Dynamic Lyα jets

¹ Astronomical Institute, Slovak Academy of Sciences, 059 60 Tatranská Lomnica, Slovakia e-mail: koza@astro.sk
² Sterrekundig Instituut, Universiteit Utrecht, PO Box 80 000, 3508 TA Utrecht, The Netherlands
³ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029, Blindern, 0315 Oslo, Norway
⁴ Code 7663, Naval Research Laboratory, Washington, DC 20375, USA

Received: 30 July 2008
Accepted: 13 February 2009

Abstract

Context. The solar chromosphere and transition region are highly structured and complex regimes. A recent breakthrough has been the identification of dynamic fibrils observed in Hα as caused by field-aligned magnetoacoustic shocks.

Aims. We seek to find whether such dynamic fibrils are also observed in Lyα.

Methods. We used a brief sequence of four high-resolution Lyα images of the solar limb taken by the Very high Angular resolution ULtraviolet Telescope (VAULT), which displays many extending and retracting Lyα jets. We measured their top trajectories and fitted parabolas to the 30 best-defined ones.

Results. Most jet tops move supersonically. Half of them decelerate, sometimes superballistically, the others accelerate. This bifurcation may arise from incomplete sampling of recurrent jets.

Conclusions. The similarities between dynamic Lyα jets and Hα fibrils suggest that the magnetoacoustic shocks causing dynamic Hα fibrils also affect dynamic Lyα jets.