No description available.

No description available.

Using the Wide Field Camera for the United Kingdom Infrared Telescope (UKIRT), we measure the near-infrared colors of near-Earth objects (NEOs) in order to put constraints on their taxonomic classifications. The rapid-response character of our observations allows us to observe NEOs when they are close to the Earth and bright. Here we present near-infrared color measurements of 86 NEOs, most of which were observed within a few days of their discovery, allowing us to characterize NEOs with diameters of only a few meters. Using machine-learning methods, we compare our measurements to existing asteroid spectral data and provide probabilistic taxonomic classifications for our targets. Our observations allow us to distinguish between S-complex, C/X-complex, D-type, and V-type asteroids. Our results suggest that the fraction of S-complex asteroids in the whole NEO population is lower than the fraction of ordinary chondrites in the meteorite fall statistics. Future data obtained with UKIRT will be used to investigate the significance of this discrepancy.

The recent discovery of objects near the 5:1 Neptune resonance prompts the study of the size, structure, and surface properties of this population to determine if these parameters are consistent with a ‘Nice model’ type evolution of the outer Solar System. Previous TNO discovery surveys have primarily targeted the ecliptic plane, where discovery of high inclination objects such as the 5:1 resonators is unlikely, and theoretical work on the evolution of the outer Solar System has focused on structure in and around the main Kuiper belt and largely ignored the distant resonant TNOs. I tracked these objects for several semesters, measured their positions accurately, and determined precise orbits. Integrating these orbits forward in time revealed that three objects are 5:1 resonators, and one object is not resonant but may have been resonant in the past. I constrained the structure of the 5:1 resonance population based on the three detections and determined that the minimum population in this resonance was much larger than expected, 1900(+3300,−1400) with H < 8. I compared this large population with the orbital distribution of TNOs resulting from a Nice model evolution and determined that the population in the real 5:1 resonance is ~20–100 times larger than the model predicts. However, the structure of the 5:1 resonance in this model was consistent with the orbital distribution I determined based on the detections. The orbital distribution of the scattering population in the Nice model is consistent with other models and survey results, leading to the conclusion that the 5:1 resonance cannot be a steady state transient population produced via resonance sticking from the scattering objects. To test the origin of the 5:1 resonators, I measured the objects’ surface colors in multiple wavelength ranges and compared their surface reflectance to TNOs from a large color survey, ColOSSOS. The 5:1 resonators have a consistent selection criteria to the TNOs from the ColOSSOS survey, so these samples have known selection biases and can be usefully compared to each other. The surfaces of the three 5:1 resonators showed three different spectral reflectance shapes, indicating that these three objects do not share a common formation location. The surface properties and orbital distribution of current 5:1 resonators are consistent with the remnant of a large captured population, partially resupplied by the scattering objects. However, the scattering event which produced this large 5:1 population remains unexplained. / Graduate

We present new models for two low-mass X-ray binaries (LMXB), 4U 1822-371 and V1408 Aql (= 4U 1957+115). The eclipsing LMXB 4U 1822-371 is the prototypical accretion disk corona (ADC) system. We have obtained new time-resolved UV spectroscopy of 4U 1822-371 with the Advanced Camera for Surveys/Solar Blind Channel on the Hubble Space Telescope and new V- and J- band photometry with the 1.3-m SMARTS telescope at Cerro Tololo Inter-American Observatory. We use the new data to construct the UV/optical spectral energy distribution of 4U 1822-371 and its orbital light curve in the UV, V , and J bands. We derive an improved ephemeris for the optical eclipses and confirm that the orbital period is changing rapidly, indicating extremely high rates of mass flow in the system; and we show that the accretion disk in the system has a strong wind with projected radial velocities up to 4400 km s⁻¹. We show that the disk has a vertically extended, optically thick component at optical wavelengths. This component extends almost to the edge of the disk and has a height equal to ~0.5 of the disk radius. As it has a low brightness temperature, we identify it as the optically thick base of the disk wind, not as the optical counterpart of the ADC. Like previous models of 4U 1822-371, ours needs a tall obscuring wall near the edge of the accretion disk, but we interpret the wall as a layer of cooler material at the base of the disk wind, not as a tall, luminous disk rim. V1408 Aql is a black hole candidate. We have obtained new optical photometry of this system in 2008 and 2009 with the Argos photometer on the 2.1-m Otto Struve telescope and optical spectra with the low resolution spectrometer on the Hobby Eberly telescope. From the data we derive an improved optical orbital ephemeris and a new geometric model for the system. The model uses only a simple thin disk without the need for a warped disk or a large disk rim. The orbital variation is produced by the changing aspect of the irradiated secondary star with orbital phase. The new model leaves the orbital inclination unconstrained and allows for inclinations as low as 20 degrees. The spectra is largely featureless continuum with He II and occasionally H[alpha] emission lines, and an absorption line from Na D. The lines are highly variable in strength and wavelength, but the variations do not correlate with orbital phase. / text

W.G. Sebald’s final novel Austerlitz is often framed as a work of “postmemorial” Holocaust fiction. While trauma theory has generated valuable insights about the novel, its emphasis on witnessing (or failing to bear witness) tends to elide other important aspects of the text, most notably the careful attention Austerlitz brings to bear on physical things, spaces, and structures. This essay draws on recent work in object-oriented philosophy to suggest a new theoretical framework for reading Sebald’s last novel. Taking Austerlitz’s meticulous descriptions of the physical world as my starting point, I trace how the text cultivates what Jane Bennett calls a “vital materialism,” or a theory of matter that attends to the vitality of nonhuman objects. Instead of reading ‘through’ these descriptions for what goes unrepresented (“the main scenes of horror,” in Sebald’s phrase), I examine how the novel’s attention to physical surfaces troubles the distinction between material things and immaterial processes like subjectivity, memory, and affective response. Viewed in this light, I suggest that we might understand Sebald’s ‘surface readings’ not as a failure to get beyond the surface to the depths, but as part of an alternative archival practice—one that facilitates, in turn, different modes of ethical engagement. / text

<p>Neutron stars are some of the most fascinating objects in Nature. Essentially all aspects of physics seems to be represented inside them. Their cores are likely to contain deconfined quarks, hyperons and other exotic phases of matter in which the strong interaction is the dominant force. The inner region of their solid crust is penetrated by superfluid neutrons and their magnetic fields may reach well over 10¹²Gauss. Moreover, their extreme mean densities, well above the densities of nuclei, and their rapid rotation rates makes them truly relativistic both in the special as well as in the general sense. This thesis deals with a small subset of these phenomena. In particular the exciting possibility of trapping of gravita-tional waves is examined from a theoretical point of view. It is shown that the standard condition <i>R</i> < 3<i>M</i> is not essential to the trapping mechanism. This point is illustrated using the elegant tool provided by the optical geometry. It is also shown that a realistic equation of state proposed in the literature allows stable neutron star models with closed circular null orbits, something which is closely related to trapped gravitational waves. Furthermore, the general relativistic theory of elasticity is reviewed and applied to stellar models. Both static equilibrium as well as radially oscillating configurations with elasticsources are examined. Finally, Killing tensors are considered and their applicability to modeling of stars is discussed</p>

Using multi-wavelength and multi-epoch observations we examine the evolution of circumstellar disks around pre-main sequence stars from massive, optically thick flared disks to wispy debris disks. We examine a young cluster of nearby stars, identifying likely members and studying dust properties using 3-24μm photometry and accretion rates using optical spectroscopy. We find that 79% of the stars have disks and that almost all of the stars with disks are actively accreting. The stars that show evidence for evolution in their dust properties also exhibit a decrease in the accretion activity suggesting that the evolution of the dust and gas is closely connected. Focusing on a sub-sample of transition disks we study the source of recently discovered infrared variability and whether it can be used to further our understanding of disk structure. We are particularly interested in sources that show a ’seesaw’ behavior in their SED in which the short wavelength infrared flux increases while the long wavelength flux decreases causing the SED to pivot about one wavelength. We develop simple geometric models of disks with nonaxisymmetric structure and find that the precession of this structure is not able to reproduce the strength or the wavelength dependence of observed infrared variability while a model with an inner warp whose scale height rapidly varies is much more successful. We follow this up with detailed observations covering a wide range of wavelengths from optical to mid-infrared of six transition disks in order to better understand the physical source of the variability. We find that the variability is consistent with a variable scale height of the inner disk, finding direct evidence for this effect in two transition disks. Contemporaneous measures of the infrared flux and the accretion rate find in some cases a correlation between these two properties, although in none of our stars is it likely that the accretion rate variability is the source of the infrared variability. The most likely cause is either a companion embedded in the disk or a dynamic interface between the stellar magnetic field and the disk.

No description available.

This thesis argues that the concepts of curiosity and the marvellous resurface at different moments in cultural history, most notably in periods of transition and epistemological uncertainty. The sixteenth- and seventeenth-century ‘culture of curiosity,’ which is characterised by the amateur collector’s engagement with rare and boundary-crossing objects in the process of assembling a cabinet of curiosities, presents a rich contextual foil against which to place the practice of the Surrealists and of some contemporary artists and curators; it has profound resonances for the relationship between modernism and postmodernism, and between art and science. Within modernism, the Surrealists initiated a large-scale, fundamental probing of the principles underlying rationalist thought, and of the categories and hierarchies of academic art and bourgeois taste, which had dominated Western culture since the Enlightenment; and within postmodernism, artists and curators who revert to practices of collecting and appropriate protocols of the natural sciences question institutional frameworks of knowledge production, identity formation and meaning making through material artefacts. In both instances, curiosity and the marvellous – and the related themes of classification and dilettantism – have emerged as especially effective and resonant means of reading dominant culture against the grain. More specifically, this thesis contends that the Surrealist marvellous is rooted in the early modern discourse of the marvellous and monstrous which was characterised by ‘paradoxes of classification.’ This is particularly evident in the Surrealists’ engagement with objects testifying to the natural marvellous and the natural fantastic: stones, coral and insects, among other things and creatures, carry distinctly subversive implications of obscuration, entanglement and excess, metamorphosis and mimicry, and deviation and transgression, straddling the boundaries between art and nature, and art and representation. Furthermore, contemporary artistic and curatorial practice drawing on the ‘age of the marvellous’ – which, in this perspective, extends to Surrealism, with the potential to recur at any time thereafter – is primarily concerned with overcoming ‘white cube’ and Beaux-Arts-Museum historicity, aesthetics and display rationales by reintroducing subjectivity, doubt and digression into the context of the museum and the sciences. In this regard, scepticism towards intellectual certainties and accomplished systems of classification leads to an informed recourse to moments in history when the meanings of objects were being constantly negotiated rather than set in stone.