The Chromosphere-Corona Transition Region in Late-Type Stars

Author(s):  
C. Jordan
Keyword(s):  
1983 ◽  
Vol 102 ◽  
pp. 311-338
Author(s):  
Jeffrey L. Linsky

In this review based largely on observations with the IUE and Einstein satellites, I will summarize the different roles that magnetic fields play in controlling the structure and energy balance in the chromospheres and transition regions of late-type stars. Solar observations clearly show that magnetic flux tubes are the dominant structural element in the solar atmosphere, but the rotational modulation of plages (structures that are bright in ultraviolet emission lines) that overlie dark starspots provide strong evidence that magnetic flux tubes are the dominant structural elements in late-type stellar atmospheres as well. The wide range of radiative loss rates (and thus heating rates) observed in chromospheric and transition region emission lines also provides evidence for the importance of magnetic fields, but it is not yet clear whether the most active stars can be understood in terms of a large fractional coverage by solar-like magnetic flux tubes or whether brighter flux tubes are needed. I propose that the existence of a boundary between solar-like stars and those with little or no hot plasma, as well as the different types of G-K giants and supergiants, can be understood in terms of the fractional surface coverage by closed magnetic structures. Transition region downflows, the chromospheric heating mechanism, and the relative heating rates at different layers can be simply explained by the control of the energy balance by magnetic fields. Finally, I will intercompare models computed for active and quiet regions on the Sun with similar models computed for active and quiet stars, that is stars with intrinsically bright or weak emission lines.


1996 ◽  
Vol 176 ◽  
pp. 355-369 ◽  
Author(s):  
F. M. Walter

The solar surface contains of bright regions (plages) and dark regions (sunspots) superposed on the photosphere. If the solar analogy is valid, then active late-type stars should also exhibit bright, spatially distinct plages. These plages can be detected by rotational modulation of chromospheric flux, or by Doppler imaging in chromospheric/transition region lines. I review the evidence for the existence of plages, with particular emphasis on two very active systems: AR Lacertae, for which we have sequences of Doppler imaging observations since 1984, and AB Doradus, which we observed extensively in 1994. I conclude that we need to be cautious when relying on the solar analogy to interpret observations of the most active late-type stars.


1997 ◽  
Vol 478 (2) ◽  
pp. 745-765 ◽  
Author(s):  
Brian E. Wood ◽  
Jeffrey L. Linsky ◽  
Thomas R. Ayres

1994 ◽  
Vol 144 ◽  
pp. 315-321 ◽  
Author(s):  
M. G. Rovira ◽  
J. M. Fontenla ◽  
J.-C. Vial ◽  
P. Gouttebroze

AbstractWe have improved previous model calculations of the prominence-corona transition region including the effect of the ambipolar diffusion in the statistical equilibrium and energy balance equations. We show its influence on the different parameters that characterize the resulting prominence theoretical structure. We take into account the effect of the partial frequency redistribution (PRD) in the line profiles and total intensities calculations.


1997 ◽  
Vol 161 ◽  
pp. 707-709 ◽  
Author(s):  
Jun Jugaku ◽  
Shiro Nishimura

AbstractWe continued our search for partial (incomplete) Dyson spheres associated with 50 solar-type stars (spectral classes F, G, and K) within 25 pc of the Sun. No candidate objects were found.


2002 ◽  
Vol 4 ◽  
pp. 393-393
Author(s):  
A. Boselli ◽  
J. Lequeux ◽  
G. Gavazzi
Keyword(s):  

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