Molonglo – its Galactic legacy
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Molonglo – its Galactic legacy. James Caswell (ATNF, CSIRO). Reminiscences that:. Highlight achievements and the People involved. (with abbreviated references, adequate to identify papers via ADS).

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Molonglo – its Galactic legacy

James Caswell (ATNF, CSIRO)

Reminiscences that:

Highlight achievements and the People involved.

(with abbreviated references, adequate to identify papers via ADS).

The early users of the Molonglo Cross at 408 MHz drew the world’s attention to the Galactic capabilities of a high resolution telescope operating at quite low frequency. Low enough to show prominent emission from non-thermal sources (e.g. supernova remnants), yet high enough to see the weak emission from thermal sources (HII regions),

These observations emphasised the immensely better, and more complete, studies possible for Galactic sources when studied with southern hemisphere instruments.

Early users maintained a tradition of publishing in Australian Journal of Physics.

Major Galactic studies with the (408 MHz) Cross

Kesteven 1968a,b; Supernova remnants (SNRs)

Pulsars – various – see later

Shaver and Goss 1970 SNRs and HII regions

Continued by

Green, Clark (David), Caswell, Crawford 1975

Little 1974 - the Galactic centre

Additional Galactic studies with the Cross

Batty (1974) - a brave venture into low frequency recombination line emission.

Calabretta (1982) – planetary nebulae.

X-ray binaries – especially the recognition of SS433 and its surrounding SNR; Cir X-1 and its nebula (Clark et al. 1975 and later).

Barnes & Caswell (1983 etc – more SNRs.

and ,lest it slip through the cracks between Galactic and extragalactic:

The Magellanic Clouds, especially SNRs – Clarke, Mills, Little,Turtle et al., continuing to the MOST era.

Pulsar studies with the Cross

Vela Pulsar - Large, Vaughan & Mills 1968a

Pulsar surveys – majority of known pulsars, 9/16 in 1968 – Large, Vaughan & Wielebinski, 1968b

New pulsar survey1978: 155 new discoveries, doubling existing known sample (1978 Manchester et al); so again the majority of known pulsars from Molonglo;

……………..see next image……………

Returning to the continuum:

Crucial follow-up needed:

Spectral index measurements.


Recombination line checks to prevent HII regions from being mis-classified as SNRs.

Complementary spectral line e.g. HI absorption to establish distances, initially investigated with the Parkes interferometer (Caswell et al. 1975)

Some key achievements from follow-up:

Recognition of many new SNRs. I have not attempted to keep count, but suspect that the role of the cross in SNRs was similar to its role in pulsars. Although no-one seems to have been counting, for many years it was responsible for about half of those known.

Small diameter Galactic source counts from the Cross (and later, the MOST): these provide one of the major constraints on the number of possible young (in past millennium) SNRs.

The MOST – a new era of Galactic studies

843 MHz, and a synthesis mode using EW arm, allowed a beam size as small as 43 arcsec, and many valuable SNR maps e.g.

Roger et al. 1986

Milne et al. 1987

Whiteoak and Green 1996

Some key achievements from follow-up:

Recognition of remarkable morphologies amongst Supernova remnants:

A preponderance of ‘barrels’ (Kesteven and Caswell 1987)

….also, see for example next image from Roger et al. 1988…..

Key achievements, continued:

Delineation of other remarkable morphologies amongst Supernova remnants:

The smoke plume (Roger et al. 1985).

The Wild Goose (Caswell et al. 1985).

The Tornado (Caswell et al. 1989).

The Snake (Gray et al. 1991).

Maintaining the Galactic and Magellanic Clouds SNR momentum

Specifically: University of Sydney students using ATCA to study SNRs:

e.g. Shaun Amy

Brian Gaensler

Andrew Gray

Spectral index, polarization, complementary spectral line (intervening HI , and OH masers at 1720 MHz in associated shocked gas) at high spatial resolution (from the ATCA),

Key achievements, continued:

Discovery of more potential SNR-PSR associations, and follow-up from initial MOST observations.

e.g. G308.8-0.1 (Caswell et al. 1992) and G292.2-0.5, recognised from MOST maps as SNRs (with embedded pulsar), with the association verified by ATCA mapping.

……..see next image (from Caswell et al. 2004)……..

In conclusion:

As a user from outside the Sydney University community, I congratulate you on an instrument that has made such profound contributions to Galactic astronomy.

The University opened the instrument’s availability not only to collaborative projects, but also provided outside users with fully reduced data for their own studies. I, with many others, am deeply appreciative of this far-sighted generosity.

I eagerly await the many valuable Galactic opportunities with the next incarnation as SKAMP.

James Caswell

Molonglo – its Galactic legacy