Distinguishing Circumstellar from Stellar Photometric Variability in Eta Carinae

Abstract

The interacting binary Eta Carinae remains one of the most enigmatic massive stars in our Galaxy despite over four centuries of observations. In this work, its light curve from the ultraviolet to the near-infrared is analysed using spatially resolved HST observations and intense monitoring at the La Plata Observatory, combined with previously published photometry. We have developed a method to separate the central stellar object in the ground-based images using HST photometry and applying it to the more numerous ground-based data, which supports the hypothesis that the central source is brightening faster than the almost-constant Homunculus. After detrending from long-term brightening, the light curve shows periodic orbital modulation ($\Delta V$ $\sim$ 0.6 mag) attributed to the wind-wind collision cavity as it sweeps around the primary star and it shows variable projected area to our line-of-sight. Two quasi-periodic components with time scales of 2-3 and 8-10 yr and low amplitude, $\Delta V$ $<$ 0.2 mag, are superimposed on the brightening light-curve, being the only stellar component of variability found, which indicates minimal stellar instability. Moreover, the light curve analysis shows no evidence of `shell ejections' at periastron. We propose that the long-term brightening of the stellar core is due to the dissipation of a dusty clump in front of the central star, which works like a natural coronagraph. Thus, the central stars appear to be more stable than previously thought since the dominant variability originates from a changing circumstellar medium. We predict that the brightening phase, due mainly to dust dissipation, will be completed around 2032 $\pm$ 4 yr, when the star will be brighter than in the 1600's by up to $\Delta V$ $\sim$ 1 mag.

26 pages, 19 figures. Accepted to appear on MNRAS

References in corpus (17)

• Pulsational Pair-Instability Supernovae
• The UV Scattering Halo of the Central Source Associated with Eta Carinae
• A multispectral view of the periodic events in eta Carinae
• Modeling the RXTE light curve of $\eta$ Carinae from a 3-D SPH simulation of its binary wind collision
• Possible Implications of Mass Accretion in Eta Carinae
• $\eta$ Carinae's Dusty Homunculus Nebula from Near-Infrared to Submillimeter Wavelengths: Mass, Composition, and Evidence for Fading Opacity
• Ancient eruptions of Eta Carinae: A tale written in proper motions
• The Chrysalis Opens? Photometry from the Eta Carinae HST Treasury Project, 2002-2006
• The fossil wind structures of Eta Carinae: changes across on 5.54-year cycle
• Long-Term Optical Monitoring of Eta Carinae. Multiband light curves for a complete orbital period
• $\eta$ Carinae Baby Homunculus Uncovered by ALMA
• A disrupted molecular torus around Eta Carinae as seen in 12CO with ALMA
• The Eta Carinae optical 2009.0 event, a new "eclipse-like" phenomenon
• VLTI-AMBER velocity-resolved aperture-synthesis imaging of Eta Carinae with a spectral resolution of 12000. Studies of the primary star wind and innermost wind-wind collision
• A moderately precise dynamical age for the Homunculus of Eta Carinae based on 13 years of HST imaging
• BRITE-Constellation reveals evidence for pulsations in the enigmatic binary $\eta$ Carinae
• Photometric variability of WC9 stars

Cited by in corpus (6)

• Spectroscopic Signatures of the Vanishing Natural Coronagraph of eta Carinae
• The orbital kinematics of eta Carinae over three periastra with a possible detection of the elusive secondary's motion
• $\eta$ Carinae: high angular resolution continuum, H30$\alpha$ and He30$\alpha$ ALMA images
• Changes in the Na D${}_1$ Absorption Components of $\eta$ Carinae Provide Clues on the Location of the Dissipating Central Occulter
• Long-term evolution in ionization of ejecta illuminated by Eta Carinae
• Eta Carinae: an evolving view of the central binary, its interacting winds and its foreground ejecta