We present optical and near-infrared UBVRIJHK photometry of stars in the Galactic globular cluster M4 (NGC 6121) based upon a large corpus of observations obtained mainly from public astronomical archives. We concentrate on the RR Lyrae variable stars in the cluster, and make a particular effort to accurately reidentify the previously discovered variables. We have also discovered two new probable RR Lyrae variables in the M4 field: one of them by its position on the sky and its photometric properties is a probable member of the cluster, and the second is a probable background (bulge?) object. We provide accurate equatorial coordinates for all 47 stars identified as RR Lyraes, new photometric measurements for 46 of them, and new period estimates for 45. We have also derived accurate positions and mean photometry for 34 more stars previously identified as variable stars of other types, and for an additional five non-RR Lyrae variable stars identified for the first time here. We present optical and near-infrared color-magnitude diagrams for the cluster and show the locations of the variable stars in them. We present the Bailey (period-amplitude) diagrams and the period-frequency histogram for the RR Lyrae stars in M4 and compare them to the corresponding diagrams for M5 (NGC 5904). We conclude that the RR Lyrae populations in the two clusters are quite similar in all the relevant properties that we have considered. The mean periods, pulsation-mode ratios, and Bailey diagrams of these two clusters show support for the recently proposed "Oosterhoff-neutral" classification.
The catalog contains the results from star brightness measures in the first ten (UBVRIJKLMN) broad wavelength bands (Johnson 1965) and the additional bandpass H (Johnson et al. 1968). Data in the above system that have been published up to June 1977 are included. The source reference (Morel and Magnenat 1978) states that there are 5943 entries in the data set with data for 4494 stars. However, a count of the records by coded number shows that there are only 4486 unique entries (not 4494). The catalog includes coded identification numbers (Geneva system), 11 magnitudes, numbers of measurements in each filter, and references.
We present UBVRI photometry of 44 Type Ia supernovae (SNe Ia) observed from 1997 to 2001 as part of a continuing monitoring campaign at the Fred Lawrence Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics. The data set comprises 2190 observations and is the largest homogeneously observed and reduced sample of SNe Ia to date, nearly doubling the number of well-observed, nearby SNe Ia with published multicolor CCD light curves.
Wolf-Rayet (WR) stars have strong, hot winds, with mass-loss rates at least a factor of 10 greater than their O-star progenitors, although their terminal wind speeds are similar. In this paper, we use the technique of multiband linear polarimetry to extract information on the global asymmetry of the wind in a sample of 47 bright Galactic WR stars. Our observations also include time-dependent observations of 17 stars in the sample. The path to our goal includes removing the dominating component of wavelength-dependent InterStellar Polarization (ISP), which normally follows the well-known Serkowski law. We include a wavelength-dependent ISP position angle parameter in our ISP law and find that 15 stars show significant results for this parameter. We detect a significant component of wavelength-independent polarization due to electron scattering in the wind for 10 cases, with most WR stars showing none at the ~0.05% level precision of our data. The intrinsically polarized stars can be explained with binary interaction, large-scale wind structure, and clumping. We also found that 5 stars out of 19 observed with the Stromgren b filter (probing the complex {lambda}4600-4700{AA} emission-line region) have significant residuals from the ISP law and propose that this is due to wind asymmetries. We provide a useful catalog of ISP for 47 bright Galactic WR stars and upper limits on the possible level of intrinsic polarization.
We present CCD UBVI photometric and medium/high resolution spectroscopic observations obtained in the field of the previously unstudied dissolving open cluster candidates NGC 5385, NGC 2664 and Collinder 21. Our analysis is based on the discussion of star counts, photometry, radial velocity distribution, and proper motions available from the Tycho 2 catalogue (<I/259>). All three aggregates clearly emerge from the mean Galactic field, but, regrettably, the close scrutiny of proper motions and radial velocities reveals that we are not facing any physical group. Instead, what we are looking at are just chance alignments of a few bright unrelated stars. Our analysis casts some doubt on the Bica et al. (2001A&A...366..827B) criterion to look for Possible Open Cluster Remnants. It seems mandatory to define a better criterion to adopt for further investigations.
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.
