The periodicity of the eta Carinae events

A. Damineli (1), M. F. Corcoran (3,4), D. J. Hillier (2), O. Stahl(5), R. S. Levenhagen (1), N.V. Leister (1), J. H. Groh (1), M. Teodoro (1), J. F. Albacete Colombo (6), F. Gonzalez (7), J. Arias (8), H. Levato (7), M. Grosso (7), N. Morrell (9), R. Gamen (7), G.Wallerstein (10), V. Niemela (11)

(1)Instituto de Astronomia, Geofisica e Ciencias Atmosfericas da Universidade de Sao Paulo,
(2)Department of Physics and Astronomy,University of Pittsburgh,
(3)CRESST and X-ray Astrophysics Laboratory,
(4) Universities Space Research Association,
(5)ZAH, Landessternwarte,
(6)Facultad de Ciencias Astronomicas y Geofisicas de La Plata,
(7)Complejo Astronomico El Leoncito,
(8)Departamento de Física, Universidad de La Serena,
(9)Las Campanas Obseratory,
(10)Department of Astronomy, University of Washington,
(11)In memoriam

Extensive spectral observations of eta Carinae over the last cycle, and particularly around the 2003.5 low excitation event, have been obtained. The variability of both narrow and broad lines, when combined with data taken from two earlier cycles, reveal a common and well defined period. We have combined the cycle lengths derived from the many lines in the optical spectrum with those from broad-band X-rays, optical and near-infrared observations, and obtained
a period length of P=2022.7+/-1.3 d.

Spectroscopic data collected during the last 60 years yield an average period of P=2020+/-4 d, consistent with the present day period. The period cannot have changed by more than DeltaP/P=0.0007 since 1948. This confirms the previous claims of a true, stable periodicity, and gives strong support to the binary scenario. We have used the disappearance of the narrow component of HeI 6678 to define the epoch of the Cycle 11 minimum, T0=JD 2,452,819.8. The next event is predicted to occur on 2009 January 11 (+/-2 days). The dates for the start of the minimum in other spectral features and broad-bands is very close to this date,
and have well determined time delays from the HeI epoch.

Reference: MNRAS
Status: Manuscript has been accepted