42 research outputs found
The X-Ray and Spectropolarimetric View of Mass Loss and Transfer in Massive Binary Stars
The majority of massive stars are members of binary systems. In order to have a better understanding of their evolutionary pathways, the mass and angular momentum loss from massive binaries needs to be well understood. Self consistent explanations for their behavior need to be valid across many wavelength regimes in order to illuminate key phases of mass loss to completely determine how it affects their evolution. In this dissertation I present the results of X-ray and specropolarimetric studies on one Roche-lobe overflow binary (β Lyr) and two colliding wind binaries (V444 Cyg and WR 140).
In β Lyr a repeatable discrepancy between the secondary eclipse in total and polarized light indicates that an accretion hot spot has formed on the edge of the disk in the system. This hot spot may also be the source of the bipolar outflows within the system. The existence of a hot spot and its relationship to bipolar outflows is important in understanding the mass transfer dynamics of Roche-lobe overflow binaries.
The absorption of the 2.0 keV spectral fit component in V444 Cyg suggests that the shock has a large opening angle while analysis of the X-ray light curves places the stagnation point farther away from the O star than theoretically expected. Combining this with evidence of polarimetric variability in V444 Cyg\u27s optical emission lines shows that the effects of radiative inhibition or braking are significant for this close binary and may be important in other colliding wind systems.
Long term X-ray monitoring of the shock formed by the winds in WR 140 shows conflicting evidence for unexpected intrinsic hard X-ray emission. Spectral analysis shows that the low energy thermal tail is causing the observed higher energy emission. On the other hand, light curve analysis of the absorption feature near periastron passage suggests that there may be intrinsic hard X-ray emission from the system. WR 140\u27s polarimetric behavior is consistent with the formation of dust near periastron passage, better polarimetric monitoring of the system is needed.
The work presented in this dissertation is one small step toward a better understanding of the processes involved in mass loss in binary systems. Continued studies of these three objects, in addition to other important systems, will provide important new constraints on the mass loss structures that influence the future evolution of massive binary systems
Barriers and Contradictions in the Resettlement of Single Homeless People
Research in one local authority area suggests that a number of social policy difficulties and contradictions need to be resolved if single homeless people are to be resettled effectively. In particular, there are competing pressures on social housing providers, who are expected to meet the needs of socially excluded individuals while also creating sustainable communities and operating in a cost efficient manner. The government needs to clarify that meeting housing need is a priority for social landlords, and provide adequate funding for long-term support, if single homeless people are to find appropriate permanent accommodation
Optical Coronagraphic Spectroscopy of AU Mic: Evidence of Time Variable Colors?
We present coronagraphic long slit spectra of AU Mic's debris disk taken with
the STIS instrument aboard the Hubble Space Telescope (HST). Our spectra are
the first spatially resolved, scattered light spectra of the system's disk,
which we detect at projected distances between approximately 10 and 45 AU. Our
spectra cover a wavelength range between 5200 and 10200 angstroms. We find that
the color of AU Mic's debris disk is bluest at small (12-35 AU) projected
separations. These results both confirm and quantify the findings qualitatively
noted by Krist et al. (2005), and are different than IR observations that
suggested a uniform blue or gray color as a function of projected separation in
this region of the disk. Unlike previous literature that reported the color of
AU Mic's disk became increasingly more blue as a function of projected
separation beyond approximately 30 AU, we find the disk's optical color between
35-45 AU to be uniformly blue on the southeast side of the disk and
decreasingly blue on the northwest side. We note that this apparent change in
disk color at larger projected separations coincides with several fast, outward
moving "features" that are passing through this region of the southeast side of
the disk. We speculate that these phenomenon might be related, and that the
fast moving features could be changing the localized distribution of sub-micron
sized grains as they pass by, thereby reducing the blue color of the disk in
the process. We encourage follow-up optical spectroscopic observations of the
AU Mic to both confirm this result, and search for further modifications of the
disk color caused by additional fast moving features propagating through the
disk.Comment: Accepted by AJ, 13 pages, 8 figures, 1 tabl
Modeling the Optical to Ultraviolet Polarimetric Variability from Thomson Scattering in Colliding-wind Binaries
peer reviewedAbstract
Massive-star binaries are critical laboratories for measuring masses and stellar wind mass-loss rates. A major challenge is inferring viewing inclination and extracting information about the colliding-wind interaction (CWI) region. Polarimetric variability from electron scattering in the highly ionized winds provides important diagnostic information about system geometry. We combine for the first time the well-known generalized treatment of Brown et al. for variable polarization from binaries with the semianalytic solution for the geometry and surface density CWI shock interface between the winds based on Cantó et al. Our calculations include some simplifications in the form of inverse-square law wind densities and the assumption of axisymmetry, but in so doing they arrive at several robust conclusions. One is that when the winds are nearly equal (e.g., O+O binaries) the polarization has a relatively mild decline with binary separation. Another is that despite Thomson scattering being a gray opacity, the continuum polarization can show chromatic effects at ultraviolet wavelengths but will be mostly constant at longer wavelengths. Finally, when one wind dominates the other, as, for example, in WR+OB binaries, the polarization is expected to be larger at wavelengths where the OB component is more luminous and generally smaller at wavelengths where the WR component is more luminous. This behavior arises because, from the perspective of the WR star, the distortion of the scattering envelope from spherical is a minor perturbation situated far from the WR star. By contrast, the polarization contribution from the OB star is dominated by the geometry of the CWI shock
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Constraining the Movement of the Spiral Features and the Locations of Planetary Bodies within the AB Aur System
We present new analysis of multi-epoch, H-band, scattered light images of the
AB Aur system. We used a Monte Carlo, radiative transfer code to simultaneously
model the system's SED and H-band polarized intensity imagery. We find that a
disk-dominated model, as opposed to one that is envelope dominated, can
plausibly reproduce AB Aur's SED and near-IR imagery. This is consistent with
previous modeling attempts presented in the literature and supports the idea
that at least a subset of AB Aur's spirals originate within the disk. In light
of this, we also analyzed the movement of spiral structures in multi-epoch
H-band total light and polarized intensity imagery of the disk. We detect no
significant rotation or change in spatial location of the spiral structures in
these data, which span a 5.8 year baseline. If such structures are caused by
disk-planet interactions, the lack of observed rotation constrains the location
of the orbit of planetary perturbers to be >47 AU.Comment: 8 pages, 3 figures, 1 table, Accepted to Ap
Informatics Enhanced SNP Microarray Analysis of 30 Miscarriage Samples Compared to Routine Cytogenetics
Purpose: The metaphase karyotype is often used as a diagnostic tool in the setting of early miscarriage; however this technique has several limitations. We evaluate a new technique for karyotyping that uses single nucleotide polymorphism microarrays (SNP). This technique was compared in a blinded, prospective fashion, to the traditional metaphase karyotype. Methods: Patients undergoing dilation and curettage for first trimester miscarriage between February and August 2010 were enrolled. Samples of chorionic villi were equally divided and sent for microarray testing in parallel with routine cytogenetic testing. Results: Thirty samples were analyzed, with only four discordant results. Discordant results occurred when the entire genome was duplicated or when a balanced rearrangement was present. Cytogenetic karyotyping took an average of 29 days while microarray-based karytoyping took an average of 12 days. Conclusions: Molecular karyotyping of POC after missed abortion using SNP microarray analysis allows for the ability to detect maternal cell contamination and provides rapid results with good concordance to standard cytogenetic analysis