I comment on some of the steps required to convert raw instrumental magnitudes, derived by profile-fitting or synthetic-aperture photometry from CCD images, to final calibrated photometry on a standard system. The status of the DAO program to obtain homogeneous BV photometry for star clusters and nearby galaxies will also be discussed.

CCD flat fielding using an illuminated dome screen is discussed. Rings of reduced response caused by dust specks on the cryostat entrance window indicate the required uniformity of screen illumination but may not divide satisfactorily because of telescope flexure. Illumination colour is important for shorter-wavelength, broad-band filters. Flat fields can be distorted significantly by light scattered off telescope baffles. Special precautions are needed for uv flat fielding. The Mt John TH 7882 CDA chip is slightly sensitive to polarisation. Dome flat-fielding accuracy of 0.3% would seem achievable.

With the ability to obtain simultaneous photometry of many objects, CCD time-series photometry is a potentially powerful method for obtaining data, even under non-photometric conditions. In particular, the ability to utilize one or more comparison stars on the same frame without the need to move the telescope to a different field makes for a higher duty cycle than conventional photoelectric photometry. In addition, the ability to determine the local sky in a variety of ways plus the ability to use more complex analysis techniques such as profile fitting and curves of growth permits a variety of analysis options. Some of the advantages of utilizing CCDs and the techniques used in time-series photometry of compact objects are discussed. With the flexibility of modern CCD control systems, possibilities for real-time or near real-time data analysis using readily available computer technology are stressed. Brief discussions of periodicity analysis considerations and other aspects of the data acquisition are presented.

Using CCDs to obtain time-series light curve information is an increasing area of interest in astronomy. For brighter, high signal-to-noise sources, the data collection and reduction procedures are very robust and easy to use. However, for fainter, low signal-to-noise objects we must resort to new methods. These include the use of optimum data extraction techniques, a fuller understanding of the CCD itself, and a more complete error model. This paper will provide a brief introduction to CCD time-series photometry and then explore the above new methods in relation to real observational situations.

CCD’s have made possible the extension of intermediate-band photometric systems, including the Strömgren uvby system, to larger, fainter and cooler stars, with successful applications in old disk and globular clusters. Some of the applications in globular clusters demonstrate the ability to remove foreground stars from photometric diagrams and have enabled a re-evaluation of the evolutionary correction needed for distance modulus determination for metal-poor stars. We have developed an additional index based on measurement of the Ca II H and K lines which retains sensitivity to metallicity changes for extremely metal-poor stars. Finally, we are testing the utility of CCD H/β photometry in the unusual and old open cluster Melotte 66.

From the theory of CCD operation and our experience since 1986 with a Photometries CCD camera, we provide practical suggestions for achieving high-precision photometry on a small telescope (61-cm).

After a brief review of the traditional opportunities as well as the problems of doing photometry from space vehicles over a wide variety of wavelength regimes, several topics will be discussed. These include the factors associated with various types of spacecraft orbits (for example, near-earth, geosynchronous, planetary cruise) and with the different kinds of vehicles and platforms used (expendable, shuttle attached payloads, permanent stations, multi-purpose spacecraft, small and large projects). Since ground-based capabilities are constantly improving and expanding, it is necessary to assess those that might compete with space-based photometry. Finally, the present state of space observations as they pertain to “classical,” high precision, high speed and multi-object photometry will be reviewed; possibilities for the future will be addressed briefly.

The star mappers on board the ESA Hipparcos satellite will be used as one part of the Tycho project to obtain photometric data of a quasi B and V band magnitude for the 500,000 brightest stars and one broad-band magnitude T for a further 500,000 stars. Approximately 150 million single observations of these stars will be collected during a 4.5-year mission of the satellite.

The accuracy of the photometric data gained is expected to be 0.03 mag on the average at B = 10.5 mag for non-variable stars. We shall get T magnitudes for stars down to a limiting magnitude of about B = 12 mag depending on the galactic latitude. We will give an overview of the calibration procedure and present some of the first results.

A series of 40 HST WFC exposures in v (F555W) and i (F785LP) have been obtained of two fields in M81, in order to search for Cepheid variables. This has provided an ideal opportunity to compare how the photometry programs DoPHOT and DAOPHOT cope with undersampled images, and present our ‘best solution’ to the problem of reducing WFC photometry for faint stars in crowded fields.

One of the first stellar photometry programs completed with the High Speed Photometer (HSP) on the Hubble Space Telescope (HST) was visual and ultraviolet observations of the Crab pulsar. We obtained continuous observations on four consecutive days using a visual filter (4000 - 7000 Å) and an additional observation, approximately two months later, using an ultraviolet filter (1600 - 3000 Å). Each observation has a time resolution of 10.7 μsec and spans approximately 30 minutes in duration. In addition to the observations made with the HSP, contemporaneous UBVR observations were also made at Jodrell Bank and McDonald Observatory. Some of the more prominent results include the following: 1) the main pulse arrival time is the same in the UV as it is in the optical and the radio regions of the spectrum, 2) there is essentially no difference in the shape of the optical pulse from one observation to the next, 3) the “flatness” of the peak of the main pulse suggests that the main pulse has been resolved in time, and 4) in accordance with the trend of observations from the radio to infrared wavelengths, the main pulse is slightly narrower in the UV than in the optical.

A second HSP science observing program was a long-term program to monitor the eclipsing dwarf nova, Z Chamaeleontis (Porb = 107 minutes). We obtained a total of 42 observations of Z Cha in the UV (1120 - 1580 Å) each with a duration of approximately 45 minutes and separated by approximately three days. Although the majority of the observations cover the eclipse of the white dwarf and hot spot, a few observations were obtained outside-of-eclipse in order to obtain the complete light curve. During the course of this program, Z Cha underwent two “normal” outbursts in which the shape of the light curve changed dramatically. We will present a comparison of the light curve in quiescence with that during a “normal” outburst and quantify such geometrical and physical parameters as temperature and size of the white dwarf, hot spot, and accretion disk.

The Optical Monitors are small optical telescopes which will fly on board of the X-ray satellites SPECTRUM-X-GAMMA (JET-X experiment) and XMM. Their main scientific applications are the simultaneous observations (imaging) in the optical and UV band of the optical counterparts of X-ray sources, with limiting magnitudes of about mv=22 (JET-X) and 24 (XMM). The OMs are developed in order to perform also serendipitous observations with high photometric precision of bright stars falling in the field of view, which should allow the detection of stellar microvariability at a level better than 10−5. The main characteristics of the instruments are presented and the problems to be solved in order to reach the scientific goals are briefly discussed.

I explore the scientific gains that can be achieved by siting small (1 to 2-meter), special-purpose telescopes on the moon with the goal of high- precision observations.