arXiv: Solar and Stellar Astrophysics最新文献_第4页

Fast photometric variability of very low mass stars in IC 348: detection of superflare in an M dwarf IC 348中非常低质量恒星的快速光度变异性:对M矮星超级耀斑的探测

arXiv: Solar and Stellar Astrophysics Pub Date : 2020-11-13 DOI: 10.1093/mnras/staa3574

Samrat Ghosh, S. Mondal, S. Dutta, R. Das, S. Joshi, S. Lata, Dhrimadri Khata, A. Panja

引用次数: 2

A theoretical scenario for Galactic RR Lyrae in the Gaia data base: constraints on the parallax offset 盖亚数据库中天琴座RR星系的理论场景:视差偏移的约束

arXiv: Solar and Stellar Astrophysics Pub Date : 2020-11-12 DOI: 10.1093/mnras/staa3558

M. Marconi, R. Molinaro, V. Ripepi, S. Leccia, I. Musella, G. De Somma, M. Gatto, M. Moretti

引用次数: 6

Coronal mass ejections observed by heliospheric imagers at 0.2 and 1 au 日冕物质抛射由日球层成像仪在0.2和1au观测

arXiv: Solar and Stellar Astrophysics Pub Date : 2020-11-10 DOI: 10.1051/0004-6361/202039490

C. R. Braga, A. Vourlidas

{"title":"Coronal mass ejections observed by heliospheric imagers at 0.2 and 1 au","authors":"C. R. Braga, A. Vourlidas","doi":"10.1051/0004-6361/202039490","DOIUrl":"https://doi.org/10.1051/0004-6361/202039490","url":null,"abstract":"Context. We study two coronal mass ejections (CMEs) observed between April 1-2, 2019 by both the inner Wide-Field Imager for Parker Solar Probe (WISPR-I) and the inner heliospheric imager (HI-1) on board STEREO-A. This is the first study of CME observations from two viewpoints in similar directions but at considerably different solar distances. Aims. Our objective is to understand how the PSP observations affect the CME kinematics, especially due to its proximity to the Sun. Methods. We estimate the CME positions, speeds, accelerations, propagation directions and longitudinal deflections using imaging observations from two spacecraft, and a set of analytical expressions that consider the CME as a point structure and take into account the rapid change in spacecraft position. Results. We find that both CMEs are slow ($< 400 km s^{-1}$), propagating eastward of the Sun-Earth line. The second CME seems to accelerate between $sim 0.1$ to $sim 0.2 au$ and deflect westward with an angular speed consistent with the solar rotation speed. We find some discrepancies in the CME solar distance (up to $0.05 au$, particularly for CME #1), latitude (up to $sim10^{circ}$) and longitude (up to $24^{circ}$) when comparing results from different fit cases (different observations or set of free parameters). Conclusions. Discrepancies in longitude are likely due to the feature tracked visually rather than instrumental biases or fit assumptions. For similar reasons, the CME #1 solar distance, as derived from WISPR-I observations, is larger than the HI-1 result, regardless of the fit parameters considered. Error estimates for CME kinematics do not show any clear trend associated to the observing instrument. The source region location and the lack of any clear in situ counterparts (both at near-Earth and at PSP) support our estimate of the propagation direction for both events.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82086455","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}

引用次数: 9

Several Populations of Sunspot Group Numbers – Resolving a Conundrum 太阳黑子群数的几个种群——解决一个难题

arXiv: Solar and Stellar Astrophysics Pub Date : 2020-11-10 DOI: 10.5194/EGUSPHERE-EGU21-282

L. Svalgaard

引用次数: 1

Mount Suhora high cadence photometric survey of T Tauri-type stars 苏霍拉山对金牛座T型恒星的高节奏光度测量

arXiv: Solar and Stellar Astrophysics Pub Date : 2020-10-31 DOI: 10.32023/0001-5237/69.3.2

M. Siwak, M. Dr'o.zd.z, Karolina Gut, M. Winiarski, W. Ogłoza, G. Stachowski

引用次数: 0

Modelling long-period variables – II. Fundamental mode pulsation in the non-linear regime 长周期变量建模- 2。非线性状态下的基模脉动

arXiv: Solar and Stellar Astrophysics Pub Date : 2020-10-26 DOI: 10.1093/mnras/staa3356

M. Trabucchi, P. Wood, N. Mowlavi, G. Pastorelli, P. Marigo, L. Girardi, T. Lebzelter

{"title":"Modelling long-period variables – II. Fundamental mode pulsation in the non-linear regime","authors":"M. Trabucchi, P. Wood, N. Mowlavi, G. Pastorelli, P. Marigo, L. Girardi, T. Lebzelter","doi":"10.1093/mnras/staa3356","DOIUrl":"https://doi.org/10.1093/mnras/staa3356","url":null,"abstract":"Long-period variability in luminous red giants has several promising applications, all of which require models able to accurately predict pulsation periods. Linear pulsation models have proven successful in reproducing the observed periods of overtone modes in evolved red giants, but they fail to accurately predict their fundamental mode periods. Here, we use a 1D hydrodynamic code to investigate the long-period variability of M-type asymptotic giant branch stars in the nonlinear regime. We examine the period and stability of low-order radial pulsation modes as a function of mass and radius, and find overtone mode periods in complete agreement with predictions from linear pulsation models. In contrast, nonlinear models predict an earlier onset of dominant fundamental mode pulsation, and shorter periods at large radii. Both features lead to a substantially better agreement with observations, that we verify against OGLE and Gaia data for the Magellanic Clouds. We provide simple analytic relations describing the nonlinear fundamental mode period-mass-radius relation. Differences with respect to linear predictions originate from the readjustment of the envelope structure induced by large-amplitude pulsation. We investigate the impact of turbulent viscosity on linear and nonlinear pulsation, and probe possible effects of varying metallicity and carbon abundance.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76108436","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}

引用次数: 14

Angular momentum transport from magnetoconvection and the magnetic modulation of the solar differential rotation 从磁对对流的角动量输运和太阳微分旋转的磁调制

arXiv: Solar and Stellar Astrophysics Pub Date : 2020-10-26 DOI: 10.1051/0004-6361/202039912

G. Rüdiger, M. Küker

{"title":"Angular momentum transport from magnetoconvection and the magnetic modulation of the solar differential rotation","authors":"G. Rüdiger, M. Küker","doi":"10.1051/0004-6361/202039912","DOIUrl":"https://doi.org/10.1051/0004-6361/202039912","url":null,"abstract":"In order to explain the modulation of the solar rotation law during the activity minima and maxima the angular momentum transport by rotating magnetoconvection is numerically simulated when a convective box is penetrated by an inclined azimuthal magnetic field. Turbulence-induced kinetic and magnetic stresses {em and} the Maxwell stress of the large-scale magnetic background field are the basic transporters. Without rotation the sign of the total stress naturally depends on the signs of the field components as positive (negative) $B_theta B_phi$ transport the angular momentum poleward (equatorward). For fast enough rotation, however, the turbulence-originated $Lambda$ effect starts to dominate the transport of the angular momentum. The simulations show that positive angles between the azimuthal field and the two meridional magnetic field components (as expected to be realized by induction of solar-type rotation laws) reduce the inward radial as well as the equatorward latitudinal transport by the rotating magnetoconvection. In accordance with the observations the magnetically influenced rotation law at the solar surface proves to be flatter than the nonmagnetic one even displaying a slightly decelerated equator .","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80176546","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}

引用次数: 0

arXiv: Solar and Stellar Astrophysics Pub Date : 2020-10-23 DOI: 10.1093/mnras/staa3310

G. Rauw, Y. Nazé

{"title":"Similar but different: the varied landscape of Onfp/Oef stars variability","authors":"G. Rauw, Y. Nazé","doi":"10.1093/mnras/staa3310","DOIUrl":"https://doi.org/10.1093/mnras/staa3310","url":null,"abstract":"The Oef category gathers rapidly rotating and evolved O-stars displaying a centrally reversed He II 4686 emission line. The origin of the variability of their photospheric and wind spectral lines is debated, with rotational modulation or pulsations as the main contenders. To shed new light on this question, we analysed high-quality and high-cadence TESS photometric time series for five Oef stars. We also collected a new time series of spectra for one target (lambda Cep) which had been the subject of specific debates in the last years. These observations reveal the variety of Oef behaviours. While space-based photometric data reveal substantial red noise components in all targets, only zeta Pup seems to display a long-lived periodicity. In our sample, stars exhibit a dominant signal at low frequencies but it appears relatively short-lived. This is reminiscent of rotational modulations by transient photospheric spots, though this scenario is challenged by the case of HD 14442, whose 1.230 d$^{-1}$ signal significantly exceeds the critical rotational frequency. In parallel, no evidence of persistent p-mode non-radial pulsations is found in either photometry or spectroscopy of the stars, only temporary excitation of g-mode pulsations could offer an alternative explanation for the dominant signals. Finally, the revised luminosities of the stars using GAIA-DR2 show that they are not all supergiants as zeta Pup. The question then arises whether the Oef peculiarity denotes a homogeneous class of objects after all.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89280134","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}

引用次数: 2

Oscillations of 2D ESTER models 二维酯模型的振荡

arXiv: Solar and Stellar Astrophysics Pub Date : 2020-10-21 DOI: 10.1051/0004-6361/201935538

D. Reese, G. Mirouh, F. Lara, M. Rieutord, B. Putigny

{"title":"Oscillations of 2D ESTER models","authors":"D. Reese, G. Mirouh, F. Lara, M. Rieutord, B. Putigny","doi":"10.1051/0004-6361/201935538","DOIUrl":"https://doi.org/10.1051/0004-6361/201935538","url":null,"abstract":"Recent numerical and theoretical considerations have shown that low-degree acoustic modes in rapidly rotating stars follow an asymptotic formula and recent observations of pulsations in rapidly rotating delta Scuti stars seem to match these expectations. However, a key question is whether strong gradients or discontinuities can adversely affect this pattern to the point of hindering its identification. Other important questions are how rotational splittings are affected by the 2D rotation profiles expected from baroclinic effects and whether it is possible to probe the rotation profile using these splittings. Accordingly, we numerically calculate pulsation modes in continuous and discontinuous rapidly rotating models produced by the 2D ESTER (Evolution STEllaire en Rotation) code. This spectral multi-domain code self-consistently calculates the rotation profile based on baroclinic effects and allows us to introduce discontinuities without loss of numerical accuracy. Pulsations are calculated using an adiabatic version of the Two-dimensional Oscillation Program (TOP) code. The variational principle is used to confirm the high accuracy of the pulsation frequencies and to derive an integral formula that closely matches the generalised rotational splittings, except when modes are involved in avoided crossings. This potentially allows us to probe the the rotation profile using inverse theory. Acoustic glitch theory, applied along the island mode orbit deduced from ray dynamics, can correctly predict the periodicity of the glitch frequency pattern produced by a discontinuity or the Gamma1 dip related to the He II ionisation zone in some of the models. The asymptotic frequency pattern remains sufficiently well preserved to potentially allow its detection in observed stars.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77120207","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}

引用次数: 5

An evidence-based assumption that helps to reduce the discrepancy between the observed and predicted 7Be abundances in novae 一个基于证据的假设，有助于减少新星中观测到的与预测的7Be丰度之间的差异

arXiv: Solar and Stellar Astrophysics Pub Date : 2020-10-19 DOI: 10.1093/mnrasl/slaa190

P. Denissenkov, C. Ruiz, S. Upadhyayula, F. Herwig

{"title":"An evidence-based assumption that helps to reduce the discrepancy between the observed and predicted 7Be abundances in novae","authors":"P. Denissenkov, C. Ruiz, S. Upadhyayula, F. Herwig","doi":"10.1093/mnrasl/slaa190","DOIUrl":"https://doi.org/10.1093/mnrasl/slaa190","url":null,"abstract":"Recent spectroscopic measurements of the equivalent widths of the resonant Be II doublet and Ca II K lines and their ratios in expanding nova ejecta indicate surprisingly high abundances of $^7$Be with a typical mass fraction $X_mathrm{obs}(^7mathrm{Be}) = 10^{-4}$. This is an order of magnitude larger than theoretically predicted values of $X_mathrm{theor}(^7mathrm{Be})sim 10^{-5}$ for novae. We propose how this discrepancy can be reduced. We use an analytical solution of the $^7$Be production equations to demonstrate that $X_mathrm{theor}(^7mathrm{Be})$ is proportional to the $^4$He mass fraction $Y$ in the nova accreted envelope and then we perform computations of 1D hydrostatic evolution of the $1.15,M_odot$ CO nova model that confirm our conclusion based on the analytical solution. Our assumption of enhanced $^4$He abundances that helps to reduce the discrepancy between $X_mathrm{obs}(^7mathrm{Be})$ and $X_mathrm{theor}(^7mathrm{Be})$ is supported by UV, optical and IR spectroscopy data that reveal unusually high values of $Y$ in nova ejecta. We also show that a significantly increased abundance of $^3$He in nova accreted envelopes does not lead to higher values of $X_mathrm{theor}(^7mathrm{Be})$ because this assumption affects the evolution of nova models resulting in a decrease of both their peak temperatures and accreted masses and, as a consequence, in a reduced production of $^7$Be.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88043924","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}

引用次数: 0