LARGE AND KINEMATICALLY UNBIASED SAMPLES OF G- AND K-TYPE STARS. III. EVOLVED YOUNG DISK STARS IN THE BRIGHT STAR SAMPLE

Abstract

ABSTRACT Photometry of evolved young disk population C and K stars in the Bright Star Catalogue, south of Dec. = +30° and between 0h and 12h R.A., is calibrated for luminosity, reddening, and metallicity on the basis of results for members of the Hyades and Sirius superclusters. The photometry is mainly on the four-color, intermediate-band, and RI systems although DDO and Geneva photometry are also included. New DDO photometry is presented for 120 stars. The calibrations lead to values of P[Fe/H], E (b -y), and modulus, respectively, of -0.31 ± 0.03 (σ) dex, 0.030 and 8.0 t ± 0.16 (σ) mag for NGC 752; +0.09 ± 0.06 (σ) dex, 0.058 mag and 9.95 ± 0.29 mag for NGC 2423; +0.24 ± 0.07 (σ) dex, 0.128 mag and 8.00 ± 0.15 (σ) mag for NGC 6633; -0.27 0.02(σ) dex, 0.018 mag and 9.40 ± 0.35 (σ) mag for NGC 2287; and -0.08 dex, 0.038 mag and 8.8 mag for one star in NGC 3532. The Cm index in the DDO system is correlated with unreddened values of(b Y) Cm = 0.70 (b -y) -0.192 for solar composition. The resulting values of ΔCN, measured by ΔCm, show strong correlation with the derived metallicities, P[Fe/H]; P[Fe/H] = 3.3ΔCN for P[Fe/H]≤ +0.3 dex and 10.0 ΔCN for P[Fe/H]> +0.3dex. The existence of stars with P[Fe/H] > +0.3 dex needs spectroscopic confirmation. The spread of CN strength among cluster giants, at a given temperature, may be a function of the metal abundance of the cluster stars. This effect, plus observational error, restricts detection of CN/Fe values between 0.5 and 2 but if CN/Fe > 2 defines "CN-strong" stars, there are none in the young disk sample. Also, less than 5% of the young disk stars have CN/Fe < 0.5. The only nonvariable, peculiar (CH and CH-like) stars in the young disk population are mild Ba ii and weak C-band objects. Stars with composite spectra in the sample include HR 3279, a member of the Sirius supercluster, HR 3, not previously noted as composite, and HR 2773, the central star in the young disk cluster Cr 135, which appears to have an early-type companion with Mv near 0 mag. Although the distribution of the young disk stars in the (U,V) plane appears nonrandom, there is no evidence for undetected aggregates such as the Sirius and Hyades superclusters. The motion of the Sun with respect to these young disk objects is (U,V,W) = (-15, +14 +6) km sec-1.