Issue |
A&A
Volume 400, Number 2, March III 2003
|
|
---|---|---|
Page(s) | 541 - 552 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20030092 | |
Published online | 03 March 2003 |
The open cluster distance scale
A new empirical approach
1
Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead, CH41 1LD, UK e-mail: ms@astro.livjm.ac.uk
2
South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa e-mail: dmk@saao.ac.za
Corresponding author: S. M. Percival, smp@astro.livjm.ac.uk
Received:
21
November
2002
Accepted:
9
January
2003
We present new photometry for a sample of 54 local G and K stars with
accurate Hipparcos parallaxes in the metallicity range
.
We use this sample to develop a completely model-independent main sequence (MS) fitting method which
we apply to 4 open clusters – the Hyades, Praesepe, the Pleiades and NGC 2516 – which all
have direct Hipparcos parallax distance determinations. Comparison of our MS-fitting results
with distances derived from Hipparcos parallaxes enables us to explore whether the
discrepancy between the Hipparcos distance scale and other MS-fitting methods found for some
clusters is a consequence of model assumptions.
We find good agreement between our results and the Hipparcos ones for the Hyades and Praesepe.
For the Pleiades and NGC 2516, when adopting the solar abundance determined from spectroscopy, we
find significant disagreement at a level similar to that found by other MS-fitting studies.
However, the colour-colour relationship for both these clusters suggests that their metallicity is
significantly subsolar. Since the MS-fitting method relies on matching the cluster colours to a
template MS, we argue that, when applying this method, the appropriate metallicity to adopt is the
photometric subsolar one, not the solar abundance indicated by spectroscopy.
Adopting photometric metallicities for all 4 clusters, we find complete agreement with the
Hipparcos results and hence we conclude that the mismatch between the spectroscopic and
photometric abundances for the Pleiades and NGC 2516 is responsible for the discrepancies in distance
estimates found by previous studies. The origin of this mismatch in abundance scales remains an
unsolved problem and some possible causes are discussed.
Key words: stars: abundances / stars: distances / open clusters and associations: individual: Hyades, Pleiades
© ESO, 2003
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