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We address the shocks from acoustic pulses and wave trains in general one-dimensional flows, with an emphasis on the application to super-Eddington outbursts in massive stars. Using approximate adiabatic invariants, we generalize the classical equal-area technique in its integral and differential forms. |
We present the results of 45 transit observations obtained for the transiting exoplanet HAT-P-32b. The transits have been observed using several telescopes mainly throughout the YETI network. |
The Hanle effect in strong spectral lines is the physical mechanism that should be increasingly exploited for quantitative explorations of the magnetism of the quiet solar chromospheric plasma. Here we show, by means of multilevel radiative transfer calculations and new spectropolarimetric observations, that the ampli... |
We present a novel relaxation method to build three-dimensional rotating structures of barotropic bodies using the SPH technique. The method is able to relax gaseous structures in rigid as well as differential rotation. |
The well-studied carbon star, V Hya, showing evidence for high-speed, collimated outflows and dense equatorial structures, is a key object in the study of the poorly understood transition of AGB stars into aspherical planetary nebulae. Using the STIS instrument onboard HST, we have obtained high spatial-resolution lon... |
Getman et al. (2021) reports the discovery, energetics, frequencies, and effects on environs of $>1000$ X-ray super-flares with X-ray energies $E_X \sim 10^{34}-10^{38}$~erg from pre-main sequence (PMS) stars identified in the $Chandra$ MYStIX and SFiNCs surveys. Here we perform detailed plasma evolution modeling o... |
We present Suzaku XIS observation of V2491 Cyg (Nova Cyg 2008 No. 2) obtained in quiescence, more than two years after the outburst. The nova was detected as a very luminous source in a wide spectral range from soft to hard X-rays. |
In this study, we conducted a comprehensive analysis of the SX Phoenicis (SX Phe) type star CY Aquarii (CY Aqr). Our investigation included a detailed $O-C$ analysis based on a 90-year observational dataset, augmented by 1,367 newly determined times of maximum light. |
We identified blue straggler stars (BSSs) in 53 open clusters utilizing data from Gaia DR3. Most of these clusters are situated in the outer regions of the Galactic disc, encompassing structures such as the warp and the Outer arm. |
A 20 second cadence TESS monitoring campaign of 226 low-mass flare stars during Cycle 3 recorded 3792 stellar flares of >10^32 erg. We explore the time-resolved emission and substructure in 440 of the largest flares observed at high S/N, 97% of which released energies of >10^33 erg. |
The daily measurements of the disc-integrated solar radio flux, observed by the Radio Solar Telescope Network (RSTN), at 245, 410, 610, 1415, 2695, 4995, and 8800 MHz during the time interval of 1989 January 1 to 2019 December 17, are used to investigate the temporal evolution of radial differential rotation of solar c... |
Nova Sagittarii 1943 (V1148 Sgr) was an 8th-mag optical transient that was unusual in having a late-type spectrum during its outburst, in striking contrast to the normal high-excitation spectra seen in classical novae. Unfortunately, only an approximate position was given in the discovery announcement, hampering follo... |
We present the first version of a Nearby Stellar Systems Catalog for Exoplanet Imaging Missions (dubbed by the direct imaging community as "ExoCat") for use in exoplanet direct imaging mission planning. This version, ExoCat-1, includes 2347 stars taken from the Hipparcos Catalogue with measured parallaxes >... |
On the Sun,jets in light bridges are frequently observed with high-resolution <a href="http://instruments.The" rel="external noopener nofollow" class="link-external link-http">this http URL</a> respective roles played by convection and the magnetic field in triggering such jets are not yet <a href="http://clear.We" rel... |
The bulk of solar flare emission originates from very compact sources located in the lower solar atmosphere and seen in various wavelength ranges: near optical, UV, EUV, soft and hard X-rays, and gamma-ray emission, yet very few spatially resolved imaging observations to determine the structure of these regions exist. ... |
The 18O/17O ratio of the Solar System is 5.2 while that of the interstellar medium (ISM) and young stellar objects is ~4. This difference cannot be explained by pollution of the Sun's natal molecular cloud by 18O-rich supernova ejecta because (1) the necessary B-star progenitors live longer than the duration of st... |
The accelerated electrons during solar flares produce radio bursts and nonthermal X-ray signatures. The quasi-periodic pulsations (QPPs) and fine structures in spatial-spectral-temporal space in radio bursts depend on the emission mechanism and the local conditions, such as magnetic fields, electron density, and pitch... |
The prominent Thackeray's globules are a collection of cloudlets seen in silhouette against the bright emission of the IC 2944 HII region, ionized by the Collinder 249 cluster of early-type stars (placed at 2331$\pm$30 pc, derived from a Gaia DR3 analysis of the parallaxes of 11 massive stars). Here we present the... |
We present basic observational data and association membership analysis for 45 young and active low-mass stellar systems from the ongoing RECONS photometry and astrometry program at the Cerro Tololo Inter-American Observatory. Most of these systems have saturated X-ray emission (log(Lx/Lbol) > -3.5) based on X-ray ... |
AR Herculis is an RR Lyrae star of type RRab whose spectral type ranges from A7 to F3. Its visual brightness varies between 10.59 mag and 11.63 mag (V). |
Hundred observations of Delta Scorpii, from April to September 2011, made for AAVSO visually and digitally with a commercial CMOS camera have been plotted. The three most luminous pixels either of the target star and the two reference stars are used to evaluate the magnitude through differential photometry. |
We present Fe, Si, and Ca abundances for 61 giants in Plaut's Window (l=-1,b=-8.5) and Fe abundances for an additional 31 giants in a second, nearby field (l=0,b=-8) derived from high resolution (R~25,000) spectra obtained with the Blanco 4m telescope and Hydra multifiber spectrograph. The median metallicity of re... |
The first few hours of a supernova (SN) contain significant information about the progenitor system. The most modern wide-field surveys that scan the sky repeatedly every few days can discover all kinds of transients in those early epochs. |
The Carina nebula hosts a large number of globulettes. The majority are of planetary mass, but there are also those with masses of several tens up to a few hundred Jupiter masses. |
Quasi-biennial oscillation (QBO) of solar magnetic activities is intrinsic to dynamo mechanism, but still far from fully understood. In this work, the phase and amplitude asymmetry of solar QBO of Halpha flare activity in the northern and southern hemispheres is studied by the ensemble empirical mode decomposition, th... |
We present a multi-instrument analysis of the rapidly oscillating Ap (roAp) star HD 42659. We have obtained $B$ photometric data for this star and use these data, in conjunction with TESS observations, to analyse the high-frequency pulsation in detail. |
Solar S-bursts are short duration ($<1$ s at decameter wavelengths) radio bursts that have been observed during periods of moderate solar activity, where S stands for short. The frequency drift of S-bursts can reflect the density variation and the motion state of the electron beams. |
For a long time XMMU J010331.7-730144 was proposed as a high-mass X-ray binary candidate based on its X-ray properties, however, its optical behaviour was unclear - in particular previous observations did not reveal key Balmer emission lines. In this paper we report on optical and X-ray variability of the system. |
The mass-loss mechanism in normal K--M giant stars with small variability amplitudes is not yet understood, although they are the majority among red giant stars. We present high-spatial and high-spectral resolution observations of the 2.3 micron CO lines in the M7 giant BK Vir with a spatial resolution of 9.8 mas and ... |
The interaction between Alfven-wave turbulence and the background solar wind affects the cross helicity in two ways. Non-WKB reflection converts outward-propagating Alfven waves into inward-propagating Alfven waves and vice versa, and the turbulence transfers momentum to the background flow. |
It has been proposed that accretion-induced collapse (AIC) of massive white dwarfs (WDs) is an indispensable path for the formation of neutron star (NS) binaries. Although there are still no direct evidence for the existence of AIC events, several kinds of NS systems are suggested to originate from the AIC processes. |
The importance of magnetic fields in three-dimensional magnetoconvection models of the Sun's photosphere is investigated in terms of their influence on the continuum intensity at different viewing inclination angles, and on the intensity profile of two [O I] spectral lines. We use the RH numerical radiative transf... |
Surface granulation can be predicted with the mass, metallicity, and frequency of maximum power of a star. Using the orders-of-magnitude larger APOGEE-Kepler sample, we recalibrate the relationship fit by Corsaro et al. (2017) for "flicker", an easier-to-compute diagnostic of this granulation. |
The dynamo process is believed to drive the magnetic activity of stars like the Sun that have an outer convection zone. Large spectroscopic surveys showed that there is a relation between the rotation periods and the cycle periods: the longer the rotation period is, the longer the magnetic activity cycle period will b... |
There is evidence that protoplanetary disks--including the protosolar one--contain crystalline dust grains on spatial scales where the dust temperature is lower than the threshold value for their formation through thermal annealing of amorphous interstellar silicates. We interpret these observations in terms of an ext... |
The properties of blue supergiants are key for constraining the end of the main sequence (MS) of massive stars. Whether the observed drop in the relative number of fast-rotating stars below $\sim$21$\,$kK is due to enhanced mass-loss rates at the location of the bistability jump, or the result of the end of the MS is ... |
A chemo-dynamical analysis of 115 metal-poor candidate stars selected from the narrow-band Pristine photometric survey is presented based on CFHT high-resolution ESPaDoNS spectroscopy. We have discover 28 new bright (V < 15) stars with [Fe/H]<-2.5 and 5 with [Fe/H]<-3.0 for success rates of 40% (28/70) and 19... |
RZ Cas is a short-period Algol-type system showing episodes of mass transfer and Delta Sct-like oscillations of its mass-gaining primary component. We analyse high-resolution spectra of RZ Cas that we obtained during a spectroscopic long-term monitoring lasting from 2001 to 2017. |
We present the outcome of a highly-sensitive search for magnetic fields on the cool supergiant Betelgeuse. A time-series of six circularly-polarized spectra was obtained using the NARVAL spectropolarimeter at Télescope Bernard Lyot (Pic du Midi Observatory), between 2010 March and April. |
We investigate the pulsational stability of massive (M >~ 120 Msun) main sequence stars of a range of metallicities, including primordial, Population III stars. We include a formulation of convective damping motivated by numerical simulations of the interaction between convection and periodic shear flows. |
Context. The solar chromosphere is the interface between the solar surface and the solar corona. |
Magnetic twist is thought to play an important role in coronal loops. The effects of magnetic twist on stable magnetohydrodynamic (MHD) waves is poorly understood because they are seldom studied for relevant cases. |
The Gaia-ESO Public Spectroscopic Survey (GES) is conducting a large-scale study of multi-element chemical abundances of some 100 000 stars in the Milky Way with the ultimate aim of quantifying the formation history and evolution of young, mature and ancient Galactic populations. However, in preparing for the analysis... |
We present a catalog of 166 spectroscopically identified hot subdwarf stars from LAMOST DR1, 44 of which show the characteristics of cool companions in their optical spectra. Atmospheric parameters of 122 non-composite spectra subdwarf stars were measured by fitting the profiles of hydrogen (H) and helium (He) lines w... |
We revisited the short period Type II Cepheids (T2Cs), called the BL Herculis (BLHs), in the Galactic Field to derive a homogeneous analysis of their Fourier parameters. Only V-band data were compiled to make sure that it was directly comparable between the known variables of the OGLE-III catalogue and the 59 individu... |
Context. To enable radial velocity (RV) precision on the order of ~0.1 m/s required for the detection of Earth-like exoplanets orbiting solar-type stars, the main obstacle lies in mitigating the impact of stellar activity. |
We present an asteroseismic study of the solar-like stars KIC 11395018, KIC 10273246, KIC 10920273, KIC 10339342, and KIC 11234888 using short-cadence time series of more than eight months from the Kepler satellite. For four of these stars, we derive atmospheric parameters from spectra acquired with the Nordic Optical... |
It is believed that eta Carinae is actually a massive binary system, with the wind-wind interaction responsible for the strong X-ray emission. Although the overall shape of the X-ray light curve can be explained by the high eccentricity of the binary orbit, other features like the asymmetry near periastron passage and... |
We derived the coronal magnetic field, plasma density, and temperature from the observation of polarization and intensity of radio thermal free-free emission using the Nobeyama Radioheliograph (NoRH) and extreme ultraviolet (EUV) observations. We observed a post-flare loop on the west limb 11 April 2013. |
Photophoresis is a physical process that transports particles in optical thin parts of protoplanetary disks, especially at the inner edge and at the optically surface. To model the transport and resulting effects in detail, it is necessary to quantify the strength of photophoresis for different particle classes as a f... |
We present a detailed Monte Carlo simulation of the population of the hot branch of the white dwarf luminosity function. We used the most up-to-date stellar evolutionary models and we implemented a full description of the observational selection biases. |
Recent discoveries of carbon-enhanced metal-poor stars like SMSS J031300.36-670839.3 provide increasing observational insights into the formation conditions of the first second-generation stars in the Universe, reflecting the chemical conditions after the first supernova explosion. Here, we present the first cosmologi... |
Context. GJ 581, an M3 dwarf, hosts a rich system of exo-planets, some of which are potentially within or at the edge of the Habitable Zone. |
This paper describes an adaptation of the Optimal Localized Averaging (OLA) inversion technique, originally developed for geo- and helioseismological applications, to the interpretation of solar spectroscopic data. It focuses on inverting the thermodynamical properties of the solar atmosphere assuming that the atmosph... |
A detailed observation of microglitch phenomenon in relatively slow radio pulsars is presented. Our analyses for these small amplitude jumps in pulse rotation frequency ($\nu$) and/or spin down rate ($\dot{\nu}$) combine the traditional manual detection method (which hinges on careful visual inspections of the residua... |
The hydrogen Lyman-$\alpha$ (H {\sc i} Ly$\alpha$) emission during solar flares has rarely been studied in spatially resolved images and its physical origin has not been fully understood. In this paper, we present novel Ly$\alpha$ images for a C1.4 solar flare (SOL2021-08-20T22:00) from the Extreme Ultraviolet Imager ... |
We report on initial results from a Spitzer program to search for very low-mass brown dwarfs in Ophiuchus. This program is an extension of an earlier study by Allers et al. which had resulted in an extraordinary success rate, 18 confirmed out of 19 candidates. |
The "stellar" solution to the cosmological lithium problem proposes that surface depletion of lithium in low-mass, metal-poor stars can reconcile the lower abundances found for Galactic halo stars with the primordial prediction. Globular clusters are ideal environments for studies of the surface evolution of l... |
Filamentary structures, or long and narrow streams of material, arise in many areas of astronomy. Here we investigate the stability of such filaments by performing an eigenmode analysis of adiabatic and polytropic fluid cylinders, which are the cylindrical analog of spherical polytropes. |
We aim to provide a detailed characterization of near-infrared spectra for young LT brown dwarfs, including robust spectral typing, calibrating spectral indices, identifying possible binaries, and selecting suitable spectral standards. We processed and analyzed archival spectra from VLT/X-shooter for a sample of 56 dw... |
An inverted U burst with equally developed ascending and descending branches observed by Giant Ukrainian Radio Telescope (GURT) on 18 April 2017 in meter wavelengths band is discussed. This U burst was attributed to the high coronal loop above the limb active region NOAA 12651. |
We run numerical simulations to study high-power wind accretion in a massive binary system during a high mass loss event. The system consists of an evolved primary star with a zero age main sequence mass of $ M_{1} = \rm 100~M_{\odot}$ and a hot secondary star with a mass ranging from $ M_{2} = \rm 30-80~M_{\odot}$, o... |
We assess the accuracy of radial velocities of 671 stars located near Galactic clusters, measured by Robert Trumpler between 1924 and 1947 using the Lick Observatory 36 inch refractor equipped with prism spectrometers. We find that Trumpler's velocities share the same zero-point and scale as modern IAU radial velo... |
Context: Stars with about 1$-$2 solar masses at the red giant branch (RGB) represent an intriguing period of stellar evolution, i.e. when the convective envelope interacts with the fast-rotating core. During these mixing episodes freshly synthesized lithium can come up to the stellar surface along with high angular mo... |
Aims. Other stars are known to have magnetic cycles similar to that of the Sun. |
Numerous spherical ``shells" have been observed in young star-forming environments that host low- and intermediate-mass stars. These observations suggest that these shells may be produced by isotropic stellar wind feedback from young main-sequence stars. |
Accurate surface rotation measurements are crucial to estimate stellar ages and improve our understanding of stellar rotational evolution. Comparisons of datasets obtained from different space missions on common targets represent in this sense a way to explore the respective biases and reliability of the considered in... |
We present high speed photometric observations of 20 faint cataclysmic variables, selected from the Sloan Digital Sky Survey and Catalina catalogues. Measurements are given of 15 new directly measured orbital periods, including four eclipsing dwarf novae (SDSS0904+03, CSS0826-00, CSS1404-10 and CSS1626-12), two new po... |
Solar eruptive events such as coronal mass ejections and eruptive flares are frequently associated with the emergence of magnetic flux from the convection zone into the corona. We use three dimensional magnetohydrodynamic numerical simulations to study the interaction of coronal magnetic fields with emerging flux and ... |
Decameter hectometric (DH; 1-14 MHz) type-IV radio bursts are produced by flare-accelerated electrons trapped in post-flare loops or the moving magnetic structures associated with the CMEs. From a space weather perspective, it is important to systematically compile these bursts, explore their spectro-temporal characte... |
We present NLTE Li abundances for 88 stars in the metallicity range -3.5 < [Fe/H] < -1.0. The effective temperatures are based on the infrared flux method with improved E(B-V) values obtained mostly from interstellar NaI D lines. |
In the lower solar atmosphere, the chromosphere is permeated by jets known as spicules, in which plasma is propelled at speeds of 50 to 150 kilometers per second into the corona. The origin of the spicules is poorly understood, although they are expected to play a role in heating the million-degree corona and are asso... |
A new magnetic field-generation mechanism based on the Nernst effect is considered in hot massive stars. This mechanism can operate in the upper atmospheres of O and B stars where departures from the LTE form a region with the inverse temperature gradient. |
We perform, for the first time, a detailed long-term activity study of the binary system $\zeta$ Ret. We use all available HARPS spectra obtained between the years 2003 and 2016. |
We report the serendipitous discovery from WASP archive photometry of a binary star in which an apparently normal A-type star (J0247-25A) eclipses a smaller, hotter subdwarf star (J0247-25B). The kinematics of J0247-25A show that it is a blue-straggler member of the Galactic thick-disk. |
Specola Solare Ticinese is an observatory dedicated to Sunspot Number counting, which was constructed in 1957 in Locarno, Southern Switzerland, as an external observing station of the Zurich Federal Observatory. When in 1981 the responsibility of the determination of the International Sunspot Number was assumed by the... |
(Abridged) Water is a key tracer of dynamics and chemistry in low-mass protostars, but spectrally resolved observations have so far been limited in sensitivity and angular resolution. |
The transition from early Of stars to WN type objects is poorly understood. O-type supergiants with emission lines (OIf+) are considered to be intermediate between these two classes. |
Magnetic reconnection is a fundamental physical process converting magnetic energy into not only plasma energy but also particle energy in various astrophysical phenomena. In this letter, we show a unique dataset of a solar flare where various plasmoids were formed by a continually stretched current sheet. |
For more than thirty years, the dynamical maintenance of the thin solar tachocline has remained one of the central outstanding problems of stellar astrophysics. Three main theories have been developed to explain the tachocline's thinness, but so far none of them has been shown to work convincingly in the extreme p... |
It is generally considered that the emission of microwave zebra pattern (ZP) structures requires high density and high temperatures, which is similar to the situation of the flaring region where primary energy releases. Therefore, the parameters analysis of ZPs may reveal the physical conditions of the flaring source ... |
Blazhko stars from the extended $BVI_{\mathrm C}$ time series of RRab stars in the globular cluster, M3, are analysed. This is the largest sample of Blazhko stars with full details of their Blazhko properties in a homogeneous stellar system. |
The sharpest optical images of the R136 cluster in the Large Magellanic Cloud are presented, allowing for the first time to resolve members of the central core, including R136a1, the most massive star known. These data were taken using the Gemini speckle imager Zorro in medium-band filters with effective wavelengths s... |
NGC 6388 and NGC 6441 are two massive Galactic bulge globular clusters which share many properties, including the presence of an extended horizontal branch (HB), quite unexpected because of their high metal content. In this paper we use HST's WFPC2, ACS, and WFC3 images and present a broad multicolor study of thei... |
We search for superflares from 4,068 cool stars in 2+ years of Evryscope photometry, focusing on those with high-cadence data from both Evryscope and TESS. The Evryscope array of small telescopes observed 575 flares from 284 stars, with a median energy of 10^34.0 erg. |
Young stellar populations provide a record of past star formation, and by establishing their members' dynamics and ages, it is possible to reconstruct the full history of star formation events. Gaia has greatly expanded the number of accessible stellar populations, with one of the most notable recently-discovered ... |
We present the analysis of the multicolour CCD observations in the 2010 season of the Blazhko RRc star TV Boo. TV Boo shows a complex Blazhko modulation dominated by two independent modulations with P_{fm1}=9.74 d and P_{fm2}=21.43 d long periods. |
We analyzed TESS data of the IW And-type dwarf nova ST Cha during ordinary dwarf nova states. We have identified an orbital period of 0.285360(1) d. |
This short review paper gives an overview of recently observed transverse, propagating velocity perturbations in coronal loops. These ubiquitous perturbations are observed to undergo strong damping as they propagate. |
Solar flares are sudden energy release events in the solar corona, resulting from magnetic reconnection, that accelerates particles and heats the ambient plasma. During a flare, there are often multiple, temporally and spatially separated individual energy release episodes that can be difficult to resolve depending on... |
I consider some of the challenges and opportunities facing helio- and asteroseismology, which reflect major themes of presentation and discussion from the HELAS IV international conference "Seismological Challenges for Stellar Structure". I concentrate in particular on the exciting prospects for asteroseismolo... |
[Abridged.] We present multiwavelength observations of the black hole binary system, A0620-00. Using the Cosmic Origins Spectrograph on the Hubble Space Telescope, we have obtained the first FUV spectrum of A0620-00. |
We study the possibility to reproduce the statistical relations of the sunspot activity cycle, like the so-called Waldmeier relations, the cycle period - amplitude and the cycle rise rate - amplitude relations, by means of the mean field dynamo models with the fluctuating \alpha-effect. The dynamo model includes the l... |
Magnetic reconnection, a change of magnetic field connectivity, is a fundamental physical process in which magnetic energy is released explosively. It is responsible for various eruptive phenomena in the universe. |
We present the initial results of our investigation of the star-forming complex W49, one of the youngest and most luminous massive star forming regions in our Galaxy. We used Spitzer/Infrared Array Camera (IRAC) data to investigate massive star formation with the primary objective to locate a representative set of pro... |
Alfven waves are considered to be viable transporters of the non-thermal energy required to heat the Sun's quiescent atmosphere. An abundance of recent observations, from state-of-the-art facilities, have reported the existence of Alfven waves in a range of chromospheric and coronal structures. |
The interplanetary magnetic fluctuation spectrum obeys a Kolmogorovian power law at scales above the proton inertial length and gyroradius which is well regarded as an inertial range. Below these scales a power law index around $-2.5$ is often measured and associated to nonlinear dispersive processes. |
In a Comment by Perez et al (2014) it is claimed that recently published simulations of Beresnyak (2014) are grossly underresolved, compared to theirs, and that Beresnyak (2014) failed to estimate numerical error. Both claims are contrary to the fact. |
Thanks to the large amount of spectroscopic and photometric data assembled in the last couple of decades, the assumption that all globular clusters (GCs) contain a simple mono-metallic stellar population has been modified. Besides the common variations in the elements created/destroyed in the H-burning processes, spre... |
Our goal is to determine, with high accuracy, the physical and orbital parameters of two double-lined eclipsing binary systems, where the components are two giant stars. We also aim to study the evolutionary status of the binaries, to derive the distances towards them by using a surface brightness-colour relation, and... |
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