The corona of the young solar analog EK Draconis.

Details The corona of the young solar analog EK Draconis. The corona of the young solar analog EK Draconis.

Sep 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...301..201g&link_type=abstract

Astronomy and Astrophysics, v.301, p.201

Astronomy and Astrophysics

Astrophysics

48

Stars: Activity, Stars: Coronae, Radio Continuum: Stars, X-Rays: Stars, Stars: Individual: Hd 129333

Scientific paper

First coronal microwave and new soft X-ray observations of the very active, near-Zero-Age Main-Sequence (ZAMS) dG0e star EK Dra = HD 129333 show that this analog of the young Sun is more luminous in both emissions than most single M-dwarf flare stars. Variations in the 8.4GHz flux include modulation with the optically determined rotation period of 2.7 days. This result points to a non-uniform filling of the corona with energetic electrons due to an incomplete coverage of the surface with active regions and a source volume that is not concentric with the star. The radio luminosity varying between logL_R_=13.6 and 14.6 (L_R_ in erg/s/Hz) shows evidence for unpolarized gyrosynchrotron flares, while strongly polarized flares were absent during the observations. This star is the first young, truly solar-like main sequence G star discovered in microwaves. Having just arrived on the main sequence, it conclusively proves that young, solar-like G stars can maintain very high levels of radio emission after their T Tau phase. The X-ray observations were obtained from the ROSAT All-Sky Survey (RASS). The average X-ray luminosity amounts to logL_X_=29.9 (L_X_ in erg/s). A Raymond-Smith type plasma model fit yields two plasma components at temperatures of 1.9 and 10MK, with volume emission measures of 1.2 and 2.5.10^52^cm^-3^, respectively. The X-ray light curve is significantly variable, with the photon count rate from the cooler plasma being strongly modulated by the rotation period; the emission from the hotter plasma is only weakly variable. Modeling of the source distribution in the stellar corona yields electron densities of the order of 4.10^10^cm^-3^ or higher for the cool plasma component. It indicates that a considerable portion of EK Dra's high X-ray luminosity is due to high-density plasma rather than large emission volume. Parameters for an X-ray flare indicate an electron density of 1.75.10^11^cm^-3^ and a source height of (1-2).10^10^cm, compatible with a few times the scale height of the cooler plasma component.

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