Speckle observations of 145 double stars and suspected double stars are presented and discussed. On the basis of multiple observations, a total of 280 position angle and separation measures are determined, as well as 23 high-quality nondetections. All observations were taken with the (unintensified) Rochester Institute of Technology fast-readout CCD camera mounted on the Lowell-Tololo 61 cm telescope at the Cerro Tololo Inter-American Observatory during 1999 October. We find that the measures, when judged as a whole against ephemeris positions of binaries with very well-known orbits, have root mean square deviations of 18+/-03{deg} in position angle and 13+/-2mas in separation. Eleven double stars discovered by Hipparcos were also successfully observed, and the change in position angle and/or separation since the Hipparcos observations was substantial in three cases.
As a part of a CCD survey of galaxies belonging or projected onto the Coma and Hercules Superclusters and to the A262, Virgo and Cancer clusters, we present isophote maps and photometric profiles of 87 galaxies (85 taken with the V, 25 with the B and 3 with the U Johnson filters). For the objects in common we compare our results with those in the RC3.
Continuing a CCD survey of galaxies belonging or projected onto the Coma and Hercules Superclusters, to the A262 and Cancer clusters, we present isophote maps and photometric profiles in the Johnson system of 111 galaxies (67 in the V and B bands, 42 only in V, 2 only in B) obtained with the 2.1m telescope at San Pedro Martir (Baja California, Mexico).
CCD UBVIc imaging photometry was carried out in the fields of the open clusters Pismis 8 and Pismis 13, located in the Vela-Puppis region in our Galaxy. MK spectral types have also been determined for a number of stars located in the fields of these two clusters which were used to secure membership among the brightest stars. Since our photometry goes to a fainter limit than previous studies we could provide better reddening, distance and age determinations. Both clusters are located close to the edge of the local arm in the third quadrant. Pismis 8 is a cluster about 5-7My old located at 2000pc from the Sun, while Pismis 13 was found at 2750pc with a probable age of about 100My. The estimate of the slopes of the mass functions in both cases yielded x=1.7 and x=2.1 for Pismis 8 and 13 respectively.
We present results of a study that combines UBVI photometry, MK spectral classification and proper motions in the area of the, up to now unknown, open cluster Ruprecht 58 at the Puppis region.
We present V magnitudes, (B-V) and (U-B) colours of close visual double star components, and their differences as well as separations and position angles of 40 visual double stars. The common properties of the members of this sample are the small angular separation {rho}, which is less than 7", and the common spectral type of the primaries, which are of G-type. The observations made with the Bessel U, B and V filters, while the astrometry was performed in the V filter only. For the observations, the CCD camera attached to the Cassegrain focus of the 90 cm Dutch telescope, at La Silla, Chile, had been used. From the analysis of the data we concluded that from the sample of the fourty double stars observed seven proved to be physical pairs, while the rest must have common origin components.
The h and chi Per "double cluster" is examined using wide-field (0.98x0.98{deg}) CCD UBV imaging supplemented by optical spectra of several hundred of the brightest stars. The UBV photometry was obtained from observations with the 0.9m telescope at Kitt Peak National Observatory using the Mosaic CCD camera (0.43arcsec/pix) on 1999 February 3. Conditions were photometric with a seeing about 1.3arcsec. The Mosaic camera consists of eight individual SITe 2048x4096 CCD chips arranged in two rows of four to produce a final image equivalent to 8192x8192 pixels (098x098{deg}) but with modest (35-50pix) gaps. Our imaging data set contains short (0.5s in V and B and 2s in U), medium (2s in V and B and 10s in U), and long (100s in V and B and 300s in U) integrations, each consisting of five dithered exposures that were combined to fill in gaps between the eight chips. Analyzing the data near the cluster nuclei results in identical reddenings E(B-V) (0.56+/-0.01), distance moduli (11.85+/-0.05), and ages (12.8+/-1.0Myr) for the two clusters. In addition, the initial mass function slope for each of the cluster nuclei is found to be quite normal for high-mass stars ({Gamma}=-1.3+/-0.2), indistinguishable from a Salpeter value. The masses of the two clusters are found to be 3700M_{sun}_ and 2800M_{sun}_ for h and {chi} when integrating the present-day mass function from 1 to 120M_{sun}_.
CCD UBV photometry of 2279 stars in Sextans A is presented. Differences with the photometric scales of Sandage and Carlson (1985AJ.....90.1019S) and Hoessel et al. (1983ApJ...274..577H) are discussed; recalibration of the Sandage and Carlson data for Cepheids in Sextans A results in a smaller value for the distance modulus, {mu}=25.6. A similar value for the distance modulus is obtained from the colour-colour diagram. Colour-colour and colour-magnitude diagrams for the whole galaxy and for different parts are presented indicating a general star formation activity all over Sextans A. The contribution of stars brighter than M_pg_=-3 to the total blue light of the galaxy amounts to 25%, a much higher value than what is found for other dwarf irregular galaxies in the Local Group. The integrated birthrate per unit mass of massive stars for the galaxy is found to be much higher than in the Magellanic Clouds, suggesting that the rate in Sextans A was probably smaller in the past. Different slopes for high mass and low mass IMF parts are needed to account for its low surface brightness. The formation of massive stars seems to be favoured for systems of decreasing mass or, given the relation between total mass and metal content, for galaxies of decreasing metallicity.
We present UBVRI and H{alpha} photometry of the extremely compact, starburst cluster NGC 3603. Ground-based images, Hubble Space Telescope (HST) archival data, as well as Chandra X-ray data have been used for this study. We present, for the first time, optical color-magnitude diagrams (CMDs) for the stars in the cluster core down to V=22mag. A well-defined main sequence (MS) as well as low-mass pre-main-sequence (PMS) stars can clearly be seen in the CMDs. This result confirms the finding by Eisenhauer et al. (1998ApJ...498..278E) that low-mass stars are forming in the starburst cluster. We also derive an age (1+/-1Myr) and distance of the cluster (V_0_-M_V_=14.2+/-0.2mag, i.e., d=6.9+/-0.6kpc).
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