Andrea Mehner, Kris Davidson, Roberta M. Humphreys, Kazunori Ishibashi, John C. Martin, Maria Teresa Ruiz, Frederick M. Walter
Stellar wind-emission features in the spectrum of eta Carinae have decreased
by factors of 2-3 relative to the continuum within the last 10 years. We
investigate a large data set from several instruments (STIS, GMOS, UVES)
obtained between 1998 and 2011 and we analyze the progression of spectral
changes in the direct view of the star, in the reflected polar-on spectra at
FOS4, and at the Weigelt knots. We find that the spectral changes occurred
gradually on a timescale of about 10 years and that they are dependent on the
viewing angle. The line strengths declined most in our direct view of the star.
About a decade ago, broad stellar wind-emission features were much stronger in
our line of sight view of the star than at FOS4. After the 2009 event, the
wind-emission line strengths are now very similar at both locations.
High-excitation He I and N II absorption lines in direct view of the star
strengthened gradually. The terminal velocity of Balmer P Cyg absorption lines
now appears to be less latitude-dependent and the absorption strength may have
weakened at FOS4. Latitude-dependent alterations in the mass-loss rate and the
ionization structure of eta Car's wind are likely explanations for the observed
spectral changes.
View original:
http://arxiv.org/abs/1112.4338
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