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Title:
Spectroscopic EUVE Observations of the Active Star AB Doradus
Authors:
Rucinski, Slavek M.; Mewe, Rolf; Kaastra, Jelle S.; Vilhu, Osmi; White, Stephen M.
Publication:
Astrophysical Journal v.449, p.900 (ApJ Homepage)
Publication Date:
08/1995
Origin:
APJ; KNUDSEN
ApJ Keywords:
STARS: ACTIVITY, STARS: CORONAE, STARS: INDIVIDUAL CONSTELLATION NAME: AB DORADUS, STARS: LATE-TYPE, STARS: PRE-MAIN-SEQUENCE, ULTRAVIOLET: STARS
DOI:
10.1086/176108
Bibliographic Code:
1995ApJ...449..900R

Abstract

We present observations of the pre-main-sequence, rapidly rotating (0.515 day) late-type star, AB Doradus (HD 36705), made by the Extreme Ultraviolet Explorer (EUVE) satellite. A spectrum from 80 to 700 Å with a resolution Δλ ≍ 0.5-2 Å was accumulated between 1993 November 4-11, with an effective exposure time of about 40 hours. No obvious EUV flares were detected during the observation. The data constrain the coronal temperature structure between several 104 K up to roughly 2 × 107 K through a differential emission measure analysis using the optically thin MEKA plasma model. The resulting differential emission measure (DEM) distribution shows: (1) dominant emission from plasma between about 2 × 106 and 2 × 107 K, which may show a substructure with two components around 3 × 106 and 107 K; (2) very little emission from plasma between 105 and 2 × 106 K; and (3) emission from plasma below about 105 K. If solar photospheric abundances are assumed, then the formal DEM solution also requires the presence of a strong high-temperature component (above about 3 × 107 K) in order to explain the strong continuum emission below about 150 Å. We believe that this component of the solution is not physical: it is not present in the solution if we assume lower iron abundance, or if there is significant resonance scattering in some of the stronger (mainly iron) spectral lines with subsequent photon absorption in the lower, dense atmosphere. Finally, the DEM analysis gives a best-fit value for the interstellar hydrogen column density of NH = (2.4±0.5) × 1018 cm-2.

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