Astronomy & Astrophysics

Free access article

Issue		A&A Volume 377, Number 3, October III 2001
Page(s)		981 - 993
Section		Stellar atmospheres
DOI		10.1051/0004-6361:20011124

A&A 377, 981-993 (2001)
DOI: 10.1051/0004-6361:20011124

Direct multi-wavelength limb-darkening measurements of three late-type giants with the Navy Prototype Optical Interferometer

M. Wittkowski¹, C. A. Hummel², K. J. Johnston², D. Mozurkewich³, A. R. Hajian² and N. M. White⁴

¹ Universities Space Research Association (USRA), 300 D Street SW, Suite 801, Washington, DC 20024, USA Mailing address: U.S. Naval Observatory, AD5, 3450 Massachusetts Avenue NW, Washington, DC 20392, USA
² U.S. Naval Observatory, 3450 Massachusetts Avenue NW, Washington, DC 20392, USA
    e-mail: cah@usno.navy.mil, kjj@astro.usno.navy.mil, hajian@usno.navy.mil
³ Naval Research Laboratory, Code 7210, Washington, DC 20375, USA
    e-mail: mozurk@rsd.nrl.navy.mil
⁴ Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA
    e-mail: nmw@lowell.edu

(Received 22 January 2001 / Accepted 9 August 2001)

Abstract
We present direct measurements of the limb-darkened intensity profiles of the late-type giant stars HR 5299, HR 7635, and HR 8621 obtained with the Navy Prototype Optical Interferometer (NPOI) at the Lowell Observatory. A triangle of baselines with lengths of 18.9 m, 22.2 m, and 37.5 m was used. We utilized squared visibility amplitudes beyond the first minimum, as well as triple amplitudes and phases in up to 10 spectral channels covering a wavelength range of ${\sim}650$ nm to ${\sim}850$ nm. We find that our data can best be described by featureless symmetric limb-darkened disk models while uniform disk and fully darkened disk models can be rejected. We derive high-precision angular limb-darkened diameters for the three stars of 7.44 mas $\pm$ 0.11 mas, $6.18 {\rm mas}\pm0.07$ mas, and $6.94 {\rm mas}\pm0.12$ mas, respectively. Using the HIPPARCOS parallaxes, we determine linear limb-darkened radii of $114 R_\odot\pm 13 R_\odot$ , $56 R_\odot\pm 4 R_\odot$ , and $98 R_\odot\pm 9 R_\odot$ , respectively. We compare our data to a grid of Kurucz stellar model atmospheres, with them derive the effective temperatures and surface gravities without additional information, and find agreement with independent estimates derived from empirical calibrations and bolometric fluxes. This confirms the consistency of model predictions and direct observations of the limb-darkening effect.

Key words: techniques: interferometric -- techniques: high angular resolution -- stars: fundamental parameters -- stars: atmospheres -- stars: late-type

Offprint request: M. Wittkowski, mwittkow@eso.org

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