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Infrared Astronomy with a Balloon Telescope

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Infrared Astronomy with a Balloon Telescope FAR - INFRARED ASTRONOMY WITH A BALLOON TELESCOPE A thesis submitted for the degree of Doctor of Philosophy of the University of London and for the Diploma of Imperial College by Keith Charles Sugden MSc FRAS Blackett Laboratory Imperial College London SW7 March 1978 2 ABSTRACT The world's largest balloon telescope, of 104 cm aperture, has been designed and constructed for use in the atmospherically obscured waveband between wave- lengths of thirty and one thousand microns. Its design incorporates several novel features, including aluminium optics and construction throughout, and it was flown twice to an altitude of thirty kilometres on board the proving flights of the SRC's Stabilised Balloon Platform (SBP) during autumm 1976. It was equipped with two LHe temperature gallium-doped germanium bolometers used in adjacent, broad spectral bands (40 to 80 microns and 90 to 300 microns) for a study of suspected far-infrared emission peaks of 'active' galactic nuclei. Although serious problems with the stabilisation of the SBP precluded the execution of the intended scientific programme, brief observations during the second flight of thermal emission from the bright calibration sources Venus and Saturn per- mitted the determination of consistent figures for the noise equivalent flux density in each waveband -1 (600 and 160 Jy Hz for long and short wavelengths respectively), as well as the shape of the telescope beam pattern (FWHM = 2.2 0.3 aromin). All the tele- scope systems were shown to perform satisfactorily in the stratospheric environment and, in particular, the compensation scheme for instrumental radiation imbalance was very successful. Only minor damage was sustained by the telescope during a parachute descent into a thick pine forest on the first flight and it remains prepared for further flights on the rebuilt SBP. 3 ACKNOWLEDGEMENTS I wish to express my sincere appreciation of the constant support of my parents, Richard and Sybil Sugden of Linton-in-Craven, in the twenty-two year process that has lead to the completion of this thesis and of the encouragement, physical insight, enthusiasm and humanity of my research supervisor, Rob Joseph. During my astronomical career I have also relied on the help of the following individuals, in alphabetical order: Jim Allen who was responsible for the design and construction of the electronics package; Roy Barr and other staff in the astronomy group workshop for the speedy construction of miscell- aneous items; Mr. R.D. Clements of the R.G.O. who has supplied numerous Palomar Sky Survey reproductions and guide star charts for the programme; Rod Davies of Jodrell Bank who revitalised my astrophysical interest and supervised my M.Sc. research in collaboration with Roy Booth; Nic Jackson for photographic advice and assistance; Martin Kessler for the design of the beam chopper and for making available some of his calculations on atmospheric emission; George Masson who designed the telescope structure; Alec McAndrew for advice on the calculation of wavefront aberrations in the telescope; Peter Meikle who assisted with some of the post-,flight analysis; and David Rosen for sorting out my many computing problems. The Analytical Services Laboratory at Imperial College measured our infrared passbands, the Appleton Laboratory was responsible for the construction and operation of the Stabilised Balloon Platform, and the staff of the National Scientific Balloon Facility located at Palestine, Texas provided the integration, ballooning and recovery services with commendable efficiency and frequent good humour. I am grateful for the use of the facilities of Imperial College and for the Science Research Council's support, both for me personally and for our research project. Finally, 4 I declare my appreciation of my brother, Sig. Ugo Sugden of Cagliari, Sardinia, under whose ever hospitable roof part of this thesis was written, and of Miss Sally Reeves, now of Grand Haven, Michigan, who kindly agreed to type some of this manuscript as a labour of love and to whom I would like to dedicate this work. I would like to take this opportunity to apologise for the divers typefaces which appear in the subsequent pages: this has been due to factors beyond my control, such as emigration of personnel, excessive official workloads and indispositions. Consequently, additional acknowlegdements are due to the following: Inge Algurnawi, Sylvia Resch, Jo Vernon, Yvonne Masson and the Amazing Chicco. INDEX ABSTRACT ACKNOWLEGEMENTS LIST OF FIGURES, TABLES AND APPENDICES CHAPTER SECTION TITLE ASTRONOMY IN THE FAR-INFRARED REGION. a Celestial Sources of Far-Infra- red Radiation b Infrared Catalogues c The Galactic Centre d External Galactic Nuclei e An Observing Programme for External Galactic Nuclei II TECHNIQUES OF INFRARED ASTRONOMY a Atmospheric Absorption of Infra- red Radiation. b Platforms for Far-Infrared Observations c Infrared Telescopes d Infrared Detectors III INSTRUMENTATION a IMPERIAL COLLEGE TELESCOPE 1 Telescope Optics 2 Telescope Structure 3 Infrared Beam Chopper 4 Dewar Optics and Bolometers 5 Telescope Alignment 6 Signal Processing and Telemetry 7 Starfield Camera 8 Thermal Insulation of Equipment 9 Design Sensitivity of the Telescope b STABILISED BALLOON PLATFORM General Description 5 2 Usehy the Imperial College Telescope 3 The Coarse and Fine Pointing Modes 4 Pre-Flight Testing of the Pointing Stability c BALLOONING 1 Experimenter's Requirements and Meteorological Factors 2 NCAR Equipment for Flight Control IV FLIGHT HISTORIES a Flight 998-P, 29/30 Nov. 1976 1 Progress of the Flight, Impact and Refurbishment 2 Post-Mortem on the Flight b Flight 1003-P, 16/17 Dec.1976 1 Progress of the Flight and Impact 2 Achievements of the Flight PAYLOAD PERFORMANCE IN FLIGHT a Mechanical and Optical Aspects b Temperature Control of the Sub- systems c Stabilised Balloon Platform Pointing d Starfield Camera e Infrared Beam Modulation f Detector Noise Levels g Electronics and Telemetry 6 CONTENTS (cont'd) CHAPTER SECTION TITLE VI SCIENTIFIC ANALYSIS a 1 Introduction a 2 Outline of the analysis proce- dure and use of a de-differentia- tor b 1 Telescope beam pattern b 2 Focus of the telescope b 3 Saturn observation: unipolarity of signal b 4 Calibration of infrared sensi- tivity i) Location of infrared passbands ii)Infrared flux from Saturn iii)Infrared flux from Venus iv)Telscope sensitivity v) Discussion of telescope efficiency c 1 Introduction to analysis of putative observations c 2 Object 'X' c 3 Object 'Y' c 4 Galactic plane: discrete sources c 5 Galactic plane dust layer c 6 Saturn during flight 998-P VII CONCLUSION REFERENCES FIGURES TABLES APPENDICES 7 LIST OF FIGURES Fig. No. TITLE 1 Far-infrared map of the Galactic centre. 2 Infrared and radio spectra:galaxies detected at 100 microns. 3 Infrared and radio spectra: objects with thermal infrared emission. 4 + 5 Infrared and radio spectra: objects with synchrotron infrared emission. 6 Infrared emission from the atmosphere. 7 Atmospheric emission near the 28 micron H2 line. 8 Telescope optics, illustrating the foci. 9 Diffraction limit and image aberrations of the telescope. 10 Testing the figure of the primary mirror. 11 Testing the figure of the secondary mirror. 12 Spectral emissivity of gold in the infra- red. 13 Photograph of the telescope structure and ancilliary equipment. 14 Side view of the telescope structure. 15 Explanation of the telescope fields of view. 16 Noise spectrum of the bolometer no. 332. 17 Infrared beam chopper. 18 Photograph of an interferogram of the chopper mirror figure. 19 Plan of the dewar optics. 20 Choice of the two infrared passbands. 21 Spectral response of the two infrared channels. 22 Beam patterns of the dewar optics. 23 On-board signal handling by the IC system. 24 Field seen by the SBP X-magnetometer. 25 a Photograph of the gondola ready for launch, flight 998-P. 25 b Photograph of flight 1003-P just after re- lease. 26 NCAR flight equipment for the balloon. 8 Fig. No. TITLE 27 NCAR flight equipment for the payload. 28 a Photograph of the parachute descent, flight 998-P. 28 b Photograph of the impact scene, flight 998-P. 29 Chart of balloon positions and events, flight 1003-P. 30 a Photograph of the impact scene from the air, fl:i.ght 1003-P. 30 b Photograph of the impact scene from the ground, flight 1003-P. 31 Housekeeping data: payload temperatures, flight 1003-P. 32 Housekeeping data: temperature of the LN2 check valve, flight 1003-P. 33 Path of the telescope axis during the scans for Markarian 231. 34 Path of the telescope axis during the scans for NGC 4051. 35 Path of the telescope axis during the Galactic plane scans. 36 Recovery of the chopper motion from a stoppage, flight 998-P. 37 Housekeeping data: IC electronis voltages flight 1003-P. 38 Telescope beam profile. 39 Tilt of the beam chopping angle. 40 A small scale starfield photograph. 41 Detector signals: Saturn observation. 42 " : time delay of the Saturn observations. 43 Detector signals: Venus observation 44 : object 'X', events I, II and IV. 45 Detector signals: object 'X', events V and VI. 46 Detector signals: object 'Y', events I and II. 47 Detector signals: object 'Y', events III and IV. Fig. No. TITLE 48 Detector signals: discrete sources in the Galactic plane, events V,VII and VIII. 49 Detector signals: discrete sources in the Galactic plane, events IX, XII and XIII. 50 Detector signals: 'Saturn' during flight 998-P, events I and II. 51 Detector signals: 'Saturn' during flight 998-P, events III, IV and V 52 Path of the Telescope Axis in Celestial Co-ordinates during flight 1003-P. 53 A large scale starfield photograph: SBP tracking Gamma Corvi 54 A large scale starfield photograph: observation of Saturn, flight 1003-P 55 A large scale starfield photograph: observation of Venus, flight 1003-P 56 Correlation of azimuth oscillatious with pre-amplifier outputs.
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