We present the results of a large-scale imaging photometric study of the stellar population in the northern part of NGC 3372 in the UBVRIJHK bands with a wavelength coverage from 0.33 to 2.5{mu}m. The observations were made at Las Campanas Observatory. The optical CCD mosaics cover an area approximately of 32x22arcmin^2^ centred between the Tr 14 and Tr 16 clusters. The survey was extended to cover 12x12arcmin^2^ at the location of Tr 15. Near-infrared NICMOS3 mosaics covering the areas occupied by these clusters were obtained in the JHK photometric bands. By means of star counts in V, the centres and sizes of each cluster were redetermined yielding: Tr 14 (r=264"), Tr 15 (r=320") and Tr 16 (r=320"). It was confirmed that Cr 232 is not a true cluster. Multicolour optical photometry was obtained for 4152 stars. Two colour and colour-magnitude diagrams are presented and analysed for each individual cluster and compared to those of the field. We confirm the widespread variations in the dust density and also in the dust size distribution leading to widely different values of A_V_and reddening laws towards Tr 14 and Tr 16. No spatial patterns were found for these variations. Spectroscopic parallaxes were computed and the results are consistent with all three clusters being at a similar distance from the Sun (<d>=2.7kpc) but the data have shown very large scatter in both A_V_and d. Analyses of the extinction-corrected colour-magnitude diagrams suggest ages between 3 and 60 million years for the stars in Tr 15 and between less than 1 and 6 million years for Tr 14 and Tr 16. A small number of infrared-excess stars were found in Tr 16 and Tr 14 but not in Tr 15. The distribution of stars in Tr 14 seen in the near-infrared suggests that this cluster is partially embedded in a molecular cloud. This molecular cloud extends towards the west reaching its highest density, marked by a CO peak emission, some three arcmin to the south-west of the nucleus of Tr 14. The rich ultraviolet field created by the Tr 14 stars ionizes most of the visible HII region in its vicinity and most of the radio HII region Car I. Evidence is found of ionization fronts leading into the molecular cloud, which appears to be "wrapping" the Tr 14 cluster. Deep JHK images of the Car I region reveal the presence of an embedded stellar population illuminating a large infrared reflection nebula. It includes at least one O9-B0 star associated with an ultracompact HII region. Nebulous 2.2{mu}m emission from three of the mid-infrared sources in the Tr 14 region is also found.
New photoelectric UBVRI observations of the eclipsing variable V1016 Ori have been obtained with the AZT-11 telescope at Crimean Astrophysical Observatory and with the Zeiss-600 telescope at Mount Maidanak Observatory. Light curves are constructed from the new observations and from published and archival data. The table contains all used data.
In this paper we present and analyze CCD UBVRI photometry in the region of the three young open clusters NGC 3114, Collinder 228, and vdB-Hagen 99, located in the Carina spiral feature. NGC 3114 lies in the outskirts of the Carina nebula. We found 7 star members in a severely contaminated field, and obtain a distance of 950pc and an age less than 3x10^8^yrs. Collinder 228 is a younger cluster (8x10^6^yrs), located in front of the Carina nebula complex, for which we identify 11 new members and suggest that 30% of the stars are probably binaries. As for vdB-Hagen 99, we add 4 new members, confirming that it is a nearby cluster located at 500pc from the Sun and projected toward the direction of the Carina spiral arm. Observations were conducted at La Silla on April 13-16, 1996, with the 0.92m ESO-Dutch telescope.
An investigation on dust properties in the NW portion of NGC 6611 has been conducted polarimetrically to test the existence of abnormal extinction in that section of the open cluster in an independent way. As previously suggested for the {eta} Carinae nebula by Tapia et al. (1988, in Conference on Dust in the Universe, Bailey M.E. and Williams D.A. (eds.) Cambridge University Press, Cambridge, p.19) and subsequently confirmed by Marraco et al. (1993), the canonical relation between E_V-K_/E_B-V_ and {lambda}_max_ (the wavelength of maximum interstellar polarization) is not valid for stars belonging to dusty HII regions, as is the case for the observed portion of M 16. This may arise mainly from the presence of silicate grains of a slightly larger size than the standard ISM and also from a considerable increase in mean graphite grain size, according to previous results from Chini & Wargau (1990A&A...227..213C). About 50% of the observed stars in NGC 6611 present indications of intrinsic polarization in their measurements; a similar percentage was found in IC 2944 (Vega et al., 1994AJ....108.1834V), another young open cluster in close relation with an HII region.
We present new polarimetric UBVRI observations of 25 stars in the direction of the halo of NGC 6611, the rich stellar open cluster embedded in an ionized hydrogen complex (M16). Our plan is to characterize the interstellar material (ISM) associated with halo stars in order to make a comparison with the ISM dusty core characteristics that resulted from a previous investigation by the same authors.
We perform a study of the structure, density, and distribution of ionized circumstellar gas in the strongly interacting binary SX Cas. We apply our new model codes for electron scattering in circumstellar matter to analyze a previously unpublished, extensive linear polarization data set for SX Cas, collected during four successive observing periods in 1981-84 at the Crimean Astrophysical Observatory. These data are complemented by our polarization observations carried out in 2000 and 2005 with the KVA-60 telescope at La Palma.
We present (UBVRI) multicolor linear polarimetric data for 31 of the brightest stars in the area of the open cluster NGC 5749 considered to study the properties of the interstellar medium (ISM) towards the cluster.
We present (UBVRI) multicolor linear polarimetric data for 26 of the brightest stars in the area of the open cluster Stock 16 that were considered to study the properties of the ISM (interstellar medium) towards the cluster. Our data yield a mean polarization percentage of P~2.5%, close to the polarization value produced by the ISM with normal efficiency (P_{lambda}_max_~5E_B-V_) undergoing a color excess of E_B-V_=0.51. The mean angle of the polarization vectors, {theta}=74.9deg, agrees quite well with the expected angle produced by dust particles aligned in the direction of the galactic disk (and the magnetic field) in the region. A study of the extinction suffered by the stars in the zone was also performed combining our new data with previous photometric data. In this sense, our analysis indicates that the visual absorption affecting Stock 16 stars is mainly produced in front of the cluster by a dust cloud at approximately 500 pc from the sun. The large polarization value of the non-member star, WR 51, confirms its background star nature.
UBVRI photoelectric sequences for three low-latitude galactic globular clusters. NGC 5286, NGC 5927, and NGC 6541, are presented herein. All include fields suitable for CCD coverage. The number of stars and the range of magnitudes and colors are: * NGC 5286: 8 stars 13.6<V<15.3, 0.6<B-V<1.3 (table2) * NGC 5927: 11 stars 11.3<V<14.9, 0.3<B-V<1.6 (table3) * NGC 6541: 16 stars 12.2<V<15.7, 0.2<B-V<1.6 (table4) The stars were measured an average of seven times on at least five different nights. To the best of our knowledge, none of these stars have UBVRI photoelectric measurements reported by other authors.
