New intrinsic-colour calibration for $uvby$--$\beta$ photometry

Abstract

A new intrinsic-colour calibration ($(b$--$y{)}_o$--$\beta$) is presented for the $uvby$--$\beta$ photometric system, making use of re-calibrated Hipparcos parallaxes and published reddening maps. This new calibration for $(b$--$y{)}_o$--$\beta$, our Equation (1), has been based upon stars with $d_{Hip}<70$ pc in the photometric catalogues of Schuster et al. (1988, 1993, 2006), provides a small dispersion, $\pm 0.009$, and has a positive ``standard'' $+2.239\Delta \beta$ coefficient, which is not too different from the coefficients of Crawford (+1.11; 1975a) and of Olsen (+1.34; 1988). For 61 stars with spectra from CASPEC, UVES/VLT, and FIES/NOT databases, without detectable Na I lines, the average reddening value $<E(b-y)>=-0.001\pm 0.002$ shows that any zero-point correction to our intrinsic-colour equation must be minuscule.

18 pages, 3 figures, accepted to New Astronomy

References in corpus (3)

• Validation of the new Hipparcos reduction
• The Geneva-Copenhagen Survey of the Solar neighbourhood II. New uvby calibrations and rediscussion of stellar ages, the G dwarf problem, age-metallicity diagram, and heating mechanisms of the disk
• $uvby-H_{\beta }$ CCD photometry and membership segregation of the open cluster NGC2682 (M67)

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