We present nine color CCD intermediate-band spectrophotometry of a two square degree field centered on the old open cluster M67, from 3890$\rm \AA$ to nearly 1$\mu$. These observations are taken as a part of the BATC (Beijing-Arizona-Taipei-Connecticut) Color Survey of the Sky, for both scientific and calibration reasons. With these data we show that the BATC survey can reach its goal of obtaining spectrophotometry to a zero point accuracy of 0.01 mag, and down to V = 21 with 0.3 mag random error. We fit the color-magnitude diagrams (CMDs) with Worthey's theoretical models. The net result is the excellent fit of the 4.0 Gyr, [Fe/H] = $-0.10$ model to our data, including a good fit to the main sequence (MS) turn-off. Our data are consistent with a toy model with 50\% of the stars in M67 being binaries and a random distribution of binary mass-ratios, although other models with different mass-ratio distributions cannot be ruled out. The spatial distribution and mass function (MF) of stars in M67 show marked effects of dynamical evolution and evaporation of stars from the cluster. Blue stragglers and binary stars are the most condensed within the cluster, with degree of condensation depending on mass.We find M67 to have an elongated shape, oriented at an angle of $15^{\circ}$ relative to the galactic plane. Within its tidal radius, the observed MF of M67 between 1.2 $\rm M_\odot$ and $\rm 0.8 M_\odot$ has a Salpeter slope $\rm \eta = -1.93 \pm 0.66$. For stars of mass below 0.8 $\rm M_\odot$, $\rm \eta \sim 0$. It is plausible that the leveling-off of the MF at lower masses is a result of evaporation of lower mass stars in this mass range at a rate of one every $\sim 10^7$ years. If so, it is plausible that the IMF of M67 has the canonical field value of $\rm \eta = -2.0$.Comment: 74 pages, including 19 ps figures. Accepted for publication in AJ, Aug, 199

Based on synthetic flux spectra calculated from theoretical atmospheric models, a calibration of temperature and metallicity for the dwarfs observed in the Beijing-Arizona-Taiwan-Connecticut (BATC) multicolor photometric system is presented in this paper. According to this calibration, stellar effective temperatures can be obtained from some temperature-sensitive color indices. The sample stars have colors and magnitudes in the ranges 0.1 < d − i < 0.9 and 14.0 < i < 20.5. The photometric metallicities for these sample stars can be derived by fitting SEDs. We determine the average stellar metallicity as a function of distance from the Galactic plane. The metallicity gradient is found to be d[Fe/H]/dz = −0.37 ± 0.1 dex/kpc for z < 4 kpc and d[Fe/H]/dz = −0.06 ± 0.09 dex/kpc between 5 and 15 kpc. These results can be explained in terms of different contributions in density distribution for Galactic models 'thin disk', 'thick disk' and 'halo' components. However, for the gradient in z > 5 kpc, it could not be interpreted according to the different contributions from the three components because of the large uncertainty. So it is possible that there is little or no gradient for z > 5 kpc. The overall distribution shows a metallicity gradient d[Fe/H]/dz = −0.17 ± 0.04 dex/kpc for z < 15 kpc.

In certain CCD imaging systems, "intrapixel effects" introduce nonnegligible errors into the photometric accuracy of these systems. This effect is presumably caused by undersampling of the point source image by individual CCD pixels. This undersampling effect shows that the exact location of the source image on a pixel determines the flux detected by that pixel. Thus, as the image center drifts, for various reasons, across a pixel in a series of exposures, a difference in the response from the center to the edge of a pixel results in a variation of flux readout by that pixel. This effect could be important under superb seeing conditions, mimicking microvariability in stellar photometry for imaging systems having certain plate scales. To study this effect in detail, we carried out a full-night monitoring of bright stars in a field using the Beijing-Arizona-Taipei-14 # 14 Connecticut (BATC) observing system. This 10 hr monitoring program shows that all the stars in the field vary periodically with almost the same amplitude and frequency, but that the variations were out of phase among the stars in the field. Furthermore, the variation of all the stars diminished toward the end of the night, as the seeing became worse. Since the flux variation correlates well with the precise location of the image center on a pixel, we attribute these phenomena to the "intrapixel effect" of our CCD imaging system. In this study, we describe the nature of this undersampling effect and its influence on the photometric accuracy. We found that this effect can be modeled and removed if the seeing conditions and the intrapixel positions and motions of stars on the CCD chip are known.