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

TL;DR

This paper introduces a new calibration for the intrinsic colour index in the uvby-beta photometric system, utilizing updated parallaxes and reddening maps to improve accuracy and consistency with previous calibrations.

Contribution

The paper presents a novel intrinsic-colour calibration for (b-y)0-beta based on Hipparcos parallaxes and reddening maps, with reduced dispersion and minimal zero-point correction.

Findings

Calibration has a small dispersion of ±0.009.

The positive coefficient is similar to previous calibrations.

Reddening for selected stars is effectively zero.

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, $\pm0.009$, 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 $<E(b-y) > = -0.001\pm0.002$ shows that any zero-point correction to our intrinsic-colour equation must be minuscule.