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\IBVShead{5492}{13 January 2004}

\IBVStitletl{{\Large ${\boldmath \eta}$} C\lowercase{ar} recovering from the 2003.5 spectroscopic event}

\IBVSauth{Groh, J. H.; Damineli, A.}

\IBVSinsto{Instituto de Astronomia, Geof\'{\i}sica e Ci\^encias Atmosf\'ericas, Universidade de S\~ao Paulo, S\~ao Paulo, Brazil}

\SIMBADobjAlias{Eta Car}{HD 93308}

\IBVStyp{ LBV }

\IBVSabs{We carried out spectroscopy (3800-11000 A) of Eta Carinae}
\IBVSabs{22 weeks after the 2003.5 minimum phase. Our data show that}
\IBVSabs{the high excitation lines are recovering their strength except}
\IBVSabs{Ne[III] lambda 3868 which is absent. The comparison between}
\IBVSabs{this observation with ones on the same phase of previous cycles}
\IBVSabs{indicates that Eta Car is suffering a secular evolution superposed}
\IBVSabs{to the 5.5 yr cycle.}


\begintext

The Luminous Blue Variable star Eta Carinae suffers spectroscopic events every 5.5~yr
characterized by the fading of the high excitation lines of [Ar III], [Fe III],
[Ne III], [N~II] and [S III] (Damineli, 1996). The last of such events occurred 
around the end of June 2003 (Abraham et al., 2003). The line of highest 
excitation energy [Ne III] $\lambda$3868 vanished on June 23th, followed by
the others of decreasing energy. The narrow component of HeI $\lambda$6678 vanished on June 29th, 
which implies a period of 2025 days, when comparing present data with previous observations.
We adopt that date as the zero phase of cycle 11, in order that cycle 10 
started in December 1997 and cycle 9 in June 1992.  The ingress in the phase 
of totality for all lines occurred within days of the X-ray minimum (Corcoran, 2003).

As noted in previous spectroscopic events, different lines should recover from the 
minimum in different times, following a reverse sequence of excitation 
energy as during fading. 
Unfortunately, the star could not be observed from the ground through
October-November, when the lower excitation lines like [N II] and [Fe III] were expected to
be recovering. We succeeded to take spectra at the Observat\'orio Pico dos Dias 
(LNA/Brazil) on 2003 December 12--14, corresponding to phase 0.08. 
We used the 1.6m telescope and Coud\'e focus
to achieve spectral resolution of 0.6 {\AA} and spectral coverage from 3800
{\AA} to 11000 {\AA} with S/N $>$ 100 in the stellar continuum. Such observations proved to 
be crucial, since all the lines that have faded are showing up again, except 
for [Ne III] $\lambda$3868. The line [Ar III] $\lambda$7135 is faint but definitively present, as can be seen
in the left panel of Figure 1. This figure displays the present spectrum and another taken on August
15th, when the spectroscopic event was near the mid phase.

In the December spectrum, the narrow components of He I lines start to 
rise again, and the broad components are much stronger than those in August.  
The lines [S III] $\lambda$6312 and [Fe III] $\lambda$$\lambda$4658--4701 are mildly intense as 
compared to [N II] $\lambda$5755 that is almost half way of full recovery. HeI $\lambda$10830 is
much stronger than in the minimum. 
Another remarkable feature of our data is that [Ne III] remains absent from the spectrum 
along the last 22 weeks, almost twice the duration of totality in X-rays (Corcoran, 2003). 
[Ne III] is expected to reappear in the next weeks, indicating that the time
delay between different lines to egress from the event is spread over a time
interval of one month. These time delays could be related with
the recombination times and the progress of the ionization front in the circumstellar envelope.

\IBVSfig{6.0cm}{5492-f1.eps}{Left panel: He I, [Ar III] and [Fe II] lines near the center of the 2003.5 
spectroscopic event (August 15th) and on December 12th, when it was ending. Right panel: comparison between line
intensities in three subsequent cycles, around the same phase. We adopted the  $P=2025$ days and
T$_0 = 2452820$ (June 29, 2003) as the starting point of cycle 11. }
\IBVSfigKey{5492-f1.eps}{eta Car}{spectrum}

We have noticed previously that the spectrum is evolving secularly, in the
sense that the high and intermediate excitation lines are becoming fainter and fainter 
from cycle to cycle (Damineli et al., 1999). In the right panel of Figure 1 we compare the lines
of [Ni II] $\lambda$6666 and HeI $\lambda$6678 around phase 0.08 in the 
last three cycles. It can be seen that the secular fading is continuing, 
but the step between the previous (10) and present cycle (11) was smaller than
from cycle 9 to 10. It is seen also that the P Cygni profile in He I$\lambda$6678 is 
deeper than previously. Other lines of He I and Si II show the same trend.
Since the radial velocities of these P Cygni components are not changing, 
it seems that the stellar wind is becoming optically thicker.

\references

Abraham, Z., Dominici, T. P., Damineli, A., et al.,
2003, {\it IAUC}, {\bf 8162}, 4  
%%\BIBCODE{2003IAUC.8162....4A}

Corcoran, M. F., 2003, private communication, see \hfill\break
{\tt http://lheawww.gsfc.nasa.gov/users/corcoran/eta\_car/etacar\_rxte\_lightcurve/}

Damineli, A., 1996, {\it ApJ}, {\bf 460}, L49  
%%\BIBCODE{1996ApJ...460L.49D}

Damineli, A., Stahl, O., Wolf, B., et al., 1999, in ASP
Conf. Ser. 179, $\eta$ Carinae at the Millenium, ed J. A. Morse et al.
(San Francisco: ASP), 221

\endreferences 

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