stellar kinematics and binary separation distribution, few other minor changes including additional references

The rapid development of large-scale sky survey project has produced a large amount of stellar spectral data, which make the automatic classification of stellar spectral data a challenging task. In this paper, we have proposed a stellar spectral classification method based on a capsule network. At first, by using the one-dimensional convolutional network and short-time Fourier transform (STFT), the one-dimensional spectra of the F5, G5, and K5 types selected from the LAMOST Data Release 5 (DR5) are converted into the two-dimensional Fourier spectrum images. Then, the two-dimensional Fourier spectrum images are classified automatically by the capsule network. Because the capsule network can preserve the hierarchical pose relationships among the entities in the image, and it does not need any pooling layers, the experimental results show that the capsule network has a better classification performance, for the classifications of the F5, G5, and K5-type stellar spectra, its classification accuracy is superior to other classification methods.

We present the results of a UBVRcIc and JHKLM photometric monitoring campaign conducted in 2016–2020, low-resolution spectroscopy, and an analysis of the ASAS-3 and ASAS-SN photometric data for the semiregular variable and post-AGB candidate AU Vul (IRAS 20160+2734). The star is shown to experience quasi-periodic brightness oscillations with a variable amplitude and periods of 67–75 and 145–150 days in different time intervals. Its spectrum at maximum light is classified as that of an early G supergiant. In this spectrum H $$\alpha$$ , H $$\beta$$ , and higher Balmer lines are weakened, possibly, because of emission components, while the absorptions of s-process elements (Ba II, Sr II, and Y II) are slightly strengthened. An H $$\alpha$$ emission has been detected in the spectrum on the ascending branch of the light curve. TiO absorption bands are observed in the spectra at different brightness levels with maximum intensity at minimum light. The spectral energy distribution in the range 0.44 ( $$B$$ )–2.2 ( $$K$$ ) $$\mu$$ m corresponds to spectral types from G2I at maximum to G8I at minimum light. An emission excess has been detected in the $$L$$ and $$M$$ bands. The spectral energy distribution in the range 0.44–90 $$\mu$$ m constructed from our own observations and WISE, MSX, IRAS, and AKARI data is satisfactorily described by the sum of three components: a star and dust envelopes with $$T_{\textrm{hot}}=1000$$ K and $$T_{\textrm{cold}}=150$$ K. Using the distance based on the Gaia EDR3 parallax, $$D\approx 2300$$ pc, we have estimated the absolute magnitude, $$M_{V}\approx-4\overset{m}{.}45$$ , and the luminosity, $$L\approx 5450L_{\odot}$$ . A comparison with evolutionary models has shown that AU Vul may be at the very beginning of the post-AGB stage of evolution and have a mass $${\sim}0.55M_{\odot}$$ . We note that the star has a number of properties that distinguish it from typical post-AGB objects and make it akin to RV Tau stars.

We present our 500 pc distance-limited study of stellar fares using the Dark Energy Camera as part of the Deeper, Wider, Faster Program. The data was collected via continuous 20-second cadence g band imaging and we identify 19,914 sources with precise distances from Gaia DR2 within twelve, ~3 square-degree, fields over a range of Galactic latitudes. An average of ~74 minutes is spent on each field per visit. All light curves were accessed through a novel unsupervised machine learning technique designed for anomaly detection. We identify 96 flare events occurring across 80 stars, the majority of which are M dwarfs. Integrated are energies range from $\sim 10^{31}-10^{37}$ erg, with a proportional relationship existing between increased are energy with increased distance from the Galactic plane, representative of stellar age leading to declining yet more energetic are events. In agreement with previous studies we observe an increase in flaring fraction from M0 -> M6 spectral types. Furthermore, we find a decrease in the flaring fraction of stars as vertical distance from the galactic plane is increased, with a steep decline present around ~100 pc. We find that ~70% of identified flares occur on short timescales of ~8 minutes. Finally we present our associated are rates, finding a volumetric rate of $2.9 \pm 0.3 \times 10^{-6}$ flares pc$^{-3}$ hr$^{-1}$., 20 pages, 14 figures, 6 tables

Basal stem rot (BSR) is one of the diseases that threaten the oil palm plantations in Southeast Asia, particularly in Malaysia and Indonesia. As the oil palm plantations continue to grow, there is a need for time-effective, non-destructive, and more precise techniques for detecting BSR. Dielectric spectroscopy has been proven to be an effective method for noninvasive classification of BSR in oil palm trees. However, due to the nature of the large spectral data for spectroscopy analysis, there is a need to reduce the data without losing the main features for more efficient computation. This study investigated the feasibility of applying genetic algorithm (GA) as a feature selection algorithm to select the most significant frequencies of dielectric spectral data for identifying BSR disease in oil palms. Then, the data at the most significant frequencies were used as the input of four classifiers: linear discriminant analysis (LDA), quadratic discriminant analysis (QDA), k-nearest neighbors (kNN), and naive Bayes (NB). The results showed that the best classification accuracy was achieved using LDA classifier with the accuracy of 86.36%. Without implementing GA, the highest classification accuracy was obtained by using the QDA classifier with an accuracy of 82.22%. These results demonstrate the advantages of applying GA as a feature selection model to enhance spectral classification in the identification of BSR in oil palms using dielectric spectroscopy measurements.

Using the short-cadence data (1-min interval) of the Kepler space telescope, we conducted a statistical analysis for the characteristic time of stellar flares on Sun-like stars (SLS). Akin to solar flares, stellar flares show rise and decay light-curve profiles, which reflect the two distinct phases (rise phase and decay phase) of the flare process. We derived characteristic times of the two phases for the stellar flares of SLS, resulting in a median rise time of about 5.9 min and a median decay time of 22.6 min. It is found that both the rise time and the decay time of the stellar flares follow a lognormal distribution. The peak positions of the lognormal distributions for flare rise time and decay time are 3.5 min and 14.8 min, respectively. These time values for stellar flares are similar to the time-scale of solar flares, which supports the idea that stellar flares and solar flares have the same physical mechanism. The statistical results obtained in this work for SLS can be a benchmark of flare characteristic times when comparing with other types of stars., Published in Monthly Notices of the Royal Astronomical Society: Letters, 5 pages, 2 figures, 2 tables, 3 ancillary files

This article is a brief survey of our previous work devoted to searching for candidate type FK Com giant stars and an analysis of data for yet another new candidate, KIC 7732964. Establishing that KIC 7732964 belongs to this group of stars requires further study of the evolutionary status of the star (dwarf, subdwarf, or giant). The star has fast rotation and high flare activity, which are more typical of dwarf or subgiant stars. As for other candidates, in the case of KIC 7732964 additional spectral observations are required to establish the absence of binarity, refine the value of the acceleration of gravity, and its spectral classification.

This paper is a continuation of our earlier work devoted to determining the orbit and mass of the star 61 Cyg and the changes in the photometric characteristics of its components. The purpose of this work has been to refine the orbital elements, estimate the masses, and search for possible manifestations of periodic components in deviations from the orbital motion. Observations on two instruments at the Pulkovo Observatory have been used in this work: the normal astrograph during 1895-1919 and the 26-inch refractor during 1957-2019, as well as the earliest micrometric measurements by V. Ya. (F.G.W.) Struve during 1819-1837. Relative positions of the components determined from observations with the normal astrograph during 1895-1999 are published for the first time. Because of its closeness to the Sun and the spectral class of the components K5V and K7V, 61 Cyg is regarded as a probable candidate parent star of an exoplanet. Because of the combined observations with the 26-inch refractor and the transformation of all the data to a unified system, a gap in the observations from the beginning of the twentieth century has been filled. The modern astrophysical parameters of this star together with data published in the Gaia DR2 survey have been used. To check the orbit, the radial orbital acceleration W has been calculated from our data and found to be in good agreement with the acceleration derived by other authors from spectral observations. Possible periodic deviations from the orbital motion of the star are also discussed.

Stars of spectral types O and B produce neutron stars (NSs) after supernova explosions. Most of NSs are strongly magnetised including normal radio pulsars with $B \propto 10^{12}$ G and magnetars with $B\propto 10^{14}$ G. A fraction of 7-12 per cent of massive stars are also magnetised with $B\propto 10^3$ G and some are weakly magnetised with $B\propto 1$ G. It was suggested that magnetic fields of NSs could be the fossil remnants of magnetic fields of their progenitors. This work is dedicated to study this hypothesis. First, we gather all modern precise measurements of surface magnetic fields in O, B and A stars. Second, we estimate parameters for log-normal distribution of magnetic fields in B stars and found $\mu_B = 2.83\pm 0.1$ $\log_{10}$ (G), $\sigma_B=0.65\pm 0.09$ for strongly magnetised and $\mu_B = 0.14\pm 0.5$ $\log_{10}$ (G), $\sigma=0.7_{-0.27}^{+0.57}$ for weakly magnetised. Third, we assume that the magnetic field of pulsars and magnetars have $2.7$ DEX difference in magnetic fields and magnetars represent 10 per cent of all young NSs and run population synthesis. We found that it is impossible to simultaneously reproduce pulsars and magnetars populations if the difference in their magnetic fields is 2.7 DEX. Therefore, we conclude that the simple fossil origin of the magnetic field is not viable for NSs., Comment: 23 pages, accepted for publication in MNRAS on 19 April 2021

We present the results of a search for stellar flares in the first data release from the Next Generation Transit Survey (NGTS). We have found 610 flares from 339 stars, with spectral types between F8 and M6, the majority of which belong to the Galactic thin disc. We have used the 13 second cadence NGTS lightcurves to measure flare properties such as the flare amplitude, duration and bolometric energy. We have measured the average flare occurrence rates of K and early to mid M stars and present a generalised method to measure these rates while accounting for changing detection sensitivities. We find that field age K and early M stars show similar flare behaviour, while fully convective M stars exhibit increased white-light flaring activity, which we attribute to their increased spin down time. We have also studied the average flare rates of pre-main sequence K and M stars, showing they exhibit increased flare activity relative to their main sequence counterparts., 21 pages, 13 figures, 5 tables. Accepted for publication in the Monthly Notices of the Royal Astronomical Society

Swift J004929.5-733107 is an X-ray source in the Small Magellanic Cloud (SMC) that has been reported several times, but the optical counterpart has been unclear due to source confusion in a crowded region of the SMC. Previous works proposed [MA93] 302 as the counterpart, however we show here, using data obtained from the S-CUBED project, that the X-ray positio is inconsistent with that object. Instead we propose a previously unclassified object which has all the indications of being a newly identified Be star exhibiting strong HU emission. Evidence for the presence of significant I-band variability strongly suggest that this is, in fact, a Be type star with a large circumstellar disk. Over 18 years worth of optical monitoring by the OGLE project reveal a periodic modulation at a period of 413d, probably the binary period of the system. A SALT optical spectrum shows strong Balmer emission and supports a proposed spectral classification of B1-3 III-IVe. The X-ray data obtained from the S-CUBED project reveal a time-averaged spectrum well fitted by a photon index = 0.93 pm 0.16. Assuming the known distance to the SMC the flux corresponds to a luminosity 10E35 erg/s. All of these observational facts suggest that this is confirmed as a Be star-neutron star X-ray binary (BeXRB) in the SMC, albeit one with an unusually long binary period at the limits of the Corbet Diagram., 9 pages 12 figures

This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made., The goal of the Ariel space mission is to observe a large and diversified population of transiting planets around a range of host star types to collect information on their atmospheric composition. The planetary bulk and atmospheric compositions bear the marks of the way the planets formed: Ariel’s observations will therefore provide an unprecedented wealth of data to advance our understanding of planet formation in our Galaxy. A number of environmental and evolutionary factors, however, can affect the final atmospheric composition. Here we provide a concise overview of which factors and effects of the star and planet formation processes can shape the atmospheric compositions that will be observed by Ariel, and highlight how Ariel’s characteristics make this mission optimally suited to address this very complex problem. © The Author(s) 2021., D.T., S.F., S.M., E.S., and A.N. acknowledge the support of the Italian Space Agency (ASI) through the ASI-INAF contract 2018-22-HH.0. D.T., C.C., D.F., and L.P. acknowledge the support of the PRIN-INAF 2016 “The Cradle of Life - GENESIS-SKA (General Conditions in Early Planetary Systems for the rise of life with SKA”. D.T., S.F., S.M. D.F, J.M., F.O., P.W. acknowledge the support of the Italian National Institute of Astrophysics (INAF) through the INAF Main Stream project “Ariel and the astrochemical link between circumstellar discs and planets” (CUP: C54I19000700005). S.M. acknowledges support from the European Research Council via the Horizon 2020 Framework Programme ERC Synergy “ECOGAL” Project GA-855130. M.K. acknowledges funding by the University of Tartu ASTRA project 2014-2020.4.01.16-0029 KOMEET “Benefits for Estonian Society from Space Research and Application”, financed by the EU European Regional Development Fund. J.M.D.K. gratefully acknowledges funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through an Emmy Noether Research Group (grant number KR4801/1-1) and the DFG Sachbeihilfe (grant number KR4801/2-1), as well as from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme via the ERC Starting Grant MUSTANG (grant agreement number 714907). The research of O.P. is funded by the Royal Society, through Royal Society Dorothy Hodgkin Fellowship DH140243. M.P. thanks the support to NuGrid from STFC (through the University of Hull’s Consolidated Grant ST/R000840/1), and access to VIPER, the University of Hull High Performance Computing Facility. M.P. acknowledges the support from the ”Lendulet-2014” Program of the Hungarian Academy of Sciences (Hungary), from the ERC Consolidator Grant (Hungary) funding scheme (Project RADIOSTAR, G.A. n. 724560), by the National Science Foundation (NSF, USA) under grant No. PHY-1430152 (JINA Center for the Evolution of the Elements). M.P. also thanks the UK network BRIDGCE and the ChETEC COST Action (CA16117), supported by COST (European Cooperation in Science and Technology). M.I. thanks the support by JSPS KAKENHI 18H05439. C.D. acknowledges financial support from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709), and the Group project Ref. PID2019-110689RB-I00/AEI/10.13039/501100011033.

Modern theories of planetary system formation predict a large population of planetesimals, which are remnants of the primordial matter of the protoplanetary cloud and, at the same time, embryos of small bodies that we observe in our solar system. The planetesimals play an important role in the dynamic and physical evolution of the planetary system. Gravitational scattering of planetesimals which are enriched with volatile elements might cause the volatile and organic compounds to enter the interior of the planetary system, triggering the formation of planetary atmospheres and further development of life. Small bodies inside planetary systems can evaporate due to the increasing insolation at close distances from the mother star, leading to the development of activity akin to the activity of comets in our solar system. The study of cometary activity in our solar system is aimed primarily at the investigation of the physical processes in the early stages of the development of the protoplanetary cloud. Until recently, it was not possible to study small bodies in other planetary systems because their small size makes it very difficult to detect by direct methods. Over the past 10 years, two space missions, Kepler and TESS (The Transiting Exoplanet Survey Satellite), have been equipped for continuous photometric monitoring to find exoplanets by transit, i. e. monitoring the changes in brightness of a star due to the passage of a smaller object across its disk. The presence of high-precision photometric measurements of the luminosity curves of about 200 000 stars, which are available in the public domain, potentially makes it possible to identify rather small changes in the luminosity curves of stars due to the passage of a body with gas-dust coma (exocomet) across the stellar disk. The article considers a number of issues related to the discovery and study of exocomets. The main detection methods based on the analysis of photometric and spectral series of observational data of space missions as well as ground-based observational complexes are considered. We provide a brief review of the main projects devoted to the results of theoretical modeling and experimental studies of the manifestations of exocometary activity. Known cases of manifestations of exocometary activity in planetary systems of stars of different spectral classes are described and the main characteristics of such stars and their planetary systems are given. We discuss the prospects for further research of these still very exotic objects. The importance of such research for understanding evolutionary processes in our own solar system is emphasized.

We present the first high accuracy UBVRI(RI)c CCD light curves of the poorly investigated eclipsing system V680 Mon = GSC 7428 218 (P = 8.54d, V = 10.02m). They were used to find the photometric solutions and to derive the physical characteristics of the components. The highest known eccentricity e = 0.613 was found in the class of systems with eccentric orbits. The orientation of the orbital ellipse ω = 357° is not convenient for apsidal motion investigation. High accuracy of our observations allows to find the reliable parameters of the system: M1 = 3.3 $${{M}_{ \odot }}$$ (B7 V), M2 = 1.8 $${{M}_{ \odot }}$$ (A2 V). We estimate the age of the components to be 70 mega-years. The photometric parallax π = 0.00109(1)″, derived from our observations, is two times smaller than the value π = 0.0025(9)″ from GAIA DR1, affected by the presence of the K3 V optical companion of the investigated star. The light curves solution demonstrates the presence of a third light, which can be assigned to a star of A4 V spectral class. The light time effect is found in the minima timings, so the source of the third light is physically connected to the eclipsing system. The parameters of the third body orbit are derived.

Publications in astrophysics are nowadays mainly published and read in digitized formats. Astrophysical publications in both research and in popular outreach often use colorful representations of stars to indicate various stellar types, that is, different spectral types or effective temperatures. Computer generated and computer displayed imagery has become an integral part of stellar astrophysics communication. There is, however, no astrophysically motivated standard color palette for illustrative representations of stars and some stars are actually represented in misleading colors. We use pre-computed PHOENIX and TLUSTY stellar model spectra and convolve them with the three standard color matching functions for human color perception between 360$\,$nm and 830$\,$nm. The color matching functions represent the three sets of receptors in the eye that respond to red, green, and blue light. For a grid of main sequence stars with effective temperatures between 2300$\,$K and 55,000$\,$K of different metallicities we present the red-blue-green and hexadecimal color codes that can be used for digitized color representations of stars as if seen from space. We find significant deviations between the color codes of stars computed from stellar spectra and from a black body radiator of the same effective temperature. We illustrate the main sequence in the color wheel and demonstrate that there are no yellow, green, cyan, or purple stars. Red dwarf stars (spectral types M0V - M9V) actually look orange to the human eye. Old white dwarfs such as WD$\,$1856$+$534, host to a newly discovered transiting giant planet candidate, occur pale orange to the human eye, not white. Our freely available software can be used to generate color codes for any input spectrum such as those from planets, galaxies, quasars etc., Comment: 13 pages, 5 figures, published in Astronomische Nachrichten / Astronomical Notes

We use 343,747 sources from LAMOST DR5 to do star/galaxy/QSO classification with machine learning approaches. Specifically, the 312,767 spectral labeled stars (G, K, M, F, A) are used to do star classification. The photometry of u, g, r, i, z, J, and H are used as machine learning features. For star/galaxy/QSO classification, the k nearest neighbor algorithm (KNN), decision tree (DT), random forest (RF) and support vector machine (SVM) perform well. For star classification, the accuracy of RF and SVM classification are higher than the accuracy of KNN and DT. The area under receiver operating characteristic curves of the four models are approaching to 1. The accuracy, precision, recall, f_score, Matthews correlation coefficient are always greater than 0.5. The four models perform all right in predicting the nature of sources and the star label.

We present the first photometric observations and light curve modelling of the discovered systems GSC 01870-00458 and USNO-A2.0-0975 04721840. Our modelling was carried out using a recent Windows interface version of Wilson and Devinney code based on model atmospheres provided by Kurucz. The accepted models revealed absolute and physical parameters that can be used to study the evolutionary states of systems. The parameters show that primary component is more massive and hotter than the secondary component for both systems, and spectral types of the system components were adopted. Locations of both systems on theoretical mass-luminosity and mass-radius curves revealed a good fit for components of both systems except for the secondary component of the system GSC 01870-00458.

Models are developed for spectral classes of GZh and Zh coal concentrates based on diffuse-reflection IR spectra, by independent modeling of class analogs. The spectral classes derived for such coal are shown to be clearly distinct. Individual models of spectral classes for samples of GZh and Zh concentrates from different enrichment facilities are created and compared. On the basis of the spectral classes, which reflect the chemical structure of a limited mass of coal, the coal rank may be established, and concentrates from different enrichment facilities may be compared and contrasted. In addition, rapid quality control is possible.

ZZ PsA is a neglected bright southern contact binary system with maximum V magnitude of 9.26. We present the first multi-band photometric analysis and find the system to be in deep contact (>95%) with an extremely low mass ratio of 0.078. The primary has a mass of 1.213 M? in keeping with its reported spectral class of F6. In order to determine if ZZ PsA is a merger candidate we outline the current status regarding the instability mass ratio and develop new relationship linking the mass of the primary to the instability mass ratio of the system and the degree of contact. We find that ZZ PsA along with two other examples from the literature to be merger candidates while an additional three require further observations to be confirmed as potential merger candidates., 7 pages, 6 figures Accepted MNRAS

A medium- and high-resolution spectroscopic survey of helium-rich hot subdwarfs is being carried out using the Southern African Large Telescope (SALT). Objectives include the discovery of exotic hot subdwarfs and of sequences connecting chemically-peculiar subdwarfs of different types. The first phase consists of medium-resolution spectroscopy of over 100 stars selected from low-resolution surveys. This paper describes the selection criteria, and the observing, classification and analysis methods. It presents 107 spectral classifications on the MK-like Drilling system and 106 coarse analyses ($T_{\rm eff}, \log g, \log y$) based on a hybrid grid of zero-metal non-LTE and line-blanketed LTE model atmospheres. For 75 stars, atmospheric parameters have been derived for the first time. The sample may be divided into 6 distinct groups including the classical `helium-rich' sdO stars with spectral types (Sp) sdO6.5 - sdB1 (74) comprising carbon-rich (35) and carbon-weak (39) stars, very hot He-sdO's with Sp $\lesssim$ sdO6 (13), extreme helium stars with luminosity class $\lesssim 5$ (5), intermediate helium-rich subdwarfs with helium class 25 -- 35 (8), and intermediate helium-rich subdwarfs with helium class $10 - 25$ (6). The last covers a narrow spectral range (sdB0 -- sdB1) including two known and four candidate heavy-metal subdwarfs. Within other groups are several stars of individual interest, including an extremely metal-poor helium star, candidate double-helium subdwarf binaries, and a candidate low-gravity He-sdO star., MNRAS Accepted 18/11/20, 20 pages + 26 pages supplementary material

This is a theoretical study of changes in several characteristics of the spectra of early-type supergiants owing to scattering of continuum radiation. Thomson scattering on free electrons is treated as the scattering mechanism, although the approach used here is quite general. The reason for changes in the spectral class of a star with constant bolometric luminosity and surface temperature is elucidated and the necessary conditions for their realization are introduced. The effect of scattering in the continuum on the magnitude of the intensity jumps in the hydrogen spectrum depending on the degree of ionization is studied. The conditions under which the Schuster mechanism for formation of emission lines sets in are clarified both for an isothermal atmosphere and for an atmosphere with a temperature gradient.

Published data indicate a substantial increase in the differential rotation parameter ∆Ω of stars hotter than 6700 K. By analyzing the shape of the light curves and the presence of a specific set of peaks in their power spectra, we have found that 47 of 57 objects with Teff greater than 7500 K that were studied can be identified as pulsating stars and only 10, as stars with brightness variation owing to rotational modulation. After eliminating the pulsating variables, for the stars with Teff greater than 7500 K the average value of ∆Ω= 0.051±0.01 rad/day. This conclusion conflicts with our earlier assumption that the peaks in the power spectra for ROTD stars are caused by a possible manifestation of differential rotation. Further independent evidence for a low value of ∆Ω for stars in spectral class A has been obtained from Zeeman-Doppler charts for the star γ Gem, with an estimate for the differential rotation parameter of the star of 0.0073±0.0023 rad/day.

The Visible Infrared Imaging Radiometer Suite (VIIRS) on board the Suomi-NPP (SNPP) and NOAA-20 (N20) spacecrafts is a multispectral Earth-observing instrument with bands covering wavelengths from visible to long-wave infrared. Among these bands is a panchromatic day/night band (DNB) with a broad spectral response ranging from 500 to 900 nm, and a high dynamic range spanning over seven orders of magnitude, allowing for observations to take place during both daytime and nighttime. The DNB operates at three gain levels, with low- and mid-gain stages and two high-gain stages (HGSs). The HGS is capable of detecting dim city lights during Earth-view observations at night as well as bright stars through the instrument space-view port. Since SNPP and N20 are at opposite points of the same orbit, each VIIRS instrument is able to observe the same stars with the DNB in successive orbits. This will allow us to make a direct comparison of the relative calibration of each instrument using stars over a range of spectral classes. In this article, we develop methodology for accurately identifying target stars in order to make proper comparisons between the DNB HGS of each instrument. We then take observations from multiple stars in order to compute the ratio in the measured irradiance for each instrument as a function of spectral class. For K-type stars, which have the least spectral change over the DNB wavelength range, we measure a calibration bias between the SNPP and N20 DNB HGS of approximately 4%, which is stable over the duration of the N20 mission.

Recent progress in spectral classification is largely attributed to the use of convolutional neural networks (CNNs). While a variety of successful architectures have been proposed, they all extract spectral features from various portions of adjacent spectral bands. In this article, we take a different approach and develop a deep spectral feature fusion method, which extracts both local and interlocal spectral features, capturing thus also the correlations among nonadjacent bands. To our knowledge, this is the first reported deep spectral feature fusion method. Our model is a two-stream architecture, where an intergroup and a groupwise spectral classifier operate in parallel. The interlocal spectral correlation feature extraction is achieved elegantly, by reshaping the input spectral vectors to form the so-called nonadjacent spectral matrices. We introduce the concept of groupwise band convolution to enable the efficient extraction of discriminative local features with multiple kernels adopting the local spectral content. Another important contribution of this work is a novel dual-channel attention mechanism to identify the most informative spectral features. The model is trained in an end-to-end fashion with a joint loss. Experimental results on real datasets demonstrate excellent performance compared with the current state of the art.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited., Different properties of quasars may be observed and analyzed through the many ranges of the electromagnetic spectrum. Pioneering studies showed that an “H-R diagram” for quasars was needed to organize these data, and that more than two dimensions were necessary: a four-dimensional Eigenvector (4DE1) parameter space was proposed. The 4DE1 makes use of independent observational properties obtained from the optical and UV emission lines, as well as from the soft-X rays. The 4DE1 “optical plane,” also known as the quasar Main Sequence (MS), identifies different spectral types in order to describe a consistent picture of QSOs. In this work, we present a spectroscopic analysis focused on the comparison between two sources, one radio-loud (PKS2000-330, urn:x-wiley:00046337:media:asna20210084:asna20210084-math-0001) and one radio-quiet (Q1410+096, urn:x-wiley:00046337:media:asna20210084:asna20210084-math-0002), both showing Population A quasar spectral properties. Optical spectra were observed in the infrared with VLT/ESO, and the additional measures in UV were obtained through the fitting of archive spectra. The analysis was performed through a nonlinear multicomponent decomposition of the emission line profiles. Results are shown in order to highlight the effects of the radio-loudness on their emission line properties. The two quasars share similar optical spectroscopic properties and are very close on the MS classification while presenting significant differences on the UV data. Both sources show significant blueshifts in the UV lines but important differences in their UV general behavior. While the radio-quiet source Q1410+096 shows a typical Pop A UV spectrum with similar intensities and shapes on both CIVλ1549 and SiIVλ1392, the UV spectrum of the strong radio-loud PKS2000-330 closely resembles the one of Population B of quasars. © 2021 The Authors. Astronomische Nachrichten published by Wiley-VCH GmbH., A.D.M. acknowledges the support of the INPhINIT fellowship from “la Caixa” Foundation (ID 100010434). The fellowship code is LCF/BQ/DI19/11730018. A.D.M. and A.d.O. acknowledge financial support from the State Agency for Research of the Spanish MCIU through the project PID2019-106027GB-C41 and the “Center of Excellence Severo Ochoa” award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709).

This is a study of spectral and photometric observations of the binary system with an X-ray component V725 Tauri=A0535+262. It consists of a giant star HDE 245770 of spectral class O9.7 and the pulsar A0535+26 with a pulsation period of ~103 s. Active stages of this object, accompanied by “giant” X-ray outbursts, have been observed repeatedly. The last events occurred during 2009-2011. Our studies in 2017-2020 yielded the following data: over the last three years the B and V band brightness of the object has remained at a high level and began to decrease at the end of 2019. Here, beginning in 2016 a gradual increase in the radiative fluxes in the Hβ and Hα emission lines has been observed. At present the equivalent widths of these lines exceed the values recorded during the time of the gigan X-ray outburst of 2011. Previous studies have shown that a similar combination of the characteristics of this object, specifically an increase in emission line fluxes as the brightness decreases. is detected just before the onset of an active stage.