New 4-colour BV(RI)_KC_ CCD photometry to a limiting magnitude of V=~19 is presented for 1428 objects observed towards the direction of the young, open cluster IC 2391. We observed 36 (2'x3') fields within 17arcmin of the nominal cluster core. By fitting the theoretical isochrones of D'Antona & Mazzitelli (1994ApJS...90..467D) to a combination of colour-magnitude and colour-colour diagrams, we have identified 17 stars as probable cluster members with a further 85 stars as possible members. The brightness distribution of low-mass members is compared with the luminosity function observed for the Pleiades and we estimate that the contamination due to background giants should be small.
We present CCD photometry in B, V, and I for a sample of globular clusters in the Virgo central giant elliptical galaxy M87. Our measured sample comprises 270 objects brighter than V~23.4mag and with distances r>25" (>2kpc) from the center of the galaxy. In agreement with the recent study of Cohen, we find no detectable gradient of mean cluster color (metallicity) in (B-V) or (V-I) with radial distance. The cluster system does, however, display a large dispersion in color at any radius, corresponding to sigma([Fe/H])~0.6 about a mean metallicity (Fe/H]>~-1.1 according to our color index scale. The difference in mean color between the globular clusters and the underlying halo light of the galaxy itself, found previously by Strom and coworkers and by Cohen, shows up strongly in all of our color indices; we find virtually no clusters as red as mean color of the halo stars at any radius.
The minimum timings of eclipsing binaries V418 Aql, SU Boo, RV CVn, CR Cas, GV Cyg, V432 Per, and BD+42 2782 were collected and analyzed. Their long-term behavior was studied via period analysis, revealing a periodic term in eclipse times. We derived 576 new times of minimum. Hence, to describe the periodic variation, a third-body hypothesis was proposed and the resulting orbital periods are as follows: 70, 7.4, 53, 37, 27, 53, and 18 yr, respectively. For the system V432 Per an additional 9.5 yr variation was also found. The predicted minimum masses of these distant bodies were calculated and their detectability discussed. The light curves of SU Boo and RV CVn were analyzed using the PHOEBE program, resulting in physical parameters of the components. New variable stars in the field of V418 Aql were discovered.
KUV 05134+2605 is one of the 21 pulsating DB white dwarfs (V777 Her or DBV variables) known so far. The detailed investigation of the short-period and low-amplitude pulsations of these relatively faint targets requires considerable observational efforts from the ground, long-term single-site or multi-site observations. The observed amplitudes of excited modes undergo short-term variations in many cases, which makes determining pulsation modes difficult. We aim to determine the pulsation frequencies of KUV 05134+2605, find regularities between the frequency and period components, and perform an asteroseismic investigation for the first time.
CCD observations have been used to study 16 of the previously known variables in the Oosterhoff type II globular cluster M9. The properties of the RR Lyrae variables in M9 are compared with those in the Oosterhoff type I cluster M3. Methods devised by Simon, Jurcsik, & Kovacs have been used to derive physical parameters for the stars from Fourier analysis. The mean metal abundance so derived for M9, [Fe/H]=-1.77, is in good agreement with the metal abundance derived from spectroscopic observations. All methods for calculating the absolute magnitudes of RR Lyrae variables from Fourier coefficients indicate that the RR Lyrae variables in M9 are more luminous than those in M3. However, there are three RR Lyrae stars in M3 that may be as bright as the M9 stars. These three are thought to be in a more advanced evolutionary state than the other M3 RR Lyrae stars. Absolute magnitudes have also been derived for the RR Lyrae stars in M68 and M107. The different methods predict that RR Lyrae stars in metal-poor clusters are more luminous than those in more metal-rich clusters, but there are inconsistencies in the relative luminosities derived by the different methods.
We present BVI CCD photometry for more than 10,000 stars in the innermost region (0.3'<r<~4') of the globular cluster M 3. When added to the previous photographic photometry by Buonanno et al. (1994A&A...290...69B) reaching as far as r~7', this results in an homogeneous data-set including about 19,000 stars measured in this cluster, which can be now regarded as one of the main templates for stellar population studies.
We report deep UBVR CCD photometry of stars in a portion of an arm of M 31, 20kpc southwest of the nucleus. The color-magnitude diagram shows a main sequence that reaches from Mv=-0.7 (at our photometric limit) to Mv=-6.2 and a well-populated giant region. The R, B-R diagram separates the stars rather clearly into three groups, the main sequence, intermediate-color stars (which include the brighter foreground stars), and the red giants. Reddening is found to average E(B-V)=0.13+/-0.04. To determine a reliable luminosity function, we have eliminated foreground contamination and have evaluated our sample completeness, using a large number of artificial stars in the DAOPHOT reduction routine. The corrected luminosity function, which extends from Mv=-5 to -1, has a logarithmic slope of 0.57+/-0.07 for all stars and 0.53+/-0.06 for main-sequence stars only. This value is similar to that reported for galaxies in general (Freedman 1985ApJ...299...74F and 1986, IAUS 116, 61).
The transiting planet WASP-12 b was identified as a potential target for transit-timing studies because a departure from a linear ephemeris has been reported in the literature. Such deviations could be caused by an additional planet in the system. We attempt to confirm the claimed variations in transit timing and interpret their origin. We organised a multi-site campaign to observe transits by WASP-12 b in three observing seasons, using 0.5-2.6-metre telescopes. We obtained 61 transit light curves, many of them with sub-millimagnitude precision. The simultaneous analysis of the best-quality datasets allowed us to obtain refined system parameters, which agree with values reported in previous studies. The residuals versus a linear ephemeris reveal a possible periodic signal that may be approximated by a sinusoid with an amplitude of 0.00068+/-0.00013d and period of 500+/-20 orbital periods of WASP-12 b. The joint analysis of timing data and published radial velocity measurements results in a two-planet model that explains observations better than do single-planet scenarios. We hypothesise that WASP-12 b might not be the only planet in the system, and there might be the additional 0.1M_Jup_ body on a 3.6-d eccentric orbit. A dynamical analysis indicates that the proposed two-planet system is stable on long timescales.
The properties of the early-type binary Cyg OB2 #5 have been debated for many years and spectroscopic and photometric investigations yielded conflicting results. We have attempted to constrain the physical properties of the binary by collecting new optical and X-ray observations. The optical light curves obtained with narrow-band continuum and line-bearing filters are analysed and compared. Optical spectra are used to map the location of the He II 4686 and H-alpha line-emission regions in velocity space. New XMM-Newton as well as archive X-ray spectra are analysed to search for variability and constrain the properties of the hot plasma in this system.
20 CCD images of the globular cluster M68, taken during 14th - 17th April 1989 with the 1.5m Danish telescope in La Silla, have been the subject of a photometric investigation.
