Probing a G5III stellar atmosphere
by microlensing variations in the Hα line
Probing the atmosphere of the bulge G5III star
OGLE-2002-BUL-69
by analysis of microlensed Hα line
First posted: 4-Jun-2004
Abstract
We discuss high-resolution,
time-resolved spectra of the caustic exit of the binary microlensing
event OGLE 2002-BLG-69 obtained with UVES on the VLT. The source star
is a G5III giant in the Galactic Bulge. During such events, the source
star is highly magnified, and a strong differential magnification
around the caustic resolves its surface. Using an appropriate model
stellar atmosphere generated by the PHOENIX v2.6 code we obtain a model
light curve for the caustic exit and compare it with a dense set of
photometric observations obtained by the PLANET microlensing follow up
network. We further compare predicted variations in the Hα
equivalent width with those measured from our
spectra. While the model and observations agree in the gross features,
there are discrepancies suggesting shortcomings in the model,
particularly for the Hα line core, where we have detectedamplified
emission from the stellar chromosphere after the source star's trailing
limb exited the caustic. This achievement became possible by the
provision of the very efficient OGLE-III Early Warning System, a
network of small telescopes capable of nearly-continuous
round-the-clock photometric monitoring, on-line data reduction, daily
near-real-time modelling in order to predict caustic crossing
parameters,and a fast and efficient response of a 8m class telescope to
a ``Target-Of-Opportunity'' observation request.
The corresponding paper has been published as
A&A 419, L1 (2004)
back to the PLANET Homepage