scholarly journals Modeling Stellar Activity-rotation Relations in Unsaturated Cool Stars

2021 ◽  
Vol 916 (2) ◽  
pp. 99
Author(s):  
Alison O. Farrish ◽  
David Alexander ◽  
Christopher M. Johns-Krull ◽  
Minjing Li
Keyword(s):  
Stellar Activity ◽  
Cool Stars

Period-Activity Relations in Close Binary Systems

1983 ◽  
Vol 102 ◽  
pp. 199-202
Author(s):  
Gibor Basri ◽  
Robert Laurent ◽  
Fredrick Walter
Keyword(s):  
Magnetic Fields ◽  
Spectral Type ◽  
Binary Systems ◽  
Close Binary ◽  
Dynamo Theory ◽  
Stellar Activity ◽  
Level Of Activity ◽  
Cool Stars ◽  
Ultraviolet Observations ◽  
Extra Parameter

Since the advent of extensive ultraviolet observations of cool stars, it has been clear that the stellar activity observed is not directly correlated with the star's position on the HR diagram (Basri and Linsky 1979, Stencel et al. 1980). Observations of an important chromospheric diagnostic, the MgII resonance lines, led to the conclusion that stellar chromospheric activity had only a weak dependence on spectral type, and exhibited large variations within a given spectral type. Because of the strong observed correlation of solar activity with magnetic fields, the field is thought to be a natural candidate for the extra parameter which predicts the level of activity. Unfortunately, it is quite difficult to measure magnetic fields directly in most cool stars. Another method with which to examine correlations between magnetic field and stellar activity indirectly is the hypothesis that magnetic fluxes are directly related to a combination of the convective and rotational parameters of a star through its generation in a magnetic dynamo. The α-ω dynamo theory (Parker, 1979) predicts a direct correlation between differential rotational velocities and field generated. Durney and Robinson (1982) predict basically a linear dependence of the emergent flux on the angular velocity of the star. One might therefore expect that in stars with the same fundamental stellar parameters, the amount of activity observed would depend on the rotational velocities. This is difficult to test because most cool stars are slow rotators and only a few rotational velocities are known.

scholarly journals Spectroscopic and Photometric Studies of an X-ray–Selected Sample of Chromospherically Active Binary Stars

1992 ◽  
Vol 135 ◽  
pp. 389-392 ◽  
Author(s):  
Robert P. Stefanik ◽  
Laurence A. Marschall ◽  
Harold L. Nations
Keyword(s):  
Binary Stars ◽  
Binary Star ◽  
Optical Spectra ◽  
Physical Characteristics ◽  
Point Sources ◽  
Stellar Activity ◽  
X Ray ◽  
Cool Stars

Data from the Einstein X-Ray satellite continue to provide useful information for studies of x-ray emitting objects. The Einstein Medium Sensitivity Survey (EMSS), a tabulation of serendipitously discovered point sources from the Einstein database, included a number of objects which were identified, on the basis of spot sampling of optical spectra, as likely binary star systems (Fleming 1988, Silva et al. 1987; Takalo & Nousek 1988). Because the sample is limited primarily by X-ray flux, the physical characteristics of these stars are of considerable interest for understanding the origins of stellar activity among cool stars.

Stellar Activity in Coeval Open Clusters: Praesepe and the Hyades

1998 ◽  
Vol 506 (1) ◽  
pp. 347-359 ◽  
Author(s):  
David Barrado y Navascués ◽  
John R. Stauffer ◽  
Sofia Randich
Keyword(s):  
Open Clusters ◽  
Stellar Activity

scholarly journals The chemistry of cool circumstellar envelopes

1987 ◽  
Vol 122 ◽  
pp. 551-552
Author(s):  
L.A.M. Nejad ◽  
T. J. Millar
Keyword(s):  
Kinetic Model ◽  
Chemical Kinetic ◽  
Time Dependent ◽  
Circumstellar Envelopes ◽  
Chemical Kinetic Model ◽  
Ion Molecule Reactions ◽  
Cool Stars

We have developed a time-dependent chemical kinetic model to describe the chemistry in the circumstellar envelopes of cool stars, with particular reference to IRC + 10216. Our detailed calculations show that ion-molecule reactions are important in the formation of many of the species observed in IRC + 10216.

scholarly journals Infrared Measurements of Stellar Magnetic Fields

1994 ◽  
Vol 154 ◽  
pp. 437-447 ◽  
Author(s):  
Steven H. Saar
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Pressure Support ◽  
Field Research ◽  
Future Directions ◽  
Rotation Rates ◽  
Infrared Measurements ◽  
Cool Stars ◽  
Rs Cvn Variables ◽  
Stellar Magnetic Fields

I review the advantages, techniques, and results of measurement of magnetic fields on cool stars in the infrared (IR). These measurements have generated several important results, including the following: the first data on the magnetic parameters of dMe and RS CVn variables; evidence for field strength confinement by photospheric gas pressure; support for the correlation between magnetic flux and rotation, with possible saturation at high rotation rates; indications of horizontal and/or vertical magnetic field structure; and evidence of spatial variations in B over a stellar surface. I discuss these results in detail, and suggest future directions for IR magnetic field research.

scholarly journals Observing Dynamos in Cool Stars

2014 ◽  
Vol 186 (1-4) ◽  
pp. 457-489 ◽  
Author(s):  
Z. Kővári ◽  
K. Oláh
Keyword(s):  
Cool Stars

scholarly journals Stellar activity and magnetic shielding

2009 ◽  
Vol 5 (S264) ◽  
pp. 385-394 ◽  
Author(s):  
J.-M. Grießmeier ◽  
M. Khodachenko ◽  
H. Lammer ◽  
J. L. Grenfell ◽  
A. Stadelmann ◽  
...  
Keyword(s):  
Dipole Moment ◽  
Magnetic Dipole ◽  
Magnetic Dipole Moment ◽  
Direct Interaction ◽  
Planetary Atmosphere ◽  
Stellar Activity ◽  
Planetary Environment ◽  
Atmospheric Loss ◽  
Planetary Magnetic Field ◽  
Planetary Habitability

AbstractStellar activity has a particularly strong influence on planets at small orbital distances, such as close-in exoplanets. For such planets, we present two extreme cases of stellar variability, namely stellar coronal mass ejections and stellar wind, which both result in the planetary environment being variable on a timescale of billions of years. For both cases, direct interaction of the streaming plasma with the planetary atmosphere would entail servere consequences. In certain cases, however, the planetary atmosphere can be effectively shielded by a strong planetary magnetic field. The efficiency of this shielding is determined by the planetary magnetic dipole moment, which is difficult to constrain by either models or observations. We present different factors which influence the strength of the planetary magnetic dipole moment. Implications are discussed, including nonthermal atmospheric loss, atmospheric biomarkers, and planetary habitability.

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