The periodicity of the η 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.A.; GONZALEZ, F.; ARIAS, J.; LEVATO, H.; GROSSO, M.; MORRELL, N. I.; GAMEN, R. C.; WALLERSTEIN, G.; NIEMELA, V. S.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

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 P/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 He I 6678 to define the epoch of the Cycle 11 minimum, T 0 = JD 245 2819.8. 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 He I epoch.