CHROMOSPHERIC CA-II H AND K EMISSION AMONG SUBDWARFS

Echelle spectra have been obtained of the Ca rr H and K lines for a sa mple of metal-poor subdwarf stars as well as for a number of nearby Po pulation I dwarfs selected from among those included in the Mount Wils on HK survey. Phe main conclusion of this paper is that Ca rr H- and K -line emission does occur among subdwarfs. It is particularly notable among those subdwarfs with colours of B - V greater than or equal to 0 .75; all such stars observed exhibit chromospheric emission, although emission is observed among some subdwarfs bluer than this colour. The Ca II K emission profile in most subdwarfs exhibits an asymmetry of V/ R > 1, similar to that seen in the integrated light of the solar disc, Two quantitative indicators of the contrast between the peaks in the emission profile and the neighbouring photospheric line profile are in troduced. Measurements of these indicators show that the level of Ca I I emission among the subdwarfs is similar to that among low-activity P opulation I dwarfs.