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AWSoM Magnetohydrodynamic Simulation of a Solar Active Region with Realistic Spectral Synthesis
Landi, Enrico; van der Holst, Bart; Szente, Judit +6 more
For the first time, we simulate the detailed spectral line emission from a solar active region (AR) with the Alfvén Wave Solar Model (AWSoM). We select an AR appearing near disk center on 2018 July 13 and use the National Solar Observatory's Helioseismic and Magnetic Imager synoptic magnetogram to specify the magnetic field at the model's inner bo…
The Chemical Composition of Extreme-velocity Stars
Hawkins, Keith; Frebel, Anna; Ji, Alexander P. +5 more
Little is known about the origin of the fastest stars in the Galaxy. Our understanding of the chemical evolution history of the Milky Way and surrounding dwarf galaxies allows us to use the chemical composition of a star to investigate its origin and to say whether it was formed in situ or was accreted. However, the fastest stars, the hypervelocit…
Blazars at Very High Energies: Emission Modelling
Zech, Andreas; Sol, Hélène
Blazars are very broadband cosmic sources with spectra spanning over twenty orders of magnitude in frequency, down to the 100 MHz regime in the radio range, up to VHE at several tens of TeV. The modelling of their spectral energy distribution at high energies currently considers two main classes of models, leptonic and lepto-hadronic, which both s…
First Laboratory Measurement of Magnetic-field-induced Transition Effect in Fe X at Different Magnetic Fields
Tian, Hui; Bai, Xianyong; Si, Ran +14 more
The magnetic field is extremely important for understanding the properties of the solar corona. However, there are still difficulties in the direct measurement of the coronal magnetic field. The magnetic-field-induced transition (MIT) in Fe X, appearing in coronal spectra, was discovered to have prospective applications in coronal magnetic field m…
Inflow of low-metallicity cool gas in the halo of the Andromeda galaxy
Afruni, Andrea; Fraternali, Filippo; Pezzulli, Gabriele
As the closest L* galaxy to our own Milky Way, the Andromeda galaxy (M31) is an ideal laboratory for studies of galaxy evolution. The AMIGA project has recently provided observations of the cool (T ~ 104 K) phase of the circumgalactic medium (CGM) of M31, using HST/COS absorption spectra along ~40 background QSO sightlines, located up t…
Extending the FIP bias sample to magnetically active stars. Challenging the FIP bias paradigm
van Driel-Gesztelyi, L.; Kriskovics, L.; Baker, D. +6 more
Context. The different elemental abundances of the photosphere and the corona are striking features of not only the Sun, but of other stars as well. This phenomenon is known as the first ionisation potential (FIP) effect, and its strength can be characterized by the FIP bias, the logarithmic abundance difference between low- and high-FIP elements …
Transient obscuration event captured in NGC 3227. III. Photoionization modeling of the X-ray obscuration event in 2019
Kaastra, J. S.; Kriss, G. A.; Bianchi, S. +16 more
Context. A growing number of transient X-ray obscuration events in type I active galactic nuclei suggest that our line of sight to the central engine is not always free. Multiple X-ray obscuration events were reported in the nearby Seyfert 1.5 galaxy NGC 3227 from 2000 to 2016. In late 2019, another X-ray obscuration event was identified with Swif…
Searching for the Signal of a Primordial Black Hole from CMB Lensing and γ-Ray Emissions
Qiu, Taotao; Tan, Xiu-Hui; Xia, Jun-Qing +1 more
In this letter, we search for the signal of primordial black holes (PBHs) by correlating the γ-ray emissions in the MeV energy band produced by the Hawking evaporation and the lensing effect of the cosmic microwave background (CMB). We use the conservative case of the astrophysical model as much as possible in the calculations, since the potential…
Unprecedented change in the position of four radio sources
Frey, Sándor; Melnikov, Alexey; Titov, Oleg +8 more
Astrometric positions of radio-emitting active galactic nuclei (AGNs) can be determined with sub-milliarcsec accuracy using very long baseline interferometry (VLBI). The usually small apparent proper motion of distant extragalactic targets allow us to realize the fundamental celestial reference frame with VLBI observations. However, long-term astr…
The Photometric Study of Six W UMa Systems and Investigation of the Mass-Radius Relations for Contact Binary Stars
Davoudi, Fatemeh; Poro, Atila; Paki, Ehsan +13 more
We present the photometric analysis of six short-period systems (EI Oct, V336 TrA, NX Boo, V356 Boo, PS Boo, and V2282 Cyg). This is the first photometric analysis of these systems except for V336 TrA. Observations were conducted for 27 nights at three observatories in the northern and southern hemispheres. We calculated a new ephemeris for each o…