... M 67

Tables 1 and 3 are only available in electronic form via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/382/899

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... survey

WIYN Open Cluster Study. IX.

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...1,

Hubble Fellow.

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... IRAF

IRAF is distributed by the National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.

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...$V \sim 18.5$

Note that the B-V colour-magnitude diagram cuts off at $V \sim 17.5$ due to the limiting B magnitude ( $B \sim 18.5$) and the stellar colours at that magnitude ( $B-V \sim 1$); see Fig. 2.

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... criterion

We note that the magnitude limits of the existing proper-motion surveys (i.e. $V \sim 16$) are much brighter than the faint limit of our survey ( $V \sim 18.5$). Consequently, these variability statistics may not be representative of cluster members fainter than $V \sim 16$.

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... activity

This statement is, of course, dependent on the sensitivity limits of the existing X-ray data. The ROSAT PSPC observations of Belloni et al. (1998) have a limiting $L_X \approx 8 \times 10^{29}$ erg s^-1, which is roughly a factor of 10³ above the X-ray luminosity of the Sun at the peak of its activity cycle (Haisch & Schmitt 1996; Acton 1996). Thus, considerably deeper X-ray observations will be required to definitively rule out the presence of X-ray emission from these "non-X-ray sources".

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