We present deep JHK images of I Zw 18, the most metal-deficient Blue Compact Dwarf (BCD) galaxy known, and analyze them in conjunction with archival HST/WFPC2 optical images. To investigate the stellar populations, we have divided the main body of I Zw18 into eight regions, and fit the optical, near-infrared (NIR), and hybrid optical-NIR colors of these and the C component with evolutionary syn...

We report on new B, V and I CCD photometry of the glob-ular cluster M54 that was aimed at the study of its variable stars. With respect to the previous most recent work on M54 we have nearly doubled the number of detected variable stars: M54 can now be classified as intermediate in the Oosterhoff groups. The metallicity distribution for the cluster and the Sgr dSph field is obtained from the re...

Gravitational microlensing is not achromatic when the star being microlensed is resolved by the lens. We show how narrow-band photometry and moderateto high-resolution spectroscopy can be used to reconstruct the stellar surface intensity distribution of a microlensed star. Such microlens imaging can provide a unique opportunity to study the surfaces of normal red giants where Doppler imaging is...

We present Strömgren uvby photometry for a sample of 31 high Galactic latitude stars selected from the PalomarGreen Survey. The data include photometric magnitudes accurate to ≤ 0.01 mag in most cases, plus colours and the reddening free [c1] and [u−b] indices, which possess a precision of better than 0.02 and 0.04 mag, respectively. The latter should be suitable for the reliable determination ...

We present a direct image of the innermost companion to the red giant δ Andromedae using the Stellar Double Coronagraph at the Palomar Observatory. We use a Markovchain Monte Carlo based algorithm to simultaneously reduce the data and perform astrometry and photometry of the companion. We determine that the companion is most likely a main-sequence K-type star and is certainly not the previously...

■ Abstract The Hubble space telescope observations of the northern Hubble deep field, and more recently its counterpart in the south, provide detections and photometry for stars and field galaxies to the faintest levels currently achievable, reaching magnitudes V ∼ 30. Since 1995, the northern Hubble deep field has been the focus of deep surveys at nearly all wavelengths. These observations hav...

Online Digital Sky Survey (DSS) material is often used to obtain information on newly discovered variable stars for older epochs (e.g. Nova progenitors, flare stars, . . . ). We present here the results of an investigation of photometry on online digital sky survey material in small fields calibrated by CCD sequences. We compared different source extraction mechanisms and found, that even down ...

We present photometry of two transits of the giant planet WASP-4b with a photometric precision of 400–800 parts per million and a time sampling of 25–40 s. The two midtransit times are determined to within 6 s. Together with previously published times, the data are consistent with a constant orbital period, giving no compelling evidence for period variations that would be produced by a satellit...

We report high-cadence time-series photometry of the recently-discovered transiting exoplanet system HD 17156, spanning the time of transit on UT 2007 October 1, from three separate observatories. We present a joint analysis of our photometry, previously published radial velocity measurements, and times of transit center for 3 additional events. Adopting the spectroscopically-determined values ...

We present near-IR photometry of a selected sample of southern hemisphere E+A galaxies. The sample includes 50 galaxies from nearby (z ∼ 0.05) and distant (z ∼ 0.3) clusters as well as E+A galaxies from the field (z ∼ 0.1). We also observed 13 normal early-type galaxies from the field and from clusters to be compared with the E+A sample. The photometry includes J , H and Ks apparent magnitudes ...