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Astron. Astrophys. 317, 694-700 (1997)

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A millimetre search for dust in the globular clusters M 3 and M 22

A.J. Penny 1, A. Evans 2 and M. Odenkirchen 3

1 Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, U.K.
2 Department of Physics, Keele University, Keele, Staffordshire, ST5 5BG, U.K.
3 Sternwarte der Universität Bonn, Auf dem Hügel 71, D-5300 Bonn 1, Germany

Received 15 January 1996 / Accepted 17 June 1996

Abstract

We have conducted the first millimetre wavelength search for interstellar dust within globular clusters, by carrying out observations of M 3 and M 22. We have found no dust in the central [FORMULA] and [FORMULA] of the clusters, respectively, to a limit of [FORMULA] (M 3) and [FORMULA] (M 22), depending on the absorption efficiency assumed for the dust. If, as we argue, the appropriate absorption efficiency is for circumstellar rather than interstellar dust, the smaller upper limits are appropriate. These limits are comparable with, or somewhat tighter than, those obtained in previous searches at other wavelengths, although tighter upper limits on mass per unit area or on mass per unit beam are generally provided by IRAS data. However, observations at millimetre wavelengths are sensitive to dust at significantly lower temperatures. These results are consistent with previous searches for dust in clusters, which have given upper limits below [FORMULA], except for a possible detection in 47 Tuc at the [FORMULA] level.

M 3 and M 22 are expected to have produced some 0.05 [FORMULA] and [FORMULA] [FORMULA] of dust respectively since their last Galactic plane crossing, as calculated from the rate of injection of dust into the interstellar medium by evolving member stars and from the orbits of the clusters. The discrepancy between observation and theory is discussed.

Key words: dust – globular clusters: general – globular clusters: individual (M 3) – globular clusters: individual (M 22) – Galaxy: kinematics and dynamics – dust; extinction

Send offprint requests to: A. J. Penny

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© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998
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