Long-Term Optical Monitoring of Eta Carinae. Multiband light curves for a complete orbital period

TL;DR

This study presents a comprehensive, multi-year optical monitoring of Eta Carinae, revealing its brightness variations over an entire orbital cycle and providing valuable data for understanding its binary nature and periodic events.

Contribution

It offers the first homogeneous, long-term optical light curves of Eta Carinae covering a complete orbital period, including detailed observations before, during, and after periastron.

Findings

Eta Carinae's brightness increased steadily since 1998.

Reached its brightest magnitude (~4.7) around 2006, the brightest since the 1860s.

The brightness trend reversed in 2007, stabilizing since then.

Abstract

The periodicity of 5.5 years for some observational events occurring in Eta Carinae manifests itself across a large wavelength range and has been associated with its binary nature. These events are supposed to occur when the binary components are close to periastron. To detect the previous periastron passage of Eta Car in 2003, we started an intensive, ground-based, optical, photometric observing campaign. We continued observing the object to monitor its photometric behavior and variability across the entire orbital cycle. Our observation program consisted of daily differential photometry from CCD images, which were acquired using a 0.8 m telescope and a standard BVRI filter set at La Plata Observatory. The photometry includes the central object and the surrounding Homunculus nebula. We present up-to-date results of our observing program, including homogeneous photometric data collected between 2003 and 2008. Our observations demonstrated that Eta Car has continued increasing in brightness at a constant rate since 1998. In 2006, it reached its brightest magnitude (V ~ 4.7) since about 1860s. The object then suddenly reverted its brightening trend, fading to V = 5.0 at the beginning of 2007, and has maintained a quite steady state since then. We continue the photometric monitoring of Eta Car in anticipation of the next "periastron passage", predicted to occur at the beginning of 2009.