The CCD observations of a sky area in the NGC 6913 cluster were performed with the 2-meter telescope of the Terskol Peak Observatory (Northern Caucasus, Russian Federation). The magnitudes and coordinates of stars down to V=20mag were determined for a 7'x5' field. The equatorial coordinates of stars were obtained in the reference system of the USNO A2.0 catalog (Cat. <I/252>) with an accuracy of 0.35". The relationship between the instrumental photometric system and the Johnson UBVR system was derived.
Table 2 presents standard broad band U, B, V, R photoelectric photometry of AX Persei. Each value represents the average of the observations during a night. The uncertainty of these night-means is of a few x 0.001mag in the B, V and R bands, and up to 0.02mag in the U band. Table 3 presents observed spectrophotometric parameters of the spectrum: the line fluxes, fluxes in the local continuum and the radial velocities.
We present extensive UBVR photometry of the Galactic globular cluster (GGC) NGC 6712 obtained with the ESO Very Large Telescope (VLT) which reaches down to 2 mag below the main-sequence turn-off and allows us for the first time to determine the age of this cluster.
In this paper we present the Johnson-Cousins UBVR CCD photometry of the stars in King 2, an old open cluster towards the galactic anticenter. We have obtained the colour-magnitude diagram, the colour excess, the reddening, an estimate of the metallicity, and the distance modulus. The comparison of the observational colour-magnitude diagram with the theoretical simulations based on stellar models with convective overshoot shows that a major revision of the model structure is required. To this aim, we explore the possibility that the formulation of convective overshoot for stars in the mass range 1 to 2M_{sun}_ ought to be different from the one currently in use. The point of major uncertainty that we see to affect the stars in this domain is whether or not convective overshoot may erode the gradient in molecular weight in the regions surrounding the convective core. We find that models, in which this is not allowed to occur, better fit the overall morphology of the colour-magnitude diagram of King 2. In addition to this, analyzing the width of the main sequence band we suggest that a significant fraction of the stars are members of binary systems, and evaluate the range spanned by their mass ratios. Finally, we derive the luminosity function and the mass function for the main sequence stars of the cluster.
The theory of binary star formation predicts that close binaries (a<100au) will experience periodic pulsed accretion events as streams of material form at the inner edge of a circumbinary disk (CBD), cross a dynamically cleared gap, and feed circumstellar disks or accrete directly onto the stars. The archetype for the pulsed accretion theory is the eccentric, short-period, classical T Tauri binary DQ Tau. Low-cadence (~daily) broadband photometry has shown brightening events near most periastron passages, just as numerical simulations would predict for an eccentric binary. Magnetic reconnection events (flares) during the collision of stellar magnetospheres near periastron could, however, produce the same periodic, broadband behavior when observed at a one-day cadence. To reveal the dominant physical mechanism seen in DQ Tau's low-cadence observations, we have obtained continuous, moderate-cadence, multiband photometry over 10 orbital periods, supplemented with 27 nights of minute-cadence photometry centered on four separate periastron passages. While both accretion and stellar flares are present, the dominant timescale and morphology of brightening events are characteristic of accretion. On average, the mass accretion rate increases by a factor of five near periastron, in good agreement with recent models. Large variability is observed in the morphology and amplitude of accretion events from orbit to orbit. We argue that this is due to the absence of stable circumstellar disks around each star, compounded by inhomogeneities at the inner edge of the CBD and within the accretion streams themselves. Quasiperiodic apastron accretion events are also observed, which are not predicted by binary accretion theory.
The results of a UBVR photometry observations are presented for eclipsing binary V1481 Cyg in the open cluster NGC 7128. The binary was observed between 1993 and 1995 with the 1m and 0.6m telescopes at Maidanak Observatory (Uzbekistan).
The distribution of N*, the number of OB stars per association or cluster, appears to follow a universal power-law form (N*)^-2^ in the local universe. We evaluate the distribution of N* in the Small Magellanic Cloud using recent broadband optical and space-ultraviolet data, with special attention to the lowest values of N*. We find that the power-law distribution in N* continues smoothly down to N*=1. This strongly suggests that the formation of field massive stars is a continuous process with those in associations and that the field stars do not originate from a different star formation mode.
Photoelectric UBV observations were made with the ESO 1m telescope and the ESO photometer on 6 nights between 1970-04-01 and 1970-05-03. The observations were centered around (B1950)13:24-62:23 The positions and identifications of the 3 sequences were computed by B. Skiff (Lowell Obs.) in September 2010, from a comparison of the published charts with the computer screen-plots of UCAC2.
The results concerning photoelectrically observed UBV magnitudes and colors of bright to intermediately faint stars near three globular clusters (NGC 2808, 5927, and 6101) are assembled.
We report on the progress of our ongoing photometric monitoring program of spotted late-type stars with automatic photoelectric telescopes (APTs) on Mt. Hopkins in Arizona and on Mt. Etna in Sicily. We present 9250 differential UBV and/or V(RI)c observations for altogether 23 chromospherically active stars, singles and binaries, pre-main-sequence and post-main-sequence, taken between 1991 and 1996. For a description of the UBV and (RI)c photometric system, see e.g. <GCPD/01> and <GCPD/54>
