EDP Sciences
Free Access
Volume 433, Number 1, April I 2005
Page(s) 305 - 312
Section Stellar atmospheres
DOI https://doi.org/10.1051/0004-6361:20041765

A&A 433, 305-312 (2005)
DOI: 10.1051/0004-6361:20041765

Aldebaran's angular diameter: How well do we know it?

A. Richichi1 and V. Roccatagliata1, 2

1  European Southern Observatory, Karl-Schwarzschildstr. 2, 85748 Garching bei München, Germany
    e-mail: arichich@eso.org
2  Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy

(Received 31 July 2004 / Accepted 28 November 2004 )

The bright, well-known K5 giant Aldebaran , $\alpha$ Tau , is probably the star with the largest number of direct angular diameter determinations, achieved over a long time by several authors using various techniques. In spite of this wealth of data, or perhaps as a direct result of it, there is not a very good agreement on a single angular diameter value. This is particularly unsettling if one considers that Aldebaran is also used as a primary calibrator for some angular resolution methods, notably for optical and infrared long baseline interferometry. Directly connected to Aldebaran's angular diameter and its uncertainties is its effective temperature, which also has been used for several empirical calibrations. Among the proposed explanations for the elusiveness of an accurate determination of the angular diameter of Aldebaran are the possibility of temporal variations as well as a possible dependence of the angular diameter on the wavelength. We present here a few, very accurate new determinations obtained by means of lunar occultations and long baseline interferometry. We derive an average value of $19.96\pm0.03$ milliarcsec for the uniform disk diameter. The corresponding limb-darkened value is $20.58\pm0.03$ milliarcsec, or $44.2\pm0.9$ $R_{\odot}$. We discuss this result, in connection with previous determinations and with possible problems that may affect such measurements.

Key words: occultations -- techniques: high angular resolution -- techniques: interferometric -- stars: fundamental parameters -- stars: individual: $\alpha$ Tau -- stars: individual: Aldebaran

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© ESO 2005