INFRARED HIGH ANGULAR RESOLUTION MEASUREMENTS OF STELLAR SOURCES IV -ANGULAR DIAMETERS AND EFFECTIVE TEMPERATURES OF 15 LATE-TYPE STARS

We have measured the angular diameter of fifteen late-type stars in th e near-infrared using the technique of lunar occultations. Included ar e ten giant stars in the spectral range K0-M10, three M supergiants an d two carbon stars. The resulting uniform-disk angular diameters are i n the range 2.5 to 10.0 milliseconds of are (mas), and the average for mal error is 0.17 mas. In one case where the same occultation has been observed from two different locations, the two diameter determination s agree well within the formal errors. Six of the sources had been res olved earlier by previous lunar occultation observations, and our resu lts are in general agreement and show good reliability. The remaining nine sources are resolved here for the first time. In the case of one carbon star, we find a significant departure of the brightness profile from a simple uniform disk model. In addition, we have obtained near- infrared (and partially visual) photometric observations for all the s ources. Complementing this with available literature data at other wav elengths, we have computed the bolometric fluxes, and used them to der ive the effective temperatures. For this purpose, we have applied a no minal limb-darkening correction to the angular diameters. The average accuracy of our angular diameter determinations is at the level of app roximate to 4%, making it possible in principle to achieve uncertainti es of 2% or approximate to 50 K in the effective temperatures, provide d that sufficiently accurate bolometric fluxes are available. Due to p roblems such as scarcity of photometric data and variability, bolometr ic fluxes represent at present an important limitation in this field. With this work, the set of angular diameter measurements obtained by o ur group comprises about 50 cool stars. This database will be used in a separate work to derive a refined calibration of the effective tempe rature of M giant stars.