PLEAS£ TYPE THE UNIVERSITY OF NEW SOUTH WALES Thesis/Project Report Sheet Surname or Fam ily name: Dempsey Fi rst name : Jessica Other name/s: Tui Abbreviation for degree as given in the University ca len dar : PhD School: Physics Faculty: Science Title : The view from the ice at the bottom of the world: Optical Astronomy from Antarctica Abstract 350 words maximum: (PLEAS£ TYPE) The high Antarctic plateau may offer the best site on earth for optical astronomy. This thesis work includes the construction of an infrared cloud-observing instrument, COBBER, which utilises a thermopile detector optimised at lOf.Lm. COBBER was installed at Dome C in January 2003. In 71 observing days, only four days of cloud were measured. A detailed study of the effect of auroral emission on optical observations is conducted. Analysis of auroral measurements at South Pole show that in an average winter season, the B band sky brightness is below 21.9 mag/arcsec2 for 50% of the observing time. In V band, the median sky brightness contribution is 20.8 mag/arcsec2 in an average winter. Calculations are used to show that at Dome C, the contribution to sky background in Band Vis up to 3.1 magnitudes less than at South Pole. The first optical stellar spectra observed from the high Antarctic plateau were taken at South Pole station with the Antarctic Fibre Optic Spectrometer (AFOS). The AFOS was installed on a dual­ telescope alt-az mount in January of 2003. A thorough instrument analysis revealed tower sinkage and telescope flexure problems that were overcome with more frequent pointing runs. Two years of AFOS observations are described, including selection of sources, design of observing scripts and the creation of a data reduction method for the data. AFOS data was analysed to determine if the H20 atmospheric absorption bands in the spectra could be used to detect daily variations in the precipitable water vapour (PWV) content of the atmosphere. The PWV values obtained by comparing the AFOS data with synthetic spectra created with MODTRAN were compared to similar measurements taken at South Pole with a 350flm radiometer and balloon-borne radiosondes. The PWV values from these instruments showed good agreement with the AFOS results. Observations of the moon were used to study the earthshine spectrum to detect variations in the earth albedo over a 24-hour period. The earth albedo was successfully detected though poor weather conditions prevented study of any long-term trends in the data. Declaration relating to disposition of project report/thesis I am fully aware of the policy of the University relat ing to the retention and use of higher degree project reports and theses, namely that the University retains the copies subm itted for exam ination and is free to all ow the m to be consulted or borrowed . S u ~ect to the provisions of the Copyright Act 1968. the University may issue a project report or thesis in whole or in part, in photostat or microfilm or other copying medium . I also authorise the publication by University Microfilms of a 350 word abstract in Dissertatian Abstracts International (applicable to doctorates only) . .... ............ ... ..... .. ... ... ' "'" .!2/!.1/9!1. ...... ............... Date The University recogn ises that there may be exceptional circumsta,,._.,, , "'-tu " ,, ~ ,.,,"''""u'', uo -.ul-'~ ,,~ uo onditions on use . Requests for restriction for a period of up to 2 years must be made in w riting to the Registrar. Requests for a longer period of restr iction may be considered in exceptional circumstances if accompanied by a letter of support fro m the Supervisor or Head of School. Such requests must be submitted with the thesis/project report . FOR OFFICE US£ ONLY Date of completion of requirements for Award: Lf( ( /(JS Reaistrar and Deoutv Pr incioal THIS SHEET IS TO BE GLUED TO THE INSIDE FRONT COVER OF THE THESIS The view from the ice at the bottom of the world: Optical Astronomy from Antarctica by Jessica Tui Dempsey A thesis submitted in satisfaction of the requirements for the degree of Doctor of Philosophy in the Faculty of Science. THE UNIVERSITY OF NEW SOUTH WALES_ I~ SYDNEY· AUSTRALIA UNSW 1 1 FEB 2005 LIBRARY For Rodney (1968-2000) Not Without Peril. Statement of Originality I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, nor material which to a substantial extent has been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is acknowledged. (Signed). £ Abstract The high Antarctic plateau has shown exceptional potential for infrared and sub­ millimeter astronomy. Though ground level seeing at South Pole is comparatively poor, new measurements at Dome C have shown the best seeing of any site in the world. As the science case for the optical potential of Dome C strengthens, it is now necessary to quantify the properties of the Antarctic atmosphere for optical astron­ omy, and to demonstrate that astronomical telescopes can be built, maintained and successfully operated in Antarctic conditions. This thesis work includes the construction of an infrared cloud-observing instru­ ment, COBBER (Cloud OBserver), which directs radiation from the sky through a hemispherical ZnSe lens onto a thermopile detector optimised at 10.um. COBBER was installed at Dome C in January of 2003. In 71 observing days, only four days of cloud were recorded. A detailed study of the effect of auroral emission on optical observations has been conducted. Analysis of auroral measurements at South Pole show that in an aver­ age winter season, the B band sky brightness is below 21.9 magnitudes per square arcsecond for 50% of the observing time. In V band, the median sky brightness contribution is 20.8 magnitudes per square arcse,eond in an average winter. Calcu­ lations are used to show that at Dome C, the contribution to sky background in B and Vis up to 3.1 magnitudes less than at South Pole. The use of notch filters to reduce the contribution of the strongest emission lines and bands is also calculated. The science that optical astronomy could potentially achieve with an ELT at Dome C is discussed with reference to the effect auroral emission would have on particular astronomical observations. The first optical stellar spectra observed from the high Antarctic plateau were taken at South Pole station with the Antarctic Fibre Optic Spectrometer (AFOS). The AFOS was installed at South Pole station on a dual-telescope alt-az mount in Abstract ii January of 2003. A thorough instrument study revealed tower sinkage and telescope flexure problems that were overcome with more frequent pointing runs. An analysis of wavelength-dependent attenuation observed in some of the stellar spectra is also presented. Two years of AFOS observations are described, including the selection of sources, the design of observing scripts and the creation of a data reduction method for the stellar spectra collected with the AFOS. AFOS data were analysed to determine if the H20 atmospheric absorption bands in the spectra could be used to detect daily variations in the precipitable water vapour (PWV) content of the atmosphere. The AFOS data was compared with spectra created using the MODTRAN atmospheric modelling program. The resulting PWV values from these daily fits were compared with measurements obtained by a 350J.tm radiometer, and daily balloon-borne ra­ diosondes, at South Pole. The PWV values measured with both instruments showed excellent agreement with the AFOS results, with an accuracy of 10%. In late 2003, the AFOS collected several 24 hour-long observations of the dark side of the moon. These observations were used to study the earthshine spectrum in an effort to detect variations in the earth albedo over a 24 hour period. These obser­ vations are of interest in the search for life on extra-solar planets. The earth albedo was successfully detected in the earthshine measurements. Poor weather conditions at South Pole affected a large percentage of the observations and prevented study of any long-term trends in the earth albedo. Contents Abstract ...... 1 Acknowledgments . viii 1 Introduction 1 1-1 The Antarctic Continent 2 1-2 Site Characterisation . 8 1-2.1 Automated Weather Stations 9 1-2.2 AASTO ....... 10 1-2.3 Optical Site Testing . 14 1-3 DomeC ...... 18 1-3.1 Cloud cover 18 1-3.2 AASTINO. 20 1-4 AFOS ..... 24 1-4.1 History. 26 1-5 Thesis Goals . 27 2 Auroral contribution to optical sky brightness 29 2-1 Introduction . 29 2-1.1 Auroral line intensities and spatial extent . 31 2-1.2 Previous Studies 34 2-2 AFOS Measurements . 36 2-2.1 2000 Lunar Eclipse, South Pole 36 2-3 Auroral Data from South Pole . 37 2-4 Auroral Intensity at Dome C and Dome A 40 Contents iv 2-5 Sky brightness in standard photometric bands 43 2-5.1 B band. 44 2-5.2 Vband 46 2-5.3 R band. 48 2-6 Discussion . 49 2-7 Conclusions 53 3 Cloud cover at Dome C 60 3-1 COBBER ....... 60 3-1.1 COBBER design 61 3-1.2 Testing.