HDE228766 is a very massive binary system hosting a secondary component, which is probably in an intermediate evolutionary stage between an Of supergiant and an WN star. The wind of this star collides with the wind of its O8 II companion, leading to relatively strong X-ray emission. Measuring the orbital variations of the line-of-sight absorption toward the X-ray emission from the wind-wind interaction zone yields information on the wind densities of both stars. X-ray spectra have been collected at three key orbital phases to probe the winds of both stars. Optical photometry has been gathered to set constraints on the orbital inclination of the system. The X-ray spectra reveal prominent variations of the intervening column density toward the X-ray emission zone, which are in line with the expectations for a wind-wind collision. We use a toy model to set constraints on the stellar wind parameters by attempting to reproduce the observed variations of the relative fluxes and wind optical depths at 1 keV. The lack of strong optical eclipses sets an upper limit of about 68 degrees on the orbital inclination. The analysis of the variations of the X-ray spectra suggests an inclination in the range 54 - 61 degrees and indicates that the secondary wind momentum ratio exceeds that of the primary by at least a factor 5. Our models further suggest that the bulk of the X-ray emission arises from the innermost region of the wind interaction zone, which is from a region whose outer radius, as measured from the secondary star, lies between 0.5 and 1.5 times the orbital separation.
We present an analysis of wind absorption in the C II $λ1335$ doublet towards 40 classical T Tauri stars with archival far-ultraviolet (FUV) spectra obtained by the Hubble Space Telescope. Absorption features produced by fast or slow winds are commonly detected (36 out of 40 targets) in our sample. The wind velocity of the fast wind decreases with disk inclination, consistent with expectations for a collimated jet. Slow wind absorption is detected mostly in disks with intermediate or high inclination, without a significant dependence of wind velocity on disk inclination. Both the fast and slow…
The Space Weather effects in the near-Earth environment as well as in atmospheres of other terrestrial planets arise by corpuscular radiation from the Sun, known as the solar wind. The solar magnetic fields govern the solar corona structure. Magnetic-field strength values in the solar wind sources - key information for modeling and forecasting the Space Weather climate - are derived from various solar space- and ground-based observations, but, so far not accounting for specific types of radio bursts. These are "fractured" type II radio bursts attributed to collisions of shock waves with corona…
Probing Solar Wind Structures with Solar Energetic Particle Observations from Solar Orbiter
Macau University of Science and Technology（澳门科技大学）；University of Arizona（亚利桑那大学）；Shandong University（山东大学）；Southwest Research Institute（西南研究院）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；Kiel University（基尔大学）
Analyses of Galactic late O dwarfs (O8-O9.5V) raised the `weak wind problem': spectroscopic mass loss rates ($\dot{M}$) are up to two orders of magnitude lower than the theoretical values. We investigated the stellar and wind properties of Galactic late O giants (O8-O9.5III). We performed a spectroscopic analysis of nine O8-O9.5III stars in the ultraviolet (UV) and optical regions using the model atmosphere code CMFGEN. From the UV region, we found $\dot{M}$ $\sim$ $10^{-8}-10^{-9}$ $\mathrm{M_\odot}$ $\mathrm{yr^{-1}}$ overall. This is lower by $\sim 0.9 - 2.3$ dex than the predicted values b…
Probing the Solar Corona and the Solar Wind Using Angular Broadening Observations with the SKA
New Jersey Institute of Technology（新泽理工学院）；Tata Institute of Fundamental Research（塔塔基础研究所）；North-West University（西北大学）；University of Glasgow（格拉斯哥大学）；University of California, Los Angeles（加州大学洛杉矶分校）；Physical Research Laboratory（物理研究实验室）；Indian Institute of Technology Indore（印度印多尔理工学院）；University of Turku（图尔库大学）；Northumbria University（诺森比亚大学）
Probing the wind and evolutionary state of the quiescent luminous blue variable Var$\,$2 in the Galaxy M33: constraints from self-consistent non-LTE modeling
In this paper, we present high-resolution HST/COS observations of the extreme magnetic O star NGC 1624-2. These represent the first ultraviolet spectra of this archetypal object. We examine the variability of its wind-sensitive resonance lines, comparing it to that of other known magnetic O stars. In particular, the observed variations in the profiles of the CIV and SiIV doublets between low state and high state are the largest observed in any magnetic O-type star, consistent with the expected properties of NGC 1624-2's magnetosphere. We also observe a redshifted absorption component in the lo…
Serving as the progenitors of electromagnetic and gravitational wave transients, massive stars have received renewed interest in recent years. However, many aspects of their birth and evolution remain opaque, particularly in the context of binary interactions. The centre of our galaxy hosts a rich cohort of very massive stars, which appear to play a prominent role in the ecology of the region. In this paper we investigate the binary properties of the Arches cluster, which is thought to host a large number of very massive stars. A combination of multi-epoch near-IR spectroscopy and photometry w…
Recent observations from Parker Solar Probe have revealed that the solar wind has a highly variable structure. How this complex behaviour is formed in the solar corona is not yet known, since it requires omnipresent fluctuations, which constantly emit material to feed the wind. In this article we analysed 14 upflow regions in the solar corona to find potential sources for plasma flow. The upflow regions were derived from spectroscopic data from the EUV Imaging Spectrometer (EIS) onboard Hinode determining their Doppler velocity and defining regions which have blueshifts stronger than $-6\,km\,…
Probing Coronal Activity Using Radio Signals Based on the 2021 superior conjunction of Mars: the Downlink Data from Tianwen-1
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；University of Chinese Academy of Sciences（中国科学院大学）；Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦阿纳伯格天文研究所）；Southeast University（东南大学）
Subsurface convection zones are ubiquitous in early-type stars. Driven by narrow opacity peaks, these thin convective regions transport little heat but play an important role in setting the magnetic properties and surface variability of stars. Here we demonstrate that these convection zones are \emph{not} present in as wide a range of stars as previously believed. In particular, there are regions which 1D stellar evolution models report to be convectively unstable but which fall below the critical Rayleigh number for onset of convection. For sub-solar metallicity this opens up a \emph{stabilit…
In this contribution, we present the MOBSTER Collaboration, a large community effort to leverage high-precision photometry from the Transiting Exoplanet Survey Satellite (\textit{TESS}) in order to characterize the variability of magnetic massive and intermediate-mass stars. These data can be used to probe the varying column density of magnetospheric plasma along the line of sight for OB stars, thus improving our understanding of the interaction between surface magnetic fields and massive star winds. They can also be used to map out the brightness inhomogeneities present on the surfaces of Ap/…
Probing the Nature of the Circumstellar Material Surrounding SN 2024ggi: A Search for Precursor Emission and Constraints from Radio Observations
University of Toronto（多伦多大学）；The Hebrew University of Jerusalem（耶路撒冷希伯来大学）；Western Sydney University（西悉尼大学）；Gifu University（岐阜大学）；California Institute of Technology（加州理工学院）
Probing hadronic gamma-ray and high-energy neutrino emission from Gaia DR2 star clusters
Friedrich-Alexander-Universität Erlangen-Nürnberg（埃尔朗根-纽伦堡大学）；Istituto Nazionale di Astrofisica, Osservatorio Astrofisico di Arcetri（国家天体物理研究所，阿切特里天文台）；Sapienza Università di Roma（罗马智慧大学）；Istituto Nazionale di Fisica Nucleare, Sezione di Roma（国家核物理研究所，罗马分部）；Instituto de Astrofìsica de Andalucìa, CSIC（安达卢西亚天体物理学研究所，西班牙高等科学研究理事会）；Erlangen Centre for Astroparticle Physics（埃尔朗根高能粒子物理中心）
We discuss Electron Cyclotron Maser Emission (ECME), observed in the form of highly circularly polarized pulses, from a few hot magnetic stars. This emission is one of the manifestations of stellar wind-magnetic field interaction. With the Giant Metrewave Radio Telescope (GMRT), we have observed ECME from four magnetic B/A type stars. Currently, we are trying to understand certain properties of the ECME pulses and their dependences on the magnetospheric plasma. Here we briefly review all those works which have used ECME observed from hot magnetic stars to infer some physical properties of the …
We analyse ALMA observations of the SO($J_K=6_5-5_4$) emission of the circumstellar envelope of oxygen-rich AGB star R Dor, probing distances between 20 and 100 au from the star where the nascent wind is building up. We give evidence for the slow wind to host, in addition to a previously observed rotating disc, a radial outflow covering very large solid angles and displaying strong inhomogeneity both in direction and radially: the former takes the form of multiple cores and the latter displays a radial dependence suggesting an episode of enhanced mass loss having occurred a century or so ago.
Cosmic Rulers: Masers as Tools for Probing Structure in the Galaxy and Beyond, from AU to kpc
Nicolaus Copernicus University in Torun（托伦哥白尼大学）；University of Manchester（曼彻斯特大学）；University of Western Australia（西澳大利亚大学）；SOKENDAI (The Graduate University for Advanced Studies)（综合研究大学院大学）；Keele University（基尔大学）
Star-forming (SF) regions embedded inside giant molecular clouds (GMCs) are potential contributors to Galactic gamma rays. The gamma-ray source 3FHL J1907.0+0713 is detected with a significance of roughly 13$σ$ in the 0.2 $-$ 300 GeV energy range after the removal of gamma-ray pulsation periods of PSR J1906+0722 from the Fermi-LAT data set of about 10 years. The energy spectrum of 3FHL J1907.0+0713 is best-fitted to a power law model with a spectral index of 2.26 $\pm$ 0.05. The CO($J$ = 1$-$0) data taken by NANTEN2 revealed that 3FHL J1907.0+0713 is overlapping with a GMC having a peak veloci…
