SIMBAD references

NGC 3532 is a very rich southern open cluster of age ∼200-350Myr; 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-ray 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_x∼4x10²⁸erg/s in the center of the field. We detected ∼50 X-ray sources above a 4 σ 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.