Table of contents

Redshift surveys remain an important constraint on cosmological parameters and a key to characterizing the nature and evolution of the large‐scale distribution of galaxies. I discuss redshift surveys as a route to exploration of other issues associated with large‐scale structure including the low surface brightness universe and the links between star formation and the galaxy distribution.

In the light of recent significant progress on both the observational and theoretical fronts, we review the status of white dwarf stars as cosmochronometers. These objects represent the end products of stellar evolution for the vast majority of stars and, as such, can be used to constrain the ages of various populations of evolved stars in the Galaxy. For example, the oldest white dwarfs in the solar neighborhood (the remnants of the very first generation of intermediate‐mass stars in the Galactic disk) are still visible and can be used, in conjunction with cooling theory, to estimate the age of the disk. More recent observations suggest the tantalizing possibility that a population of very old white dwarfs inhabits the Galactic halo. Such a population may contribute significantly to baryonic "dark" matter in the Milky Way and may be used to obtain an independent estimate of the age of the halo. In addition, white dwarf cosmochronology is likely to play a very significant role in the coming era of giant 8–10 m telescopes when faint white dwarf populations should be routinely discovered and studied in open and globular clusters.

In order to optimize the occulting process of a classical Lyot coronagraph for imaging faint satellites next to Jovian planets, we designed a coronagraph with a variable‐diameter occulting disk (Hg mask). We present the description of the Hg‐mask coronagraph developed at the Observatório Nacional, Rio de Janeiro, and the imaging test on Neptune's satellite Proteus.

A small CCD photometer dedicated to the detection of extrasolar planets has been developed and put into operation at Mount Hamilton, California. It simultaneously monitors 6000 stars brighter than 13th magnitude in its 49 deg² field of view. Observations are conducted all night every clear night of the year. A single field is monitored at a cadence of eight images per hour for a period of about 3 months. When the data are folded for the purpose of discovering low‐amplitude transits, transit amplitudes of 1% are readily detected. This precision is sufficient to find Jovian‐size planets orbiting solar‐like stars, which have signal amplitudes from 1% to 2% depending on the inflation of the planet's atmosphere and the size of the star. An investigation of possible noise sources indicates that neither star field crowding, scintillation noise, nor photon shot noise are the major noise sources for stars brighter than visual magnitude 11.6.

Over one hundred variable stars have been found in each star field. About 50 of these stars are eclipsing binary stars, several with transit amplitudes of only a few percent. Three stars that showed only primary transits were examined with high‐precision spectroscopy. Two were found to be nearly identical stars in binary pairs orbiting at double the photometric period. Spectroscopic observations showed the third star to be a high mass ratio single‐lined binary. On 1999 November 22 the transit of a planet orbiting HD 209458 was observed and the predicted amplitude and immersion times were confirmed. These observations show that the photometer and the data reduction and analysis algorithms have the necessary precision to find companions with the expected area ratio for Jovian‐size planets orbiting solar‐like stars.

The VIRMOS Consortium had the task to design and manufacture two spectrographs for the ESO Very Large Telescope, VIMOS (Visible Multi‐Object Spectrograph) and NIRMOS (Near Infrared Multi‐Object Spectrograph). This paper describes how the mask manufacturing unit (MMU), which cuts the slit masks to be used with both instruments, meets the scientific requirements and manages the storage and the insertion of the masks into the instrument. The components and the software of the two main parts of the MMU, the mask manufacturing machine and the mask handling system, are illustrated together with the mask material and with the slit properties. Slit positioning is accurate within 15 μm, equivalent to 003 on the sky, while the slit edge roughness has an rms on the order of 0.03 pixels on scales of a slit 5^'' long and of 0.01 pixels on the pixel scale (0205). The MMU was successfully installed during 2000 July/August at the Paranal Observatory and is now operational for spectroscopic mask cutting, in compliance with the requested specifications.

Owing to their spectral properties, Herbig‐Haro (HH) objects can be discovered using photometric methods through a combination of filters, sampling the characteristic spectral lines and the nearby continuum. The data are commonly processed through direct visual inspection of the images. To make data reduction more efficient and the results more uniform and complete, an automated searching scheme for HH objects is developed to manipulate the images using IRAF. This approach helps to extract images with only intrinsic HH emissions. By using this scheme, the pointlike stellar sources and extended nebulous sources with continuum emission can be eliminated from the original images. The objects with only characteristic HH emission become prominent and can be easily picked up. In this paper our scheme is illustrated by a sample field and has been applied to our surveys for HH objects.

I present a variation on Osaki's tidal thermal instability model for SU UMa behavior. I suggest that in systems with the lowest mass ratios, the angular momentum dissipation in an eccentric disk is unable to sustain the disk on the hot side of the thermal instability. This decoupling of the tidal and thermal instabilities in systems with q≲0.07 allows a better explanation of the "echo" outbursts of EG Cnc and the short supercycles of RZ LMi and DI UMa. The idea might also apply to the soft X‐ray transients.

Stunted outbursts have been reported in old novae and nova‐like cataclysmic variables by Honeycutt, Robertson, and Turner. These 0.4–1 mag outbursts were concluded to be either mass transfer events or disk outbursts similar to dwarf nova eruptions, but seen under unusual conditions. Honeycutt, Robertson, and Turner did not have enough evidence to favor either of these possibilities. This paper uses additional long‐term photometry and analysis to argue that the similarities of these stunted outbursts to dwarf nova eruptions are now so numerous that the dwarf nova outburst choice is strongly favored. The similarities discussed here include the range of outburst spacings, the coherence and stability of the outbursts, and the presence of isolated outburst/dip pairs. As part of this discussion we note the presence of unexpectedly stable clocks over 9 years for the repetition interval of dwarf nova outbursts in SY Cnc and of stunted outbursts in FY Per.

We have obtained 7 nights of time‐resolved VI photometry of the double‐lined cataclysmic variable Phoenix 1. We detect two candidate orbital periods, 0.1344 day and 0.2683 day. The former, which would correspond to a single modulation caused by viewing the irradiated face of the secondary star, is the less favored choice based on the folded light curves. The latter, which would correspond to a double modulation with unequal minima depths caused by ellipsoidal variation of the secondary star, is inconsistent with the observed late spectral type (M2–5) of the secondary star. However, we discuss some recent results from the literature that may make it possible to reconcile the longer orbital period and later spectral type. Some ambiguity remains as to which of these two periods is the true orbital period.

Nine binary candidates have been identified from a sample of 64 hot subdwarf sdO/OB/OC stars selected from the Palomar‐Green Survey. Three of the binary candidates had been identified previously. The binary candidates emerged from BVRI photometric observations and were identified by their intrinsic color excesses in two‐color plots and by comparison to synthetic binary system colors. The data presented here are the initial results of a larger program aimed at identifying helium‐rich hot subdwarf binary systems suitable for more detailed investigation of their fundamental stellar parameters and evolutionary status.

We present an analysis of AAVSO visual observations of the Mira variable R Cen from 1918 to 2000. The period of the dominant mode has been steadily decreasing from 550 days at JD 2,434,000 (1951) to its present value of 505–510 days. In the same interval, the pulsational amplitude has decreased by 3 mag, from 5.5–11.8 V to 6.3–9.1 V. We suggest that both are caused by a He‐shell flash, as the period decrease is similar to that of other He‐shell flash stars such as R Hya, R Aql, and T UMi. The period change is consistent with the luminosity drop expected immediately after the flash, as predicted by He‐shell flash models for stars of 2–3 M_⊙ or less.

The light curve shows the familiar pattern of alternating deep and shallow minima, giving the appearance of double maxima. While the amplitude of the main mode has decreased 3 mag in the last 50 years, the amplitude of the secondary mode near 274 days has remained almost constant, so that the double maxima have nearly vanished from the light curve in recent years. The power spectrum between 1930 and 1966 shows harmonics up to 8 times the main frequency at 1/548 cycle day⁻¹. The most likely explanation for the double‐peaked light curve is a resonance between two modes.