Serendipitous discovery of an irregular and a semi-regular type variable in the field of BY Draconis

We present new evidence of the optical variability of two red giant stars: HD 172468 and HK Dra, based on photometric and spectroscopic observations. These stars had been included as check stars in our photometric monitoring program of BY Dra and turned out to be variable. HD 172468, whereas almost constant for most of the time, suddenly started t o drop in brightness to such a low level to become undetectable. We suspect that such an abrupt event may be an "obscurational" minimum, that is typic al of eruptive RCB stars, or may be due to the variable extinction by circu mstellar dust in a young Orion type object. HK Dra, already known as an irregular variable, is characterised by periodi c flux modulation with season-to-season changes of the photometric period, as inferred from a periodogram analysis. It also shows changes of the light curve peak-to-peak amplitude and shape. Such a behaviour in giant stars is commonly found among semi-regular giants (SR) at the Asymptotic Giant Bran ch (AGB). Our radial velocity measurements rule out that HK Dra may be a cl ose binary system.