GHOST Commissioning Science Results II: a very metal-poor star witnessing the early Galactic assembly

This study focuses on Pristine$\_180956.78$$-$$294759.8$ (hereafter P180956, [Fe/H] $=-1.95\pm0.02$), a star selected from the Pristine Inner Galaxy Survey (PIGS), and followed-up with the recently commissioned Gemini High-resolution Optical SpecTrograph (GHOST) at the Gemini South telescope. The GHOST spectrograph's high efficiency in the blue spectral region ($3700-4800$~\AA) enables the detection of elemental tracers of early supernovae (e.g. Al, Mn, Sr, Eu), which were not accessible in the previous analysis of P180956. The star exhibits chemical signatures resembling those found in ultra-faint dwarf systems, characterised by very low abundances of neutron-capture elements (Sr, Ba, Eu), which are uncommon among stars of comparable metallicity in the Milky Way. Our analysis suggests that P180956 bears the chemical imprints of a small number (2 or 4) of low-mass hypernovae (\sim10-15\msun), which are needed to reproduce the abundance pattern of the light-elements (e.g. [Si, Ti/Mg, Ca] $\sim0.6$), and one fast-rotating intermediate-mass supernova (\sim300\kms, \sim80-120\msun). Both types of supernovae explain the high [Sr/Ba] of P180956 ($\sim1.2$). The small pericentric (\sim0.7\kpc) and apocentric (\sim13\kpc) distances and its orbit confined to the plane (\lesssim 2\kpc), indicate that this star was likely accreted during the early Galactic assembly phase. Its chemo-dynamical properties suggest that P180956 formed in a system similar to an ultra-faint dwarf galaxy accreted either alone, as one of the low-mass building blocks of the proto-Galaxy, or as a satellite of Gaia-Sausage-Enceladus. The combination of Gemini's large aperture with GHOST's high efficiency and broad spectral coverage makes this new spectrograph one of the leading instruments for near-field cosmology investigations.Comment: Submitted to MNRAS. 8 figures, 15page

The Maunakea Spectroscopic Explorer Book 2018

(Abridged) This is the Maunakea Spectroscopic Explorer 2018 book. It is intended as a concise reference guide to all aspects of the scientific and technical design of MSE, for the international astronomy and engineering communities, and related agencies. The current version is a status report of MSE's science goals and their practical implementation, following the System Conceptual Design Review, held in January 2018. MSE is a planned 10-m class, wide-field, optical and near-infrared facility, designed to enable transformative science, while filling a critical missing gap in the emerging international network of large-scale astronomical facilities. MSE is completely dedicated to multi-object spectroscopy of samples of between thousands and millions of astrophysical objects. It will lead the world in this arena, due to its unique design capabilities: it will boast a large (11.25 m) aperture and wide (1.52 sq. degree) field of view; it will have the capabilities to observe at a wide range of spectral resolutions, from R2500 to R40,000, with massive multiplexing (4332 spectra per exposure, with all spectral resolutions available at all times), and an on-target observing efficiency of more than 80%. MSE will unveil the composition and dynamics of the faint Universe and is designed to excel at precision studies of faint astrophysical phenomena. It will also provide critical follow-up for multi-wavelength imaging surveys, such as those of the Large Synoptic Survey Telescope, Gaia, Euclid, the Wide Field Infrared Survey Telescope, the Square Kilometre Array, and the Next Generation Very Large Array.Comment: 5 chapters, 160 pages, 107 figure

Stamp forming of composite materials : an experimental and analytical study

Composite materials are fast gaining popularity as an alternative to metals for structural and load bearing applications in aerospace, automotive, alternate energy and consumer applications industries. With the advent of thermoplastic composites and advances in recycling technologies, fully recyclable composites are gaining ground over traditional thermosetting composites. For the widespread use of composite material, the cost of manufacturing is one of the key challenges. Stamp forming has been proven to be effective for mass production of components. This thesis investigates the feasibility of using stamp forming technique for the processing of thermoplastic, recyclable composite materials. The investigation includes a detailed experimental study based on the strain measurements using a non-contact optical strain measurement system in conjunction with the stamping equipment to record and measure the formability of the thermoplastic composites in real time. A statistical analysis approach based on Design of Experiments and ANOVA was used to identify the influence of process parameters on the forming behaviour of the composite materials. Significant changes in the forming modes, including increased biaxial stretch and plane strain, experienced by the composite blanks were analysed. The research on the forming modes show that the composite materials can be stamp formed for mass production. To develop a finite element material model to elucidate the response of the material to temperature, an experimental characterisation was undertaken for the two composite materials used. This formed the basis of a temperature dependent, non-linear elastic orthotropic material model which was incorporated into LS-Dyna explicit finite element code. The results from the finite element simulations showed a high degree of correlation with the experimental results. Significant improvement was made over the existing constitutive models of the material library by including the thermal effects on the stress-strain behaviour of the composite materials. This improvement is a world's first in implementing thermal dependency with non-linear orthotropic behaviour for composite materials. This temperature dependency is vital for accurate simulation of stamp forming of heated composite materials. The analysis of the strain measurements and forming modes indicate that significant reduction in compressive strains can be achieved with the application of temperature and blank holder forces. This finding has important ramifications to real world manufacturing where any failure in the flange region could propagate to the areas of interest in a processed part. A through the thickness strain estimate has been studied to illustrate the effect of the forming parameters. An important conclusion that resulted from this investigation is the need for a judicial choice of the process parameters which are paramount to the quality of the manufactured part. These results indicate that composite materials have the potential to exhibit superior forming behaviour compared to aluminium. Currently, aluminium is considered as an attractive, lightweight alternative to steel in the body panels of automobiles. The results from this study indicate that thermoplastic composites have superior forming characteristics to aluminium and hence, have a potential to be the material of choice to reduce the weight of automobiles. - provided by Candidate

Finite Element Analysis and optimization of process parameters during stamp forming of composite materials

In the manufacture of parts for high performance structures using composite materials, the quality and robustness of the parts is of utmost importance. The quality of the produced parts depends largely on the process parameters and manufacturing methodologies. This study presents the use of a temperature dependant orthotropic material for a coupled structural-thermal analysis of the stamp forming process. The study investigated the effects of process parameters such as pre-heat temperature, blank holder force and process time on the formability of composite materials. Temperature was found to be the dominant factor governing the formability of the composite material while higher blank holder forces were deemed to be important for achieving high quality of the parts manufactured. Finally, an optimum set of parameters was used to compare the simulations with experimental results using an optical strain measurement system