http://www.dspace.cam.ac.uk:80/handle/1810/214758 Fri, 24 May 2013 23:20:51 GMT 2013-05-24T23:20:51Z http://www.dspace.cam.ac.uk:80/retrieve/462924/ioa_logo-Small.jpg http://www.dspace.cam.ac.uk:80/handle/1810/214758 http://www.dspace.cam.ac.uk:80/handle/1810/244604 Title: Photograph of memorial medallion of Alfred Russel Wallace Authors: Bruce-Joy, Albert; Spencer, Arthur Description: Photograph by Arthur Spencer of memoral medallion of Alfred Russel Wallace by Albert Bruce-Joy (1915) placed in Westminster Abbey. Also accompanying list of subscribers and advertisement. Fri, 01 Jan 1915 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/244604 1915-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/244601 Title: Sir Robert Ball Authors: Downey, William; Downey, Daniel Description: b/w portrait of astronomer Sir Robert Ball (1840-1913) by W.&D. Downey, London. Thu, 01 Jan 1891 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/244601 1891-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/244592 Title: Plates from "An account of the Aurora Borealis, seen near Cambridge,..." Authors: Morgan, John Holdsworth; Barber, John Thomas; Chabot, C.; Andrews, J. Description: "An account of the Aurora Borealis, seen near Cambridge, October the 24th, 1847: together with those of September 21, 1846, and March 19, 1847, seen at the Cambridge Observatory" by John H. Morgan and John T. Barber. Cambridge: Macmillan, Barclay, and Macmillan, London: G. Bell, Fleet Street. 1848? Scans of 12 plates, printed by C. Chabot, plates II-X by J. Andrews. Sat, 01 Jan 1848 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/244592 1848-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/244373 Title: Inscription on reprint cover Authors: Chandrasekhar, Subrahmanyan Description: Subrahmanyan Chandrasekhar (1910-95) later Nobel prize winner and astrophysicist in 1934 was a student at Trinity College and had visited Soviet observatories in 1933. F.J.M. Stratton (1881-1960) was Director of the Solar Physics Observatory, in Cambridge in 1934. Mon, 01 Jan 1934 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/244373 1934-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/244349 Title: 3-inch refractor telescope Authors: Bateman Description: Identification image only. Telescope is a good example of an amateur astronomy telescope from early 20th cent. Mon, 01 Jan 1900 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/244349 1900-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/244348 Title: 12-inch celestial globe Authors: Denoyer-Geppert Description: A celestial globe for teaching purposes. The stand is home made, the original broke. This image is for identification purposes only. Mon, 01 Jan 1968 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/244348 1968-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243982 Title: Heliostat of solar tunnel, Cambridge Observatories Authors: Jones, Derek H.P. Description: A small photographic print, showing the heliostat of the solar tunnel at Cambridge Observatories, B. E. J. Pagel can just be seen at top L.H. coner. Sat, 31 Aug 1957 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243982 1957-08-31T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243766 Title: Echelle 30g/mm. Authors: Bausch & Lomb Inc. Description: Identification photograph Fri, 01 Jan 1965 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243766 1965-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243765 Title: 47 mm. diameter lens Authors: Steinheil Description: Identification photograph Wed, 01 Jan 1930 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243765 1930-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243764 Title: 72 mm. diameter lens Authors: Broadhurst Clarkson & Co. Description: Identification photograph. Sun, 01 Jan 1950 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243764 1950-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243763 Title: 8-inch lens for spectrometer Authors: Grubb Parsons Description: Identification photograph Sun, 01 Jan 1961 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243763 1961-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243635 Title: Quasi-stars and the Schönberg–Chandrasekhar limit Authors: Ball, Warrick Heinz Abstract: The mechanism by which the supermassive black holes that power bright quasars at high redshift form remains unknown. One possibility is that, if fragmentation is prevented, the monolithic collapse of a massive protogalactic disc proceeds via a cascade of triaxial instabilities and leads to the formation of a quasi-star: a growing black hole, initially of typical stellar-mass, embedded in a hydrostatic giant-like envelope. Quasi-stars are the main object of study in this dissertation. Their envelopes satisfy the equations of stellar structure so the Cambridge STARS code is modified to model them. Analysis of the models leads to an extension of the classical Schönberg–Chandrasekhar limit and an exploration of the implications of this extension for the evolution of main-sequence stars into giants. In Chapter 1, I introduce the problem posed by the supermassive black holes that power high-redshift quasars. I discuss potential solutions and describe the conditions under which a quasi-star might form. In Chapter 2, I outline the Cambridge STARS code and the modifications that are made to model quasi-star envelopes. In Chapter 3, I present models of quasi-stars where the base of the envelope is located at the Bondi radius of the black hole. The black holes in these models are subject to a robust upper fractional mass limit of about one tenth. In addition, the final black hole mass is sensitive to the choice of the inner boundary radius of the envelope. In Chapter 4, I construct alternative models of quasi-stars by drawing from work on convection- and advection-dominated accretion flows around black holes. To improve the accuracy of my models, I incorporate corrections owing to special and general relativity into a variant of the STARS code that includes rotation. The evolution of these quasi-stars is qualitatively different from those described in Chapter 3. Most notably, the core black holes are no longer subject to a fractional mass limit and ultimately accrete all of the material in their envelopes. In Chapter 5, I demonstrate that the fractional mass limit found in Chapter 3, for the black holes in quasi-stars, is in essence the same as the Schönberg–Chandrasekhar limit. The analysis demonstrates how other similar limits are related and that limits exist under a wider range of circumstances than previously thought. A test is provided that determines whether a composite polytrope is at a fractional mass limit. In Chapter 6, I apply this test to realistic stellar models and find evidence that the existence of fractional mass limits is connected to the evolution of stars into the red giants. Mon, 02 Jul 2012 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243635 2012-07-02T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243617 Title: Rotation and magnetism in massive stars Authors: Potter, Adrian Thomas Abstract: Rotation has a number of important effects on the evolution of stars. Apart from structural changes because of the centrifugal force, turbulent mixing and meridional circulation can dramatically affect a star's chemical evolution. This leads to changes in the surface temperature and luminosity as well as modifying its lifetime. Rotation decreases the surface gravity, causes enhanced mass loss and leads to surface abundance anomalies of various chemical isotopes all of which have been observed. The replication of these physical effects with simple stellar evolution models is very difficult and has resulted in the use of numerous different formulations to describe the physics. We have adapted the Cambridge stellar evolution code to incorporate a number of different physical models for rotation, including several treatments of angular momentum transport in convection zones. We compare detailed grids of stellar evolution models along with simulated stellar populations to identify the key differences between them. We then consider how these models relate to observed data. Models of rotationally-driven dynamos in stellar radiative zones have suggested that magnetohydrodynamic transport of angular momentum and chemical composition can dominate over the otherwise purely hydrodynamic processes. If this is the case then a proper consideration of the interaction between rotation and magnetic fields is essential. We have adapted our purely hydrodynamic model to include the evolution of the magnetic field with a pair of time-dependent advection--diffusion equations coupled with the equations for the evolution of the angular momentum distribution and stellar structure. This produces a much more complete, though still reasonably simple, model for the magnetic field evolution. We consider how the surface field strength varies during the main-sequence evolution and compare the surface enrichment of nitrogen for a simulated stellar population with observations. Strong magnetic fields are also observed at the end of the stellar lifetime. The surface magnetic field strength of white dwarfs is observed to vary from very little up to 10^9G. As well as considering the main-sequence evolution of magnetic fields we also look at how the strongest magnetic fields in white dwarfs may be generated by dynamo action during the common envelope phase of strongly interacting binary stars. The resulting magnetic field depends strongly on the electrical conductivity of the white dwarf, the lifetime of the convective envelope and the variability of the magnetic dynamo. We assess the various energy sources available and estimate necessary lifetimes of the common envelope. Mon, 02 Jul 2012 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243617 2012-07-02T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243583 Title: Observatory Club 1947 Jan 30. Authors: Solar Physics Observatory Description: A small card inviting Dr W. H. Steavenson to a meeting of the Observatory Club. On headed card of Solar Physics Observatory, University of Cambridge. Wed, 01 Jan 1947 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243583 1947-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243554 Title: Plates in the region of [lambda] 4250 taken June 1-11, 1911 Authors: Anon. Description: A list of solar spectra plates taken in 1911 by JHB? possibly of 12, Campden Hill Gardens, London W. Probably picked up at an RAS meeting on 14 April 1916 by someone from the Solar Physics Laboratory? Sat, 01 Jan 1916 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243554 1916-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243519 Title: Interior of Cambridge solar tunnel Authors: Anon. Description: A series of b/w photographs of the solar tunnel established at Cambridge in the Solar Physics Observatory building. Sat, 01 Jan 1955 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243519 1955-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243507 Title: 36-inch reflector at Solar Physics Observatory Authors: Anon. Description: Two b/w photographs showing the 36-inch/3-foot reflector of the Solar Physics Observatory at South Kensington. The telescope later came to Cambridge 1912-1953. Mon, 01 Jan 1912 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243507 1912-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243506 Title: Diagram of a spectrometer made in Cambridge Observatory workshop Authors: Anon. Description: Diagram of a spectrometer made in 1959 at the Cambridge Observatory. Thu, 01 Jan 1959 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243506 1959-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243409 Title: Section of wood plank from roof of Thorrowgood Telescope dome Authors: Anon. Description: A section of wood plank from the dome/house of the Thorrowgood Telescope, probably dating from 1927, when established by amateur astronomer William John Thorrowgood (1862 - 1928) at his home in Wimbledon. Sat, 01 Jan 1927 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243409 1927-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243408 Title: Original star from roof-top dome of Cambridge Observatory Authors: Mead, John Clement Description: Image is an identification photograph for the star. The stars were an architectural embellishment to the Observatory and were originally gilded. Wed, 01 Jan 1823 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243408 1823-01-01T00:00:00Z