We investigate the distribution of the interstellar dust towards six small volumes of the sky in the region of the Gum nebula. New high-quality four-colour uvby and H-beta Stromgren photometry obtained for 352 stars in six selected areas of Kapteyn, complemented with data obtained in a previous investigation for two of these areas, were used to estimate the colour excess and distance to these objects. The obtained colour excess versus distance diagrams, complemented with other information, when available, were analysed in order to infer the properties of the interstellar medium permeating the observed volumes. On the basis of the overall standard deviation in the photometric measurements, we estimate that colour excesses and distances are determined with an accuracy of 0.010mag and better than 30%, respectively, for a sample of 520 stars. A comparison with 37 stars in common with the new Hipparcos catalogue attests to the high quality of the photometric distance determination. The obtained colour excess versus distance diagrams testify to the low density volume towards the observed lines-of-sight. Very few stars out to distances of 1kpc from the Sun have colour excesses larger than E(b-y)=0.1mag. In spite of the low density character of the interstellar medium towards the Puppis-Vela direction, the obtained reddening as a function of the distance indicates that two or more interstellar structures are crossed towards the observed lines-of-sight. One of these structures may be associated with the very low density wall of the Local Cavity, which has a distance of 100-150pc from the Sun. Another structure might be related to the Gum nebula, and if so, its front face would be located at about 350pc from the Sun.
Stroemgren uvby{beta} photometry observations obtained for 205 stars in the general direction of a void in the IRAS 100-{mu}m emission from the Lupus dark cloud complex are presented and analysed. The colour excess versus distance diagram confirms the existence of a region depleted from interstellar material, which is also seen in the ROSAT soft X-ray background emission map. The distance to the surrounding material is estimated as being within the interval from 60 to 100pc. This result is in disagreement with previous distance estimates to the supposed supernova that has been suggested as responsible for clearing the region from dust. As an alternative, the data presented support the suggestion that the void may have been produced by the detachment of material from the interface between LoopI and the Local Bubble as a consequence of hydromagnetic instabilities. Moreover, the distribution of colour excess as a function of distance supports a value of ~150pc as the most probable distance to the dark cloud known as Lupus1.
Stromgren and H{beta} photometry of 130 stars in the Carina section of the Milky Way is presented. The color excesses and the distances of all stars are obtained. A good agreement is found between the CM and HR diagrams and the spatial distribution of these stars.
The aim of this work is to study the capacity of the uvby H_{beta}_ system for detecting the chemically peculiar (CP) stars based on the effect that peculiar features in the flux distribution have on all the Stroemgren-Crawford indices. Our study focuses on the classical magnetic peculiar stars (CP2), though Am star s (CP1) are also included for comparison with cool CP2 stars. Satisfactory results were obtained for hot CP2 stars: the definition of a new index p, which is a linear combination of uvby H_{beta}_ colours, allowed us to separate a high percentage of hot CP2 stars from normal stars. According to this new index, 60 new CP2 candidates are proposed. The working sample was extracted from The General Catalogue of Ap and Am stars by Renson et al. (1991, Cat. <III/162>). Photometric observations to enlarge the sample of CP2 stars with complete uvby H_{beta}_ photometry were carried out. These observations are also reported in the present paper. The new index p is also used to correct the reddening of early CP2 stars computed as if they were normal stars.
We present uvby{beta} CCD photometry of the central region of the double cluster h&{chi} Persei. We identify =~350 stars, of which 214 were not included in Oosterhof's catalogue. Our magnitude limit V=16.5 allows us to reach early F spectral type and obtain very accurate fits to the ZAMS. We derive reddening values of E(b-y)=0.44+/-0.02 for h Persei and E(b-y)=0.39+/-0.05 for {chi} Persei. From the ZAMS fitting, we derive distance moduli V_0_-M_V_=11.66+/-0.20 and V_0_-M_V_=11.56+/-0.20 for h and {chi} Persei respectively. These values are perfectly compatible with both clusters being placed at the same distance and having identical reddenings. The shift in the main-sequence turnoff and isochrone fitting, however, show that there is a significant age difference between both clusters, with the bulk of stars in h Persei being older than {chi} Persei. There is, however, a significant population of stars in h Persei which are younger than {chi} Persei. All this argues for at least three different epochs of star formation, corresponding approximately to logt=7.0, 7.15 and 7.3.
Unpublished uvby-{beta} photoelectric photometry of the open cluster NGC 6882/5 is presented. Utilizing already tested distance determinations through photometric techniques, it is found that there are at least two distinct star accumulations in the direction of the open cluster NGC 6882/5. A brief discussion is made of the nature of the previously found short period variables.
We report results of spectroscopic and photometric observations of ten delta Sct stars and one eclipsing binary in the open cluster NGC 1817, and of ten delta Sct stars and two other variables in the open cluster NGC 7062. For all targets in NGC 1817 and for three targets in NGC 7062 the radial velocity and projected rotational velocity are determined. For all stars the effective temperature and surface gravity is measured.
Results of 131 stars from Renson's (1991, Cat. <III/162>) catalogue of Ap and Am stars observed with the {Delta}-a system are presented. With few exceptions the probability division of Renson for membership in the CP2 group of peculiar stars is nicely reflected by peculiar values of {Delta}-a. Comparison with already available {Delta}-a values yields slightly larger values due to a minor shift in the g_1_ filter sampling the depression. For a description of the {Delta}-a and Stroemgren photometric system, see e.g. <GCPD/75> and <GCPD/04>, respectively.
The catalogue of accurate uvby-H{beta} and J2000 coordinates for 7842 stars in an area of 65'x40' around NGC 1817. We mark the selection of probable members of NGC 1817, combining this photometric study with the previous astrometric analysis (Balaguer-Nunez et al. 2004, Cat. <J/A+A/426/819>). Also given is the cross-identification of stars in common with the astrometry (Balaguer-Nunez et al. 2004, Cat. <J/A+A/426/819>), WEBDA (http://obswww.unige.ch/WEBDA), Hipparcos (ESA, 1997, Cat. <I/239>), Tycho-2 (Hog et al., 2000, Cat. <I/250>) and USNO-A2 (Monet et al., 1998, Cat. <I/252>) catalogues.
Table 1 contents 471 simultaneous measurements collected in each of the four uvby colours of the Stroemgren photometric system for the eclipsing binary system AB Cas. Because of an instrumental problem, 82 points in the b channel (during the last observational night) had to be rejected (the corresponding magnitudes are listed as 0.0000). The data are magnitude differences (Du,Dv,Db,Dy) of the variable star minus comparison star in the instrumental system versus Heliocentric Julian Day. Table 2 is the same, but for H{beta} (80 points). The comparison star is BD+70 0188. The origin in time is the Julian Day 2447117. The observations were carried out (by E. Rodriguez, A. Claret, J.L. Sedano, J.M. Garcia and R. Garrido) during 1987 and 1988 using the 0.90m telescope at the Sierra Nevada Observatory, Spain.
