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Infrared high angular resolution measurements of stellar sources *
IV. Angular diameters and effective temperatures of fifteen late-type stars
A. Richichi 1,
S. Ragland 1,
B. Stecklum 2 and
Ch. Leinert 3
Received 15 December 1997 / Accepted 17 July 1998
We have measured the angular diameter of fifteen late-type stars in the near-infrared using the technique of lunar occultations. Included are ten giant stars in the spectral range K0-M10, three M supergiants and two carbon stars. The resulting uniform-disk angular diameters are in the range 2.5 to 10.0 milliseconds of arc (mas), and the average formal error is 0.17 mas. In one case where the same occultation has been observed from two different locations, the two diameter determinations agree well within the formal errors. Six of the sources had been resolved earlier by previous lunar occultation observations, and our results 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 sources. Complementing this with available literature data at other wavelengths, we have computed the bolometric fluxes, and used them to derive the effective temperatures. For this purpose, we have applied a nominal limb-darkening correction to the angular diameters. The average accuracy of our angular diameter determinations is at the level of 4%, making it possible in principle to achieve uncertainties of 2% or 50 K in the effective temperatures, provided that sufficiently accurate bolometric fluxes are available. Due to problems such as scarcity of photometric data and variability, bolometric fluxes represent at present an important limitation in this field.
With this work, the set of angular diameter measurements obtained by our group comprises about 50 cool stars. This database will be used in a separate work to derive a refined calibration of the effective temperature of M giant stars.
Key words: occultation stars: fundamental parameters stars: late type stars: circumstellar matter
* Based on observations collected at TIRGO (Gornergrat, Switzerland) and at Calar Alto (Spain). TIRGO is operated by CNR - CAISMI Arcetri, Italy. Calar Alto is operated by the German-Spanish Astronomical Center.
Send offprint requests to: A. Richichi e-mail: email@example.com
Online publication: September 14, 1998