We present CCD uvby{beta} photometry for stars in the central area of the young open cluster NGC 663. We find that the reddening is highly variable, with values ranging from E(b-y)=0.639+/-0.032 in the central part to E(b-y)=0.555+/-0.038 in the south-east. The distance modulus is found to be 11.6+/-0.1mag. (2.1kpc), and the age logt=7.25+/-0.1 years (25+7/-5Myr).
We present uvby-{beta} photometry of 116 X-ray flux-selected active stars in the directions of the Orion (40), Taurus-Auriga (58) and Scorpius OB2-2 (18) star forming regions. Additionally, we give near IR JHK photometry of 20 active stars in the Taurus-Auriga direction. The program stars were selected from the ROSAT All Sky Survey and EINSTEIN X-ray surveys and are spectroscopically confirmed weak-line T Tauri stars and weak-line T Tauri star candidates. The photometry confirms the young nature of the program stars and also indicates that a significant fraction of the sample could be foreground objects. The data given here probably represent the largest homogeneous uvby-{beta} photometric sample of new WTTS and WTTS candidates. Many objects in the sample are observed photometrically for the first time.
This paper presents first complete uvby light curves of the late-type detached eclipsing binary ZZ UMa (G0V + G8V, P=2.2993d). This binary system has been observed during eight campaigns at the Calar Alto Observatory (Almeria, Spain) and at the Sierra Nevada Observatory (Granada, Spain). 294 points distributed over the binary period and covering both eclipses are given. The comparison stars used to calculate the differential light curves (SAO 15242 and SAO 15251) were confirmed as being good reference stars with constant flux. These observations are part of a 6 year uvby and H{beta} monitoring program of low mass eclipsing binaries whose main objective is to provide accurate absolute astrophysical parameters for late-type main sequence stars. Details about the standardisation process and accuracy of the photometry are also given. The internal accuracy of the standard photometry measured as the mean RMS of the differences between standard and observed values for the standard stars observed along the program is only a few millimagnitudes. Detailed analysis of ZZ UMa, based on these light curves, will be published separately (Clement et al., 1997, Cat. <J/A+AS/123/59>).
Precision uvbyCaH{beta} photometry of the nearby old open cluster, NGC752, is presented. The mosaic of CCD fields covers an area ~42' on a side with internal precision at the 0.005-0.010mag level for the majority of stars down to V~15. The CCD photometry is tied to the standard system using an extensive set of published photoelectric observations adopted as secondary standards within the cluster. Multicolor indices are used to eliminate as nonmembers a large fraction of the low probability proper-motion members near the faint end of the main sequence, while identifying 24 potential dwarf members between V=15.0 and 16.5, eight of which have been noted before from Vilnius photometry. From 68 highly probable F dwarf members, we derive a reddening estimate of E(b-y)=0.025+/-0.003 (E(B-V)=0.034+/-0.004), where the error includes the internal photometric uncertainty and the systematic error arising from the choice of the standard (b-y,H{beta}) relation. With reddening fixed, [Fe/H] is derived from the F dwarf members using both m_1_ and hk, leading to [Fe/H]=-0.071+/-0.014(sem) and -0.017+/-0.008(sem), respectively. Taking the internal precision and possible systematics in the standard relations into account, [Fe/H] for NGC 752 becomes -0.03+/-0.02. With the reddening and metallicity defined, we use the Victoria-Regina isochrones on the Stromgren system and find an excellent match for (m-M)=8.30+/-0.05 and an age of 1.45+/-0.05Gyr at the appropriate metallicity.
Differential Stroemgren photometry of the eclipsing binary V578 Mon expressed relative to the primary comparison star NGC 2244-115 (HD 46106). The data were obtained at the SAT telescope at La Silla in 1992 (49 observations by J. Andersen) and in 1994 (199 observations by H. Hensberge) and have an accuracy of typically 3 millimag.
In order to increase the limited number of B-stars with accurately known dimensions, and also the number of well studied eclipsing binaries in open clusters, we have undertaken observations and studies of four southern double-lined eclipsing B-type binaries; DW Car, BF Cen, AC Vel, and NSV 5783. Complete uvby light curves were observed between January 1982 and April 1991 at the Danish 0.5m telescope at ESO La Silla, since 1985 known as the Stroemgren Automatic Telescope (SAT). Standard indices for the systems and the comparison stars, as well as additional minima observations for AC Vel, have been obtained later at SAT. For DW Car and AC Vel, high-resolution spectra for definitive spectroscopic orbits have also been obtained; they are presented as part of the detailed analyses of these systems. A few spectra of NSV 5783 are included in the present paper.
We present and analyze two seasons of intense photometric monitoring in the Stroemgren uvbyH{beta} system of {eta} Carinae (October 1992-August 1994). The luminous blue variable (LBV) in the core did not show much S Dor activity, i.e. it was in a relatively quiescent stage. This situation was very favourable for studying its optical micro variations. It appears that the central LBV pulsates (presumably in a non-radial mode) like other massive evolved stars, the {alpha} Cyg variables. The quasi-period is 58.56d. The linear ephemeris is: JD_max_=2448875.0 +58.56 E. Support was found for the existence of the presumed periodicity of 52.4d of the so-called "dimples", shallow dips in the light curve which only last for a few days. The cause may be the eclipse of a small companion or of a hot spot in an accretion disk. The H{beta} index became bluer by ~0.07mag during the last 11/2 years and shows an oscillation in anti-phase with the 58.56d pulsation, suggesting that the HII region(s) responsible for the hydrogen line emission has a relatively high luminosity. This is another reason to suppose that a second luminous source, perhaps a luminous disk (with a hot spot), may be present in the {eta} Car system.
