Gladys Vieira Kober

X-Ray Spectral Variation of η Carinae through the 2003 X-Ray Minimum

We report the results of an observing campaign on η Car around the 2003 X-ray minimum, mainly using the XMM-Newton observatory. These are the first spatially resolved X-ray monitoring observations of the stellar X-ray spectrum during the minimum. The hard X-ray emission, associated with the wind-wind collision (WWC) in the binary system, varied strongly in flux on timescales of days, but not significantly on timescales of hours. The X-ray flux in the 2-10 keV band seen by XMM-Newton was only 0.7% of the flux maximum seen by RXTE. The slope of the X-ray continuum above 5 keV did not vary in any observation, which suggests that the electron temperature of the hottest plasma did not vary significantly at any phase. Through the minimum, the absorption to the stellar source increased by a factor of 5-10 to NH ~ (3-4) × 1023 cm-2. These variations were qualitatively consistent with emission from the WWC plasma entering into the dense wind of the massive primary star. During the minimum, X-ray spectra also showed significant excesses in the thermal Fe XXV emission line on the red side, while they showed only a factor of 2 increase in equivalent width of the Fe fluorescence line at 6.4 keV. These features are not fully consistent with the eclipse of the X-ray plasma and may suggest an intrinsic fading of the X-ray emissivity. The drop in the WWC emission revealed the presence of an additional X-ray component that exhibited no variation on timescales of weeks to years. This component may be produced by the collision of high-speed outflows at v ~ 1000-2000 km s-1 from η Car with ambient gas within a few thousand AU from the star.

INTERSTELLAR AND EJECTA DUST IN THE CAS A SUPERNOVA REMNANT

Infrared continuum observations provide a means of investigating the physical composition of the dust in the ejecta and swept up medium of the Cas A supernova remnant (SNR). Using low-resolution Spitzer IRS spectra (5-35 ?m), and broad-band Herschel PACS imaging (70, 100, and 160 ?m), we identify characteristic dust spectra, associated with ejecta layers that underwent distinct nuclear burning histories. The most luminous spectrum exhibits strong emission features at ~9 and 21 ?m and is closely associated with ejecta knots with strong Ar emission lines. The dust features can be reproduced by magnesium silicate grains with relatively low Mg to Si ratios. Another dust spectrum is associated with ejecta having strong Ne emission lines. It has no indication of any silicate features and is best fit by Al2O3 dust. A third characteristic dust spectrum shows features that are best matched by magnesium silicates with a relatively high Mg to Si ratio. This dust is primarily associated with the X-ray-emitting shocked ejecta, but it is also evident in regions where shocked interstellar or circumstellar material is expected. However, the identification of dust composition is not unique, and each spectrum includes an additional featureless dust component of unknown composition. Colder dust of indeterminate composition is associated with emission from the interior of the SNR, where the reverse shock has not yet swept up and heated the ejecta. Most of the dust mass in Cas A is associated with this unidentified cold component, which is 0.1 M ?. The mass of warmer dust is only ~0.04 M ?.

The Mass of the Cepheid V350 Sgr

V350 Sgr is a classical Cepheid suitable for mass determination. It has a hot companion which is prominent in the ultraviolet and which is not itself a binary. We have obtained two high resolution echelle spectra of the companion at orbital velocity maximum and minimum with the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) in the 1320 to 1510 \AA\/ region. By cross-correlating these spectra we obtained the orbital velocity amplitude of the companion with an uncertainty in the companion amplitude of 1.9 km sec

The extended interacting wind structure of Eta Carinae

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Interstellar Absorption-Line Evidence for High-Velocity Expanding Structures in the Carina Nebula Foreground

. This provides a mass ratio of the Cepheid to the companion of 2.1. The ultraviolet energy distribution of the companion provides the mass of the companion, yielding a Cepheid mass of 5.2

An HST COS "SNAPshot" Spectrum of the K-Supergiant (Lambda)Vel (K4Ib-II)

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0.3 M

Resolving the Massive Binary Wind Interaction Of Eta Carinae with HST/STIS

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Analysis of the spectrum of {eta} Car (Nielsen+, 2009)

. This mass requires some combination of moderate main sequence core convective overshoot and rotation to match evolutionary tracks.