As part of an ongoing project to investigate the cluster formation and chemical evolution history in the Large Magellanic Cloud (LMC), we have used the CTIO 0.9m telescope to obtain CCD imaging in the Washington system of NGC 2161, SL 874, and KMHK 1719 - three unstudied star clusters located in the outer region of the LMC. We measured T1 magnitudes and C-T1 colors for a total of 9611 stars distributed throughout cluster areas of 13.6x13.6arcmin^2^. Cluster radii were estimated from star counts distributed throughout the entire observed fields. Careful attention was paid to setting apart the cluster and field star distributions so that statistically cleaned color-magnitude diagrams (CMDs) were obtained. Based on the best fits of isochrones computed by the Padova group to the (T1, C-T1) CMDs, the {delta}T1 index, and the standard giant branch procedure, ages and metallicities were derived for the three clusters.
Colour-magnitude diagrams (CMDs) are presented for the first time for 10 star clusters projected on to the Small Magellanic Cloud (SMC). The photometry was carried out in the Washington system C and T1 filters allowing the determination of ages by means of the magnitude difference between the red giant clump and the main-sequence turnoff (MSTO), and metallicities from the red giant branch (RGB) locus.
We present CCD photometry in the Washington system C and T1 passbands down to T1~22 in the fields of L35, L45, L49, L50, L62, L63 and L85, seven poorly studied star clusters in the inner region of the Small Magellanic Cloud (SMC). We measured T1 magnitudes and C-T1 colours for a total of 114826 stars distributed throughout cluster areas of 13.7x13.7arcmin^2^ each. Cluster radii were estimated from star counts distributed throughout the entire observed fields.
We present CCD photometry in the Washington system C, T1 and T2 passbands down to T1~23 in the fields of L3, L28, HW 66, L100, HW 79, IC 1708, L106, L108, L109, NGC 643, L112, HW 84, HW 85 and HW 86, 14 Small Magellanic Cloud (SMC) clusters, most of them poorly studied objects. We measured T1 magnitudes and C-T1 and T1-T2 colours for a total of 213 516 stars spread throughout cluster areas of 14.7x14.7arcmin^2^ each. We carried out an in-depth analysis of the field star contamination of the colour-magnitude diagrams (CMDs) and statistically cleaned the cluster CMDs.
With the aim of enlarging the number of studied LMC clusters in the age range 8.0~<log(t)~<9.0, we focus here on a sample of mostly unstudied cluster candidates. We present, for the first time, CCD Washington CT1T2 photometry of stars in the field of 26 LMC clusters. The studied clusters turned out to be small angular size objects with ages within the age range 8.0~<log(t)~< 9.0, which are projected or immersed in dense star fields.
We present Washington photometry of the giant branches of the relatively metal-rich globular cluster NGC 6388 and compare it with 47 Tuc. By examining the spatial distribution of stellar colors across the red giant branch and using spectroscopic data on several bright giants, we found that NGC 6388's center is affected by differential reddening of at least {DELTA}E(B-V)~0.1. Most of the width of the red giant branch is caused by that differential reddening. The southeastern outer regions of the cluster seem to be less affected by variable dust extinction, and we find that NGC 6388 is slightly more metal-rich than 47 Tuc, with a distinct asymptotic giant branch. We have put an upper limit on possible variations in [Fe/H] for NGC 6388, finding that it must be less than ~0.2dex. It is unlikely that such a small range in metallicity could be responsible for the blue horizontal branch and blue tail stars in a cluster with a metallicity similar to the more massive 47 Tuc, which only exhibits a red horizontal branch.
This paper completes the series of cataclysmic variables (CVs) identified from the Sloan Digital Sky Survey (SDSS) I/II. The coordinates, magnitudes, and spectra of 33 CVs are presented. Among the 33 are eight systems known prior to SDSS (CT Ser, DO Leo, HK Leo, IR Com, V849 Her, V405 Peg, PG1230+226, and HS0943+1404), as well as nine objects recently found through various photometric surveys. Among the systems identified since the SDSS are two polar candidates, two intermediate polar candidates, and one candidate for containing a pulsating white dwarf. Our follow-up data have confirmed a polar candidate from Paper VII and determined tentative periods for three of the newly identified CVs. A complete summary table of the 285 CVs with spectra from SDSS I/II is presented as well as a link to an online table of all known CVs from both photometry and spectroscopy that will continue to be updated as future data appear.
A thorough analysis of the multicolour CCD observations of the RRab-type variable, CZ Lacertae, is presented. The observations were carried out in two consecutive observing seasons in 2004 and 2005 within the framework of the Konkoly Blazhko Survey of bright, northern, short-period RRab variables.
We present a method which uses colour-colour cuts on the Sloan Digital Sky Survey (SDSS) photometry to select white dwarfs with hydrogen-rich (DA) atmospheres without the recourse to spectroscopy. This method results in a sample of DA white dwarfs that is 95 per cent complete at an efficiency of returning a true DA white dwarf of 62 per cent. The approach was applied to SDSS Data Release 7 for objects with and without SDSS spectroscopy.
We present a comprehensive analysis of DB white dwarfs drawn from the Sloan Digital Sky Survey, based on model fits to ugriz photometry and medium-resolution spectroscopy from the Sloan Digital Sky Survey. We also take advantage of the exquisite trigonometric parallax measurements recently obtained by the Gaia mission. Using the so-called photometric and spectroscopic techniques, we measure the atmospheric and physical parameters of each object in our sample (Teff, logg, H/He, Ca/He, R, M), and compare the values obtained from both techniques in order to assess the precision and accuracy of each method. We then explore in great detail the surface gravity, stellar mass, and hydrogen abundance distributions of DB white dwarfs as a function of effective temperature. We present some clear evidence for a large population of unresolved double-degenerate binaries composed of DB+DB and even DB+DA white dwarfs. In the light of our results, we finally discuss the spectral evolution of DB white dwarfs, in particular the evolution of the DB-to-DA ratio as a function of Teff, and we revisit the question of the origin of hydrogen in DBA white dwarfs.
