An overview of the photometric events, trends and brightenings of eta Carinae

A. M. van Genderen, C. Sterken, W. H. Allen and W. S. G. Walker

(1) Leiden University Observatory, Postbus 9513, NL-2300RA Leiden, The Netherlands
(2) Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
(3) Alvine Estate, Vintage Lane, RD 3, Blenheim, New Zealand
(4) 272 Heath Road, Awanui R D 1, New Zealand 0451

Using new and archived ground-based optical and near-infrared photometry (covering more than three decades) and space-based (HST) narrow-band photometry, we document the morphological character of optical and near-infrared photometric features at seven periastron passages of eta Carinae, of the secular brightening 1952-1998, of the brightening episodes after the 1997.9 and 2003.5 events, and of two types of UV oscillations, with the purpose of getting some insight in the causes of these variations.

The optical peaks could be the climax of the expansion phase of the primary due to tidal effects. The dips can be explained by obscuration of the secondary's circumstellar structure by the (polar) wind of the primary. The wavelength dependency of the rates of the slow secular brightening (1952-1997.9), and of the fast brightenings of the central star and Homunculus after the 1997.9 and 2003.5 events are investigated. The brightenings can be interpreted as an extinction decrease with an extinction law R~5.

The primary's luminosity and mass-loss rate were likely stable over the last 35 year. The long-term UV oscillations are interpreted as revolution-modulated H-emission variation in the equatorial plane, whereas the short-term UV oscillations are due to stellar pulsations.

Reference: The Journal of Astronomical Data 2006, Volume 12, 3
Status: Manuscript has been accepted