We use a Lucky Imaging system to obtain I-band images with much improved angular resolution on a 2.5 m telescope. We present results from a 10-night assessment campaign on the 2.56 m Nordic Optical Telescope and quantify the performance of our system in seeings better than 1.0 . In good seeing we have acquired near diffraction-limited images; in poorer seeing the angular resolution has been routinely improved by factors of 2.5-4. The system can use guide stars as faint as I = 16 with full performance and its useful field of view is consistently larger than 40 diameter. The technique shows promise for a number of science programmes, both galactic (e.g. binary candidates, brown dwarfs, globular cluster cores) and extragalactic (e.g. quasar host galaxies, damped Lyman-α absorbers).

Low light level charge‐coupled devices (L3CCDs) have recently been developed, incorporating on‐chip gain. They may be operated to give an effective readout noise of much less than one electron by implementing an on‐chip gain process allowing the detection of individual photons. However, the gain mechanism is stochastic and so introduces significant extra noise into the system. In this paper we examine how best to process the output signal from an L3CCD so as to minimize the contribution of stochastic noise, while still maintaining photometric accuracy. We achieve this by optimizing a transfer function that translates the digitized output signal levels from the L3CCD into a value approximating the photon input as closely as possible by applying thresholding techniques. We identify several thresholding strategies and quantify their impact on the photon counting accuracy and the effective signal‐to‐noise ratio. We find that it is possible to eliminate the noise introduced by the gain process at the lowest light levels. Reduced improvements are achieved as the light level increases up to about 20 photon pixel−1 and above this there is negligible improvement. Operating L3CCDs at very high speeds will keep the photon flux low, giving the best improvements in signal‐to‐noise ratio.

No abstract

No abstract

The Las Campanas Infrared Survey, based on broadband optical and near-infrared photometry, is designed to robustly identify a statistically significant and representative sample of evolved galaxies at redshifts z > 1. We have completed an H-band imaging survey over 1.1 deg 2 of sky in six separate fields. The average 5 detection limit in a 4 00 diameter aperture is H $ 20:8. Here we describe the design of the survey, the observation strategies, data-reduction techniques, and object identification procedures. We present sample near-infrared and optical photometric catalogs for objects identified in two survey fields. The optical images of the Hubble Deep Field-South region obtained from the literature reach 5 detection thresholds in a 4 00 diameter aperture of U $ 24:6, B $ 26:1, V $ 25:6, R $ 25:1, and I $ 24:2 mag. The optical images of the Chandra Deep Field-South region obtained from our own observations reach 5 detection thresholds in a 4 00 diameter aperture of V $ 26:8, R $ 26:2, I $ 25:3, and z 0 $ 23:7 mag. We perform object detection in all bandpasses and identify e 54,000 galaxies over 1408 arcmin 2 of sky in the two fields. Of these galaxies, $14,000 are detected in the H band and $2000 have the colors of evolved galaxies, IÀHe3, at ze1. We find that (1) the differential number counts NðmÞ for the H-band-detected objects has a slope of d log NðmÞ=dm ¼ 0:45 AE 0:01 mag À2 at Hd19 and 0:27 AE 0:01 mag À2 at He19, with a mean surface density %7200 deg À2 mag À1 at H ¼ 19. In addition, we find that (2) the differential number counts for the H-banddetected red objects has a very steep slope, d log Nðm; I À He3Þ=dm ¼ 0:84 AE 0:06 mag À2 at Hd20 and 0:32 AE 0:07 mag À2 at He20, with a mean surface density %3000 deg À2 mag À1 at H ¼ 20. Finally, we find that (3) galaxies with red optical to near-IR colors (IÀH > 3) constitute %20% of the H-band-detected galaxies at Hd21, but only %2% at Hd19. We show that red galaxies are strongly clustered, which results in a strong field-to-field variation in their surface density. Comparisons of observations and predictions based on various formation scenarios indicate that these red galaxies are consistent with mildly evolving early-type galaxies at z $ 1, although with a significant amount of ongoing star formation, as indicated by the large scatter in their VÀI colors.