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 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.
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.
The catalog contains UBVRI photoelectric observations of 223 stars, mostly in an approximately 2-degree zone centered on the celestial equator. The catalog is intended to provide a uniform set of new standards, available to various sizes of telescopes in both hemispheres, on an internally consistent, homogeneous system. Most of the stars are in Selected Areas 92-115 and fall in the magnitude range of about 7 to 12.5 in V and color range -0.3 to +2.0 in B-V. The data include equatorial coordinates, photoelectric magnitudes and colors, numbers of observations, and computed internal errors. See the complete description by Wayne H. Warren Jr., either in plain ascii (file adc.doc) or in LaTeX format (file adc.tex)
New broadband UBVRI photoelectric observations on the Johnson-Kron-Cousins photometric system have been made of 202 stars around the sky, and centered at the celestial equator. These stars constitute both an update of and additions to a previously published list of equatorial photometric standard stars. The list is capable of providing, for both celestial hemispheres, an internally consistent homogeneous broadband standard photometric system around the sky. When these new measurements are included with those previously published by Landolt (1992, Cat. II/183), the entire list of standard stars in this paper encompasses the magnitude range 8.90<V<16.30, and the color index range -0.35<(B-V)<+2.30.
UBVRI photoelectric observations have been made of 109 stars around the sky, centered more or less at -50{deg} declination. The majority of the stars fall in the magnitude range 10.4<V<15.5 and in the color index range -0.33<(B-V)<+1.66. These new broadband photometric standard stars average 16.4 measurements each from data taken on 116 different nights over a period of 4yr. Similar data are tabulated for 19 stars of interest that were not observed often enough to make them well-defined standard stars.
High-quality CCD-based UBVRI photometry is presented for ~45000 stars distributed among 60 different fields centered on the celestial equator and at {delta}{approx}-50{deg}. This photometry has been calibrated to the standard Johnson UBV and Kron-Cousins RI systems via observations of the UBVRI standard stars presented in the works of Landolt. The majority of the stars in our photometric catalog fall in the magnitude range 12<~V<~22 and in the color range -0.3<~(B-V)<~1.8. Each star averages 67 measures in each UBVRI filter from data taken on 250 different photometric nights over a period of ~6.5yr from two different telescopes. Our final photometric database effectively extends the UBVRI standard star network defined by Landolt to much fainter magnitudes and increases the number density of stars within pre-existing standard fields. Hence, these new, fainter standards serve as suitable calibrators for investigators who employ either small or large-aperture telescopes for their observational projects.
UBVRI photoelectric observations have been made of 335 stars around the sky, and centered approximately at +50{deg} declination. The majority of the stars fall in the magnitude range 9<V<16, and in the color range -0.3<(B-V)<+1.8. Those 243 stars best suited as new broadband photometric standard stars average 12.5 measures each from data taken on 98 different nights over a period of 17 years at the Kitt Peak National and Lowell Observatories.
Photometry on the UBVRI Kron-Cousins system is presented for 102 stars covering the magnitude range 7 to 16 in the nine Harvard E-regions. These stars, at declination close to -45{deg}, are suitable for use as Southern Hemisphere standards in the photometry of faint stars and galaxies. The large magnitude range in most fields makes the sequences useful for the calibration of the Pickering-Racine wedge, a device widely used to extend photometric sequences to fainter limits on photographic plates. Positions accurate to a few arcseconds as well as identification charts are given for each star.
