{'fraction_non_alphanumeric': 0.029856533540131833, 'fraction_numerical': 0.017060876308646764, 'mean_word_length': 4.850340136054422, 'pattern_counts': {'":': 0, '<': 1, '<?xml version=': 0, '>': 1, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
A Search For High-Energy Gammarays from Supernova SN1987A

In chapter 5 we present optical spectroscopy in the range U3400-7900A for a total of 52 planetary nebulae (PNe) in the Large Magellanic Cloud (LMC) and 18 in the Small Magellanic Cloud (SMC). This sample contains a large selection of objects of low luminosity, with measurements of line intensities down to -10% of H/?. Brighter objects have line intensities measured down to -2% of H/?. Reddening estimates from Balmer line ratios have been determined: unreddened and reddened line intensities are tabulated. In chapter 6 we present echelle observations of 16 LMC PNe in the [O III] X500lk emission line, 10 of which are previously unobserved. An important property of these objects is that they lie far from the centre of the LMC and hence, their velocities provide strong constraints on the rotation of the LMC. These data have been used in conjunction with previously published data to redetermine the position angle of the kinematic line of nodes, <90, and the systemic Galactocentric velocity, V0, of the LMC. After analysis of our data, combined with data available in the literature, we confirm the previous values derived from PNe, where 6>o~170° and Vo~40kms . The LMC is confirmed to consist of a single disk, and not a dual disk structure as originally proposed by Freeman, Illingworth and Oemler. In chapter 7, we examine the effects of stellar effective temperature, and stellar and nebular metallicities, on the emission line fluxes used in the planetary nebular cosmic distance scale determinations. An absolute calibration of this distance scale is made by determining the metallicitycorrected, cut-off in the luminosity function of PNe. The distance modulus to the LMC is derived by fitting shell He burning PN nucleus evolutionary tracks (presented in chapter 3) to the observations. Distance modulii, relative to the LMC, are also derived for the SMC, Galactic Bulge, M31, and the Virgo cluster, after correcting the absolute PN nuclei luminosities for both stellar age and metallicity effects, and using the observed luminosity function cut-offs for these systems. In all the cases where Cepheid distances are known, a -0.14 mag zero-point offset is found with respect to the PN distance scale. It is concluded that the principle source of uncertainty in the PN distance scale is the intrinsic upper luminosity cut-off of the PN nuclei which, in turn, is critically dependent upon the stellar age (and therefore, mass) distribution, and the treatment of mass loss in the stellar evolutionary models.