NGC 3532 is a very rich southern open cluster of age \sim 200 - 350 Myr ; it is therefore a good candidate to investigate the X-ray activity–age–rotation relationship at ages intermediate between the Pleiades and the Hyades , where , to our knowledge , X-rays studies exist for only one cluster ( NGC 6475 ) .
We have performed an X-ray study of NGC 3532 using HRI observations retrieved from the ROSAT archive .
The observations have a limiting sensitivity L _ { \mathrm { x } } \sim 4 \times 10 ^ { 28 } erg sec ^ { -1 } in the center of the field .
We detected \sim 50 X-ray sources above a 4 \sigma threshold , half of which have a known optical counterpart within 10 arcsec ; 15 of the X-ray sources have at least one cluster member as optical counterpart .

A comparison of NGC 3532 with the nearly coeval cluster NGC 6475 indicates that the former cluster is considerably X-ray underluminous with respect to NGC 6475 .
However , because of the existence of possible selection effects , additional X-ray and optical observations are needed before definitively concluding that the X-ray properties of NGC 3532 and NGC 6475 are significantly different .