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The increasing importance of narrow-band radiations is traced in the recent history of radio astronomy. The need for multi-channel spectrometers to observe these radiations is stressed. The theoretical basis of spectral analysis is given with particular emphasis on autocorrelation or interference methods. A twenty-channel radio-frequency spectrometer designed on interference principles has been constructed and found to perform in accordance with its theory of operation. When used in conjunction with a 25-metre telescope and a hydrogen receiver the spectrometer is capable of producing low-noise wideband spectra at high speed. The spectrometer output was recorded on punched cards, and subsequent data processing was by digital methods. A large area including the position of the spiral galaxy M31 was surveyed with the help of the spectrometer. One hundred and forty-three independent spectra of the 21-cm radiation of atomic hydrogen were obtained and are analyzed in terms of area, velocity, and shape. The major axis of the nebula is found to extend about 2.5° either side of the centre, in agreement with the work of van de Hulst, Raimond, and van Woerden (1957). The length of the minor axis, after correction for the effect of the antenna beamwidth, is only 40', a result which indicates a reduction in the inclination (of the plane of the galaxy to the line of sight) from 14.5° to 8.2°. This lower value leads to an upward revision of the optical axial ratio (of galactic thickness to galactic diameter) to 0.2, while maintaining a low ratio (0.07, Schmidt, 1957) for the distribution of atomic hydrogen. A high axial ratio would clear the way for a reinterpretation of the optical velocities of emission nebulae in M31 (Mayall, 1950), which have so far appeared to be in violent contradiction to the radio velocities (van de Hulst et al, 1957). It is suggested that many of these emission objects may lie some distance from the plane of the galaxy. The position angle of M31, as revealed by the spectrometer observations is distinctly less than the 38° established optically. A new value of 33° is proposed and it is suggested that the former value can be accounted for in terms of an increased axial ratio and the observed asymmetries in the light distribution. The velocity of the centre of gravity of M31 has been obtained by summation of all 143 spectra. The result, -295.6±0.4 km/sec with respect to the local standard of rest, is in complete agreement with that found by van de Hulst (ibid). Radial motions of a few km/sec are possible in the outer parts of M31 but their presence has not been established. Many of the spectra have multiple peaks, which may be interpreted in terms of spiral structure. The velocities of certain concentrations of atomic hydrogen are measurable but their positions are not resolved by the antenna beam. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Thesis (Ph.D.)--Ohio University, March, 2004. / Title from PDF t.p. Includes bibliographical references (p. 95-101)

Study of the time variable sources and phenomena in Astrophysics provides us with important insights into the stellar evolution, galactic evolution, stellar population studies and cosmological studies such as number density of dark massive objects. Study of these sources and phenomena forms the basis of Time Domain surveys, where the telescopes while scanning the sky regularly for a period of time provides us with positional and temporal data of various Astrophysical sources and phenomena happening in the Universe. Our vantage point within the Milky Way galaxy greatly limits studying our galaxy in its entirety. In such a scenario our nearest neighbour The Andromeda galaxy (M31) proves to be an excellent choice as its proximity and inclination allows us to resolve millions of stars using space based telescopes. Zwicky Transient Facility (ZTF) is a new optical time domain survey at Palomar Observatory, which has collected data in the direction of M31 for over 6 months using multiple filters. This Thesis involves exploitation of this rich data set. Stars in M31 are not resolved in ZTF as it is a ground based facility. This requires us to use the large public catalogue of stars observed with Hubble Space Telescope (HST): The Panchromatic Hubble Andromeda Treasury (PHAT). The PHAT catalogue provides us with stellar coordinates and observed brightness for millions of resolved stars in the direction of the M31 in multiple filters. Processing of the large volumes of data generated by the time domain surveys, requires us to develop new data processing pipelines and utilize statistical techniques for determining various statistical features of the data and using machine learning algorithms to classify the data into different categories. End result of such processing of the data is the astronomical catalogues of various astrophysical sources and phenomena and their light curves. In this thesis we have developed a data processing and analysis pipeline based on Forced Aperture Photometry Technique. Since the stars are not resolved in ZTF, we performed photometry at pixel level. Only small portion of the ZTF dataset has been analyzed and photometric light curves have been generated for few interesting sources. In our preliminary investigations we have used a Machine Learning Algorithm to classify the resulting time series data into different categories. We also performed cross comparison with data from other studies in the region of the Andromeda galaxy.