Bibcode
DOI
Gomez de Castro, Ana I.; Franqueira, M.
Bibliographical reference
Astrophysical Journal v.482, p.465
Advertised on:
6
1997
Citations
25
Refereed citations
23
Description
BP Tau is one of the few classical T Tauri stars for which the presence
of a hot spot in the surface has been reported without ambiguity. The
most likely source of heating is gravitational energy released by the
accreting material as it shocks with the stellar surface. This energy is
expected to be radiated mainly at UV wavelengths. In this work we report
the variations of the UV spectrum of BP Tau for 1992 January 5-19, when
the star was monitored with IUE during two rotation periods. Our data
indicate that lines that can be excited by recombination processes, such
as those from O I and He II, have periodic-like light curves, whereas
lines that are only collisionally excited do not follow a periodic-like
trend. These results agree with the expectations of the magnetically
channeled accretion models. The kinetic energy released in the accretion
shocks is expected to heat the gas to temperatures of ~106 K, which
henceforth produces ionizing radiation. The UV (Balmer) continuum and
the O I and He II lines are direct outputs of the recombination process.
However, the C IV, Si II, and Mg II lines are collisionally excited not
only in the shock region but also in inhomogeneous accretion events and
in the active (and flaring) magnetosphere, and therefore their light
curves are expected to be blurred by these irregular processes. We also
report the detection of warm infalling gas from the presence of
redshifted (81 km s-1) absorption components in some of the
high-resolution Mg II profiles available in the IUE and Hubble Space
Telescope archives.