arXiv: Solar and Stellar Astrophysics最新文献

{"title":"Kelvin–Helmholtz Instability in Solar Atmospheric Jets","authors":"I. Zhelyazkov, R. Chandra","doi":"10.1142/11920","DOIUrl":"https://doi.org/10.1142/11920","url":null,"abstract":"In this article I have discussed the recent ap- proaches in studying the Kelvin-Helmholtz (KH) instability of magnetohydrodynamic (MHD) waves propagating in solar atmo- sphere jets. The main focus is on the modeling the KH instability developing in coronal mass ejections in view of its (instability) contribution to triggering a wave turbulence subsequently leading to an effective coronal heating. KH instability of MHD waves in coronal active regions recently observed and imaged in unprece- dented detail in EUV thanks to the high cadence, high-resolution observations by SDO/AIA instrument, and spectroscopic obser- vations by Hinode/EIS instrument is a challenge for modeling this event. It is shown that considering the solar mass flows of coronal mass ejections as moving cylindrical twisted magnetic flux tubes the imaged instability can be explained in terms of unstable m = 3 MHD mode. Obtained critical jet speeds for the instability onset as well as the linear wave growth rates are in good agreement with observational data.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89057901","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Optical interferometry and Gaia measurement uncertainties reveal the physics of asymptotic giant branch stars","authors":"A. Chiavassa, K. Kravchenko, F. Millour, G. Schaefer, M. Schultheis, B. Freytag, O. Creevey, V. Hocd'e, F. Morand, R. Ligi, S. Kraus, J. Monnier, D. Mourard, N. Nardetto, N. Anugu, J. L. Bouquin, C. Davies, J. Ennis, T. Gardner, A. Labdon, C. Lanthermann, B. Setterholm, T. Brummelaar","doi":"10.1051/0004-6361/202037832","DOIUrl":"https://doi.org/10.1051/0004-6361/202037832","url":null,"abstract":"Context. Asymptotic giant branch stars are cool luminous evolved stars that are well observable across the Galaxy and populating Gaia data. They have complex stellar surface dynamics Aims. On the AGB star CL Lac, it has been shown that the convection-related variability accounts for a substantial part of the Gaia DR2 parallax error. We observed this star with the MIRC-X beam combiner installed at the CHARA interferometer to detect the presence of stellar surface inhomogeneities. Methods. We performed the reconstruction of aperture synthesis images from the interferometric observations at different wavelengths. Then, we used 3D radiative hydrodynamics simulations of stellar convection with CO5BOLD and the post-processing radiative transfer code Optim3D to compute intensity maps in the spectral channels of MIRC-X observations. Then, we determined the stellar radius and compared the 3D synthetic maps to the reconstructed ones focusing on matching the intensity contrast, the morphology of stellar surface structures, and the photocentre position at two different spectral channels, 1.52 and 1.70 micron, simultaneously. Results. We measured the apparent diameter of CL Lac at two wavelengths and recovered the radius using a Gaia parallax. In addition to this, the reconstructed images are characterised by the presence of a brighter area that largely affects the position of the photocentre. The comparison with 3D simulation shows good agreement with the observations both in terms of contrast and surface structure morphology, meaning that our model is adequate for explaining the observed inhomogenities. Conclusions. This work confirms the presence of convection-related surface structures on an AGB star of Gaia DR2. Our result will help us to take a step forward in exploiting Gaia measurement uncertainties to extract the fundamental properties of AGB stars using appropriate RHD simulations.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83019130","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Toward Next Generation Solar Coronagraph: Diagnostic Coronagraph Experiment","authors":"K. Cho, H. Yang, J.-O. Lee, S. Bong, J. Kim, S. Choi, J. Park, K.-H. Cho, J. Baek, Y.-H. Kim, Y.‐D. Park","doi":"10.5303/JKAS.2020.53.3.87","DOIUrl":"https://doi.org/10.5303/JKAS.2020.53.3.87","url":null,"abstract":"Korea Astronomy and Space Science Institute (KASI) has been developing a next-generation coronagraph (NGC) in cooperation with NASA to measure the coronal electron density, temperature, and speed simultaneously using four different filters around 400 nm. KASI organized an expedition team to demonstrate the coronagraph measurement scheme and the instrumental technology through the 2017 total solar eclipse (TSE) across the USA. The observation site was in Jackson Hole, Wyoming, USA. We built an eclipse observation system, so-called Diagnostic Coronal Experiment (DICE), which is composed of two identical telescopes to improve a signal to noise ratio. The observation was conducted with 4 wavelengths and 3 linear polarization directions according to the planned schedule in a limited total eclipse time of about 140 seconds. Polarization information of corona from the data was successfully obtained but we were not able to obtain global information of coronal electron temperature and speed in the corona due to a low signal-to-noise ratio of the optical system and a strong emission from the prominence located in the western limb. In this study, we report the development of DICE and observation results from the eclipse expedition. TSE observation and analysis by using our own developed instrument gave an important lesson that a coronagraph should be carefully designed to achieve the scientific purpose of this study. And it was a very useful experience in the way for the success of follow-up NASA-KASI joint missions called the Balloon-borne Investigation of the Temperature and Speed of Electrons in the Corona (BITSE) and COronal Diagnostic EXperiment (CODEX).","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84150157","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Gaia-ESO Survey: an extremely Li-rich giant in globular cluster NGC 1261","authors":"N. Sanna, E. Franciosini, E. Pancino, A. Mucciarelli, M. Tsantaki, C. Charbonnel, R. Smiljanic, X. Fu, A. Bragaglia, N. Lagarde, G. Tautvaišienė, L. Magrini, S. Randich, T. Bensby, A. Korn, A. Bayo, M. Bergemann, G. Carraro, L. Morbidelli","doi":"10.1051/0004-6361/202038435","DOIUrl":"https://doi.org/10.1051/0004-6361/202038435","url":null,"abstract":"Lithium rich stars in globular clusters are rare. In fact, only 14 have been found so far, in different evolutionary phases from dwarfs to giants. Different mechanisms have been proposed to explain this enhancement, but it is still an open problem. Using spectra collected within the Gaia-ESO Survey, obtained with the GIRAFFE spectrograph at the ESO Very Large Telescope, we present the discovery of the first Li-rich star in the cluster NGC 1261, the second star known in the red giant branch bump phase. The star shows an extreme Li overabundance of A(Li)_LTE=3.92pm0.14, corresponding to A(Li)_NLTE=3.40 dex. We propose that the Li enhancement is caused by fresh Li production through an extra mixing process (sometimes referred to as {em cool bottom burning}) or could be a pre-existing Li overabundance resulting from binary mass transfer, likely from a red giant branch star, because of the low barium abundance. To unambiguously explain the Li enhancement in globular cluster stars, however, a reliable determination of the abundance of key species like Be, 6Li, 12C/13C, and several s-process elements is required, as well as detailed modeling of chromospheric activity indicators.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85206374","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The GALAH survey: characterization of emission-line stars with spectral modelling using autoencoders","authors":"K. Čotar, T. Zwitter, G. Traven, J. Bland-Hawthorn, S. Buder, M. Hayden, J. Kos, G. Lewis, S. Martell, T. Nordlander, D. Stello, J. Horner, Y. Ting, M. Žerjal","doi":"10.1093/mnras/staa2524","DOIUrl":"https://doi.org/10.1093/mnras/staa2524","url":null,"abstract":"We present a neural network autoencoder structure that is able to extract essential latent spectral features from observed spectra and then reconstruct a spectrum from those features. Because of the training with a set of unpeculiar spectra, the network is able to reproduce a spectrum of high signal-to-noise ratio that does not show any spectral peculiarities even if they are present in an observed spectrum. Spectra generated in this manner were used to identify various emission features among spectra acquired by multiple surveys using the HERMES spectrograph at the Anglo-Australian telescope. Emission features were identified by a direct comparison of the observed and generated spectra. Using the described comparison procedure, we discovered 10,364 candidate spectra with a varying degree of H$alpha$/H$beta$ emission component produced by different physical mechanisms. A fraction of those spectra belongs to the repeated observation that shows temporal variability in their emission profile. Among emission spectra, we find objects that feature contributions of a nearby rarefied gas (identified through the emission of [NII] and [SII] lines) that was identified in 4004 spectra, which were not all identified as having H$alpha$ emission. Positions of identified emission-line objects coincide with multiple known regions that harbour young stars. Similarly, detected nebular emission spectra coincide with visually-prominent nebular clouds observable in the red all-sky photographic composites.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74217324","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Empirical bolometric correction coefficients for nearby main-sequence stars in the Gaia era","authors":"Z. Eker, F. Soydugan, S. Bilir, V. Bakış, F. Aliçavuş, S. Ozer, G. Aslan, M. Alpsoy, Y. Kose","doi":"10.1093/mnras/staa1659","DOIUrl":"https://doi.org/10.1093/mnras/staa1659","url":null,"abstract":"Nearby detached double-lined eclipsing binaries with most accurate data were studied and 290 systems were found with at least one main-sequence component having a metallicity $0.008leq Zleq 0.040$. Stellar parameters, light ratios, Gaia DR2 trigonometric parallaxes, extinctions and/or reddening were investigated and only 206 systems were selected eligible to calculate empirical bolometric corrections. NASA-IPAC Galactic dust maps were main source of extinctions. Unreliable extinctions at low Galactic latitudes $|b|leq5^o$ were replaced with individual determinations, if they exist in the literature, else associated systems are discarded. Main-sequence stars of remaining systems were used to calculate bolometric corrections ($BC$) and to calibrate $BC-T_{eff}$ relation, which is valid in the range 3100-36000 K. De-reddened $(B-V)_0$ colours, on the other hand, allowed us to calibrate two intrinsic colour effective temperature relations, where the linear one is valid for $T_{eff}>10000$ K, while the quadratic relation is valid for $T_{eff}<10000$ K, that is, both are valid in the same temperature range $BC-T_{eff}$ relation is valid. New $BC$ computed from $T_{eff}$ and other astrophysical parameters are tabulated, as well.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-06-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86969599","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ultra-long and quite thin coronal loop without significant expansion","authors":"Dong Li, D. Yuan, M. Goossens, T. Van Doorsselaere, W. Su, Ya Wang, Yang Su, Z. Ning","doi":"10.1051/0004-6361/202038433","DOIUrl":"https://doi.org/10.1051/0004-6361/202038433","url":null,"abstract":"Context. Coronal loops are the basic building blocks of the solar corona, which are related to the mass supply and heating of solar plasmas in the corona. However, their fundamental magnetic structures are still not well understood. Most coronal loops do not expand significantly, whereas the diverging magnetic field would have an expansion factor of about 5-10 over one pressure scale height. Aims. In this study, we investigate a unique coronal loop with a roughly constant cross section, it is ultra long and quite thin. A coronal loop model with magnetic helicity is presented to explain the small expansion of the loop width. Methods. This coronal loop was predominantly detectable in the 171 A channel of the Atmospheric Imaging Assembly (AIA). Then, the local magnetic field line was extrapolated by a Potential-Field-Source-Surface model. Finally, the differential emission measure analysis made from six AIA bandpasses was applied to obtain the thermal properties of this loop. Results. This coronal loop has a projected length of roughly 130 Mm, a width of about 1.5 +(-) 0.5 Mm and a lifetime of around 90 minutes. It follows an open magnetic field line. The cross section expanded very little (i.e., 1.5-2.0) along the loop length during its whole lifetime. This loop has a nearly constant temperature at about 0.7 +(-) 0.2 MK, whereas its density exhibits the typical structure of a stratified atmosphere. Conclusions. We use a thin twisted flux tube theory to construct a model for this non-expanding loop, and find that indeed with sufficient twist a coronal loop can attain equilibrium. However, we can not rule out other possibilities such as footpoint heating by small-scale reconnection, elevated scale height by a steady flow along the loop etc.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86267047","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Calibrating the surface brightness – color relation for late-type red giants stars in the visible domain using VEGA/CHARA interferometric observations","authors":"N. Nardetto, A. Salsi, D. Mourard, V. Hocdé, K. Perraut, A. Gallenne, A. Mérand, D. Graczyk, G. Pietrzyński, W. Gieren, P. Kervella, R. Ligi, A. Meilland, F. Morand, P. Stee, I. Tallon-Bosc, T. tenBrummelaar","doi":"10.1051/0004-6361/202037679","DOIUrl":"https://doi.org/10.1051/0004-6361/202037679","url":null,"abstract":"The surface brightness - color relationship (SBCR) is a poweful tool for determining the angular diameter of stars from photometry. It was for instance used to derive the distance of eclipsing binaries in the Large Magellanic Cloud (LMC), which led to its distance determination with an accuracy of 1%. We calibrate the SBCR for red giant stars in the 2.1 < V-K < 2.5 color range using homogeneous VEGA/CHARA interferometric data secured in the visible domain, and compare it to the relation based on infrared interferometric observations, which were used to derive the distance to the LMC. Observations of eight G-K giants were obtained with the VEGA/CHARA instrument. The derived limb-darkened angular diameters were combined with a homogeneous set of infrared magnitudes in order to constrain the SBCR. The average precision we obtain on the limb-darkened angular diameters of the eight stars in our sample is 2.4%. For the four stars in common observed by both VEGA/CHARA and PIONIER/VLTI, we find a 1 sigma agreement for the angular diameters. The SBCR we obtain in the visible has a dispersion of 0.04 magnitude and is consistent with the one derived in the infrared (0.018 magnitude). The consistency of the infrared and visible angular diameters and SBCR reinforces the result of 1% precision and accuracy recently achieved on the distance of the LMC using the eclipsing-binary technique. It also indicates that it is possible to combine interferometric observations at different wavelengths when the SBCR is calibrated.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88620579","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Alternation of the flickering morphology between the high and low state in MV Lyr","authors":"A. Dobrotka, H. Negoro, P. Konopka","doi":"10.1051/0004-6361/201935569","DOIUrl":"https://doi.org/10.1051/0004-6361/201935569","url":null,"abstract":"AIMS: We studied unique data of a nova-like system MV Lyr during transition from the high to low state and vice versa taken by the Kepler space telescope. We were interested in evolution of frequency components found previously by Scaringi et al. in different data also obtained by Kepler. METHODS: We divided the light curve into 10 day segments and investigated the corresponding power density spectra. We searched for individual frequency components by fitting with Lorentzian functions. Additionally, we investigated the variability using averaged shot profiles calculated from the light curve divided into 10 equally spaces subsamples. RESULTS: We found very complex changes of the power density spectra. We focused our study onto three frequency components. Strong activity increase is seen at low frequencies. Contrariwise, the high frequency part of the spectrum strongly decreases in power with specific rise in characteristic frequencies of the individual components. We discuss various scenarios of this phenomenology as reprocessing of X-rays in a receding accretion disc or a radiation from a more active region at the outer disc. Finally, we show that various cataclysmic variables show similar characteristic frequencies in their power density spectra. These are dependent on activity stage, making the situation similar to X-ray binaries.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86518502","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Additional Galactic Cepheids from the OGLE Survey","authors":"I. Soszy'nski, A. Udalski, M. Szyma'nski, P. Pietrukowicz, J. Skowron, D. Skowron, R. Poleski, S. Kozłowski, P. Mr'oz, K. Ulaczyk, K. Rybicki, P. Iwanek, M. Wrona, M. Gromadzki","doi":"10.32023/0001-5237/70.2.2","DOIUrl":"https://doi.org/10.32023/0001-5237/70.2.2","url":null,"abstract":"We report on the results of a comprehensive search for Cepheid variable stars in the fields photometricallymonitored by the OGLE Galaxy Variability Survey. We identify 742 Cepheids not included in the first release of the OGLE Collection of Galactic Cepheids and reclassify several dozen previously published variables. The upgraded collection comprises 1974 classical, 1625 type II, and 119 anomalous Cepheids located in the area of about 3000 square degrees covering the disk and bulge of the Milky Way. \u0000We present the most interesting objects in our sample: an isolated group of long-period doublemode classical Cepheids pulsating in the fundamental mode and first overtone, the first known Galactic double-mode Cepheid with the second and third overtone excited, double-mode type II Cepheids, candidates for single-mode first-overtone BL Her stars, and Cepheids showing simultaneous eclipsing variability. We also discuss type II and anomalous Cepheids that are potential members of globular clusters.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87188945","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}