ASCA X-ray observations of the super-metal-rich stars 30 Ari and eta Boo

We present X-ray observations of two late-type stars, HR 764 (30 Ari B, F4V ) and HR 5235 (eta Boo, G0IV), with photospheric metal abundances about twi ce the solar value. We have derived the coronal temperatures and metallicit ies of these stars, and compared them with those of other stellar X-ray sou rces with solar or sub-solar photospheric composition, already observed wit h ROSAT and ASCA. The X-ray spectra of the two targets can be fitted with i sothermal models yielding temperatures of 6.2 MK and 3.5 MK, and X-ray lumi nosities log L-x = 29.6 and 28.1 erg s(-1), for HR 764 and HR 5235 respecti vely. The best-fit model for HR 764, including a gaussian component which a ccounts for Fe XVII line emission from highly excited states, yields for it s corona a solar (photospheric) iron abundance, while the best-fit iron abu ndance for HR 5235 is about half solar; however, in both cases, the uncerta inties do not allow excluding values consistent with photospheric metallici ties. Instead, the data indicate significant overabundances of Mg and Si by factors 2-3 with respect to the Fe abundance, and suggest low O/Fe abundan ce ratios. We conclude that these two super-metal-rich stars appear to have coronal properties similar to those of other F and G main-sequence stars w ith "normal" photospheric abundances: in particular, HR 764 looks similar t o the Hyades F stars, while the coronal temperature, luminosity and abundan ces of HR 5235 are similar to those of other field G dwarfs slightly younge r than the Sun. The systematic pattern of O, Mg, Si, and Fe coronal abundan ces generally found for solar-type stars observed with ASCA is puzzling, be cause it does not appear related either to the photospheric composition or to the activity level.