Results 81 to 90 of about 173,010 (211)
On Generalized Additive Models for Representation of Solar EUV Irradiance
Space Weather, Volume 22, Issue 3, March 2024.Abstract In the context of space weather forecasting, solar EUV irradiance specification is needed on multiple time scales, with associated uncertainty quantification for determining the accuracy of downstream parameters. Empirical models of irradiance often rely on parametric fits between irradiance in several bands and various solar indices. We build
Daniel A. Brandt +2 more
wiley +1 more source
A Transfer Learning Method to Generate Synthetic Synoptic Magnetograms
Space Weather, Volume 22, Issue 1, January 2024.Abstract Current magnetohydrodynamics (MHD) models largely rely on synoptic magnetograms, such as the ones produced by the Global Oscillation Network Group (GONG). Magnetograms are currently available mostly from the front side of the Sun, which significantly reduces the accuracy of MHD modeling. Extreme Ultraviolet (EUV) images can instead be obtained
Xiaoyue Li +6 more
wiley +1 more source
PHOENIX model chromospheres of mid- to late-type M dwarfs
, 2005 We present semi-empirical model chromospheres computed with the atmosphere code PHOENIX. The models are designed to fit the observed spectra of five mid- to late-type M dwarfs. Next to hydrogen lines from the Balmer series we used various metal lines, e.
Andretta +36 more
core +1 more source
The Astronomical JournalYoung exoplanets trace planetary evolution, in particular the atmospheric mass loss that is most dynamic in youth. However, the high activity level of young stars can mask or mimic the spectroscopic signals of atmospheric mass loss.
Daniel M. Krolikowski +5 more
doaj +1 more source
Developments in the understanding and use of chromospheric diagnostics are discussed with emphasis on the following aspects: (1) trends emerging from semiempirical models of single stars; (2) the validity of claims that theoretical models of ...
Linsky, J. L.
core +1 more source
High-pressure transition regions in stellar model chromospheres
The Astrophysical Journal, 1979 The implications of recent ultraviolet observations of stellar transition-region lines for calculations of the Ca II and Mg II resonance lines are investigated. It is found that the adoption of high transition-region pressures for stars with active chromospheres, such as Lambda And and Alpha Aur, can be consistent with observed Ca II fluxes, contrary ...
S. L. Baliunas +3 more
openaire +1 more source
The Influence of Chromospheric Activity on Line Formation
The Astrophysical JournalOne of the primary sources of stellar spectral variability is magnetic activity. While our current understanding of chromospheric activity is largely derived from specific lines sensitive to chromospheric heating, such as the Ca ii H and K doublet ...
Mariela C. Vieytes +2 more
doaj +1 more source
Studies of the local interstellar medium [PDF]
The existing ultraviolet and optical data concerning late-type stars are discussed along with the acquisition and reduction of additional ultraviolet and simultaneous ground-based observation.
Dupree, A. K.
core +1 more source
Chromospheric and Coronal Indicators of Stellar Magnetic Structure [PDF]
Symposium - International Astronomical Union, 1983 This paper discusses attempts to derive information on magnetic structure in late-type stars, only from emission fluxes in the cores of the Ca II H and K lines, in UV emission lines and in soft X-rays — and from relations between these emission fluxes. However simpleminded and indirect this approach may seem, it brings out stimulating results.
openaire +1 more source
Correlating Intrinsic Stellar Parameters with Mg ii Self-reversal Depths
The Astrophysical JournalThe Mg ii h&k emission lines (2803, 2796 Å) are a useful tool for understanding stellar chromospheres and transition regions due to their intrinsic brightness, relatively low interstellar medium (ISM) absorption interference, and abundance
Anna Taylor +4 more
doaj +1 more source