A&A 401, 997-1007 (2003)
The Wilson-Bappu effect: A tool to determine stellar distancesG. Pace1, 2, L. Pasquini2 and S. Ortolani3
Dipartimento di Astronomia, Università di Trieste,
via G. B. Tiepolo 11, 34131 Trieste, Italy
European Southern Observatory,
Karl Schwarzschild Strasse 2, 85748
Garching bei München, Germany
Dipartimento di Astronomia, Università di Padova,
Vicolo dell'Osservatorio 5, 35122 Padova, Italy
(Received 12 July 2002 / Accepted 30 January 2003)
Wilson & Bappu (1957) have shown the existence of a remarkable correlation
between the width of the emission in the core of the K line of
the absolute visual magnitude of late-type stars.
Here we present a new calibration of the Wilson-Bappu effect
based on a sample of 119 nearby stars. We use, for the first time, width
measurements based on high resolution and high signal to noise ratio CCD
spectra and absolute visual magnitudes from the Hipparcos
Our primary goal is to investigate the possibility of using the Wilson-Bappu
effect to determine accurate distances to single stars and groups.
The result of our calibration fitting of the Wilson-Bappu
and the determination seems free of systematic effects.
The root mean square error of the fitting
is 0.6 mag. This error is mostly accounted for by measurement
errors and intrinsic variability of
, but in addition
a possible dependence on the metallicity is found, which becomes clearly
noticeable for metallicities below
detection is possible because in our sample [Fe/H] ranges from
-1.5 to 0.4.
The Wilson-Bappu effect can be used
confidently for all metallicities not lower than
, including the
LMC. While it does not provide accurate distances to single stars,
it is a useful tool to determine accurate distances to
clusters and aggregates, where a sufficient number of stars can be observed.
We apply the Wilson-Bappu effect to published
of the open cluster M 67; the retrieved distance modulus is of 9.65 mag,
in very good agreement with the best distance estimations for this
cluster, based on main sequence fitting.
stars: distances --
stars: late-type --
Offprint request: G. Pace, firstname.lastname@example.org
© ESO 2003