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Linsky \& Wood (1994, ApJ, 430, 342) discovered broad wings in the transition region lines of AU Mic, and proposed that these wings are signatures of microflares in the transition region of this active M0 Ve star. The solar analog for this phenomenon might be the ``transition region explosive events'' discussed by Dere, Bartoe, \& Brueckner (1989, Sol.\ Phys., 123, 41). Broad wings have been found in Capella's transition region lines as well, and these have also been interpreted as being caused by microflaring (Linsky et al., ApJ, to appear 20 March 1995).
We have used Goddard High Resolution Spectrograph (GHRS) observations of Procyon (F5 IV-V) and HR 1099 (K1 IV + G5 IV) to search for broad wings in the UV emission lines of these stars. We find that the transition region lines of HR 1099, which are emitted almost entirely by the K1 star, do indeed have broad wings which are even stronger than those of AU Mic and Capella. This is consistent with the association of the broad wings with microflaring since HR 1099 is a very active binary system. In contrast, the transition region lines of Procyon, an inactive star, do not show evidence for any broad wings, with the possible exception of N~V $\lambda$1239. However, these lines do seem to have a slight blue wing excess.
Linsky et al.\ (1995) found no evidence for broad wings in Capella's chromospheric lines. However, we find that the Mg~II lines of HR 1099 and AU~Mic do have broad wings. The striking resemblance between the Mg~II and C~IV lines seen for both these stars suggests that the Mg~II line profiles may be regulated by turbulent processes similar to those that control the transition region line profiles. For HR 1099 and AU Mic, microflaring may be a common occurence in the chromosphere as well as in the transition region.
This work is supported by NASA Interagency Transfer S-56500-D to the National Institute of Standards and Technology.
