Results 31 to 40 of about 1,774 (127)

Multi-wavelength Radio Continuum Emission Studies of Dust-free Red Giants [PDF]

, 2013
Multi-wavelength centimeter continuum observations of non-dusty, non-pulsating K spectral-type red giants directly sample their chromospheres and wind acceleration zones.
Brown, Alexander, Drake, Stephen, Harper, Graham M., O'Gorman, Eamon, Richards, Anita M. S.   +4 more
core   +3 more sources

Detection of mass loss in stellar chromospheres

The Astrophysical Journal, 1980
IUE observations of 47 cool giants have been made in a search for the onset of expansion in the Mg II h and k emission cores. It is found that, in a statistical sense, the longward emission peak becomes dominant above a velocity dividing line in the H-R diagram, which lies close to a temperature dividing line reported by Linsky and Haisch (1979).
R. E. Stencel, D. J. Mullan
openaire   +1 more source

Solar Flare Activity, 1937–2024: Introducing the New Hemispheric Solar Flare Index (hSFI) in the Context of 2024's Major Solar Storm Events

Space Weather, Volume 23, Issue 11, November 2025.
Abstract A new daily composite of the solar flare index (SFI) and the hemispherically‐resolved versions (hSFI) are presented for 1937 to 2024. The data set confirms that the northern hemisphere (NH) dominated solar flare activity during Solar Cycles 17 to 21, but that the southern hemisphere has dominated from Solar Cycle 22 to present.
V. M. Velasco Herrera, W. Soon, S. Knoška, A. Özgüç, G. Velasco Herrera, H. Yeşilyaprak, N. Babynets, M. Švanda, J. Muraközy, S. Qiu, D. Riveros‐Rosas, R. Connolly, M. Connolly, A. Tlatov, L. Cappellotto   +14 more
wiley   +1 more source

Comparison of Solar Imaging Feature Extraction Methods in the Context of Space Weather Prediction With Deep Learning‐Based Models

Journal of Geophysical Research: Machine Learning and Computation, Volume 2, Issue 3, September 2025.
Abstract Recently, many machine learning‐based models have been developed to predict geomagnetic activity several days in advance directly from space‐borne solar imaging. To better understand and improve these models, we compare dimensionality reduction techniques to extract abstract features from solar images for space weather‐related downstream tasks.
Maria Tahtouh, Guillerme Bernoux, Antoine Brunet, Denis Standarovski, Gautier Nguyen, Angélica Sicard   +5 more
wiley   +1 more source

Cepheid limb darkening, angular diameter corrections, and projection factor from static spherical model stellar atmospheres

, 2012
Context. One challenge for measuring the Hubble constant using Classical Cepheids is the calibration of the Leavitt Law or period-luminosity relationship.
Baade, Barmby, Barnes, Benedict, Bonanos, Burki, C.-C. Ngeow, Claret, Claret, Claret, Clement, Davis, Fouqué, Freedman, Getting, Gieren, Gieren, Gieren, Gray, Groenewegen, H. R. Neilson, Hindsley, J. Storm, Kanbur, Keller, Kervella, Kervella, Kovács, Kurucz, Leavitt, Lester, Marengo, Marengo, Marengo, Marengo, Mourard, Mérand, Mérand, Mérand, N. Nardetto, Nardetto, Nardetto, Nardetto, Nardetto, Neilson, Neilson, Neilson, Neilson, Neilson, Neilson, Ngeow, Ngeow, P. Fouqué, Parsons, Pietrzyński, Riess, Riess, Sabbey, Sasselov, Sasselov, Sasselov, Storm, Storm, Turner, van Leeuwen, Wesselink, Windmark   +66 more
core   +3 more sources

Hubble Space Telescope Constraints on the Winds and Astrospheres of Red Giant Stars [PDF]

, 2016
We report on an ultraviolet spectroscopic survey of red giants observed by the Hubble Space Telescope, focusing on spectra of the Mg II h & k lines near 2800 A in order to study stellar chromospheric emission, winds, and astrospheric absorption. We focus
Harper, Graham M., Müller, Hans-Reinhard, Wood, Brian E.   +2 more
core   +3 more sources

Stellar activity with LAMOST – II. Chromospheric activity in open clusters [PDF]

Monthly Notices of the Royal Astronomical Society, 2018
We use the LAMOST spectra of member stars in Pleiades, M34, Praesepe, and Hyades to study how chromospheric activity vary as a function of mass and rotation at different age. We measured excess equivalent widths of H$ $, H$ $, and Ca~{\sc ii} K based on estimated chromospheric contributions from old and inactive field dwarfs, and excess luminosities ...
Fang, Xiang-Song, Zhao, Gang, Zhao, Jing-Kun, Kumar, Yerra Bharat   +3 more
openaire   +2 more sources

Deriving the Coronal Separatrix‐Web With the WSA Model

Journal of Geophysical Research: Space Physics, Volume 130, Issue 8, August 2025.
Abstract We demonstrate a new capability of the Wang‐Sheeley‐Arge (WSA) model to routinely derive the coronal separatrix web (S‐web) as a standard data product. We describe our methodology for deriving the squashing factor (Q $Q$) and we use Carrington rotation (CR) 2109 to illustrate the validation of our output with that derived from the POT3D model.
Samantha Wallace, Aleida K. Higginson, David G. Simpson, Nicholeen M. Viall, Peter Wyper, C. Nick Arge   +5 more
wiley   +1 more source

Building Reliable Models of M Dwarf Chromospheres: The Spectral Diagnostics [PDF]

, 2000
As part of an ongoing project to study how reliable are the chromospheric models constructed semiempirically to fit the chromospheric spectrum of cold stars, in this paper we study how changes in the assumed chromospheric structure of dM and dMe stars ...
Mauas, Pablo Jacobo David
core   +1 more source

Wavelet Analysis of Stellar Chromospheric Activity Variations

The Astrophysical Journal, 1997
Observations of chromospheric activity variations for some lower main-sequence stars from the Mount Wilson Observatory's HK project reveal a cyclic behavior comparable to the sunspot cycle. Even in the relatively short interval that they have been observed, those stars show stellar cycles and other features, like grand minima. The quasi-periodic nature
P. Frick, S. L. Baliunas, D. Galyagin, D. Sokoloff, W. Soon   +4 more
openaire   +1 more source