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SN 2011ht: Confirming a Class of Interacting Supernovae with Plateau Light Curves (Type IIn-P): We present photometry and spectroscopy of the Type IIn supernova (SN) 2011ht, identified previously as a SN impostor. The light curve exhibits an abrupt transition from a well-defined ~120 day plateau to a steep bolometric...
astro-ph_SR
On the rotation periods of the components of the triple system TYC9300-0891-1AB/TYC9300-0529-1 in the Octans Association: Stellar rotation depends on different parameters. The range of values of these parameters causes the dispersion in the rotation period distributions observed in young stellar clusters/associations...
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Unveiling the nature of red novae cool explosions using archive plate photometry: Based on archive photographic photometry and recent CCD photometric data for red novae V4332 Sgr and V838 Mon, we established their stellar composition, exploded components, and the nature of explosions. Low temperature in the outburst ...
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Period-Colour and Amplitude-Colour relations for OGLE-$δ$ Scuti stars in the Galactic Bulge and LMC: We present an analysis on the behaviour of the Galactic bulge and the Large Magellanic Cloud (LMC) $\delta$ Scuti stars in terms of period-colour and amplitude-colour (PCAC) relations at maximum, mean and minimum ligh...
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Brightness Oscillations in Models of Young Binary Systems with Low-Mass Secondary Components: We consider a model for the cyclic brightness variations of a young star with a low-mass companion that accretes matter from the remnants of a protostellar cloud. At small inclinations of the binary orbit to the line of sigh...
astro-ph_SR
The $κ$-cookbook: a novel generalizing approach to unify $κ$-like distributions for plasma particle modeling: In the literature different so-called $\kappa$-distribution functions are discussed to fit and model the velocity (or energy) distributions of solar wind species, pickup ions or magnetospheric particles. Here...
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Two-sided-loop jets associated with magnetic reconnection between emerging loops and twisted filament threads: Coronal jets are always produced by magnetic reconnection between emerging flux and pre-existing overlying magnetic fields. When the overlying field is vertical/obilique or horizontal, the coronal jet will a...
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Survey of multiple populations in globular clusters among very low-mass stars: Recent work has shown that NIR Hubble Space Telescope (HST) photometry allows us to disentangle multiple populations (MPs) among M dwarfs of globular clusters (GCs) and investigate this phenomenon in very low-mass (VLM) stars. Here, we pre...
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Data processing of Visible Emission Line Coronagraph Onboard ADITYA L1: ADITYA-L1 is India's first dedicated mission to observe the sun and its atmosphere from a halo orbit around L1 point. Visible emission line coronagraph (VELC) is the prime payload on board at Aditya-L1 to observe the sun's corona. VELC is designed ...
astro-ph_SR
A large stellar evolution database for population synthesis studies. V. Stellar models and isochrones with CNONa abundance anticorrelations: We present a new grid of stellar models and isochrones for old stellar populations, covering a large range of [Fe/H] values, for an heavy element mixture characterized by CNONa ...
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Chromospheric Activity in 55 Cancri: II. Theoretical Wave Studies versus Observations: In this study, we consider chromospheric heating models for 55 Cancri in conjunction with observations. The theoretical models, previously discussed in Paper I, are self-consistent, nonlinear and time-dependent ab-initio computatio...
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Exploring B4: A Pulsating sdB star, in a Binary, in the Open Cluster NGC 6791: We report on Kepler photometry of the hot sdB star B4 in the open cluster NGC 6791. We confirm that B4 is a reflection effect binary with an sdB component and a low-mass main sequence companion with a circular 0.3985 d orbit. The sdB star ...
astro-ph_SR
Metallicities from high resolution spectra of 49 RR Lyrae Variables: Accurate metallicities of RR Lyrae are extremely important in constraining period-luminosity-metallicity relationships (PLZ), particularly in the near-infrared. We analyse 69 high-resolution spectra of Galactic RR Lyrae stars from the Southern African...
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Observation of "Topological" Microflares in the Solar Atmosphere: We report on observation of the unusual kind of solar microflares, presumably associated with the so-called "topological trigger" of magnetic reconnection, which was theoretically suggested long time ago by Gorbachev et al. (Sov. Ast. 1988, v.32, p.308) ...
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Investigation of the Progenitors of the Type Ia Supernovae Associated With the LMC Supernova Remnants 0505-67.9 and 0509-68.7: Although Type Ia supernovae have been heavily scrutinized due to their use in making cosmological distance estimates, we are still unable to definitively identify the progenitors for the enti...
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Models for Metal-Poor Stars with Different Initial Abundances of C, N, O, Mg, and Si. III. Grids of Isochrones for $-2.5 \le$ [Fe/H] $\le -0.5$ and Helium Abundances $Y = 0.25$ and $0.29$ at Each Metallicity: Stellar evolutionary tracks for $0.12 \le M/M_\odot \le 1.0$ have been computed for each of several variati...
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Towards solar measurements of nuclear reaction rates: Nuclear reaction rates are a fundamental yet uncertain ingredient in stellar evolution models. The astrophysical S-factor pertaining to the initial reaction in the proton-proton chain is uncertain at the 1% level, which contributes a systematic but generally unpropa...
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Revisiting the Cygnus OB associations: OB associations play an important role in Galactic evolution, though their origins and dynamics remain poorly studied, with only a small number of systems analysed in detail. In this paper we revisit the existence and membership of the Cygnus OB associations. We find that of the h...
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A stellar relic filament in the Orion star forming region: We report the discovery of the oldest stellar substructure in the Orion star forming region (OSFR), the Orion relic filament. The relic filament is physically associated with the OSFR as demonstrated by Gaia DR2 photometry and astrometry, as well as targeted ra...
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Detailed opacity calculations for astrophysical applications: Nowadays, several opacity codes are able to provide data for stellar structure models, but the computed opacities may show significant differences. In this work, we present state-of-the-art precise spectral opacity calculations, illustrated by stellar applic...
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A $ΔR\sim 9.5$ mag Super Flare of An Ultracool Star Detected by $\text{SVOM/GWAC}$ System: In this paper, we report the detection and follow-ups of a super stellar flare GWAC\,181229A with an amplitude of $\Delta R\sim$9.5 mag on a M9 type star by $\text{SVOM/GWAC}$ and the dedicated follow-up telescopes. The estimat...
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Extended radio emission associated with a breakout eruption from the back side of the Sun: Context. Coronal mass ejections (CMEs) on the Sun are the largest explosions in the Solar System that can drive powerful plasma shocks. The eruptions, shocks, and other processes associated to CMEs are efficient particle accele...
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Spectroscopic subsystems in nearby wide binaries: Radial velocity (RV) monitoring of solar-type visual binaries has been conducted at the CTIO/SMARTS 1.5-m telescope to study short-period systems. Data reduction is described, mean and individual RVs of 163 observed objects are given. New spectroscopic binaries are disc...
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A catalogue of 323 cataclysmic variables from LAMOST DR6: In this work, we present a catalog of cataclysmic variables (CVs) identified from the Sixth Data Release (DR6) of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). To single out the CV spectra, we introduce a novel machine-learning algorith...
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Forward asteroseismic modeling of stars with a convective core from gravity-mode oscillations: parameter estimation and stellar model selection: We propose a methodological framework to perform forward asteroseismic modeling of stars with a convective core, based on gravity-mode oscillations. These probe the near-cor...
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The Gaia DR1 Mass-Radius Relation for White Dwarfs: The Gaia Data Release 1 (DR1) sample of white dwarf parallaxes is presented, including 6 directly observed degenerates and 46 white dwarfs in wide binaries. This data set is combined with spectroscopic atmospheric parameters to study the white dwarf mass-radius relati...
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Sunspot splitting triggering an eruptive flare: We investigate how the splitting of the leading sunspot and associated flux emergence and cancellation in active region NOAA 11515 caused an eruptive M5.6 flare on 2012 July 2. Our study employs multi-wavelength observations from HMI, AIA and ChroTel. Emerging flux formed...
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High Resolution Optical and NIR Spectra of HBC 722: We present the results of high resolution (R$\ge$30,000) optical and near-IR spectroscopic monitoring observations of HBC 722, a recent FU Orionis object that underwent an accretion burst in 2010. We observed HBC 722 in optical/near-IR with the BOES, HET-HRS, and IGRI...
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OH maser toward IRAS 06056+2131: polarization parameters and evolution status: We present high angular resolution observations of OH maser emission towards the high-mass star forming region IRAS 06056+2131. The observations were carried out using the UK radio interferometer array, Multi-Element Radio Linked Interfero...
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The Mass of the Compact Object in the X-Ray Binary Her X-1/HZ Her: We have obtained the first estimates of the masses of the components of the Her X-1/HZ Her X-ray binary system taking into account non-LTE effects in the formation of the H_gamma absorption line: mx=1.8Msun and mv=2.5Msun. These mass estimates were made...
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Chemical mixing in low mass stars: I. Rotation against atomic diffusion including radiative accelerations: When modelling stars with masses larger than 1.2Msun with no observed chemical peculiarity, atomic diffusion is often neglected because, on its own, it causes unrealistic surface abundances compared with those o...
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Correlation between the optical veiling and accretion properties: A case study of the classical T Tauri star DK Tau: Classical T Tauri stars (cTTs) accrete from their circumstellar disk. The material falls onto the stellar surface, producing an accretion shock, which generates veiling in a star's spectra. In addition...
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Coronal Polarization: We present an overview of the physical mechanisms responsible for the coronal polarization at different wavelength regimes. We also review different techniques using coronal polarization to determine various quantities necessary for understanding the thermodynamic properties of the solar coronal p...
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The first stars: CEMP--no stars and signatures of spinstars: (Abridged) The CEMP--no stars are "carbon-enhanced-metal-poor" stars that in principle show no evidence of s-- and r--elements from neutron captures. We try to understand the origin and nucleosynthetic site of their peculiar CNO, Ne--Na, and Mg--Al abundances...
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The Infrared Evolution of Dust in V838 Monocerotis: Luminous Red Variables (LRVs) are most likely eruptions that are the outcome of stellar mergers. V838 Mon is one of the best-studied members of this class, representing an archetype for stellar mergers resulting from B-type stars. As result of the merger event, nova-l...
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Candidate Coronagraphic Detections of Protoplanetary Disks around Four Young Stars: We present potential detections of H-band scattered light emission around four young star, selected from a total sample of 45 young stars observed with the CIAO coronagraph of the Subaru telescope. Two CTTS, CI Tau and DI Cep, and two...
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An independent analysis of the brown dwarf atmosphere monitoring (BAM) data: large-amplitude variability is rare outside the L/T transition: Observations of variability can provide valuable information about the processes of cloud formation and dissipation in brown dwarf atmospheres. Here we report the results of an ...
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H2O Maser Polarization of the Water Fountains IRAS 15445-5449 and IRAS 18043-2116: We present the morphology and linear polarization of the 22-GHz H2O masers in the high-velocity outflow of two post-AGB sources, d46 (IRAS 15445-5449) and b292 (IRAS 18043-2116). The observations were performed using The Australia Tele...
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Basal magnetic flux and the local solar dynamo: The average unsigned magnetic flux density in magnetograms of the quiet Sun is generally dominated by instrumental noise. Due to the entirely different scaling behavior of the noise and the solar magnetic pattern it has been possible to determine the standard deviation of...
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Modelling convection in A star atmospheres. Bisectors and lineshapes of HD108642: We present a code, VeDyn, for modelling envelopes and atmospheres of A to F stars focusing on accurate treatment of convective processes. VeDyn implements the highly sophisticated convection model of Canuto and Dubovikov (1998) but is f...
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M dwarf luminosity, radius, and $α$-enrichment from $I$-band spectral features: Despite the ubiquity of M dwarfs and their growing importance to studies of exoplanets, Galactic evolution, and stellar structure, methods for precisely measuring their fundamental stellar properties remain elusive. Existing techniques fo...
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New Low-Mass Stars in the 25 Orionis Stellar Group and Orion OB1a Sub-association from SDSS-III/BOSS Spectroscopy: The Orion OB1a sub-association is a rich low mass star (LMS) region. Previous spectroscopic studies have confirmed 160 LMSs in the 25 Orionis stellar group (25 Ori), which is the most prominent overdensi...
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A Granulation "Flicker"-based Measure of Stellar Surface Gravity: In Bastien et al. (2013) we found that high quality light curves, such as those obtained by Kepler, may be used to measure stellar surface gravity via granulation-driven light curve "flicker". Here, we update and extend the relation originally presented ...
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Recipe for inferring sub-surface solar magnetism via local mode-coupling using Slepian basis functions: Direct seismic imaging of sub-surface flow, sound-speed and magnetic field is crucial for predicting flux tube emergence on the solar surface, an important ingredient for space weather. The sensitivity of helioseis...
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Quiet-Sun intensity contrasts in the near ultraviolet: We present high-resolution images of the Sun in the near ultraviolet spectral range between 214 nm and 397 nm as obtained from the first science flight of the 1-m Sunrise balloon-borne solar telescope. The quiet-Sun rms intensity contrasts found in this wavelength ...
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Observational and model analysis of a two-ribbon flare possibly induced by a neighbouring blowout jet: In this paper, we present unique observations of a blowout coronal jet that possibly triggered a two-ribbon confined C1.2 flare in a bipolar solar active region NOAA 12615 on 2016 December 5. The jet activity initia...
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The Gaia-ESO Survey: Carbon abundance in the Galactic thin and thick disks: This paper focuses on carbon that is one of the most abundant elements in the Universe and is of high importance in the field of nucleosynthesis and galactic and stellar evolution. Even nowadays, the origin of carbon and the relative importan...
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Proton and electron temperatures in the solar wind and their correlations with the solar wind speed: The heating and acceleration of the solar wind remains one of the fundamental unsolved problems in heliophysics. It is usually observed that the proton temperature $T_i$ is highly correlated with the solar wind speed ...
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Exploring B4: A Pulsating sdB star, in a Binary, in the Open Cluster NGC 6791: We report on Kepler photometry of the hot sdB star B4 in the open cluster NGC 6791. We confirm that B4 is a reflection effect binary with an sdB component and a low-mass main sequence companion with a circular 0.3985 d orbit. The sdB star ...
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Outbursts and stellar properties of the classical Be star HD 6226: The bright and understudied classical Be star HD 6226 has exhibited multiple outbursts in the last several years during which the star grew a viscous decretion disk. We analyze 659 optical spectra of the system collected from 2017-2020, along with a UV ...
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Correlation between lithium abundances and ages of solar twin stars: We want to determine the lithium abundances of solar twin stars as a function of stellar age to provide constraints for stellar evolutions models and to investigate whether there is a connection between low Li abundance and the occurrence of planets. ...
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Simultaneous X-ray and Radio Observations of Rotating Radio Transient J1819-1458: We present the results of simultaneous radio and X-ray observations of PSR J1819-1458. Our 94-ks XMM-Newton observation of the high magnetic field 5*10^13 G pulsar reveals a blackbody spectrum (kT~130 eV) with a broad absorption feature...
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V405 Peg (RBS 1955): A Nearby, Low-Luminosity Cataclysmic Binary: (Abridged). The cataclysmic binary V405 Peg, originally discovered as ROSAT Bright Source (RBS) 1955 (= 1RXS J230949.6+213523), shows a strong contribution from a late-type secondary star in its optical spectrum, which led Schwope et al. to suggest it to...
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Warm Breeze from the starboard bow: a new population of neutral helium in the heliosphere: We investigate the signals from neutral He atoms observed from Earth orbit in 2010 by IBEX. The full He signal observed during the 2010 observation season can be explained as a superposition of pristine neutral interstellar He ...
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Active region upflows: 1. Multi-instrument observations: Upflows at the edges of active regions (ARs) are studied by spatially and temporally combining multi-instrument observations obtained with EIS/Hinode, AIA and HMI/SDO and IBIS/NSO, to derive their plasma parameters. This information is used for benchmarking data-...
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HD66051: the first eclipsing binary hosting an early-type magnetic star: Early-type magnetic stars are rarely found in close binary systems. No such objects were known in eclipsing binaries prior to this study. Here we investigated the eclipsing, spectroscopic double-lined binary HD66051, which exhibits out-of-eclipse ...
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Direct MD simulation of liquid-solid phase equilibria for two-component plasmas: We determine the liquid-solid phase diagram for carbon-oxygen and oxygen-selenium plasma mixtures using two-phase MD simulations. We identified liquid, solid, and interface regions using a bond angle metric. To study finite size effects,...
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On the role of tachoclines in solar and stellar dynamos: Rotational shear layers at the boundary between radiative and convective zones, tachoclines, play a key role in the process of magnetic field generation in solar-like stars. We present two sets of global simulations of rotating turbulent convection and dynamo. Th...
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No evidence of chemical anomalies in the bimodal turnoff cluster NGC 1806 in the LMC: We have studied the chemical composition of NGC 1806, a massive, intermediate-age globular cluster that shows a double main sequence turnoff. We analyzed a sample of high-resolution spectra (secured with FLAMES at the Very Large Tel...
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Rapidly varying A-type stars in the SuperWASP archive: The searches for transiting exoplanets have produced a vast amount of time-resolved photometric data of many millions of stars. One of the leading ground-based surveys is the SuperWASP project. We present the initial results of a survey of over 1.5 million A-type s...
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A census of Coronal Mass Ejections on solar-like stars: Coronal Mass Ejections (CMEs) may have major importance for planetary and stellar evolution. Stellar CME parameters, such as mass and velocity, have yet not been determined statistically. So far only a handful of stellar CMEs has been detected mainly on dMe stars ...
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Shock-Cloud Interaction in the Solar Corona: Flare associated coronal shock waves sometimes interact with solar prominences leading to large amplitude prominence oscillations. Such prominence activation gives us unique opportunity to track time evolution of shock-cloud interaction in cosmic plasmas. Although the dynami...
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The Pair-Instability Mass Gap for Black Holes: Stellar evolution theory predicts a "gap" in the black hole birth function caused by the pair instability. Presupernova stars that have a core mass below some limiting value, Mlo, after all pulsational activity is finished, collapse to black holes, whereas more massive one...
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Coevality in Young Eclipsing Binaries: The ages of the components in very short period pre-main sequence (PMS) binaries are essential to an understanding of their formation. We considered a sample of 7 PMS eclipsing binaries (EBs) with ages 1 to 6.3 MY and component masses 0.2 to 1.4 Msun The very high precision with w...
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Identification, mass and age of primary red clump stars from spectral features derived with the LAMOST DR7: Although red clump (RC) stars are easy to identify due to their stability of luminosity and color, about 20-50% are actually red giant branch (RGB) stars in the same location on the HR diagram. In this paper, a...
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The low-mass stellar mass functions of rich, compact clusters in the Large Magellanic Cloud: Context. We use Hubble Space Telescope photometry of six rich, compact star clusters in the Large Magellanic Cloud (LMC), with ages ranging from 0.01 to 1.0 Gyr, to derive the clusters' stellar mass functions (MFs) at their h...
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On the Lira law and the nature of extinction towards Type Ia Supernovae: We have studied the relation between the color evolution of Type Ia Supernovae (SNe Ia) from maximum light to the Lira law regime and the presence of narrow absorption features. Based on a nearby sample of 89 SNe Ia we have found that the rate of ...
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Stellar mid-life crisis: subcritical magnetic dynamos of solar-like stars and the breakdown of gyrochronology: Recent observations reveal the surprising breakdown of stellar gyrochronology relations at about the Sun's age hinting that middle-aged, solar-like stars transition to a magnetically inactive future. We prov...
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The GRAVITY Young Stellar Object survey -- I. Probing the disks of Herbig Ae/Be stars in terrestrial orbits: The formation and the evolution of protoplanetary disks are important stages in the lifetime of stars. The processes of disk evolution and planet formation are intrinsically linked. We spatially resolve with G...
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Evolution of the post merger remnants from the coalescence of oxygen-neon and carbon-oxygen white dwarf pairs: Although multidimensional simulations have investigated the processes of double WD mergers, post-merger evolution only focused on the carbon-oxygen (CO) WD or helium (He) WD merger remnants. In this work, we...
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FUV variability of HD 189733. Is the star accreting material from its hot Jupiter?: Hot Jupiters are subject to strong irradiation from the host stars and, as a consequence, they do evaporate. They can also interact with the parent stars by means of tides and magnetic fields. Both phenomena have strong implications f...
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G-band and Hard X-ray Emissions of the 2006 December 14 flare observed by Hinode/SOT and RHESSI: We report on G-band emission observed by the Solar Optical Telescope onboard the Hinode satellite in association with the X1.5-class flare on 2006 December 14. The G-band enhancements originate from the footpoints of flar...
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Magnetic feature tracking, what determines the speed?: Recent observations revealed that small magnetic elements abundant at the solar surface move poleward with a velocity which seems to be lower than the plasma velocity $U_{\theta}$. Guerrero et al. (2011) explained this discrepancy as a consequence of diffusive spre...
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The AstraLux Multiplicity Survey: Extension to Late M-dwarfs: The distribution of multiplicity among low-mass stars is a key issue to understanding the formation of stars and brown dwarfs, and recent surveys have yielded large enough samples of nearby low-mass stars to study this issue statistically to good accuracy. P...
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J-type carbon stars: A dominant source of 14N-rich presolar SiC grains of type AB: We report Mo isotopic data of 27 new presolar SiC grains, including 12 14N-rich AB (14N/15N>440, AB2) and 15 mainstream (MS) grains, and their correlated Sr and Ba isotope ratios when available. Direct comparison of the data for the MS...
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Precision southern hemisphere VLBI pulsar astrometry II: Measurement of seven parallaxes: Accurate measurement of pulsar distances via astrometry using very long baseline interferometry enables the improvement of Galactic electron density distribution models, improving distance estimates for the vast majority of puls...
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Triple evolution: an important channel in the formation of type Ia supernovae: Type Ia supernovae (SNe Ia) are thought to be the result of thermonuclear explosions in white dwarfs (WDs). Commonly considered formation pathways include two merging WDs (the double degenerate channel), and a single WD accreting material ...
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Observation of flux tube crossings in the solar wind: Current sheets are ubiquitous in the solar wind.They are a major source of the solar wind MHD turbulence intermittency. They may result from non-linear interactions of the solar wind MHD turbulence or are the boundaries of flux tubes that originate from the solar su...
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Chromospheric swirls I. Automated detection in H$α$ observations and their statistical properties: Chromospheric swirls are considered to play a significant role in the dynamics and heating of the upper solar atmosphere. It is important to automatically detect and track them in chromospheric observations and determin...
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Evolved Massive Stars at Low-metallicity II. Red Supergiant Stars in the Small Magellanic Cloud: We present the most comprehensive RSG sample for the SMC up to now, including 1,239 RSG candidates. The initial sample is derived based on a source catalog for the SMC with conservative ranking. Additional spectroscopic R...
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Primeval very low-mass stars and brown dwarfs - VI. Population properties of metal-poor degenerate brown dwarfs: We presented 15 new T dwarfs that were selected from UKIRT Infrared Deep Sky Survey, Visible and Infrared Survey Telescope for Astronomy, and Wide-field Infrared Survey Explorer surveys, and confirmed with...
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Twenty-Five Sub-Arcsecond Binaries Discovered By Lunar Occultations: We report on 25 sub-arcsecond binaries, detected for the first time by means of lunar occultations in the near-infrared as part of a long-term program using the ISAAC instrument at the ESO Very Large Telescope. The primaries have magnitudes in the ran...
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Derivations and Observations of Prominence Bulk Motions and Mass: In this chapter we review observations and techniques for measuring both bulk flows in prominences and prominence mass. Measuring these quantities is essential to development and testing of models discussed throughout this book. Prominence flows are comp...
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Saturation of large-scale dynamo in anisotropically forced turbulence: Turbulent dynamo theories have faced difficulties in obtaining evolution of large-scale magnetic fields on short dynamical time-scales due to the constraint imposed by magnetic helicity balance. This has critical implications for understanding the l...
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Mapping the Local Halo: Statistical Parallax Analysis of SDSS Low-Mass Subdwarfs: We present a statistical parallax study of nearly 2,000 M subdwarfs with photometry and spectroscopy from the Sloan Digital Sky Survey. Statistical parallax analysis yields the mean absolute magnitudes, mean velocities and velocity elli...
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Type Ia Single Degenerate Survivors Must Be Overluminous: In the single-degenerate (SD) channel of a Type Ia supernovae (SN Ia) explosion, a main-sequence (MS) donor star survives the explosion but it is stripped of mass and shock heated. An essentially unavoidable consequence of mass loss during the explosion is that ...
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A Search for Interstellar Carbon Chain Alcohol HC4OH in Star-Forming Region L1527 and Dark Cloud TMC-1: We report a sensitive search for the rotational transitions of the carbon chain alcohol HC4OH in the frequency range of 21.2-46.7 GHz in the star-forming region L1527 and the dark cloud TMC-1. The motivation was la...
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Investigating Gaia EDR3 parallax systematics using asteroseismology of Cool Giant Stars observed by Kepler, K2, and TESS I. Asteroseismic distances to 12,500 red-giant stars: Gaia EDR3 has provided unprecedented data that generate a lot of interest in the astrophysical community, despite the fact that systematics a...
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Diffraction-limited Visible Light Images of Orion Trapezium Cluster With the Magellan Adaptive Secondary AO System (MagAO): We utilized the new high-order (250-378 mode) Magellan Adaptive Optics system (MagAO) to obtain very high spatial resolution observations in "visible light" with MagAO's VisAO CCD camera. In the...
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Models of Individual Blue Stragglers: This chapter describes the current state of models of individual blue stragglers. Stellar collisions, binary mergers (or coalescence), and partial or ongoing mass transfer have all been studied in some detail. The products of stellar collisions retain memory of their parent stars a...
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The quest for stable circumbinary companions to post-common envelope sdB eclipsing binaries Does the observational evidence support their existence?: Context. Period variations have been detected in a number of eclipsing close compact binary subdwarf B stars (sdBs) and these have often been interpreted as caused by c...
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Zeeman Doppler maps. II: the perils of eschewing physics: For the observational modeling of horizontal abundance distributions and of magnetic geometries in chemically peculiar (CP) stars, Zeeman Doppler mapping (ZDM) has become the method of choice. Comparisons between abundance maps obtained for CP stars and predicti...
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The Herschel Cold Debris Disks: Confusion with the Extragalactic Background at 160 mu: The Herschel "DUst around NEarby Stars (DUNES)" survey has found a number of debris disk candidates that are apparently very cold, with temperatures near 22K. It has proven difficult to fit their spectral energy distributions with ...
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Survey of Nearby FGK Stars at 160 microns with Spitzer: The Spitzer Space Telescope has advanced debris disk science tremendously with a wealth of information on debris disks around nearby A, F, G, K and M stars at 24 and 70 microns with the MIPS photometer and at 8-34 microns with IRS. Here we present 160 micron obser...
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Binarity and Accretion in AGB Stars: HST/STIS Observations of UV Flickering in Y Gem: Binarity is believed to dramatically affect the history and geometry of mass loss in AGB and post-AGB stars, but observational evidence of binarity is sorely lacking. As part of a project to search for hot binary companions to cool ...
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Magnetic field variations and the seismicity of solar active regions: Dynamical changes in the solar corona have proven to be very important in inducing seismic waves into the photosphere. Different mechanisms for their generation have been proposed. In this work, we explore the magnetic field forces as plausible mecha...
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Properties of ion-cyclotron waves in the open solar corona: Remote observations of coronal holes have strongly implicated the resonant interactions of ion-cyclotron waves with ions as a principal mechanism for plasma heating and acceleration of the fast solar wind. In order to study these waves, a WKB (Wentzel-Kramers-...
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A Multi-Survey Approach to White Dwarf Discovery: By selecting astrometric and photometric data from the Sloan Digital Sky Survey (SDSS), the L{\'e}pine & Shara Proper Motion North Catalog (LSPM-North), the Two Micron All Sky Survey (2MASS), and the USNO-B1.0 catalog, we use a succession of methods to isolate white dwa...
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Most Lithium-rich Low-mass Evolved Stars Revealed as Red Clump stars by Asteroseismology and Spectroscopy: Lithium has confused scientists for decades at almost each scale of the universe. Lithium-rich giants are peculiar stars with lithium abundances over model prediction. A large fraction of lithium-rich low-mass e...
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Characteristics of Flight Delays during Solar Flares: Solar flare is one of the severest solar activities on the sun, and it has many important impacts on the near-earth space. It has been found that flight arrival delays will increase during solar flare. However, the detailed intrinsic mechanism of how solar flares in...
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