AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 82. A Stellar and Variable Star Melange
Display, Thursday, June 3, 1999, 9:20am-4:00pm, Southwest Exhibit Hall

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[82.05] Stellar Angular Diameters from the NPOI and Mark III: A Comparison

T. E. Nordgren (USNO - NPOI)

With recent advances in measuring stellar angular diameters, comparisons to various atmosphere models can best be made provided that diameter measurements are obtained over a range of wavelengths. For instance, in order to understand the effects of molecular opacities in cool stellar atmospheres, angular diameter measurements must be made at wavelengths in both the optical and infrared. Over the last decade, interferometers operating in the optical (Mark III and NPOI) and infrared (IOTA and PTI) have undertaken large surveys of stellar angular diameters. These observations span the spectral range from 451 nm with Mark III to 2.2 microns with IOTA and PTI. However, before comparisons can be made between diameters from different telescopes observing at different wavelengths one must first know what, if any, difference exists between diameter measurements from different telescopes observing at the same wavelength. The NPOI has just finished a program of observing late-type giant and supergiant stars with Mark III diameters. The difference in mean wavelengths between these two surveys is only 50 nm. Preliminary results show the Mark III diameters average less than 2% larger than the NPOI diameters but with a rms scatter making the difference between these two surveys consistent with zero.

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