Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006apj...644..464a&link_type=abstract
The Astrophysical Journal, Volume 644, Issue 1, pp. 464-474.
Astronomy and Astrophysics
Astronomy
4
Stars: Coronae, Stars: Individual (Hd 117555), Stars: Individual (Hd 111812), Stars: Individual (Hd 113001B), Stars: Individual (Vz 1128), Ultraviolet: Stars
Scientific paper
A Far Ultraviolet Spectroscopic Explorer (FUSE) pointing on the ultrafast rotating yellow giant FK Comae Berenices (HD 117555; vsini~163 km s-1) recorded emission profiles of C III λ977 (T~8×104 K) and O VI λ1031 (T~3×105 K) that are exceptionally broad and asymmetric, but nearly identical in shape, aside from a blueward absorption component in the latter (identified as interstellar O I, rather than, say, a C III outflow feature). The FWHMs exceed 500 km s-1, twice the broadest far-UV line shape of any normal late-type star observed to date, but similar to the Hα profiles of FK Com, and following the trend of other fast spinning early G giants that often display ``superrotational'' broadening of their UV ``hot'' lines. Although the red-asymmetric O VI λ1031 profile is suggestive of an outflow at ~3×105 K, the weaker member of the doublet, λ1037, does not display the differential absorption pattern expected from a warm wind. Furthermore, at times the chromospheric Mg II λ2796 + λ2803 composite profile, from a collection of International Ultraviolet Explorer (IUE) echellegrams obtained two decades earlier, is nearly identical in shape to red-asymmetric O VI λ1031. A contemporaneous optical Doppler map places the photospheric dark spots mainly in the polar regions of the approaching hemisphere. The dominantly redward biased profiles of C III and O VI could be explained if the associated emission zones were leading the starspots in phase and partially rooted in lower latitudes.
Ayres Thomas R.
Brown Alexander
Harper Graham M.
Ilyin Ilya V.
Korhonen Heidi
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