Abstract Changes in the flux and spectrum of Eta Carinae ( η Car) since 1900 have been attributed to the evolution of the central binary by some. Others suggest evolution in the occulting ejecta. The ...brightness jump in the 1940s, which coincided with the appearance of narrow forbidden emission lines, may have been caused by the clearing and ionization of intervening circumstellar ejecta. The brightening changed at a slower pace up through 40 yr later. Here we continue earlier studies focused on the long-term, showing that the forbidden line emission increased in the early 1990s with no noticeable increase in the brightness of the Homunculus. We interpret that the increase in narrow-line emission is due to decreased extinction in the line of sight (LOS) from the central binary to the Weigelt clumps. In 2000, the central stellar core increased in brightness at a faster rate without associated changes in the Homunculus. By 2018, hundreds of narrow-line absorptions from singly ionized metals in our LOS from ( η Car) disappeared, thought to be caused by increased ionization of metals. These three events (1990, 2000, and 2018) are explained by the dissipation of circumstellar material within the Homunculus close to the binary. Combining these changes with the steadiness of the Homunculus and the primary winds over the past four decades indicates that circumstellar ejecta in our direction have been cleared.
Abstract
Eta Carinae (
η
Car) exhibits a unique set of P Cygni profiles with both broad and narrow components. Over many decades, the spectrum has changed—there has been an increase in observed ...continuum fluxes and a decrease in Fe
ii
and H
i
emission-line equivalent widths. The spectrum is evolving toward that of a P Cygni star such as P Cygni itself and HDE 316285. The spectral evolution has been attributed to intrinsic variations such as a decrease in the mass-loss rate of the primary star or differential evolution in a latitudinal-dependent stellar wind. However, intrinsic wind changes conflict with three observational results: the steady long-term bolometric luminosity; the repeating X-ray light curve over the binary period; and the constancy of the dust-scattered spectrum from the Homunculus. We extend previous work that showed a secular strengthening of P Cygni absorptions by adding more orbital cycles to overcome temporary instabilities and by examining more atomic transitions.
cmfgen
modeling of the primary wind shows that a time-decreasing mass-loss rate is not the best explanation for the observations. However, models with a
small
dissipating absorber in our line of sight can explain both the increase in brightness and changes in the emission and P Cygni absorption profiles. If the spectral evolution is caused by the dissipating circumstellar medium, and not by intrinsic changes in the binary, the dynamical timescale to recover from the Great Eruption is much less than a century, different from previous suggestions.
Abstract
Previous Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) longslit observations of Eta Carinae (
η
Car) identified numerous absorption features in both the stellar ...spectrum, and in the adjacent nebular spectra, along our line of sight (LOS). The absorption features became temporarily stronger when the ionizing far-ultraviolet radiation field was reduced by the periastron passage of the secondary star. Subsequently, dissipation of a dusty structure in our LOS has led to a long-term increase in the apparent brightness of
η
Car, an increase in the ionizing ultraviolet (UV) radiation, and the disappearance of absorption from multiple velocity-separated shells extending across the foreground Homunculus lobe. We use HST/STIS spectro-images, coupled with published infrared and radio observations, to locate this intervening dusty structure. The velocity and spatial information indicate the occulter is ≈1000 au in front of
η
Car. The Homunculus is a transient structure composed of dusty, partially ionized ejecta that eventually will disappear due to the relentless rain of ionizing radiation and wind from the current binary system along with dissipation and mixing with the interstellar medium. This evolving complex continues to provide an astrophysical laboratory that changes on human timescales.
Infrared observations of the dusty, massive Homunculus Nebula around the luminous blue variable
Carinae are crucial to characterize the mass-loss history and help constrain the mechanisms leading to ...the Great Eruption. We present the 2.4 - 670
m spectral energy distribution, constructed from legacy ISO observations and new spectroscopy obtained with the
Using radiative transfer modeling, we find that the two best-fit dust models yield compositions which are consistent with CNO-processed material, with iron, pyroxene and other metal-rich silicates, corundum, and magnesium-iron sulfide in common. Spherical corundum grains are supported by the good match to a narrow 20.2
m feature. Our preferred model contains nitrides AlN and Si
N
in low abundances. Dust masses range from 0.25 to 0.44
but
≥ 45
in both cases due to an expected high Fe gas-to-dust ratio. The bulk of dust is within a 5″ × 7″ central region. An additional compact feature is detected at 390
m. We obtain
= 2.96 × 10
, a 25% decline from an average of mid-IR photometric levels observed in 1971-1977. This indicates a reduction in circumstellar extinction in conjunction with an increase in visual brightness, allowing 25-40% of optical and UV radiation to escape from the central source. We also present an analysis of
CO and
CO
= 5 - 4 through 9 - 8 lines, showing that the abundances are consistent with expectations for CNO-processed material. The
C II line is detected in absorption, which we suspect originates in foreground material at very low excitation temperatures.
Abstract We present infrared aperture-masking interferometry (AMI) observations of newly formed dust from the colliding winds of the massive binary Wolf–Rayet system WR 137 with JWST using the Near ...Infrared Imager and Slitless Spectrograph (NIRISS). NIRISS AMI observations of WR 137 and a point-spread function calibrator star, HD 228337, were taken using the F380M and F480M filters in 2022 July and August as part of the Director’s Discretionary Early Release Science program #1349. Interferometric observables (squared visibilities and closure phases) from the WR 137 “interferogram” were extracted and calibrated using three independent software tools: ImPlaneIA, AMICAL, and SAMpip. The analysis of the calibrated observables yielded consistent values except for slightly discrepant closure phases measured by ImPlaneIA. Based on all three sets of calibrated observables, images were reconstructed using three independent software tools: BSMEM, IRBis, and SQUEEZE. All reconstructed image combinations generated consistent images in both F380M and F480M filters. The reconstructed images of WR 137 reveal a bright central core with a ∼300 mas linear filament extending to the northwest. A geometric colliding-wind model with dust production constrained to the orbital plane of the binary system and enhanced as the system approaches periapsis provided a general agreement with the interferometric observables and reconstructed images. Based on a colliding-wind dust condensation analysis, we suggest that dust formation within the orbital plane of WR 137 is induced by enhanced equatorial mass loss from the rapidly rotating O9 companion star, whose axis of rotation is aligned with that of the orbit.
Eta Carinae, the closest, active, massive binary containing a highly unstable Luminous Blue Variable, exhibits expanding, compressed wind shells, seen in emission, that are spatially and spectrally ...resolved by Hubble Space Telescope/Space Telescope Imaging Spectrograph. Starting in 2009 June, these structures were mapped across its 5.54-yr, highly elliptical, binary orbit to follow temporal changes in the light of Fe iii 4659 Å and Fe ii 4815 Å. The emissions trace portions of fossil wind shells, that were formed by wind–wind interactions across each cycle. Over the high-ionization state, dense arcs, photoionized by far-ultraviolet radiation from the hot secondary, are seen in Fe iii. Other arcs, ionized by mid-ultraviolet radiation from the primary star, are seen in Fe ii. The Fe iii structures tend to be interior to Fe ii structures that trace extensive, less disturbed primary wind. During the brief periastron passage when the secondary plunges deep into the primary's extremely dense wind, on the far side of primary star, high-ionization Fe iii structures fade and reappear in Fe ii. Multiple fossil wind structures were traced across the 5.7-yr monitoring interval. The strong similarity of the expanding Fe ii shells suggests that the wind and photoionization properties of the massive binary have not changed substantially from one orbit to the next over the past several orbital cycles. These observations trace structures that can be used to test 3D hydrodynamical and radiative-transfer models of massive, interacting winds. They also provide a baseline for following future changes in η Car, especially of its winds and photoionization properties.
The Na D absorption doublet in the spectrum of η Carinae is complex, with multiple absorption features associated with the Great Eruption (1840s), the Lesser Eruption (1890s), and the interstellar ...clouds. The velocity profile is further complicated by the P Cygni profile originating in the system’s stellar winds and blending with the He i λ5876 profile. The Na D profile contains a multitude of absorption components, including those at velocities of −145 km s−1, −168 km s−1, and +87 km s−1, which we concentrate on in this analysis. Ground-based spectra recorded from 2008 to 2021 show significant variability of the −145 km s−1 absorption throughout long-term observations. In the high-ionization phases of η Carinae prior to the 2020 periastron passage, this feature disappeared completely but briefly reappeared across the 2020 periastron, along with a second absorption at −168 km s−1. Over the past few decades, η Carinae has been gradually brightening, which is shown to be caused by a dissipating occulter. The decreasing absorption of the −145 km s−1 component, coupled with similar trends seen in absorptions of ultraviolet resonant lines, indicate that this central occulter was possibly a large clump associated with the Little Homunculus or another clump between the Little Homunculus and the star. We also report on a foreground absorption component at +87 km s−1. Comparison of Na D absorption in the spectra of nearby systems demonstrates that this redshifted component likely originates in an extended foreground structure consistent with a previous ultraviolet spectral survey in the Carina Nebula.
ABSTRACT
The binary η Carinae is the closest example of a very massive star, which may have formed through a merger during its Great Eruption in the mid-19th century. We aimed to confirm and improve ...the kinematics using a spectroscopic data set taken with the Cerro Tololo Inter-American Observatory 1.5-m telescope over the time period of 2008–2020, covering three periastron passages of the highly eccentric orbit. We measure line variability of H α and H β, where the radial velocity and orbital kinematics of the primary star were measured from the H β emission line using a bisector method. At phases away from periastron, we observed the He ii 4686 emission moving opposite the primary star, consistent with a possible Wolf–Rayet companion, although with a seemingly narrow emission line. This could represent the first detection of emission from the companion.
FUV spectra of η Car, recorded across two decades with HST/STIS, document multiple changes in resonant lines caused by dissipating extinction in our line of sight. The FUV flux has increased nearly ...tenfold, which has led to increased ionization of the multiple shells within the Homunculus and photodestruction of H2. Comparison of observed resonant line profiles with CMFGEN model profiles allows separation of wind–wind collision and shell absorptions from the primary wind P Cygni profiles. The dissipating occulter preferentially obscured the central binary and interacting winds relative to the very extended primary wind. We are now able to monitor changes in the colliding winds with orbital phase. High-velocity transient absorptions occurred across the most recent periastron passage, indicating acceleration of the primary wind by the secondary wind, which leads to a downstream, high-velocity bow shock that is newly generated every orbital period. There is no evidence of changes in the properties of the binary winds.
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