The periodicity of the Eta Carinae events

DAMINELI, A.; HILLIER, D. J.; CORCORAN, M. F.; STAHL, O.; LEVENHAGEN, R. S.; LEISTER, N. V.; GROH, J. H.; TEODORO, M.; COLOMBO, J. F. ALBACETE; GONZALEZ, J. F.; ARIAS, J.; LEVATO, H.; GROSSO, M.; MORRELL, N.; GAMEN, R.; WALLERSTEIN, G.; NIEMELA, V.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

Blackwell Publishing

Año: 2008 vol. 384 p. 1649 - 1656

0035-8711

Extensive spectral observations of η 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 Ppres = 2022.7 +/- 1.3 d. Spectroscopic data collected during the last 60 yr yield an average period of Pavg = 2020 +/- 4 d, consistent with the present-day period. The period cannot have changed by more than ΔP/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 = JD2452819.8. The next event is predicted to occur on 2009 January 11 (+/-2 d). The dates for the start of the minimum in other spectral features and broad-bands are very close to this date, and have well-determined time-delays from the HeI epoch.