Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...526..445a&link_type=abstract
The Astrophysical Journal, Volume 526, Issue 1, pp. 445-450.
Astronomy and Astrophysics
Astronomy
12
Stars: Activity, Stars: Coronae, Stars: Flare, Stars: Individual (Hd 93497, Hd 4128), Stars: Late-Type, Ultraviolet: Stars
Scientific paper
The close visual double μ Velorum (HD 93497; G6 III+dF) consists of a yellow giant and a fainter companion currently 2" apart. Recently μ Vel was the source of a large flare recorded by the Extreme Ultraviolet Explorer. The long 1.5 day decay phase was like the extremes seen on hyperactive RS CVn-type binaries. The primary, μ Vel A is a 3 Msolar star, in the ``rapid braking zone'' redward of G0 III. Yellow giants are not commonly reported as flare stars, perhaps because the first-crossers are relatively rare and not well represented in the observational samples. The secondary star is classified G2 V, but the 1700 Å energy distribution places it earlier on the main sequence, probably F4 or F5 V, in a class also not usually known for coronal variability. The long duration of the μ Vel event suggests that it occurred in a significantly elongated structure of moderate density, ne<~109 cm-3. If it was a magnetic plasmoid, like a coronal mass ejection on the Sun, then such events might play a role in shedding angular momentum from active evolved stars. The associated spin-down could control the activity survival time of red giants (in later stages of evolution than the first-crosser μ Vel) whose dynamos were rejunvenated by dredge-up of angular momentum from the interior, or more exotic sources, such as cannibalism of close-in substellar companions during the first or second ascent.
Ayres Thomas R.
Brown Alexander
Osten Rachel Ann
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