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- Weigelt, G., et al.
(författare)
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VLTI-MATISSE chromatic aperture-synthesis imaging of eta Carinae's stellar wind across the Br alpha line Periastron passage observations in February 2020
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 652
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Tidskriftsartikel (refereegranskat)abstract
- Context. Eta Carinae is a highly eccentric, massive binary system (semimajor axis similar to 15.5 au) with powerful stellar winds and a phase-dependent wind-wind collision (WWC) zone. The primary star, eta Car A, is a luminous blue variable (LBV); the secondary, eta Car B, is a Wolf-Rayet or O star with a faster but less dense wind. Aperture-synthesis imaging allows us to study the mass loss from the enigmatic LBV eta Car. Understanding LBVs is a crucial step toward improving our knowledge about massive stars and their evolution. Aims. Our aim is to study the intensity distribution and kinematics of eta Car's WWC zone. Methods. Using the VLTI-MATISSE mid-infrared interferometry instrument, we perform Br alpha imaging of eta Car's distorted wind. Results. We present the first VLTI-MATISSE aperture-synthesis images of eta Car A's stellar windin several spectral channels distributed across the Br alpha 4.052 mu m line (spectral resolving power R similar to 960). Our observations were performed close to periastron passage in February 2020 (orbital phase similar to 14.0022). The reconstructed iso-velocity images show the dependence of the primary stellar wind on wavelength or line-of-sight (LOS) velocity with a spatial resolution of 6 mas (similar to 14 au). The radius of the faintest outer wind regions is similar to 26 mas (similar to 60 au). At several negative LOS velocities, the primary stellar wind is less extended to the northwest than in other directions. This asymmetry is most likely caused by the WWC. Therefore, we see both the velocity field of the undisturbed primary wind and the WWC cavity. In continuum spectral channels, the primary star wind is more compact than in line channels. A fit of the observed continuum visibilities with the visibilities of a stellar wind CMFGEN model (CMFGEN is an atmosphere code developed to model the spectra of a variety of objects) provides a full width at half maximum fit diameter of the primary stellar wind of 2.84 +/- 0.06 mas (6.54 +/- 0.14 au). We comparethe derived intensity distributions with the CMFGEN stellar wind model and hydrodynamic WWC models.
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| 2. |
- Groh, J. H., et al.
(författare)
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Detection of high-velocity material from the wind-wind collision zone of Eta Carinae across the 2009.0 periastron passage
- 2010
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 517
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Tidskriftsartikel (refereegranskat)abstract
- We report near-infrared spectroscopic observations of the Eta Carinae massive binary system during 2008-2009 using the CRIRES spectrograph mounted on the 8m UT 1 Very Large Telescope (VLT Antu). We detect a strong, broad absorption wing in He I lambda 10833 extending up to -1900 km s(-1) across the 2009.0 spectroscopic event. Analysis of archival Hubble Space Telescope/Space Telescope Imaging Spectrograph ultraviolet and optical data identifies a similar high-velocity absorption (up to -2100 km s(-1)) in the ultraviolet resonance lines of Si IV lambda lambda 1394, 1403 across the 2003.5 event. Ultraviolet resonance lines from low-ionization species, such as Si II lambda lambda 1527, 1533 and CII lambda lambda 1334, 1335, show absorption only up to -1200 km s(-1), indicating that the absorption with velocities -1200 to -2100 km s(-1) originates in a region markedly more rapidly moving and more ionized than the nominal wind of the primary star. Seeing-limited observations obtained at the 1.6m OPD/LNA telescope during the last four spectroscopic cycles of Eta Carinae (1989-2009) also show high-velocity absorption in He I lambda 10833 during periastron. Based on the large OPD/LNA dataset, we determine that material with velocities more negative than -900 km s(-1) is present in the phase range 0.976 <= phi <= 1.023 of the spectroscopic cycle, but absent in spectra taken at phi <= 0.947 and phi >= 1.049. Therefore, we constrain the duration of the high-velocity absorption to be 95 to 206 days (or 0.047 to 0.102 in phase). We propose that the high-velocity absorption component originates in shocked gas in the wind-wind collision zone, at distances of 15 to 45 AU in the line-of-sight to the primary star. With the aid of three-dimensional hydrodynamical simulations of the wind-wind collision zone, we find that the dense high-velocity gas is along the line-of-sight to the primary star only if the binary system is oriented in the sky such that the companion is behind the primary star during periastron, corresponding to a longitude of periastron of omega similar to 240 degrees-270 degrees. We study a possible tilt of the orbital plane relative to the Homunculus equatorial plane and conclude that our data are broadly consistent with orbital inclinations in the range i = 40 degrees-60 degrees.
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| 6. |
- Gull, Theodore R., et al.
(författare)
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Eta Carinae : A Tale of Two Periastron Passages
- 2021
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Ingår i: Astrophysical Journal. - : Institute of Physics (IOP). - 0004-637X .- 1538-4357. ; 923:1, s. 102-102
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Tidskriftsartikel (refereegranskat)abstract
- Since 2002, the far-ultraviolet (FUV) flux (1150–1680 Å) of Eta Carinae, monitored by the Hubble Space Telescope/Space Telescope Imaging Spectrograph, has increased by an order of magnitude. This increase is attributed to partial dissipation of a line-of-sight (LOS) occulter that blocks the central core of the system. Across the 2020 February periastron passage, changes in the FUV emission show a stronger wavelength dependence than occurred across the 2003 July periastron passage. Across both periastron passages, most of the FUV spectrum dropped in flux then recovered a few months later. The 2020 periastron passage included enhancements of FUV flux in narrow spectral intervals near periastron followed by a transient absorption and recovery to pre-periastron flux levels. The drop in flux is due to increased absorption by singly ionized species as the secondary star plunges deep into the wind of the primary star, which blocks the companion's ionizing radiation. The enhanced FUV emission is caused by the companion's wind-blown cavity briefly opening a window to deeper layers of the primary star. This is the first time transient brightening has been seen in the FUV comparable to transients previously seen at longer wavelengths. Changes in resonance line-velocity profiles hint that the dissipating occulter is associated with material in LOS moving at −100 to −300 km s−1, similar in velocity of structures previously associated with the 1890s lesser eruption
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| 8. |
- Gull, T. R., et al.
(författare)
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The Strontium Filament within the Homunculus of Eta Carinae
- 2001
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Ingår i: Bulletin of the American Astronomical Society. ; 33:4, s. 1505-1505
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Konferensbidrag (refereegranskat)abstract
- During a series of HST/STIS observations of Eta Carinae and associatedejecta, we noticed a peculiar emission filament located a few arcsecondsnorth of the central source. While bright in nebular standards, it issubmerged in a sea of scattered starlight until moderately highdispersion, long-slit spectroscopy with the STIS (R 8000) brings theemission lines out. The initial spectrum, centered on 6768A with theSTIS G750M grating, led to identification of twenty lines fromsingly-ionized species including [Sr II], [Fe II], [Ti II], [Ni II], [MnII], and [Co II] (Zethson, etal., 2001, AJ 122, 322). No Balmer emissionis detected from this filament and the Fe II 2507,9 lines, known to bepumped by Lyman alpha radiation in other regions near the centralsource, are not detected. Followup observations have led to detection ofhundreds more emission lines from iron group elements in neutral andsingly-ionized states. Thus far all are excited by less than 10 eV. Thispeculiar nebular emission is thought to be due to very intense stellarradiation, stripped of uv flux shortward of Lyman alpha, bathing aneutral structure. We are systematically identifying the many lines(over 90% identified) and measuring line intensities that will then bemodeled to determine excitation mechanisms, temperature and density. Two[Sr II] and two Sr II lines have now been measured. Bautista, etal. (inpreparation) have modeled the strontium flux ratios and find that largeradiation fluxes and/or high strontium abundances may account for thedetected emission. These observations were supported by STIS GTO fundingand GO funding through the STScI.
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