Meeting the science goals for many current and future ground-based optical large-area sky surveys requires that the calibrated broadband photometry is both stable in time and uniform over the sky to 1% precision or better. Past and current surveys have achieved photometric precision of 1%–2% by calibrating the survey’s stellar photometry with repeated measurements of a large number of stars obs...

Photometry is presented in R, J, H, K of the z=2.37 QSO 0820+296 and its environment. Colours and magnitudes of most of the objects within 50 arcsec of the QSO suggest they are a group of galaxies at the QSO redshift with a young stellar population.

We present a new census of the Orion Nebula Cluster over a large field of view ( 30′ × 30′), significantly increasing the known population of stellar and substellar cluster members with precisely determined properties. We develop and exploit a technique to determine stellar effective temperatures from optical colors, nearly doubling the previously available number of objects with effective temp...

We present differential stellar population models, which allow improved determinations of the ages, iron and α-element abundances of old stellar populations from spectral fitting. These new models are calibrated at solar abundances using the predictions from classical, semi-empirical stellar population models. We then use the predictive power of fully synthetic models to compute predictions for...

Stellar photometry of nearby irregular galaxies of the Local Group is used to identify and study the young and old stellar populations of these galaxies. An analysis of the spatial distributions of stars of different ages in face-on galaxies shows that the young stellar populations in irregular galaxies are concentrated toward the center, and form local inhomogeneities in star-forming regions, ...

We present an analysis of NICMOS photometry and low-resolution grism spectroscopy of low-mass stars and sub-stellar objects in the young star-forming region NGC 1333. Our goal is to constrain the ratio of low-mass stars to substellar objects down to 20 MJup in the cluster as well as constrain the cluster

The dominant stellar population of the central bulge of the Milky Way is old, with roughly solar metallicity. The age is very similar to that of the old metal rich bulge globular clusters and to 47 Tucanae, which has an age of 13 Gyr. Stellar composition measurements from Keck/HIRES confirm that bulge stars are enhanced in Mg and Ti. New HST/NICMOS data are consistent with an old stellar popula...

We present results of large-aperture (D1@) JK photometry and CCD BV RI photometry near the centers of three distant (0.111 z1 0.22), rich Abell clusters of galaxies. The colors of the integrated light are consistent with those of nearby E and S0 galaxies. The absence of anomalous reddening implies that no more than 2 h~1% (1 p limit) of the dark matter in these clusters can be in the form of lo...

Received ; accepted – 2 – ABSTRACT We present 5 filter photometry of 21 carbon stars, 15 asteroids, 15 cataclysmic variables, 6 metal-poor stars, 5 Cepheids, 1775 field stars, blue horizontal branch (BHB) stars and RR Lyrae stars in the globular clusters M 15 and M 2, two primary standards, and 19 secondary standards. The photometry was carried out using a filter set identical to that which wil...

We present infra-red (JHK) photometry of 52 isolated Be stars of spectral types O9–B9 and luminos-ity classes III–V. We describe a new method of reduction, enabling separation of interstellar reddening and circum-stellar excess. Using this technique we find that the disc emission makes a maximum contribution to the optical (B − V) colour of a few tenths of a magnitude. We find strong correlatio...