Photoelectric photometry of Comet Halley from Mt Tamborine observatory

0083-6656/88 $0.00+ .50 Copyright © 1988 Science Press & Pergamon Journals Ltd.

Vl.~.aain Astronomy, Vol. 31, pp. 165--166, 1988

P H O T O E L E C T R I C P H O T O M E T R Y OF C O M E T H A L L E Y FROM MT TAMBORINE OBSERVATORY

B. 1 2 3 4

D.

Carter

2

i

1,2 J.

Manfroid

C.

Sterken

**

Mt Tamborine Observatory Department of Physics, University of Queensland Institut d'Astrophysique, Universit~ de Liege Astrofysisch Instituut, Vrije Universiteit Brussel

ABSTRACT Post-perihelion photoelectric observations of comet Halley carried out during several weeks are reported. The measurements confirm the existence of large-amplitude night-to-night changes. I. INTRODUCTION The authors participated in the IHW photometry net and carried out observations of comet Halley before and after perihelion passage. This paper reports measurements made by Australian astronomers at Mt Tamborine observing station, a private observatory located close to Australia's east coast about 80 km south of Brisbane.

2. THE OBSERVATIONS All observations were carried out using a standard IAU/IHW filterset which was used in a modified filterwheel of a Pacific Presision Model

124 digital photometer mounted on the Mt Tamborine 32-cm

cassegrain telescope (for a description of the instrument see Page, 1985). The photomultiplier used was a cooled EMI 6256B tube. Observations were carried out through a 3' diaphragm in the usual way, and the sky background measurements were taken at a large distance off the visual

image of the cometary nucleus. Because of extremely

unfavourable weather conditions, at some occasions only a very small number of standard stars and extinction stars could be measured. Due to this situation, rigorous extinction coefficients * Senior Research Associate, F.N.R.S. Belgium *~Research Associate, N.F.W.O. Belgium 165

166 could not be determined, and mean estimated values were used. This of course reflects itself in the final precision, which we estimate to be of the order of about 0. ] mag. 3. RESULTS AND CONCLUSIONS Table

] lists the numerical results for the 484 nm continuum band,

and for the C2 emission band at 520 nm. The data indicate that the cometary head exhibited significant large amplitude irregular variations on a time scale of several days. Unfortunately the data are too few in number to allow any conclusions regarding the true rotational period of the comet.

In spite of the limited precision, our

results stress the usefulness of cometary photoelectric photometry using modest amateur equipment. Compared to photometric estimates made visually,

the photoelectric technique offers higher precision,

and also the possibility to measure in different

Table Date 6503.20 6504.20 6506.20 6510.20 6523.20 6524.20 6526.]0 6527.05 6528.10 6530.05 6531.]0 6535.90 6538.10

ACKNOWLEDGEMENTS

1.

filter passbands.

Measured magnitudes 484nm 5.8 5.8 5.7 6.3 6.9 6.8 6.4 6.4 6.1 6.4 6.7 6.3 6.5

52Ohm C2 4.0 4 ] 3 6 4 5 5 6 54 4 8 5 2 4.5 5.2 5.7 4.9 5.5

The observers are indebted to Dr. A'Hearn for

providing IHW filters, to Dr. B.J. O'Mara, Dr. J.E. Ross, Mr. R.Webb of H e

Physics Department, University of Queensland, and to Mr. P.

Mitropoulos, Mt Tamborine Observatory,

for their assistance in the

redesign of the filterwheel. C.S. and J.M. acknowledge financial support from the Belgian National Fund for Scientific Research,

from

the Vrije Universiteit Brussel, and from ~ e Universite de l'Etat a Liege. REFERENCES Page, A.A.

(1985) Australian Journal of Astronomy,

1, 41.