Investigating chromospheric magnetic activity on young stars and the wide field CAMera for UKIRT

Hertzprung-Russell diagrams are one of the most important tools for understanding pre-main sequence evolution when combined with theoretical evolutionary tracks. They are not only used to deduce the properties of the stars they are charting but to estimate the ages of clusters that house them and to investigate the age spreads for episodes of star formation. It is therefore vital that the determination of these dia­grams and tracks are built on solid theoretical and observational foundations. How­ever, work in recent years points to a potential problem. It has long been known that pre-main sequence stars exhibit regions of magnetic activity on their stellar surfaces similar to active regions observed on the Sun. What is not yet well known is the extent to which these active regions cover the stellar surfaces.Most spectral classification relies on moderate resolution optical spectra which tend to be dominated by the non-active photosphere which is hotter than the active regions. Resultant effective temperatures are overestimated if a large portion of the pre-main sequence stellar surface is covered in active regions, which in turn can lead to substantial error in mass and age calculations. This thesis presents a novel approach to measuring the distribution of magnetic regions on T Tauri stars which aims to over­come limitations of other observing techniques such as Doppler imaging or Zeeman measurements. The central line emission from the strong visible Call H & K lines are a proxy indicator of surface magnetic fields and are known through observations of the Sun to be enhanced above active plage regions. Simultaneous optical spectroscopic and photometric observations of a significant sample of fast rotating T Tauri stars in the nearby clusters p Ophiuchus & Upper Scorpius have allowed us to ascertain a di­rect correlation between variations in the Call doublet emissions and light intensities. Computer simulations which model the surface conditions as understood on T Tauri stars and generate correlations which mimic those in the observational data offer a manipulable tool for estimating how much of the stellar surface is covered.The Wide Field CAMera for the UKIRT Telescope on Mauna Kea is currently the most capable infrared imaging survey wide field camera in the world. The instrument focal plane consists of four Hawaii-II 2048 x 2048 IR detectors, to facilitate the best operating conditions and practises for the camera these detectors must be carefully characterised such that inherent qualities can either be corrected or accounted for. The second part of this thesis details the detector characterisation work carried out prior to the instrument delivery to the telescope. Obtaining a correct and stable operating temperature regardless of ambient temperature in the dome enclosure is key to the camera functioning optimally to carry out highly successful surveys. Presented here is a full model of the camera's thermal behaviour for the main instrument and the infrared detectors

Two-stage crustal growth in the Arabian-Nubian shield: Initial arc accretion followed by plume-induced crustal reworking

Island-arc accretion during the assembly of Gondwana has been widely regarded as the main mechanism for Neoproterozoic crustal growth in the Arabian-Nubian Shield (ANS). However, processes involved to transform the newly accreted juvenile terranes into a typical continental crust remain unclear. Here, we present geochemical, isotopic, and U-Pb geochronological data from the El-Shadli volcanic province (80 km × 35 km and > 10 km thick) in the Eastern Desert of Egypt, which lies in the north-western part of the ANS, and overlies strongly deformed, previously accreted arc terranes. The El-Shadli volcanic province consists mainly of a mafic-felsic bimodal suite and subordinate intermediate rocks that intrude the mafic rocks of the suite. The bimodal suite rocks are tholeiitic, whereas the intermediate rocks have a calc-alkaline affinity. The bimodal suite and the intermediate rocks both yield U-Pb zircon ages of ~ 700 Ma implying they are coeval. High zircon εHf(t) values for the bimodal suite (average εHf(t) = +11.46) as well as the intermediate rocks (average εHf(t) = +9.76) indicate they were either magmatic extractions derived directly from a depleted mantle source, or the products of remelting of juvenile crust. Oxygen isotope data for zircon yield similar δ18O values for both the bimodal suite (average δ18O = 4.94‰) and intermediate rocks (average δ18O = 4.79‰). These are lower than typical mantle values indicating the parental magma in both cases interacted with hydrothermal fluids. Based on the petrological, geochemical, and isotopic data, we suggest that the El-Shadli bimodal suite and the intermediate rocks were produced by reworking of MORB-like and arc-like oceanic lithosphere, respectively, most likely driven by a mantle plume during the break-up of Rodinia. The recognition of the El-Shadli volcanic province as a likely mantle plume-induced post-kinematic magmatism provides a mechanism for the transformation of newly accreted juvenile crustal terranes into a chemically stratified normal continental crust. In addition, such plume events may result in new mantle extractions that are converted into new continental crust

LCROSS (Lunar Crater Observation and Sensing Satellite) Observation campaign : strategies, implementation, and lessons learned

NASA's LCROSS (Lunar Crater Observation and Sensing Satellite) mission was designed to explore the nature of previously detected enhanced levels of hydrogen near the lunar poles. The LCROSS mission impacted the spent upper stage of the launch vehicle into a permanently shadowed region of the lunar surface to create an ejecta plume. The resultant impact crater and plume were then observed by the LCROSS Shepherding Spacecraft as well as a cadre of telescopes on the Earth and in space to determine the nature of the materials contained within the permanently shadowed region. The Shepherding Spacecraft then became a second impactor which was also observed by multiple assets. The LCROSS Observation Campaign was a key component of the LCROSS mission. The goal of the Observation Campaign was to realize the scientific benefits of extending the LCROSS observations to multiple ground and space-based assets. This paper describes the LCROSS Observation Campaign and provides an overview of the Campaign coordination and logistics as well as a summary of the observation techniques utilized at a multitude of observatories. Lessons learned from the LCROSS Observation Campaign are also discussed to assist with the planning of future unique observing events.48 page(s