Results 61 to 70 of about 334 (164)
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
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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
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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
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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
Betelgeuse: Detection of the Expanding Wake of the Companion Star
The Astrophysical JournalRecent analyses conclude that Betelgeuse, a red supergiant star (HD 39801), likely has a companion object with a period of ∼2000 days orbiting at only 2.3 R _⋆ , deep in the chromosphere of the supergiant.
Andrea K. Dupree +3 more
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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
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Stellar Model Chromospheres. H. Procyon (F5 Iv/v)
The Astrophysical Journal, 1974 Derivation of a model for the chromosphere and upper photosphere of Procyon (F5 IV-V) based on calibrated observations of the K and 8542-A lines of Ca II, the k(2796-A) line of Mg II, and the K-line wings. The feasibility of this model synthesis approach to derive a preliminary model chromosphere is demonstrated despite the lack of spatial and ...
Thomas R. Ayres +2 more
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Lyα Emission from K and M Dwarfs: Intrinsic Profiles, Variability, and Flux in the Habitable Zone
The Astrophysical JournalLyman-alpha (Ly α ) is the most prominent ultraviolet (UV) emission line in low-mass stars, playing a crucial role in exoplanet atmospheric photochemistry, heating, and escape.
Sarah Peacock +6 more
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The non-active stellar chromosphere: Ca ii basal flux★ [PDF]
, 2014 M. Isabel Pérez Martínez +2 more
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HWO Target Stars and Systems: A Survey of Archival UV and X-Ray Data
The Astronomical JournalWe assess archival high-energy data for key stars on the Habitable Worlds Observatory (HWO) Target Stars and Systems 2025 list, as stellar radiation is critical to shaping and interpreting planetary atmospheres.
Sarah Peacock +16 more
doaj +1 more source