NAI AND KI SCATTERING IN CIRCUMSTELLAR ENVELOPES - NEW DETECTIONS AROUND GIANTS AND THE NAI LAMBDA-5896 KI LAMBDA-7699 LINE RATIO/

We present new scattering measurements of KI or NaI in circumstellar e nvelopes, with the discovery of emissions around beta Peg (M2.5II-III) , rho Per (M4IIb-IIIa) and CE Tau (M2Iab-Ib), expanding on previous de tections to very low mass-loss rates (10(-9) M. yr(-1)). Supplementary data for alpha Ori and mu Cep, and upper limits for TX Psc, Y CVn, rh o Cas and BU Gem are also given. We homogeneously reanalysed the line surface brightnesses of the envelopes in order to consider the NaI lam bda 5896/KI lambda 7699 line ratio. This ratio is found to be around 3 , within a factor of 2, for the envelopes of mu Cep, alpha Her and o C eti. It is considerably different for alpha Ori, in the sense that NaI is about 80 times too faint. CE Tau also seems to display a similar e ffect. Our analysis suggests that NaI interstellar absorption on the l ine of sight of Betelgeuse is the simplest explanation, though not com pletely convincing. Despite its location in the galactic plane, the Na I-emitting shell around mu Cep would not be so strongly affected by in terstellar NaI owing to a favourable Doppler shift. If the Betelgeuse NaI faintness is due to such an interstellar mutilation (and possibly also to inhomogeneities in the envelopes and measurement errors), our observations strengthen the evidence for a low condensation of K and N a in oxygen-rich envelopes with moderate mass-loss rates (up to simila r to 2-4. 10(-6) M. yr(-1)). We briefly examine other possible, althou gh less probable, explanations like some Na overabundance on mu Cep, o r Na versus K differentiation, as found in comets.