We have obtained UBVRI images with the Kitt Peak National Observatory and Cerro Tololo Inter-American Observatory 4m telescopes and Mosaic cameras of seven dwarfs in (or near) the Local Group, all of which have known evidence of recent star formation: IC 10, NGC 6822, WLM, Sextans B, Sextans A, Pegasus, and Phoenix. We construct color-magnitude diagrams (CMDs) of these systems, as well as neighboring regions that can be used to evaluate the degree of foreground contamination by stars in the Milky Way.
UBVRI photoelectric observations have been made on the Johnson-Kron-Cousins photometric system of 526 stars centered on the celestial equator. The program stars within a 298 number subset have sufficient measures that they are capable of providing, for telescopes of intermediate and large size in both hemispheres, an internally consistent homogeneous broadband standard photometric system around the sky. The stars average 29 measures each on 19 nights. The majority of the stars in this paper fall in the magnitude range 11.5 < V < 16.0, and in the color range -0.3 < (B-V) < +2.3.
The three open clusters Be 15, Be 80 and NGC 2192 have been observed using CCD UBV(RI)C photometry at the San Pedro Martir Observatory, Mexico within the framework of our open-cluster survey. The fundamental parameters of interstellar reddening, distance and age have been derived, and also the metallicity for NGC 2192 (solar metallicity has been assumed for the other two).
UBVRI photoelectric photometry was obtained in the field of the open cluster Tr 18. From the analysis of the data we confirm that several distant OB stars were wrongly assumed as cluster members in previous investigations. The true distance modulus is 10.95, equivalent to a distance of 1550pc with the adopted age of (9.0+/-1.0)x10^7^yr. The GH Car Cepheid variable is very much probably a cluster member in view of its spatial position and the average absolute magnitude. However, some arguments are given to suggest that the reality of this cluster is still an open question. The observations in the Cousins system were carried out during 9 nights in April 1989 at Cerro Tololo Interamerican Observatory, with a single channel photometer attaéched to the 60cm Lowell telescope. The positions and identifications with large astrometric surveys was achieved by B. Skiff (Lowell Obs.) in 2010.
We present wide-field, ground-based Johnson-Cousins UBVRI photometry for 48 Galactic globular clusters based on almost 90000 public and proprietary images. The photometry is calibrated with the latest transformations obtained in the framework of our secondary standard project, with typical internal and external uncertainties of order a few millimagnitudes. These data provide a bridge between existing small-area, high-precision HST photometry and all sky-catalogues from large surveys like Gaia, SDSS, or LSST. For many clusters, we present the first publicly available photometry in some of the five bands (typically U and R). We illustrate the scientific potential of the photometry with examples of surface density and brightness profiles and of colour-magnitude diagrams, with the following highlights: (i) we study the morphology of NGC 5904, finding a varying ellipticity and position angle as a function of radial distance; (ii) we show $U$-based colour-magnitude diagrams and demonstrate that no cluster in our sample is free from multiple stellar populations, with the possible exception of a few clusters with high and differential reddening or field contamination, for which more sophisticated investigations are required. This is true even for NGC 5694 and Terzan 8, that were previously considered as (mostly) single-population candidates.
We report new detailed surface U, B, V, R, and I photometry of 81 stellar structures in the disk of the barred galaxy NGC 3367. The images show many different structures, indicating that star formation is going on in most parts of the disk. NGC 3367 is known to have a very high concentration of molecular gas distribution in the central regions of the galaxy and bipolar synchrotron emission from the nucleus, with two lobes (at 6kpc) forming a triple structure similar to a radio galaxy. We have determined the U, B, V, R, and I magnitudes and U-B, B-V, U-V, and V-I colors for the central region (nucleus), a region which includes supernova 2003 AA, and 79 star associations throughout NGC 3367.
The very luminous blue supergiant HD 80077 has been claimed to be a member of the young open cluster Pismis 11, and hence a hypergiant. Membership of the cluster would mean that it is one of the brightest stars in the Galaxy, and one of the few evolved very massive stars whose distance can be accurately determined. We carry out a comprehensive study of the open cluster Pismis 11, which allows us to derive with accuracy its distance and reddening. We obtained UBVRI photometry of the cluster field and low-resolution spectroscopy of a number of putative members. We derive spectral types from the spectra and determine that the reddening in this direction is standard. We then carry out a careful photometric analysis that allows us to determine individual reddening values, deriving unreddened parameters that are used for the main sequence fit.
We investigate the relationship between the spatial distributions of stellar populations and of neutral and ionized gas in the Local Group dwarf irregular galaxy Sextans A. We have resolved various populations of stars via deep UBV(RI)_C imaging over an area with diameter 5.3 arcmin. We arrive at 2525 stars detected in V and at least one other band. We provide here the magnitudes, colors, and absolute positions for the stars.
The UBVRI light curves of 7 late-type dwarfs amongst the fastest rotators of the Alpha Per cluster (vsini>=140km/s) are presented. The shape of the light curves suggests that the photometric variations are most often dominated by a single group of cool spots located at intermediate or high latitude on the stellar surface. Assuming that starspots are good tracers of the stellar magnetic field, the smooth light curves indicate the existence of a large scale, slowly varying magnetic structure at the surface of these ultrafast rotators. For a description of the UBVRI photometric system, see e.g. <GCPD/08>
