Metallicity and absolute magnitude calibrations for UBV photometry

Details Metallicity and absolute magnitude calibrations for UBV photometry Metallicity and absolute magnitude calibrations for UBV photometry

Oct 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006mnras.371.1793k&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Volume 371, Issue 4, pp. 1793-1812.

Astronomy and Astrophysics

Astronomy

13

Stars: Abundances: Stars: Distances: Solar Neighbourhood, Stars: Abundances, Stars: Distances, Solar Neighbourhood

Scientific paper

Calibrations are presented here for metallicity ([Fe/H]) in terms of the ultraviolet excess, [δ(U - B) at B - V = 0.6, hereafter δ0.6], and also for the absolute visual magnitude (MV) and its difference with respect to the Hyades (ΔMHV) in terms of δ0.6 and (B - V), making use of high-resolution spectroscopic abundances from the literature and Hipparcos parallaxes. The relation [Fe/H]-δ0.6 has been derived for dwarf plus turn-off stars, and also for dwarf, turn-off, plus subgiant stars classified using the MV-(B - V)0 plane of Fig. 11, which is calibrated with isochrones from Bergbusch & VandenBerg (and also VandenBerg & Clem). The [Fe/H]-δ0.6 relations in our equations (5) and (6) agree well with those of Carney, as can be seen from Fig. 5(a). Within the uncertainties, the zero-points, +0.13(+/-0.05) of equation (5) and +0.13(+/-0.04) of equation (6), are in good agreement with the photometric ones of Cameron and of Carney, and close to the spectroscopic ones of Cayrel et al. and of Boesgaard & Friel for the Hyades open cluster. Good quantitative agreement between our estimated [Fe/H] abundances with those from uvby-β photometry and spectroscopic [Fe/H]spec values demonstrates that our equation (6) can be used in deriving quality photometric metal abundances for field stars and clusters using UBV data from various photometric surveys.
For dwarf and turn-off stars, a new hybrid MV calibration is presented, based on Hipparcos parallaxes with σπ/π <= 0.1 and with a dispersion of +/-0.24 in MV. This hybrid MV calibration contains δ0.6 and (B - V) terms, plus higher order cross-terms of these, and is valid for the ranges of +0.37 <= (B - V)0 <= +0.88,- 0.10 <= δ0.6 <= +0.29 and 3.44 <= MV <= 7.23. For dwarf and turn-off stars, the relation for ΔMHV is revised and updated in terms of (B - V) and δ0.6, for the ranges of -0.10 <= δ0.6 <= +0.29, and +0.49 <= (B - V)0 <= +0.89, again making use of Hipparcos parallaxes with σπ/π <= 0.1. These parallaxes for metal-poor dwarf and turn-off stars in our sample reveal that the difference of ΔMHV(B - V) relative to Hyades at (B - V) = +0.70 should be 1.37mag, instead of the 1.58mag given by Laird et al. In general, Hipparcos parallaxes are larger than ground-based ones, causing a divergence of our ΔMHV(B - V,δ0.6) relation (the solid line in Fig. 15b), from the one of Laird et al. (the dashed line) for the range +0.10 <= δ0.6 <= +0.29 our absolute magnitudes are fainter, as has been confirmed for local subdwarfs by Reid. Our final calibrations for ΔMHV(B - V, δ0.6), equations (16) and (17), are third-order polynomials in δ0.6, pass through the origin, and provide photometric distances in reasonable agreement with those obtained directly from Hipparcos parallaxes (Fig. 18).

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