Eta Carinae's 2014.6 Spectroscopic Event: Clues to the Long-term Recovery from its Great Eruption

Abstract

Aims. Every 5.5 years eta Car's light curve and spectrum change remarkably across all observed wavelength bands. We compare the recent spectroscopic event in mid-2014 to the events in 2003 and 2009 and investigate long-term trends. Methods. Eta Car was observed with HST STIS, VLT UVES, and CTIO 1.5m CHIRON for a period of more than two years in 2012-2015. Archival observations with these instruments cover three orbital cycles. Results. Important spectroscopic diagnostics show significant changes in 2014 compared to previous events. While the timing of the first HeII 4686 flash was remarkably similar to previous events, the HeII equivalent widths were slightly larger and the line flux increased compared to 2003. The second HeII peak occurred at about the same phase as in 2009, but was stronger. The HeI line flux grew in 2009-2014 compared to 1998-2003. On the other hand, Halpha and FeII lines show the smallest emission strengths ever observed. Conclusions. The basic character of the spectroscopic events has changed in the past 2-3 cycles; ionizing UV radiation dramatically weakened during each pre-2014 event but not in 2014. The strengthening of HeI emission and the weakening of the lower-excitation wind features in our direct line of sight implies a substantial change in the physical parameters of the emitting regions. The polar spectrum at FOS4 shows less changes in the broad wind emission lines, which may be explained by the latitude-dependent wind structure of eta Car. The quick and strong recovery of the HeII emission in 2014 supports a scenario, in which the wind-wind shock may not have completely collapsed as was proposed for previous events. All this may be the consequence of just one elementary change, namely a strong decrease in the primary's mass-loss rate.

arXiv comment19 pages, 8 figures, accepted in A&A

References in corpus (41)

• CHIRON - A Fiber Fed Spectrometer for Precise Radial Velocities
• The Structure of the Homunculus: I. Shape and Latitude Dependence from H2 and [Fe II] Velocity Maps of Eta Carinae
• In Hot Pursuit of the Hidden Companion of Eta Carinae: An X-ray Determination of the Wind Parameters
• Latitude-dependent effects in the stellar wind of Eta Carinae
• 3D modelling of the colliding winds in Eta Carinae - evidence for radiative inhibition
• Spiralling out of control: 3D hydrodynamical modelling of the colliding winds in $\eta$Carinae
• Near-Infrared interferometry of Eta Carinae with high spatial and spectral resolution using the VLTI and the AMBER instrument
• Direct measurement of the size and shape of the present-day stellar wind of Eta Carinae
• High-excitation emission lines near eta Carinae, and its likely companion star
• Constraints on decreases in Eta Carinae's mass loss from 3D hydrodynamic simulations of its binary colliding winds
• Eta Carinae across the 2003.5 minimum: Spectroscopic Evidence for Massive Binary Interactions
• A multispectral view of the periodic events in eta Carinae
• On the influence of the companion star in Eta Carinae: 2D radiative transfer modeling of the ultraviolet and optical spectra
• On the He II Emission In Eta Carinae and the Origin of Its Spectroscopic Events
• A Change in the Physical State of $\eta$ Carinae?
• Detection of He II 4686 in eta Carinae
• The Early Spectra of Eta Carinae 1892 to 1941 and the Onset of Its High Excitation Emission Spectrum
• The Systemic Velocity of Eta Carinae
• A spectroscopic event of eta Car viewed from different directions: The data and first results
• Eta Carinae's Brightness Variations Since 1998: HST Observations of the Central Star
• Accretion by the Secondary in Eta Carinae During the Spectroscopic Event: I. Flow Parameters
• The Chrysalis Opens? Photometry from the Eta Carinae HST Treasury Project, 2002-2006
• A Sea Change in Eta Carinae
• He II 4686 in eta Carinae: collapse of the wind-wind collision region during periastron passage
• Secular Changes in Eta Carinae's Wind 1998-2011
• X-ray Emission from Eta Carinae near Periastron in 2009 I: A Two State Solution
• Critical Differences and Clues in Eta Car's 2009 Event
• 3D radiative transfer simulations of Eta Carinae's inner colliding winds - I. Ionization structure of helium at apastron
• The H-alpha Variations of eta Carinae During the 2009.0 Spectroscopic Event
• A companion as the cause of latitude-dependent effects in the wind of Eta Carinae
• The Source of the Helium Visible Lines in Eta Carinae
• Accretion onto the Companion of Eta Carinae During the Spectroscopic Event: III. the He II 4686 Line
• VLT-UVES observations of the Balmer line variations of eta Carinae during the 2003 spectroscopic event
• The Orientation of the Eta Carinae Binary System
• Accretion-Induced Collimated Fast Wind Model for Eta Carinae
• Explaining the Early Exit of Eta Carinae from its 2009 X-Ray Minimum with the Accretion Model
• Wind-wind collision in the eta Carinae binary system - III. The HeII 4686 line profile
• Mid-Cycle Changes in Eta Carinae
• Near-Infrared Evidence for a Sudden Temperature Increase in Eta Carinae
• Suzaku Monitoring of Hard X-ray Emission from Eta Carinae over a Single Binary Orbital Cycle
• N II 5668-5712, a New Class of Spectral Features in Eta Carinae

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