From radio to X-ray: The quiescent atmosphere of the dMe Flare Star EV Lac
Citation:
Osten, R. A., Hawley, S. L., Allred, J., Johns-Krull, C. M., Brown, A. & Harper, G. M. `From radio to X-ray: The quiescent Atmosphere of the dMe Flare Star EV Lac? in The Astrophysical Journal, 647, (2), 2006, pp 1349-1374Download Item:
From Radio to X-ray.pdf (published (author copy) peer-reviewed) 1.331Mb
Abstract:
We report on multi-wavelength observations spanning radio to X-ray wavelengths
of the M dwarf flare star, EV Lacertae, probing the characteristics of
the outer atmospheric plasma from the upper chromosphere to the corona. We
detect the star at a wavelength of 2 cm (15 GHz) for the first time. UV and FUV
line profiles show evidence of nonthermal broadening, and the velocity width
appear to peak at lower temperatures than in the Sun; this trend is confirmedin another active M dwarf flare star. Electron density measurements indicate
nearly constant electron pressures between log T =5.2 and 6.4. At higher coronal
temperatures, there is a sharp increase of two orders of magnitude in density
(ne ~1013 cm?3 at log T =6.9). X-ray, EUV, FUV and NUV spectra constrain the
DEM from the upper chromosphere through the corona. The coronal pressures
are inconsistent with the assumption of hydrostatic equilibrium, either through
EM modeling or application of scaling laws, and imply large conductive loss rates
and a large energy input at the highest temperatures. The timescales for radiative
and conductive losses in EV Lac?s upper atmosphere imply that significant
continued heating must occur for the corona to maintain its quiescent properties.
The high frequency radio detection requires the high temperature X-ray-emitting
coronal plasma to be spatially distinct from the radio emission source. Length
scales in the low-temperature corona are markedly larger than those in the hightemperature
corona, further suggestions of an inhomogeneous mixture of thermal
and nonthermal coronal plasma.
Author's Homepage:
http://people.tcd.ie/harpergDescription:
PUBLISHED
Author: HARPER, GRAHAM
Type of material:
Journal ArticleCollections:
Series/Report no:
The Astrophysical Journal647
2
Availability:
Full text availableLicences: