Light Echoes from Eta Carinae's Great Eruption: Spectrophotometric Evolution and the Rapid Formation of Nitrogen-rich Molecules

Abstract

We present follow-up optical imaging and spectroscopy of one of the light echoes of $\eta$ Carinae's 19th-century Great Eruption discovered by Rest et al. (2012). By obtaining images and spectra at the same light echo position between 2011 and 2014, we follow the evolution of the Great Eruption on a three-year timescale. We find remarkable changes in the photometric and spectroscopic evolution of the echo light. The $i$-band light curve shows a decline of $\sim 0.9$ mag in $\sim 1$ year after the peak observed in early 2011 and a flattening at later times. The spectra show a pure-absorption early G-type stellar spectrum at peak, but a few months after peak the lines of the [Ca II] triplet develop strong P-Cygni profiles and we see the appearance of [Ca II] 7291,7324 doublet in emission. These emission features and their evolution in time resemble those observed in the spectra of some Type IIn supernovae and supernova impostors. Most surprisingly, starting $\sim 300$ days after peak brightness, the spectra show strong molecular transitions of CN at $\gtrsim 6800$ Å. The appearance of these CN features can be explained if the ejecta are strongly Nitrogen enhanced, as it is observed in modern spectroscopic studies of the bipolar Homunculus nebula. Given the spectroscopic evolution of the light echo, velocities of the main features, and detection of strong CN, we are likely seeing ejecta that contributes directly to the Homunculus nebula.

arXiv commentaccepted in ApJL

References in corpus (33)

• Cosmic-Ray Rejection by Laplacian Edge Detection
• Las Cumbres Observatory Global Telescope Network
• Mass Loss: Its Effect on the Evolution and Fate of High-Mass Stars
• SN 2006gy: Discovery of the most luminous supernova ever recorded, powered by the death of an extremely massive star like Eta Carinae
• ULySS: A Full Spectrum Fitting Package
• The Cassiopeia A Supernova was of Type IIB
• Luminous Blue Variable eruptions and related transients: Diversity of progenitors and outburst properties
• The Structure of the Homunculus: I. Shape and Latitude Dependence from H2 and [Fe II] Velocity Maps of Eta Carinae
• Discovery of Precursor LBV Outbursts in Two Recent Optical Transients: The Fitfully Variable Missing Links UGC 2773-OT and SN 2009ip
• Testing LMC Microlensing Scenarios: The Discrimination Power of the SuperMACHO Microlensing Survey
• Tycho Brahe's 1572 supernova as a standard type Ia explosion revealed from its light echo spectrum
• Scattered-Light Echoes from the Historical Galactic Supernovae Cassiopeia A and Tycho (SN 1572)
• Echoes from Ancient Supernovae in the Large Magellanic Cloud
• Microslit Nod-shuffle Spectroscopy - a technique for achieving very high densities of spectra
• SN 1994W: An Interacting Supernova or Two Interacting Shells?
• SN 2011ht: Confirming a Class of Interacting Supernovae with Plateau Light Curves (Type IIn-P)
• Spectral Identification of an Ancient Supernova using Light Echoes in the LMC
• Direct Confirmation of the Asymmetry of the Cas A Supernova with Light Echoes
• A Revised Historical Light Curve of Eta Carinae and the Timing of Close Periastron Encounters
• Faint Supernovae and Supernova Impostors: Case studies of SN2002kg/NGC2403-V37 and SN 2003gm
• Light echoes reveal an unexpectedly cool Eta Carinae during its 19th-century Great Eruption
• Unmasking the Supernova Impostors
• Innocent Bystanders: Carbon Stars from the Sloan Digital Sky Survey
• Near-IR Spectra of Red Supergiants and Giants. I- Models with Solar and with Mixing-Induced Surface Abundance Ratios
• A Model for the 19th Century Eruption of Eta Carinae: CSM Interaction Like a Scaled-Down Type IIn Supernova
• Possible Recovery of SN 1961V In Hubble Space Telescope Archival Images
• Asymmetry in the Outburst of SN 1987A Detected Using Light Echo Spectroscopy
• Broad-band Spectroscopy of the Ongoing Large Eruption of the Luminous Blue Variable R71
• Comparing Eta Carinae with the Red Rectangle
• Light Echoes of Transients and Variables in the Local Universe
• Cleaning up Eta Carinae: Detection of Ammonia in the Homunculus
• On the Interpretation of Supernova Light Echo Profiles and Spectra
• Molecules in η Carinae

Cited by in corpus (20)

• Luminous Blue Variables are Antisocial: Their Isolation Implies that they are Kicked Mass Gainers in Binary Evolution
• Connecting the progenitors, pre-explosion variability, and giant outbursts of luminous blue variables with Gaia16cfr
• Light-echoes from the plateau in Eta Carinae's Great Eruption reveal a two-stage shock-powered event
• Simulating the formation of $\eta$ Carinae's surrounding nebula through unstable triple evolution and stellar merger-induced eruption
• Constraints on Type IIn Supernova Progenitor Outbursts from the Lick Observatory Supernova Search
• Exceptionally fast ejecta seen in light echoes of Eta Carinae's Great Eruption
• Discovery of an intermediate-luminosity red transient in M51 and its likely dust-obscured, infrared-variable progenitor
• Progenitor, environment, and modelling of the interacting transient, AT 2016jbu (Gaia16cfr)
• A new and unusual LBV-like outburst from a Wolf-Rayet star in the outskirts of M33
• The Spectral Temperature of Optically Thick Outflows with Application to Light Echo Spectra from $\eta$~Carinae's Giant Eruption
• Spectroscopic observations of progenitor activity 100 days before a Type Ibn supernova
• The Blue Supergiant Progenitor of the Supernova Imposter AT~2019krl
• A moderately precise dynamical age for the Homunculus of Eta Carinae based on 13 years of HST imaging
• Unveiling the Nature of SN 2011fh: a Young and Massive Star Gives Rise to a Luminous SN 2009ip-like Event
• Finding $\eta$ Car Analogs in Nearby Galaxies Using Spitzer: II. Identification of An Emerging Class of Extragalactic Self-Obscured Stars
• The canonical Luminous Blue Variable AG Car and its neighbor Hen 3-519 are much closer than previously assumed
• Spatial distribution and kinematics of the molecular material associated with $\eta$ Carinae
• Discovery of Five Candidate Analogs for $\eta$Carinae in Nearby Galaxies
• Ultraviolet Mg II emission from fast neutral ejecta around Eta Carinae
• Comparison of Diversity of Type IIb Supernovae with Asymmetry in Cassiopeia A Using Light Echoes