11273(  1) - 03/30/07 11:21  - [  1]

                  HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11273

Version: 1    Check-in Time: 30-Mar-2007 15:21:42       STScI Edit Number: 0

Title
Tracing the wind interface of the massive binary Eta Carinae
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Type             Cycle     Parallel Pointing Tolerance
AR               16        <none>
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Investigators
                                                                                     Contact?
    PI: Dr. Krister E. Nielsen            Catholic University of America
   CoI: Dr. Theodore R. Gull              NASA Goddard Space Flight Center              N
   CoI: Dr. Michael Corcoran              NASA Goddard Space Flight Center              N
   CoI: Dr. Kenji Hamaguchi               Universities Space Research Association       N
   CoI: Dr. John D. Hillier               University of Pittsburgh                      N

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Abstract

The binarity of Eta Carinae has been debated for a long time, but most recent
evidence favors a binary star interpretation. However, very little is known about
the nature of the companion star. Over Eta Carinae's spectroscopic period many
observable wind lines in the NUV/Optical region, have been shown to exhibit peculiar
line profiles with unusual velocity shifts relative to the system velocity. Some of
the lines are exclusively blue-shifted over the entire 5.54 yr cycle and their
ionization/excitation imply formation in the interface between the two massive
stars. Especially, the He I emission lines are mainly formed in the wind interface
region. Since the wind momentum is much larger for the primary star than its
companion, the wind interface is located fairly close to the companion.
Consequently, by tracing the He I emission we can construct a radial velocity curve
that will describe the motion of the companion star and will derive the relation
between the masses of the binary system stars. Furthermore, we will measure velocity
and intensity variations in H I and Fe II to further investigate the
ionization/excitation structure throughout Eta Carinae's wind. The analysis of the
central source of Eta Carinae, due to the closeness of the two stars in the binary
system (30 AU) and the intervening matter in line-of-sight towards Eta Carinae, is
extremely dependent on data obtained with high angular resolving power. The HST
archival data is crucial for the continuance of this project.
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