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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

The edge-on, nearby spiral galaxy NGC 5907 has long been used as the prototype of a "non-interacting" warped galaxy. We report here the discovery of two interactions with companion dwarf galaxies that substantially change this picture. First, a faint ring structure is discovered around this galaxy that is likely due to the tidal disruption of a companion dwarf spheroidal galaxy. The ring is elliptical in shape with the center of NGC 5907 close to one of the ring's foci. This suggests the ring material is in orbit around NGC 5907. No gaseous component to the ring has been detected either with deep Hα images or in Very Large Array (VLA) HI 21-cm line maps. The visible material in the ring has an integrated luminosity ≤ 10 8 L ⊙ and its brightest part has a color R-I ∼ 0.9. All of these properties are consistent with the ring being a tidally-disrupted dwarf spheroidal galaxy. Second, we find that NGC 5907 has a dwarf companion galaxy, PGC 54419, projected to be only 36.9 kpc from the center of NGC 5907, close in radial velocity (∆V = 45 km s −1 ) to the giant spiral galaxy. This dwarf is seen at the tip of the HI warp and in the direction of the warp. Hence, NGC 5907 can no longer be considered "non-interacting," but is obviously interacting with its dwarf companions much as the Milky Way interacts with its dwarf galaxies. These results, coupled with the finding by others that dwarf galaxies tend to be found around giant galaxies, suggest that tidal interaction with companions, even if containing a mere 1% of the mass of the parent galaxy, might be sufficient to excite the warps found in the disks of many large spiral galaxies.

We present Spitzer observations for a sample of close major-merger galaxy pairs (KPAIR sample) selected from 2MASS/SDSS-DR3 cross-matches. The goals are to study the star formation activity in these galaxies and to set a local bench mark for the cosmic evolution of close major mergers. The Spitzer KPAIR sample (27 pairs, 54 galaxies) includes all spectroscopically confirmed spiral-spiral (S+S) and spiral-elliptical (S+E) pairs in a parent sample that is complete for primaries brighter than K=12.5 mag, projected separations of 5 ≤ s ≤ 20h −1 kpc, and mass ratios ≤ 2.5. The Spitzer data, consisting of images in 7 bands (3.6, 4.5, 5.8, 8, 24, 70, 160µm), show very diversified IR emission properties. Compared to single spiral galaxies in a control sample, only spiral galaxies in S+S pairs show significantly enhanced specific star formation rate (sSFR=SFR/M), whereas spiral galaxies in S+E pairs do not. Furthermore, the SFR enhancement of spiral galaxies in S+S pairs is highly mass-dependent. Only those with M > ∼ 10 10.5 M show significant enhancement. Relatively low mass (M ∼ 10 10 M ) spirals in S+S pairs have about the same SFR/M compared -2to their counterparts in the control sample, while those with 10 11 M have on average a ∼ 3 times higher SFR/M than single spirals. There is evidence for a correlation between the global star formation activities (but not the nuclear activities) of the component galaxies in massive S+S major-merger pairs (the "Holmberg effect"). There is no significant difference in the SFR/M between the primaries and the secondaries, nor between spirals of SEP < 1 and those of SEP ≥ 1, SEP being the normalized separation parameter. The contribution of KPAIR galaxies to the cosmic SFR density in the local universe is only 1.7%, and amounts to ρ . KPAIR = 2.54 × 10 −4 (M yr −1 Mpc −3 ).