Early Australian Optical and Radio Observations of Centaurus A

Transcription

1 Early Australian Optical and Radio Observations of Centaurus A Peter Robertson A Bruce Slee A, B and Wayne Orchiston A A Centre for Astronomy, James Cook University, Townsville, Qld 4811, Australia B Australia Telescope National Facility, CSIRO, Epping, NSW 2121, Australia The Many Faces of Centaurus A, Sydney, 28 June 3 July 2009

2 Early Australian observations of Cen A Contents Paramatta Observatory and the discovery of NGC 5128 Dover Heights and the discovery of Cen A New Zealand expedition and the first optical identification Further observations of Cen A in the 1950s Back to the future

3 Acknowledgments Marie Louise Ayres (National Library of Australia) Rob Birtles (CSIRO Canberra) Margy Burn (National Library of Australia) Glen Cozens (James Cook University) Ron Ekers (Australia Telescope National Facility) Rod Home (University of Melbourne) Barnaby Norris (Australia Telescope National Facility) Harry Wendt (James Cook University) Early Australian observations of Cen A

4 Paramatta Observatory and the discovery of NGC 5128 Thomas Makdougall Brisbane ( ) Governor of New South Wales [courtesy State Library of NSW]

5 Paramatta Observatory constructed in Recovery of Encke s comet in June 182 Transit telescope used for Catalogue of 7385 stars

6 Dunlop s cottage at Paramatta 9 inch reflecting telescope erected in backyard James Dunlop ( ) [courtesy State Library of NSW]

7 Dunlop s solo work on the catalogue of 621 nebulae and star clusters completed in 1826 Published in the Royal Society s Philosophical Transactions in 1828 Thomas Brisbane and James Dunlop awarded Gold Medal of the Royal Astronomical Society in the same year 1828

8 First observed on 4 August His description of Dunlop 482 (NGC 5128): A very singular double nebula a little unequal. These two nebula are completely distinct from each other, and no connection of the nebulous matters between them Fig. 20 is a good representation.

9 Dover Heights and the Discovery of Centaurus A Early Australian observations of Cen A

10 Dover Heights Site in 1943 Shore defense radar antenna on the blockhouse Antenna removed in 1946 and the blockhouse used for discrete radio source observations from 1947 to 1953

11 Pioneers of radio astronomy Karl Jansky (Bell Labs, New Jersey) Grote Reber (Wheaton, Illinois) James S. Hey (TRE, Malvern, UK) 1946

12 John Bolton, Gordon Stanley and Joe Pawsey

13 The sea interferometer and signals from the Cygnus A source

14 The first three papers Nature February 1948 Australian Journal of Scientific Research H March i 1948 Nature July 1948

15 Probably Cygnus type variable overlapping of the Centaurus and 5.47 sources has so far prevented their accurate location

16 New Zealand Expedition and the First Optical Identifications Early Australian Observations of Cen A

17 Further cliff top observations near Auckland in 1948

18 Identification of Source The limits in the position of the source enclose NGC This object is classed as an extragalactic nebula. It is a seventh magnitude object with a peculiar spectrum. Baade calls it a freak and it is referred to by Shapley as a pathological specimen though no details are known at present as to the exact nature of its peculiarity. Three page report December 1948

19 John Bolton, Gordon Stanley and Bruce Slee. Nature paper in July 1949: It is found that all three sources correspond within limits of experimental error to positions of certain nebulous objects. Centaurus A (NGC 5128) Taurus A (the Crab Nebula) Virgo A (M87)

20 First Radio Spectrum of Cen A Flux densities from three Yagi pairs operating at three frequencies, circa 1949 Typical non thermal spectrum of the unresolved central components The flux density at 100 MHz is about 2000 Jy

21 First Measurement of Angular Size Phase switched 100 MHz compound interferometer in early 1952 Two 4 Yagi antennas with variable spacing up to 21 wavelengths along the cliff top Slow fringes in top row are mainly due to the extended Cen A source. Total flux density about five times that in the central sources Fast fringes at the end of second row are due to the compact inner Cen A components

22 Hole in the ground telescope at Dover Heights

23 Cen A contours at 400 MHz with the 80 ft dish Cen A is clearly resolved 400 MHz with extensions out to 6 deg Central sources are not completely resolved, but their orientation is correct Flux density of the central sources is about 600 Jy

24 Further Observations of Cen A in the 1950s Early Australian observations of Cen A

25 Bernie Mills Interferometer at Badgery s Creek 1952 One of three 101 MHz broadside arrays Base lines to 300 metres Confirmed the intensity and position of Cen A Confirmed the optical identification of Cen A

26 The 18.3 MHz Array at Hornsby Valley 1952 Array consisted of six rows of dipoles arranged in a North South direction with a beamwidth of 17 deg Used as a transit telescope with declination shifted by varying the phasing along the array Operation was only possible at night when interference dropped to a low level

27 18.3 MHz Scans in RA at Five Declinations Excess emission between declinations 42 and 52 deg at RA of h is mostly due to Cen A Peaks at the 22/32 deg scans are from Sgr A at the Galactic centre 18.3 MHz flux density of CenA was measured by interpolating a feasible baseline; its value of 5300 Jy includes the extended component

28 The 85.5 MHz Mills Cross at Fleurs 1955 The North South arm with the receiver hut on the left Each arm was 1500 ft long and beamwidth was 49 arcmin Weakest detectable source had a flux density of ~5 Jy Beamwidth was 49 arcmin

29 Mills Cross Map of Cen A Kevin Sheridan s 85.5 MHz map from 1956 Extended source is 6 deg in the North South orientation, but the central components are barely resolved by the 49 arcmin beam Total 85.5 MHz flux density is 8700 Jy

30 The 36 ft transit dish at Potts Hill The dish was primarily used for HI surveys In 1955 Piddington and Trent made a 600 MHz all sky continuum survey (beamwidth 3.3 deg) In 1958 Hindman and Wade made a 1400 MHz continuum survey of several strong sources (beamwidth 1.4 deg)

31 600 MHz contours from the 36 ft dish (1955) Map is constructed from transit scans taken at many elevations Extended contours are clearly larger than the beam (inset), but the inner two lobes are unresolved Strong sources Taurus A (inset), Sgr A and Cygnus A are clearly visible

32 1400 MHz contours from the 36 ft dish (1958) Hindman & Wade s map of Cen A (beamwidth 1.4 deg) Source extends over 6 deg. in Declination The two central lobes are being resolved

33 Back to the Future [courtesy Life magazine 1951] Early Australian observations of Cen A

34 Paramatta Observatory The Greenwich of the Southern Hemisphere

35 Stone pier for transit telescope Government House at Parramatta [courtesy Glen Cozens]

36 back to Dover Heights 1989 Bruce Slee and John Bolton

37 Bruce Slee Sixty years of radio astronomy