LMC X-1: A New Spectral Analysis of the O-star in the binary and surrounding nebula

We provide new observations of the LMC X-1 O star and its extended nebula structure using spectroscopic data from VLT/UVES as well as H$\alpha$ imaging from the Wide Field Imager on the Max Planck Gesellschaft / European Southern Observatory 2.2m telescope and ATCA imaging of the 2.1 GHz radio continuum. This nebula is one of the few known to be energized by an X-ray binary. We use a new spectrum extraction technique that is superior to other methods to obtain both radial velocities and fluxes. This provides an updated spatial velocity of $\simeq 21.0~\pm~4.8$ km s$^{-1}$ for the O star. The slit encompasses both the photo-ionized and shock-ionized regions of the nebula. The imaging shows a clear arc-like structure reminiscent of a wind bow shock in between the ionization cone and shock-ionized nebula. The observed structure can be fit well by the parabolic shape of a wind bow shock. If an interpretation of a wind bow shock system is valid, we investigate the N159-O1 star cluster as a potential parent of the system, suggesting a progenitor mass of $\sim 60$ M$_{\odot}$ for the black hole. We further note that the radio emission could be non-thermal emission from the wind bow shock, or synchrotron emission associated with the jet inflated nebula. For both wind and jet-powered origins, this would represent one of the first radio detections of such a structure.Comment: 7 Figures, 4 Table

Selecting Sagittarius: a study in kinematics and metallicities

"A thesis submitted to Macquarie University for the degree of Doctor Philosophy, Department of Physics and Astronomy""July 2014"Thesis by publication.Bibliography:pages 147-158.The Sagittarius dwarf galaxy obtained its name from the constellation of the Archer, in which it lies. The dwarf spheroidal itself is part of a much larger system, the parent to a stream of stars which gracefully arches around the entirety of the Milky Way. This system of the Sagittarius dwarf and stream can help us probe how galaxies like the Milky Way formed, and what the dark matter halo of our Galaxy looks like. The current hierarchical scenario for galaxy development holds that many smaller mergers eventually built up into larger galaxies, such as the one we reside in now. The left over building blocks from the process of galaxy assembly should remain identifiable today as distinct structures in the smooth Milky Way halo. The Sagittarius dwarf and stream provide us with the best studied, and most complete, example of such a structure. We investigate the Sagittarius system in detail, obtaining and analysing new spectroscopic data from the Anglo-Australian Telescope. This research project entailed the selection of candidate Sagittarius members from existing photometric data, followed by detailed spectroscopic observations of over 24,110 stars in regions of the Sagittarius dwarf and stream, a sample roughly an order of magnitude larger than previous studies. For each of these stars, we measure kinematics and metallicities. The project is primarily observational, examining the properties of the Sagittarius system, with a comparison to existing models in order to constrain the mass profile of the Milky Ways dark matter halo, through which Sagittarius falls. We find that the distribution of stellar radial velocities in the core corresponds to the predictions of a pressure-supported model for the progenitor to the Sagittarius dwarf galaxy and stream system. We also note that the average metallicity appears to rise in the innermost two degrees of the Sagittarius dwarf core, a property that has been observed in other Local Group dwarf galaxies. We develop a new selection technique to distinguish Sagittarius stream members from a model of the smooth Galactic halo, and find reasonable agreement between our data and the predictions of a simulation in which Sagittarius orbits a Milky Way with a triaxial dark matter halo. This selection technique also yields a surprise detection of the Sextans dwarf in the region of the Sagittarius stream. We additionally apply our methodology to observations of a single field in the Orphan Stream, with promising results. The results of this thesis, both methods and data, have a number of important applications for future research. The technique developed here for distinguishing likely members of stellar overdensities from the smooth Galactic halo can be applied to other datasets covering other areas of the sky. The stellar velocities and metallicities obtained for the Sagittarius core and stream can be used to refine new models for the interaction of Sagittarius and the Milky Way, thereby constraining the properties of the progenitor and of the Galaxy's dark matter halo. Finally, follow-up observations of our targets (such as with high resolution spectroscopy) will allow more detailed analysis of the properties of Sagittarius as well as the other stellar structures identified in this work.Mode of access: World wide web1 online resource (xviii,158 pages) illustrations (some coloured), graphs, chart

Hermes and the Sagittarius dwarf : a low metallicity goldmine?

The Sagittarius dwarf galaxy and its vast associated stellar stream represent the most dramatic example of a satellite accreting onto the Milky Way in the past few billion years. We present an in-depth characterisation of the Sagittarius core using spectra of over 7,000 red giant stars taken with AAOmega on the AAT, and show the first results of stream and core data together. Future observations with HERMES will yield detailed abundances to compare with models of chemical enrichment.2 page(s

Significant populations, lessons learned from the Sagittarius stream

Wrapping around the Milky Way, the Sagittarius dwarf galaxy and its associated stream form the dominant substructure in the halo. Through the use of spectroscopic and photometric selection criteria as well as statistical selection, we have identified 106 likely members of the Sagittarius stream. With this selection we found that the Sagittarius trailing arm exhibits a metallicity gradient, evolving from -0.59 dex to -0.97 dex over the stream. This selection technique is but one possibility for processing of the astronomical data and we note several possible future improvements

The Galah survey : classification and diagnostics with t-SNE reduction of spectral information

Galah is an ongoing high-resolution spectroscopic survey with the goal of disentangling the formation history of the Milky Way using the fossil remnants of disrupted star formation sites that are now dispersed around the Galaxy. It is targeting a randomly selected magnitude-limited (V ≤ 14) sample of stars, with the goal of observing one million objects. To date, 300,000 spectra have been obtained. Not all of them are correctly processed by parameter estimation pipelines, and we need to know about them. We present a semi-automated classification scheme that identifies different types of peculiar spectral morphologies in an effort to discover and flag potentially problematic spectra and thus help to preserve the integrity of the survey results. To this end, we employ the recently developed dimensionality reduction technique t-SNE (t-distributed stochastic neighbor embedding), which enables us to represent the complex spectral morphology in a two-dimensional projection map while still preserving the properties of the local neighborhoods of spectra. We find that the majority (178,483) of the 209,533 Galah spectra considered in this study represents normal single stars, whereas 31,050 peculiar and problematic spectra with very diverse spectral features pertaining to 28,579 stars are distributed into 10 classification categories: hot stars, cool metal-poor giants, molecular absorption bands, binary stars, Hμ/Hβ emission, Hμ/Hβ emission superimposed on absorption, Hμ/Hβ P-Cygni, Hμ/Hβ inverted P-Cygni, lithium absorption, and problematic. Classified spectra with supplementary information are presented in the catalog, indicating candidates for follow-up observations and population studies of the short-lived phases of stellar evolution

Месяц за хмару заходзіць

Месяц за хмару заходзіць, / Он больше не будзе свяціць. / Уехаў мой мілы далёка, / Он больше не будзе любіць

Цячэ вада каламутна

Цячэ вада каламутна, / – Чаму, дзеўка, така смутна? / – Я не смутна, а сярдзіта, / Бо ўчора была біта