Results 31 to 40 of about 1,834 (171)

In the Trenches of the Solar–Stellar Connection. VII. Wilson–Bappu 2022

The Astrophysical Journal Supplement Series, 2023
The Wilson–Bappu effect (WBE) is a remarkable correlation between the width of the chromospheric emission core of the Ca ii 3934 Å K line and stellar absolute visual magnitude over an astonishing range, from diminutive red dwarfs to bloated yellow ...
Thomas Ayres
doaj   +1 more source

Periodic Density Structures Observed in Ulysses Data: First Results

Journal of Geophysical Research: Space Physics, Volume 131, Issue 3, March 2026.
Abstract Periodic density structures (PDSs) are advecting quasi‐periodic (periodicities between several minutes and several hours) density enhancements observed in the solar wind and corona. There is strong evidence that PDSs are formed at the Sun.
Brent M. Randol, Nicholeen Viall, Larry Kepko, Simone Di Matteo   +3 more
wiley   +1 more source

Relations of Rotation and Chromospheric Activity to Stellar Age for FGK Dwarfs from Kepler and LAMOST

The Astrophysical Journal Supplement Series
The empirical relations between rotation period, chromospheric activity, and age can be used to estimate stellar age. To calibrate these relations, we present a catalog, including the masses and ages of 52,321 FGK dwarfs, 47,489 chromospheric activity ...
Lifei Ye, Shaolan Bi, Jinghua Zhang, Tiancheng Sun, Liu Long, Zhishuai Ge, Tanda Li, Xianfei Zhang, Xunzhou Chen, Yaguang Li, Jianzhao Zhou, Maosheng Xiang   +11 more
doaj   +1 more source

On the Freeze‐In Distance of Solar Wind Fluid Entropy Variability in the Corona

Journal of Geophysical Research: Space Physics, Volume 131, Issue 3, March 2026.
Abstract The strong correlation between solar wind entropy and the frozen‐in ion charge state ratio O7+/O6+ ${\mathrm{O}}^{7+}/{\mathrm{O}}^{6+}$ indicates that entropy variability on timescales of hours or longer is preserved from its solar source. This prompts the question: where in the solar atmosphere does this entropy variability come from, and at
Aidan J. Nakhleh, Nicholeen M. Viall, Susan T. Lepri, Jim M. Raines   +3 more
wiley   +1 more source

Heating of Stellar Chromospheres and Transition Regions [PDF]

Symposium - International Astronomical Union, 2004
To explain the heating of stellar chromospheres and transition regions, two classes of heating mechanisms have been considered: dissipation of acoustic and magnetic waves generated in stellar convection zones; and dissipation of currents generated by photospheric motions of surface magnetic fields.
openaire   +1 more source

The California Legacy Survey. VI. The Fate of Activity Cycles in Sun-like Stars

The Astronomical Journal
We analyze the spectra of 91 solar-type G- and K-type main-sequence dwarfs in the solar neighborhood to assess activity trends with stellar properties.
Howard Isaacson, Stephen R. Kane, Brad Carter, Andrew W. Howard   +3 more
doaj   +1 more source

Solar Activity Impacts on Ionospheric Scintillation and Precise Point Positioning Based on Multi‐Year GNSS and Scintillation Observations

Space Weather, Volume 24, Issue 3, March 2026.
Abstract Solar activity induces ionospheric irregularities that degrade Global Navigation Satellite System (GNSS) performance through amplitude and phase scintillation. Although numerous studies have investigated event‐driven or regional responses, the nonlinear coupling between solar radiation, ionospheric scintillation, and precise point positioning (
Jincheng Li, Qi Liu, Xiaomin Luo, Manuel Hernández‐Pajares, Enric Monte‐Moreno, Guangxia Wang, Heng Yang, Chuanding Zhang, Li Yang, Yaoyao Liu   +9 more
wiley   +1 more source

Basal Chromospheric Flux and Maunder Minimum-type Stars: The quiet-Sun Chromosphere as a Universal Phenomenon

, 2012
Aims: We demonstrate the universal character of the quiet-Sun chromosphere among inactive stars (solar-type and giants). By assessing the main physical processes, we shed new light on some common observational phenomena.
Baliunas, Brandenburg, Buchholz, Cuntz, Cuntz, Duncan, Hall, Hauschildt, J. H. M. M. Schmitt, Judge, Judge, Judge, Judge, K.-P. Schröder, Keppens, Konstantinova-Antova, M. Cuntz, M. I. Pérez Martínez, M. Mittag, Mittag, Pasquini, Pevtsov, Pérez Martínez, Rammacher, Riethmüller, Schmitt, Schrijver, Schrijver, Schrijver, Schrijver, Schröder, Schröder, Schröder, Schwarzschild, Strassmeier, Stȩpień, Suzuki, Vögler, White, Wöger   +39 more
core   +1 more source

Magnetic Activity in M-type Stars Based on LAMOST DR11 and TESS Observations

The Astrophysical Journal Supplement Series
We have used 898,351 M-type stellar spectra released by Large Sky Area Multi-Object Fiber Spectroscopic Telescope DR11 to calculate the equivalent width of the Ca II infrared triplet (IRT) lines, the residual chromospheric emission, and the parameter ${R}
Linfeng Ren, Li-yun Zhang, Xianming L. Han, Tianhao Su, Wenjie Li, Yinpeng Wang, Prabhakar Misra   +6 more
doaj   +1 more source

A New Method for Probabilistic Spatiotemporal Forecasts of Solar Soft X‐Ray “S‐Class” (>X10) Superflares

Journal of Geophysical Research: Space Physics, Volume 131, Issue 2, February 2026.
Abstract Solar superflares of S‐class (>X10 in soft X‐rays) pose extreme space weather hazards, yet their prediction remains a fundamental challenge owing to their rapid and transient natures and the limitations of conventional event‐based forecasts. We introduce for the first time, a probabilistic spatiotemporal framework designed to identify extended
V. M. Velasco Herrera, G. Velasco Herrera, W. Soon, A. Özgüç, N. Babynets, A. Tlatov, M. Švanda, S. Qiu, S. Baliunas, B. Kotan, G. González González, L. A. Bautista Flores, M. Pazos   +12 more
wiley   +1 more source