As part of an extensive program focused on the global properties and evolution of active stars, high-precision UBV(RI)c and UBV photometry of 18 selected stars is presented. UBV(RI)c observations were collected at the European Southern Observatory over the intervals 21-28 September 1994 and 25 November - 05 December 1994. Additional UBV photometry obtained late in 1994 by Catania Astrophysical Observatory Automatic Photoelectric Telescope is also presented. Significant evolution of the light curves, period variations and evidence for long-term variability of the global degree of spottedness are found. Some spectral classifications are revised and photometric parallaxes are compared, whenever possible, with the values measured by the Hipparcos satellite. These observations are finalized to the construction of an extended photometric database, which can give important clues on topics such as the stability of spotted areas, differential stellar rotation, solar-like activity cycles and the correlation between inhomogeneities at different atmospheric levels.
We present homogeneous and standardized UBV(RI)_c_ photometry for nearly 550 M stars selected from the Hipparcos satellite data base (Cat. <I/239>) using the following selection criteria: lack of obvious variability (no Hipparcos variability flag); {delta}<+10{deg}, (V-I)>1.7; and V magnitude fainter than about 7.6. Comparisons are made between the current photometry, other ground-based data sets and Hipparcos photometry. We use linear discriminant analysis to determine a luminosity segregation criterion for late-type stars, and principal component analysis to study the statistical structure of the colour indices and to calibrate absolute magnitude in terms of (V-I) for the dwarf stars. Various methods are used to determine the mean absolute magnitude of the giant stars. We find 10 dwarf stars, apparently previously unrecognized (prior to Hipparcos) as being within 25pc, including five within 20pc.
The southern open cluster NGC 4852 was re-observed in the UBVRI passbands to refine its intrinsic fundamental parameters. An extended spectral coverage was also undertaken aimed at obtaining a clear picture of the kind of stars inhabiting the cluster upper main sequence.
We analyse CCD broad band (UBV(RI)c) photometric data obtained in the fields of the poorly studied open clusters NGC 2425 and NGC 2635. Both clusters are found to be of intermediate age thus increasing the population of open clusters known to be of the age of, or older than, the Hyades. More explicitly, we find that NGC 2425 is a 2.2Gyr old cluster, probably of solar metallicity, located at 3.5kpc from the Sun. NGC 2635 is a Hyades age (600Myr) cluster located at a distance of 4.0kpc from the Sun. Its Colour Magnitude Diagram reveals that it is extremely metal poor for its age and position, thus making it a very interesting object in the context of Galactic Disk chemical evolution models.
We present CCD broad band photometric observations in the fields of the Third Galactic Quadrant open clusters NGC 2580 and NGC 2588 (V(I)c and UBV(RI)c respectively). From the analysis of our data we found that NGC 2580 is located at a distance of about 4kpc and its age is close to 160Myr. As for NGC 2588, it is placed at about 5kpc from the Sun and is 450Myr old. This means that NGC 2588 belongs to the extension of the Perseus arm, whereas NGC 2580 is closer to the local arm structure. The luminosity functions (LFs) have been constructed for both clusters down to V~20 together with their initial mass functions (IMFs) for stars with masses above M~1-1.5M_{sun}_. The IMF slopes for the most massive bins yielded values of x~1.3 for NGC 2580 and x~2 for NGC 2588. In the case of this latter cluster we found evidence of a core-corona structure produced probably by dynamical effect. In the main sequences of both clusters we detected gaps, which we suggest could be real features.
We present BVRcIc CCD photometry in the fields of six Galactic open clusters toward the Perseus spiral arm. These data, complemented with J, H and Ks magnitudes from 2MASS, have been used to determine the following ages, distances and colour excesses E(B-V) for these clusters: 40Myr, 3180_-380_^+440^pc, 0.54+/-0.03mag (Berkeley 96); 250Myr, 2410_-200_^+220^pc, 0.77+/-0.06mag (Berkeley 97); 70Myr, 2490_-170_^+180^pc, 0.51+/-0.05mag (King 12); 160Myr, 2830_-150_^+160^pc, 0.88+/-0.09mag (NGC 7261); 280Myr, 2450_-170_^+190^pc, 0.24+/-0.03mag (NGC 7296); 160Myr, 2750_-210_^+220^pc, 0.49+/-0.02mag (NGC 7788). We found gaps in the mass function of clusters Be 97, King 12 and NGC 7788 in the mass intervals [1.3-1.5], [1.4-1.6] and [1.5-1.7] solar masses, respectively.
Ages derived from the low mass stars still contracting onto the main sequence often differ from ages derived from the high mass ones that have already evolved away from it. We investigate the general claim of disagreement between these two independent age determinations by representing UBVRI photometry of the young galactic open clusters NGC 2232, NGC 2516, NGC 2547 and NGC 4755, spanning the age range ~10-150Myr.
Extensive optical and infrared photometry as well as low and high resolution spectroscopy are used as inputs in deriving robust estimates of the reddening, distance and nature of the progenitor of V838 Mon, the 2002 outbursting event that produced a most spectacular light-echo.
Deep CCD UBV(RI)c photometry has been carried out in the area of the open cluster Stock 16. The different photometric diagrams indicate the presence of three superimposed stellar groups, all composed of early type stars.
The Asiago photographic archive has been searched for plates containing the symbiotic stars Hen 2-468, QW Sge, LT Del, V407 Cyg, K 3-9, V335 Vul, FG Ser and Draco C-1. A total of 635 plates imaging the program stars have been found and the brightness estimated using the Henden & Munari (2000A&AS..143..343H) UBV(RI) photometric sequences. These historical data have allowed for the first time the determination of the orbital periods of Hen 2-468 (774 days) and QW Sge (390.5 days), a significant improvement in the orbital period of LT Del (465.6 days) and for V407 Cyg an evaluation of the Mira's pulsation period and complex lightcurve shape in the red (R and I bands). Some previously unknown outbursts have been discovered too.
